Eliminating adversary WMD: lessons for future conflicts
The failure to find substantial evidence of nuclear, biological, and chemical weapons in Iraq has exposed serious weaknesses in the U.S. understanding of the weapons of mass destruction (WMD) threat posed by its adversaries and in its ability to deal with these threats. A rancorous and highly politicized debate, primarily about the intelligence assessments of Iraqi WMD capabilities before Operation Iraqi Freedom, has dominated the national discussion of WMD in Iraq for months. Although Iraqi WMD capabilities remain elusive and, indeed, weapons may never be found, elimination operations conducted there provide important lessons.
The United States must begin to develop a permanent capability to plan for and conduct WMD elimination operations. The Department of Defense (DOD) in particular must begin to build such a capability as part of its overall approach to combating WMD proliferation. To be effective, however, DOD must work in concert with interagency partners and avoid a go-it-alone approach to this national priority.
Preserving the knowledge and experience gained in Iraq and Afghanistan and translating them into effective structures and doctrine will be key challenges for military and civilian planners. Incorporating WMD elimination into early planning, ensuring access to key enabling capabilities, providing sufficient time to train units and exercise concepts, and, perhaps most importantly, following a program-centric approach to address the totality of adversary programs and stockpiles are all critical to future success.
As tensions between Iraq and the United States worsened in mid-to-late 2002 and as preparations began for Operation Iraqi Freedom, policymakers and military planners began to wrestle with the challenges posed by Iraqi weapons of mass destruction (WMD). Indeed, Iraqi defiance and deception in the face of United Nations (UN) sanctions, coupled with growing fears of WMD transfer to terrorist organizations–most prominently al Qaeda–were two primary reasons for confronting Saddam Hussein. Just as in the first Gulf War in 1991, deterring and defending against possible Iraqi use of WMD against coalition forces were key concerns for planners. However, as the crisis escalated in 2002, Department of Defense (DOD) planners began to foresee another challenge: how to remove comprehensively and permanently the threat of Iraqi WMD, not just to U.S. troops but also to the Middle East region and the world.
When faced with this challenge in late fall 2002, military planners and supporting DOD organizations realized that the comprehensive elimination of an adversary WMD program would entail far more than targeting enemy sites for destruction. A new mission, WMD elimination, was created, and planners began trying to define, adapt, and incorporate this mission into existing and developing war plans. As they did, they discovered critical gaps in U.S. preparations for dealing with a WMD-armed adversary.
While DOD made great strides over the last 10 years in improving the U.S. military’s ability to fight and win in a WMD environment, far less attention was paid to the tasks of locating, understanding, and removing (or disposing of) an adversary program. In Operation Desert Storm, these tasks were not addressed until after the cease-fire agreement, and then they were handled as postconflict activities under UN management. In the leadup to Iraqi Freedom, policy and military experts disagreed about what exactly the role of the military would be; how long, if at all, it would assume primary responsibility; and when and to whom it would hand off mission responsibility.
Despite these uncertainties, planners began crafting concepts of operation to allow troops on the ground to locate, characterize, and secure Iraqi WMD and attendant development programs and delivery systems–a process that came to be known as exploitation. Even as WMD exploitation plans progressed, strategies to deal with the actual disposition or destruction of Iraqi WMD stocks, weapons, and production capabilities lagged far behind. Given the long and tortuous history surrounding Iraq’s illicit weapons programs and the UN role in attempting to eliminate these capabilities verifiably, it was unsurprising that the actual disposition or destruction of Iraqi WMD was initially considered a secondary task that would fall primarily to non-DOD organizations. As such, destruction issues were not addressed as early and to the same degree as other WMD elimination tasks.
Some within DOD assumed that rapid regime change itself would produce conditions under which adversary WMD and associated programs could be located and disposed of cooperatively and peaceably. Others assumed that rapid military victory would allow some of the slower processes of WMD elimination to be delayed until the end of major combat operations, when security conditions would permit nonmilitary and non-U.S. partners to perform the required tasks. As conflict drew closer, planners reassessed some of these assumptions and took steps to formulate and build additional elimination capabilities. But, as has since become clear, many assessments and assumptions remained relatively unaltered from prewar through warfighting. Particularly in the critical area of prewar intelligence, only after the start of combat operations were serious problems identified.
A relatively new mission, or at least a newly rediscovered one (if one includes the precedent of post-World War II Germany), WMD elimination has suffered from serious growing pains in Iraqi Freedom: incorrect planning assumptions and intelligence, lack of preparation time, and problems with execution and implementation, among others. Yet there were demonstrable successes. Without a doubt, there are important lessons to be learned from the Iraq experience.
Operation Iraqi Freedom
In late 2002, DOD began designing an exploitation task force that could locate, identify, characterize, and (to a very limited extent) secure and disable adversary WMD capabilities. DOD settled on a multitiered and sequenced approach to eliminating the WMD problem in Iraq. At the first level, site assessment teams (SATs)–comprised of fewer than a dozen individuals and forward deployed with maneuver elements–would locate and identify sites of interest and perform first-order analysis of whatever was uncovered. At the second level, three mobile exploitation teams (METs) would perform confirmatory analysis on sites and evidence uncovered by SATs, as well as other sites identified on an ad hoc basis. With greater analytical, logistical, and manpower capabilities, METs would systematically exploit sites and people of interest as
maneuver elements pushed ahead toward objectives. Manning SATs and METs were both military and civilian experts from across the services and various defense agencies.
To provide command, control, and supporting capabilities to these newly formed units, military planners selected the 75th Field Artillery Brigade from the U.S. Army III Corps and renamed it the 75th Exploitation Task Force (XTF). With much of its heavy equipment unavailable for combat because it was floating off the coast of Turkey, this unit would instead lead the effort to find and secure Iraqi WMD. However, there remained a growing concern within the Office of the Secretary of Defense that even the new capabilities anticipated by the 75th XTF would be insufficient to disable and eliminate the nuclear, biological, and chemical capabilities expected to be found in Iraq. Thus, in late March 2003, the Defense Threat Reduction Agency (DTRA) established Task Force Disablement and Elimination (TF D/E) to take the lead in disabling and disposing of any weapons or WMD-related equipment and materials discovered by the 75th XTF or other units. In addition, special operations forces would play an important role in finding and neutralizing WMD threats.
Supporting the 75th XTF and these other units was a range of individuals and organizations drawn from across DOD and other government agencies, which included intelligence specialists, microbiologists, physicists, chemists, and other scientific experts and uniformed personnel experienced in handling hazardous materials. For example, the U.S. Army Nuclear and Chemical Agency created a nuclear disablement team to assist DTRA and TF D/E efforts. (1) The Army’s Technical Escort Unit also contributed its unique experience with detecting, monitoring, rendering safe, and escorting WMD materials. In addition to this specialized expertise, the 75th XTF required myriad enabling capabilities drawn from major supported commands in theater, notably Army V Corps and Marine Corps I Marine Expeditionary Force (MEF). Such capabilities included transportation (air and ground), logistics, communications, linguists, and security and explosive ordnance disposal. Similarly, connections with the Intelligence Community and U.S. Government and nongovernmental scientists behind the front lines provided important reach-back analytical capabilities.
The speed and professionalism with which the 75th XTF and other elimination organizations activated and deployed were commendable but could not fully compensate for the lack of preexisting plans, doctrine, training, exercising, and resources. It was not until early 2003 that the 75th XTF was able to bring its constituent elements together to begin training, developing, and testing specific tactics, techniques, and procedures. At the same time, general guidance from senior-level military and civilian leaders was being refined. As conflict commenced in mid-March, the weaknesses of the intelligence guiding the targeting process and shaping exploitation priorities posed increasing challenges. Moreover, the task force lacked the organic transportation, communication, and security assets necessary to establish and maintain positive control over key sites and positions. V Corps and I MEF, which supplied many of these enabling capabilities when they were not resident within the 75th XTF, had to reconcile competing priorities. Delays and shortfalls inevitably followed. Finally, as the hunt for Iraqi weapons of mass destruction grew more complex and the smoking gun evidence of WMD programs proved surprisingly elusive, exercising effective and integrated command and control over all the different units associated with the hunt became more difficult. Throughout, individuals and units charged with finding and eliminating the weapons had to deal with ad hoc, evolving organizational structures that were managed by several different offices and commands.
As major combat operations drew to a close in late April 2003, significant changes regarding the elimination mission were under way. With little WMD material to disable or destroy, efforts shifted toward an investigatory approach. Leaders both in theater and in the United States recognized the need to make forensic and analytical components larger and more robust. On-the-ground intelligence, particularly human intelligence, would need to expand substantially, and operations would have to move away from the site-centric approach that prevailed during the early weeks of the war. Replacing it was an approach that focused more on gleaning intelligence from people and documentation. In line with this shift, in late April and May, the 75th XTF began transferring its responsibility for WMD exploitation operations to the nascent Iraq Survey Group (ISG). In June 2003, the 75th XTF resumed its prior designation as the 75th Field Artillery Brigade and returned home to Fort Sill, Oklahoma.
The ISG assumed full operational control for the mission in mid-June 2003, but it took several weeks before the organization was fully deployed and functioning in support of the WMD elimination mission. In Washington, concerns over the WMD search continued to escalate, and in Iraq, operations slowed as leadership of the elimination mission remained unclear. Unfortunately, in the operational pause that occurred as the 75th XTF began to step down and as the ISG started to form, operating conditions in Iraq continued to deteriorate as a result of looting, insurgency, and terrorism. By most accounts, it was not until midsummer, when David Kay took control, that the ISG became fully operational. In the transition period between the 75th XTF and the ISG, however, many sites had suffered depredations caused by looting and destruction, intentional or otherwise, seriously hampering long-term efforts to get to the bottom of Iraq’s prewar WMD efforts. Meanwhile, security conditions continued to decline, and the permissive conditions needed to reduce dependence upon military capabilities for these operations never materialized.
Much of the success of the 75th XTF, special operations forces, and the follow-on ISG has been masked by the seemingly futile hunt for WMD stockpiles in Iraq, but certain accomplishments should not be overlooked. In a matter of weeks, a large conventional unit was transformed into a site exploitation organization. In the course of the development and deployment of the 75th XTF, the U.S. military built a preliminary force structure, plans, definitions, and community around the entirely new concept of WMD elimination. With little training, few concepts of operation, and no doctrine, these teams operated safely on the battlefield in a hostile environment. As conditions and requirements changed, the organization adapted–first, as preexisting intelligence regarding sites proved less useful than hoped, and later, as the scope of the mission broadened to encompass a full accounting of Iraqi WMD programs and their history (as under the ISG). While not uncovering the large-scale stockpiles or extensive research, development, and production programs that many anticipated, the ISG has shed considerable light on illicit Iraqi WMD activities. Moreover, it has done so in an environment where much information was lost to looting, vandalism, and coordinated destruction.
Given the extent of nuclear, biological, and chemical proliferation around the globe, the United States can ill afford to assume that any significant future adversary would not possess a WMD capability. WMD threats to U.S. interests and operations may stem from either a hostile state or a transnational actor bent on subverting American interests or mission success. As demonstrated by evidence uncovered in Afghanistan, the public exhortations of terrorist leaders, and repeated incidents over the last decade, certain terrorist organizations have a serious and growing interest in acquiring and using nuclear, biological, and chemical weapons. With numerous states currently seeking or possessing such weapons, preparations for prevailing against WMD use will be critical to military strategy and planning. Developing effective WMD elimination capabilities, however, is equally important.
Elimination operations can play a vital role in the ongoing war on terrorism by removing sources of precursor agents or raw materials, denying access to developmental facilities, scientists, and their knowledge, and securing completed weapons. Precluding the opportunity for terrorist organizations to acquire weapons of mass destruction from a sympathetic regime or to gain control of materials, know-how, and weapons in the chaotic aftermath of a military campaign is essential. Elimination operations cannot substitute for the range of tools needed to deal with active WMD proliferation between states or from states to groups. But in wartime and postwar scenarios, conducting speedy and comprehensive WMD elimination operations may be the first, best, and only effective tool.
In addition, the United States may have to enter a state to secure, remove, or destroy portions or all of its WMD arsenal or infrastructure when growing domestic discontent or destabilization caused by radical elements risks the use or proliferation of such weapons or their technology. WMD elimination could become necessary even where WMD materials were either previously unknown or unsuspected. Emerging intelligence or outright discovery of weapons or related materials in destabilized or deteriorating regions or states would pose serious proliferation risks that might be solved only through elimination operations.
Russelectric keeps it real-time with custom monitoring software
Hingham, Mass.-based Russelectric Inc. has introduced new custom SCADA software for use with power control systems. The software is designed to provide interactive monitoring, real-time and historical trending, comprehensive reporting, distributed networking and alarm management.
According to Russelectric, the SCADA system allows operators to monitor and control a facility’s entire power system through a full-color, interactive computer screen. The screen uses point-and-click options to access PLC setpoints, analog or digital readout displays appearing on a switchgear’s front panel and can be used to run system tests. An operator can also view real-time engine data and the alarm history of the power system through the software.
On the screen display, color-coding is used to indicate the system status and the positions of all power-switching devices. Operating parameters are also viewable and can be updated for real-time monitoring. With the real-time capabilities of the SCADA software, flashing lamps on a switchgear annunciator panel also flash on the SCADA display allowing real-time notification of system anomalies. Event logging, alarm locking and help screens are also standard with the program.
Russelectric completely customizes the screen display for each power application, which it said provides the most realistic diagram of the system. The SCADA software can operate as a stand-alone platform or a networked application using Russelectric’s client/ server architecture. This, Russelectric said, permits data to be accessed either locally or remotely.
The company also offers a series of optional SCADA enhancements such as zoom, meter value displays, over lay displays and selector switch operations, which can be integrated into the software package. A simulation system that uses SCADA graphics and can be used for offline training is also available as an option.
Besides its new custom SCADA software, Russelectric also offers a line of automatic transfer switches; combination transfer-bypass/isolation switches; generator power control systems for prime power, emergency power, peak shaving, cogeneration and utility paralleling; and retrofit turbine control systems for gas, steam, and hydro systems. The company has manufacturing plants in Hingham and Broken Arrow, Okla.
APEC highlights discord among 5 countries in 6-party talks
The Asia-Pacific Economic Cooperation forum summit through Sunday in Hanoi served as an opportunity for the international community to demonstrate its unity against North Korea following its Oct. 9 nuclear test.
But it also highlighted discord among countries involved in the six-party talks on Pyongyang’s nuclear issue, with Japan and the United States calling for tough measures to persuade the North to terminate its nuclear programs, while China and South Korea favoring a softer approach to avoid provoking Pyongyang.
The APEC summit was the first occasion where leaders of five countries of the talks except North Korea — the United States, China, Russia, Japan and South Korea — gathered after Pyongyang agreed to return to the talks last month following one-year hiatus.
Japan and the United States hoped to include a strong message against North Korea in APEC leaders’ declaration, but China, the closest supporter of Pyongyang and chair of the six-party talks, staunchly resisted.
”We will not accept any statements other than an oral one,” China had said, according to a diplomatic source.
China’s stance apparently reflected its hope of not provoking North Korea ahead of the resumption of the six-party talks, expected in December, and avoid giving an excuse to North Korea to walk out of the talks again.
South Korea, Russia and some Southeast Asian countries with close ties to North Korea also joined China’s side, eventually overriding the hardliners. As a result, the message over Pyongyang’s moves was only read out by Vietnamese President Nguyen Minh Triet, who chaired the two-day APEC summit, and was not translated into a written document.
The verbal presentation expressed ‘’strong concern” over North Korea’s nuclear test and urged Pyongyang to take ”concrete and effective steps” to abandon its nuclear programs.
Vietnam was supportive of China from the beginning, with a senior Vietnamese Foreign Ministry official saying, ”We just want to avoid a result of bringing a collapse of the six-party talks.”
”Only the United States and Japan’s fuss stood out,” a diplomatic source of a Southeast Asian country recalled.
Meanwhile, in a meeting with U.S. President George W. Bush and South Korean President Roh Moo Hyun held on the sidelines of the APEC summit on Saturday, Bush failed to win support from Seoul for fully participating in U.S.-led multilateral efforts to interdict the North’s transfer of nuclear and other weapons of mass destruction.
While expressing support to ”the principles and goals” of the multilateral operations, called the Proliferation Security Initiative, Roh told reporters after their talks that South Korea ”is not taking part in the full scope” of the PSI.
The South Korean rejection came as a major diplomatic setback for the Bush administration, which has been working to make sure that other nations continue to implement sanctions and stop North Korea’s weapons proliferation until Pyongyang returns to the six-party talks and takes ”concrete” steps to abandon its nuclear programs.
In another bilateral talk between the South Korean leader and Russian President Vladimir Putin on Sunday, Russia indicated that it is in a closer stance to China and South Korea, which have pressed for holding ”dialogue” with North Korea.
According to South Korean sources, the two leaders agreed to the importance of promoting dialogue as well as putting pressure on and not to admit the North as a nuclear power.
Meanwhile, Japanese Prime Minister Shinzo Abe maintained its tough line, calling at the APEC summit on Sunday for the need to ”pressure” North Korea toward realizing its denuclearization and criticizing the country for not dealing sincerely with the issue of its abductions of Japanese nationals, according to Japanese government officials.
On the outcome that a statement on the North Korean issue resulted in a chairperson’s oral message, a Japanese government official said after the APEC summit that the APEC members decided to choose such form because the forum is basically a place to ”discuss economic issues.”
But the official refused to comment further in detail on what kind of discussions were held.
”China’s power in APEC is massive,” a senior Japanese Foreign Ministry official said.
Bush to press Roh to implement sanctions on N. Korea
U.S. President George W. Bush said Friday he will press South Korean President Roh Moo Hyun to implement a U.N. Security Council sanctions resolution against North Korea when they meet Saturday on the sidelines of an annual Asia-Pacific summit in Hanoi.
”I’ll, of course, talk to the South Korean president about implementing the…resolution,” Bush told reporters when asked whether he thinks Seoul is sufficiently cooperating on sanctions against Pyongyang.
South Korea said Monday it will neither expand its role in multilateral operations, called the Proliferation Security Initiative, to interdict transfer of weapons of mass destruction and delivery systems nor take any new steps to ”punish” Pyongyang ahead of the six-party talks on North Korea’s nuclear programs.
White House spokesman Tony Snow told reporters that the United States wants to ”have the South Koreans playing a role” in the PSI.
Bush, speaking together with Australian Prime Minister John Howard after their meeting, said the two agreed to raise North Korea as one of the key issues for the summit Saturday and Sunday of the Asia-Pacific Economic Cooperation forum.
”We have a chance to solve this issue peacefully and diplomatically,” Bush said, noting that North Korea has agreed late last month to return to the six-party talks, which have been stalled for nearly a year.
Against this backdrop, Bush said, ”It’s important for the world to see that the Security Council resolutions…are implemented.”
”So part of my discussions will be how to fully implement those sanctions that the world has asked for, but also it’s a chance to set the conditions right so that the six-party talks will succeed,” Bush said.
Snow said Bush and Howard agreed on the need to keep pressure on North Korea until the nuclear issue is resolved diplomatically through the six-party talks.
Bush said he will also raise the issue when he meets bilaterally with his counterparts from China, Japan and Russia — the three other six-party members along with South and North Korea and the United States — on the sidelines of the APEC summit.
The resolution was adopted after North Korea carried out its first nuclear test Oct. 9 following its test-firing of seven ballistic missiles, including a long-range Taepodong-2 missile, in July.
Transfer machining with a twist
Multiaxis turret modules are an emerging machining technology that offers system builders and users an alternative to conventional single-spindle modules. Compared to a single spindle, the turret head brings advances in speed, accuracy, and power, and when mated to the three-axis module, a degree of flexibility. Together, the benefits of the two machine tool systems offer a new dimension of performance for flexible or dedicated machining systems.
The modern turret head has its origins in high-volume machining applications in the automotive industry. Transfer line manufacturers often include large turret heads in their systems, usually for the purpose of using multispindle heads. A typical application is making multiple holes in automatic transmission housings. A turret with multihead spindles allows completion of drilling, reaming, and tapping operations with accuracy and speed. These large turret heads can be in excess of 31.5″ (800 mm) across the turret, and are normally mated to a single-axis slide unit.
Modern multiaxis modules grew in part out of the requirement to add a measure of flexibility to dedicated machining systems. Instead of relying on sinde-axis slide units and fixed machine configurations, machining system manufacturers could purchase multiaxis “building blocks” for each station. These multiaxis modules offer the ability to be reprogrammed for new parts, without making major modifications to the basic machine structure. They also allow programming functions such as circular and helical interpolation to be used, minimizing the need for dedicated tooling.
Multi turret modules at their most basic have at least three linear axes. Although large turret heads have been utilized in the past, these were typically on a single, horizontal axis. The addition of two more linear axes separates the modern design from its predecessor.
The essence of what makes the module unique, the turret head contains from two to eight spindles in a radial or semi-radial arrangement. Indexing the turret to the next spindle changes the tool, replacing the function of a normal toolchanger. The size of a turret head is typically determined by the transmittable horsepower, and the dimension across the turret from one spindle mounting surface to the one directly opposite it. Spindles are typically of either a cartridge or multispindle design, with different taper sizes and internal constructions possible to match application requirements.
Optional rotary axes add the ability to access more than one side of the workpiece, and allow machining of complex forms. A fourth axis is becoming a standard, while the fifth axis is typically called for in aerospace applications and for complex automotive parts.
The concept of a multiaxis turret module can also be used as the basis for a highly productive turret machining center. Such machines can be designed with multiple turrets that approach the workpiece simultaneously to complete multiple features in a fraction of the time it would take a conventional, single-spindle machining center. Multiple turrets can also machine the same set of features on multiple workpieces for increased throughput.
Unique machine configurations not possible with cartridge spindles and toolchangers are straightforward with a turret machining center. Because the tool-change operation does not require accessing a tool magazine and changing arm, the cutting axis of the turret head can be positioned in any orientation. This can be of particular benefit for workpieces with features on four or five sides, eliminating the expense and complexity of additional rotary axes.
Current turret technology offers users two to eight spindle stations in the turret. Odd numbers of turret stations are possible, but most turret heads feature an even number of stations, which can be configured to mount an odd number of spindles. Balance of the spindles and tooling around the turret head is important. The mass of the spindles should be as evenly distributed around the turret head as possible for the fastest index times and minimal controller tuning. In some cases, dummy spindles or counterweights of solid steel can provide the necessary balance.
Indexing is accomplished using a sliding pinion shaft that alternately engages the working spindle, or by a ring gear or jackshaft in the turret. This feature allows a single spindle motor to power the cutting spindle and index the turret. Standard AC servomotors with encoders can be used. Similarly, indexing requires no special control features; typically, the control’s spindle-orient function can handle the job. Bidirectional indexing capability can bring the next required spindle into position as quickly as possible.
Modern turrets no longer require a “lift to index” function as part of the tool-change sequence. The turret and its spindles stay in the same plane during indexing, reducing indexing time and eliminating the possibility of introducing contaminants into the turret.
The turret head must be locked securely into position during cutting to maintain accuracy and to transmit cutting vibrations to the machine’s mass center. This is accomplished using either tapered shot pins or face tooth couplings.
Unlike standard cylindrical shot pins, which require clearance between the pin and bore, tapered shot pins lock up with no leftover clearance. As a result, accuracy improves substantially. Tapered shot pins are typically used for turrets under 15.75″ (400 mm) and in applications involving moderate cutting forces.
Originally designed as an efficient method of dynamic torque transmission, the face tooth or Hirth-gear coupling has proved an extremely stable platform for the transmission of cutting forces in the static condition. Applications such as dial index tables and the turret head benefit from the six– dimensional accuracy and high rigidity of the Hirth gear. Clamping and unclamping of the coupling is usually hydraulic, with a backup spring set that locks the gear together as a default. This prevents any undesired rotation in case of a power failure.
The Hirth gear system can be used for any size turret. It is especially suited for turrets 15.75″ and larger, for applications involving heavy cutting forces, and when extreme precision is required.
Some turret designs employ simultaneous spindle rotation. Modern turret head designs use isolated spindle rotation-only the working spindle used for cutting rotates-resulting in more power available for the working spindle and elimination of vibration from other rotating spindles.
The included angle of the turret head refers to the angle between the axes of the spindles. Turret heads are generally configured at 90 deg or 180 deg; the 90 deg configuration is more compact, while 180 deg or flat arrangements offer more radial space for large-diameter tools.
Spindle size and internal construction can be tailored to match application requirements. Users can specify the types and quantities of bearings, sealing methods, speed, and precision of the spindle.
Multispindle heads give turret heads capabilities beyond the conventional single-spindle module with tool changer. Multispindle heads that offer dual feature patterns allow the same turret station to machine two unique sets of features. While small multispindle heads are available for single-spindle modules, their size and complexity is limited by the capacity of the toolchanger. Depending on turret size, the turret head can accommodate multispindle heads up to 18″ (457 mm) or larger.
Regardless of taper, all spindles must have locking methods that are accessible from the front of the spindle. Examples are HSK version C, ABS, ER collets, and DIN 55058. Spindle taper sizes can range from HSK50C to HSK125C-equivalent to CAT30V to CAT60V in capability.
Spindle reaches can be specified to minimize tool gage lengths, and allow full utilization of the tools’ capabilities. Right-angle heads, double-ended spindles, and adjustable-angle spindle heads can complement the capabilities of standard in-line spindles.
LEAD: Bush fails to win Roh’s full support on PSI against N. Korea
U.S. President George W. Bush failed to win support from South Korean President Roh Moo Hyun on Saturday for fully participating in U.S.-led multilateral efforts to interdict North Korea’s transfer of nuclear and other weapons of mass destruction.
South Korea ”is not taking part in the full scope” of the multilateral operations, called the Proliferation Security Initiative, Roh told reporters along with Bush after their talks on the sidelines of a summit of the Asia-Pacific Economic Cooperation forum in Hanoi.
But Roh noted, ”We support the principles and goals of the PSI and will fully cooperate in preventing WMD material transfer in the Northeast Asian region.”
Despite the South Korean rejection, Bush did not make any tough comments on Roh’s position, apparently out of political considerations, merely saying, ”I appreciate the cooperation we’re receiving from South Korea.”
White House spokesman Tony Snow later told reporters that Bush understands ”political constraints” in South Korea, noting that in the U.S. midterm elections on Nov. 7, Bush’s Republican Party lost control of Congress to the Democrats for the first time in 12 years.
The meeting came after South Korea said Monday it will neither expand its role in the PSI nor take any new steps to ”punish” Pyongyang ahead of the six-party talks on North Korea’s nuclear programs.
Snow refused to characterize Roh’s remarks when repeatedly asked whether the United States is satisfied.
But when asked whether the United States expects South Korea to interdict North Korean vessels, Snow said Roh ”did indicate that there were some movements within his government but he did not specify.”
The South Korean rejection came as a major diplomatic setback for the Bush administration, which has been working to make sure that other nations continue to implement sanctions and stop North Korea’s weapons proliferation until Pyongyang returns to the six-party talks and takes ”concrete” steps to abandon its nuclear programs.
Bush has repeatedly warned North Korea against selling nuclear arms to other nations or non-state entities such as terrorists, saying Washington would consider it a ”grave threat” and hold Pyongyang ”fully accountable” for the consequences.
Roh said he and Bush agreed to ”fully support” a U.N. Security Council sanctions resolution adopted against North Korea after it conducted its first nuclear test Oct. 9 following its test-firing of seven ballistic missiles, including a long-range Taepodong-2 missile, in July.
”Our two countries will implement this resolution in a faithful manner,” Roh said.
Roh said he and Bush also agreed to ”actively seek to resolve the North Korean nuclear issue within the six-party talks framework, and also by actively engaging in bilateral talks within this framework.”
Bush said, ”Our desire is to solve the North Korean issue peacefully.”
”We want the North Korean leaders to hear that if it gives up its weapons, nuclear weapons ambitions, we would be willing to enter into security arrangements with the North Koreans, as well as move forward new economic incentives for the North Korean people,” Bush said.
Snow also emphasized that doing so would lead to formally ending the 1950-1953 Korean War, and said Bush sees ”a moment of opportunity” as North Korea agreed late last month to return to the six-party talks, which have been stalled for a year.
Bush and Roh agreed not to tolerate a nuclear North Korea, U.S. and South Korean officials said.
China, South Korea, Japan, Russia and the United States are working to set the stage for North Korea to come back to the table and resume the six-party talks possibly in early December.
The officials said Bush and Roh also discussed the ongoing bilateral negotiations to conclude a free trade agreement as well as Iraq and other Middle East issues.
Based Optimization Drives Mill Profitability, Product Quality
Advanced process control such as model-based analysis, virtual sensors, and model predictive control are now able to impact more aspects of pulping and papermaking
Global competition and escalating raw material and energy costs have forced pulp and paper manufacturers to continuously seek improved efficiencies and lower costs in their operations, while at the same time producing higher quality, more consistent products. Systems and techniques are needed that enable process managers and operators to run their production lines within strategic constraints based on costs, quality, and demand criteria.
One set of emerging applications that delivers on these needs is advanced process control based on model predictive control (MPC) technology. This technology has been utilized for years in many process industries and more recently has moved into pulp mill operations. Now, improved information and control systems are providing the opportunity to extend these applications further into the papermaking process. High quality and robust process models incorporating detailed first principles of pulping and papermaking operations, as well as data driven artificial intelligence techniques, are a key source of systems analysis and online process optimization.
Multivariable process models are now being deployed to improve understanding and control of unit operations as well as entire plants, both in offline and online applications. Solutions currently in use include:
* Model-based multivariable process analysis
* Benchmarking
* Virtual sensors
* MPC
Through innovative product applications, MPC helps paper-makers improve and optimize their processes with low-risk high-return projects. From multivariable analysis and bench-marking to online virtual sensors and controls, process model applications provide the next step in process optimization.
MPC-based applications can be used to optimize specific unit operations or applied across entire operations. With a focus on improved quality and reduced variable costs, these applications will greatly improve paper mill operations in the coming years. Voith Paper Automation provides model-based analysis and optimization through its WebProfit optimization products and services. These applications are delivered as integrated solutions with OnQ quality control system (QCS) installations and OnControl distributed control system (DCS) packages or as stand-alone optimization to legacy systems.
The Growing Meed for Process Optimisation
The business case for new techniques in process optimization has been clearly driven over the past several years by market forces. Increased global competition and higher raw material and energy costs have forced pulp and paper producers to continuously focus on doing more with less. At the same time, converters and end users are demanding better performance and more consistent quality from the products they use.
Under these increasing demands, consistent profitability and even survival of many pulp and paper producers requires improved efficiency and utilization of resources. Beyond basic production procedure and maintenance improvements, sophisticated process optimization approaches hold the key to competitive advantage in today’s global marketplace.
Systems and techniques are needed that enable production lines to run at strategic constraints based on costs, quality, and demand criteria. Typically, the targets of advanced optimization practices are:
* Increased throughput
* Reduced raw material costs
* Reduced energy consumption
* Reduced chemical costs
* Improved quality/reduced variability
Model-Based Optimisation
One approach to process optimization is model-based analysis, prediction, and control. Process models can provide a great deal of information and utility ranging from generalized materials balances through the mill to complex multivariable control of quality properties.
Advanced process control applications have been applied for decades in many continuous and batch process industries. More recently, many pulp mills have applied these same techniques to improve yields and quality based on the ability of these systems to predict results for systems with slow and nonlinear dynamics. Now, improved information technology and measurement systems, including the DCS and robust process historians, are providing the data and connectivity required to extend these advanced process control applications throughout the entire papermaking process.
The preferred process modeling technique is based on first principles knowledge of energy and mass transfer throughout the process. First principles models provide stable and robust descriptions of a process throughout its entire range of operation. However, in a complex system such as a paper machine where all initial conditions are not fully known and where outcomes are affected by unmeasured external influences, equation-based models cannot always accurately describe the process.
Process models can combine process knowledge required to create first principles models with historical data and artificial intelligence, such as neural networks and genetic algorithms. Such models can lead to significant improvements in understanding, control, and profitability. This approach can be used to improve specific unit operations or can be implemented mill-wide.
Transfer machining with a twist
Multiaxis turret modules are an emerging machining technology that offers system builders and users an alternative to conventional single-spindle modules. Compared to a single spindle, the turret head brings advances in speed, accuracy, and power, and when mated to the three-axis module, a degree of flexibility. Together, the benefits of the two machine tool systems offer a new dimension of performance for flexible or dedicated machining systems.
The modern turret head has its origins in high-volume machining applications in the automotive industry. Transfer line manufacturers often include large turret heads in their systems, usually for the purpose of using multispindle heads. A typical application is making multiple holes in automatic transmission housings. A turret with multihead spindles allows completion of drilling, reaming, and tapping operations with accuracy and speed. These large turret heads can be in excess of 31.5″ (800 mm) across the turret, and are normally mated to a single-axis slide unit.
Modern multiaxis modules grew in part out of the requirement to add a measure of flexibility to dedicated machining systems. Instead of relying on sinde-axis slide units and fixed machine configurations, machining system manufacturers could purchase multiaxis “building blocks” for each station. These multiaxis modules offer the ability to be reprogrammed for new parts, without making major modifications to the basic machine structure. They also allow programming functions such as circular and helical interpolation to be used, minimizing the need for dedicated tooling.
Multi turret modules at their most basic have at least three linear axes. Although large turret heads have been utilized in the past, these were typically on a single, horizontal axis. The addition of two more linear axes separates the modern design from its predecessor.
The essence of what makes the module unique, the turret head contains from two to eight spindles in a radial or semi-radial arrangement. Indexing the turret to the next spindle changes the tool, replacing the function of a normal toolchanger. The size of a turret head is typically determined by the transmittable horsepower, and the dimension across the turret from one spindle mounting surface to the one directly opposite it. Spindles are typically of either a cartridge or multispindle design, with different taper sizes and internal constructions possible to match application requirements.
Optional rotary axes add the ability to access more than one side of the workpiece, and allow machining of complex forms. A fourth axis is becoming a standard, while the fifth axis is typically called for in aerospace applications and for complex automotive parts.
The concept of a multiaxis turret module can also be used as the basis for a highly productive turret machining center. Such machines can be designed with multiple turrets that approach the workpiece simultaneously to complete multiple features in a fraction of the time it would take a conventional, single-spindle machining center. Multiple turrets can also machine the same set of features on multiple workpieces for increased throughput.
Unique machine configurations not possible with cartridge spindles and toolchangers are straightforward with a turret machining center. Because the tool-change operation does not require accessing a tool magazine and changing arm, the cutting axis of the turret head can be positioned in any orientation. This can be of particular benefit for workpieces with features on four or five sides, eliminating the expense and complexity of additional rotary axes.
Current turret technology offers users two to eight spindle stations in the turret. Odd numbers of turret stations are possible, but most turret heads feature an even number of stations, which can be configured to mount an odd number of spindles. Balance of the spindles and tooling around the turret head is important. The mass of the spindles should be as evenly distributed around the turret head as possible for the fastest index times and minimal controller tuning. In some cases, dummy spindles or counterweights of solid steel can provide the necessary balance.
Indexing is accomplished using a sliding pinion shaft that alternately engages the working spindle, or by a ring gear or jackshaft in the turret. This feature allows a single spindle motor to power the cutting spindle and index the turret. Standard AC servomotors with encoders can be used. Similarly, indexing requires no special control features; typically, the control’s spindle-orient function can handle the job. Bidirectional indexing capability can bring the next required spindle into position as quickly as possible.
Modern turrets no longer require a “lift to index” function as part of the tool-change sequence. The turret and its spindles stay in the same plane during indexing, reducing indexing time and eliminating the possibility of introducing contaminants into the turret.
Multi turret modules at their most basic have at least three linear axes. Although large turret heads have been utilized in the past, these were typically on a single, horizontal axis. The addition of two more linear axes separates the modern design from its predecessor.
The essence of what makes the module unique, the turret head contains from two to eight spindles in a radial or semi-radial arrangement. Indexing the turret to the next spindle changes the tool, replacing the function of a normal toolchanger. The size of a turret head is typically determined by the transmittable horsepower, and the dimension across the turret from one spindle mounting surface to the one directly opposite it. Spindles are typically of either a cartridge or multispindle design, with different taper sizes and internal constructions possible to match application requirements.
Optional rotary axes add the ability to access more than one side of the workpiece, and allow machining of complex forms. A fourth axis is becoming a standard, while the fifth axis is typically called for in aerospace applications and for complex automotive parts.
The concept of a multiaxis turret module can also be used as the basis for a highly productive turret machining center. Such machines can be designed with multiple turrets that approach the workpiece simultaneously to complete multiple features in a fraction of the time it would take a conventional, single-spindle machining center. Multiple turrets can also machine the same set of features on multiple workpieces for increased throughput.
Unique machine configurations not possible with cartridge spindles and toolchangers are straightforward with a turret machining center. Because the tool-change operation does not require accessing a tool magazine and changing arm, the cutting axis of the turret head can be positioned in any orientation. This can be of particular benefit for workpieces with features on four or five sides, eliminating the expense and complexity of additional rotary axes.
Current turret technology offers users two to eight spindle stations in the turret. Odd numbers of turret stations are possible, but most turret heads feature an even number of stations, which can be configured to mount an odd number of spindles. Balance of the spindles and tooling around the turret head is important. The mass of the spindles should be as evenly distributed around the turret head as possible for the fastest index times and minimal controller tuning. In some cases, dummy spindles or counterweights of solid steel can provide the necessary balance.
Indexing is accomplished using a sliding pinion shaft that alternately engages the working spindle, or by a ring gear or jackshaft in the turret. This feature allows a single spindle motor to power the cutting spindle and index the turret. Standard AC servomotors with encoders can be used. Similarly, indexing requires no special control features; typically, the control’s spindle-orient function can handle the job. Bidirectional indexing capability can bring the next required spindle into position as quickly as possible.
Modern turrets no longer require a “lift to index” function as part of the tool-change sequence. The turret and its spindles stay in the same plane during indexing, reducing indexing time and eliminating the possibility of introducing contaminants into the turret.
The turret head must be locked securely into position during cutting to maintain accuracy and to transmit cutting vibrations to the machine’s mass center. This is accomplished using either tapered shot pins or face tooth couplings.
Unlike standard cylindrical shot pins, which require clearance between the pin and bore, tapered shot pins lock up with no leftover clearance. As a result, accuracy improves substantially. Tapered shot pins are typically used for turrets under 15.75″ (400 mm) and in applications involving moderate cutting forces.
Originally designed as an efficient method of dynamic torque transmission, the face tooth or Hirth-gear coupling has proved an extremely stable platform for the transmission of cutting forces in the static condition. Applications such as dial index tables and the turret head benefit from the six– dimensional accuracy and high rigidity of the Hirth gear. Clamping and unclamping of the coupling is usually hydraulic, with a backup spring set that locks the gear together as a default. This prevents any undesired rotation in case of a power failure.
The Hirth gear system can be used for any size turret. It is especially suited for turrets 15.75″ and larger, for applications involving heavy cutting forces, and when extreme precision is required.
Some turret designs employ simultaneous spindle rotation. Modern turret head designs use isolated spindle rotation-only the working spindle used for cutting rotates-resulting in more power available for the working spindle and elimination of vibration from other rotating spindles.
The included angle of the turret head refers to the angle between the axes of the spindles. Turret heads are generally configured at 90 deg or 180 deg; the 90 deg configuration is more compact, while 180 deg or flat arrangements offer more radial space for large-diameter tools.
Spindle size and internal construction can be tailored to match application requirements. Users can specify the types and quantities of bearings, sealing methods, speed, and precision of the spindle.
Multispindle heads give turret heads capabilities beyond the conventional single-spindle module with tool changer. Multispindle heads that offer dual feature patterns allow the same turret station to machine two unique sets of features. While small multispindle heads are available for single-spindle modules, their size and complexity is limited by the capacity of the toolchanger. Depending on turret size, the turret head can accommodate multispindle heads up to 18″ (457 mm) or larger.
Regardless of taper, all spindles must have locking methods that are accessible from the front of the spindle. Examples are HSK version C, ABS, ER collets, and DIN 55058. Spindle taper sizes can range from HSK50C to HSK125C-equivalent to CAT30V to CAT60V in capability.
Spindle reaches can be specified to minimize tool gage lengths, and allow full utilization of the tools’ capabilities. Right-angle heads, double-ended spindles, and adjustable-angle spindle heads can complement the capabilities of standard in-line spindles.
Turret spindle designs are modular, facilitating change-out for repair, change to a different spindle design entirely, or modification of the order of a given set of spindles in the turret head. This flexibility allows easy future reconfiguration.
Other features of modern multiaxis turret modules include coolant-through or flood-coolant capability and contamination protection via air purge, which maintains a low internal pressure within the turret and spindles to exclude contaminants.
Construction of three-axis modules uses either box ways or linear bearings. Box way slides offer high rigidity, excellent damping, and superior transmission of cutting vibrations. They’re also less sensitive to crashes and contamination.
Linear bearing construction features much lower friction forces, allowing use of smaller axis servomotors and drives as well as higher linear-speed capability. Box ways are used for applications involving high cutting forces and those in which durability, not speed, is the primary objective. Linear bearing construction is used in applications requiring higher feed rates.
Advocacy update: the new Congress: how the recent elections will affect initiatives in 2007
The 2006 midterm elections caused a seismic shift in the U.S. Congress that could have far-reaching effects for parks and recreation for at least the next two years. Early predictions by election experts that the Democrats would gain control of both Houses of Congress proved to be true, albeit by only a razor-thin margin in the Senate.
But what will the results mean for parks and recreation?
Committee and Subcommittee Chairmanships
First and foremost, the most significant impact of the Democratic takeover of Congress is the resulting change in leadership of both the House and the Senate. Every Senate and House committee and subcommittee chairmanship will transfer from Republican control to Democratic control before the start of the 110th Congress. All legislation must pass through the committees, and the influence and control of the chairs and the subcommittee chairs is manifold.
The Democrats are in the process of naming new chairmen now. The Democratic leadership has named most of the major committee chairmen as of this writing, although subcommittee chairs have yet to be chosen. As the Republicans cede control of Congress to the Democrats, their role changes to minority status and their highest status on committees and subcommittees is ranking member.
The 109th Congress was continually challenged by adopting a comprehensive budget for each fiscal year. This past year, the committees made excellent progression preparing appropriations bills for the 2007 fiscal year. However, only two of the 12 appropriations bills were passed before Congress got caught up in election year politics.
When the results of the 2006 elections became clear, the Republican leadership made little attempt to pass the remaining appropriations bills. For many reasons the Republican leadership preferred to punt the thorny budget deliberations to the 110th Congress, and chose to fund the federal government with a series of Continuing Resolutions. The last CR funding federal government operations was expected to expire in mid-February.
The budgets of the Bush years have not been kind in providing adequate funding for federal technical assistance and grant programs to local, regional and state park and recreation agencies. Valuable programs, such as the Rivers, Trails, and Conservation Assistance Program of the National Park Service, which provides planning services and technical assistance to local and state governments on greenway projects, trails and conservation projects, has been proposed for cuts in the past two years, just as many other assistance programs have been cut.
While prospects for the new Congress would seem to be much better for NRPA’s policy and legislative agenda with regard to re-building these diminished federal programs, it should be noted that there is no quick fix on the horizon. Funding will be tight for a number of years to come, and our gains can at best be incremental. However, on the bright side, this should be a Congress that is more willing to agree with our agenda and more receptive to our point of view on these appropriations and assistance programs.
One of the most anticipated and expected changes from the new Congress will be new direction in environmental policy and conservation initiatives. Sustainable energy resources, climate change, public lands use policies, endangered species protection, clean water, air pollution and a host of other environmental and conservation issues will be high on the priority list.
A Mathematical Model for Interplanetary Logistics
This article demonstrates a methodology for designing and evaluating the operational planning for interplanetary exploration missions. A primary question for space exploration mission design is how to best design the logistics required to sustain the exploration initiative. Using terrestrial logistics modeling tools that have been extended to encompass the dynamics and requirements of space transportation, an architectural decision method has been created. The model presented in this article is capable of analyzing a variety of mission scenarios over an extended period of time with the goal of defining interesting mission architectures that enable space logistics. This model can be utilized to evaluate different logistics trades, such as a possible establishment of a push-pull boundary, which can aid in commodity pre-positioning. The model is demonstrated on an Apollo-style mission to both provide an example and validate the methodology.
The development of an interplanetary supply chain requires the unification of two traditionally separate communities: aerospace engineering and operations research. In order to create an effective means of communication between both communities, a distinct terminology has been developed and is detailed extensively in Section I. Specifically, the definition of the commodities or supplies, and the elements or physical containment and propulsion units used to transport the commodities are detailed. Furthermore, the network definition is presented as well as the definition and description of the time expanded network, which is the terrestrial modeling technique employed for the space logistics model. Section II describes the components of the interplanetary logistics problems. Section III presents the problem formulation and constraints. In Section IV a description of the optimization methodology developed to solve this problem is discussed. In Section V the problem formulation and solution methodology is applied for the example of an Apollo-style mission to both explain the implementation and validate the methodology presented. Section VI reviews the contributions of this article and describes continuing work in this area.
The goal of the interplanetary logistics problem is to determine feasible mission architectures to satisfy the demand generated by the needs of exploration. The key concept of the interplanetary logistics problem is that the demand of crew, consumables, equipment and other exploration requirements at in-space locations drives the mission requirements. Therefore, the first required input for the interplanetary logistics problem is the definition of these supplies. For example, if the exploration mission is a sortie style mission to investigate a particular location, the demand might consist of a few crew members at a specific location and the supplies necessary to both support the crew and enable the exploration activities.
Given the demand of the mission, it is necessary to determine how and when the supplies on Earth will be transported to the in-space locations. As missions become more complex and evolve over a period of time, a solution may become less obvious. Since the goal is to minimize the cost of any mission, it is desirable to optimize the timing and method of transport of the supplies to in-space locations. Therefore, it is necessary to define all pathways and structures used for transport, and allow the optimizer to analyze the different architectures to select the best one.
Given this information, the interplanetary logistics problem can determine low cost mission architectures that satisfy the exploration demand. The solution generated will detail the scheduling and assignment of supplies to vehicles for in-space transport and launch scheduling requirements. More importantly, however, the output of this problem can be used to determine a push-pull boundary for the supplies, the potential of a specific location, either on a surface or in-space for storing supplies, benefits of in-situ resource utilization over multiple missions, or even the sensitivity of mission architectures to changes in vehicle parameters.
The first step in developing a model for interplanetary logistics is defining a concrete nomenclature that describes the components of the problem. The problem fundamentally consists of three components: the commodities or supplies that must be shipped to satisfy a mission demand, the elements or physical structures used to both hold and move the commodities, and the network or pathways the elements and commodities travel on. The following sub-sections define the parameters that describe each of these components.
The goal of the space logistics project is to determine how to meet the demand for the exploration missions. As such, we are investigating how to optimally ship multiple types of commodities. For the purpose of the logistics problem, a commodity will be defined as a high-level aggregate of a type of supply, such as crew provisions. Thus, we will define a set of k = 1,…, K commodities, each with the following parameters:
* Denote the demand of each commodity as d^sup k^.
* Denote the origin of each commodity as so^sup k^.
* Define the destination of each commodity as sd^sup k^.
* Define the availability interval of each commodity as to^sup k^ = [sto^sup k^, eto^sup k^], where sto^sup k^ is the starting time of the interval and eto^sup k^ is the ending time of the interval.
* Define the delivery interval of each commodity as td^sup k^ = [std^sup k^, etd^sup k^], where std^sup k^ is the starting time of the interval and etd^sup k^ is the ending time of the interval.
* Define the unit mass of each commodity as m^sup k^ when it arrives at the destination.
* Define the unit volume of each commodity as v^sup k^ when it arrives at the destination.
* Define the number of specified waiting sequences as nw^sup k^.
By defining a waiting sequence as part of the commodity input, a number of wait arcs along the path can be specified, which allows onroute destinations to be designated. For each waiting arc sequence I where 0
* Define the static node of the wait sequence as sw^sub l^^sup k^.
* Define the required waiting time period as pw^sub l^^sup k^.
* Define the wait interval for each wait sequence as = [tw^sub l^^sup k^, etw^sub l^^sup k^], where stw^sub l^^sup k^ is the starting time of wait interval l of commodity k, etw^sub l^^sup k^ is the ending time of wait interval l of commodity k, and etw^sub l^^sup k^ - stw^sub l^^sup k^ ? pw^sup l^^sup k^.
It is important to note that in this model a crew member is treated as a commodity. In practice crewed missions are treated differently during mission planning: however, for the purposes of the architectural design tool created by this model, crew can be considered a commodity with highly restrictive parameter values. By narrowing the availability and delivery windows for a crew commodity, the feasible shipment pathways are limited and reasonable architectures for crewed flights can be obtained.
Elements
In order to ship the commodities from the origin to the destination locations, we require ‘containers’ to both hold the commodities and provide propulsion to move the mass through space. These components can be abstracted to a single definition of an element. Elements are physical, indivisible functional units that transport the commodities from origin to destination. An element is classified by the amount of commodity capacity and propulsive capability it possesses. Elements can be divided into two classes: non-propulsive elements M^sub N^ and propulsive elements Mp. The element parameters are (Figure 1) as follows:
* The maximum fuel mass of a propulsive element m, m euro M^sub p^ is denoted by mf^sup m^.
* The specific impulse of the fuel in element m is denoted by I^sub sp^^sup m^.
* The structural mass of element m is denoted by ms^sup m^.
* The mass capacity of element m is denoted by CM^sup m^.
* The volume capacity of element m is denoted by CV^sup m^.
* The cost of element m is denoted by Cost^sup m^.
Networks
In order to transfer the commodities and elements from the origin node to the destination node, the trajectories must be defined. The purpose of the interplanetary logistics model developed in this article is to analyze the multiple choices available for routing all of the commodities and elements to determine the best logistics architecture. To model the different available trajectories, a network model of space is created to represent the possibilities available for transferring commodities to their respective destination. The following sections detail the development of the space network utilized to form the model presented in this article.
The physical network, or static network, represents the set of physical locations, or nodes, and the connections, or arcs, between them. The physical nodes, or static nodes, represent the different physical destinations in space, including the origin and destination of all the commodities, as well as the possible locations for transshipment. Three types of nodes have been identified: Body nodes, Orbit nodes and Lagrange point nodes. These classifications distinguish the type of information required to define a node of each type. The physical arcs, or static arcs, represent the physical connections between two nodes, that is, an element can physically traverse between these two nodes. We define an arc (si, sj) to be a static arc that represents a feasible transfer from static node si to static node sj.
The mathematical description of the static network is given below:
* Define the static network as a graph GS, where GS = (NS, AS).
* Define the set of nodes, NS = {s1,…, sn}, in the static network.
* Define the set of arcs, AS ? NS × NS in the static network.
An example of an Earth-Moon static network is provided in Figure 2. In this picture we can see the connection of the Earth surface nodes to the Earth orbit node, representing launches and returns. Similarly, the lunar surface nodes are connected to the lunar orbit node, representing descent and ascent trajectories. In addition, the orbit nodes, as well as the first Earth-Moon Lagrangian point, are connected by in-space trajectories.
In order to analyze sequences of missions that evolve over an extended period of time, and to account for the time-varying properties that can arise in certain astrodynamic relationships, we have chosen to introduce time expanded networks as a modeling tool. In the time expanded network the absolute time interval under consideration is discretized into T time periods of length ?t. A copy of each static node is made for each of the time points and the nodes are connected by arcs according to the following rules:
* The arc must exist in the static network.
* The arc must create a connection that moves forward in time.
* The arc must represent a feasible transfer, with respect to the orbital dynamics.
The mathematical description of the time expanded network is given below:
* Define the time expanded network as a graph G, where G = (N, A).
* Define the set of nodes in the time expanded network as N = {i = (si, t) si euro NS, t = 1,…,T}. To simplify the notation, for a given node i euro N, let s(i) and t(i) denote the physical node and the time period corresponding to node i, i.e., if i = (si, t) then s(i)= si and t(i)= t.
* Define node s as the general source that generates the supply of elements. This node is connected to every node in the network where an element can originate.
* Define the set of arcs in the time expanded network as A ? N x N. An arc a = (i, j) = ((si, t), (sj, t + T^sup t^^sub si,sj^)) exists if and only if there exists an arc (si, sj) in the static network, and the transit time from static node si to static node sj starting at time t is T^sup t^^sub si,sj^. Note that if si = sj, then T^sup t^^sub si,sj^ =1 for all t.
* Define path p as a sequence of nodes. In particular, let f(p) and l(p) denote the first node and the last node of path p. If path p originates at node s, f(p) = s for all such p.
Using the static network depicted in Figure 2, we can create the time expanded network in Figure 3. Here, the time expanded network is notional as not all arcs are represented, but how the trajectories evolve in time can be readily seen.
To account for the fact that on certain transfer arcs two burns occur, we slightly modify the time expanded network. We first introduce a new fictitious static node labeled fie. Note that this node is not related to the static network. On every transfer arc (i, j), s(i) ? s(j) requiring two burns we add a new auxiliary node k = (fic, t) with two arcs; one connects i to k and the other one k to j. The value of t is irrelevant. In this new network, each arc (i, j) with s(i) ? s(j) corresponds to a single burn. All such arcs are called burn arcs and we denote the set of all burn arcs as AB.
The fuel mass fraction, which represents the ratio of the fuel mass to the initial mass, for element m to execute the burn corresponding to arc a C A^sub 8^ is defined as:
The execution of a space mission requires logistical decisions at every step. Logistics are required to accumulate all of the required commodities for space missions, as well as procure and assemble all elements at the launch site. However, since at the time of launch all of the items required to perform a space mission are co-located at the launch pad, the terrestrial logistics can be decoupled from the interplanetary logistics model. Therefore, the interplanetary logistics model encompasses all of the logistical decisions required between the launch pad and the locations in-space.
There are numerous decisions made during space missions that can be modeled and optimized to create a better mission description. Although, from a system perspective, it would be desirable to make all of these decisions concurrently, due to computational limitations this is not a reasonable approach. Instead, the interplanetary logistics model is decomposed into three fundamental components: launch packing and scheduling, element packing and in-space network optimization.
Launch is a highly constrained transportation activity, where although traditional allocation and packing decisions are required, many additional constraints are necessary to model a feasible launch. For this reason the launch problem is decoupled at Low Earth Orbit (LEO), creating a boundary between the launch allocation and the in-space network optimization. This assumption is assumed to be only slightly restrictive, since for many mission architectures there exists a delay at LEO before proceeding to in-space destinations. Launching focuses on selecting the appropriate elements to perform the launch, satisfying the payload requirements for launch, and scheduling requirements for launch vehicles and launch sites.