Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2002-07-08
2004-06-29
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C702S003000
Reexamination Certificate
active
06757612
ABSTRACT:
BACKGROUND OF THE INVENTION
A fundamental characteristic of mankind's use of the low-Earth-orbit (LEO) environment is that devices placed there usually result in the generation of orbital debris as a by-product. When payloads are launched, operational debris pieces and rocket bodies are also often placed in the environment. In some cases, these objects have not remained on orbit as inert hulks; spontaneous disintegrations have often replaced a single large piece of debris piece with up to hundreds of smaller pieces. In fact, approximately 50% of all objects currently tracked were generated by fragmentations of one type or another.
Even payloads themselves tend first to become derelicts before they decay from the environment; presently approximately four out of every five such objects are useless hazards to navigation. From this it may be concluded that the average orbital life of the typical payload is, at least, several times greater than its functional life. Finally, although not yet a significant contributor to the buildup of debris in the LEO environment, collisions may become more frequent as the environment becomes increasingly crowded.
Taken together, approximately 95% of all mass in LEO is trash, and a host of smaller, yet dangerous, objects are suspected to be present. With the exception of very few cases of retrieval (e.g., Long Duration Exposure Facility, or LDEF), the only debris removal mechanism operating in the environment is drag due to the residual atmosphere at LEO altitudes. Even this mechanism was shown to be ineffective above an altitude of 750 km.
Since the continued use of the LEO environment is assured during the upcoming era of International Space Station (ISS) and the anticipated proliferation of LEO constellations of communication satellites (comsat), navigation satellites and other high-value systems, a present desideratum would be the development of methods to assess the impact of mankind's activities on the environment and, in turn, the impact of the evolving environment on mankind's further use. Presumably, if successful in this pursuit, the user community will be able to determine, with sufficient lead-time, what activities and policies are most likely to lead to a stable and desirable environment in the long term. In addition to large-scale LEO debris environment issues, predictive risk assessment models are urgently needed relative to high-value assets, whether individual in nature (e.g., ISS) or operational collectives (e.g., comsat constellations).
The utilization of space is increasing as commercial, military, government, research, and academic agencies discover new ways to exploit the use of this environment. With the increase in the numbers of satellites and debris orbiting Earth comes the increase in importance of protecting the safety of manned and unmanned space-based assets. This explosive growth rate is expected to increase with the deployment of large satellite constellations, both military and commercial. The advent of large low-Earth-orbit (LEO) satellite constellations presents a significant new issue for the orbital-debris environment; this presence of large numbers of commercial satellites is a new phenomenon for modelers of space debris.
Policies, specifically NASA Management Instruction 1700.8 and the Department of Defense Space Policy, dictate NASA and Department of Defense space-faring agencies to strive to minimize or reduce accumulation of space debris consistent with mission requirements and costs. All commercial activities are subject to the Department of Transportation (DOT) Office of Commercial Space Transportation's regulations requiring them to address safety issues with respect to launches, including the risks associated with orbital debris and on-orbit proliferation.
Results of the National Science and Technology Council Committee on Transportation Research and Development Interagency Report on Orbital Debris (1995) concluded:
“There is a need to characterize the orbital debris environment, even when observations are not practical, such as when the size or altitude of objects makes measurements difficult. Modeling, then, is required to combine existing measurements and theory in such a way that predictions can be made. Several types of models are required to make these predictions:
(1) A model to describe future launches, the amount of debris resulting from these launches, and the frequency of accidental or intentional explosions in orbit (traffic model).
(2) A model to describe the number of fragments, fragment size, and velocity distribution of ejected fragments resulting from a satellite explosion or collision (breakup models).
(3) A model which will make long-term predictions of how debris orbits will change with time (propagation model).
(4) A model which predicts collision probabilities for spacecraft (flux or risk model).
(5) A model which predicts hazards in the near term from a breakup event.
SUMMARY OF THE INVENTION
The Particle-in-a-Box (PIB) model of the present invention was developed specifically to address concerns (1) through (5) stated above. Results show the model provides an effective predictive tool to address the above concerns. A concluding recommendation of the interagency report stated that NASA and Department of Defense should continue current activities in orbital-debris research with particular attention to those orbits where critical national security payloads may be located, including International Space (ISS) and telecommunication constellations. This PIB model accomplishes this task with a limited object-size resolution. Recommendations also stressed the importance of focused studies on debris and emerging LEO systems. This invention provides a commercially available user-friendly space environment modeling package much needed by government agencies and commercial entities to address these policies and requirements.
The original PIB model was a single-particle, single-stratum averaged treatment of LEO, capable of global evolutionary and stability analysis. Without sacrificing its capabilities, the model resolution is increased by more than an order of magnitude from the original PIB model, resulting in substantial pay-off. The increased ability of the model to accept detailed phenomenological data represents a quantum leap in modeling applicability, as was shown by analysis of impact-risk-assessment studies of high-value assets such as the International Space Station and constellation, with cataloged objects (40 centimeter objects and larger).
An exemplary embodiment addresses impact risks significant for all space-based assets, including astronauts on extra-vehicular activity (EVA). This increase in fidelity improves the global (evolutionary and stability) analysis, which the PIB was originally developed to perform.
In developing a mathematical model of any evolving system, one must first choose a relevant parameter as the “state” quantity. In developing the current model, the number of objects resident in the LEO environment at any given time was selected. The primary reason for this choice is that if an object can be seen, it can be counted—the number of objects on orbit is a direct observable subject, of course, to an appreciation of possible incompleteness, especially at higher altitudes and smaller sizes. The basic equation of the model is presented as follows:
{dot over (N)}=A+BN+CN
2
(1)
Where: N=number of objects on orbit
{dot over (N)}=time rate of change of the number of objects
A=deposition coefficient
B=removal coefficient
C=collision coefficient
The form of the equation follows from the assumptions that: (1) deposition reflects the rate at which users of the LEO environment choose to populate it with new objects; (2) decay due to atmospheric drag and/or random (debris sweeper) removal may be represented as a finite probability per unit time of the decay of any given LEO object; and (3) the theory for collisions between members of the population may be developed along a line of reasoning
Cheung Ken C. K.
Nishimoto Daron L.
Talent David L.
Creighton Wray James
Gutierrez Anthony
Hoff Marc S.
Narasimhan Meera P.
Oceanit Laboratories, Inc.
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