STM Project Overview
Pat Mantey (PI),
Gabriel Elkaim (Co-PI),
John Musacchio (Co-Pi)
Management of space traffic is a growing problem, with the increase in the number of satellites launched, and the growing volume of space debris. Preliminary investigations of the concept of a "Space Traffic Management System" (STM) were made in the 2007 Summer Session project of the International Space University (ISU) . In their report, a number of tasks were identified that should be more carefully analyzed. With this as a starting point, our project is endeavoring to establish a Space Traffic Management Research Center, investigating and analyzing in more detail some of the preliminary concepts and results from that study. To that end, we have already in a relatively short period of time with a modest budget made progress in investigating key STM research questions.
Our effort is divided into two areas of focus: improving the tracking uncertainty of satellites and debris and understanding the economic issues of STM. Since beginning our work nine months ago, we have made significant early progress, including publication of a paper at the ION-GNSS conference . We focused our early tracking accuracy investigation on comparing the positions of GPS satellites, whose positions are known with very high accuracy, to their positions as published in TLE data published by NORAD. Using a closed form analytical method, we have found a systematic bias in the TLE reference frame that can be estimated using a single quaternion error, and this bias can be exploited to reduce tracking errors . In future work we will repeat our analysis to LEO satellites with orbital data available, and ascertain the consistency of this bias. This combined with other data on the cost-benefit of reduced uncertainty yield results that indicate if future owner operators need to augment their payloads with GPS or other positioning sensors.
Our research indicates that orbital position and uncertainty can be both estimated and improved, and there remains a strong possibility of using our validated results to determine orbital covariance based entirely on the TLEs themselves. That is, future research will indicate if the sequence of TLEs can be used in a Kalman filter type scheme to bound the uncertainty in position; this will be validated on satellites with known orbit data. If successful, this would mean that position uncertainty can be calculated from the published TLEs, and the economic effect of the improved data can be computed.
Our initial economics investigation focused on whether a satellite owner operator would have an economic incentive to follow the collision avoidance maneuvers prescribed by a hypothetical, centralized STM system. Our preliminary results suggest that such a STM system would need to have a tracking accuracy on the order of 2x2x5 km in order for an operator to find it economic to heed the recommendations of such a system.
Another key aspect of the STM problem is its international character. To achieve any mitigation, individual nations must incur costs to de-orbit de-commissioned satellites, reduce explosions of launch vehicles, conduct collision avoidance, while the benefits of such investments are shared by the entire world community. Whenever individuals have to act to protect a shared resource, there is a potential for a tragedy of the commons scenario – individual decision makers will under-invest in protection if they only see a fraction of the benefits coming from the investment. The same problem arises in the area of environmental protection. Consequently, there has been a stream of literature in the past 10 years that seeks to understand how nations can form coalitions by signing International Environmental Agreements (IEAs) to counter the potential for tragedy of the commons scenarios. We are currently studying how the models of IEAs, usually applied to domains such as green house gas emissions, can be applied to the problem of STM. Most of the literature supposes that nations will only join an IEA if it is in their individual self interest, so some nations might choose not to join – particularly those nations that have a high cost for reducing their pollution output and/or a low individual benefit from improving global pollution. These asymmetries also exist in the STM field, as nations differ greatly in their reliance on space, as well as having the technology for mitigation. In the green house gas domain, nations contribute to a global CO2 concentration – a single number that characterizes the "state" of the system. In STM this is not quite the case, as there are many different orbits – debris in a sun synchronous orbit ought not affect geostationary satellites for instance. We are working to understand how these differences might affect the likely outcomes of IEA like coalitions in the STM field. Our work in this area will appear at a conference .
 A. Muldoon, and G. Elkaim, "Improved Orbit Estimation Using GPS Measurements for Conjunction Analysis," Institute of Navigation Global Navigation Satellite Systems Conference, 2009.
 "Space Traffic Management: Final Report," International Space University Report, Beijing China, 2007.
 M. Singer, J. Musacchio "Model of an International Environmental Agreement Among Asymmetric Nations Applied to Debris Mitigation," to appear in 60th International Astronautical Congress, Daejeon, Korea, Oct. 2009.