STM Project Overview
Pat
Mantey (PI),
Gabriel Elkaim (Co-PI),
John Musacchio (Co-Pi)
Supported by UC Santa Cruz/NASA University Afiliated Research Center
Background:
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) [2]. 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.
Technical Summary:
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 [1]. 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 [1]. 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 [3].
[1] A. Muldoon, and G. Elkaim, "Improved Orbit Estimation Using GPS
Measurements for Conjunction Analysis," Institute of Navigation Global
Navigation Satellite Systems Conference, 2009.
[2] "Space
Traffic Management: Final Report," International Space University Report,
Beijing China, 2007.
[3]
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.