Swan, et al., (2010) reported that the Big Sky theory of Space Debris, or the “what, me worry?” approach, has faded into the past as have Sputnik and the Saturn rocket. The space community now recognizes that the continuous growth of objects remaining in orbit has lead to an arena where space debris mitigation and removal becomes mandatory. Indeed, the Space Elevator community is concerned about space debris numbers and densities because of its dramatic growth over the last three years. During the study, the team addressed many issues to include:
• The probabilities of collision in Low Earth Orbit (LEO), in Geosynchronous Earth Orbit (GEO), and in Medium Earth Orbit (MEO).
• The growth rate as it threatens an operational space elevator.
• A reasonable approach for space elevator developers to ensure infrastructure safety.
• Approaches to interrupt sources of debris.
• Mitigation of risk for the space elevator community through design, operations, policies, and lowering the threat.
To assess the risk to a space elevator, we have used methodology from the 2001 International Academy of Astronautics (IAA) Position Paper on Orbital Debris2
“The probability (PC) that two items will collide in orbit is a function of the spatial density (SPD) of orbiting objects in a region, the average relative velocity (VR) between the objects in that region, the collision cross section (XC) of the scenario being considered, and the time (T) the object at risk is in the given region.”
PC = 1 – e(-VR x SPD x XC x T)
Using this formula, we calculate the Probability of Collision for LEO, MEO, and GEO. Our focus is on LEO - - as fully two thirds of the threatening objects are in the
200-2000 km (LEO) regime. The threat from Space Debris can be reduced to manageable levels with relatively modest design and operational “fixes.” Our hope is that this study will raise the awareness of the problem (and spur action to implement policies and directives to mitigate and reduce the risk of collision) to the
space elevator stakeholders and all other users of the near Earth space environment.
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