SPACE JUNK
A PROPOSAL TO MITIGATE, RECYCLE, OR REMOVE
ORBITAL DEBRIS
Space Studies Capstone
14 February 2001
University of North Dakota
by
Steven Bavaro, David Gilmore,
Bob Hatfield, and Jim Wilds
“One
man’s trash is another man’s treasure.”—Anonymous.
INTRODUCTION:
We would like to propose that our Capstone class work on the problem of orbital debris. This project, admittedly not glamorous, is important and has relevance to every aspect of the Space Studies program at UND. Included in this project are difficult technological challenges, human factor implications, policy and legal problems, commercial applications and space history. Interesting synergies between these academic areas also exist. The problem of orbital debris is general enough to allow for several possible solutions e.g. a laser to deflect small debris, a satellite to gather larger debris, a group to work on law and policy, and would therefore be advantageous for a group project. This is also an opportunity for our class to assist in cleaning up Earth’s space environment and in doing so preserve space accessibility in the future.
WHAT IS SPACE JUNK?
Space junk is a popular term used to describe man-made orbital garbage. Types of debris include non-functioning and remnants of satellites, launch vehicles, shrouds, and discarded fuel. As of June 2000, the U.S. Space Command tracked more than 8,900 man-made objects in space. These objects consist of 2,671 functioning satellites, 90 space probes launched out of Earth orbit, and 6,096 pieces of orbital debris such as lens caps and other forms of trash. Space Command radar can detect debris larger than a baseball in low Earth orbit or larger than volleyball in geosynchronous orbit.[1]
HUMAN FACTORS:
Orbital debris is a very real threat to the space shuttle as well as the ISS. The space shuttle was and continues to be peppered with small bits of space debris such as paint chips causing the replacement of more than eighty windows to date.[2] Using information from Space Command, NASA routinely changes the orbits of the shuttle and the ISS to avoid large pieces of orbital debris.[3] The ISS is shielded to survive debris strikes such as man-made or natural meteoroid fragments as large as 2 cm in diameter. However, this leaves a coverage gap of debris between 2 and 10 cm in size, where objects are too big to be shielded yet too small to be detected by Space Command systems. There is a 20 percent chance of a catastrophic impact for each decade the ISS is in orbit.[4] This threat to the ISS makes orbital debris mitigation a prescient and important goal. Debris could puncture the space station forcing evacuation of the damaged module because of depressurization.[5] A plum-sized object with an impact velocity of 6 miles per second a speed typical of LEO could potentially rip a 5-inch hole in a space station module. If the impacting object were larger, the result could be a catastrophic “unzipping” of a space station module thus releasing its contents into space.
ROBOTICS:
One possible solution to orbital debris is the use of robotic satellites. Rather than send humans to a dangerous environment, we could use autonomous robots to do the job. If each robotic satellite was to gather several objects, it might carry several burn-in rockets and several nets, all being accessible by the robotic arm. Normal operation is not time-critical; therefore the robots would be equipped with normal hydrazine rockets for rapid changes of orbit and clusters of ion engines for slower, more fuel-efficient maneuvers. Of course, ground control could always override the onboard navigation computer, but the robotic satellite could be largely autonomous.
ORBITAL MECHANICS:
It is straightforward for a robot (e.g. the space shuttle docking with the Hubble Space Telescope, Solar Max, Mir, ISS, progress auto-docking with Mir, NEAR rendezvousing and landing on the Eros Asteroid) in one orbital plane to intercept and dock with other objects in the same orbital plane. However, rendezvous and grappling a tumbling derelict satellite will certainly be a technical challenge. Changing the inclination of an orbit is very fuel-intensive. So much so that a robot that changes its inclination more than a few degrees would be 99% fuel tank. It would probably be cheaper to place two robots in orbit, one at each inclination, rather than lift all that fuel to orbit to change inclinations. Based on this, a simple strategy would be to select the orbits with the most debris and place robots in that particular orbit. The first step is to triage the hazards: largest threats to least threats. Anything that threatens the ISS falls into the “largest threats” category. Robots are assigned to the orbits in order of number of threats: most threats gets the first robot, least threats gets the last. Robots will gather threats in priority order, changing speed to adjust apogee, perigee, eccentricity and time of right ascending node to match target’s orbit.
POLICY:
We think this class should try to formulate a clear, consistent U.S. policy on orbital debris and propose an international agreement for debris mitigation. In the U.S., at the presidential level, the Reagan White House in February 1988 stated: “All space sectors will seek to minimize creation of space debris.”[6] NASA began to mitigate space debris in 1982 with the venting of unspent propellants and gases from Delta rocket upper stages to prevent unwanted explosions. “NASA Management Instruction 1700.8, Policy for Limiting Orbital Debris Generation, identifies its policy to employ design and operations that limit the generation of orbital debris.”[7] Department of Defense space policy, Air Force regulation SDR 55-1, and U.S. Space Command regulation 57.2, all require that space debris be minimized as much as possible consistent with mission requirements. The Department of Transportation, in charge of commercial space transportation, requires (Office of Commercial Space Transportation’s regulation Chapter III, 14 Code of Federal Regulations (CFR) part III) that each applicant address the risk of orbital debris along with other safety issues such as launch and reentry.[8]
LAW:
There are many laws and international agreements, which could potentially be important in orbital debris mitigation or removal. In the U.S., two kinds of law could apply to orbital debris. The first is regulatory law, where the Department of Transportation in the Commercial Space Launch Act regulates commercial launches. In land remote sensing, the Department of Commerce (DOC) via the Land Remote Sensing Policy Act of 1992 has the authority to regulate satellites. The second type of law that could be applied to damage caused by orbital debris is U.S. tort law.[9]
Several international agreements have potential bearing on orbital debris. The Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, has several provisions (Article VI, VIII, and IX), which could pertain to orbital debris. The Convention on International Liability for Damage Caused by Space Objects is another treaty that applies to orbital debris. Other applicable agreements are: The Convention on Registration of Objects Launched into Outer Space, and The Agreement on the Rescue of Astronauts, the Return of Astronauts, and the Return of Objects Launched into Outer Space. If the orbital debris is radioactive, then The Limited Test Ban Treaty, The Convention on Early Notification of a Nuclear Accident, and The Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency are additional agreements, which could pertain to radioactive orbital debris. Finally, if our class designs a satellite to destroy or remove orbital debris generated by another state, then several issues would come up under international law. Article VIII of the Outer Space Treaty expressly gives ownership of satellites and even component parts to the launching state. “Under customary international law, state property remains state property unless expressly relinquished.”[10] In a relevant maritime law, the U.S. has held that sunken ships remain the property of the flag state. However, if the debris posed a threat to other space users, an argument could be made that a state may take measures to lawfully protect itself from harm.[11]
COMMERCIAL AND ENVIRONMENTAL CONSIDERATIONS:
Wouldn’t it be great to figure out a way to recycle some “junk” satellites or their components? Recycling could have commercial applications if it became profitable to salvage satellites in space. This is because of the tremendous cost of getting material to orbit in the first place. An example is retrieval of an old military spy telescope, salvage it in orbit and transfer it to one of the La Grangian points for astronomical or Earth science use. In this example, several areas of interest would be involved: military, technical, orbital mechanics, commercial, policy, law, astronomy, history, and Earth science. This example also yields two environmental benefits--cleaning up Earth’s orbit and recycling a satellite.
CONCLUSION:
Mitigation, recycling, or removal of space junk would be a great project for this Capstone class. Orbital debris poses a clear and present danger to satellites, the space shuttle, the ISS, and space-walking astronauts. It is a multifaceted problem involving many areas of the Space Studies program at UND. This project would provide ample opportunity for each Capstone student to showcase their creativity, work on a significant set of problems, and allow interaction between academic areas. Finally, the goal of cleaning up Earth’s space junk is an environmentally friendly, noble, and practical task.