From his office at NASA’s Johnson Space Center in Houston, Nicholas Johnson oversees the space agency’s efforts to track the current status of orbital debris and predict the future. That work has attracted far more attention both nationally and internationally since January 2007, when China destroyed one of its own satellites during testing of an anti-satellite (A-Sat) weapon, and the February 2009 collision between a workingtelecommunications satellite and the retired Russian Cosmos 2251 spacecraft.
With a budget of roughly $5 million and a staff of 20, NASA’s Orbital Debris Program Office conducts research to determine not only the number of small objects in orbit, but also their material density and shape. In addition, that money pays for observations made by the University of Michigan’s Orbital Debris Survey Telescope in Chile to view objects in geosynchronous orbit. NASA and the U.S. Department of Defense (DoD) also rely on the Massachusetts Institute of Technology’s Haystack Observatory to monitor debris in low Earth orbit. The two agencies plan to augment their observation capabilities with a new optical telescope being built on an island in the Kwajalein Atoll to look at debris in geosynchronous orbit and debris in low inclination orbits.
Johnson leads U.S. government endeavors to work cooperatively with international partners to share data on existing debris and limit future production. He heads the U.S. delegation to the Inter-Agency Space Debris Coordination Committee (IADC) and serves as the U.S. technical expert on orbital debris for the United Nations.
Johnson spoke recently with Space News correspondent Debra Werner.
What is NASA’s role with respect to debris and what is the Defense Department’s role?
NASA has the only center of expertise for orbital debris research in the U.S. government. We support all U.S. government agencies, commercial industry and the international community.
When it comes to characterizing the environment, DoD and NASA have a complementary relationship. DoD has responsibility for tracking things larger than 10 centimeters. NASA has responsibility for characterizing the environment for anything smaller than that. NASA also has the responsibility to predict the future environment for both large and small pieces. It’s actually very difficult.
How do you do this?
NASA and DoD jointly fund about 1,000 hours of annual observations by telescopes and radars to characterize the environment for debris smaller than 10 centimeters. We can see things down to 5 millimeters. We can’t track them the way DoD does. But we can detect them, determine how big they are and what their orbits are in terms of inclination and altitude. With that information we can build statistical models of the environment. We’ve been doing this for almost 20 years. So we get very good statistics. Unfortunately, the environment is very dynamic.
The Chinese A-Sat test created over 3,000 large pieces of debris that DoD can see. We think it created over 200,000 particles down to 1 centimeter. The vast majority are still in orbit. The collision between Cosmos and Iridium created over 2,000 large pieces and probably over 100,000 particles down to 1 centimeter. To make matters even worse, the two events occurred at very similar altitudes. So we had this infusion of debris at an altitude where there are a lot of Earth observation satellites, meteorological satellites, just a flock of satellites. So every satellite now is much more at risk than it was three years ago.
Now, having said that, remember that the Iridium satellite was the first operational satellite ever destroyed by impact with debris. The probabilities are still low. Most satellites are more at risk from solar activity, component failure or radiation, but debris is climbing in the priority of things you really have to worry about.
Do you use computer modeling to predict the amount of debris in orbit?
Yes. The model predicts that if we quit launching around the world today, after a few decades the amount of debris would start to climb because of these accidental collisions.
Are more collisions inevitable?
Absolutely. The collision last year was just the most dramatic evidence of that. Since then, there has been a great deal of emphasis on collision avoidance. But even if every operational spacecraft had the ability to do collision avoidance, that’s only 1,000 of the 21,000 large objects up there. The uncontrollable objects will continue to run into each other, whether they are old spacecraft, rocket bodies or smaller pieces of debris. We predict one will happen roughly once every five years for the next few decades.
Can debris be removed from orbit?
NASA doesn’t have a charter to remove debris. No U.S. government agency does. It’s very challenging both technologically and economically. There are some ways we could start moving debris with existing technology, but the cost would be unaffordable. If you give me $100 million, I could go up and move a rocket body, but that’s not going to improve the environment long-term. We need to find something which is both technically feasible and affordable.
If your primary concern is to protect spacecraft in the near term, then what you really want to do is get rid of small debris. The DoD tracks things larger than 10 centimeters, but the smaller particles are untracked.
How could you gather up small particles?
One idea is to use ground-based lasers to radiate a particle and change its orbit to make it fall back to Earth more quickly. There are some technical issues and it is very, very expensive.
Are there political and diplomatic issues as well?
Absolutely. Some of these concepts are less provocative in terms of international treaties than others. Debris could be perturbed by ground-based, air-based or space-based lasers. Of course once you talk about space-based lasers, there are potential problems.
There are other issues. Under the Outer Space Treaty, everybody has perpetual rights to vehicles placed in orbit whether they are defunct spacecraft or rocket bodies. The United States is only responsible for a minority of the debris now in orbit. Most of the mass of the debris in orbit is from the Russian Federation. Unless you have international cooperation in removing debris, it is very, very hard to make significant inroads.
As of today, the U.S. government doesn’t have a policy for removing debris. But clearly, based on what we’ve been doing in the international community for the past 15 years, you have to assume that if we ever did come up with a good idea that was affordable, it would almost certainly be an international undertaking.
Has the international community focused on the issue of debris?
Yes. We stood up the IADC in 1994 with three national space agencies and the European Space Agency. Now, all the major space-faring organizations are part of IADC. Its sole purpose is to share information on orbital debris research.
Is there an international push for debris removal?
It’s premature. We don’t know how to do the removal yet. Once we do, there will be plenty of time to form whatever international relationship we need.
I’ve been the U.S. technical expert on orbital debris at the United Nations for the last 14 years. We made tremendous strides. Our last major accomplishment was the issuance of space debris mitigation guidelines that were endorsed by the entire U.N. General Assembly. We’ve partitioned this problem into two segments: Don’t create new debris unless it is absolutely necessary and, if you do, hopefully it’s short-lived.
When you look out 10 years, what does the debris situation look like?
That’s a direct function of what we do in the next 10 years. We have guidelines. If everybody follows the guidelines, the change in the environment will be very, very modest. One of the good things about debris is that by and large, debris has characteristics which allow it to come back to Earth more quickly than satellites.
One of the saving graces of the Cosmos-Iridium collision was that the Iridium spacecraft was a relatively new design made of composite materials. Those materials are lightweight for their size and are affected by drag much more than other particles. The Iridium particles will fall out much faster than the Cosmos particles even though the satellites were in identical orbits. As we continue to change how we build spacecraft, hopefully if bad things happen, the affect on the environment will not be as severe.
In addition to ground-based telescopes and radars, do you also track debris with space-based instruments?
Yes and no. Last year, DoD launched the Space Tracking and Surveillance System, two demonstration spacecraft to look at new technologies to track not only debris but spacecraft. That will push our capabilities further. Will we ever grow to a full space-based surveillance system? There’s a lot of desire to do that. Right now, that is a DoD responsibility. Until that day, we have to rely on our ground-based radars and telescopes.