Space tracking is about to become much more demanding
This article originally appeared in the Nov. 12, 2018 issue of SpaceNews magazine.
Spacecraft operators long for precise data. If they could shrink the bubble of uncertainty around the location of spacecraft and orbital debris, they could spend less time analyzing possible collisions and less fuel maneuvering to avoid them.
Spacecraft and debris tracking is a serious problem that is about to get worse as companies prepare to send hundreds or thousands of satellites into megaconstellations, said Paul Graziani, Analytical Graphics Inc. chief executive and co-founder.
Commercial companies can help solve the problem by offering data to pinpoint the location of space objects more accurately than the information the U.S. government provides but often are frustrated by what they see as the military’s reluctance to embrace commercial space situational awareness products, Graziani, told SpaceNews correspondent Debra Werner in an interview last week.
The Trump administration’s decision to move Space Traffic Management duties to the Commerce Department may provide an opening. AGI executives are optimistic they will find a more receptive audience there for their products and services.
Graziani has led AGI since he left General Electric Space Division in 1989 to help establish the Exton, Pennsylvania, firm. AGI sells a wide range of analysis and visualization software, including satellite tracking tools.
AGI also operates the Commercial Space Operations Center, a commercial center that helps government and commercial satellite operators track satellites and spacecraft.
Is debris currently a big threat to orbiting spacecraft?
It’s quite a problem and getting worse by the moment. There are various ways of looking at it. There are the threats that we know about, roughly 25,000 objects larger than 10 centimeters. Those are quite a hazard. The International Space Station has to maneuver to avoid these things. Sometimes they hit things. In 1996, a French satellite was hit by a piece of debris.
How do you see the threat of orbital debris changing?
The existing situation is bad. If you follow the trends, you see it’s getting worse and worse because there are more and more objects either being launched or objects being created when things explode.
Occasionally, a booster with some residual fuel in the tank explodes. Then, you get a bunch more objects in space. The smaller objects we can’t track are a much larger problem.
We only track a fraction of the objects in orbit. Right?
We don’t have the sensors nor do we have the processing software to track the smaller things. When they are very small they’re less of a problem. There are millions of things the size of paint flecks, for instance that might cause a problem because they’re moving at high speed but generally are OK. There are about 250,000 objects that are two centimeters and up. We’re only tracking 25,000. You can’t see 90 percent of the objects you need to worry about. That’s a real problem. If you can see something coming, you might be able to do something about it if your spacecraft is maneuverable.
How will the launch of megaconstellations change the picture?
Right now, the number of active spacecraft is probably around 1,400 or so. Several of these large constellations are in and of themselves more than that number. There are several problems there. First off, you just increase the number of objects in space. That’s problem one. Problem two, these objects are maneuvering, typically frequently, because they have to maintain their position correctly in the constellation. To do that, they have to frequently maneuver ever so slightly. That causes a tracking problem.
When things don’t maneuver in space, you can predict several days ahead where that object is going to be. However, if things are maneuvering you don’t know where it’s going to be. They can burn thrusters just a little bit and it can change its orbit position quite a bit. The fact that these things are going to be active and you’re going to have thousands of them raises the problem up to a whole other level.
Also, the spacecraft in a megaconstellation operate at the same altitude. That makes it worse in terms of density or probability of conjunction. When things are at different altitudes, sometimes those objects never cross paths. But when you have thousands of objects all at the same altitude, they pose conjunction risks with each other.
What should be done in terms of tracking and warning?
First off, you have to have the sensors that can track the small objects. In low Earth orbit, you want to get down to around two centimeters. The U.S. Air Force Space Fence is supposed to do that. In geosynchronous orbit, people are talking about observing objects down to 10 centimeters or so.
Next, you have to be able to process a tremendous number of orbits. You’ve got to take in millions of observations a day. Out of that, you’ve got to produce a couple of hundred thousand orbits continuously. Taking the observations from telescopes and radars and RF antennas and processing those into orbits is a big job.
You also mentioned maneuvers.
It is nice if you have a cooperative situation where an owner-operator of a spacecraft can tell you, “Hey, I plan to maneuver at this point during the day.” That helps a lot. If it’s an uncooperative spacecraft, a foreign government for instance that doesn’t tell you about their maneuvers, you’ve got to figure that out. Once you have that information, you have to see if two objects are going to get close enough that they would want to maneuver.
Some operators don’t take all conjunction alerts very seriously because the bubble of uncertainty is so large.
This is a big problem. Current systems track with an accuracy in low Earth orbit of somewhere in the neighborhood of 1.5 to 3 kilometers. In geosynchronous orbit, they track with an accuracy of plus or minus five to 10 kilometers. In geosynchronous orbit, people worry about objects coming within 50 kilometers because of the uncertainty. Obviously 50 kilometers is a big space and if you knew objects were 50 kilometers apart you wouldn’t be worried.
Even with the number of objects we are tracking today, 24,000 or so, you get a tremendous number of warnings. A few years ago, one of the commercial geosynchronous owner-operators said that over a 50-day period they got 11,000 warnings. The number of warnings these megaconstellations would receive with the kind of accuracy would be absolutely ridiculous. Some of them are going to get 824 warnings per hour. That doesn’t work.
What’s the solution?
If you can improve the accuracy of the orbits and additionally know how accurate your orbits are at any point in time, because the accuracy varies, you can provide actionable information. We can say, “Given the conditions right now, we have accuracy of 100 to 200 meters in geosynchronous orbit and 25 to 50 meters in low Earth orbit.” With that accuracy, there are a small number of times per year where somebody would have to maneuver their spacecraft.
Clearly, some of these constellations have tremendous value. At the same time, there are problems that need to be dealt with. Moving the space traffic management function to the Department of Commerce is one of the actions being taken to address that problem.
Anything else you want to say?
We are hoping, and other companies are hoping, the government will take better advantage of commercial capabilities in this area. We’ve been providing capabilities since 1996 when a French satellite was hit by debris. We built an automated capability to ease our workload and do all-on-all conjunction assessment, meaning you check every object that you’re tracking against every other object to see if there are problems.
In the early 2000s, we created a system called Socrates that made that information available to the world for free on CelesTrak, a website that distributes information to the world in parallel to what the government is doing using the government information.
Then about eight years ago the commercial satellite owner-operators began sending us their maneuver schedules. We clear them with each other as well as with government data to make sure nothing is going to hit anything else. Now we have this Commercial Space Operations Center. The problem is that the U.S. government just isn’t interested in using commercial data. We are optimistic the Department of Commerce is going to take advantage of commercial capabilities.