How would ELROI let us know which satellites are which?

Many manmade objects are in orbit around Earth. How do we know which are which? The problem is, we don’t. Not always, anyway. Oftentimes, we can identify satellites and debris. Our abilities to do so, however, are imperfect. As the amount of traffic in orbit increases, our imperfect abilities will become more troublesome. An interesting solution to this problem being developed at Los Alamos National Laboratory is ELROI – the Extremely Low Resource Optical Identifier. We spoke with David Palmer, a scientist at the lab who is developing ELROI, to learn more about this technology.

What need is there for space object identification?

Nowadays a single rocket launch can release over a hundred satellites, and it can take weeks, months, or never until a satellite operator can figure out which is which. They point their radio antenna and shout at each object in turn until one answers back, and then they can talk to it, commission it, and start operating it. Until then, the satellite is useless. Sometimes none of them answer back, and without knowing which one is theirs it is hard to figure out what is wrong and how to fix it. There are about a hundred payloads in space today that are still unidentified and are listed in the satellite catalog only as OBJECT X.

Space is big, as someone said, but the parts that we actually use, close to Earth and in the GEO belt, are getting pretty crowded. There are a couple of thousand active satellites, and ten times as many pieces of debris. In the next year or two SpaceX alone will double the number of active satellites, along with hundreds more cubesats and other satellites. New radars are coming online that will boost the number of tracked debris pieces up towards a million.

With all those objects whizzing around, things can crash into each other at orbital velocities, producing shrapnel that can hit other objects, producing even more shrapnel until space becomes unusable. The US Air Force and other organizations are tracking as much as they can and calling up spacecraft operators so that they can dodge if a collision looks imminent. However, it’s harder to keep track of things without labels, and even if you know a collision is coming you have to know which satellite it is so you know who to call.

How easy is it now to identify space objects, and what initiatives are underway – such as ELROI – to make identification easier?

Right now, radars and telescopes track all the objects that are released from each launch, and as the operators figure out which satellite is theirs, they change the name in the catalog from OBJECT X to the correct identity. Then the radars and telescopes have to re-observe each object every week or so to keep track of how its orbit has drifted and make sure that this thing that they are seeing now is the same as the one they saw last week. They need to repeat this each week for the rest of the object’s orbital life. In the 1980s there was a solar storm that puffed up the atmosphere causing a lot of unexpected drag on the satellites and we lost track of a lot of them – some for a while and some forever.

Some of the more advanced satellites carry GPS units and can figure out their own orbits and send the information to the ground, and that helps a lot. But even then, that only works if they turn on properly and stops when the satellite is retired and its radio is turned off. There are various proposals to add dedicated radio transmitters just for tracking and identification, but those are bulky and power hungry, and radio interference is a big problem that means you don’t want all the dead satellites in space to beep forever.

ELROI (which stands for Extremely Low Resource Optical Identifier) is our solution. This is a little flashing light that can be built into a solar-powered package the size of a Scrabble tile. The flashing light can be seen with a small telescope on the ground and its blinks encode a “license plate number” that tells you exactly which satellite it is.

Since it is solar powered and completely self-contained it doesn’t depend on any of the other spacecraft systems working. You can attach this to any object going into space, even to a rocket body or other debris piece that doesn’t have power or communications systems of its own. It is small and simple enough that adding it to a cubesat doesn’t mean you have to take off anything else. Since it is just a blinking light, you don’t have to turn it off at end-of-mission because it doesn’t cause any radio noise. You can identify the satellite from launch until the time it re-enters.

How did you become interested in developing ELROI?

I was working on the problem of space debris and tracking. I was also working on the uses for very sensitive cameras we had developed at Los Alamos National Laboratory. I was also observing pulsars out in space, where you can detect a very weak signal because it repeats with an extremely accurate period. Putting them all together, I realized that I had a solution for a very important problem facing the world.