Four different ways to keep satellites alive

In 2011, the communications satellite operator Intelsat and the Canadian firm MacDonald, Dettwiler and Associates (builders of the robot arm on the International Space Station) announced an agreement. MDA would build a robotic servicing vehicle to refuel Intelsat's 55 spacecraft in geosynchronous orbit. That agreement was later cancelled; however, MDA has put out some materials to continue marketing the idea. Also last year, a new American company, Vivisat, was formed, to do the same mission with a somewhat different approach. Rather than refueling the spacecraft, they would attach a module with its own propulsion system. The end result would be the same: the spacecraft wouldn't need to be sent to the "graveyard" just because its propellant was exhausted.

This week, Vivisat has announced plans to have two of the modules built by ATK, an experienced aerospace company. So the vision of robotic satellite servicing continues to advance (although it seems painfully slow progress to those of us who have worked on the concept since 1999.) Also, since this is a private sector initiative, it is strictly business-case based, rather than having to rely on the vagaries of government funding. Private enterprise can also be more aggressive than government, as SpaceX has showed the world.

Not to be outdone, NASA has been contributing knowledge and resources to the satellite servicing game. Their Robotic Refueling experiments on ISS are ultimately targeted at GEO spacecraft as well. These experiments are more consistent with the Intelsat-MDA approach, in that they are testing ways of adding propellant to spacecraft that weren't designed to be refueled. Presumably the robotic mechanisms there would be tele-operated, as they were in the RRM experiments. One might be concerned that controlling robots over such large distances and long time delays would be highly risky, but a recent control experiment between ISS and the ground provides grounds for optimism.

The notional servicing mission NASA has conceived  uses a traveling fuel truck to go from customer to customer. Another concept they have discussed is an actual "service station" in GEO, a central point where the refueling of all GEO birds takes place. At this early stage it's unclear whether the customers use their own propellant to get to the service station, or whether a "tow truck" takes them there. The former approach requires less hardware, while the latter provides the ability to move dead satellites as well as functioning ones.

The "tow truck" concept itself represents yet another approach to keeping GEO satellites alive. It does not add fuel to the satellites; rather, it simply promises that, when they run out of propellant, the tow truck will take them to the graveyard. This ability to exhaust propellant could add several months to a couple of years of life to each spacecraft. It's not as long an extension as the other concepts promise; but it is much, much simpler technically. And the technology to dock spacecraft autonomously MUST be developed by any of the other methods anyway! NASA is working on it . For the record, a program that I conceived and managed for DARPA demonstrated it in the lab in 2005. The "tow truck" method has legal, insurance, and contractual implications, which have received some study .

Here are the bottom lines:

1. The space community seems to have moved past the point of skepticism regarding on-orbit servicing.

2. None of these four methods are perfect: the "life extension module" wastes expensive hardware by using it only once; the two refueling approaches require very complex manipulations; and the "tow truck" method doesn't provide as much life extension as the others (although it has other advantages.)

3. Autonomous rendezvous and docking is essential to any servicing method. Once docked, the robotic mechanisms have a static target (in relative space) to deal with rather than a dynamic one. This technology must be given very high priority.

4. The NASA and private efforts need to be integrated into a public-private joint enterprise. SpaceX could not have accomplished its missions to ISS without significant NASA support. Community leaders must establish that same kind of cooperation, to make robotic on-orbit servicing a reliable and profitable activity.

Doing more with less

Here's a column from FloridaToday.com that recommends that NASA do exactly that: find ways to be more innovative and get more exploration done using existing resources.

It's probably obvious to most readers that robots offer that opportunity: robotic space operations are MUCH cheaper and safer than the same operations done by astronauts.

Some parts of NASA seem to be getting that. Goddard Space Flight Center is leading an initiative to put a servicing station in geosynchronous orbit. Some earlier concepts to do that were manned, but I presume we are now talking about robotic operations there. Good thing, given how intense the radiation levels in GEO are.

Another initiative, to assemble a telescope at the Space Station using robotics, doesn't look like it will be funded this year. But hopefully the planning will go on.

What could put all this into high gear would be a COMMERCIAL initiative for robotic servicing of GEO spacecraft. There's a good business case for it, as laid out in this MIT master's thesis . (Truth in advertising: I was the sponsor.) When you keep spacecraft in GEO operating longer, whether by refueling them or by simply allowing their fuel to deplete, everyone wins. The satellite operator derives revenue for a longer time; the servicing provider gets a fee for the refueling or disposal service.

It's time to put that business plan into action!

Controlling robots from the Space Station

The BBC reports that a ground robot has been controlled successfully from the International Space Station . Why does this matter?

1. It means that it should work equally well in the other direction. So, for instance, if you are trying to control robots refueling satellites in geosynchronous orbit, you could use this delay-tolerant technique.

2. It shows a path to preparing for settlements on Mars. CEO of XCOR Aerospace, Jeff Greason, has laid out a strategy for developing a Mars settlement that begins with a landing on Phobos, and controlling robots on the Martian surface from there. This ISS robot-control demo shows that that idea will work, or at least the control part of it.

There are also even more advanced communications approaches being tested, although not on the Space Station yet, like this advanced optical communications approach .

Coolness. There are other nifty robotic things going on on ISS--for example, they have experimented with refueling satellites using teleoperated robots. They are thinking about having a refueling station in GEO, and about using robots to build things at ISS, like giant telescopes.

So ISS is becoming a lab for New Space testing! That's very important, because it really shows a mental shift at NASA. NASA became famous because of human spaceflight accomplishments--but this really will be the century of robots in space. NASA has decided to become a part of it.