ARM and the Mars-Forward NASA
by Martin Elvis
|Then ask what ARM has done for NASA’s thinking. The “Mars-forward” approach is breaking up the old way of thinking about Mars missions.|
Start by admitting that ARM is not a science mission. In some sense, as Rick Binzel said at SBAG-11, it really doesn’t matter what the mission does, so long as technologies get developed and tested that help us get to Mars. As it turns out, ARM does this. The asteroid is a bonus, and ground-based asteroid surveys are already getting a useful boost from NASA’s interest in ARM, although not the thermal-IR space-based survey that many asteroid scientists want, including me.
Then ask what ARM has done for NASA’s thinking. The answer is buried in the slides for the SBAG, but it is a pretty good answer. The “Mars-forward” approach is breaking up the old way of thinking about Mars missions. Some examples:
• Michele Gates presented a “Split Mission Concept” for a human Mars mission, i.e. send cargo to Mars orbit ahead of humans using powerful solar electric propulsion (SEP) developed for, and proven by, ARM. This makes the human segment smaller and more affordable. (slides 4 & 5 of her presentation.)
• Also in the Split Mission Concept: don’t take crew Earth-ascent/descent vehicle (Orion) to Mars and back; transfer in highly elliptical orbit (HEO) or a distant retrograde orbit (DRO) around the Moon on both the outbound and return legs. This saves taking about 20 metric tons of mass to and from Mars, and allows for some hardware reuse on later missions. ARM helps by demonstrating deep space rendezvous and docking and by having a habitat module in one variant of the human ARM mission. This option also shows how NASA is now including multiple missions in its Mars-forward planning: finally, they are getting away from the single-shot approach and moving to a sustained program.
• Pat Troutman put out the idea of using Stickney crater on Phobos as a low radiation environment. With Phobos behind, Mars above, and crater walls all around it‚ it’s about as sheltered as can be for a surface. (Even Kim Stanley Robinson didn’t think of that in Red Mars.) That benign environment allows long stays, up to 900 days. Astronauts stationed in Stickney could teleoperate rovers on the surface without noticeable latency. A first Phobos mission would be greatly helped by using ARM Option B hardware. (slides 14 and 16 of his presentation)
• ARM Option B (“pick up a rock”) requires grippers to hold onto the rock. The “microspine” grippers being developed to do this could also be used for climbing steep rock faces, e.g. lava tubes on Mars (or the Moon.) These are interesting in themselves, but could also serve as good radiation shelters for a crewed Mars outpost or settlement. (This was an offhand comment by Dan Mazanek in his presentation about Option B.)
• More mundanely, but still usefully, developing a lightweight version of the International Docking Adapter (IDA) brings docking capability to all deep space missions, including Mars missions. The big implication is that this allows for more flexible mission architectures.
|By cutting the Gordian knot of too much choice, ARM focused engineering thought on one specific mission. That focus is what has got NASA off the dime of dithering about direction.|
So there’s a lot of new thinking emerging from taking ARM as a starting point. People within the agency had been toying with these ideas, sometimes for decades, but had no way to get them priority, funding, and a tight schedule. Somehow ARM has been a catalyst for all this to bloom. Offline discussions at SBAG-11 suggest that there’s a lot more that hasn’t come out publicly yet but should by the time of the Mission Concept Review (MCR) in February 2015.
Still, why ARM and not a deep space habitat, as Rick Binzel suggested? Couldn’t that be just as good a catalyst? Maybe, but probably not. Here’s why:
• ARM rapidly converged on a single well-defined orbit for energetic and safety reasons. The lunar retrograde orbit is stable for centuries, allaying concerns that ARM could accidentally target Earth. A deep space habitat could go into the same orbit, but there are other contenders including GEO, the Earth-Moon Lagrange points, or a lower lunar orbit. Each orbit has its own special mission implications. By cutting the Gordian knot of too much choice, ARM focused engineering thought on one specific mission. That focus is what has got NASA off the dime of dithering about direction. “ARM is it” is a powerful tool to give engineers specific problems to solve, and not too large an array of possibilities.
• ARM is the right level of challenge. Brent Barbee’s plot of delta-v versus mission duration makes obvious the huge gap from a lunar mission to a Mars mission. The asteroids provide capability stepping-stones (not actual way stations) to building to Mars-capable missions. But having humans learn how to work with an asteroid several tenths of an AU from Earth for the first time would not be smart. Working out the kinks while telemetry delays are minimal and the astronauts are able to get home relatively fast is simply prudent.
• High power SEP is not needed for a deep space habitat, but is essential for ARM. Proving SEP for Mars pre-deployment of cargo needs a long flight and a return to inspect the condition of the hardware, like a deep space LDEF. So why not go somewhere specific (i.e. an asteroid—where else is there?) and bring something back?
• In fact, interacting with an uncooperative body is not easy. The history of humans interacting with failed satellites and upper stages is not encouraging. In five out of six satellite captures by the Space Shuttle, Plan A failed or was nonexistent, and in four of those cases a plan was improvised. On STS-87, the orbiter was almost lost when it nearly collided with the Spartan payload. The much larger masses and the rough boulder-strewn and likely unstable surfaces of asteroids present a significantly larger challenge. That’s all the more reason to practice close to home first.
• Grabbing a rock from the surface of a larger asteroid (ARM Option B) tests much of the technology needed to land on Phobos or Deimos in a simpler, lower-g environment (slide 15 of Troutman’s presentation).
|Judging by the SBAG-11 presentations from NASA, the developers of these technologies are really energized by ARM and by the prospect of other natural follow-on missions.|
That leaves no technology developed for ARM that would not be needed for future Mars missions, at which point bringing back the rock is just a bonus that we might as well embrace. That can be for science, on the one hand. But on the other, space resource utilization is also coming to the fore, and was mentioned by Michele Gates (slide 11 of Gates’s presentation). Originally thought of as enabling for exploration, commercial mining now makes it to the charts. Providing successful demonstrations of water extraction from a carbonaceous asteroid, for example, would be a big step in making the case for profitable space mining. Surprisingly, representatives of neither Deep Space Industries nor Planetary Resources present at SBAG-11 spoke up for this use of ARM.
The other bonus is the realization that either one of the ARM options is able to test several planetary defense methods to accurately deflect an asteroid from Earth impact. It’s not enough to say a gravity tractor is just F=ma. Accuracy is vital so as not to accidentally push the potentially hazardous object through a “keyhole,” turning into an actually hazardous object! Accuracy requires lots of trials. ARM is the first of these.
Judging by the SBAG-11 presentations from NASA, the developers of these technologies are really energized by ARM and by the prospect of other natural follow-on missions, probably to another asteroid in a “native” orbit‚ to Phobos and/or Deimos, and then to the Martian surface. The actual sequence of missions is still being worked out. There’s an unofficial goal of getting the Phobos/Deimos mission launched in the early-mid 2030s because, for reasons involving orbital mechanics, the trips are easier then. That puts urgency into getting the first missions started. ARM has the momentum now. Let’s do it.