If it’s up to Elon Musk, people are going to the red planet – and soon. Over the past few days, our senior space master Eric Berger has been analyzing in detail the plans of Musk’s interplanetary transport system, and our chief scientist Dr. John Timmer has explored the science of how to generate resources on Mars. But Musk’s thoughts of coming to Mars and living there – both the details and the whitewashed blank bits – still seem like science fiction to many people. It’s all well and good to talk about building a huge rocket and a self-sufficient colony on Mars, but that’s something else entirely to do the.
So who better to discuss the differences between science and sci-fi than a real sci-fi author – someone who spent years studying the problems of survival on Mars before coming up with a killer story about exactly how it could work? And we just happen to know the perfect person: author Andy Weir, whose best-selling novel The Martian (and the subsequent Ridley Scott movie) covers much of the same ground Musk wants to cover, though Musk dreams on a much larger scale.
“In-situ resource generation”
While Musk and SpaceX envision a long-term plan involving thousands of launches to Mars, the company wants to return most of those spacecraft to Earth — otherwise, as Musk explained, we’d end up with a giant “spacecraft graveyard.” Mars. This leaves us with two options: the Mars spacecraft must take their return fuel with them, or they must somehow generate it on Mars (“in situ”, as the terminology goes). Since every gram of mass that goes to Mars has to be paid for in fuel (including the mass of the fuel itself), generating the fuel On Mars is much preferable to lugging all that fuel around and paying the mass fine for it.
Musk’s rockets run on methane and, as John Timmer discusses in detail, making methane on Mars isn’t actually complicated. Take some carbon dioxide from the atmosphere, mix it with hydrogen (which you can crack from water molecules, which Mars has in surprising abundance), add energy, pressure and a catalyst, and boom, you’ve got methane and water.
“It turns out that Mars is very cooperative when it comes to the Sabatier response,” Weir said in a long conversation with Ars earlier this week. “All you need to do it is carbon dioxide, water and energy. And presumably you will take an energy source with you when you colonize Mars, such as a reactor or just tons and tons of solar panels, although the correct answer is reactor.’
In The Martian‘s fictional Ares missions, future NASA chose to send tanks of hydrogen along in its ascent vehicles, effectively preparing the gas instead of having to extract it from the environment. “But I wrote that at a time when Mars was widely believed to have very little water,” Weir said. “Since then, thanks to Curiosity, we’ve learned that Mars is riddled with water. You can literally just scoop up the dirt and dry it out and you get…” Here he paused, looking up briefly to remember the fact: “… there are thirty-five gallons of water for every cubic yard of soil, so all the hydrogen what you can hope for. It’s all there.”
Life, the universe and rocket engines
Musk didn’t shy away from daring (or possibly madness) with the rocket SpaceX plans to use for its Mars missions either. The planned interplanetary transport system will require a launch vehicle currently dubbed the “BFR” (which ostensibly stands for “Big Falcon Rocket” – that’s their story and they’re sticking to it), the first stage of which uses a massive cluster of forty-two Raptor engines to provide nearly four times the thrust of the first stage of the Saturn V Moon rocket.
The reasons for opting for a slew of smaller engines rather than a few massive engines are many, but there are also risks – especially around the complexity of the plumbing and controls to run so many separate thrusters. The only other example of a launch vehicle with something approaching that many engines is the ill-fated Soviet N1 booster, which packed thirty NK-15 kerolox engines into its first stage. Between February 1969 and November 1972, four N1 boosters flew from Baikonur and all four exploded. Three of the explosions were related to or directly caused by the complex KORD system that managed the N1’s engine package. (KORD is an acronym for “Control of Rocket Engines” – “KOntrol Racketnykh Dvigateley” or Контроль ракетных двигателей.)
But comparisons between the underfunded N1 and the potential failures awaiting Musk’s ITS BFR aren’t necessarily valid or helpful. We asked Weir how he felt about Musk’s idea of putting forty-two engines on a rocket.
“It makes me feel good,” he replied. “The more motors you have, the more safe failure points you have. In other words, if, you know, if four engines fail on the climb when you have forty-two, you just burn the other thirty-eight a little longer. If four of your five Saturn V engines fail during takeoff, then you’re superfucked.”
“The complexity that the Soviets ran into with the N1 was all about operating systems, and now we have computers that can handle that sort of thing… So yeah, I think lots of small engines is a good approach,” he laughed. “The only question is how much mass you end up putting on the booster to have all those motors — to have a whole bunch of motors instead of one big one. One big one can be a more mass efficient method of getting the same thrust than the equivalent number of small.”