Confronting the Credibility Gap for Crewed Exploration of Mars
(Notes from talk on September 22, 2016, at the Mars Society Conference)
Look at this amazing picture of Mars! I don't think I have to try very hard to convince you that it would be cool to stand in Gale Crater and look through the haze towards Mt Sharp. But to achieve our goal and send humans to Mars we have to convince a lot more people, and that's what I'm here to talk about today.
First, a bit of information about me. I did a PhD on gravitational waves at Caltech, and got an opportunity to sword fight with my collaborator. More recently I'm the levitation engineer at Hyperloop One, where we're building high speed vacuum trains. On Mars, I made this neat 3D printed ring and then later did some research into emergent flow networks using MOLA data. The Mars crust has deformed, the geoid has changed, and so the rivers don't always go the way you might expect. (arXiv:1606.05224)
So, I'm here to talk about a difficult issue, but I'm not here to criticize pointlessly. It's easy to be negative. I am overwhelmingly enthusiastic about Mars exploration and extended habitation. The credibility gap amongst Mars crewed exploration advocates is a serious issue that hampers that effort. It's vitally important to raise our profile among the general public, since ultimately they will foot the bill, and in general opinions on crewed space exploration range from ignorance to ambivalence to skepticism. And this is not entirely unwarranted. I'm going to talk about three different aspects of credibility, working from the outside in. First, I'm going to talk about public credibility, as mediated by an occasionally unreliable or sensationalist media. Second, I'm going to talk about mixed messaging within the space community, and reconciling authority with humanity. Last, I'm going to offer a couple of illustrative examples to point out that there are still serious unsolved problems relating to crewed exploration, namely entry descent and landing (EDL) and earth return. We have to be more internally and externally honest about confronting our ignorance in this regard.
First up, let's talk about the role of media. Mars One is a perfect case study. More publicity than any other human Mars mission has gotten in years, and also completely vacuous. I googled "Mars One credibility" and got 189,000 hits. The first 6 hits include how Bas Lansdorp, the CEO of Mars One, whose only job is to know everything about putting people on Mars and keeping them alive, got absolutely smashed here in a debate with MIT students last year. "Do you realise the astronauts will run out of nitrogen on day 59 and die?" So Mars One isn't really funny, it has probably set back the credibility of the movement by a decade. Hype, opacity, haste, are all hallmarks of counterproductive media strategy. There is a dark side to publicity.
Let's look at a few examples of imperfect media coverage. Here are two cases from the recent, and highly flawed study suggesting that space radiation caused heart disease in the handful of Apollo astronauts who already died - at rather advanced ages, given their lifestyles! What blew my mind here is that there is not one, but two different stock photos of depressed astronauts in space suits. The ultimate slow news day is hand wringing about radiation or wishy washy psych factors.
The other major kind of shonky coverage covers mythical propulsion. The idea is that spending 6 months getting there is too long, so we can't go until we have warp drive. And so we have articles about actual warp drive. I did my PhD on this sort of thing, not only is it complete garbage, even if it wasn't, it would still be extremely inefficient. Yet these articles have images where we know how many windows the spaceship has! We also have "Mars in three days", from 1g acceleration the whole way with lasers a million million times more powerful than any existing laser, and no mention of how to slow down, how to get back, or how to handle the thermal issues of being shot with the death star. And then you have the EM/reactionless drive, which is less efficient than a Hall effect thruster, and also impossible. Not to mention the VASIMR thruster, about which no-one ever mentions the need for gigantic gigawatt scale space nuclear reactors. Sure, it's cool and an interesting propulsion system to research, but the full picture should be available.
Of course, it's not all bad. A lot of these articles are actually pretty good, the headline just refers to the most controversial aspect of the article to be click baity. The writers aren't bad people, to be writing about Mars already they're one of us, maybe they just need some expert help. I reached out to the writers of the articles I referred to and one of them has already gotten back to me. Which leads me to a deeper point - it's easy to sit in the ivory tower and criticise, what I'm trying to do is show that communication between the general public and the experts is mediated by the media, and we can collate the information better. Sometimes they even get it unbelievably right - how good was The Martian? The first step is to take the Socratic approach (no longer punishable by death) and ask questions. Search Google, Quora, or even the Mars Society Facebook page. And, if you want to be told you're wrong by a thousand people, you can try Twitter.
So, what are warning signs an article is probably bullshit? Does it violate laws of physics? Does it promote transit times of less than 90 days? Does it involve warp drive? What about content-free hand-wringing over psych factors? No-one is saying that psych factors aren't an issue for crews in space for years at a time, but there's a gulf of credibility between the typical slow news day and some actual serious stuff backed by real data. Does the article have no quotations or endorsements from recognized experts? Does it have no reference to peer reviewed papers? Does it have a naked agenda, or uncritical reporting? Lastly, does the headline ask a rhetorical question to which there is an obvious answer: No!?
What can we do to help? Reach out and if you're an expert, make sure your local writers have you on their rolodex. If you like working with writers, consider joining the Science and Entertainment Exchange. Many of my colleagues have consulted on Marvel Movies, and it's always a lot of fun getting a whispered phone call at 2am saying "you're a physicist, how can I destroy the world?" "well, strictly between you and me…"
So we can help improve media coverage, and our problems are solved, right? Well, not really. It's easy to criticise, but it's unfair to do so without also taking a hard look at our own internal messaging. Even the pros make mistakes, and we need to be honest and circumspect about it. To what extent are we responsible for the credibility gap? We should know better than anyone that there are real challenges that can't be wished away, that Mars is hard, and that "all you gotta do" doesn't really cut it when human lives are on the line. Yes, humans will die in space, and on the ground building space machines, but I'm sure we can all agree that we want to minimize people dying for stupid reasons. And so, as a couple of illustrative examples, I'm going to look at the titans of the movement and nitpick for a bit. First, Elon Musk's suggestion that space radiation can be solved with a column of water between the astronaut and the sun. This only works if the column is of a comparable size to the gyroradius of protons in the solar magnetic field, which is a few thousand km. So, the pros sometimes make mistakes, as we saw with SpaceX's last attempted launch. And then the original slides for Mars Direct, I saw as a kid when the Mars Direct book tour came to Australia, which suggested a first launch in 1997. We earn no credibility by pushing optimistic or aggressive timelines. Or, for example, our own Robert Zubrin's oped in 2012 in the Washington Post, suggesting 3 Falcon Heavies to fly 2 humans to Mars, a mission plan that no expert I know hasn't found a problem with. The Dragons are too heavy to land on Mars, and too crowded for people to live in, once all the provisions are also added, like Gemini but for 150 weeks instead of 2. It doesn't pass the sniff test - it smells of desperation. Falcon Heavy is a terrific rocket, but it's not for humans to Mars, or back.
At the end of the day, though, Elon or Bob miscommunicating some small aspect of a hypothetical mission is not the end of the Earth. It's easy to be critical, let's be constructive. Let's go one level deeper and look at two giant issues which are recognized but mostly unsolved, that of EDL and Earth Return. Rob Manning (JPL chief engineer of Pathfinder, MSL, and LDSD) held a series of conferences at JPL starting in 2004, recounted in Chapter 5 of his enjoyable book. At these conferences, the EDL challenge was recognized, defined, explored, and even now, 12 years later, there is no dominant, obvious solution architecture. A lot of the proposed solutions will be covered in the following talk by Kshitij Mall, so instead I'm going to describe only the problem. A great book if you are looking for a description of the state of the art is (MSL's EDL lead) Adam Stelzner's "The Right Kind of Crazy".
What is the EDL problem? We don't know how to land more than about 1T on the Martian surface. We obviously need to land 10-100T for human missions. Existing solutions do not scale. Without >10T landing, we have no Mars ascent vehicle, we have no ability to return to Earth, so we have no program. This is a serious issue! Entry, descent, and landing is composed of 3 parts. The entry part is where a heat shield is used to slow down from 5.7km/s, which is escape velocity, to terminal velocity, which is around 500m/s or Mach 2. This procedure burns off more than 99% of the kinetic energy, and the limiting factor is that Mars' atmosphere is really thin. The ballistic coefficient is a measure of surface density, or 'thickness', defined as the mass divided by the heat shield surface area. For all successful landers, it has been very very low, between 60 and 150kg/m^2. If we imagine a heatshield as big as the biggest payload fairing we can imagine, maybe 11m diameter, then we have a vehicle on the surface of perhaps 11T, which is really too low. This methodology, a gigantic flat flying saucer, has no headroom. Blunt bodies do not scale to 10T-100T range - there is simply not enough atmosphere to slow you down before you hit some tall mountain. There have been a few attempts (ADEPT, LDSD) to increase the size of the heat shield, but they are marginal, structurally problematic, relatively unguided, and have poor scaling characteristics. We need a new approach to entry. Bi/triconic hypersonic lifting bodies are, in my opinion, our best hope.
The good news is that landing, under subsonic propulsion, does scale extremely well. But there is still the descent problem. At 500m/s, the vehicle is still supersonic, which complicates propulsion. Heritage solutions use a gigantic supersonic parachute originally developed for Viking. The key issue is that parachutes also don't scale. They don't scale on mass, on timeline, or peak structural loads. On mass, it's pretty clear that the shroud cross section scales with vehicle mass, as does the canopy area, so the mass has to scale at least as vehicle mass to the 1.5. For 10T-100T payloads, we're talking a parachute the size of a stadium, since the Kerbal approach doesn't work where parachutes are made of fermions that obey the Pauli exclusion principle. A parachute of this size, mass aside, can't inflate fast enough to catch the vehicle before it makes a rather small but deeply unfortunately crater. And last, even if these scaling arguments were acceptable, all of LDSD's parachutes, at only 26m diameter still broke, for reasons we do not fully understand. There are potential solutions, SpaceX seems to be serious about supersonic retropropulsion, but nothing that's understood for certain, and it does our movement no favours to pretend that every problem, including these problems, are trivial.
The second major unsolved engineering issue to cover is Earth return. Of the three phases of a crewed exploration mission, outbound, surface, and return, return is by far the hardest. Deep space life support, razor thin margins, tiny mass allowances, long term machine reliability, completely unsupported launch ops, no indigenous industrial capacity whatever. Broadly speaking, there are two potential Earth return architectures. One is a tiny, even LESS-sized vehicle to fly to Mars orbit and rendezvous with a vehicle big enough to contain humans for 6 months to get home, which has to carry a lot of fuel and generally be a battlestar galactica. The other approach is direct Earth return from the surface of Mars. While on the one hand you need a much larger vehicle, you can't get away from 30T landings anyway. So you have to solve the EDL problem. And on the plus side you don't have some orbiting autonomous platform, orbital rendezvous, and Mars is the easiest place to get return fuel, by far. That said, even in Mars Direct, the Earth return vehicle (ERV) architecture is not explicitly sketched out, though clearly the vehicle is a lot smaller and the margins a lot tighter than the outbound voyage. On the plus side, it may be just possible to fly back from Mars with a single stage, which greatly simplifies vehicle architecture.
There remains a substantial credibility gap in crewed Mars exploration, but I hope I've sketched a set of ideas for improving the discourse going forward, both on a public and internal messaging level. I've been writing a (free!) book on these and other as-yet-unsolved crewed Mars mission engineering challenges and I encourage you to read it, leave comments and questions, and help us get specific! It can be found at www.caseyhandmer.com/home/mars .