I’ve been thinking all summer about NASA’s Constellation program. In general, I think it’s great to be getting out of low Earth orbit…but I think the strategic goals of the Vision for Space Exploration and the technical solutions in Constellation are somewhat lacking. My experience this summer at Johnson Space Center, and the Augustine Commission’s generally open mind, have made me very hopeful – I’ve noticed that the people at JSC aren’t as gung-ho Orion-is-the-best-thing-to-hit-space-since-John-Glenn as I feared they would be. (That seems to happen more at Marshall Spaceflight Center, where they are building Ares, and in the mind of Mike Griffin, who has called anybody who wants the current architecture to change “ignorant.” Note that that includes famous people like Buzz Aldrin and a lot of top-flight engineers.)
The current Constellation architecture is a result of basically two factors:
(1) A knee-jerk response to the Columbia disaster. NASA wanted safety during reentry, and it decided that capsules never burn up in reentry. (Never mind that while Shuttle had two major disasters in ~130 missions, Apollo had two major disasters in ~20. The tildes are because both numbers depend a little on how you count.)
(2) The Vision for Space Exploration, which sets a “Moon sorties first, then Mars sorties, and I guess we can support ISS until it’s just barely finished” mission for NASA.
That first item is a terrible point to be feeding directly into strategic planning and design work, because it limits creativity and ingenuity. Right now, Constellation is operating under the assumption that it should use as little new technology as possible. Compare that to the Apollo design days, when engineers designed their spacecraft with materials that had yet to be invented. The second item takes away from Constellation the kind of grandiose vision that could really attract attention and acclaim to NASA. We have gotten complacent with our space program; it seems routine to the ordinary Earthling. That’s the exact opposite of what we need to nuture strong public support of the space program (and science and technology in general): astronauts, flight controllers, scientists, and engineers need to be heroes again.
So where do I think NASA should go, and what should it do to get there? First of all, let’s take a look at the capabilities that NASA has now.
NASA has an incredible low-Earth-orbit capability. The Shuttle lets us bring a lot of mass into orbit. It also lets us bring a lot of mass down from orbit, which is crucially important for the Space Station’s science architecture and is a capability that Orion ignores. We also have a lot of experience with rendezvous, capture, and docking, from the assembly of ISS, Hubble servicing missions, and the like – going all the way back to Gemini – also a versatile capability virtually ignored by Orion. Finally, ISS has given us a lot of long-duration spaceflight experience.
NASA is also very good at getting robots to and operating them on Mars. Sure, several missions failed, but each of those did so because of a specific technical reason which all have known fixes. The last four major missions (Phoenix, MER1 and 2, and MRO) were all – or still are! – rousing successes.
Now let’s look at what’s problematic about today’s space program. The Shuttle is horrendously expensive to operate. It is also unsafe, not because its design is inherently flawed, but because each launch requires a total refurbishment of the vehicle and the vehicles are effectively 20-30 years old.
Here’s what I think NASA ought to do strategically, and (without doing any detailed trade studies, because though I’m a Ph.D. candidate in spacecraft engineering, I am acting as but a humble blogger here) how I think it could get there.
1. Set our sights on Mars.
Specifically, set our sights on Martian habitation – a commitment to putting people there, and keeping them there (probably on rotation). Consider options to encourage long-duration stays measured up to ten years, including options involving everything from technical advances to careful planning of launch opportunities to social factors, like perhaps looking for a cadre of gender-mixed single astronauts, or married couples in technical professions with no children.
Visit the Moon if feasible and desirable. (And hey, with some planetary science background and a lot of space passion, I have a hard time picking any one planet over another. Except Europa, which always wins with me.) But the overriding, single goal should be to go to Mars. Don’t even say “Use the Moon as a proving ground for long-term operations,” because (a) the Moon is fundamentally different from Mars, (b) we’ve been testing long-duration stays on ISS for a decade, and (c) that explicitly has us going to the Moon as a destination first. We all know that saying “plan a road trip from Boston to San Francisco” will result in a much shorter time driving than saying, “plan to drive from Boston to San Fran, but stop in NYC.” Or “plan to drive from Boston to NYC, then to SF,” in analogy to Constellation now. (Especially because if Congress gets bored in New York, we’ll never make it West.)
2. Develop a Shuttle-evolved launch vehicle.
I call this Shuttle-evolved rather than Shuttle-derived because I don’t want to just take advantage of Shuttle technologies – which are 30 years old. I want to move to a new launch vehicle in a truly evolutionary fashion: bring in the good aspects of the Shuttle (versatile orbital capabilities, reusability, landing capability at aerospace support facilities, “routine access to space” paradigm) and eliminate the bad (expense, extensive refurbishments between flights, lack of modularity, outdated tech) by mutating the existing designs with the latest technology.
Here’s what I think this looks like:
Build a three-part launch vehicle, vertically stacked and parallel-staged: Strap-on boosters, one- or two-staged core booster, and lifting-body, glide-landing vehicle. Derive the strap-on boosters directly from the Space Shuttle solid rocket boosters (SRBs). Derive the core booster from Delta, Atlas, and Saturn heritage with Ares development. And derive the vehicle from the Shuttle, as well as existing lifting-body vehicle development.
Take the SRBs and equip them with deployable parafoil wings, landing gear, and UAV avionics, making them into “flyback” boosters (FSRBs) without adding too much mass. After booster separation, these rockets would tumble away from the core booster (I’ll just call this the “core”), and pop out parafoils, then use GPS to navigate back to a recovery field. No splashdown means no expensive water recovery and refurbishment!
The disposable core would then continue to orbit and jettison the top-mounted vehicle. The new vehicle, unlike the existing Shuttle, would not have the three main engines – I’ve moved those onto the disposable core. (Of course, since STS Main Engines are expensive, maybe we’d want to look at something cheaper, maybe J2-derived. Or, since SMEs are reusable and incredibly reliable, maybe we look at a way to recover part of the core.) If the new vehicle gets its reentry glide from a lifting body, it doesn’t need the STS’s orbiter wings. And if we use everything we’ve learned since Apollo about composites, hypersonics, and thermal engineering, the heat shield could be a lot smaller. All these things remove mass from the vehicle, making it more capable in orbit and reducing the propellant mass (i.e., cost) required to get it there. I would even suggest reducing the size of the vehicle, perhaps to accomodate a crew of five and/or a smaller payload than the Shuttle.
Once in orbit, the vehicle would be a workhorse, including a crew cabin, cargo bay, robotic manipulator, air lock, orbital maneuvering system, and docking capability with ISS. Call it a “mini-Shuttle” if you like. My goal is to design the launch system to eliminate the extra mass of the STS main engines from the orbiter vehicle. The vehicle should be designed as a lifting body and get as much leverage out of the latest composites tech as possible to minimize spaceframe weight. The lifting-body design should also be optimized with anything we’ve learned from capsules, the Shuttle, SpaceShipOne, and thermal materials researchers to make reentry safe and reliable. We’re going to have to solve a lot of these reentry problems anyways, to get through Mars’ thin atmosphere. (Here’s another thought: the dangerous thing about reentry is the plasma. That’s what killed Columbia, yet Columbia made it through most of its reentry before the plasma eating its wing from the inside destroyed the vehicle. Maybe we can design a spacecraft such that the plasma forms around the vehicle in some desirable way, and then gets channeled away from the vehicle in a way to give it some desirable flight characteristics?) And finally, these vehicles should be made as modular as possible, to eliminate the extensive costs of post-launch STS refurbishment.
Hey, woah, go figure. This architecture looks like an Ares V, but a little smaller overall and with a lifting-body vehicle instead of an Apollo-era capsule. I did that on purpose: Ares development can feed directly into this effort.
3. Use our rendezvous and ISS assembly experience to get out of LEO
Our experience with the Apollo lunar module tells me that a true “spacecraft” does not necessarily look like a launch or reentry vehicle – nor should it include the engines and heat shields required for those tasks unless they are specific mission requirements for that vehicle, as those are the highest-mass elements of a space vehicle. The lesson here is that the optimal vehicles for launch, space operations, and reentry are very different from one another. It’s stupid to carry your Earth reentry heat shield with you all the way to Mars, and its stupid to carry your fuel tanks, star trackers, and long-term life support with you during reentry. (This is what makes the Orion/Altair combination an inappropriate set of vehicles for NASA’s flagship operations: Altair is good at landing on the Moon, and Orion is good at reentry into Earth’s atmosphere, and neither is optimized for anything else.) Couple that with the fact that, by now, we’re extremely good at orbital assembly operations, and throw into the mix a low-cost, mostly-reusable launch vehicle, and I think we have the way to get to Mars.
Develop and build, in Earth orbit, a dedicated interplanetary transfer vehicle. Assembling the vehicle over the course of several launches is a good idea because it can then be big and include elements with several different purposes: lunar landers, Mars landers, habitation modules, Earth- and Mars-departure stages, refillable fuel tanks. In putting this thing together, we ought to look very seriously into deployable or inflatable habitats, because then we could assemble a vehicle with a very large interior volume in relatively few launches. NASA is already doing this with TransHab, and Bigelow Aerospace has privately launched two inflatable, pressurized habitats into LEO. And we should look into innovative solutions to the challenges of long-term duration missions in this vehicle: for example, some think that the Earth departure stage, once spent, should be reeled out on the end of a tether and the whole thing spun to give the astronauts at least lunar gravity; the outer shell of the inflatable could be covered in UV-hardening material to give it good structure once deployed; and we could make a double-layered inflatable with the outer layer filled with water for radiation absorption and cooling. This should allow us to assemble a Mars transit vehicle with plenty of crew capacity for the months-to-years-long voyage there and back.
The transfer vehicle can be left in Mars orbit and re-used on the trip home. Once back at Earth orbit, crews would either return to the surface on a reentry vehicle they brought with them the whole time, or they could be picked up by a new launch.
One might argue that, since I’m calling for NASA to develop at least three separate vehicles (Earth launch/LEO ops/entry, planetary transit, and planetary descent/ascent), some requiring several launches to assemble, that the entire program cost will run more expensive than other alternatives out there. However, the great advantage to this architecture is that we will get what we pay for, in a dramatic gain to LEO and planetary capability!
4. Use the Direct-to-Mars architecture and ISRU
Robert Zubrin has been plugging this for a while:
Once on Mars, use in-situ resource utilization for all it’s worth. There’s plenty of iron and magnesium in Mars rocks, and there’s plenty of carbon, hydrogen, and oxygen at the poles (at least). Figure out how to build human habitats using Martian materials. Extract fuels from the soil and atmosphere. Look into fueling – or even building and assembling! – Mars ascent stages on the Red Planet. Maybe we can break down Martian materials to form composites or fabrics to produce more inflatable structures on the surface.
Design nothing to be sent to Mars that has only a single use in it. Find ways to use spent Mars landing stages, parachutes, ballutes, and aeroshells as raw materials. We should, again, look into inflatable habitats to minimize descent mass and volume but maximize habitat space.
Land greenhouses and hydroponics facilities. Use algae and plants to recycle carbon dioxide into oxygen and provide essential nutrients for the crew. Look into extracting medicinal compounds from plants. Make the colony as self-sufficient as it can possibly be. The great thing is that solutions to these challenges will directly impact and improve everyday life on Earth, giving ordinary non-space-enthusiast citizens something to point to and say, “the human space program gave me that.”
As you might have guessed, my two biggest problems with Constellation are the explicit lunar destination and the Orion vehicle. I hope to see the Augustine Commission, Obama Administration, and NASA be a bit more open-minded to alternatives as they consider the purpose of the human spaceflight program. Hopefully we’ll see something that looks really awesome, to connect with and inspire a generation that has grown up hearing all about the legacy of Apollo. I’m tentatively optimistic, especially because of the direct-to-Mars options outlined here, and we’ll just have to see what happens…