I’ve talked a lot on my blog about the various technologies that are important for a society to master before they can become a truly spacefaring society. I figured just for kicks, and in an effort to tone-down on the snarkiness and NASA-bashing that is oh-so-easy to get caught up in, I’d put up a list of what I think some of those technologies are and why. I doubt this will be a complete list, and the list isn’t in any particular order, but with that said, here goes:
- Reusable Orbital Transportation: I wouldn’t consider our society to be truly spacefaring until we had an off-earth population at least as high as Tehachapi, with the number of trips to orbit per day at least as high as the daily number of general aviation flights in and out of Mojave Airport. That’s a pretty darned low bar to set, but orders of magnitude more than what we’ve currently acheived after nearly 40 years. Expendables are still useful, will still be around for a while, will still be economically viable in the near to medium term, but are utterly incapable of supporting this kind of a traffic rate. When you factor everything (including third party liability insurance, manufacturing costs, launch licensing costs, etc, etc, etc), you eventually reach the point where you realize that long-term, reusability is not an option, it has to come standard. Here’s a few subtechnologies that I think will be important to master:
- High Longevity Rocket Engines: Right now the best rocket engines in use by the big boys are only really good for 100-200 full duration firings before they start having issues (usually related to the brazing on tube-wall nozzles or mushrooming of the cooling lands for channel-wall designs). That’s a start, but really the number needs to get to at least 1000 before we’re really getting anywhere. Remember, jet engines also handle very high energy densities, high temperatures, fast moving, close tolerance parts. They also started out with lifetimes between major overhaul measured in single-digit hours. Nowadays they’ve improved substantially. I think there’s room for improvement for rocket engines too. The Chamber-Saddle-Jacket design used by XCOR, SPL, and MSS is one approach that might lead to high longevity rocket engines, but more methods that cover more of the design space need to be worked out.
- Low-Maintenance Reusable TPS: RLVs in order to be fast turnaround really need better and more reliable Thermal Protection Systems. While there may be some mileage to be gained from quick-removable ablative panels and such, at some point a truly reusable system (whether it be radiative, regenerative, or transpiration based, or some combination of the three) needs to be fielded. Particularly one that can be tested in advance.
- Aerobraking: For any commerce outside of LEO, the ability to reduce fuel requirements at certain points in the trip by use of aerobraking starts becoming very important. By not having to carry all the fuel to completely propulsively brake into LEO for instance, you can get away with much smaller vehicles, a much higher amount of actual passengers or payload per amount of mass lifted out of gravity wells, and much simpler logistics and performance demands on interorbital space transports. Not to mention that they make reusing interorbital space transports a lot easier. The technologies needed here might include improved TPS designs, ways of more accurately determining the atmospheric densities along the aerobraking trajectory, and improved techniques for navigation and control during the aerobraking maneuver.
- On-Orbit Propellant Transfer: I bet you were wondering when I’d get back on this hobby horse. The ability to transfer propellant on-orbit is at the heart of any spacefaring society. Without the ability to refuel and reuse space transports, you’re stuck with essentially single-use throw-away systems little better than what we had during the Apollo Program three decades ago. On-orbit refueling also creates transportation nodes which tend to be the nuclei of commercial activity. It allows you to more completely disaggregate your in-space transportation systems from your earth-to-orbit systems. Combined with other techniques like On-Orbit Assembly and On-Orbit Construction, you can create almost any sort of transportation infrastructure imagineable.
- Long-Term On-Orbit Propellant Storage: While being able to transfer propellants to orbit is important, the ability to store propellants (especially cryogens) for long duration with low or no boil-off is also very important. This makes propellant depots, propellant tankers, and other such things viable. Much as “coaling stations” made rapid oceanic transportation viable on earth, propellant depots throughout manned space will also play a key role in enabling interplanetary commerce.
- On-Orbit Assembly: The ability to routinely and affordably assemble prefabricated structures on orbit, whether they be satellites, stations, or even vehicles is also very useful. It allows you to build things on-orbit that would be too big volume or mass-wise to easily loft on a single earth-to-orbit booster. Big boosters start really running into some serious issues after a certain size (like how to physically handle something that big, noise levels, developing massive engines, etc–at some point you will want to do something too big to fly even on a dozen Saturn Vs–deal with it). People like to talk about how much more expensive it costs to do anything in space compared to a factory floor on earth. But when you include the cost of building/operating a booster big enough to avoid having to build stuff in space, it starts looking really wise to attack the cost of working in space instead of continually trying to build bigger and bigger Uber-Launchers.
- On-Orbit Construction: You’re going to reach a point where you want parts with contiguous volumes bigger than can be safely launched on the biggest boosters, and possibly bigger than can be handled on the biggest boosters with inflatable structures. Things like dry-docks for building/repairing/overhauling/maintaining other vessels, very large propellant tanks, cycler ships, zero-G arenas, space habitats, etc. Just as with on-orbit assembly, you’re eventually going to want to do something big enough that the cheapest way to do it is going to be fabricating it in space. That means shipping up smaller pieces, and actually welding or riveting or bonding them together. Maybe even going so far as shipping raw materials there and having mini-mills produce sheet and plate and structural members. Tinker-toy construction can get you a long way, but at some point you’re going to want to go with something more substantial, and figuring out how to do that sooner, rather than later, will lower the cost barrier that you have to overcome to do stuff like that.
- Closing the Water Loop (Or at Least Getting Close): One of the big consumables for manned spaceflight is water. There have been plenty of ideas for closing the water loop, by recycling water from respiration, laundry, dishes, showers, excratory fluids, etc. These need to be fleshed out. Even though the cost of transportation needs to go down a whole lot for any of this to become feasible, attacking the water loop is one of the highest gain-to-effort ratio tasks out there.
- Extraterrestrial Navigation: Right now things like GPS make terrestrial navigation very easy. For a truly spacefaring society, something like the XPPS technology I wrote about a few months ago would be very helpful. Also a system of low-cost navigational satellites, ground stations, etc througout the regions of manned activity might also be very helpful.
- Low-Maintenance Space Nuclear Power: While there are many areas in the solar system where solar power is adequate, there are also a whole bunch of areas where it isn’t. Space Nuclear Power gives a spacefaring society the flexibility it needs to be able to access places that otherwise would be very difficult. A society that hugs tiny slivers of the moon because it can’t otherwise handle the nightspan electricity generation can hardly be called truly spacefaring (though it’d still be a step-up from where we are now).
- Space Tugs: Clark made a fairly good point about the idea of space tugs. Basically, like in CSI’s preferred station delivery method, you have the brains and docking system in the tug, allowing the bigger vehicles to not have to have as fine of guidance and docking equipment. This also allows you to deliver dumb cargoes to a safe distance from the station, and have the tug bring them in for final docking. Lastly, it also allows you to launch the payloads into a lower parking orbit, and then have the tug swoop down and get it. You’d be surprised how much more efficient that can end up being, particularly if the station is at a moderately high altitude (to avoid drag or other issues). Since the tug is at a shallower part of the delta-V curve, just a little bit of propellants goes a much longer way than for the orbital vehicle that is already at the very, very steep part of the curve. There’s a reason why tugboats are used so much in modern ports–they just make sense.]
- In-Situ Resource Utilization: This one was so obvious I forgot to include it. Basically, if you don’t know how to extract resources off-planet, you’re not a spacefaring society. In fact, many of the reasons for going off-planet in the first place almost inherently assume some level of ISRU. The most important near term ISRU technology being ISPP or In-Situ Propellant Production. Once you can get propellants produced off-planet, you no longer have to ship them all the way from home. That allows your transportation network to become amazingly more efficient fast. Basically, it allows you to “reset the Delta-V curve” frequently, which keeps you from needing super-high mass fractions anywhere, which makes construction, maintenance, etc of vehicles a lot easier. Once we have ISRU fed propellant depots on the lunar surface, in LUNO or at L1, on the Martian Surface, and in Mars Orbit, transportation between the Earth, Moon, and Mars will become substantially cheaper. Even idea’s like Elon Musk’s one-way mars colonists could benefit from fueling stations in orbit and on the surface. That makes the landers reusable, which drives that cost down and reliability up (remember, landing almost anywhere off earth requires VTVL, with most places not having any abort modes–your lander has to be rock-solid reliable, and the best way to guarantee that is by making it reusable, testing the heck out of it on earth, then testing the heck out of it on Mars once it gets there). If combined with a tug, it also allows you to pick how aggressive your aerobraking is, whether it is just aerocapture, with a tug bringing you the rest of the way in, or out-and-out aerobraking. Plus, if the ship can be sent back to earth, and reused, the capital cost for that goes down too. Not to mention you’re going to have at least some colonists pansying out, and you’re going to want at least some level of commerce going on even for a “self-sufficient” colony (true self-sufficiency is a really dumb idea unless you have absolutely no other choice).
- Artificial Gravity: By this I mostly mean spinning stations up and stuff to get artificial gravity from centrifugal accelerations. The sooner we figure this one out the better. Right now, we have no idea what the health vs gravity curve looks like. We only have two main data sets, one at microgravity, and one at full Earth gravity. For all we know you can get sufficient fluid settling by 1/20th of a G to avoid the most severe of the microgravity health deterioration issues. Or it could require 19/20ths. We flat out don’t know. Variable gravity techniques like the xGRF station that Kirk mentioned in comments would go a long way to resolving that. Once we know what the curve looks like, making stations that actually take advantage of artificial gravity will allow people to live on-orbit in a lot more convenience. It also simplifies a lot of the life support problems that exist from having a microgravity station. I’m sure there’ll still be plenty of microgravity research stations or free-flyers. It’s just that I think that most of the transportation nodes or industrial facilities will have sizable artificial gravity sections even if they also have a non-spinning zero-G area.]
[Updates #2 and 3:
Anyhow, as I said, this list isn’t exhaustive, and I tried to mostly stick to stuff that could be done today, as opposed to longer-term (or more dubious) stuff like carbon nanotubes, self-replicating robots, nuclear fusion, nuclear propulsion, etc.
These are the kinds of technologies that I think NASA would be better off developing than merely pursuing an old-school Apollo rehash. Unlike today’s NASA, NASA in the age of Apollo had the balls to actually try new things and develop technologies where it made sense and where it made the goal easier. At the start of the Apollo program, we had zero experience with things like orbital rendezvous and docking, but instead of pansying out, NASA went and developed the expertise. Today’s NASA seems to be trying to go back to the moon without actually developing any of the near-term feasible technologies that would actually allow it to do something substantially more useful and relevant than what we did thirty-some-odd years ago. Instead of spending billions of dollars trying to “fill a much needed gap in US space transportation capabilities”, NASA would accomplish a whole lot more if it spent at least some of that money on developing one or two of the above technologies first. Instead of spending $5B on yet-another-medium-lift-expendable, they could borrow a page from the DoD, tell ATK that it’s going to have to put some skin in the game, and use some of the freed up money to demonstrate on-orbit refueling. Maybe use $1B to fund two “big boys” to do it the “business as usual” route, and use another $.5B doing a more commercial approach.
At the end of the decade in addition to a worthless medium lift booster that it would already have, NASA would likely have two or three good methods to pick from for orbital refueling, developed to the point that the rest of the Project Orion could take advantage of it. With several commercial companies and the EELVs and the Stick all able to launch propellants and exploration components, that might allow NASA to avoid needing to develop a separate HLV, and go directly to a reusable EDS. That’d save a lot of money, expedite the program, and allow for a much more substantial program with a much higher probability of expediting the beginning of commercial utilization of cislunar space. The stuff that the guys at MSFC and JSC could work on at that point would be really, really exciting. Possibly the kind of stuff that’d get people wanting to work for NASA again.
Or they could just treat this as a welfare program for aging rocket nerds. Unfortunately you can guess what’s most likely to happen.
Any thoughts, additions, etc?
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