Several people have already brought up the DIRECT v2.0 architecture paper that was rolled out at AIAA Space 2007 this last week, as well as the snazzy new website that the DIRECT team just launched. I just wanted to give a few of my own thoughts.
First off, I really got a kick out of the “safer, simpler, sooner” subtitle. Isn’t it ironic how hollow ATKs claims about the Shaft appear these days. Oh well, there’s no idea too stupid for an entrenched bureaucracy to fight for to the bloody end.
Ross, Chuck, the Metschans, Antonio, and the others deserve a good deal of respect for putting together a rather solid case. As I’ve said in the past, I think having NASA develop any new launch vehicles is a big mistake–launcher development and operations are NASAs core incompetencies after all. However, politics is the art of the attainable, and the DIRECT concept shows how NASA could develop an architecture that is not only more affordable, more robust, and more capable than the planned architecture, but more importantly is a lot more friendly to commercial cooperation. NASA’s current concept of commercial and international collaboration–the notion that commercial space entities and foreign countries should eagerly wait with bated breath for the construction of a lunar outpost before any serious involvement–is a sick joke.
I was only very tangentially involved with the DIRECT team’s v2.0 development, but I’m glad to see that some of the memes I’ve been trying to spread took root in their latest development.
The biggest and most important of these improvements over v1.0 revolves around orbital propellant depots. I may sound like a “Jonny-one-note” on this topic, but I’m still convinced that the ability to store and transfer cryogenic propellants on-orbit is one of the key enabling technologies needed for a spacefaring society. Ross and team did a very good job of highlighting how important such technologies can decrease the odds of losing expensive missions, enable a much more capable NASA lunar architecture, and provide a massive increase in demand for commercial launch services.
As I’ve mentioned many times previously here, with the current architecture, a delay on the Ares I launch will more or less doom the multi-billion dollar hardware already on orbit. The time pressures likely to exist in trying to get off a lunar mission within 14 days of the first launch greatly increase the odds of making fatal mistakes like have been made in the past. Now, it is probably possible to build stages that can last longer on-orbit without excessive boiloff, but by having the ability to “top-off” the tank, this issue completely goes away. At worst delays would necessitate launching some more fuel before leaving.
The ability to “top-off” the EDS in orbit, or to transfer propellants launched on one launch to the earlier launch can both greatly increase the payload capacity of a 2-launch mission. The problem with doing a 2-launch mission without propellant transfer is that it’s very difficult to evenly divide a lunar mission into two roughly identically sized launches. One of the two launchers will end up launching substantially lighter. But if you can transfer propellants, you can now pretty much divide the payload evenly, because you have an infinitely divisible medium that can be transfered back and forth as needed. More importantly, with propellant transfer and dry-launch techniques, a single Jupiter-232 mission could perform the same mission as a much more expensive Ares-1/Ares-V combo.
On a related note, by having propellant transfer capabilities and infrastructure in both LEO and L1/LUNO, several design decisions can be revisited. Right now, with the fragile, no-orbital-infrastructure approach taken in ESAS, if the CEVs engines don’t light for the Trans-Earth-Injection burn, the crew is probably dead. Even with an ISS-like base on the surface, unless they have a bunch of backup vehicles, there’s very little chance of a successful rescue mission being mounted in-time. Issues like this are part of what drove the CEV back to using hypergols instead of higher performance cryogenic combinations. Once you have some infrastructure in space, such issues become inconveniences instead of fatal mishaps. If your engine doesn’t light, you just redock with the L1 node, and wait for a rescue, or possibly try to effect a repair. Or maybe you could transfer propellant back to the lunar lander and head back for the surface, etc.
The most important benefit of the latest DIRECT architecture is the development of a potentially massive new LEO launch market. As I see it, there really are only two major potential markets out there for LEO delivery services that actually have the potential to generate demand for the dozens to hundreds of flights per year that would enable RLVs to really shine–personal spaceflight and propellant deliveries. And by designing a NASA architecture that intentionally takes advantage of such developments to the maximum extent possible, NASA could really help promote and catalyze the development of a robust commercial LEO launch industry. As the Centaur team pointed out over a year ago, even 2-4 moon missions per year would provide a several-fold increase in the demand for commercial earth to orbit launch services. And because propellants are even more finely divisible than people are, such a market could be very helpful for early orbital RLV operators.
But beyond the NASA demand for propellants, having NASA as an anchor tenant could be very useful for making propellant depots a reality sooner rather than later. As I’ve discussed in previous posts, propellant depots suffer from a chicken and egg kind of problem. Nobody is going to want to privately fund a depot before there are customers for such a depot, and nobody is going to want to fund businesses can act as customers for depots until the depots exist. It might be possible to break this chicken and egg problem without NASAs help by either finding a way to get a minimalist depot built for the low enough cost that someone would be willing to take the risk, or by trying to codevelop the depot and one of its potential customers…but both of those approaches are very uncertain from a business and a financing standpoint.
With NASA as an anchor tenant however, it becomes a lot easier for other businesses to then spring up that can take advantage of the new capabilities. Businesses such as cislunar tourism, or possibly changing the way upper stages are done today. For instance, a Falcon I upper stage refueled in LEO could deliver its full payload to GEO or LUNO, or even interplanetary trajectories. In fact, a Falcon I refueled in LEO could provide almost half the GEO capability of an Atlas V 401 (for a tiny fraction of the price). A Centaur stage refueled in LEO could put a Sundancer sized module into Lunar Orbit, etc.
But some have expressed concern about the idea of putting “risky technologies” on the critical path for NASA’s return to the moon. They seem to believe that it would be best to take the lowest technical risk approach from the start, and then only add on things like propellant depots as after-the-fact performance enhancements. I think this view is shortsighted for several reasons, but first I’d like to draw an analogy. Back in the early Apollo days, there was a big debate over the mission architecture. One of the mission architectures that had a lot of favor originally was the “direct ascent” architecture. That architecture avoided the need for orbital rendezvous (which at that point was just as unproven and risky as propellant transfer is today), but at the cost of requiring a much larger NASA developed vehicle (NOVA). Had NASA not taken the smart move of putting “risky unproven technologies” like orbital rendezvous on their critical path, the Apollo program probably would’ve failed. As CFE points out in his latest blog post, if the Apollo program had taken the further technical risk of developing EOR technologies such as propellant transfer, they might have even been able to avoid the program cancellation that came from trying to run two very expensive launch vehicles.
If the ESAS architecture, by avoiding “risky unproven technologies” like propellant transfer, was able to provide a basic lunar transportation infrastructure for a couple of billion over a couple of years, it would be one thing. But in spite of avoiding any technology that really has the potential to make ESAS even remotely useful, they’re still looking at spending $60-100B and the better part of two decades to develop a bare-bones lunar transportation architecture that’s only a little more capable than the one fielded by NASA 40 years ago. What’s the point in “avoiding technical risks” if it doesn’t actually allow you to do things in a cheaper, quicker, or more sustainable fashion? By taking such a hyperconservative approach, and by abandoning most real new space technology R&D, NASA’s setting itself up for stagnation over the next decade or so.
In life, and particularly in engineering, there are some risks that end up being riskier to avoid than to meet head-on and overcome. For NASA, orbital propellant transfer is one of them. So, I applaud the DIRECT team’s latest release for its emphasis on this technology that’s been neglected for far too long. The rest of the report is pretty good too…
Latest posts by Jonathan Goff (see all)
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