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May 29, 2004
The great launch vehicle debate
Greg Allison (NSS), Bob Zubrin (Mars Society), and Rick Tumlinson (Space Frontier Foundation) debated on launch vehicles after the shuttle here at ISDC today. Greg and Rick argued for private development, with an eventual heavy lift only when a real market for it exists. Rick particularly emphasized prizes and incentives. Bob argued for a government-developed heavy-lift vehicle, possibly shuttle derived. Greg referred to the "Shuttle protection agency" effect, that really needs to get the shuttle out of the way before we can get the private development we need. Bob argued against on-orbit assembly due to experience with cost of ISS assembly.
Final score: 4 votes for Greg, 26 for Rick, and 32 for Bob.
My guess is Greg confused everybody with his fast-talking southern-accented argument from evolution :-) Or else they mistook him for Ralph Nader...
Posted by apsmith at May 29, 2004 03:35 PM
Comments
Arthur,
> Bob argued against on-orbit assembly due to
> experience with cost of ISS assembly.
I wasn't able to make it to ISDC, but I have to
say it's too bad that Zubrin won-out again. He's
a nice guy and I agree with him on ISRU. He just
doesn't seem to get it yet about the importance of
commercial space.
Instead of using ISS as an excuse to dismiss using
on-orbit assembly, why don't we instead find out
what was done wrong, and how things could be done
better in the future. I say our experience with
the cost of HLVs in the Apollo program and the
end result of that should be as much of a point
against HLVs and HLV based architectures as the
ISS is against on-orbit assembly.
~Jonathan Goff
Posted by: Jonathan Goff at June 1, 2004 03:46 PM
Jon, that's an excellent point. I think Greg Allison and Rick Tumlinson sort of addressed that (along the lines of "you think the organization that wasted all that money on ISS should waste more money on an HLV?) but the question of what exactly caused ISS to be so expensive didn't really come up.
Any particular thoughts you have on the matter? Bigelow's doing things cheaper, but he's still launching his 'hotel' in a single piece, inflating it in orbit, which doesn't see to shed much light on how you would combine the components (and fuel) needed for a lunar return or Mars mission.
Posted by: Arthur Smith at June 1, 2004 04:06 PM
Arthur,
Good questions. I'm not entirely positive myself, and this would be better answered in an article than a blog comment (but I don't yet have time to do a full article), but for now I think there are a few big keys:
1-Flight Rate
The ISS was pretty much tied to Proton and the Shuttle for most of the assembly launches. Neither of which are capable of particularly high flight rate. If an on-orbit assembled structure requires say 20 launches on a certain vehicle, it will cost a lot more if that vehicle can only fly 4 times a year, than if it can fly once a week.
2-Chunk Size
The chunk size they used forced them to go with a single launch vehicle--the Shuttle. If they could have chosen a different size that was a bit smaller for their pieces, they might have been launchable on different boosters, thus greatly reducing the fligh-rate issues above.
3-Shirtsleeves or Plug'n'Play are better than EVA
If you can design an on orbit structure so that as much of the assembly is done in a pressurized environment, or done by simply plugging two modules together, you can reduce the amount of EVA needed, and hence the cost.
4-The benefits of a simple tug
A simple tug, that includes a robotic arm and all the avionics, propulsion, power, etc to move pieces from a delivery orbit then take them to the assembly orbit, and berth them together would've been a big win. That way, you don't have to haul all the assembly equipment up and down the gravity well each time. Also, even using a tug to bring the payload from ~200km up to 440km makes a big payload difference according to Henry Spencer. Lastly, this allows you the benefit of berthing over docking, without requiring the Shuttle.
A couple other thoughts that might help for lunar missions:
5-System Size--Small is Sometimes Beautiful
Figure out how small you can break your system up into. Instead of one big Apollo sized mission, why can't you break it up into smaller pieces?
I won't go into too much detail, but there is good reason to believe that there are some benefits to be had from working with one-man vehicles instead of three-man. As you add orbital fueling depots in LEO and L1 (as well as ISRU), it can allow you to quickly upgrade back to 3-man vehicles without requiring anywhere near as big of a booster.
6-Practice Makes Perfect
This is similar to the flight-rate point above. If you build a lot of something, it becomes easier. You learn more of what can go wrong, and how to avoid it. Your procedures become more mature and reliable, and you can fix problems as they appear. If each car was a one-of-a-kind affair, it would be very difficult to get high reliability, no matter how many times you reused it. Likewise with lunar transportation systems--the more you make them and the more you use them, the easier it is to get high reliability and low cost. This also tends to emphasise point 5 above. If you can fly three times as many lunar flights, you start getting efficiencies of scale for your launcher, and for your other vehicles. For example, if you buy a Falcon V, it may cost $12M plus range fees. If you buy four of them at a time, the price per launch will go down.
Anyhow, those are just a few off-the-cuff thoughts. This might be a good one to bring up on sci.space.tech or sci.space.policy.
--------------------------------------------------
A minor nit on another thing you said, I think that Bigelow is actually building a several piece hotel, but that the main piece is the inflatable module, but there will be other components assembled to it. If you look at the picture they gave space.com you can see at least three, if not four components (the inflatable, a node, a big service module, and then the solar panels) So he is at least intending some on-orbit assembly. See picture at:
http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=h_nautilus_bigelow_02.jpg&cap=Bigelow%20Aerospace%20have%20planned%20a%20series%20of%20inflatable%20structure%20tests%20in%20space.%20Plan%20is%20to%20evolve%20testing%20and%20hardware%20to%20establish%20the%20Nautilus%20outpost%20in%20Earth%20orbit.%20Image%20Credit:%20Bigelow%20Aerospace
Anyhow, that's about long enough for now.
~Jonathan Goff
Posted by: Jonathan Goff at June 1, 2004 06:38 PM
Another good reason for cost: lack of focus. A design can't be tightly tailored to a task (and hence, optimally cheap) if it doen't actually have a task. ISS seems to have been designed based upon a politically convenient output ("lets have an international space station") rather than an intended purpose.
This is where commerce shines. Government projects can set goals, but only commerce can objectively define and monitor usefulness. A commercial space station would be built to fulfill a need, could be tightly tailored to that need, and the financier could measure via profits whether it was paying its way - or whether it had become a "white elephant".
Posted by: Julian Morrison at June 8, 2004 06:11 AM
