Tuesday, July 14, 2009

Let's Get Away From This Model Of Space Flight

Because it's like building an ocean liner to cross the Atlantic and setting fire to it when you reach New York.

11 Comments:

Anonymous Al R said...

The shuttle was a step in the right direction, but I suppose you could argue that it only replaced setting fire to the ocean liner by taking it apart completely and reassembling it again.

It's a shame that the various steps toward single stage to orbit (DC-X etc) which all looked so promising in the 90s came to naught.

July 15, 2009 10:28 PM  
Blogger Paul McAuley said...

I think it's a shame the X-15 wasn't developed further. Was DC-X a modernised version?

Coming down won't be as easy as going up until someone develops the self-healing nanotech diamond/fullerene heatshield.

July 16, 2009 4:01 PM  
Anonymous Al R said...

DC-X was the McDonnel Douglas concept for a rocket that took off and landed on its tail, Tin Tin style. They did a lot of testing with the scaled-down prototype, but the project effectively died when it was taken over by NASA.

Powered re-entry would solve most of the heatshield problems - but that's a way aways...

July 16, 2009 5:33 PM  
Blogger PeteY said...

I've been holding off commenting on this, as I'm naturally reluctant to accuse a SF author of being unrealistic. But I'm still irked, so here goes.

Reusable shuttles make things more expensive, both for the cost of the refurbishment, and because you're trying to get as much hardware back as possible, things you carry up and down, and that reduces payload capacity. Effectively things like wings count as payload.

If you try to do SSTO, you can, just, but you can't take any decent payload with you. That includes you.

DC-X was cute but desperately misleading - it never went more than a mile or so up, and could never have made it to orbit or anything like. Also, carrying fuel up to orbit to brake on the way down results in a (chorus) vastly reduced payload capacity. Oh, and it tipped over and went boom one day.

One thing that really would work would be Project Orion, but it is a bit dirty. Other nukes (did anyone ever do a study into a NERVA/DUMBO style launch vehicle?) might be effective but the same problem applies. Glass plains, cancer.

Space elevators would be nice (am I laughing?), but even those are unlikely to be satisfactory for manned flights, as it takes too long to crawl up the cable.

In all, you're stuck, apparently forever, riding staged chemical rockets with (some) throwaway bits. You may not like it, but there it is. The best thing would be to mass-produce them cheaply, like Soyuz.

July 17, 2009 2:03 AM  
Anonymous Al R said...

Pete: I take your point but the DC-X was never claimed to be able to reach orbit - it was a demonstrator of the basic principle of tail-landing. My understanding was that the SSTO version would have been about three times larger and could have been made to work. It was killed, if I remember rightly, because of design issues with the fuel tank, not because of any fundamental flaws in the concept. The intended payload to orbit (I just googled this - didn't know it off the top of my head) was 20,000 pounds, or around nine tons - not nothing. Maybe they were being over-optimistic.

You're right that reusability will imply hauling things up and down that eat into your payload capacity. But we cheerfully accept this model for air travel. Granted, you couldn't get very far in a plane without wings, but we accept the trade-off in efficiency required by the need to carry things like wheels.

I've also been thinking about the slowness of space elevators recently and I guess the decider will be what you do when you get up there. If you only to get to orbit, or maybe to the Moon, the idea of a days-long crawl up the elevator will be intolerable. If you're going on to Mars or beyond, you'll accept it (much as we accept hours of faffing around in airports for long distance journeys). I do agree that for short journeys, there will need to be a quicker means, so I doubt that elevators will ever displace crewed/passenger-carrying spacecraft. Whether those will be based around staged rockets, or some other technology, is another question entirely. There's a whole slew of air-breathing rocket concepts out there, as well as piggy-back vehicles and wackier things like laser-beam powered craft or ships that are boosted up to escape velocity in linear accelerator tunnels. Granted, we might be looking far into the future here, but then I'm not expecting a space elevator any time soon.

I spoke to a bunch of NASA people recently and I sensed genuine regret that the orbiter concept was being discarded. The orbiter design may have been flawed in some regards, but it never underwent a direct failure: the two shuttle losses were both caused by damage being inflicted on the orbiter by some other part of the system.

Any way, all good stuff and it's good to debate the pros and cons.

July 17, 2009 9:57 AM  
Blogger Paul McAuley said...

Pete, I accept all your arguments, but I'm still disappointed that we're stuck with a model in which it's easier and cheaper to throw complex and expensive machines away after a single use, than to reuse them over and again. It might be the only practical way of doings things at the moment, but it's no way to build a sustainable space programme. I'm also disappointed that the only true spacecraft ever built was the Lunar Excursion Module. At the moment, everything that goes up has to come down again, in one way or another. Bah.

There were plans to use a nuclear thermal nuclear rocket as part of the Saturn stack but it didn't come to anything. And I think the Russians testbeded a prototype but didn't take it any further than that. Luckily. I think the supporters of Project Orion style nuclear-powered spaceships suggested using them only for interplanetary (or interstellar) flight. You'd have to be pretty desperate (or Dr Evil) to launch a spaceship into orbit on top of a string of exploding nuclear bomblets!

July 17, 2009 11:27 AM  
Anonymous Al R said...

I've got Dyson JR's book on the Orion concept somewhere, but I seem to have mislaid it during the house move. I believe the idea of launching this thing off the ground was taken semi-seriously, at least for a while, but then this was at a time when nukes were being proposed for all sorts of civilian applications, such as making harbours or excavating new railroad routes through the Rockies. Remember, the atom is your friend.

July 17, 2009 11:45 AM  
Anonymous Anonymous said...

By the way, Paul, did you ever pick up the Haynes manual? I saw it first on your site, but don't know if you bought a copy. I got mine a couple of days ago in a Borders stock clearance (our local branch is shutting down). I recommend it unreservedly.

July 17, 2009 11:47 AM  
Anonymous Al R said...

That was me, by the way.

July 17, 2009 11:48 AM  
Blogger Paul McAuley said...

Orion: Nuke 'em on the way into orbit. It's the only way to be sure. Wasn't there a proposal to nuke the Sahara to release a deep aquifer?

I did get the Haynes book - a bit basic, but not bad. Haven't found any obvious bloopers, and it contains some pics I hadn't seen before and some nice cutaway stuff (a bit light on exploded diagrams, though). If anyone is teetering on the brink of buying it, Ian Sales has given it a favourable review.

July 17, 2009 3:39 PM  
Blogger PeteY said...

Al - I'll have to refresh my DC-X lore. Regarding the elevators, another consideration against human travel that way is the slow transit across the van Allen belt. Maybe a shielded pod could help there though, I dunno.

I highly recommend George Dyson's Project Orion. It was indeed intended to launch direct from the Earth's surface originally. The idea was to have a huge, heavy ship, which could make more efficient use of the means of propulsion and would also give a smoother ride. They talked about crews of hundreds or thousands, and Saturn by 1970. The atmospheric test ban treaty put an end to this idea, but other variants were envisaged, including putting a small Orion on top of a Saturn V S-1C.

It would make a nice alternate history idea, say the Sixties with the Cold War getting hot in space. Is there such a thing as atompunk yet?

July 18, 2009 1:43 AM  

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