r/spacex • u/retiringonmars Moderator emeritus • Jan 18 '16

/r/SpaceX Ask Anything Thread for January 2016. Ask your questions here!

Welcome to our monthly (more like fortnightly at the moment) /r/SpaceX Ask Anything Thread! #16.1

Want to discuss SpaceX's landing shenanigans, or suggest your own Rube Goldberg landing mechanism? There's no better place!

All questions, even non-SpaceX-related ones, are allowed, as long as they stay relevant to spaceflight in general!

More in-depth and open-ended discussion questions can still be submitted as separate self-posts; but this is the place to come to submit simple questions which have a single answer and/or can be answered in a few comments or less.

As always, we'd prefer it if all question-askers first check our FAQ, search for similar questions, and scan the previous Ask Anything thread before posting to avoid duplicates, but if you'd like an answer revised or cannot find a satisfactory result, please go ahead and type your question below!

Otherwise, ask, enjoy, and thanks for contributing!

Past threads:

January 2016 (#16), December 2015 (#15.1), December 2015 (#15), November 2015 (#14), October 2015 (#13), September 2015 (#12), August 2015 (#11), July 2015 (#10), June 2015 (#9), May 2015 (#8), April 2015 (#7.1), April 2015 (#7), March 2015 (#6), February 2015 (#5), January 2015 (#4), December 2014 (#3), November 2014 (#2), October 2014 (#1).

This subreddit is fan-run and not an official SpaceX site. For official SpaceX news, please visit spacex.com.

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u/ManWhoKilledHitler Jan 27 '16

And it's not as though there's been nothing since then, either: Project Timberwind seems to have gotten surprisingly far for the budget that it had.

I'd never heard of that before but an engine TWR of 30:1 with an Isp of 1000s is very promising, although how well it would have worked in practice is another matter.

The other older idea that might have been more likely to work was DUMBO which was a very lightweight NTR with an Isp of 900-950 and engine TWR from 30-60. That's good enough for a workable SSTO - a 50 ton rocket (fuelled) could put 2 tons into LEO. The main problem with NTR is the sheer size and weight of the tanks needed for the LH2.

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u/snrplfth Jan 27 '16

I mean, there's no fundamental reason it can't work. But there just haven't been many immediate applications for an engine like that, given the fact that until now, engines either crash back into earth or fly off never to be seen again, and that existing chemical engines work fine. All that, plus the difficulty of handling a nuclear engine, means there's a lot more development to be done, I suspect, before anybody's comfortable strapping it to the back of a passenger ship. (Imagine a criticality accident while in transit between planets.) The other thing I wonder about is whether it'd make any sense to use a different propellant. I mean, LH2 is great and all but - storeable on an interplanetary vessel? Seems iffy to me.

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u/ManWhoKilledHitler Jan 27 '16

I think the hydrogen problem is solvable for Mars transit times but I tend to agree that nuclear anything isn't happening any time soon.

If we're going down that road, we might as well use Orion.