Sep 292011
A video showing a mostly-reusable version of the SpaceX Falcon 9. It looks reasonably practical, with a minimum of ridiculocity… no wings, scramjets or need for advanced materials. The basic concept is more than forty years old, going back to not only Phil Bono’s Saturn S-IVB stage recoverability concepts, but even further to Chrysler Mercury-Redstone recoverability concepts. Ditching parachutes entirely is a ballsy move, but if your rockets are sufficiently reliable – maybe Xcor rockets on the capsule – then chutes aren’t needed.
[youtube sSF81yjVbJE]
12 Responses to “SpaceX Grasshopper RLV”
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Very interesting, but all the extra fuel weight for that would be insane and limit the lift capacity. Even then some back up parachutes would be a great idea.
That is ballsy, but wouldn’t the extra fuel used for the retro rockets would weigh a lot more than parachutes, not to mention take up more volume?
Based on the calculations I’ve seen, the margins for this are razor thin. It would be better with the availability of orbital refueling stations. I would also suggest doing the launch/recovery from an island not owned by the US – otherwise the liability insurance would be crushing when one of these things runs out of fuel and drops on someone’s McMansion in Cocoa Beach. I was also disappointed to learn that Musk is getting further into bed with the government.
The thing that bothers me about this was alluded to in another comment — dang, that’s got to use a lot of fuel for descent, and of course every kilogram is a kilogram less payload.
I imagine that after a few launches the rocket could be adapted easily for a one-way trip.
But I’m just very dubious. I’d think that a real world solution at this point would shed the fuel tanks and focus on recovering the more expensive parts. Or that the main booster would split into four parts, each with a parachute, landing in the ocean. If you recover them, great; if you don’t, it’s not a big deal.
What this does do is allow experience with a lander of some size that might prove useful, say, as a private Altair lunar lander to go atop SLS. I’m thinking this methodology was chosen by Musk so that anyone involved with DC-X, and Kistler can have their experience preserved–a home for them provided to keep folks in circulation. There is more at stake than just getting the absolute most out of a particular vehicle which led to the over-optimisation of LVs for many years–otherwise they probably would have gone for the chute method.
Here is what I would like to know. Who got Beals filiment winding equipment? That big pressure fed BA-2 concept might have been a good SRB replacement…
The thing that seems dicey to me is recovering the second stage. It’s higher and moving at greater velocity, the weight penalty for the recovery fuel would be much worse, and the recovery site surely must be a lot farther down range.
If the launch site is Cape Canaveral, just where does it land, anyway? And how does it come back home? I suspect that Musk must have some other launch site in mind if he really does intend to recover the second stage. Cape York Peninsula, perhaps? A Pacific island?
Here are a couple of odd thoughts, for which I’m not the person to do the math … If the first stage is recoverable and the second stage isn’t, could it make any sense for the second stage to be a relatively inexpensive solid-fuel rocket? Perhaps that could simplify and shorten launch setup and fueling operations. (But that would do away with the advantage of common components.) Alternatively, could a liquid-fueled second stage continue on into orbit with less propellant than it would need for recovery at a ground site? Once in orbit, perhaps it could be refueled at a depot and used as a space tug or a lunar transfer stage. That seems like the sort of thing that Musk would want to do anyway, in the long term …
> If the launch site is Cape Canaveral, just where does it land, anyway?
Cape Canaveral, presumably. Note the “overhead”view of the capsule staging off the upper stage… it’s ocuring over dry land (looks like Asia, maybe). Since any launch out of the US would have the vehicle actually be in orbit before it spent any amount of time over dry land, this means that the upper stage is in fact in orbit. If it has sufficient cross range (seems unlikely), then the upper stage can simply come down after the first orbit. if it doesn’t, it just has to wait on orbit until it lines up again with Canaveral.
> If the first stage is recoverable and the second stage isn’t, could it make any sense for the second stage to be a relatively inexpensive solid-fuel rocket?
No. Solid rockets stink compared to good liquid rockets. And that performance hit *hurts* in an upper stage. A solid first stage is better, since the lower Isp doesn’t hurt as bad for a first stage. In general, you want high performance upper stages.
If it has sufficient cross range (seems unlikely), then the upper stage can simply come down after the first orbit. if it doesn’t, it just has to wait on orbit until it lines up again with Canaveral.
Hmm. Musk is essentially saying that if you have enough propellant in orbit you don’t need thermal protection tiles or ablative heat shields (not to mention parachutes) to bring your ship home intact.
I wonder what the “nearly dry weight” of the second stage would be. You’d think that without aerobraking a fair amount of fuel and oxidizer would be required to return the upper stage from orbit — you’d essentially need enough oomph to put the empty second stage into orbit from the ground, right? And you probably wouldn’t want to leave that LOX sitting up there in your fuel tank for too much time while you waited for a favorable return geometry …
Whether the upper stage stays up there to be repurposed and refueled or comes down again to be serviced and relaunched, I think this makes a really good argument for an on-orbit propellant depot.
Solid rockets stink compared to good liquid rockets. And that performance hit *hurts* in an upper stage.
Well, the PAM and the IUS use solids … I realize that relatively long-term on-orbit storage and easy starting in zero gee are probably the reasons that solids were chosen, but still, they can’t be *that* awful, can they? (OK, I won’t be too surprised if the answer is “Hell, yes!”)
I was mainly wondering whether the simplicity, (potentially) lower cost, and easy ground storability of a single-use solid rocket might make it preferable to a reusable liquid-fueled second stage *that carried enough extra propellant to enable it to return intact from orbit.*
According to this article SpaceX was going to use a parachute-splashdown system but they’ve projected that the rocket-landing system provides a greater number of re-uses for each component.
http://www.newscientist.com/blogs/shortsharpscience/2011/09/falcon-rockets-to-land-on-thei.html?DCMP=OTC-rss&nsref=online-news
Aha. According to the article:
In due time, SpaceX aims to have the second stage also re-enter behind a heat shield on its nose, and do the same vertical rocket landing.
OK. that makes sense, if the weight and energy budgets work out.
I interviewed with SpaceX last February. Fly out interview at their headquarters, 5 hours long. Then I didn’t get the job. Gah.
Hey, at least you got the interview. I’ve had some doozies… 1999 I interviewed at Stennis, and finally figured out *far* into the interviewing process that they had the wrong guy (I design rockets; they wanted a plumber. No, really). I interviewed at one of the startups in the late 1990’s, and the interview seemed really strained, almost antagonistic… later found out through the grapevine that the guy who owned the place thought I was there to spy on ’em. Of course there was also the problem of actually *getting* the job at ATK-Maryland… I showed up on day one, and the people I was supposed to work for had no idea that a new contractor was supposed to come on board that day. They weren’t any more thrilled when the *second* contractor showed up an hour or two later. Then a third, then a fourth…