It seems someone’s decided to dust off one of NASA’s old designs.
Let’s see, it’s cheap, and could be flying before NASA’s CEV, and there’s no dangers of it being damaged by falling foam. Sounds like a good idea to me.
Sounds cool. I don’t get the falling foam reference, though?
The article explains that since the boosters do not use cryogenic fuel, its tanks do not need to be insulated by foam. Therefore there’s no danger of fallng foam striking the orbiter.
But the HL-20 uses Shuttle-style thermal protection tiles, so I think it would be just as fragile as the Shuttle. Personally, I think it’s better to build an orbiter that can withstand being hit by foam rather than eliminating the foam, but maybe that’s just me.
I also wonder if it wouldn’t be even cheaper to copy the Soyuz design rather than the HL-20 design. NASA itself uses Soyuz capsules in the role the HL-20 was originally developed for, i.e. alternate transport and emergency return (“lifeboat”) for the Space Station.
Now if someone could revive the X-33/VentureStar project, that would be cool…
It wasn’t the tiles which the foam damaged that caused the loss of Columbia by the RCC (Reenforced Carbon Carbon) panels on the leading edge of the wings. Those things are insanely brittle and can’t be made any stronger. If the HL-20 doesn’t use the RCCs, it shouldn’t be a problem. And scr4, you’re right, since even if the thing doesn’t use cryogenic fuels there’s always the danger that it could slam into a bird on the way up.
From the page I linked to:
“…heating in the flight environment on this concept was predicted to be within the limits of Space Shuttle-based high-temperature, reusable surface insulation (HRSI) everywhere except at the nose of the vehicle, where Shuttle-based carbon-carbon thermal protection was required.”
Well, perhaps the guys building the new version of the HL-20 will modify the design so they don’t have to use the RCC nose cone. Or maybe not.
It probably is one of the hotest areas. The shuttle banks to make one side lead and take most of the heat in turn, but you can’t do that to the nose.
OTOH, maybe a small nose cone would be disposable if needed and simply replaced on each trip.
This isn’t a bad idea, but the problem is that such a piece would be irregularly shaped and yet have to meet extremely tight tolerences, plus be manufactured and inspected to be free of voids. Attachment is also an issue; you obviously can’t have hardware poking through the nosecone, so it has to be attached from the back side, but you have to somehow provide access to do that if it is to be replacable. (When RCC pieces on the Shuttle have to be replaced it requires a partial tear-down of the wing.) NASA considered doing this early in Shuttle development, after it became clear that active cooling methods and hot structures would be insufficent to take the heating load. They found that the cost was prohibitive, though in retrospect they vastly overestimated the reliability and underestmated the maintainence cost of the STS tile and carbon-carbon heat protection system.
CEV isn’t so much a step backwards as sideways; we do have a lot of experience with landing capsules (Mercury, Gemini, Apollo) and the Gemini was so accurate that they had a couple of near misses with the capsule impacting dangerously close to the retrieval ship. From a “how many things can go wrong” standpoint a stack-and-capsule vessel has considerably less complexity and more opportunity for abort.
Color me somewhat skeptical of SpaceDev’s numbers; I’d hazard that they are throwing out a low-end SWAG and calling it fun. The development of a heat protection or abatement system is very complex and failure prone, and something that AFAIK SpaceDev doesn’t have any prior experience in.
BTW, NASA’s schedule and budget on CEV deployment is pretty wack; the booster is all more or less off-the-shelf stuff with new interfaces, and the CEV itself is a pretty simple vehicle. A crash program could have this thing flying in 3-4 years. Instead, they’re still dinking around and requiring prospective contractors to repeatedly submit proposals as they change system requirements the way Paris Hilton changes sex partners. I’m starting to think that a lot of their thumbsitting owes to waiting for a new political administration to come along and revamp/axe the CEV.
It’s a pretty pathetic mess, really. Meanwhile, if SpaceDev or someone else can build a commercially viable private personnel space transporter, more power to them. I’m just not to confident in their self-confidence.
Stranger
The first Mercury heatshield was cut to fit with a router on the bed of a pickup truck. 
Bush axed the lifeboat that was planned after the RL-20, X-something or other. Now private business is going to make it.
You make other good points, BTW. My nose solution would surely have been implemented if that simple.
Yeah, but it was a simple spherical-shaped shield, not a complex shaped nosepiece, and it was ablative, not reusable.
That would have been the X-38. The lifeboat configuration X-38 was somewhat different than the HL-20 in that it was never intended to have any onboard engines other than RCS (reaction control system, to orient the craft) and reentry OMS (orbital maneuvering system). It wasn’t capable of achieving orbit on its own–it would have been flown (empty) either inside the Shuttle payload bay or on top of an unspecified booster with an orbital maneuvering module to the ISS and used strictly as a lifeboat.
Well, maybe or maybe not. Sometimes things are done or not done based not upon the objective merits but because of past experience with a particular type of system, or because some lead engineer has a preference for one thing over another, or because the head senator overseeing the budget committee wants the project to go to the company in his state regardless of the merit of their proposal. As I said, it’s not a bad idea to utilize replaceable, ablative shielding; it just may not be feasable for a given design. One of the design requirements right now for CEV is that the reentry shield needs to be able to withstand X number of reentries without refurbishment. X keeps changing on a weekly, if not daily basis–NASA can’t seem to decide on just how “reusable” they need this thing to be–but it would make a lot more sense at this point, IMHO, if they’d make the thing so that it can be readily detached and replaced should it be damaged or should a sufficiently resilliant material not be developed. But I’m not working on that proposal (whew!), so it ain’t my problem.
Stranger