Re: Impractical Spaceflight

Philip Witham (
Wed, 19 Aug 1998 15:15:08 -0700

Mark, I'll reply to your two posts in one, here:

>> launch site, refuel before launch. The towing back part is not the
>> biggest problem.
>True, but where exactly are you going to land these things? Towing back
>your second stage from a few thousand miles away is not going to be >fast or cheap.
Agreed, I could see spending hundreds of thousands of dollars on average to tow it back between several hundred and several thousand miles, depending on how closely you can control the de-orbit burn.

>>From $10,000 per pound to $100 per pound? Your figures listed $50 per
>pound in 60s dollars, which would be what? $500 per pound today? So
>how can you get down to a fifth of that?
The dollar has not depreciated by ten to one over that time.

>100,000 pounds at $500 per pound == $50,000,000.
The smaller Excalibur is a $20,000,000 launch in recent dollars, putting up 100,000Lbs.

>You mean the shuttle can survive an in-flight failure and land? You >have some proof of that?
When did I say such a thing? Come, now, putting words in somebody else's mouth will quickly make this an angry conversation.

And you are right, I ignored vertical landing SSTO's. I would add then, that vertical landing is an advantage of having vertical landing capability (!), and not of having one stage to orbit. Again, my argument (repeating Truax) is against SSTO, and against complexity where simple solutions exist.

>And again, they fail explosively because there's nothing else they can
>do, because they're not designed to survive such failures.
If you think so, then design it to land, and develop it sufficiently that it stands a small chance of exploding. But this is independent of the decision of the number of stages.

>>Are you also assuming your SSTO blows up 5% of the time? I would.
>Why? It can be designed not to blow up, because it can land safely if
>it loses an engine.
Because nobody gets away with engineering reality. We are talking about a design comparison here. With the same people working to the same design goals, is one high-tech stage with turbopumps, pushed to the utmost in structural strength to weight ratio, more reliable than two pressure fed stages with fewer total engines and enormously fewer parts, and large strength margins?

Look at the engines alone: (oversimplified) A pump fed motor is a pump and a thrust chamber. A pressure fed motor is a thrust chamber. You cannot assert that a pump fed motor is therefor more reliable.

>Nope; the majority of failures of *any* launcher since the first
>successful US launch has been due to an engine failing to ignite or
>shutting down early (the shuttle, incidentally, has had only one in->flight SSME shutdown). Many of them blew up as a consequence, but that >was because they weren't designed to do anything else.
I'd like to see the statistics on that, do you have a reference handy? Clearly ignition failures before launch that resulted in an abort (non-catastrophic shutdown) wouldn't count here, so I'm not sure what to make of this.

>(If you want a list, try Titan IV, Altas-Centaur, Russian manned lunar
>booster, Ariane upper stages, Saturn I/V, etc, etc... and didn't the
>Delta Clipper survive one engine failure in testing?).
I don't understand what you said here, a list of what?

>Why do you keep harping on about winged reentry? The only winged SSTO
>design I know of is Skylon.

Again, sorry to ignore vertical landing. There have been a number of winged (lifting body) SSTO proposals, including the X-30.

>They are if you design them to be (e.g. AFAIK the Saturns had strong >blast curtains around the engines to control any such explosion), and >few of those failures I've mentioned were catastrophic. In fact with >the possible exception of the Russian launcher I can't remember any.
I can't remember many in-flight launch failures in rockets that were not catastrophic. Have I been missing something? I must not be getting something here.

(next post)
>Uh, this is the aeronautical side of NASA, who've done quite a lot for
>improving efficiency of aircraft in the last few decades.
And I have respect for all of NASA but the manned space flight operations.

>> to payload) of around 100:1 in their theoretical fully developed >>form.
>So (approximately) does the shuttle, and some other launch vehicles; >and Roton claims 7,000lbs payload for a <400,000lb launch mass, say >55:1. The shuttle's what, 2000 tons with a 30 ton payload? 70:1?
Yes. But with an SSTO, that 1 or 2% comes directly out of the performance and structural margins, and forces the ultimate from everything. With two stages, the payload (or next stage) is about 10-20% of the stage liftoff mass. This makes SSTO payload calculations very uncertain, and even then, SSTOs are lower in performance than simpler two stage rockets.

>Uh, Roton, Skylon, Kistler's SSTO design before they canned it, etc, >etc. I don't know of any SSTO outside the government that's not >supposed to be operational very quickly. As far as I'm aware the first >Roton is supposed to carry 7,000lbs to orbit after initial testing.
I am not aware of any SSTO design being funded enough to make it to operational capability, including the Roton. Yes, I'm making a bet on that one that I hope to be wrong about.