Re: SPACE: Roton in New Scientist
Mon, 17 Aug 1998 06:11:17 -0700 (PDT)

Philip Witham [] wrote:
>Truax's designs are re-useable. He was probably the first proponent of >re-useable rockets, and argued in favor of such during the Apollo project.

I'm pretty sure Von Braun was well ahead on that, but not very good at getting them built in reality. With effectively infinite funding and very short timescales on those projects there was no point developing a reusable rocket.

>Many people have a hard time believing that you can recover a rocket in
>the ocean, but it has been proven and demonstrated many times.

Well, the shuttle does it on every launch, but AFAIR throwing away the boosters would actually be cheaper than refurbishing them. Certainly towing a stage back from the middle of the ocean is a lot harder than refuelling an SSTO that just landed at the launch site.

>Modern satellites are light in part because of the cost per pound of putting >them up with "modern" launchers. As the cost of orbiting mass goes down, the >cost of developing satellites will go down as well, as one can make simpler >spacecraft if you have more mass to work with.

Possibly, but if you reduce the cost per pound by a factor of ten and increase the mass by a factor of ten you've done nothing to reduce the cost to launch the satellite. Unless there are significant advantages to making them larger there's no gain... and the current trend seems to be towards smaller satellites, not larger.

>As the total cost goes down, the risk goes down, and you spend less on >reliability, and the cost goes down more.

But you can't spend less on reliability when a) you're still paying $50,000,000 to put each satellite up and b) you're losing millions of dollars per day every time one fails. On-orbit spares are a possibility, but still increase costs.

>If the satellites cost $10^9, why put more than one on each launch?

Because if you put one five-ton satellite on a launcher designed for a fifty-ton payload your cost-per-pound just went up by another factor of ten. There's no benefit to reducing that cost if you can't use up all the payload mass.

>This is again the point where most folks follow their intuition rather than
>the facts: The cost does not go up very fast with scale, but it does go
>up rapidly with complexity.

But you're talking the cost of the launcher, not the cost of actually putting a satellite into space. And the complexity of an SSTO can be lower, because it doesn't have to be totally reliable the way an expendable does; if you lose an engine on an ELV you probably lose the payload, if you lose an engine on a reusable SSTO you make an emergency landing.

>And as you make a rocket bigger, you can build it simpler, because various >effects give you better performance as the scale goes up.

But that doesn't matter if you waste 90% of the payload and it blows up 5% of the time; where's the cost saving?

>I don't mean to be nasty, but this is like saying you'll save money buying
>a Mercedes-Benz rather than a pickup truck because in an impact, your
>groceries are less likely to get splattered.

And if those groceries were worth ten times the cost of the car, and the car crashed five trips out of a hundred, it would be a very significant gain. You're ignoring the financial reality here.

>Most launch failures in rockets, by the way, are explosions.

Almost all launch failures I can think of are engines shutting down or failing to ignite. That they generally lead to explosion is merely down to the attitude of ELV designers; there's nothing they can do to bring it back down safely, so why worry?