Stuff like that. It’s interesting, but I don’t think I actually have a lot to add to the conversation other than questions.

~Jon

May I make a suggestion for one further entry into your Orbital Access Methodologies posts? Have you considered a SStS/MXER combination? (That’s Single Stage to Sub-oribit / Momentum eXchange – Electrodynamic Reboost). Launch a payload on a suborbital trajectory and where it rendezvous with and is captured by the end of a rotating tether in LEO. The rotation of the tether then picks up the payload and transfers it to a higher orbit. The transfer of momentum from the tether to the payload is then replenished by pushing current through the tether to create a Lorentz force against the Earth’s magnetic field. The same process can be used in reverse to deorbit a payload, thus reducing the requirements for the performance of the TPS.

I don’t think we can really move out into the solar system in large numbers until we learn to master conservation of momentum and energy. Conventional rocketry may be required to get us up out of the gravity well and atmosphere of the Earth, but there’s no reason why we should continue wasting valuable resources to accelerate and decelerate payloads once in space.

If you’d like more info, take a look at the Tethers Unlimited website (http://www.tethers.com/MXTethers.html).

You haven’t, which is why I like it here. I’m insistent about the things that make space hard, not to discourage efforts but because fifty years of underestimating the full scope of the challenge has actually retarded progress. It has done so by inspiring “great leap forward” programs and designs that almost always fail, instead of incremental improvements that accumulate. It has done so by obscuring the great difference between thrilling stunts like Apollo and sustainable capabilities, so ; .

Most insidiously, by feeding great and premature expectations, it has left too much of the public thinking “Space? yeah, we tried that back in the day — didn’t pan out, kinda like jetpacks and flying cars.” And it’s left too many space fans taking it for granted that we should be much farther along — so they look for scapegoats to explain the gap, or the One True Design or One True Program or One True Free Market Bonanza to close it.

~Jon

1) the “mighty Saturn nostalgia” that grew up as part of disillusionment with STS: you know, comparing STS’ LEO payload unfavorably to that of an S-V, ignoring the 100,000 kg of the orbiter.

2) the “throw away the jetliner” argument for RLvs: “Just think how expensive air travel would be if you used a 7X7 only once.” The people who advance that as a decisive argument usually omit the footnote: “In this analogy the 7X7 capable of a round trip would be a very significantly different vehicle with greater development cost, smaller payload… and oh yes, you can’t refuel at the destination, so the return trip uses a kinda hairy alternate mode, demanding a whole ‘nother set of features that are dead weight on the first leg…”

I know these are stunningly obvious, but I at least have to keep them near the front of my mind to appreciate just how hard cost-effective RLVs will be. When people sneer at ELVs as “disintegrating totem poles” or at “the artillery model,” there’s an implication that everyone from Peenemunde to KSFC and Baikonur must have been retarded not to simply follow the reusable aviation model from the beginning; just listen to Eugen Sanger, just keep pushing the X-15 higher and faster, yada yada.

NO, I insist; they were fine engineers who hated to throw away precision hardware every bit as much as anyone today — but getting a payload to orbit was just barely possible that way.

Getting it to orbit with something that can return for re-use really is a lot harder. Doing so often enough to make the development worthwhile is harder still. And doing so in a context in which you have to create most of your markets as you go, and carry with you most of the “destination” facilities that are taken for granted with aviation, is even harder than that.

While I basically agree with your two points, I don’t see how that supports your first sentence. To me, if anything, they reinforce the point I’m trying to make about high flight rate–that high flight rates are absolutely crucial for RLVs. Both being able to achieve them technically, and being able to find enough demand to justify them. But yeah, the technical demands of an RLV also contribute to the need for higher flight rates to make the economics work.

That said, two quibbles.

First regarding your first point, every orbital rocket has to take the rocket + payload into orbit (though for TSTO ELVs or RLVs you only have to haul part of the rocket all the way). The difference with an RLV is that you have more parasitic mass that you have to take up. But even a Centaur or a Falcon still has to drag its upper stage all the way to orbit. They do get to ditch their fairings on the way up, but the fairings are only part of the upper stage mass.

Second, while the RLVs do have subsystems that I agree with you, will probably weigh more than comparable subsystems on an ELV, for the markets I’ll be talking about in the next parts, an ELV payload would need to provide most of that parasitic mass anyway. For instance, if you’re flying people on an ELV, you also need TPS, recovery gear, etc. Which means that for the markets I’ll be talking about, the penalty for RLVs is much lower than for RLVs launching satellites.

~Jon