Re: the "Spencer Launcher"
- From: "Stefan D." <hot_esteban@xxxxxxxxxxx>
- Date: 11 Dec 2005 10:57:13 -0800
Henry Spencer wrote:
....
> Launcher Concept
>
> I fiddled around with this a bit, and here's what I came up with.
>
> The first stage is a shuttle ET, the modern aluminum-lithium version,
> about 26t of tank (all masses in metric tons) holding about 720t of
> propellant. The LOX tank at the top needs to lose the pointed nose, in
> favor of a blunter tank end with an interstage ring extending up, but that
> shouldn't be at all hard -- we can use the tooling currently used to
> build the *bottom* of the LOX tank. With no SRBs, a fair bit of heavy
> structure can be deleted; I assume that suffices to cover the interstage
> ring's mass.
>
> At the bottom of the tank, we put seven RS-68s, a ring of six around a
> seventh. The engines are about 48t, and throw in another 10t for a thrust
> structure. The RS-68's sea-level Isp is 357s, and its vacuum Isp is 409s;
> I assume an average of 380s. Takeoff thrust/weight is 1.25, about the
> same as the Saturn V.
>
> The last mass property of interest is residual propellant at the end of
> the burn. NASA's designs seem to assume the orthodox rule of thumb, 1%...
> which is ridiculous. The S-IVB specified 0.25%, and typically achieved
> even better. I'm specifying 0.25%, or about 2t of residuals.
>
> On top of this is the second stage... another shuttle ET! Same capacity
> and mass, same blunted nose. This one has only two RS-68s (14t), with a
> smaller thrust structure (5t). Here the Isp is the full vacuum 409s. The
> thrust/weight at ignition is about 0.8, which is okay for an upper stage.
> Same 0.25% residuals. Needs an altitude-start variant of the RS-68, but
> that should be pretty trivial -- it's a much simpler and less cranky
> engine than the SSME.
>
> On top is 100t of payload. A fairing, if needed, is charged against
> payload.
How would one design a launcher in this class to be reusable?
I can imaginze the booster stage to be reusable (probably the
Energia/Zenit way, with reusable flyback boosters) as the mass penalty
for making it reusable does not influence overall performance that
much.
But how would one make a large second stage reusable? All the weight
is in the engines at the bottom. How could you use the large tankage
area? Reentering sideways does not look very stable aerodynamically.
What about TPS? You can perhaps reuse just the engines, but truly
significant cost savings can probably be achieved only by reusing the
whole stage as-is, no? I think in most cases bringing your second stage
back and almost ready to go again would be worth sacrifyihg even half
of the available payload.
Stefan
....
> spsystems.net is temporarily off the air; | Henry Spencer
> mail to henry at zoo.utoronto.ca instead. | henry@xxxxxxxxxxxxx
.
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