Mass Ratio Doublecheck

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Cray74@gmail.com - 09 Aug 2005 13:25 GMT

I was wondering if someone could confirm that the masses of the
following fictional, upper stage spaceplane (VTHL) was realistic given
current aerospace technology.

The spaceplane's fueled mass is 200 metric tons, while in orbit (with
residuals, OMS fuel, cargo, etc.) it's 53 tons. Propellants are
hydrogen/oxygen at a normal 6:1 ratio. Is that fueled-to-empty ratio
technically achievable and, if so, how easily can it be achieved
current aerospace technology?

(I understand that funding, need, and political issues may entirely
moot the technological issues.)

If it is feasible, and the design targets include...

*300m/s of OMS delta-V
*Payload of 7000kg of various combinations of crew and cargo
*Low cross-range (<500km) re-entry profile is acceptable

..then is 53 tons a large enough weight budget for "frills" like a
go-around jet engine for landing, wings to help improve landing
stability and touchdown speed (vs. a pure lifting body), and perhaps
remaining growth room?

Mike Miller

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John Schilling - 15 Aug 2005 22:30 GMT

>I was wondering if someone could confirm that the masses of the
>following fictional, upper stage spaceplane (VTHL) was realistic given
[quoted text clipped - 5 lines]
>technically achievable and, if so, how easily can it be achieved
>current aerospace technology?

No. A LOX/Hydrogen launch vehicle of 200 tons fully fuelled gets you
20-25 tons of total mass in orbit. 50+ tons is right out.

>(I understand that funding, need, and political issues may entirely
>moot the technological issues.)

>If it is feasible, and the design targets include...

>*300m/s of OMS delta-V

That's going to be almost trivial.

>*Payload of 7000kg of various combinations of crew and cargo

7 tons of payload out of 20-25 tons total weight in orbit is
a bit much, especially for a "spaceplane", but not completely
out of the question. Probably best to scale it down to 4-5
tons, or scale up the vehicle proportionately.

>*Low cross-range (<500km) re-entry profile is acceptable

>..then is 53 tons a large enough weight budget for "frills" like a
>go-around jet engine for landing, wings to help improve landing
>stability and touchdown speed (vs. a pure lifting body), and perhaps
>remaining growth room?

You can't afford frills in an SSTO, and especially a spaceplane SSTO.

You also don't need them. The empty tanks in which 175+ tons of fluffy
propellants used to reside, squashed into anything resembling a lifting
body and then loaded with only 20-25 tons of spaceplane, will give you
a sufficiently low planform loading that you don't *need* extra wing
area to keep the landing speed down. BOTE, I get about 25-30 pounds
per square foot[1].

And you've got *rocket* engines for the go-around. For half the weight
of a minimal set of turbofans[2], you can carry enough reserve fuel for
a three-second burn that will boost you onto a zoom climb back to at
least 3,000 feet AGL. In an aircraft with the wing loading of a light
piston twin, that's plenty of altitude for a go-around.

[1] Sorry about the regression to English units; I just can't grok wing
loading in SI/MKS.

[2] And a negligible fraction of the cost.

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Cray74@gmail.com - 19 Aug 2005 11:58 GMT

> You can't afford frills in an SSTO, and especially a spaceplane SSTO.

I said this was an upper stage, not an SSTO. You even quoted me where I
said it was an "upper stage spaceplane."

Mike Miller

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Space Forum / Space Flight / August 2005

Mass Ratio Doublecheck