Re: Spacecraft Operability and the Discovery problems

richard schumacher <no-spam@xxxxxxxxxxx> wrote:
>In article <1121662490.675350.172670@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
> "Duncan Young" <smudog@xxxxxxxxx> wrote:
>
>> >Indeed, it was observed at the time that once the decision had been
>> >made to go with a drop tank, NASA should have reconsidered the decision to
>> >use two stages -- it's not clear that a booster stage was actually needed,
>> >even under conservative design rules, given the use of a drop tank to
>> >lighten the orbiter. But the decision had been made, so reversing it was
>> >impossible...
>>
>> I'm curious as to what configuration would have allowed a drop tank and
>> to keep the SSMEs on the orbiter and stop the thing tipping over at
>> launch and keeping the tankage weight down...
>> Not to say it is impossible - just my mind is boggling at the layout.
>
>Same layout but SSMEs angled a little more to keep them thrusting
>through the center of mass.
>
>
>>
>> Two overwing tanks?
>
>Two tanks of the same volume weigh more than one, and there are twice as
>many plumbing interfaces to go wrong.

Keep in mind that though the bulk of the ET is hydrogen tank,
the propellant mass of the ET is 85% LOX or so.

Once you're considering a drop tank, it's not unreasonable
to see if you want to have just one propellant in the drop
tank or both. Having the LOX internal to a shuttle, with a
drop fuel tank, keeps the CG pretty centered during launch.

One could even do an "overhead" mounting, with the tank
above the shuttle rather than below, so no fittings go
through the reentry TPS. With a little effort, you can
probably line up the tanks so that there is very little
if any vertical shift in the CG during the burn.

In any case, given that LOX is where the mass is,
managing how you store it is most of the CG problem,
other than the sheer bulk of the LH2 tank and how
that affects how close to centerline you can fit
its component CG.


-george william herbert
gherbert@xxxxxxxxx

.

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