Re: Space Shuttle Grounding....depressing....

Andrew Swallow (am.swallow@xxxxxxxxxxxxxxx) writes:
> Matt Ion wrote:
>> Andrew Swallow wrote:
>>
>>> Matt Ion wrote:
>>> [snip]
>>>
>>>> Having the fuel tank where it is isn't really a mistake per se; it's
>>>> a design necessity. Launching with cold-damaged seals in the
>>>> solid-fuel boosters despite a manufacturer's warning against just
>>>> such a problem is a mistake. Coating it with a flaky material that
>>>> sheds chunks during liftoff is a mistake.
>>>
>>> Since the main engines are in the orbiter it has to
>>> be at the bottom. The main fuel tank could have been
>>> placed above the orbiter. Fuel pipes through the
>>> nose, with covers to give it a nice aerodynamic shape.
>>>
>>> When the fuel tank is jettisoned it would have to
>>> be pushed sideways to get it out of the way but
>>> that is not hard.
>>
>> True, but the support structures would have been a lot more complex,
>> especially to get any decent amount on strentgh in them. The Orbiter
>> would then have to support the full weight of the tank through whatever
>> structure supports it on the ground - right now the SRBs support the
>> whole structure and the tank supports the weight of the Orbiter - or
>> you'd have to add something to the launch structure to help support at
>> least part of the tank's weight.
>
> During ascension the engines take the weight of three times the entire
> structure. Once the SRBs have been jettisoned the weight of the
> orbiter, the fuel tank and the remaining fuel have to be carried by the
> current orbiter's skeleton.
>
> If the fuel tank is above the engines the load baring structure can be
> simple columns, as used in buildings. With the tank off to the side the
> structure is that of a crane. The connecting bars acting as leavers
> multiplying the forces enormously. The centre of gravity also changes
> during flight. This will require a very complicated structure.
>
>> Then you have to figure out where to put the SRBs - you couldn't leave
>> them on the tank in its current design, as the Orbiter would then be in
>> their exhaust wash, unless you redesigned the tank and/or mounting
>> system to hold them FAR out from the ship or splay them outward,
>> although it's still risky putting the shuttle in between their washes.
>> Or you could latch them directly to the shuttle, but that would
>> translate a lot of vibration to the orbiter.
>
> Or give the orbiter a fourth engine and a bigger fuel tank.

Given that the SRBs each put out 3,000,000 pounds of thrust, you'd
need to add 6,000,000 pounds of thrust in eliminating the SRBs.

As the SSMEs only put out around 400,000 pounds of thrust each,
you're going to need not one more, but about fifteen of them. Plus,
the starter three.

> The SRBs are heavy so the mass trade off could be very interesting.

Most of that is fuel. Most of any rocket, as lift off, is fuel.

Andre

--
" I'm a man... But, I can change... If I have to... I guess. "
The Man Prayer, Red Green.

.

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