Re: rocket question

Eric <nospam@xxxxxxxxx> wrote in news:vvudna_6yNoSX8
_enZ2dnUVZ_s2dnZ2d@xxxxxxxxxxx:

> Bob May wrote:
>
>> The Shuttle is going to orbit with a single stage system so why do you
>> think
>> that it takes 3 stages to get to orbit? How long do you consider that it
>> takes to consider an orbit to be non-degrading? The moon's orbit is
>> degrading so consider the time scale.
>>
>> --
>> Why do penguins walk so far to get to their nesting grounds?
>
> The shuttle only looks like a single stage - the boosters are stage 1
> and 2, the liquid fuel engine is stage 3. It needs to shed that weight
> in order to reach orbit if it hopes to bring any kind of a payload with it.
> At least thats the way I understand it.

You're misunderstanding the use of the word "stage".

The shuttle is a single stage to orbit with solid boosters assist
during initial ascent. The external tank is used from ignition to
MECO (main engine cut off).

Some launchers also use two sets of solids, one set that ignites on
the ground at launch, and another set of "air start" boosters that
ignite when the first set of boosters fall off. But those are not
considered "stages".

A stage is a section of the booster that contains engines and fuel.
When the fuel is used up, this section is discarded so that the
next "stage", or section with engines and fuel, can be used. The
second stage cannot be used until jettison of the previous "stage".

Think Saturn V. The movie Apollo 13 illustrates is well enough.



> As for my orbit question - you have a good point about the moon. So let me
> modify my question and ask instead that the orbit be good for several
> years. I'm just real curious how big of a system it would take to put a
> small light-weight science package in orbit for a few years - just for
> grins.
> Eric

Based on current designs, even if the launcher had no payload many
systems leave the final stage in orbit for some time. The payload
seperates from the booster and uses it's own small engine to put it
into it's final orbit. Many rocket bodies stay in orbit for years,
depending on the mission, for example geosynchronous satellites.

Theoritically, you could use a slightly modified Minuteman III.
Those already can achieve high velocities (24,000 kmh - ISS orbits
at <18,000 kmh) to deliver their payloads (nukes) on suborbital
arcs to targets on the other side of the planet. However, these
systems don't go for low altitudes. They use ballistic trajectories
that go way up (1120km ceiling, ISS orbits at about 350+ km) so the
reentry warhead comes more or less straight down. That is, they use
more energy to go up where as to acheive orbit you need to use more
energy to across, to acheive orbital velocity. I don't know the
specifics, but if the flight path is changed they should be able to
acheive orbital velocity and only require a small additional final
stage. The point being that these missiles aren't all that big and
their payloads aren't vey big, and the unit cost isn't all that high,
which seemed to be the crux of your question.

http://en.wikipedia.org/wiki/Minuteman_missile

The Russians are doing something similar now with modified sub
launched missiles with mixed success.

http://www.space.com/adastra/adastra_cosmos_mystery_050907.html

You might try sci.astro.satellites.visual-observe. Folks more
knowledgeable than I may be able to give a more concrete answer.

Brian
--
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