Re: Google Cindy Sheehan (was: Re: Peace Mom)


"Josh Hill" wrote:
> "w.d.greene" wrote:
>>"Josh Hill" wrote:
>
>>> Estimated cost of building the DC-Y single stage to take off vehicle
>>> -- a reusable spaceship that would slash the cost of putting stuff in
>>> orbit -- $6 billion.
>>
>>Um, no.
>>
>>Single-stage to orbit (SSTO) does not work. It cannot work. Any
>>fledgling
>>aerospace engineer with just a passing knowledge of the rocket equation
>>understands this. Space Shuttle is 1.5 stages and it can only pull it off
>>by being the highest performing system ever built.
>
> I'm not sure I understand why you say that. The Shuttle was
> state-of-the art in the 70's, but it's hardly that now -- both engine
> design and structural materials have improved, with further
> improvements on the horizon.

This is a common misunderstanding that is unforutnately repeated over and
over in the mass media. With regards to the engines, the space shuttle main
engines are the highest performance, high thrust engines ever built. Could
they be higher in performance? Yes. Theoretically, you might be able to
squeeze out another one or two percent in specific impulse. But that's it.
Why? It has nothing whatsoever to do with 1970's technology or 2010
technology or even 2000 BCE technology. It has to do with the fundamental
properties of hydrogen and oxygen and the rest of the periodic table.

The solid boosters could be of higher performance, but again probably only
marginally without radical changes (like maybe going to liquid propellant
boosters).

Yes, there have been materials improvements. However, some of them have
already been incorporated into the orbiter, the external tank, the engines,
and the solid motors. See, these things are regularly and routinely updated
and upgraded.

The Shuttle is, in fact, in many ways 2000's technology with only a few
exceptions here and there.

> I found a few papers that rough out SSTO proposals, including this
> one:
>
> http://www.ssdl.gatech.edu/main/ssdl_paper_archive/iaf-st-87-07.pdf
>
> Short on details and I don't know enough to fill them in, but I don't
> see any assumptions there that seem outlandish, e.g., they posit a 10%
> mass reduction for the vehicle.

In order for SSTO to work, the propellant mass fraction has to be on the
order of 91% to 93% of the net liftoff weight (post engine ignition and
hold-down). That doesn't leave much for the rest of the vehicle as in tanks
and structure and engines and wings and landing gear and, oh yeah, payload.

Yes, the assumptions are outlandish once they're stacked up one on top of
another. It's interesting to note that the gross liftoff weight is roughly
the same as Shuttle and yet it delivers less half of the payload.



.

Relevant Pages

  • Re: Google Cindy Sheehan (was: Re: Peace Mom)
    ... the space shuttle ... >>engines are the highest performance, ... It has nothing whatsoever to do with 1970's technology or 2010 ... An expanding nozzle or better ...
    (misc.writing)
  • Re: Ares vs DIRECT
    ... we are flying the shuttle and the EELVs! ... except for the easy stuff, like the avionics and engines, for instance. ... If it involves inline SRBs, and upper stages that don't reach orbit, ... There are no physical barriers to SSTO flight. ...
    (sci.space.policy)
  • Re: Ares vs DIRECT
    ... we are flying the shuttle and the EELVs! ... except for the easy stuff, like the avionics and engines, for instance. ... If it involves inline SRBs, and upper stages that don't reach orbit, ... There are no physical barriers to SSTO flight. ...
    (sci.space.policy)
  • Re: Ares vs DIRECT
    ... we are flying the shuttle and the EELVs! ... except for the easy stuff, like the avionics and engines, for instance. ... If it involves inline SRBs, and upper stages that don't reach orbit, ... There are no physical barriers to SSTO flight. ...
    (sci.space.policy)
  • Re: Ares vs DIRECT
    ... we are flying the shuttle and the EELVs! ... except for the easy stuff, like the avionics and engines, for instance. ... If it involves inline SRBs, and upper stages that don't reach orbit, ... There are no physical barriers to SSTO flight. ...
    (sci.space.policy)