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Brute force re-entry



 
 
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  #22  
Old August 26th 04, 06:54 PM
Jeff Findley
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"Ash Wyllie" wrote in message
...
Aerodynamic lift simply isn't enough. It always comes packaged with a
certain amount of drag, and at hypersonic speeds actually quite a bit of
it. When you do the numbers, it just doesn't work. If the drag is low
enough to stretch the deceleration out that long, you don't have enough
lift to hold you up. Period. Full stop.


Does that also mean that the Sanger skip bomber would not work?


Yes, but did you really expect scientists of that era to truly understand
hypersonic aerodynamics? It's a tricky field, even today.

Jeff
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  #23  
Old August 26th 04, 06:56 PM
Jeff Findley
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"Rodney Kelp" wrote in message
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They could send up some solid fuel boosters that the shuttle could dock

with
and use for braking. How how long would it take to brake from 18k mph to
about 200mph without exceeding 2 G's?


That would be insane. You'd need "solid fuel boosters" with very nearly as
much energy as the SRB's and the ET used to *launch* the shuttle in the
first place (the gravity, altitude, and drag losses are far less than the
energy needed to get to orbital velocity).

To get your "solid fuel boosters" into orbit would require a launch vehicle
bigger than any ever built.

Jeff
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  #24  
Old September 2nd 04, 06:44 PM
dave schneider
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(Derek Lyons) wrote:
"Carey Sublette" wrote:

In the world of aerospace "elegant" and "cheap" generally have a low
correlation coefficient.
A counter-argument is offered by Jeff Bell on spacedaily.com:
http://www.spacedaily.com/news/rocketscience-03zy.html

I.e. that a straightforward semi-ballistic capsule is the way to go to get
costs down, and safety up, for the next generation of manned spaceflight.
This philosophy is consonant with the "big dumb launcher" school of thought
for launch systems.


The problem with that argument is that it concentrates solely on cost
and safety. The proponents of that argument handwave away such minor
concerns as whether or not the total system capability can be had as
cheaply (both from a fiscal and engineering point of view) under their
scheme as under another.


But the main thing lost, compared to STS-1, is downmass capability. I
happen to think this is important, and definitely worth coming up with
ways to handle, but there are a lot of people - appearently in the
professional community as well as here - who think that there is very
little need for more downmass than can be put in lockers in a capsule.

Upmass is trivial in comparison, setting aside the ISS dilemma that
some important upmass is form-factored into the shuttle. And even the
winged OPS proposals were seperating crew from cargo, so EELV loads
for upmass would have been inevitable under those schemes, too.

/dps
  #25  
Old September 2nd 04, 09:46 PM
Anthony Garcia
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"william mook" wrote in message
om...
"Anthony Garcia" wrote in message

m...
"william mook" wrote in message
om...

http://science.ksc.nasa.gov/shuttle/...s/gidefinl.pdf

Here's some information on what goes into reusable spacecraft

design.

http://www.astronautix.com/lvs/shuenara.htm

Here's a picture of an alternative to the Shuttle, that in my
estimation would have been better than the Shuttle's present delta
wing.

An even better version would have been a slender cylinder with
straight wings deployed at subsonic speeds. Think of a tomahawk
cruise missle. This was proposed for the Russian PKA

[snip]

How are these alternatives any better?


They're less costly and safer.


Are they truely safer and less costly? How do we know this?

[snip]
There are no free lunches. You had it right the first time. Cross
range is reduced with the proposed wing structures. The footprint of
allowable landing sites from a given deorbit burn is reduced as a
result. So what? We have the ability to precisely control orbital
parameters of the deorbit burn and hit the landing site even with
reduced cross range. So, the issue is, should we keep cross range far
in excess of what we need to accomplish the mission, or reduce the
size of the wings and improve all the factors you mentioned?

The choice is clear, we should reduce cross range and make a smaller
less expensive and safer vehicle capable of carrying more payload.


I do see your point. Perhaps if one presumes that the deorbit burn can
provide a large component of the cross range requirement then yes, you
have a very good point.

  #26  
Old September 4th 04, 03:20 AM
Allen Meece
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They could send up some solid fuel boosters that the shuttle could dock
with
and use for braking. How how long would it take to brake from 18k mph to
about 200mph without exceeding 2 G's?


That would be insane. You'd need "solid fuel boosters" with very nearly as
much energy as the SRB's and the ET used to *launch* the shuttle in the
first place
This is the second poster who erroneously contends that it takes as much to
brake an empty shuttle out of orbit as it did to get the fully fueled orbiter
into orbit.
C'mon guys, it only takes a fraction of the launch fuel to brake the empty
craft.
But there's no need to "send up" an SRB to brake it, just hang onto the ET
and use its spare liquid fuel for braking and then cut it loose.
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~
  #27  
Old September 4th 04, 04:05 AM
Allen Meece
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Isn't the quantity of energy being shed going from orbit to ground the
same regardless of the angle of reentry? The energy to be shed is
determined by the orbit and the spacecraft mass right
True, Brute force reentry sheds it faster with a steep plunge while the
elegant lifting body approach is to shed the same energy over a longer time
using suitable heat radiators, flying and skipping rather than diving.
  #28  
Old September 4th 04, 04:14 AM
Allen Meece
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Incorrect. The space shuttle re-enters at a flight path angle typically
between -1 and -1.5 degrees. That's hardly "steep".
Also incorrect. The shuttle's flight path angle in the atmosphere is 20 --
25 degrees.
You're thinking about the initial orbital departure angle, not the average
sink rate along the entire descent.
The shuttle's reentry path IS STEEP. It is a high wing-loading, controlled
brute force reentry. Hardly as graceful as a good lifting body like the
cancelled [!?] X-38 would do.
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~
  #29  
Old September 4th 04, 04:27 AM
Allen Meece
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If your TPS can't shead the heat while out of the atmosphere, the "skipping"
trajectory will be worse in terms of total
heat load than a "traditional" re-entry.
Well, yes, of course the heat will have to be radiated away at the top of
each skip. Later, when the ship has lost the speed necessary to skip out of the
atmosphere, it will have to shed head via convection. Maybe copper heat pipes
from the nose connecting to some fins or feathers in the slipstream to
transfer the nose's heat to the ambient frigid air which is about -75C.
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~
  #30  
Old September 4th 04, 04:46 AM
Allen Meece
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It would be a major
engineering challenge to develop a deployable structure of significant
span that *could* take hypersonic speeds -- we're having enough trouble
with fixed structures.
But how do we know that? Especially since it depends on the flight profile.
Look, there's hypersonic speed in the atmosphere where the air is dense and
there's hypersonic speed in the stratosphere where there are scattered
molecules. There's no reason why a well-designed Rogallo Wing would not deploy
in the stratosphere, and provide lift for a slow descent.
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~
 




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