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Orbital Space Place project



 
 
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  #11  
Old July 28th 03, 05:18 PM
TKalbfus
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If we're planning on having these fins still on the JDAM when it's
time to direct the ordnance to the target, we'd better not be falling
from a very high altitude. Aerothermodynamics, you know. They're
certainly not suitable for ballistic flight intercontinentally or,
probably, even regionally.

Mary


The fins would fold up into the body of the capsule during reentry. Once the
capsule has slowed down sufficiently, the fins would unfold and direct the
capsule toward the landing site as it fell. In essence it is an Earth lander.
Building an Earth lander is easier than building a Moon lander. To build a Moon
lander you need the rocket engines to slow the ship down from orbital velocity
to the velocity of the Moon's surface. The Earth lander only has to slow down
from terminal velocity after it has reentered the Earth's atmosphere. We've
landed things on Mars as well such as the Viking landers. Only on Earth we have
runways so people tend to want to use them, so they build gliders with wheels
to keep our airports busy.
  #12  
Old July 28th 03, 08:06 PM
Henry Spencer
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In article ,
Allen Thomson wrote:
Is there an estimate for how good a CEP one could expect these
days for a capsule with steerable lift like Apollo and Soyuz...


ESA's ARD demonstrator had a goal of landing within 5km of its target, and
in fact did so. That was with conventional parachutes, i.e. with no
maneuvering capability during final descent.

maybe some sort of parasail for final corrections?


If you're doing a land touchdown, it's highly desirable to have a
steerable parachute, for obstacle avoidance if nothing else. Using a
parafoil also offers the option of using a flare maneuver for final
deceleration. (Parachute touchdown velocities are a bit high without some
sort of final braking, unless you oversize the capsule to provide room for
a lengthy shock-absorber stroke.)

(Assuming that,
unlike the very scary recent Soyuz landing, things work right.)


There was nothing particularly scary about that landing. A bit unpleasant
for the crew, but no significant added risk.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |
  #13  
Old July 28th 03, 08:11 PM
Henry Spencer
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In article ,
Cardman wrote:
Landing jets or rockets can be used to slow down the capsule
for a soft landing once it gets close to the ground. The capsule should be
falling at 100 mph or so the capsule should go from 100 mph to 0 with a
tolerable acceleration just before making contact with the ground.


Sounds kind of risky to me for a manned craft.
After all if you get a failure in your landing system, then hitting
the ground at 100 mph is a not a good idea.


The combined weight of parachute and braking rockets is usually minimum at
a descent rate of about 20m/s (40mph), so there is no particular reason to
design for faster. In practice, the usual preference is to design for
about half that, specifically so that a landing-system failure is
survivable.

Then making sure that your fuel reaches these engines is a key design
point, when again you would get squashed astronauts if your fuel lines
get blocked.


The usual preference in such systems is solid fuel, which has no plumbing.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |
  #15  
Old July 29th 03, 04:29 AM
stephen voss
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Rand Simberg wrote:

On Sat, 26 Jul 2003 13:54:05 +1000, in a place far, far away, Brett
O'Callaghan made the phosphor on my
monitor glow in such a way as to indicate that:


(I expect they'll go "Something with Wings", as I guess the capsule
approach might be perceived as a backwards step).



Anything that has to be delivered with a Delta IV or Atlas V is a
backwards step.


You mean like plastic disposable twin blade razors are a step back from
straight edge reusable razors like your grandfather used?

This whole reusable mantra is sentimentality not common sense.
If you can deliver missions using ultracheap and reliable disposable
rockets why do you even need reusable rockets?

You dont need a reusable rocket to launch most satellites.
The only purpose for a reusable spacecraft is if you need to return
cargo(cargo meaning stuff or people) to the earth.

  #16  
Old July 29th 03, 04:40 AM
Rand Simberg
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On Mon, 28 Jul 2003 23:29:59 -0400, in a place far, far away, stephen
voss made the phosphor on my monitor glow in such a
way as to indicate that:

Anything that has to be delivered with a Delta IV or Atlas V is a
backwards step.


You mean like plastic disposable twin blade razors are a step back from
straight edge reusable razors like your grandfather used?


No. Those are affordable.

This whole reusable mantra is sentimentality not common sense.
If you can deliver missions using ultracheap and reliable disposable
rockets why do you even need reusable rockets?


You can't deliver missions that most people are interested in that
way.

You dont need a reusable rocket to launch most satellites.


Who cares? That's entirely beside the point.

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  #17  
Old July 29th 03, 05:41 AM
Henry Spencer
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In article ,
stephen voss wrote:
This whole reusable mantra is sentimentality not common sense.
If you can deliver missions using ultracheap and reliable disposable
rockets why do you even need reusable rockets?


If that could be done, then we wouldn't. Trouble is, it can't be. Not
for a definition of "reliable" that would be considered acceptable for any
other form of transportation -- that is, the sort of reliability that is
needed to really open the skies to mankind.

Would you fly on an airline that dropped 1% of its flights in the ocean?
Would you entrust a multi-million-dollar cargo to such an airline? For an
expendable rocket, a loss rate of only 1% is considered excellent; most US
rockets are not that good. This sort of loss rate would be considered
criminal negligence in most other fields.

It has been estimated that if you really sweated manufacturing technology
and such, you *might* be able to get a 0.1% loss rate with expendables.
That would be considered wonderful by today's launch customers, but it is
not good enough for many things people would like to do in space. It's
still orders of magnitude worse than even advanced aircraft.

To do any better, you need systems in which every vehicle can be
flight-tested repeatedly before carrying paying payloads.

You dont need a reusable rocket to launch most satellites.


If all you want to do is to launch "most" satellites, that's true. If
your dreams of what should be done in space go no farther than launching
occasional ultra-expensive communications satellites (and losing 1% of
them), expendables are fine. If you see the night sky as a black wall,
forever closed to most human activities, there's no problem.

As H.G. Wells put it, in "The Country of the Blind": "Their imagination
had shriveled with their eyes."
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |
  #18  
Old July 29th 03, 07:21 PM
Earl Colby Pottinger
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Mary Shafer :

On 28 Jul 2003 16:18:45 GMT, (TKalbfus) wrote:

If we're planning on having these fins still on the JDAM when it's
time to direct the ordnance to the target, we'd better not be falling
from a very high altitude. Aerothermodynamics, you know. They're
certainly not suitable for ballistic flight intercontinentally or,
probably, even regionally.


The fins would fold up into the body of the capsule during reentry. Once

the
capsule has slowed down sufficiently, the fins would unfold and direct

the
capsule toward the landing site as it fell. In essence it is an Earth

lander.

Oh, great. Moving parts to fail. That's a good idea.

Mary


But failure is an option here. The flaps are not needed for the capsule to
re-enter safely, or to land on the ground. Thier purpose is to shink the
landing foot print. If they fail, the people in the capsule are still safe
and still land alive, it is that they may end up 10 kilometers from ground
zero instead of 100 meters, and since the landing in the footprint is
semi-random they still may endup 10 meters from ground zero.

Adding parts that may fail is not a problem if the parts work most of the
time and them make things better. It is adding parts that when they fail
that they do kill you that is the problem.

Earl Colby Pottinger

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  #19  
Old July 29th 03, 08:33 PM
G EddieA95
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his whole reusable mantra is sentimentality not common sense.
If you can deliver missions using ultracheap and reliable disposable
rockets why do you even need reusable rockets?


Because they are not cheap in any sense. The Saturn V cost $180M a shot.
Space will *never* be a venue of human expansion as long as even a short
mission involves throwing away that much.
  #20  
Old July 29th 03, 08:36 PM
G EddieA95
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Default Orbital Space Place project

capsule has slowed down sufficiently, the fins would unfold and direct the
capsule toward the landing site as it fell. In essence it is an Earth

lander.

Oh, great. Moving parts to fail. That's a good idea.


capsule has slowed down sufficiently, the fins would unfold and direct the
capsule toward the landing site as it fell. In essence it is an Earth

lander.

Oh, great. Moving parts to fail. That's a good idea.


And where would you put these fins? AIUI, the ship is a spheroid or a blunt
cone, not cylindrical.
 




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