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Multiple Engines???



 
 
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  #121  
Old January 16th 04, 08:49 PM
Axel Walthelm
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Default Why not use jets as 1st stage? (was Multiple Engines???)

wlhaught wrote:
Alright, back to powered flybacks for first stages. Are jet engines

worth the trouble of extra systems?

As I recall, I read somewhere that the shuttle uses half its fuel to
reach 1,000 mph.



You sure?

I have a copy of a speed/height/time diagram of the shuttles ascend.
1000 mph would be 1600 km/h. The diagram says that this speed is
reached within the first minute of launch at a height of about 8-10
km.

Launch takes 8.5 minutes, boosters burn 2 minutes. If you would say
half of the boosters fuel is used up at 1000 mph that would fit. But
total fuel including the fuel of the big external tank?

Ok, solid booster rocket fuel is quite heavy, and the booster burns
faster in the beginning than at the end. So maybe overall this could
be true.

But what does it mean? Solid rocket boosters are not economic?

A somewhat related fact: the shuttle has to throttle its main engines
during ascent within atmoshpere, because the fragile orbiter wings
can't stand the wind pressure.

Does anone know how much of a performance penalty this means?
(And at what height/speed this happens)
  #122  
Old January 17th 04, 06:24 AM
Hobbs aka McDaniel
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Default Why not use jets as 1st stage? (was Multiple Engines???)

(Axel Walthelm) wrote in message . com...
wlhaught wrote:
Alright, back to powered flybacks for first stages. Are jet engines

worth the trouble of extra systems?

As I recall, I read somewhere that the shuttle uses half its fuel to
reach 1,000 mph.



You sure?

I have a copy of a speed/height/time diagram of the shuttles ascend.
1000 mph would be 1600 km/h. The diagram says that this speed is
reached within the first minute of launch at a height of about 8-10
km.

Launch takes 8.5 minutes, boosters burn 2 minutes. If you would say
half of the boosters fuel is used up at 1000 mph that would fit. But
total fuel including the fuel of the big external tank?

Ok, solid booster rocket fuel is quite heavy, and the booster burns
faster in the beginning than at the end. So maybe overall this could
be true.

But what does it mean? Solid rocket boosters are not economic?

A somewhat related fact: the shuttle has to throttle its main engines
during ascent within atmoshpere, because the fragile orbiter wings
can't stand the wind pressure.

Does anone know how much of a performance penalty this means?
(And at what height/speed this happens)


Rockets become more efficent as the ambient pressure (ie: atmosphere)
drops... therefore if you could launch the exact same rocket from
say the moon or earth orbit you'd get more bang all other things
being equal (not that they would be since we don't have the infrastructure
in space to fuel and launch big ships at present). In other words
as a rocket rises from a place of high atmospheric pressure to a
place of lower pressure it is becoming more efficent AND it also
has less weight to move because so much of the original weight was
fuel that fed the engine.

-McDaniel
  #123  
Old January 17th 04, 12:32 PM
Mike Ackerman
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Default Why not use jets as 1st stage? (was Multiple Engines???)



Carsten Nielsen wrote:


There have been lots of plans of that sort.

The most important thing about it would be to lift the vehicle above
the lower dense athmosphere, not so much to get it moving at
supersonic speed.


Then how about a propeller plane as 1st stage? Recall that the Helios
holds the altitude record for a non-rocket plane, c. 100,000 feet. As
ridiculous as the Helios concept is, that record is impressive.

Although the Helios was a solar-powered electric plane, I see no reason
why that altitude couldn't be reached with a piston engine. It would
use a turbocharger with a multi-stage compressor.

Should this be the goal for TSTO? A slow booster plane with a huge wing?

Mike Ackerman

  #124  
Old January 18th 04, 11:27 PM
Sander Vesik
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Posts: n/a
Default Why not use jets as 1st stage? (was Multiple Engines???)

In sci.space.policy Axel Walthelm wrote:
wlhaught wrote:
Alright, back to powered flybacks for first stages. Are jet engines

worth the trouble of extra systems?

As I recall, I read somewhere that the shuttle uses half its fuel to
reach 1,000 mph.



You sure?

I have a copy of a speed/height/time diagram of the shuttles ascend.
1000 mph would be 1600 km/h. The diagram says that this speed is
reached within the first minute of launch at a height of about 8-10
km.

Launch takes 8.5 minutes, boosters burn 2 minutes. If you would say
half of the boosters fuel is used up at 1000 mph that would fit. But
total fuel including the fuel of the big external tank?

Ok, solid booster rocket fuel is quite heavy, and the booster burns
faster in the beginning than at the end. So maybe overall this could
be true.

But what does it mean? Solid rocket boosters are not economic?


"You should use a different flight profile that didn't try to
get to high speed while in teh densest parts of teh atmosphere"?


--
Sander

+++ Out of cheese error +++
  #125  
Old January 31st 04, 01:31 AM
spacr
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Posts: n/a
Default Why not use jets as 1st stage? (was Multiple Engines???)

Hi,

The answer to the origional question is quite simple.
The thrust to weight ratio of jet engines is BAD, really bad. The best jet
engines are around 10 or 12:1 and most are 5:1 or less. Bottom line: they
are just too friggin heavy... lol

As Always,

Jay Troetschel

"Sander Vesik" wrote in message
...
In sci.space.policy Axel Walthelm wrote:
wlhaught wrote:
Alright, back to powered flybacks for first stages. Are jet engines
worth the trouble of extra systems?

As I recall, I read somewhere that the shuttle uses half its fuel to
reach 1,000 mph.



You sure?

I have a copy of a speed/height/time diagram of the shuttles ascend.
1000 mph would be 1600 km/h. The diagram says that this speed is
reached within the first minute of launch at a height of about 8-10
km.

Launch takes 8.5 minutes, boosters burn 2 minutes. If you would say
half of the boosters fuel is used up at 1000 mph that would fit. But
total fuel including the fuel of the big external tank?

Ok, solid booster rocket fuel is quite heavy, and the booster burns
faster in the beginning than at the end. So maybe overall this could
be true.

But what does it mean? Solid rocket boosters are not economic?


"You should use a different flight profile that didn't try to
get to high speed while in teh densest parts of teh atmosphere"?


--
Sander

+++ Out of cheese error +++


  #126  
Old February 4th 04, 07:41 PM
william mook
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Default Multiple Engines???

(David Shannon) wrote in message . com...
If you wanted to use a Centaur 1 engine - an RL10 - you'd produce
20,000 lbs of thrust for Each engine - with about the same propellant
efficiency. The payload of this vehicle is 12,250 lbs with 7 elements
each with the following breakdown;

14,000 lbs - propellant
499 cf - volume
1,750 lbs - structure
20,000 lbs - thrust

Seven Rl10s cost about $35 million.


Thanks. I'm a fan of the RL10, so I'll play around with this version.
BTW, if you change the crossfeed arrangement to:

(3) and (5) feed (4),
(2) feeds (1) feeds (3), and
(6) feeds (7) feeds (5)

you can gain a little delta-V by effectively becoming a 4-stage vehicle
ie separating pairs at a time.

The empty weights are rather light - were you looking to reuse the stages?

Cheers



You're right about the four stage approach - that'll work and improve
things as well.

I'm a big fan of getting to market cheaply, but then being in a
position to fund incremental improvements of a baseline vehicle. So,
the way I see it is you create pods for the higher delta vee
components while creating a flyback booster for the lower delta vee
components. Then, extend the capacity of the flyback systems to
include all the elements.

The flyback booster consists of the minimal thermal protection needed
to re-enter the atmosphere and slow to subsonic speeds. Then, the
smallest possible wings are deployed cruise missile fashion to glide
at subsonic speeds. Loitering downrange for each booster is a
subsonic tow plane- a refurbished airliner. The airliner snags a
towline deployed by the booster and pulls the glider back to the
launch point where it is released for a glide back landing at the
airstrip associated with the launch center.

Engine pods re-enter ballistically and deploy hang-glider type
parachutes. These too are snagged mid-air and towed back to the
launch center for reuse. Flight speeds are lower for these pods and
require the adaptation of propellor driven airliners for their use
modified to operate at the speeds required.
 




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