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Oomair
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isnt possible to make cost efficient spacecraft by putting multiple types of rockets on a ship which can then alternate rocket engine at different levels of the atmosphere and eventually escape into space?
Let's start with the easiest question for you...Are you referring to manned or non-manned space flight?Oomair said:isnt possible to make cost efficient spacecraft by putting multiple types of rockets on a ship which can then alternate rocket engine at different levels of the atmosphere and eventually escape into space?
russ_watters said:Lots of engines? Sounds expensive...
Oomair said:isnt possible to make cost efficient spacecraft by putting multiple types of rockets on a ship which can then alternate rocket engine at different levels of the atmosphere and eventually escape into space?
There is no aerospike that has flown to my knowledge. There are engines that have movable skirts to help compensate for altitude, but not to the extent of the spike.Danger said:There is a compromise approach, but it's still not as good as dropping dead stages. Variable-geometry nozzles such as the (still experimental?) linear aerospike can operate at peak efficiency throughout the climb. That doesn't resolve the issue of all the dead weight, but jettisonable fuel tanks would help.
gaming_addict said:The most efficient I'm thinking right now at the moment is the strategy made by Scaled Composites for the X-Prize competition. Have an aircraft carry the spacecraft from high altitudes and launch it from there. I think the Antonov An-225 could do just that for heavier manned orbital flights.
Oomair said:what I am trying to say is that, why doesn't NASA develop manned vehicles with multiple types of engines, for example, the ship uses let's say engine A to get to one point of the atmosphere,
then engine A is shut off but not broken off the ship, then you activate engine B, C, and eventually escape into space
that way the engines are saved so NASA doesn't have to waste money to make new ones
Danger said:Oomair, you might be getting misled by some ideas that have been kicking around for atmospheric machines, such as taking off with turbojets and switching to scramjets when supersonic. Those things are not intended to go orbital, and they don't have to carry an oxydizer.
Oomair said:ok one thing i want to get straight in my head here is that does a space shuttle that is returning to orbit just dive into orbit at a high speed and makes a landing like a plane or does it stay in a suborbital area for a few hours by slowly coming down each atmospheric level so that the heat doesn't dissolve it?
You really should be careful with the words you choose. I have been on a couple of programs that looked into hybridization between air breathing and rocket propulsion systems. That's exactly what they are, hybrids. The whole "morphing" thing, other than sounding cool, is a pipe dream brought about, mostly, by people looking for government research funding. I can imagine my Chevy Blazer morphing into a Ferrari when I want to go into "race car" mode. You're saying the same thing.gaming_addict said:Oomair may have a point, but not literally with multiple engines. I've read about some 'single stage' concepts put forth by reputable aircraft companies. One of them actually envisioned a turbojet that 'morphed' and doubled as rocket engine. The turbojet seemed to close it's inlet, compressor and combustion area, and used the nozzle section as the rocket engine.
I was thinking that turbojets are rather complex and heavy. So I might propose a ramjet instead that morphs to scramjet, and finally morphing to rocket engine to reach orbit. Scramjet are indeed not intended to go orbital and that's when the rocket engine or 'rocket mode' takes over.
Oh yeah...those pesky details we have to think about I guess. Morphing...light...efficient over a wide operating range...That's not a challenge. That's unrealistic dreaming.gaming_addict said:The idea understandably, makes the vehicle carry much less oxidizer needed than would a pure-rocket design, that enormous fuel weight saved could directly translate to greater payloads carried and of course, much improved economy of space flights. The challenge now is designing a morphing engine that is efficient in wide range of flight regimes as well as light in weight.
Considering that the first real scramjet model research craft testing was in 2002 and then 2004, it may be a bit of a stretch to say "we haven't even had a manned flight yet." There's at least a couple of decades of research and development before we see anything close to a manned flight.gaming_addict said:There has been real plans to use the the scramjet for use with single stage orbital vehicles, but scramjet technology and hypersonic flight is still relatively early as of now. There's not even one manned flight conducted to date.
I would challenge you to look at the weight of a turbojet versus the combined weight of a thruster package and the associated turbo pumps and delivery systems.
gaming_addict said:-It starts by deceleration burn
-Skips over the upper atmosphere, much like a skipping stone thrown over the surface of a lake ...
The thing about the J58 is that it "morphs" into a different version of the same class of engine, i.e. air breathing. It's a big difference from trying to go between air breathing and non-air breathing. The technical difficulties that immediately come to mind to marry the two is pretty substantial.gaming_addict said:Yep, that 'hybrid' term didn't come to mind so I used 'morph' instead. When I meant the 'morphing' thing, here's what I meant:
http://en.wikipedia.org/wiki/Pratt_&_Whitney_J58
That's a real example of an engine that 'morphed' into another, from a turbojet into ramjet. So 'hybrid' it is! Sorry I'm not a native speaker so I could get lost with words :)
If I understand you correctly, the first two issues would beDanger said:I don't know how practical it would be, but my approach would be to use an air-breathing rocket with a variable geometry nozzle and something like a APU turbine to run the compressor. At ram speed, the compressor could be bypassed, then cut in the oxydizer pumps when the air runs out.
Plausible, Fred?
D H said:This is all wrong. The Shuttle has only done a skip reentry in simulations. It has never done one in reality. Skip reentry has a very low Technology Readiness Level (TRL 3, to be precise). It is one of the many technologies that need to be beefed up considerably before we even consider sending people to Mars.
Thanks for the response, Fred. You did apparently misunderstand about item #1, though. The rocket would be just a rocket, with no turbine or compressor inherent to its design.
I got you now. I can't say it's unfeasible technically. It may tough to match an APU big enough to drive a reasonable sized compressor and not go through the roof on weight.Danger said:Thanks for the response, Fred. You did apparently misunderstand about item #1, though. The rocket would be just a rocket, with no turbine or compressor inherent to its design. The compressor would be a separate structure which could be ducted into the system with a bypass circuit to force-feed the engine at low speed. With ram speed attained, the diverter valve would be flipped to 'straight-through' from the intake to the rocket. I was thinking of an aircraft APU or electric motor to power it, rather than tapping into the rocket.
FredGarvin said:* Technical engineering term for high temperature.