View Full Version : Question about space shuttles
What is the deal with vertical launch with all that gubbins? If a fighter jet can get to teh outer edge of the atmosphere why can't that tech be used?
Or is it a case of the different fuel that is needed outside the atmosphere?
Jezz_S13
04-02-2003, 08:26
yeah pretty much fuel, rocket fuel contains it's own oxidiser so no need for additional oxygen (from the air).
Jet engines rely on oxygen in the air.
hmmm
can't the engines be modifed to premix an oxidser? Could have a space taxi...
That 10K plus stuff from motor world would do it.
Originally posted by Starionman
What is the deal with vertical launch with all that gubbins? If a fighter jet can get to teh outer edge of the atmosphere why can't that tech be used?
Or is it a case of the different fuel that is needed outside the atmosphere?
Only rocket engine + fuel has power / weight ratio capable of leaving the earth. Plane would never be able to fly fast enough to get high enough to escape gravity. Plus lift from wings reduces as the atmosphere thins, ( not that this makes much difference to modern fighter jets) and the jet engine needs oxygen from the air to burn the fuel whereas the rocket has oxygen stored on board (if using oxidising reaction). Jet engine can't exceed what, 4,000kmh maybe a bit more; RAMJET engines (air is "rammed" down into the engine using a funnel shape!) work to maybe 10,000kmh ?? anyone confirm this? then flow of air through the combustion chamber becomes supersonic and a SCRAMJET engine is required for further acceleration. Last summer saw the first successful operation of a scramjet in australia so the engines are probably 2-5 years from being useful.
Hopefully NASA will mothball the shuttles and develop a "spaceplane" that uses a hybrid engine: Jet engine becomes ramjet becomes scramjet then switch to ion/nuclear rocket as the plane leaves the atmosphere.. if they put enough money forward, they could develop this in a few years. Richard Feynman (Nobel prize-winning physicist, creator of QED (Quantum Electro-Dynamics, unification of 3 of the 4 forces in the universe (not gravity)) was on the commission that investigated the Challenger disaster. He said that NASA had added the probabilities of failure of the shuttle components incorrectly to get the desired failure probability of 1 in a million. Feynman calculated the failure rate of the shuttle to be 1 in 100. Since they've now had about 200 flights and lost 2 shuttles it looks like he was about right...
Or 10k plus from motorworld.
Mr_Sukebe
04-02-2003, 11:29
I seem to remember that escape velocity to get something into orbit is something like 17,000 miles an hour, obviously a bit difficult with a jet engine.
The other key thing is height. Low earth orbit is at something like 200 miles (please correct me on what I get wrong here, trying to remember things from my youth, an awful long time ago).
The atmosphere runs out at 80,000 to 100,000 feet, which is about 20 miles max. So in short, you have no air to use for propulsion to take you the additional 180 miles and to accelerate you to a substantially larger velocity.
I guess that someone probably thought of the idea of a combined jet / rocket system. The key issue with that would be weight. Think of how much a shuttle weighs on launch, complete with it's rocket fuel. Now, try to imagine the size of the jets needed to get all that weight to 80,000 feet, bearing in mind that you're still only 10% of the way into orbit and now need the fuel/rocket system to get you the rest of the way up.
In addition, you clearly don't need the jets on the way back to earth. The shuttle as a glider prooves it.
So you'd be using jets to get just 10% of the way, after which they're useless for the rest of the mission. Quite the contrary, they will add weight and complexity which needs to be dealt with on the way back into land.
I seem to remember reading that the shuttle is one of the most complex mechanical items ever built. Part of this is because of the redundancy systems on board, as so much can and does fail during each mission.
The last thing you want is additional complexity.
How does that grab you?
Originally posted by Mr_Sukebe
In addition, you clearly don't need the jets on the way back to earth. The shuttle as a glider prooves it.
I seem to remember reading that the shuttle is one of the most complex mechanical items ever built. Part of this is because of the redundancy systems on board, as so much can and does fail during each mission.
The last thing you want is additional complexity.
I just don't like the high-speed re-entry. It subjects the shuttle to such high temperatures and buffeting.. also the shuttle is a crap glider. It is too heavy and the shape is heavily dictated by the need to survive reentry. It has to land at such a high angle of attack (nose up) that the pilots can't see the runway. It lands at a higher ground speed than any other aircraft, because any slower and it would stall or fall (therefore more dangerous). All these things are workarounds required because the shuttle is a rocket rather than an aircraft. The shuttle was designed in the late '60s and built in the 70's (I think). Would you drive a car designed in the 60s? The shuttle does have redundancies everywhere e.g. control system is 6x 386 computers of which 4 have to agree for the shuttle to do something. But it is now very old and could be so much improved..
how far out of the atmosphere are satellites?
Found this on the web:
1) Low Earth Orbit: The orbits whose heights are relatively low, around 300 to 600km, are called "low earth orbit", regardless of orbital inclination. If you translate these heights into distance, 300 to 600 km means between Tokyo and Nagoya, or just beyond Osaka, the farthest. Since the orbits are closer to the earth, energy necessary for launch is smaller. Also, low earth orbits have their merit of being lower in radiation exposure, because they are lower in height than the Van Allen radiation belt, where space radiation density is high. Low earth orbits are mainly used for manned space missions. Space Shuttles, Soyuz spacecraft, and International Space Station are launched into low earth orbits.
2) Geostationary Orbit: Geostationary orbit is a circular orbit at 36,000km above the equator. A satellite that is in geostationary orbit rotates in the same pace as the earth, one rotation in 24 hours. It means that the satellite seems to be stationary if you look it up from the earth, and that is the reason of the name of the orbit. The advantage of geostationary orbit is that a ground station can leave the antenna fixed at one designated point to communicate with a certain geostationary satellite. Practical satellites, such as communications, broadcasting, and meteorological satellites are in geostationary orbit.
3) Polar Orbit: Orbits whose orbital inclination is around 90 degrees are called "polar orbit". It means that the orbit is in north-south direction of the earth. With good selection of height and orbital inclination, the satellite in polar orbit can scan the whole earth surface. Therefore, many earth observation satellites are in polar orbit at the altitude of 700 to 900 km.
4) Geostationary Transfer Orbit: Geostationary transfer orbit is a "pre-orbit" to inject a satellite into geostationary orbit. Geostationary transfer orbit is a long elliptical orbit with the height of perigee at 250 to 450 km and the height of apogee at 36,000km. After being injected into geostationary transfer orbit by launch vehicle, the satellite will fire its onboard apogee engine at apogee whose height is 36,000km to go into geostationary orbit.
Mr_Sukebe
04-02-2003, 12:06
Dav,
I see what you're saying, however:
- I don't think there's much getting around the fact that you need to decelerate an object re-entering earths atmosphere. Quite clearly, it'll be trying to dissipate a lot of kinetic energy, and heat seems to be the main method.
Don't you think that they might well have tried an easier route if one existed, or do you think they came up with the idea just because it was an interesting challenge?
- You state that the shuttle is a bad glider, couldn't dissagree with that. Having said that, it's clearly been designed to meet a bunch of requirements, i.e.
1. Ability to carry a large payload
2. Ability to withstand a lot of heat on re-entry and be reasonably aerodynamic and so stand deceleration from over mach 20.
Again, I'd have to make the statement that it clearly works. It may be a rubbish glider, but none of them have ever been crashed, which to me suggests that it's an acceptable compromise.
- Yep, some of the electronics are ancient. But what would you rather have, tried and tested electronics that have a proven track record, or stuff that you're not quite sure about and might just break. Being fair, they're not exactly going to be playing Quake 3 whilst in orbit, so if 386s do the job and are reliable, isn't that good enough?
In addition, do you think they still use 386s, or have these now been updated as part of refurbishments?
Put it another way, concorde is older, as is a good deal of liners (QE2 anyone?) etc etc. Yes I'm sure they've had refits, but didn't the shuttle in question get a refit just 3 years ago?
You're right of course Mr. S...
One last comment:
With regard to loss of energy during descent obviously they must lose it but with a better airframe & maybe a powered descent they could lose it more slowly (maybe a sedate 5 hr descent rather than a 30 minute blast??)
Originally posted by davidra
The shuttle was designed in the late '60s and built in the 70's (I think). Would you drive a car designed in the 60s? The shuttle does have redundancies everywhere e.g. control system is 6x 386 computers of which 4 have to agree for the shuttle to do something. But it is now very old and could be so much improved..
While this is true it is also true that NASA update the shuttle fleet and everything to do with the shuttle fairly regularly considering the costs involved
For example this page shows allthe updates done to Columbia which has only flown 2 missions since this update.
The last having ended tragically.
http://science.ksc.nasa.gov/shuttle/resources/orbiters/columbia.html
Sorry, am being too critical, it is an incredible machine!
Have to say that when you see it on the launch pad it is an awesome sight. I was in the states last year and went to the space centre when a shuttle was due to go up. When the shuttle is on the pad they only let look at it from 2 or 3 miles away but the bloody thing is still awesome to see in the distance.
There was also one in the VAB which you could see the bottom of.
There was also one of those tractor things that the shuttles stand on when thay take them out to the pad and until you see it you don't realise just how huge the thing is.
Really a very awesome place.
Also the people that live nearby treat everyone who works there ( even people who are only there for a day ) like family. They really are very proud what has been achieved there.
Sorry if this sounds arsey in any way, it's not meant to be I just don't think that you can appreicate this machine until you see it or a lifesisze replica up close.
I'll shut up now.:D
Wow, would love to see it... incidentally I have seen "Enterprise" on her 747.
Just to give you an idea of sizethe tractor unit ( can't remeber what is called now :rolleyes: )
Piccy attached.
We parked up about 100 yards from one and if you were to park in a bus next to one of the tracks on the corners ( bearing in mind that this thing has four of them !!!)
it would need something like four or five buses just to be as long as one of it's foot prints.
Big really isn't the word.
How does it hold it upright?
Originally posted by AntS13
Big really isn't the word.
Bet one of you lot would still try to drift it :D:D
Originally posted by Keith_C
Bet one of you lot would still try to drift it :D:D
I'd give it a go but I think It might need lowering and bigger rims on first :D :D :D
Originally posted by davidra
How does it hold it upright?
Something like this
Also just to give a quick idea of size. The piccy attached has 3 people standing next to one of these crawlers.
And it is as wide as an eight lane highway.
Martin T
04-02-2003, 18:07
AntS13: You seem to know a bit about shuttles, do you know what happened to the X33 project?
I don't know that much really just find it interesting enuff to warrant reading everynow and again.
Saying that the X33 was cancelled because it was palgued by probelms concerning stability, engine design, efficiency and last but by no means least the considerable costs that it had already taken off of nasa and the company that was partners on it
( Lockheed ?).
I would have thought they was thinking something along the lines of building a vehicle at the space station for travel further without the worrys of re-entry and launch .
How about that. :p
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