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Dumb question - Space and jets


PODNickerz

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Hello,

I am here to ask yet another dumb question,

Why cannot jets fly into space?

Is it just because the material they are made out is not made for space or is it also because there thrusters do no have enough power to go into space?

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Well, if you don't know... it's not a stupid question. :)

Material one, they could get into space, while freezing the crew to death and even if they by some insane chance of surviving would burn up in the return into one big ball of flames.

Thrusters yes, not strong enough to get up that high for normal planes. Once you get so high, I believe the engine will cut out on you sending the plane into a free fall back to earth.

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In reagard to the power needed to get into space:

Jets need air(The Oxydizer) coming in the intake to be able to continue to burn and produce thrust. In space(or even in the very thin atmosphere at high altitudes), there is not the oxygen required to continue to burn fuel. If you try to take a 747 to 70,000 feet you will find out very fast that the engines will stall long before you can get there.

Rockets on the other hand take the oxydizer into space with them...rockets have the ability to continue to burn and produce thrust regardless of the atmosphere outside of the rocket. Stuff like hydrogen peroxide(very strong versions; not the stuff in the bottle at the drug store) is able to burn without any outside air. I am sure there are some chemistry geeks that can explain it far better than I can, but I understand the gist of it.

Aquatus1 would probably a good resource, he is incredibly smart in such matters...a PM to him would probably qive you a very good answer.

Edited by Fluffybunny
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Fluffy is essentially correct. High altitude jets require large intakes and high speeds to operate, such as the Blackbird. There has been a large amount of research on another type of jet that could be used in space: ionic jets, which inhale particles in space, charge the particles, accelerate and discharge same. The thrust is very small and practicality is limited. Solar sails would seem to be more reasonable, at least for interplanetary use.

The use of hydrogen peroxide, however, is different. Peroxide was abandoned due to the need for high energy fuels: the use of liquid oxygen along with such things as nitromethane or alcohol or any number of high energy combustibles will increase thrust over straight peroxide. Peroxide does not burn, but attains thrust by catalyst, preferably silver, which causes a relatively pure form of peroxide to partially decompose, creating heat, water, and oxygen as a byproduct. The heat causes the water to vaporize to steam (very hot), and in a controlled environment such as a rocket engine, the steering causes thrust.

Peroxide can be used also as a more conventional fuel, such as in properly designed turbine or piston engines and has essentially no pollutant exhaust if correct catalysts are used: General Dynamics used hydrogen peroxide for all manner of power during their missile programs in the '70s, including modified piston engines. The biggest problem with peroxide is that when it comes in contact with catalysts (many different types) in uncontrolled conditions, it does become violent.

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Hello,

I am here to ask yet another dumb question,

Why cannot jets fly into space?

Is it just because the material they are made out is not made for space or is it also because there thrusters do no have enough power to go into space?

Looks like some pretty good answers for you there.

Simply put, yes, jets aren't constructed for the space environment:

Their engines don't function beyond a certain altitude because they need air to breathe;

Their engines don't produce the required thrust to attain a reasonable velocity for space flight (most jets at altitudes above 60,000 feet or so, maybe less, lose their ability to fly at all because of the low air density at altitude. Extreme speed is required for things like the SR-71 or other extremely high flying jets to actually maneuver at these altitudes, and they're much lower than the threshhold of space);

They don't have thrusters which would allow maneuvering in the space environment (translation and maneuvering about the three axes);

They are not built for atmospheric re-entry (even at sub-orbital speeds);

and their cabins aren't constructed for safety in a vacuum.

That's pretty much it in a nutshell.

Regards.

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probably the only fighter jet that could escape into space was the Arrow. But that was cannceld now wasnt it. Hell there were planes to put a capcil in her and fly it into LEO and launch the capcil.

~Thanato

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Thankyou all for the answers, it clears up everything for me now

Though i have one more question,

Would a space craft with the same thrust power (power but not engine) as a jet travel faster in space? since it has no gravity in space?

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Thankyou all for the answers, it clears up everything for me now

Though i have one more question,

Would a space craft with the same thrust power (power but not engine) as a jet travel faster in space? since it has no gravity in space?

In a nutshell, yes. Let's say that the spacecraft and the jet weigh the same thing for the sake of simplicity.

A jet engine is essentially pushing an aircraft through the air. There's drag from the airplane in that situation, and there's a limit on how fast it can go for a particular power level (I do not want to get into an analysis of aerodynamics...that would just cloud the issue with complexity).

In space, drag is non existent, therefore, if a spacecraft had the same weight and power as a jet, it would accellerate at a certain rate and continuously do so until engine cutoff. Depending on the duration of the burn, it could add a heck of alot more velocity to a vehicle in space.

Let's take something like a 727 jet.

A 727, which weighs in at about 150,000 pounds (a fairly well loaded takeoff weight), will attain 550-600 miles per hour with a thrust level of about 35000 pounds, and can go no faster due to aerodynamic considerations;

a similarly heavy and powered spacecraft (lets say it's already in earth orbit at a speed af about 17,500 MPH and fires its engine for about 5 minutes) will accellerate at about 1/4 g. In 5 minutes, the spacecraft will have gained approximately 1200 MPH.

The wierd part is, the longer the rocket engine fires, the faster the vehicle will go....there's no limit, save the fuel supply. The airplane can only go so fast and no more.

The real kicker is that the spacecraft, once its engines cut off, will basically stay at the speed it attained via the engine burn (less gravitational pull, of course, but that's another thing that'll cloud the issue). The airplane, if its engines cut out, will slow down...a glide will have to be established and it has no choice but to land someplace fairly soon.

It's a somewhat complex issue, but the bottom line is that the answer to your question would be yes, a spacecraft with the same power as a jet ultimately will go faster...because of the lack of aerodynamic drag...and of course, there's no gravity out there as well for the engines to combat.

Regards.

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:alien: And since space craft do not have to be aerodynamic a space ship can ( and often dose) look like a flying BRICK with solar sails!

Engineers have no sense style or design. When astronauts go into space, they should have a Classy Ride! :tu:

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Though I would like to ad that a glider released at 5,000 feet can attain the altitude of 41,000 feet. A skilled glider pilot can often stay aloft for a very long time and even climb to dizzying hieghts by seeking out rising thermals. To do this sucessfully earns one the right to be called a triple diamond, as I recall. I could be wrong about the diamond thing though.

Personally, I prefer a bird with an engine though.

post-24472-1135385722_thumb.jpg

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:alien: And since space craft do not have to be aerodynamic a space ship can ( and often dose) look like a flying BRICK with solar sails!

Engineers have no sense style or design. When astronauts go into space, they should have a Classy Ride! :tu:

Well, that applies certainly to pure spacecraft...something like the LM or Voyager or such things. The Shuttle is most certainly aerodynamic, since it has to be in order to fly as a glider...nonetheless, it still descends somewhat like a brick.

Aerodynamics also applied to the Apollo and Mercury and Gemini spacecraft, inasmuch as the vehicle had to fly through the atmosphere in order to get into space, and a degree of aerodynamics certainly played a part in re-entry (blunt heat shields and lift vector control through roll and all that...a rather ingenious idea which still works very well).

But POD... is referring to vehicles in space, where aerodynamics has no applicability, of course.

Regards.

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Though I would like to ad that a glider released at 5,000 feet can attain the altitude of 41,000 feet. A skilled glider pilot can often stay aloft for a very long time and even climb to dizzying hieghts by seeking out rising thermals. To do this sucessfully earns one the right to be called a triple diamond, as I recall. I could be wrong about the diamond thing though.

Personally, I prefer a bird with an engine though.

True enough, Lord.

But we may be confusing POD with this one, since a glider's performance has to do with thermals and not thrust.

I enjoyed flying gliders alot. Kinda make's you get pretty good at landing, since you only get one attempt. But I too always had a preference for an engine...

I'm assuming that's your 172 there?

A honey of an airplane, great to fly, well behaved, forgiving.

Where's your front wheel fairing??

:)

Regards.

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Depends on your definition of a "jet". Jet operates by taking some fixed mass flowrate of a working fluid (air, for the most part, and in that case running it through the Brayton cycle and getting some work out of it) then producing thrust by acclerating it to a higher velocity at the outlet. Thrust is just m_dot,fluid * delta_v,fluid

Very similar is used with ion drives for space travel (which are proven). Its essentially a space jet. The specific impulse (basically how much thrust it can produce) is much lower, so you have much lower acceleration, but it lasts for a long distance. Its all about conservation of momentum. If you start throwing crap out of your space ship in one direction, it will accelerate the other direction. Maximize that by accelerating your ions out at very high velocity.

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probably the only fighter jet that could escape into space was the Arrow. But that was cannceld now wasnt it. Hell there were planes to put a capcil in her and fly it into LEO and launch the capcil.

~Thanato

Doubtful.

The Arrow would have been an incredible craft for its time but by modern standards would be nothing special. It's just one of those things us Canadians love to talk about, though.

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I'm assuming that's your 172 there?

A honey of an airplane, great to fly, well behaved, forgiving.

Where's your front wheel fairing??

No, unfortunately, it's not mine. It's a rental from the local F.B.O. When I started learning to fly, it had no fairing on the front gear and it still don't!

Good point, I didn't mean to confuse the issue, or anyone else. I just can't resist a chance to throw in a little flying when I can!

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No, unfortunately, it's not mine. It's a rental from the local F.B.O. When I started learning to fly, it had no fairing on the front gear and it still don't!

Good point, I didn't mean to confuse the issue, or anyone else. I just can't resist a chance to throw in a little flying when I can!

Hey, a little flying never hurt anyone. Especially a pilot!

Doesn't confuse me :D .

I never owned an airplane either, but I'll say this. If you fly her, she's yours...wheel fairing or not. I took my Private check ride in a 1968 150 Commuter (in 1973). Saw her parked on that same field recently...someone bought her and is re-furbishing the bird. She's got wheel fairings and a shiny new spinner!

I think she recognized me.... ;)

Regards.

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