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Knowledge_Seeker
2006-Jul-26, 07:24 PM
Why does the space shuttle launch at a verticle angle? why doesn't it launch like an airplane and gradually accelerate?

wouldnt this way be a lot cheaper, although there will be a substantial loss in speed, why is speed needed anyway?

ToSeek
2006-Jul-26, 07:33 PM
(Thread moved from Astronomy to Q&A.)

Speed is key - the overriding need is to get to 18,000 mph so the shuttle can maintain an orbit. The next goal is to get above the atmosphere away from where all the friction is - the sooner the shuttle can do that, the more it can accelerate.

(I'm sure other people here will have more authoritative answers.)

Hamlet
2006-Jul-26, 07:38 PM
Why does the space shuttle launch at a verticle angle? why doesn't it launch like an airplane and gradually accelerate?

wouldnt this way be a lot cheaper, although there will be a substantial loss in speed, why is speed needed anyway?

In order to obtain orbit, the shuttle has to reach a speed of about 17,500 mph. To get to this speed requires a lot of propellant, hence the SRB's and the large external tank. Gradually accelerating into orbit only adds to your fuel budget due to gravitational losses. You want to get to your orbital speed as quickly as is reasonable.

Knowledge_Seeker
2006-Jul-26, 08:15 PM
what if NASA created a large vaccum tube that was, say 60 miles high, that would surely repay itself by saving huge costs in fuel. (im sure this could never happen)

is the current way of getting into space the only way? could there be alternative ways in the future? (the near future)

Van Rijn
2006-Jul-26, 08:22 PM
what if NASA created a large vaccum tube that was, say 60 miles high, that would surely repay itself by saving huge costs in fuel. (im sure this could never happen)


Aside from being quite impractical, it wouldn't gain you much. Gravity is the primary issue. As previously stated, you can go up slower, but only at great cost.



is the current way of getting into space the only way? could there be alternative ways in the future? (the near future)

Various kinds of tether systems are a possibility. The synchronous skyhook, or space elevator, is the one most often discussed, but also the most technically difficult.

Mr Gorsky
2006-Jul-26, 08:25 PM
Given that some fighter jets (the Mig25 for one) claim to be able to go to "the edge of space", I would have a follow up question.

How close to "space" do they actually get, and what would it take to push them the whole way and into orbit (in addition to getting rid of the air-breathing engine of course)?

Hamlet
2006-Jul-26, 08:26 PM
what if NASA created a large vaccum tube that was, say 60 miles high, that would surely repay itself by saving huge costs in fuel. (im sure this could never happen)

is the current way of getting into space the only way? could there be alternative ways in the future? (the near future)

You would save a little on fuel launching in a vacuum since you don't have to fight atmospheric drag, but you still need to lift the shuttle against gravity and get it to an orbital velocity of 17,500 mph. The small amount of fuel saved would be dwarfed by the construction costs of a 60 mile high tube, assuming it's even technically possible.

I've seen various types of space elevators proposed, but I'm not sure how technically feasible they are.

Hamlet
2006-Jul-26, 08:45 PM
Given that some fighter jets (the Mig25 for one) claim to be able to go to "the edge of space", I would have a follow up question.

How close to "space" do they actually get, and what would it take to push them the whole way and into orbit (in addition to getting rid of the air-breathing engine of course)?

The specs I found on the Mig 25 state it has a maximum speed of Mach 3 (2283 mph) and a maximum altitude of 90,000 ft. You would need to add more than 15,000mph in delta-V to get to orbital velocity and you would need fuel to lift it high enough above the atmosphere to not burn up, let's say 120 miles (633,600 ft).

The U.S. awards astronaut status to anyone who flies above 50 miles (264,000 ft) so the Mig 25 gets about a third of the way there based on altitude, but it's nowhere close for orbital speed.

PhantomWolf
2006-Jul-26, 08:51 PM
Given that some fighter jets (the Mig25 for one) claim to be able to go to "the edge of space", I would have a follow up question.

How close to "space" do they actually get, and what would it take to push them the whole way and into orbit (in addition to getting rid of the air-breathing engine of course)?

50 miles is considered space, the only "plane" to have past that is the X-15 with a top altitude of a little over 67 miles. Lockheed's SR-71 flew at just over 16 miles. The Mig 25 has achieved 22 miles. Spacecraft One achieved 53.3 miles. Freedom 7 hit 118 miles and while the minimum Earth orbit is only about 95 miles, but the second import factor is speed.

The reason that 20 miles is called the edge of space is that over 99% of the atmosphere is below that level, but space offically starts at 50. To get to Orbit however requires quite a bit of extra oomph to get them both to the height, and most importantly, the speed.

Mr Gorsky
2006-Jul-26, 08:58 PM
Thanks for that guys.

Van Rijn
2006-Jul-26, 09:09 PM
50 miles is considered space, the only "plane" to have past that is the X-15 with a top altitude of a little over 67 miles. Lockheed's SR-71 flew at just over 16 miles. The Mig 25 has achieved 22 miles. Spacecraft One achieved 53.3 miles. Freedom 7 hit 118 miles and while the minimum Earth orbit is only about 95 miles, but the second import factor is speed.


Picky technical point: The U.S. will declare someone who gets above 50 miles an astronaut, but the international standard for the beginning of space is 100 km. And for KS's sake, I'll note that either figure is arbitrary.

Jerry
2006-Jul-26, 09:18 PM
One final point: Many 1900-1950 Sci-Fi movies used a rail or sled to give a rocket time to build up some speed before the rails curved skyward. The shuttle is over 5 million lbs, and it is difficult to move it with ground transportation - The crawler does about 2mph. In addition, if the shuttle were accelerated to a high velocity and then pointed skyward, there would be an incredible load on both space and ground systems as the momentum of the shuttle is transferred vertically.

Uranut
2006-Jul-27, 08:16 AM
One final point: Many 1900-1950 Sci-Fi movies used a rail or sled to give a rocket time to build up some speed before the rails curved skyward. The shuttle is over 5 million lbs, and it is difficult to move it with ground transportation - The crawler does about 2mph. In addition, if the shuttle were accelerated to a high velocity and then pointed skyward, there would be an incredible load on both space and ground systems as the momentum of the shuttle is transferred vertically.
Escape velocity is scalar (it should really be referred to as 'escape speed'). There is no need to 'point skyward'. As long as the vehicle is not aimed at the surface of the earth it will reach orbit if the proper speed is achieved. Please note I am not saying the 'rail or sled system' is technically feasible (I'm a scientist not an engineer).

jseefcoot
2006-Jul-27, 02:06 PM
Escape velocity is scalar (it should really be referred to as 'escape speed'). There is no need to 'point skyward'. As long as the vehicle is not aimed at the surface of the earth it will reach orbit if the proper speed is achieved. Please note I am not saying the 'rail or sled system' is technically feasible (I'm a scientist not an engineer).


I seem to remember some old pulp-era short stories, perhaps from Heinlein or Asimov, in which a rocket was launched at a shallow angle, and might appear from some viewpoints to hover in the sky, or move very slowly, as it maintained a constant escape speed. Doing it this way, the rocket took a longer, curved path to space rather than a short vertical path that is nearly straight.

There are numerous endeavors now that aim to get people into orbit, even if a low one, and even if only for sight seeing. One such project is converting a Lear jet into low-orbit craft. There is an article in the current issue of Popular Science, I believe. Would this then become the first passenger jet to make it to space?

Sticks
2006-Jul-27, 02:20 PM
I always thought it launched the way it did, because the whole thing was a compromise design to speed things up so they could get some vehicle off of the drawing board.

:shifty:

94z07
2006-Jul-27, 02:32 PM
Spacecraft One and the X15 both were dropped from more conventional aircraft around 40,000 feet I think. The first F15 was fitted with an elongated nose and reached over 80,000 feet. The SR-71ís top altitude is classified but the published figure is over 85,000 feet. The F15 was also used to fire a missile, the Pegasus, into space. A rail gun, powered by car batteries, shot iron balls into orbit. I know NASA is looking to a modern rocket for itís next launch vehicle but I wouldnít be shocked at all to see more progress in the mother-ship ala X15/B29 setup in the future

ngc3314
2006-Jul-27, 02:57 PM
Spacecraft One and the X15 both were dropped from more conventional aircraft around 40,000 feet I think. The first F15 was fitted with an elongated nose and reached over 80,000 feet. The SR-71ís top altitude is classified but the published figure is over 85,000 feet. The F15 was also used to fire a missile, the Pegasus, into space. A rail gun, powered by car batteries, shot iron balls into orbit. I know NASA is looking to a modern rocket for itís next launch vehicle but I wouldnít be shocked at all to see more progress in the mother-ship ala X15/B29 setup in the future

The F-15 was able to launch a solid-fuelled ASAT, which was successfully tested on the P78-1 satellite (somewhat to the chagrin of some solar-wind scientists, since the original announcement was that the target was a defunct DoD satellite). The Pegasus is launched from Stargazer, a somewhat-modified L-1011 airliner, and has the distinction of also using wings to shape its launch profile shortly after release. The Pegasus design offers some side benefits - they can deploy wherever needed to reach a desired orbit, and are not hostage to what other payloads might be having delays and taking up launch-pad space.

The economics of air launch involve a lot of tradeoffs - one of the biggest being that launch at really high speeds saves the most fuel and weight for the payload but exacts a huge cost penalty on the launcher once it needs its own thermal protection system. This makes the optimum launch speed no higher than Mach 3 (depending a bit on altitude). There were designs from Boeing for a winged Saturn first stage that would have been the largest winged craft flown to that time (and maybe still - substantially larger than a 747), but development costs knocked that one out as a Shuttle launch contender.

To this point, the mass ratio has limited orbital air launch to rather small payloads (although I was kind of surprised they could fit GALEX on a Pegasus). No shortage of designs - to someone, every large aircraft built since the 1950s has looked a lot like an launch vehicle - but development costs for crewed systems or large-payload vehicles have always choked things off.

George
2006-Jul-27, 03:53 PM
How many engineers and scientists does it take to figure all this out? That alone is quite a clue.

[Note: this is not related to the number of same regarding a light bulb replacement. ;)]

ZaphodBeeblebrox
2006-Jul-27, 08:53 PM
what if NASA created a large vaccum tube that was, say 60 miles high, that would surely repay itself by saving huge costs in fuel. (im sure this could never happen)

is the current way of getting into space the only way? could there be alternative ways in the future? (the near future)
Actually, Quiite a Bit MORE Economical, Would Be The Opposite Solution ...

Imagine a 60 Mile High Tower, Pressurized at One Atmosphere, The Spacecraft Could Juust Float Up to Orbit Under a Helium Envelope ...

So Guys, Is That Buildable, Or Should I Stop Reading 80s Science Fiction?

selden
2006-Jul-27, 09:18 PM
Unfortunately, a 60 high mile tower pressurized to 1 atmosphere at the top would have a pressure of many atmospheres at the bottom. (Sorry, I don't know how to calculate that pressure differential, but I suspect it might be more than modern materials could contain.) If it were only 1 atmosphere pressure at the bottom, the fall-off in pressure with altitude would be no different from having no tower at all.

I suppose one could do it with pressure barriers analogous to the locks used in the Panama canal.

(I'm ignoring the problems associated with actually constructing a building that tall.)

ZaphodBeeblebrox
2006-Jul-27, 09:51 PM
Unfortunately, a 60 high mile tower pressurized to 1 atmosphere at the top would have a pressure of many atmospheres at the bottom. (Sorry, I don't know how to calculate that pressure differential, but I suspect it might be more than modern materials could contain.) If it were only 1 atmosphere pressure at the bottom, the fall-off in pressure with altitude would be no different from having no tower at all.

I suppose one could do it with pressure barriers analogous to the locks used in the Panama canal.

(I'm ignoring the problems associated with actually constructing a building that tall.)
True ...

It's an Interesting Thought Experiment, though ...

Also, While Orbit Would STILL Be Mostly About Speed, it Would Greatly Simplify Interplanatary Missions, Specifically Those Aimed Towards The Inner Solar System, as Speed Actually Has to Be Shed to Drop Down Currently!

:think:

cjl
2006-Jul-28, 06:04 AM
But immense speed needs to be gained relative to the launch location. Keep in mind that the speed to be shed is the earth's velocity relative to the sun, and that anything attached to the earth would not help with the deceleration.

ZaphodBeeblebrox
2006-Jul-28, 02:13 PM
But immense speed needs to be gained relative to the launch location. Keep in mind that the speed to be shed is the earth's velocity relative to the sun, and that anything attached to the earth would not help with the deceleration.
True ...

But, it Would Save on Fuel, If The ONLY Maneuver Necessary ...

Was The Transfer Orbit Injection Burn, No?

:think:

jlhredshift
2006-Jul-28, 02:48 PM
If you are in a circular orbit around the Earth, then an increase in speed relative to Earth by a factor of the square root of 2 is needed, i.e. sqrt2 x 17,500 mph, approx 25000 mph, to escape Earth's gravity. If this burn was made opposite to Earth's path around the Sun then you would head for the inner solar system. You could still launch taking advantage of the Earth's rotation, the burn would just have to be when heading away from Earth orbital path, and powerful enough to be of short duration to gain the delta v to 25k mph.

mugaliens
2006-Jul-29, 03:21 PM
A vehicle that's designed to support it's weight, including massive tanks, both horizontally (for taxi, take-off, and flight), as well as vertically (when it really gets going) weighs a lot more than a vehicle that supports itself in the vertical mode only.

The increase in efficiency of flight vs the relative ineffecience of vertical-only ascent is more than offset by the additional structural weight penalty.

Drbuzz0
2007-Oct-19, 08:41 AM
I always thought it launched the way it did, because the whole thing was a compromise design to speed things up so they could get some vehicle off of the drawing board.

:shifty:

The shuttle is a compromise of compromises. I remember Griffin saying that he was frustrated that people complain the shuttle is "too complicated" and that it's "too simple" basically saying that they're complaining that nasa took the "simple" road by going with the compromise design that utulized the external tank and dispensed with the earlier parasite aircraft ideas. And that they went with the thermal tiles instead of the compressed ceramic fabric and that the shuttle uses basically the same technology as earlier spacecraft.

I think he confused "complicated" with "advanced"

The shuttle is complicated alright... Complicated like a reciprocating steam engine.

Jens
2007-Oct-19, 10:04 AM
The increase in efficiency of flight vs the relative ineffecience of vertical-only ascent is more than offset by the additional structural weight penalty.

I think this is the real key.

Another incidental point is that you could ask the question the other way around. Why doesn't an airplane doesn't take off that way? Well, for one thing, it can't. Most airplanes are heavier than their thrust, so they cannot take off vertically. They have to use their wings to generate lift. But the space shuttle is not "flying" in that sense. The wings on the orbiter are useless during the launch. It just uses power to lift it up.

Also incidentally, the space shuttle does the "roll program" soon after lift-off, so actually it is going into a slightly non-vertical direction right after lifting off.

So I think one way of looking at it is like this. Suppose that the shuttle was launched at an angle of 45 degrees. It would have to be supported in that awkward position until the moment of launch, and then would have to generate enough lift to make sure that the engine closest to the ground doesn't actually hit the ground or that the thing doesn't tip over. But if you launch it straight up, then the engines all leave the pad at the same time and so you don't have to worry about hitting anything.

And suppose you tried to launch it like an airplane. The shuttle's wings cannot be used like an airplane's wings when the external tank and everything are on it, so you'd have to accelerate down a runway and then adjust the engines to start pushing it off the ground. I think it would probably crash. In any case, nobody launches big rockets non-vertically as far as I know. I think they only do it for small missiles.

EvilEye
2007-Oct-19, 10:42 AM
I was about to say something similar. Take-off & Launch are 2 seperate parts.

Take-off is leaving the tower. It hasn't been launched until they clear the tower. Usually toward the North.

Soon after, they USUALLY do the famous "roll" and then head east. Then when over the Atlantic, they "go with throttle-up". They really are flying like an airplane albeit it very steeply, because their only next chance to ditch and land is over western Europe. That and this way, they are taking advantage of the Earths spin for an extra boost.

Jens
2007-Oct-19, 10:46 AM
No, they aren't flying like an airplane, really. An airplane requires wings, because it stays in their air by using lift from the wings. The space shuttle doesn't. It is like a big firecracker.

Maksutov
2007-Oct-19, 10:47 AM
True ...

But, it Would Save on Fuel, If The ONLY Maneuver Necessary ...

Was The Transfer Orbit Injection Burn, No?

:think:bUT tHE pROBLEM tHAT iS uACCOUNTED fOR hERE iS tHAT eNERGY hAS tO bE eXPENDED tO gET tO tHE tOP oF tHE aFOREMENTIONED tOWER. tHAT eNERGY iS eQUIVALENT tO wHAT iS aLREADY eXPENDED iN nORMAL lAUNCH mODE.

cONSERVATION iS gOOD fOR tHE eNVIRONMENT bUT nOT fOR aEROSPACE eNGINEERING.

Neverfly
2007-Oct-19, 10:58 AM
bUT tHE pROBLEM tHAT iS uACCOUNTED fOR hERE iS tHAT eNERGY hAS tO bE eXPENDED tO gET tO tHE tOP oF tHE aFOREMENTIONED tOWER. tHAT eNERGY iS eQUIVALENT tO wHAT iS aLREADY eXPENDED iN nORMAL lAUNCH mODE.

cONSERVATION iS gOOD fOR tHE eNVIRONMENT bUT nOT fOR aEROSPACE eNGINEERING.

I could reccomend a great registry fix for this...:think:

astromark
2007-Oct-19, 11:07 AM
Have you all missed the point that in order to maintain an orbital path a craft must reach that 17,500 mph To reach that velocity in the atmosphere would be troublesome... A great deal extra fuel would be required as air friction would deprive the vehicle of speed and more importantly that same air friction would as a side effect generate a great deal of heat. That could be a problem....

EvilEye
2007-Oct-19, 12:07 PM
No, they aren't flying like an airplane, really. An airplane requires wings, because it stays in their air by using lift from the wings. The space shuttle doesn't. It is like a big firecracker.


I meant directionally... not "flying" in the traditional sense.

John Mendenhall
2007-Oct-19, 12:30 PM
bUT tHE pROBLEM tHAT iS uACCOUNTED fOR hERE iS tHAT eNERGY hAS tO bE eXPENDED tO gET tO tHE tOP oF tHE aFOREMENTIONED tOWER. tHAT eNERGY iS eQUIVALENT tO wHAT iS aLREADY eXPENDED iN nORMAL lAUNCH mODE.

cONSERVATION iS gOOD fOR tHE eNVIRONMENT bUT nOT fOR aEROSPACE eNGINEERING.

M, the quantum tractors from the other thread have run over your keyboard.

John Mendenhall
2007-Oct-19, 01:36 PM
The shuttle is complicated alright... Complicated like a reciprocating steam engine.



True. There was a flurry of interest a few years ago, when it became obvious that the shuttle was not the way to go, in 'big dumb boosters'. We (still) need a way to get large payloads into space at minimum risk and expense.

There was a saying from the days of steam to diesel transition by the railroads: "On a steam engine, it takes 3 minutes to find the problem and three days to fix it. On a diesel it takes 3 days to find the problem and 3 minutes to fix it."

Jerry
2007-Oct-19, 05:45 PM
Also incidentally, the space shuttle does the "roll program" soon after lift-off, so actually it is going into a slightly non-vertical direction right after lifting off.
But it rolls upside down, actually minimizing lift from the wings.


So I think one way of looking at it is like this. Suppose that the shuttle was launched at an angle of 45 degrees. It would have to be supported in that awkward position until the moment of launch, and then would have to generate enough lift to make sure that the engine closest to the ground doesn't actually hit the ground or that the thing doesn't tip over. But if you launch it straight up, then the engines all leave the pad at the same time and so you don't have to worry about hitting anything.

There are three big issues: Air resistance, gravity, and maximum acceleration. Which uses the most energy, an elevator or an escalator? An elevator is much more efficient, especially a high speed elevator, in part because the whole time a body is being lifted, energy is needed to counter the nearly constant force of gravity. The faster a rocket gets to altitude, the more rapidly the gravity force drops off (1/r^2).

Another big factor is atmospheric drag: You cannot move at Mach 6 under 1 atmosphere of pressure: Any material we know would succumb to heat and stress.

Finally the effects of acceleration have to be considered. Carnival rides, the really puky kind, might top out 2g - fighter pilots regularly work to ~4 g and pass out at about 7. The shuttle is designed for whimps ~ 2g, and the acceleration is moderated accordingly. Non-human payload rockets have much higher g ratings - as high as 12.

So in general, rockets accelerate as quickly as the cargo allows while keeping the Mach number low. The higher the rocket, the higher the velocity of the Mach number. For the Shuttle, the Maximum dynamic stress occurs after about ~1 minute, and the thrust (both main engines and solid boosters) is throttled back until the air is thins and the stress drops off.

Larry Jacks
2007-Oct-19, 06:02 PM
The Shuttle's roll program is to put it on the proper azimuth to achieve the desired orbital inclination. To determine the inclination, take the cosine of the launch site latitude and multiply it by the sine of the azimuth, then take the arccosine of that.

Example:
Latitude of the Cape: ~28.5 degrees
Launch Azimuth: 45 degrees
Orbital inclination = arccos(cos(28.5) * sin(45) = ~51.6 degrees.

It's the pitch program that directs the Shuttle (or other boosters) to begin accelerating downrange instead of just going vertical.

publiusr
2007-Oct-19, 08:03 PM
Now there was some talk about having STS fly heads up to gain some advantages, but only Buran got away with doing that IIRC.

John Mendenhall
2007-Oct-19, 08:46 PM
For the Shuttle, the Maximum dynamic stress occurs after about ~1 minute, and the thrust (both main engines and solid boosters) is throttled back until the air is thins and the stress drops off.



How you throttle those solid boosters? We know leaks out the side isn't the way.

Larry Jacks
2007-Oct-19, 09:20 PM
There's no mechanical way to change the thrust of a solid fuel rocket once it's lit. However, you can design the propellant geometry so that thrust isn't constant. The thrust of a solid fuel rocket depends in part on the amount of propellant grain exposed to combustion. It's pretty tricky stuff but there's software available to help with the calculations. You change the thrust of a solid motor by the way you mold the propellant. It's shown briefly here (http://www.energy.kth.se/courses/4A1346/4thLecture/Propellants.pdf).

cjl
2007-Oct-19, 09:22 PM
Finally the effects of acceleration have to be considered. Carnival rides, the really puky kind, might top out 2g - fighter pilots regularly work to ~4 g and pass out at about 7. The shuttle is designed for whimps ~ 2g, and the acceleration is moderated accordingly. Non-human payload rockets have much higher g ratings - as high as 12.

Minor correction here:
Currently, amusement park rides can pull more like 4 sustained, and 5 peak, and the F-22 will pull 10+ gees sustained (and the pilots can manage that too, with special gee suits and training). The shuttle also pulls almost 5g, though the peak acceleration is right before MECO, when it is far lighter after burning off most of the fuel.