Launching space shuttles - not vertical?

[Agony]

Hello everybody,

 

I found this forum while trying to find an answer for a question(and am quite exited about the plethora of knowledge you've got here). I hope I'm posting in the right forum(since launching space shuttles is still largely dependant on newton's physics)

 

I've been watching the launch videos of a few space shuttles on youtube and noticed that all of them go up vertically in the beginning, but after reaching a certain point they will fly at about 45 degrees from what I saw.

 

First I thought it's because shuttles don't leave earth orbit so they need to kick into orbit and start going horizontal a bit early, but then I saw that Apollo 11 did the same although it had to go to the moon.

 

My question is: Wouldn't it be more efficient to go in a straight vertical line and only change course after leaving the atmosphere since earth gravity is much weaker there?

 

I guess they didn't plot the courses this way for no reason, but I simply can't see the reason they'd go horizontally, and I'd be very grateful if any of you would enlighten me on the subject.

(hope I won't be using the smiley when I hear the answer)

[iNow]

Wouldn't it be more efficient to go in a straight vertical line and only change course after leaving the atmosphere since earth gravity is much weaker there?

The shuttle actually does need to tilt to a different angle than "verticle" to ensure proper orbital insertion. Also, you'll notice the shuttle rolls to minimize the stress caused by the atmosphere.

 

Here's an article I found on a quick search, but I'm sure there are better ones available:

 

http://www.aerospaceweb.org/question/spacecraft/q0127a.shtml

...the Shuttle reaches a point about one minute after launch when the pressure force of the atmosphere rushing past the rapidly accelerating rocket reaches a peak. The roll maneuver is performed shortly before max q is reached because this "heads-down" orientation helps alleviate the stresses that the dynamic pressure loads cause on the vehicle's structure.

 

The second factor we need to consider is that for each mission, the Shuttle must launch at a certain azimuth angle in order to be inserted into the correct orbital plane. Since the launch pad (and therefore the Shuttle) sits in a fixed position, the Shuttle must perform a roll maneuver during ascent in order to orient itself to achieve the desired launch azimuth angle.

[swansont]

Another thing about reaching the proper orbit: if you went straight up, how do you shed all the extra radial momentum? You need a tangential velocity, not a radial one, for orbit. To make that change near the orbital altitude will cost you lots of energy, which means you need more fuel, which costs you more fuel at launch.

[insane_alien]

if you go straight up you'll just come straight back down again. if your going to fall and miss the earth(which is what an orbit is) then you need to be going really fast to one side.

 

it is more efficient to start the angental acceleration before you are completey out of the atmosphere so you do not have to apply much thrust to kep yourself up there.

 

the best way i can think of for you to see this is to go get Orbiter ( http://www.orbitersim.com ) this is a free space simulator and includes the shuttle(and then some) try lifting off straight up in any of the realistic craft and then trying to achieve orbit. you won't do it. then try and do what they do in reality and you'll notice that it is almost easy.

[Klaynos]

The Apollo missions went into an orbit around the earth before leaving for the moon, which is why they would have also tilted.

[Agony]

So am I correct to assume that if a space vehicle didn't need to go into orbit it would go in a straight line up if it strong enough to take all the Dynamic Pressure?

[insane_alien]

only if it wanted to waste a whole load of fuel. you can go faster on less fuel by going tangentally(you don't have gravity slowing you down.

 

you don't have to go parrallel to the surface but a good bit of tangental velocity helps.

[iNow]

I don't know if this will or will not help you to visualize it better, but I keep picturing an extremely tall mountain with two roads going to the top. One road is a straight road with no turns, pointing directly toward the top with no curves. It has a very steep slope. The other road is full of twists and curves, and wraps around the mountain like a piece of abstract art. It has a very minimal slope, but still goes upward (just little bits at a time).

 

Now, hop in your truck and head toward the top of the mountain.

 

If you take the straight road, you'd have to push the gas pedal harder and harder as you went up. Your wheels would likely start spinning as gravity pulled you back down. So, you push the gas pedal even harder and burn your fuel more quickly.

 

If you took the curved road, you'd actually travel a greater distance, and it would take a bit longer, but you'd use less energy since the truck doesn't have to work as hard to get progressively higher.

 

Now... if that doesn't work, take the truck out of the equation and picture yourself walking up the mountain. What would be "easier?" Walking straight up, or taking the meadering path?

 

 

Same with the shuttle. Is it possible to go straight up if enough energy went into the system? Absolutely. However, it's a lot easier to soften and spread out the energy being used to break away from Earth's gravity.

[John Cuthber]

I like this explanation "if you go straight up you'll just come straight back down again. if your going to fall and miss the earth(which is what an orbit is) then you need to be going really fast to one side."

Nicely put.

[swansont]

I don't know if this will or will not help you to visualize it better, but I keep picturing an extremely tall mountain with two roads going to the top. One road is a straight road with no turns, pointing directly toward the top with no curves. It has a very steep slope. The other road is full of twists and curves, and wraps around the mountain like a piece of abstract art. It has a very minimal slope, but still goes upward (just little bits at a time).

 

Now, hop in your truck and head toward the top of the mountain.

 

If you take the straight road, you'd have to push the gas pedal harder and harder as you went up. Your wheels would likely start spinning as gravity pulled you back down. So, you push the gas pedal even harder and burn your fuel more quickly.

 

If you took the curved road, you'd actually travel a greater distance, and it would take a bit longer, but you'd use less energy since the truck doesn't have to work as hard to get progressively higher.

 

Now... if that doesn't work, take the truck out of the equation and picture yourself walking up the mountain. What would be "easier?" Walking straight up, or taking the meadering path?

 

 

Same with the shuttle. Is it possible to go straight up if enough energy went into the system? Absolutely. However, it's a lot easier to soften and spread out the energy being used to break away from Earth's gravity.

 

I don't think that's an apt analogy. For starters, it's wrong.

 

The curved path lets you exert less force, and operate at a lower power, but it does not save you any energy, all else being equal. You add mgh in either case. But orbit insertion is not a matter of mechanical advantage; you don't have the normal force present as you do in the case of the truck. You have thrust and you have gravity. If the rocket doesn't have a vertical component of thrust of at least mg, the rocket doesn't take off. The truck can move forward as long as it has a force of [math]mgsin\theta[/math]. A more powerful engine can handle a larger incline.

 

The difference is that, in addition to mgh needing to be added for the rocket, you also want a certain orbital velocity, tangential to the orbit, and no radial velocity; this is what your analogy ignores. Now, you can shut off the rocket before you reach your desired altitude, and coast up, but you still have to get going tangentially, and you can't do that instantaneously. Instead of rotating the craft and doing another burn, even if you could accomplish this during the coasting phase, you just combine the two.

[iNow]

The difference is that, in addition to mgh needing to be added for the rocket, you also want a certain orbital velocity, tangential to the orbit, and no radial velocity; this is what your analogy ignores.

I suppose that's what happens when one tries to oversimplify things. I do appreciate the clarification.

 

 

Spacetime is not some sheet with a bunch of bowling balls on it.