Untraditional Space Travel

  • #1
Summary:
Trying to understand the factors of a launch concept
If an infinite amount of energy were available to create the lift mechanism for a space launch. What would be required to fire a 200lb object into low earth orbit(160km) after speeding it up in a way similar to how the large hadron collider speeds up a particle.

Assuming the launch vehicle would:
A. Use technology x to protect its cargo from the effects of the G-force's it would be exposed to
B. Have a drag coefficient of 0.04
C. Have no additional propulsion after launch
D. Launch at sea level

The first questions I am looking to understand include:
1. Trajectory wise, is it more efficient to launch the object perpendicular to the earth's surface like a rocket or at an angle like a ramp?
2. what is the minimum speed the object needs to be going when it leaves the earths surface to reach low earth orbit unassisted?
 

Answers and Replies

  • #2
Halc
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Any trajectory you put it in will come from the atmosphere. If it isn't moving at escape velocity at the time it exits the atmosphere, it will come back and go through re-entry regardless of trajectory. It cannot reach LEO unassisted.
 
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  • #3
pbuk
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This is called a space gun. Without additional propulsion to correct the course the object will either fall back to Earth or keep going for ever.
 
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  • #4
Baluncore
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Passing from the Earth's surface through the atmosphere will be difficult. If the velocity is sufficient to escape to LOE, then the object will be destroyed by the high temperatures normally only seen during re-entry.

A rocket launch to LEO does not accelerate to escape velocity until it is above most of the atmosphere. “Go with throttles up” signifies that point where it is safe to accelerate.
 
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  • #5
sophiecentaur
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Summary:: Trying to understand the factors of a launch concept

If an infinite amount of energy were available to create the lift mechanism for a space launch.
Seriously not the best way to start thinking about a launch system. We don't have any energy (money) to spare for that sort of exercise. The same basic method has been used for launches since the fifties - with good reason. It's already been pointed out that escaping without an extra manoeuvre just doesn't work.
The term "escape velocity" is only a convenient number for comparing the situations on different planets.
Also, it's fair to say that we have never had enough fuel and a big enough rocket system to 'escape' the solar system; we have always needed to use slingshot orbits to help us get anywhere interesting beyond our nearest neighbours.
 
  • #6
DaveC426913
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If an infinite amount of energy were available to create the lift mechanism for a space launch.
Seriously not the best way to start thinking about a launch system. We don't have any energy (money) to spare for that sort of exercise.
Is it possible, OotB, that this is part of a story you're developing? (There's a forum for that.)
 
  • #7
sophiecentaur
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Is it possible, OotB, that this is part of a story you're developing? (There's a forum for that.)
Jules Verne was there first, I believe.
 
  • #8
Thank you all I am now reading more into the "Space Gun" concept.

Continuing on from the original concept, are there discussions or concepts being developed related to how an infinite energy source could be used to reduce the amount of fuel required to reach escape velocity?
 
  • #9
PeroK
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Thank you all I am now reading more into the "Space Gun" concept.

Continuing on from the original concept, are there discussions or concepts being developed related to how an infinite energy source could be used to reduce the amount of fuel required to reach escape velocity?
I believe that infinite energy sources tend to be quite fuel inefficient.
 
  • #10
hutchphd
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I believe that infinite energy sources tend to be quite fuel inefficient.
How would you know? The gauge would always read ∞
 
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  • #11
Would the best use of that infinite energy be to use it to produce hydrogen fuel and use the launch methods already derived?
 
  • #12
Halc
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Infinite energy would entail infinite mass, which would prevent anything from getting into orbit at all.
Perhaps you mean just free energy, in which case you'd have to work out exactly what isn't free and find a solution that makes the most efficient use of those more limited resources.
 
  • #13
phinds
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Would the best use of that infinite energy be to use it to produce hydrogen fuel and use the launch methods already derived?
You really need to drop the concept of "infinite" energy since it doesn't exist. If you mean "however much energy is required to do ... " then say THAT, not "infinite" energy. This is a science forum and words have meaning.
 
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  • #14
DaveC426913
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are there discussions or concepts being developed related to how an infinite energy source could be used to reduce the amount of fuel required to reach escape velocity?

You are asking "If we had unlimited energy, could it be used to reduce the amount of energy required?"

Sortta like:
"My house is powered by the flow of water over Niagara Falls. Could I utilize more energy from Niagara Falls to reduce the energy that it takes Niagara Falls to power my house?"
 
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  • #15
I should not use the word energy or infinite energy it is just how it is referred to in some papers I am reading. Perhaps the correct word would be power. i.e. electrical current.

Meaning an infinite store of electrical current, such that could result from breakthroughs in fusion.

Would this be the correct reference?
 
  • #16
berkeman
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No. Please stop using the word "infinite" and we're good. :smile:
 
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  • #17
Baluncore
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The most efficient way to rise through the atmosphere is vertically, but then the least energy to enter orbit is to accelerate towards the east above the equator, taking advantage of Earth's rotation. On reaching an altitude above most of the atmosphere, say 10 km, you must find a way to convert a vertical velocity of mach 2 into an eastward mach 20. That will require energy be stored in some other convertible form. If you started on the surface with mach 40, you might have 20 left after passage through the lower atmosphere. But most of the object would have been vaporised like a meteorite in the process.

Alternatively you must revise your constraints.

The “all velocity up-front” technique you are suggesting might work from the moon where there is no atmosphere, but it is not possible from the Earth. On the Moon, a solar-powered linear-motor track could accelerate the mass, but the orbit it would enter would be an ellipse that returns to the launch track, unless there was some thrust control to convert the elliptical orbit into a more circular lunar orbit.
 
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  • #18
sophiecentaur
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OK, here's any alternative approach to the OP question. What if we had ridiculous amounts of energy available and we could use it to get things into orbit in not so much a very efficient or quick way but in a way that was convenient / a nice experience / very safe. It could involve a vast capital project (affordable, for the first time in our history)?
All that energy would probably make a space elevator feasible. That ticks all the boxes. So take-off would take several (tens of?) hours to achieve but it could involve some luxurious lifestyle whilst you are aboard the trip. Vast space ships (starships?) could be assembled up there for long distance journeys, taking generations.
SciFi material, too.
 
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  • #19
jbriggs444
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You could always use your infinite energy to compress the Earth's atmosphere into some massive underground holding tanks that you excavated using your infinite energy and then lined with steel smelted with your infinite energy.

Then use your space-gun to launch as many craft as you like without worrying about air resistance.
 
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  • #20
DaveC426913
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I should not use the word energy or infinite energy it is just how it is referred to in some papers I am reading.
This is a red flag. It makes me want to tell you you should stop reading those papers. They are probably doing you more harm than good.

Perhaps the correct word would be power. i.e. electrical current.
It doesn't matter. Energy/fuel or whatever. We assume they can be converted without needing details.

Meaning an infinite store of electrical current, such that could result from breakthroughs in fusion.
At least restrain yourself to the term 'unlimited'? :wink:


But I still don't see what your question is.

Look. given an unlimited supply of energy, you don't need to think about launch methods. It's moot.
For all you care, you can just have your space cruiser (not rocket) lift straight off its wheels from the spaceport tarmack - horizontal, and
rising at a leisurely 100ft a minute (for sight-seers) - all the way to space.

Furthermore, since you have unlimited energy,
there is no reason to power up to orbital velocity at all.

(The only reason to reach orbital velocity is so you can shut off your engines and not die in a fireball. And that's only because - with our current technology - we have a very limited supply of energy in our vehicles and must reach orbit before it runs out.)

With unlimited energy, you don't care one wit about orbital velocity. You could, at your leisure, make a circumnavigation of the Earth at
a scenic 1,000 miles per hour (to follow the sunrise perhaps) and then just turn and head for the Moon at the same leisurely 1,000 miles per hour, giving your tourists a two week cruise.

Unlimited energy renders virtually all aspects of orbital mechanics moot. And that includes re-entry - you could come down as slow as you like.
At a gentle 300 miles per hour, there's no re-entry fireball.

Unlimited energy changes everything.
 
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  • #21
Baluncore
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Unlimited energy changes everything.
Except the OP constraints; C and D; that required all the energy be invested before departure from the surface below the atmosphere.
Assuming the launch vehicle would:
A. Use technology x to protect its cargo from the effects of the G-force's it would be exposed to
B. Have a drag coefficient of 0.04
C. Have no additional propulsion after launch
D. Launch at sea level
 
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  • #22
DaveC426913
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Except the OP constraints; C and D; that required all the energy be invested before departure from the surface below the atmosphere.
Right. Well.

You're either headed for deep space real soon, or you're headed for some litho-braking real soon.
 
  • #23
jrmichler
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Summary:: Trying to understand the factors of a launch concept

If an infinite amount of energy were available to create the lift mechanism for a space launch. What would be required to fire a 200lb object into low earth orbit(160km) after speeding it up in a way similar to how the large hadron collider speeds up a particle.

Assuming the launch vehicle would:
A. Use technology x to protect its cargo from the effects of the G-force's it would be exposed to
B. Have a drag coefficient of 0.04
C. Have no additional propulsion after launch
D. Launch at sea level
It is not out of the box thinking until you do some basic calculations. Fortunately, the calculations are simple enough that only high school physics is needed.

1) Forget your assumption #1. That's science fiction.

2) Change infinite energy to as much power as needed, as discussed above.

3) If you want to accelerate in a circle, then assume a diameter, and calculate the centrifugal acceleration and force at standard escape velocity. How strong does your object need to be? It needs to withstand centrifugal forces while spinning up. You may want to try different diameters. Assume an angular acceleration, and calculate the tangential acceleration and peak power.

4) Calculate the necessary initial velocity including the effects of aerodynamic drag. Use your Cd, assume a frontal area, assume a standard atmosphere, and calculate the aerodynamic drag. This will be a numerical simulation because the aerodynamic drag decreases with increasing altitude. Iterate the initial velocity until it reaches orbit. Now go back and repeat the calculations in Step 3 at the higher velocity. It needs to withstand centrifugal forces while spinning up, and aerodynamic forces after release. How strong does the object need to be? Bonus points if you search hypersonic drag coefficients, and add the effect of velocity on drag to the simulation.
 
  • #24
Baluncore
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1) Forget your assumption #1. That's science fiction.
Technology X is science, but not necessarily fiction.
Remove air or gas by saturating the cargo, and filling the area around the cargo, with a neutral density fluid. The cargo will then be subjected to 3D hydrostatic pressure rather than to 1D acceleration forces.
 
  • #25
sophiecentaur
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Unlimited energy renders virtually all aspects of orbital mechanics moot. And that includes re-entry - you could come down as slow as you like. At a gentle 300 miles per hour, there's no re-entry fireball.
I suggested long-glide re-entry, as opposed to the present system, some while ago. It was jumped on pretty quick by PF! The orbital energy has to be dissipated, one way or another and doing it slowly means that the insides will get too hot and fry the passengers. The fireball / ablative braking system gives a short slow down time and then cools the craft in air before the internal temperature gets too high. It's a race against time to save passenger fry-up, apparently.
Active re-entry systems would avoid the friction problem and use a lot of fuel but that could be taken care of by our unlimited fuel, I guess.
 

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