Perhaps start with Jules Verne's idea of a gun to fire you to the Moon as how NOT to do it - this is an example of how they naively thought we would do it in the nineteenth century - by seeing why it doesn't work, can then get into how it is actually done:
Inspecting the projectile
Lowering it into the pit
Firing the giant canon
This may look like a "rocket" to our eyes. But actually in his story, it is a giant bullet. It gets lowered into the muzzle of the gun which was basically a big hole in the ground filled with "fulminating gun cotton" - I think basically a form of nitroglycerine, as gunpowder would take up too much space.
So - that seems natural enough.
But the problem is of course, the huge accelerations. You could send a lump of lead or some such into space from a giant gun like this, but a human would be turned to a pulp.
Jules Verne recognizes this and has shock absorbers in his "bullet" to protect his astronauts - but these in practise wouldn't do much good.
Space guns are not impossible - but you would need a far longer mussel than the one Jules Verne envisaged to have humans inside.
Can get an idea for the design of Startram
It's an idea for a maglev acceleration of humans to orbital velocities. It would launch from 0 to 8 km/ second over at least 1000 kms Startram - for details Maglev Launch: Ultra Low Cost Ultra/High Volume Access to Space for Cargo and Humans
It's a simple application of v² = 2 a s
To get a v of 8 km/sec for distance of 1000 km, that gives acceleration of 8²/1000 - and convert to meters get an acclaration of 64 m/s² per sec. Or about 6.5 g for the star tram. Probably 2000 km would be better for most customers, more like 3.25 g.
If it's a 100 km long "gun" then it's 65 g. For a 1 km gun, to acclerate to 8 km / s then that's 6,500 g.
So you can see that actually Jules Verne's gun would turn the passengers to pulp no matter how good the shock absorbers, no matter what wonderful technology he used, short of a space warp. Even if he made the gun "barrel" several kilometers in length, way beyond the resources of the "gun club" in his story, still, no amount of shock absorbers could save the lives of the astronauts.
So - some day we may be able to build a 1000 km long "gun" like this. Also are other ways could make it easier to get into space such as the orbital airships, space elevator, air breathing space planes, and single stage to orbit rockets.
But meanwhile - well we have to use rockets, which slowly accelerate into space over a similar distance.
It's like, when you turn on a garden hose, you may feel it suddenly pushes back against your hand. Or the reaction when you fire a gun. Like firing loads of bullets one after another into the ground, if you could do it fast enough, with a super fast high velocity machine gun and you had lots of bullets, you could, maybe, get so much recoil it sends you up into the air.
So - that's how all rockets get into space nowadays. It seems a crazy idea at first, no wonder Jules Verne didn't think of it.
The problem then is that you have to take all your fuel with you, at least - until we get the ability to resupply our rockets in flight using e.g. laser beams, or air breathing rockets like Skylon.
And then - the big problem is - that you have to lift, not just your rocket, but all the fuel also.
So - normally done as three stages. So first stage is a huge rocket that lifts second and third stages into orbit. Second stage is smaller - and third stage is even smaller, and then spacecraft itself separates.
Then to get to the Moon that final spacecraft also has to separate into the lunar module which goes down to the moon - and that again separates into the platform that lands there, and the part of it that stays in orbit (and rendezvous with the part of the landing stage that goes back into orbit again).
At each stage the idea is - that whenever anything is done with - immediately discard it. Because is a huge fuel penalty to continue to carry it with you when you no longer need it.
And nearly all of the fuel is used to transport more fuel + rocket engines into space. Only a tiny percent is put into actually accelerating the spacecraft itself.
Another alternative is the direct ascent, a big rocket launched from Earth, descends to the Moon with all three astronauts on board, eventually returns to Earth leaving part of it behind on the Moon, again only the command module returns. This would need more fuel and an even bigger rocket.
So you end up with this huge skyscraper of a rocket which is nearly all fuel used to launch more fuel into orbit. And just about all of what you see here, rocket, fuel and all, is discarded in the first few minutes of the mission.
That's a video of the launch of Apollo 11 to the Moon. All that, just to send a tiny craft not much bigger than a couple of telephone boxes interior volume, with three people, to the Moon.
It's 363 feet high (121 meters), same height as a 36 story skyscraper. Details: NASA's Mighty Saturn V Moon Rocket Explained (Infographic)
So is hugely inefficient. To launch an entire 36 story high building to get a tiny spaceship into orbit. And also expensive because these are all very expensive parts that need to get discarded at each stage.
When you get back to Earth you just have the descent capsule left of all that fuel, and hardware and even the descent capsule is not re-used. The entire rocket is gone and you need to build a new one.
That's why there is so much focus on need to improve re-usability in space.
So Space X want to be able to recover their very expensive first ascent stage and use it again.
But it's not just the hardware, though that will help. It's the fuel also.
You can reduce the amount of fuel needed hugely if you fire it out at a higher speed. But the only way we know to do that is with an ion thruster.
An ion thruster can use about a tenth of the total mass of fuel, perfect. But, so far, ion thrusters only work at very low thrusts. If we had an ion thruster able to propel tons of fuel a second, problem would be solved. But nobody knows how to do that.
Another idea is to just not take the fuel with you.
If you can continually refuel your spacecraft in flight, then that is a huge saving.
One way is to make it air breathing. You can use the air as reaction mass right up to the stratosphere. Problem is that the air gets very hot as it enters the rocket, so you have to do something about all that heat. And has to work at far faster than the speed of sound, which is tricky.
Anyway, that's, sort of, the approach used by Virgin Galactica, to send an aircraft up part of the way. Other ideas include
Artist's concept of it taking off into orbit
Lightcraft
It might, who knows, become the standard way to get into space some time in the future, but is a long way from achieving that potential right now.
A related idea is a mixed laser or microwave system supplying energy, and fuel on the rocket. See Laser Propulsion Could Beam Rockets into Space, and Jordin Kare's talks to the Space Show.
Other ideas include building a platform in the upper atmosphere and getting to it via airships, and continuing up using special huge airships that can't withstand the turbulent conditions of the lower atmosphere but can soar all the way to orbit, using ion thrusters in the upper atmosphere, gradually faster and faster over several days.
For this and many other ideas, see Projects To Get To Space As Easily As We Cross Oceans - A Million Flights A Year Perhaps - Will We Be Ready?
This may look like a "rocket" to our eyes. But actually in his story, it is a giant bullet. It gets lowered into the muzzle of the gun which was basically a big hole in the ground filled with "fulminating gun cotton" - I think basically a form of nitroglycerine, as gunpowder would take up too much space.
"Nothing is more easy than to reduce this mass to one quarter of its bulk. You know that curious cellular matter which constitutes the elementary tissues of vegetable? This substance is found quite pure in many bodies, especially in cotton, which is nothing more than the down of the seeds of the cotton plant. Now cotton, combined with cold nitric acid, become transformed into a substance eminently insoluble, combustible, and explosive. It was first discovered in 1832, by Braconnot, a French chemist, who called it xyloidine. In 1838 another Frenchman, Pelouze, investigated its different properties, and finally, in 1846, Schonbein, professor of chemistry at Bale, proposed its employment for purposes of war. This powder, now called pyroxyle, or fulminating cotton, is prepared with great facility by simply plunging cotton for fifteen minutes in nitric acid, then washing it in water, then drying it, and it is ready for use.""
THE QUESTION OF THE POWDERS
So - that seems natural enough.
But the problem is of course, the huge accelerations. You could send a lump of lead or some such into space from a giant gun like this, but a human would be turned to a pulp.
Jules Verne recognizes this and has shock absorbers in his "bullet" to protect his astronauts - but these in practise wouldn't do much good.
Space guns are not impossible - but you would need a far longer mussel than the one Jules Verne envisaged to have humans inside.
Can get an idea for the design of Startram
It's an idea for a maglev acceleration of humans to orbital velocities. It would launch from 0 to 8 km/ second over at least 1000 kms Startram - for details Maglev Launch: Ultra Low Cost Ultra/High Volume Access to Space for Cargo and Humans
It's a simple application of v² = 2 a s
To get a v of 8 km/sec for distance of 1000 km, that gives acceleration of 8²/1000 - and convert to meters get an acclaration of 64 m/s² per sec. Or about 6.5 g for the star tram. Probably 2000 km would be better for most customers, more like 3.25 g.
If it's a 100 km long "gun" then it's 65 g. For a 1 km gun, to acclerate to 8 km / s then that's 6,500 g.
So you can see that actually Jules Verne's gun would turn the passengers to pulp no matter how good the shock absorbers, no matter what wonderful technology he used, short of a space warp. Even if he made the gun "barrel" several kilometers in length, way beyond the resources of the "gun club" in his story, still, no amount of shock absorbers could save the lives of the astronauts.
So - some day we may be able to build a 1000 km long "gun" like this. Also are other ways could make it easier to get into space such as the orbital airships, space elevator, air breathing space planes, and single stage to orbit rockets.
USING ROCKETS
But meanwhile - well we have to use rockets, which slowly accelerate into space over a similar distance.
It's like, when you turn on a garden hose, you may feel it suddenly pushes back against your hand. Or the reaction when you fire a gun. Like firing loads of bullets one after another into the ground, if you could do it fast enough, with a super fast high velocity machine gun and you had lots of bullets, you could, maybe, get so much recoil it sends you up into the air.
So - that's how all rockets get into space nowadays. It seems a crazy idea at first, no wonder Jules Verne didn't think of it.
The problem then is that you have to take all your fuel with you, at least - until we get the ability to resupply our rockets in flight using e.g. laser beams, or air breathing rockets like Skylon.
And then - the big problem is - that you have to lift, not just your rocket, but all the fuel also.
So - normally done as three stages. So first stage is a huge rocket that lifts second and third stages into orbit. Second stage is smaller - and third stage is even smaller, and then spacecraft itself separates.
Then to get to the Moon that final spacecraft also has to separate into the lunar module which goes down to the moon - and that again separates into the platform that lands there, and the part of it that stays in orbit (and rendezvous with the part of the landing stage that goes back into orbit again).
At each stage the idea is - that whenever anything is done with - immediately discard it. Because is a huge fuel penalty to continue to carry it with you when you no longer need it.
And nearly all of the fuel is used to transport more fuel + rocket engines into space. Only a tiny percent is put into actually accelerating the spacecraft itself.
Another alternative is the direct ascent, a big rocket launched from Earth, descends to the Moon with all three astronauts on board, eventually returns to Earth leaving part of it behind on the Moon, again only the command module returns. This would need more fuel and an even bigger rocket.
"This early illustration shows a concept for Apollo which would have employed either the direct ascent or Earth orbital rendezvous mode of operation. Shown here is the all-up configuration which allowed three astronauts to travel to the surface of the Moon for up to a week's stay and return using a single spacecraft. Note the towering height of the vehicle, its return upper stage and the now familiar command module which the crew would have used for their return to Earth once the upper return stage vehicle blasted off from the lunar surface. (Photo courtesy NASA.)" chapter 14 of "Before this decade is out" online book.
So you end up with this huge skyscraper of a rocket which is nearly all fuel used to launch more fuel into orbit. And just about all of what you see here, rocket, fuel and all, is discarded in the first few minutes of the mission.
That's a video of the launch of Apollo 11 to the Moon. All that, just to send a tiny craft not much bigger than a couple of telephone boxes interior volume, with three people, to the Moon.
It's 363 feet high (121 meters), same height as a 36 story skyscraper. Details: NASA's Mighty Saturn V Moon Rocket Explained (Infographic)
So is hugely inefficient. To launch an entire 36 story high building to get a tiny spaceship into orbit. And also expensive because these are all very expensive parts that need to get discarded at each stage.
When you get back to Earth you just have the descent capsule left of all that fuel, and hardware and even the descent capsule is not re-used. The entire rocket is gone and you need to build a new one.
RE-USABILITY AND WAYS TO USE LESS FUEL
That's why there is so much focus on need to improve re-usability in space.
So Space X want to be able to recover their very expensive first ascent stage and use it again.
But it's not just the hardware, though that will help. It's the fuel also.
You can reduce the amount of fuel needed hugely if you fire it out at a higher speed. But the only way we know to do that is with an ion thruster.
An ion thruster can use about a tenth of the total mass of fuel, perfect. But, so far, ion thrusters only work at very low thrusts. If we had an ion thruster able to propel tons of fuel a second, problem would be solved. But nobody knows how to do that.
Another idea is to just not take the fuel with you.
If you can continually refuel your spacecraft in flight, then that is a huge saving.
One way is to make it air breathing. You can use the air as reaction mass right up to the stratosphere. Problem is that the air gets very hot as it enters the rocket, so you have to do something about all that heat. And has to work at far faster than the speed of sound, which is tricky.
Anyway, that's, sort of, the approach used by Virgin Galactica, to send an aircraft up part of the way. Other ideas include
Skylon, a jet that can fly directly to orbit. It is air breathing in the atmosphere and only switches to rocket propulsion once out of the atmosphere - remember with Apollo 11 just about all the fuel is gone by then - so this is a huge saving. It would launch from an ordinary runway - like an airplane - the runway needs to be strengthened but is otherwise normal. And it doesn't need booster rockets at all, it carries all its fuel on board.
Artist's concept of it taking off into orbit
FLYING TO ORBIT ON A BEAM OF LIGHT
This is a neat idea, but so far has only been tried in small scale demos, to raise models a hundred feet or so on laser beamsLightcraft
It might, who knows, become the standard way to get into space some time in the future, but is a long way from achieving that potential right now.
A related idea is a mixed laser or microwave system supplying energy, and fuel on the rocket. See Laser Propulsion Could Beam Rockets into Space, and Jordin Kare's talks to the Space Show.
Other ideas include building a platform in the upper atmosphere and getting to it via airships, and continuing up using special huge airships that can't withstand the turbulent conditions of the lower atmosphere but can soar all the way to orbit, using ion thrusters in the upper atmosphere, gradually faster and faster over several days.
For this and many other ideas, see Projects To Get To Space As Easily As We Cross Oceans - A Million Flights A Year Perhaps - Will We Be Ready?
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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