Science New Space Propulsion, using modern science.

[Frag]

Hey guys,

its a bit of a mission to read, but maybe the idea is worth the effort:

Rockets are great for getting us off the earth, lots and lots of thrust... but they use up HUGE amounts of fuel and fire for only a few minutes.

A star drive needs to be able to create large amounts of thrust, for little fuel, and then be able to slow down again once they reach another star.

I think I've solved the fuel problem.

The problem is once you use the fuel in the rocket, it all comes out of the back... the gas escaping causes forwards thrust. In space the gas just goes backwards forever, and the ship goes forwards. Once the gas is used, it's worthless, it just expands into the vacuum. but what if you could reuse the gas that youve already thrown out the back? You'd need less fuel.

But the question is, how do you capture the fuel again?

Every action has an equal and opposite reaction, capturing the gas going backwards would slow down the forwards momentum of the spaceship.

The solution? ... Dont capture it.

Use it to propell a second ship, in the OPPOSITE direction.

Once the fuel has been captured by the other ship, it will impart its backwards momentum (backwards from the point of view of the first ship) to the second ship, which happens to be the direction that the 2nd ship is travelling anyway. the fuel can then be reused by the 2nd ship to fire it back towards the first ship... in turn increasing its own forwards velocity. The reused fuel is then captured by the 1st ship, again increasing its own momentum, only to be reused by firing back towards the second ship. Rinse and repeat this process.

Replace gas from rockets with ball bearings fired from rail guns (to stop the gas dispersing in the vacuum) and you got yourself a star drive. Railguns, coil guns, cannons. Fuel, ball bearings, chickens. Anything, as long as its solid. A mass going backwards should propell the thing firing it forwards.

Now for the problems with this design. Each time the fuel is propelled backwards, it has further to go than the time before. It needs to reach the second ship, be somehow captured, and then fired back for the return journey. All the while both ships will be increasing their distance from one another. This will result in a drastic reduction in the amount of thrust delivered over time... it will steadily get weaker and weaker as fuel has to travel further and further. What may of started as a torrent will soon be down to a trickle. While the fuel would be effectively unlimited, the amount of thrust may not be sufficient to be utilised in a useful time frame.

The solution? Make first ship manned, and the second ship automated. Once the second ship is out of usable range, have it fire its fuel back towards the first ship and then leave it to make its own way through interstellar space. Abandoned, but not forgotten, it could carry useful scientific instruments and send data back to earth/the 1st ship.

Meanwhile, the first ship launches a THIRD ship and repeats the above process. It uses the fuel/ball bearings/chickens to accelerate forwards and at the same time send the third ship backwards, or in another direction, as long as the thrust from the third and any subsequent ships results in a net forwards motion.

In essense, make the 2nd and 3rd ships probes and the first a mother ship. Use the same fuel from the first ship to propell the probes to explore nearby stars while at the same time sending a manned colony ship or something similar to a star in the opposite direction. When it comes to slowing the mothership down again, repeat the probe process, but in the opposite direction.

Now all of the above will increase the mass of the first ship by a huge margin. But we can imagine that most of the mass to start off with will be fuel anyway and this fuel will be continuously reused. Constantly transfered between the mothership and her flotilla of probes heading in a cone behind her. I like to call it the Wilding Drive (Wilding being my name, vanity is one of my many flaws).

Am I on to a winner? Or are there physics at play here that I've totally overlooked? Is the mass of the launched probes going to cause problems with the mathematics involved? All comments/criticisms/cheques welcome. All I ask is you give me credit for the idea if it turns out to be useful and no-ones thought of it before.

Regards,

 

[Urwumpe]

I think you have totally ignored physics there, but it is too late to explain basic Newtonian mechanics to you there, so I leave this to others with less requirements for sleep.

 

[Frag]

Fair enough, t'was a request for comments after all. So what's the show stopper?

 

[Turbinator]

For atmospheric operations the most efficient engine design that we have the capability and technology to build today is the Aerospike Engine. Both the linear and the annular variety. A vehicle with an aerospike engine uses 25–30% less fuel at low altitudes, where most missions have the greatest need for thrust. That is at today's level of efficiency.

Twin Linear Aerospike XRS-2200 Engine

NASA's Toroidal aerospike nozzle

Good read on Attitude Control using the XRS-2200 Linear Aerospike Engine:
http://www.pwrengineering.com/datar...trolUsingTheXRS-2200LinearAerospikeEngine.pdf


---


Now for space operations the most efficient design we are capable of creating with our present level of technology is the Magnetoplasmadynamic Thruster. In theory, MPD thrusters could produce extremely high specific impulses (Isp) with an exhaust velocity of up to and beyond 110,000 m/s, triple the value of current xenon-based ion thrusters, and about 20 times better than liquid rockets. This would allow use of electric propulsion on missions which require quick delta-v maneuvers (such as capturing into orbit around another planet), but with many times greater fuel efficiency.

Magnetoplasmadynamic Thruster

Magnetoplasmadynamic Thruster Firing

 

[Frag]

A most welcome post, very interesting. However, perhaps the thread title was somewhat misleading. My apologies.

I meant the idea as a proposal using modern scientific theory, as opposed to technology. I meant using things like propellant, chemical/fission energy and celestial mechanics as opposed to space time distortion, worm hole generation or FTL travel.

I was aiming for something simple, not hugely beyond our near-term (50 years or so) technical reach and potentially viable for a manned mission to another star. More a thought experiment as opposed to a valid patented design!

I admit, my grasp of physics is... shaky. Can someone point out to an enthusiastic amateur if/why the idea isn't going to work?

 

[RisingFury]

You overlooked something.

If the rocket's exhaust travels backwards at 1000 m/s relative to the rocket... and the rocket is traveling forward at 2000 m/s, then the exhaust still travels forward at 1000 m/s. That means that as soon as your ship starts traveling faster then the exhaust velocity, you won't be able to recover your fuel.

With gas it could work up to a significant fraction of speed of light, but even with best railguns you're only looking at a few ~10 km/s.

 

[N_Molson]

I think I've solved the fuel problem.

I'm very happy of that, I hope you've called NASA ?

Edit : or Roskosmos, or ESA...

Just curious, with what are you going to power those railguns, and where are you going to store the "ammo" ?

There are some similarities with the Project Orion.

Constantly transfered between the mothership and her flotilla of probes heading in a cone behind her.

A delightful vision.

 

[Frag]

Hi rising fury, all input is hugely welcomed. I'm just throwing idea's about.

I think i might have already taken that into your point into account. The launching of multiple drones... As each drone is launched it starts in the same rest frame as the mothership, giving you that boost of a few km/s each time one is launched. The main ship may be travelling forwards at 20km/s, but so will the next vessel/probe/engine or what have you.

Refine the technology (or use something else as you quite rightly point out) to get a few 1000's km/s per launch and it might be getting up to the specific impulse of ion drives, if not more. Combine that with the huge amount of thrust that would be inherent to the system... I'm not talking perpetual motion here, just something that might be better then what we have on the board at the moment

---------- Post added at 11:55 PM ---------- Previous post was at 11:53 PM ----------

lol @ M_Nolson, im sure nasa would probably shoot me on the spot for being a heretic / too stupid to carry on living.

 

[boby_nadeau]

If I understand your "propulsion system" is a kind of newtonian ping pong game ? Each time you "tap" (hit) the ball you get away from your opponant (the other spacecraft), isn't it ?

 

[Frag]

yeah that pretty much sums it up

---------- Post added at 12:36 AM ---------- Previous post was at 12:30 AM ----------

ok, hows this... replace railguns with a bussard ramjet design. Have ship A fire all of its propellent at ship B, wait until the propellant reaches B, then fire it back at A... no crossed streams, no having to rely on the interstellar medium. Thoughts?

 

[RisingFury]

The system wouldn't have such a high average thrust...
Also, even if you took care of the technology, you'd still be left with a few nasty problems.

Thrust and fuel load aren't the main problem with rockets. It's actually the power they can generate.

You can get a huge thrust by expelling a lot of mass at low speeds or a bit of mass at high speeds.

F = O * v, where O is the mass flow O = dm / dt and v exhaust velocity.

But to expel that mass, you need this much power output:

P = 1/2 * O * v^2

So to expel a lot of projectiles very quickly, you'd need a lot of power. Which brings us to my point: Power generation is the limiting factor, not the fuel. Various current designs can be scaled up to very high thrust, if only we could generate the power to propel the fuel.


Your idea might not be more efficient, even at same power level. If you're tagging along extra robots then what's preventing you from just using that mass as propellant? There's also the problem of aiming and capturing the projectiles. Stopping a large bullet traveling very fast is also a problem...

 

[Keatah]

There's a horizontal vibratory component of the gas' momentum that needs to be contained. Otherwise, the ping-ponging squishes the gas out the "sides" of the imaginary cylinder.

 

[Tommy]

First, this would only work for a VERY short distance between ships. Once there is any significant distance you'll never get the gas/ball bearings, etc to go from one vessel to another. The reaction mass (gas or solid) will be affected by gravity (even during interstellar flight there are gravity fields), subject to normal laws of Orbital mechanics, and since it's traveling at different velocities than either vessel it will follow a different trajectory - and you won't be able to "catch" the mass since it never gets anywhere near the other vessel.

The launching of multiple drones... As each drone is launched it starts in the same rest frame as the mothership, giving you that boost of a few km/s each time one is launched. The main ship may be travelling forwards at 20km/s, but so will the next vessel/probe/engine or what have you.

This would actually cost you efficiency. First, you are accelerating all the drones, which increases the mass of the vessel. When you launch the second/third/etc drone you are, in effect, using it as reaction mass, so it has the same effect as an extremely low ISP engine. You would get more dV by using the same mass (as the drone) in regular high ISP fuel and conventional rocket engines.

 

[jedidia]

Fair enough, t'was a request for comments after all. So what's the show stopper?

First, you'd basically be driving that other ship by firing a particle cannon at it. It is tough to use without getting grilled on short distances, and totally inefficient at long distances.

Also, the situation in which you need to propell two vessels in exactly opposite directions at the same time wouldn't occur too often, if at all.

 

[Sar]

I think you didn't need to have a huge load of ammunition since you're collecting the kinetic energy of the ammunition making it stop at the other end, meaning you could just shoot the same one back n+1 times.

An issue being that you'd need to have the ships going in opposite directions in a straight line, as far as I can think of straight lines are somewhat uncommon what comes to orbital mechanics, let alone to get the both ships to have a reasonably intresting targets.

+the thing where you'd need to increase the velocity of what ever you're shooting each time you shoot it

If Nasa worked anything like codemasters It'd be ready to release.

 

[SandroSalgueiro]

This is what I think: you're forgetting about the whole process in which you propel this mass backwards. Either a catapult or a rocket engine - or anything - would waste energy to make such object start moving in the opposite direction every time it reaches the spacecraft. Here's an analogy: in your hypothetical example, you used a rail gun. A rail gun would have some kind of detonation system to impulse -and shoot- the bullet out. In the same way, the spacecraft would need to have some kind of impulse system, bringing us back to the prime problem.

I like how you developed your ideas out of pure creativity though - don't feel hindered to keep on thinking real -and crazy- things. Good luck!

 

[Frag]

Thanks sandrow. Im certainly not trained in any of this stuff, just crazy idea's over flowing from my brains!

How about photon pressure and tight beam lasers/mirrors as opposed to propellent?

 

[SandroSalgueiro]

I'm not quite familiar with the photon pressure concept, but wouldn't you end up not harnessing its energy if you reflect it?

 

[boby_nadeau]

yeah that pretty much sums it up

---------- Post added at 12:36 AM ---------- Previous post was at 12:30 AM ----------

ok, hows this... replace railguns with a bussard ramjet design. Have ship A fire all of its propellent at ship B, wait until the propellant reaches B, then fire it back at A... no crossed streams, no having to rely on the interstellar medium. Thoughts?

So what if your ball's trajectory get "curve" ("deviation"... don't know the word in english) from a gravitationnal field ? Further is your "two opponents (Spaceships), bigger is your margin of error to get the other ship, isn't it ?

 

[n0mad23]

You can do something like this with a network of tether-slings, but it's a closed system and not useful for the exploration you're looking for.

A tether-sling in Earth orbit can throw things to a tether-sling in Lunar orbit. When the first tether-sling tosses the payload it loses energy in the process and consequently its orbit drops. But a payload coming from the Moon and being caught by the tether-sling will "re-energize" by said capture, as the energy from the payload is transfered into the system.

This is the only system I can think of where energy is ping-ponged back and forth.