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Some of my ideas

Posted by: Psiberzerker - Wed Jan 11, 2012 11:42 pm
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Some of my ideas 
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Post Some of my ideas   Posted on: Wed Jan 11, 2012 11:42 pm
High, I'm Psiberzeker, and I'm a science fiction writer, among other things. I thought by way of introduction, I'd swing this concept by you guys to see what you thought. It's my ideas for N-Prize to build a cheap micro-sattelite launcher, which I won't be able to get funded in time.

The basic concept is not all that new, and seems to have been proposed in that competition, but with slight adjustments that could hopefully make it work. The idea is to use a lighter than air ballon to carry the transatmospheric booster to launch altitude, but I was thinking the envelope it'self could contain Hydrogen, as a fuel for the second stage burn. Therefore, it would carry it's weight in both stages, though there are some forseeable problems.

First, the canopy wouldn't be rigid like a tank, so under thrust, it would deform, possibly to be heated by the exhaist, and rupture to oxydise uselessly in the high atmosphere. I wasn't planning to oxydize it at all, but ionize it in a plasma-jet so I don't have to carry two propellants. (A heavy oxydizer tank would rapidly ballast out the balloon's volume)

It may be possible to use Helium, which would be preferable, as it's inert, but has the nasty habit of not staying in the container no matter how tight you thought you made it. It's also relatively rare, at least around here, especially compared to hydrogen. (The most abundant element in the universe with a lot of available sources, from hydrocarbons to the solar wind.)

About the only way I could come up with to solve the first problem is to make the engine (A linear partical accellerator with coaxial Cathode to neutralize it) the axis of a spherical balloon, hanging too far down for the ballon to distend even empty. I've run some calculations, and I should be able to expend enough to compensate for pressure so it won't burst as it gains altitude, but forcing every last molecule of hydrogen (or atom of helium) into the partical engine would be tricky as well. I'm also not sure how the ionization would interact with the upper atmosphere, so an upward lightning strike could possibly also take it out.

Also, the energy levels are rather high for the engine, so a power supply would have to be developed. I was imagining some ultralight gasseous/vaccuum state compacitor to dump into the inductor of the engine coil, but not having a lab, never developed it.

Finally, it would share the same problem as all rocket/balloons. It's at the mercy of upper level winds, so orbital insertion would be somewhat randomized, but for the application of micro sattelites, about the mass of a compact cell phone, (plus the balloon, and drive) in constelations, this would be too much of a problem. Also, for the N-prize/proof of concept, it just has to Sputnik 1 Beep Beep for 9 laps, so this isn't critical.

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Post Re: Some of my ideas   Posted on: Wed Jan 18, 2012 7:38 am
So, this thing is going to accelerate very slowly then? If so, it'll have a huge amount of drag losses. How are you going to overcome those?

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Post Re: Some of my ideas   Posted on: Wed Jan 18, 2012 2:53 pm
I think his concept is a LTA balloon with an electric rocket that floats up to the stratosphere and then transitions to a JP-Aerospace style "slow-accelerator" up to orbital velocity. Drag isn't much of an issue. Its actually a virtue as its where your lift comes from.

Psiberzerker wrote:

First, the canopy wouldn't be rigid like a tank, so under thrust, it would deform, possibly to be heated by the exhaist, and rupture to oxydise uselessly in the high atmosphere.


You need the envelope as a lifting body for every part of the flight profile except for the final orbital insertion. And if you want to recover your vehicle you will want to be able to reinflate it somehow for the drag for a gradual "self-deorbit" and landing.

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I've run some calculations, and I should be able to expend enough to compensate for pressure so it won't burst as it gains altitude, but forcing every last molecule of hydrogen (or atom of helium) into the partical engine would be tricky as well.


Most of the pressure swelling is going to come on the "free assent" where the need for thrust is the least. You would be better off designing your envelope to account for the increased volume. Low pressure gas is not a particularly efficient storage medium. You loose the advantage of H/He's mass fraction in that form. You are going to need a truly titanic envelope to have the reaction mass to reach orbital velocity.

Consider using ammonia as a lifting gas/reaction mass. It has the virtues of being simple to transition back and forth from gaseous and liquid for adjusting volume/buoyancy and its easily ionized.

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Also, the energy levels are rather high for the engine,


Heh, no kidding. Solar?

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Finally, it would share the same problem as all rocket/balloons. It's at the mercy of upper level winds,


Not when it gets going.


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Post Re: Some of my ideas   Posted on: Wed Jan 18, 2012 8:06 pm
It sounds like a JP ATO to me as well, but I have to admit that I still don't understand how that is supposed to work. It seems to me that your lift has to equal the difference between weight and buoyancy, and that lift/drag ratios for hypersonic vehicles are pretty bad (around 1:5 to 1:10 ISTR). If your thrust-to-weight ratio is say 1:100 (seems generous for an electrical drive), then you can transfer at most a tenth of your weight to lift. The rest of it has to be compensated for by buoyancy, which means that you need to be at an altitude where there is quite a lot of air, which means friction, and going around at hypersonic velocities for days on end is going to eat up a lot of fuel.

What am I missing? Is the math behind this "slow-accelerator" concept explained in John's book? I guess I should go and buy it anyway.

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Post Re: Some of my ideas   Posted on: Wed Jan 18, 2012 8:38 pm
Yeah, that is the gotcha of this approach. The transition from lift (from buoyancy or aerodynamics) to thrust acceleration climb is the tricky part that has been out of reach. Its the kind of situation where the "and a miracle happens here" caption is inserted.

There is a thin line that can be threaded to get there, but it requires a heretofore impossibly stretched out ISP. Its what has driven SCRAMJET et.al. research. JPs approach is to take a different tack and instead of trying to go really really fast to get lift, he goes really really big and light to glide on the mesosphere. It makes a certain amount of sense, but I don't know if the math or reality adds up to the same.


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Post Re: Some of my ideas   Posted on: Thu Jan 19, 2012 7:53 am
What about using a super heavy ship accelerated to escape velocity in a vacume tunnel with maglev tech and massive super capacitors? Heat is an issue and drag, but if you uad enough momentum and some good cooling....

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Post Re: Some of my ideas   Posted on: Thu Jan 19, 2012 4:12 pm
?

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Post Re: Some of my ideas   Posted on: Fri Jan 20, 2012 9:29 am
Sigma wrote:
What about using a super heavy ship accelerated to escape velocity in a vacume tunnel with maglev tech and massive super capacitors? Heat is an issue and drag, but if you uad enough momentum and some good cooling....


I don't think there is a cooling (or protection) system in existence that could stop the ship vaporising as soon as it left the tunnel at the very very high velocities required. Escape velocity is 11.2 km/s, you must need at least two or three times that to get past the drag issue (made up number). That is very very VERY fast (67000 mph)


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Post Re: Some of my ideas   Posted on: Fri Jan 20, 2012 5:25 pm
What about a separate heavy shield ahead of the craft that Burns up before the ship passes right through it? An alternate idea would be to have some rotation on the shield and have a small charge cause the disk to fly apart as many pie piece shaped chunks with parashoots?

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Post Re: Some of my ideas   Posted on: Mon Jan 23, 2012 9:20 pm
OK, to get to 67000mph (made up number, probably a big underestimation), which is about 30000m/s, and let's say you accelerate at 10g (approx 100m/s sq), you need to accelerate for (using v = u + at) 30000/100 = 300s.

Using s = 1/2at^2, that means a track of 0.5 * 100 * 300*300 = 4500000meters, that 4500 kilometers.

Hmm, that sounds wrong. Anyone see a mistake?

Anyway, that's a really long track.


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Post Re: Some of my ideas   Posted on: Mon Jan 23, 2012 10:55 pm
JamesHughes wrote:
OK, to get to 67000mph (made up number, probably a big underestimation), which is about 30000m/s, and let's say you accelerate at 10g (approx 100m/s sq), you need to accelerate for (using v = u + at) 30000/100 = 300s.

Using s = 1/2at^2, that means a track of 0.5 * 100 * 300*300 = 4500000meters, that 4500 kilometres.

Hmm, that sounds wrong. Anyone see a mistake?

Anyway, that's a really long track.


Well as escape velocity is about 11.2 Km per second. Acceleration at 10g after 1 second your travelling 100 Meters per second, after 10 seconds your travelling at 1000 meters per second 20-2000 30-3000 etc so it would only take you 120 seconds to get to 12Km per second without air resistance gravity loss etc.

In Mike Comb's bridge into space story he seems to think a linear accelerator track of only 310 kilometres would be viable for human transport and as its meant to be hard SF i assume he double checked the numbers.

http://writings.mike-combs.com/bridge.htm

Tho sticking my numbers into the formula above i get a 720 kilometre track so i wonder if he mixed up miles and km as Nasa has been known to do on occasions or maybe air resistance losses really are below .8Km at the heights stated in the story.

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Post Re: Some of my ideas   Posted on: Tue Jan 24, 2012 3:35 am
Well some of the thrust could be provided by rocket engines. The more infrastructure on the ground the less in the ship.....

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Post Re: Some of my ideas   Posted on: Tue Jan 24, 2012 10:35 am
SANEAlex wrote:
JamesHughes wrote:
OK, to get to 67000mph (made up number, probably a big underestimation), which is about 30000m/s, and let's say you accelerate at 10g (approx 100m/s sq), you need to accelerate for (using v = u + at) 30000/100 = 300s.

Using s = 1/2at^2, that means a track of 0.5 * 100 * 300*300 = 4500000meters, that 4500 kilometres.

Hmm, that sounds wrong. Anyone see a mistake?

Anyway, that's a really long track.


Well as escape velocity is about 11.2 Km per second. Acceleration at 10g after 1 second your travelling 100 Meters per second, after 10 seconds your travelling at 1000 meters per second 20-2000 30-3000 etc so it would only take you 120 seconds to get to 12Km per second without air resistance gravity loss etc.

In Mike Comb's bridge into space story he seems to think a linear accelerator track of only 310 kilometres would be viable for human transport and as its meant to be hard SF i assume he double checked the numbers.

http://writings.mike-combs.com/bridge.htm

Tho sticking my numbers into the formula above i get a 720 kilometre track so i wonder if he mixed up miles and km as Nasa has been known to do on occasions or maybe air resistance losses really are below .8Km at the heights stated in the story.


Well, you need massively more than escape velocity to overcome drag - which is a square of velocity, so massive at the speeds needed. Hence I tripled the escape velocity speed. Probably not enough tbh.


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Post Re: Some of my ideas   Posted on: Tue Jan 24, 2012 4:40 pm
Ok, we seem to be getting off on a tangent about some sort of surface-to-orbit cannon here, which is essentually the opposite of my proposal. Could we at least try to stay on topic?

JamesG wrote:
I think his concept is a LTA balloon with an electric rocket that floats up to the stratosphere and then transitions to a JP-Aerospace style "slow-accelerator" up to orbital velocity?
Yeah, except for the "Slow Accelleration" part. I think you're imagining an Ion engine, like a Hull-effect thruster, while my concept is closer to an Arc-jet combined with a partical accellerator.

The engine is essentually a plasma-torch, or anode wrapped around a cathode to ionize the helium into something a magnetic field can grip, then fed into a wave-guide to a linear accellerator, not unlike a railgun, but consisting of a long tapered coil. Like a solenoid, the iron core is replaced with the plasma stream, and the taper creates a differential so that the electrons move up the conductor, while the neuclions are forced downward at relativistic speeds.

Now, by running this up the center of a spherical balloon, I'm hoping it will reinforce the shape enough that it wiil not capsize under the drag, and accelleration pressure, with enough hanging downward to ballance the whole craft, and keep the canopy out of the stream.

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You need the envelope as a lifting body for every part of the flight profile except for the final orbital insertion. And if you want to recover your vehicle you will want to be able to reinflate it somehow for the drag for a gradual "self-deorbit" and landing
The lifting body is passive, so a sperical shape would be most mass efficient. (A sphere has the least surface to volume ratio, so contains the most fuel for the least amount of material by the Square-cube law.)

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Most of the pressure swelling is going to come on the "free assent" where the need for thrust is the least. You would be better off designing your envelope to account for the increased volume. Low pressure gas is not a particularly efficient storage medium. You loose the advantage of H/He's mass fraction in that form. You are going to need a truly titanic envelope to have the reaction mass to reach orbital velocity.
I was thinking about an expanding envelope, probably doped lycra composite, so it can contract to force helium into the engine, and also adjust as the pressure goes down. Therefore, as it gains altitute, it also gains volume to produce more lift until reaching the neutral boyancy point at launch altitude. The immense volume means both more fuel for the thrust stage, and better lift during the ascent, but is moderated by using it for a mico-sattelite, weighing grams instead of tonnes.

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Consider using ammonia as a lifting gas/reaction mass. It has the virtues of being simple to transition back and forth from gaseous and liquid for adjusting volume/buoyancy and its easily ionized.
I had, but it's also not much lighter than air, so doesn't get you high enough for free to make it worth the trouble.

Quote:
Solar?
I was thinking it would be nice to have a photo-electric coating for this, but that would require one to be developed with better than a 3rd transition efficiency. I have some ideas, but as I don't have the funding to test the engine, I'm back-burnering the power generation at the moment.

One possibility is a Rutherford Reactor, to make fuel/energy out of atmospheric nitrogen, but 1) that would have to be developed, and B) that's a lot more mass to dangle off the end. Essentually, we're talking about the pumps, and coolers to liquify the nitrogen, and a field effect seperator to attract the protions, and oxygen to be combined in a fuel cell, which would more than double the launch mass.

A lighter/lower tech solution would be to use Hydrogen, and atmospheric oxygen in a fuel cell, then ionize the waste water into a steam plasma. Unfortunately, oxygen is much rarer at this altitude, so might not be abundant enough for reliable launch. I had thought that it could be actually a cannon launcher, but at high altitude. Float up the reactor, accellerator, and micro-sattelite, then use the energy produced from Helium, and atmospheric nitrogen to launch a micro-sattelite (or antisattelite munition in my science fiction) to orbital insert(, or interdiction) velocity.

The advantage of this is a lot less mass needs to be accellerated, but I don't know that it could be done reliably enough for sattelite launch (which is why I relegated it to an Asat weapon), and it would have to have the accellerator at an angle, instead of vertical in the balloon at least during the launch phaze. That means some sort of automated ballance, and steering mechanism, to aim it, which would add more mass. In the Asat design, it could be pointed straight up, and wait until directly under the target's path.

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Post Re: Some of my ideas   Posted on: Thu Feb 02, 2012 8:05 am
Another design I'm working on is an Escape Hatch, which incorporates re-entry sheild, seat, life support, maneuvering thrust, and landing chute as an emergency return vehicle. Literally the outer door of every airlock, these could be sent up as replacments for the ISS's existing hatches. They would require a suit, which could hook to the onboard stores, but any abort is going to be at the airlock anyway, whether docked to a shuttle, or left unoccupied.

In configuration, it's not unlike the old MOOSE (Man Out Of Space Easiest, or Manned Orbital Operations Safety Equipment) system, except with a rigid shell for the shield, and docking ring round the circumference. Packed around the seat would be thrusters with combined impulse to de-orbit, oxygen tanks, fuel, communications gear, and survival equipment. An inflatable ring would make it float as a liferaft in the event of a splashdown, or could cushion the impact on landing. (Odds favor a splashdown somewhere in the ocean.)

Now, this isn't intended as a routine spaceship, but an emergency vehicle. I wouldn't even send them up with the initial launch, but they could be stacked in a cargo load for retrofitting during station assembly.

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