Earth to LEO - discuss

GCNRevenger · 2006-11-06 21:14:21

uhhhh no

dicktice · 2006-11-07 11:21:07

Of course, ohhhh no--but go ahead: tear it apart.

cjchandler · 2006-11-11 20:37:55

I'm not sure we can build a rocket that can reach the moon without stages, much less a big simple one. Even Sea Dragon had/has two stages. I don't think you'd have to revert to sending prisoners either, they'd probably to a bad job setting up the infrastructure and die, besides, there's no shortage of volenters or even paying costomers.

dicktice · 2006-11-14 18:01:38

I started a new thread "Big Dumb Boosters" to try and get at the tactic of one-way cargo trips to the Moon, which might enable single-stage direct ascent launchings, coasting to Lunar orbit, and intact landings on the Moon--as expeditions to the Moon were envisaged prior to today's computer-automated remote-presence-monitored capability. Can they be built be lightweight enough? Will single engines be sufficient? How large and heavy the vehicle at launch? Tune in....

GCNRevenger · 2006-11-14 19:11:06

I guess I really didn't explain it properly, my idea was that a large plastic pipe opened on each end could be a fuel tank. The engine assembly, probably an aerospike engine would have a gasket and large ring so that it could just fit in the bottom of the pipe to be a plug, then at the top, the payload would cover the top of the pipe. The interior cavity created could be filled with oxidizer and fuel, and maybe pressurized to avoid turbo pumps, though that wouldn't be absolutely necessary. Then the bottom engine assembly would burn the propellant and as the tank emptied, could climb up the walls of the pipe, maybe by spinning and having the inside of the pipe threaded, of some other way. This would expose some of the pipe behind the engine, where it could be burnt sort of like a hybrid rocket, or since the engine will probably be an areospike just left there to burn off and reduce weight as it goes. If there was a problem with too much of it burning quickly, the outside could be covered with some fire retardant that the engine assembly scraps off as it climbs, but I don't think that will be a problem since it can only burn where there is oxidizer, that is at the end of the pipe.

"No" for a simple reason: whatever you would build the tank out of would have to burn EXTREMELY well without confinement while being VERY strong. There is no such material. Hence, you'd be lucky if the burning tank would even reach double-digit Isp.

publiusr · 2006-12-08 15:37:38

I started a new thread "Big Dumb Boosters" to try and get at the tactic of one-way cargo trips to the Moon, which might enable single-stage direct ascent launchings, coasting to Lunar orbit, and intact landings on the Moon--as expeditions to the Moon were envisaged prior to today's computer-automated remote-presence-monitored capability. Can they be built be lightweight enough? Will single engines be sufficient? How large and heavy the vehicle at launch? Tune in....

Finally some love for larger LVs.

cjchandler · 2007-01-22 18:38:51

I read that rocket pumps make up somehting like half the cost of a rocket engine. The alt space groups seem to favor self presurizing fuels like propane and nitrus oxide, but I have a had time beliving that that's going to work for a low cost orbital rocket. Has anyone considered a sort of pulse jet pump? My thought is that if one had quite a few high pressure cylinders and then filled them with the fuel and a little bit of oxidizer and ignited it, it would get up to the chamber pressure and could be emptied with a one way valve. Sound fesible? Sort of like a piston pump without the piston.

C M Edwards · 2007-01-23 08:22:09

I read that rocket pumps make up somehting like half the cost of a rocket engine. The alt space groups seem to favor self presurizing fuels like propane and nitrus oxide, but I have a had time beliving that that's going to work for a low cost orbital rocket. Has anyone considered a sort of pulse jet pump? My thought is that if one had quite a few high pressure cylinders and then filled them with the fuel and a little bit of oxidizer and ignited it, it would get up to the chamber pressure and could be emptied with a one way valve. Sound fesible? Sort of like a piston pump without the piston.

Hmm.

I don't discount self-pressurizing propellants out of hand. However, I think something similar to what you are proposing could be employed to pressurize cryogenic fuels. The trick would lie in not blowing the whole works by introducing hot, uncombusted reactants into the propellant tanks along with the pressurizer exhaust. In the worst case scenario, the pressurizer would provide a flow path directly between the fuel and oxidizer tanks.

cjchandler · 2007-01-23 10:28:12

I wasn't really thinking of pressurizing the propellents in the main tanks, but having them under slight presure and emptying them into a small really tough presure vessel. Then a little bit of fuel or oxidizer in added, and the pressure in the small vessel get up to chamber pressure. A valve allows it to dump the propellent into the chamber, and a one way valve prevents it from going back up to the main tanks. Then it repeats. That way the main tanks don't have to be so strong and heavy.

Michael Bloxham · 2007-01-23 18:01:57

Do you mean adding and combusting a little bit of fuel and oxidizer in each little chamber to pressurize it? That would be sort of like turbocharging in car engine, except without the turbocharger. The fuel and oxidizer would have to be 'turbocharged' in seperate chambers to avoid blowing everything up, and many of these little chambers would be used sequentially to get a constant pressure feed to the main combustion chamber. That would be an excellent idea, so long as you could achieve the necessary flow rates.

cjchandler · 2007-01-23 19:34:10

That's it exactly, Michael. I think a car engine's pistons make about 30 cycles per second, and this should be pretty simmilar, so maybe only 4-8 small chambers. Don't know if that would be an advantage over turbopumps by weight, but possibly in simplicity of design.

Michael Bloxham · 2007-01-23 20:31:21

It reminds me of the method icelanders use to remount the huge tires they have on their 4x4's when they come off the rims: They spray a little kerosene inside the tire cavity and drop in a match. The pressure causes the tire to expand and collapse back onto the rim.

Would the liquid fuel expand into gas before or after admission into the sub-chamber?

cjchandler · 2007-01-24 05:30:10

hopefully, the propellent would stay liquid as it was pushed out of the small chamber, only the bit that combusted with the oxidizer would become gasseous, and could be vented seperatly once all the liquid was emptied.

Yang Liwei Rocket · 2008-02-20 09:45:55

" The US Navy has been bragging about its military might on the internet, releasing photos and videos of its magnetism-powered new railgun to the masses. "
http://techdigest.tv/2008/02/us_navy_boastin.html

See magnetic mass driver page for a similar idea.

The tech isn't there, which is why I think most of these ideas are guaranteed to fail

Terraformer · 2008-02-21 09:22:20

Ah, finally read through the entire thread. For some reason, whenever I see launch cost per kilo, I always work out how much it would cost to launch the weight of me into space.

How about using a Hydrogen filled Airship to get to a decent altitude? Then we can start burning the Hydrogen to get to Orbit?

Or maybe use H2O2 as the Oxidiser? In the prescence of Silver or Plantinum it decomposes into high-pressure steam and O2. Maybe use a Hydrogen afterburner?

Another idea would be to use an Air-breathing Ramjet propelled first stage. Unlike Scramjets, a lot of work has gone into Ramjets proving their feasiblity. The first stage would be a (suborbital?) plane that could get up to Mach 6. The first stage could be payed for through hypersonic transport and (maybe) Suborbital flights.

One idea that's been floating around in my head recently is for a 'pitted flying saucer' design. The craft would have a funnel in the middle to scoop up air. It would be flat on the bottom and curved to reduce drag at the top. A few jet engines or rockets would be used to accelerate to Mach 0.5, at which point the Ramjet would kick in and boost it to Mach 6. At either its Apogee or Max Speed (whichever is more efficient), the rockets would kick in and boost it into Orbit. A torus shaped Airship might be used to give it a higher initial altitude. On re-entry the dip on the top of the craft should (I'm hoping to build a few models and drop them off a building soon) orientate the craft bottom down for re-entry. Once the worst of the heat was over, wings would pop out and allow it to glide to a landing.

JoshNH4H · 2008-02-21 15:20:54

Initial altitude isn't really an issue, speed is. I've been considering NTR with LRB's on the side.

Terraformer · 2008-02-21 15:51:29

Damn politics, not allowing NTRs.

Grypd · 2008-02-21 15:54:44

Ah, finally read through the entire thread. For some reason, whenever I see launch cost per kilo, I always work out how much it would cost to launch the weight of me into space.
How about using a Hydrogen filled Airship to get to a decent altitude? Then we can start burning the Hydrogen to get to Orbit?

Terraformer though Height has some advantages what we are really looking for is speed and a Hydrogen balloon is very very slow. Basically the idea is that you are travelling fast enough that as you fall due to gravity you stay at the same distance from the ground.

A TSTO spaceplane launcher would give the advantages of height ie atmosphere density decreasing and speed. This would then give the upper stage a lot more of a starting shunt.

Or maybe use H2O2 as the Oxidiser? In the prescence of Silver or Plantinum it decomposes into high-pressure steam and O2. Maybe use a Hydrogen afterburner?

Hydrogen Peroxide or high test peroxide has been a rocket fuel for years and has been used from Rocket fighters to jetpacks. Its specific impulse is only 161 so not that effective. and each extra system you add to get it to be more effective adds weight and of course it gets to the point it is not worth it. H2O2 is very easy to hand but hydrogen is not and having the super cooled hydrogen on a plane needs insulation and difficulty in fueling.

GCNRevenger · 2008-02-21 18:28:59

A good time to emphasize the difference between orbital and suborbital flight: in suborbital flight, if all you want to do is stick your nose above the atmosphere, then altitude is really all you want. You don't need ground speed (speed parallel to the surface), only vertical speed (tangent to the surface) so you can gain height.

Orbital flight on the other hand is just the opposite, altitude is really not very important except to avoid crashing and avoid drag from the atmosphere. Ground speed is all important, and in fact if you had a race car with infinite acceleration and zero drag, you could enter orbit without needing to gain any altitude at all, just floor it. Another illustration can be found here: Newton's Cannonball In this example, you see how orbital flight really works, that its all about gaining ground speed so that you fall around the Earth/Moon/etc. It has (almost) nothing to do with altitude.

Obviously, it takes a lot more energy to reach orbital velocity then it takes to just hop above the atmosphere and come back down again. That takes more rocket fuel, right? Even more than you might think: for every pound of rocket fuel, you need more fuel to push that fuel, and more to push that fuel and so on. Thus the amount of fuel you need increases exponentially with the speed you need to reach. You need much more than double the fuel to go 2000mph than you do 1000mph and so on. See the Tsiolkovsky equation.

Further, as the mass of the fuel you need increases, you need bigger tanks to hold it, which makes your rocket heavier, so you need more fuel, and even more fuel to lift that extra fuel, and so on.

Lastly, after you've got this far larger amount of fuel and far bigger fuel tanks for an orbital rocket than a suborbital one, you need big rocket engines to ensure you have enough thrust to lift all that off the ground, which also weigh more, and add still additional weight, which also in turn needs more fuel, which needs more fuel, which needs more fuel.........

If you take Burt Rurtan's SpaceShipOne, double its mass for heat shield, extra life support, and OMS thrusters to make it a practical orbital vehicle, then its main booster rocket would not fit on the back of a 747 jumbo jet!

You get the picture. There are only three ways to solve this problem:

-Start at as high a speed as possible
-Use the air as propellant (jet/ramjets, LACE)
-Increase the velocity of your rocket propellant as it leaves the engine (aka Isp)

That last one is most crucial, and for thermal rockets there are three parameters that affect this:

-Amount of energy per mass of fuel (more=good)
-Molecular weight of the expelled propellant gas (less=good)
-Maximum temperature the engine can handle (more=good)

This is why orbital flight, so far, defied all attempts to make up something better than rockets. Its also why Hydrogen, despite being hard to handle, is the fuel of choice when you can use it.

Terraformer · 2008-02-22 08:02:39

I was talking about burning the Hydrogen that would be in the balloon, so only Oxygen would have to be carried in tanks.

GCNRevenger · 2008-02-22 09:56:54

Well, a balloon to boost your altitude really doesn't gain you much is the trouble, and it would restrict the practical size/mass of the rocket.

About burning the Hydrogen in the balloon, I bet it would be too much trouble to collect it (pump to squirt it into the engine), and really the balloon doesn't carry that much Hydrogen. The gas has extremely low density, particularly in a high altitude balloon.

Terraformer · 2008-02-23 05:48:55

Why do we have use Hydrogen and Oxygen anyway? I know its got the best thrust-to-weight ratio that we've discovered so far that doesn't produce toxic gasses, but what about Acids and Alkalis. I actually had this idea in the bath (no I didn't do an Archimedes ), when I thought what would happen if I filled the bath up with Cola, Lemon Juice, or Vinegar, and dropped a load of Menthos/Baking Soda into it. What would the thrust be if we used a ph1 Acid with a ph14 Alkali? A disadvantage would be storage, but that could be solved. One byproduct of the reaction would be Hydrogen,. that could be burnt with an Afterburner. Feasible? Efficient?

Terraformer · 2008-02-23 08:17:02

I'll take your silence as a 'Don't know, the only way of knowing would be with an experiment, doing the maths doesn't have the answers this time' then, should I?

Maybe burning Hydrogen with Fluorine to make Hydroflouric acid, which could be reacted with an Alkali and the Hydrogen released could be burnt normally with Oxygen?

JoshNH4H · 2008-02-23 09:26:10

a triple afterbuner?

Austin Stanley · 2008-02-23 09:43:39

Why do we have use Hydrogen and Oxygen anyway? I know its got the best thrust-to-weight ratio that we've discovered so far that doesn't produce toxic gasses

Actually this may not be true. Hydrogen and Oxygen have the highest specific impulse (change in momentum per unit of fuel), but do not necessarily produce the largest amount of thrust. In fact in general thrust is often hindered by high ISP as the more entergetic propellants need a higher flow-rate to achive the same amount of thrust in the same amount of time. The SSME are probably pretty close the the limit here. This is why the Space Shuttle has the two large SRB which have teriffic thrust but terrible ISP.

but what about Acids and Alkalis. I actually had this idea in the bath (no I didn't do an Archimedes ), when I thought what would happen if I filled the bath up with Cola, Lemon Juice, or Vinegar, and dropped a load of Menthos/Baking Soda into it. What would the thrust be if we used a ph1 Acid with a ph14 Alkali? A disadvantage would be storage, but that could be solved. One byproduct of the reaction would be Hydrogen,. that could be burnt with an Afterburner. Feasible? Efficient?

In most cases the product of a neutralization reaction is plain old water with some ions in it. While Acid-Base reactions may seem dramatic, energy wise they are pretty pathetic compared to rocket fuels. And its unlikely that any hydrogen would be formed in this case (though it can happen in some reactions). Think about it rationaly, do you real think house-hold chemicals, indeed things you can eat are entergetic enough to make an effective rocket propellent? Of course not.

Rocket propellents are highly entergetic, reactive substances. Even the most mild of them will burn/melt the flesh right off your bones. You of course cannot eat them.

Actually analysing a potential rocket propellant is not that difficult.
Step #1, determine the energy of the reaction or its enthalpy. Obviously the higher this is per gram the better.
Step #2, figure out if the products would make make good exhaust. For this you idealy need a light gas.

I'll take your silence as a 'Don't know, the only way of knowing would be with an experiment, doing the maths doesn't have the answers this time' then, should I?

Give people a chance to reply! Its pretty easy to judge that most neutralisation reactions are not going to be entergetic enough for rocket propellant. In would be a good experiment for you, measuring the enthalpy of a neutrilaztion reaction is classic chem 101 stuff.

Though more generaly speaking any acid-base reaction is a redox (oxidation reduction) reaction, which is the same kind of reaction that all chemical rocket fuels I am aware of rely upon.

Maybe burning Hydrogen with Fluorine to make Hydroflouric acid, which could be reacted with an Alkali and the Hydrogen released could be burnt normally with Oxygen?

There is no free lunch in chemistry, if you some how get the H back out of HF, you have to use as much energy as you got putting it there. Besides the fact that this reaction won't work, there are a couple other fundamental issues. How would you recapture your (highly entergetic) exhaust? And caring oxygen to react again with your hydrogen only lowers your ISP.

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