what are the different fuels for space vehicles?

Question

like.. i want you to recommend fuels for the launch vehicles, on-orbit vehicles..... separately witha the reasons for their selection.

Answer 1

Launch vehicles require a massive (rocket) amount of energy so for now we use liquid oxygen for propellant. Orbiting/probing vehicles/satellites use solar energy as primary source..

Answer 2

Launch vehicles require fuel and an oxidizer since the air is so thin to nonexistent in the upper atmosphere. I would suggest a combination of RP-1, which is a high grade of kerosene and liquid oxygen, LO2. This combo worked well in the Atlas and Delta expendable launch vehicles. You can also use the combination of Liquid hydrogen, LH2 and liquid oxygen, LO2. Somewhat more volatile but depending on your needs they work well also. The STS uses this combo with solid rocket boosters as do other expendable launch vehicles. The solid propellant, simply, is both a fuel and oxidizer combined in solid form. Once ignited it can not be throttled or controlled. In the very dangerous category we have something called Aerozine 50, a 50/50 blend of N2O4, Nitrogen Tetroxide, and Unsymetrical Dimethel-Hydrazine or UDMH. N2H4, hydrazine would be your fuel. I don't recommend this combo. It is very very dangerous. On orbit you must use a mono-propellant such as monomethel-hydrazine. Some spacecraft use an oxidized screen and spray the propellant fuel over the screen to create combustion in the vacuum of space. Again, on orbit you are limited to the mono-propellants because, obviously, there is no air up there.

Answer 3

For a launch vehicle you have a choice of crogenic, hypergolic or solid propellants. Cryogenic propellants use supercooled liquids such as liquid oxygen. Hypergolic propellants are chemicals that ignite spontaneously on contact. Solid propellants are a rubbery mixture of fuel and oxidiser.

Cryogenic propellants work very well. The shuttle uses liquid hydrogen and liquid oxygen in its main engines. This is a very efficient fuel mix. Other rockets use kerosene and liquid oxygen. The downsides of cryogenic propellants are the very low temperatures and storage conditions. The engines are also very complex, requiring pumps, igniters, etc. (Contrary to an earlier answer, those sparks you see at the base of the shuttle before take off actually do not ignite the engines: they are for burning off excess hydrogen and oxygen vapour that may pool below the shuttle and cause an explosion on engine ignition. The engine igniter is well inside the engine).

Hypergolic propellants are very good for use once you are in space. Because they ignite spontaneously, you can dispense with an ignition system. The Apollo spacecraft used a mix of unsymmetrical dimethyl hydrazine and nitrogen tetroxide in tanks pressurised with helium. They literally had two moving parts: a valve for the fuel and a valve for the oxidiser. They open, the chemicals mix and the engine burns. It keeps the engine design simple and makes it more reliable, simply by virtue of eliminating a lot of complex components. Problems with hypergolic propellants are that they are corrosive and highly toxic.

Solid propellants are very powerful, but they have a huge drawback: you cannot switch off a solid rocket engine. Once it ignites it burns to completion. Liquid fuel engines can be throttled or shut down if needed. Solid rockets can be controlled in a preselected manner, by arranging the shape of the propellant mould inside the casing such that at some points it burns less efficiently than at others, but that is fixed into the design. Once it ignites it does that whatever happens. You cannot control them 'on the fly'. They are very powerful, however, and that explains their use in things like the space shuttle and the planned Ares rocket family.

Another system used for manoeuvring in space occasionally is single propellant systems such as hydrogen peroxide. There is no combustion, as such, but there is a catalytic breakdown that results in rapid production of gas that is directed through a nozzle. Gas being forced out of the nozzle pushes the spacecraft in the opposite direction. The early Mercury spacecraft used these for attitude control, and several space probes use similar systems.

Answer 4

Well, the Saturn vehicles used concentrated kerosene and liquid oxygen to burn it. The shuttle's engines burn liquid hydrogen. The Shuttle's solid rocket boosters (the two on either side of the main tank) use a fuel that's made up of aluminum and perochlorate (it feels like a pencil erasure... kinda spongy). The Service Module that went to the moon had two fuels that ignited upon contact, so no 'ignitor' was needed (Next time you see a shuttle launch, they'll usually show the engines just prior to firing - you'll see 3 big posts throwing sparks - it's these sparks that actually ignite the liquid hydrogen & liquid oxygen.)