What factors go into choosing what thrusters to use on a spacecraft,

Kerosene is used when you need high volume energy density (first stages). Liquid hydrogen is used when you need high mass energy density (upper stages). Hypergolic propellants like hydrazine-N2O4 are used when you need to start and stop the engine a lot (spacecraft engines and reaction control thrusters)

>>8504648
Reliability/simplicity, handling characteristics, density, specific impulse

Read up on:
hydrazine monopropellant with catalytic activation - low performance but very simple, reliable engine, used in orbital systems. Hydrazine is very toxic and therefore unpleasant to handle. Various less-toxic replacements are under development, but spacecraft designers are conservative and hydrazine works.
hydrazine resistojet (or other electric heating) - higher performance than catalytic decomposition, but high electrical power requirement. Similar applications.
xenon ion thruster - very high specific impulse, low thrust, requires electrical power, careful planning, and patience since it takes a long time to change the orbit.

space-storable hypergolic combinations (such as UDMH/MMH/Aerozine-50 with dinitrogen tetroxide or MON) - simple, reliable engine, used in high-performance orbital systems and some launch systems. Very toxic.

kerosene/oxygen - standard high-density combination for launch vehicles, not easy to store in space (for one thing, the oxygen will freeze the kerosene)
hydrogen/oxygen - standard high-spacific-impulse, but unfortunately low-density (hence, requiring larger tanks) combination for launch vehicles, very difficult to store in space because hydrogen boils at such a low temperature
methane/oxygen - fancy new medium-density combination for launch vehicles, somewhat easier to store in space because the methane and oxygen are liquid at the same temperature, although maintaining cryogenic temperatures in space is somewhat challenging

rubber and rubber with ammonium perchlorate - standard solid rocket propellant for strap-on boosters and solid-fuel upper stages, good way to get lots of thrust, but environmentally unfriendly can explode

nitrogen cold-gas thruster - just compressed nitrogen in a can. Low performance, but cheap and simple. Sees some use in things like settling and attitude thrusters (ex. on the Falcon 9 reusable booster).

Depends what thrust you want, depends how much money you wanna spend, depends what engines you are able to buy

>>8504667
>>8504718
Wow, very helpful!
Did you get this information from somewhere specific or did you just know it all already?

>hydrazine monopropellant with catalytic activation - low performance but very simple, reliable engine, used in orbital systems. Hydrazine is very toxic and therefore unpleasant to handle. Various less-toxic replacements are under development, but spacecraft designers are conservative and hydrazine works.
>hydrazine resistojet (or other electric heating) - higher performance than catalytic decomposition, but high electrical power requirement. Similar applications.
>space-storable hypergolic combinations (such as UDMH/MMH/Aerozine-50 with dinitrogen tetroxide or MON) - simple, reliable engine, used in high-performance orbital systems and some launch systems. Very toxic.
Seems like these three are the ones I'm gonna have to decide between, since it's just propulsion in space for what would be an orbital system. I'll also take a look at the Xenon ion thruster though.

How much does weight of the payload play a factor in thruster choice though, once it's out in space?

>>8504718
Has there been that many cases of solid propellant rockets going boom?

>>8505034
If you count fireworks and military rockets and missiles, yeah.
>>8504819
>How much does weight of the payload play a factor in thruster choice though, once it's out in space?
A lot less than for booster stages, but generally you want enough thrust to perform any desired maneuver within the span of a few minutes or less. The shorter the burn, the more closely it approximates the instantaneous velocity changes used in classical orbital mechanics, thus simplifying and improving the efficiency of trajectories.

However, this isn't possible with electric thrusters (i.e. ion thrusters), so spacecraft that use them must use more complicated and less efficient trajectories - though the thrusters themselves make up for this inefficiency with their phenomenal specific impulse.

>>8504819
>Did you get this information from somewhere specific or did you just know it all already?
That was off the top of my head. It's pretty basic knowledge for a space enthusiast. I think I picked most of it up from hanging around the nasaspaceflight forums.

The most enjoyable thing I've read about liquid rocket propellants is "Ignition!", which is available for free online:
http://library.sciencemadness.org/library/books/ignition.pdf

Mind you, it's a single-point-of-view book with a somewhat opinionated author, so don't take it all as gospel.

>>8504819
>How much does weight of the payload play a factor in thruster choice though, once it's out in space?
With a bigger payload, they're more likely to go with a bipropellant (typically MMH/NTO) or solid-fuel rocket for major burns.

As you make things smaller, they get fiddly, so you go to simpler systems.

>>8505358
>solid-fuel rocket for major burns
i wasnt aware solid fuel was used in vacuum i thought that it was used mostly for doing big nasty burns on the ground when monster thrust is needed. How wrong am i?

>>8505484
There have been lots of them, like this:
https://en.wikipedia.org/wiki/Star_48

The smaller a solid rocket motor is, the easier it is to develop a highly reliable one. It's the big ones that tend to blow up, mostly because it's too expensive to test them many times. The performance isn't spectacular, but it's significantly better than hydrazine monoprop.

>>8505518
>https://en.wikipedia.org/wiki/Star_48
also, i was under the impression that solid boosters were prefered mostly for military reasons because they required less mantainance and could be launched with less preparation

>>8505557
They can be stored almost indefinitely very easily and require very little prep time before a launch (practically none). Liquid propellants require storage tanks, possibly cooling if they're cryogenic, possibly special handling if they are toxic and require time to pump into the rocket itself. You can see why they choose solids over the other options for ICBMs etc.

>>8505557
That is indeed why most ICBMs and SLBMs are solid rockets (not to mention, of course, the vast majority of military rockets that have nothing to do with space).

>>8504648
There is also a trajectory creating certain demands on the system.Apollo had to performance a efficient capture of the lunar stack and that forced the use of efficient and powerfull aj10 to stop 45 000kg stack in llo. Some missions can get away with electric propulsion but that would mean different transfer to the moon and is not efficient for manned missions but you could look esa proposed Pluto orbiter

>>8505569
There's still liquid fueled ICBMs out there. The Russians never quite made the full switch to solid fuel missiles that the US did. With the right hypergolic fuel/oxidizer mix storage and launch time aren't significantly different than solid fuel ICBMs. Handling and maintenance are another story. Hypergolic fuel/oxidizer mixes that can sit for long periods of time ready for launch at a moment's notice tend to be extremely toxic.

>>8504648
Projectrho

>>8505972
Fun fact: There were designs to make an N-1 derived ICBM.

>>8506016
HAHA, what the fuck was it going to carry?

MFW trump does an BFR ICBM, the payload is an ITS SIZED atom bomb yield: 2000mt

>>8506131
ITS would be a kinetic WMD even without a warhead.

Smallish for a WMD, but on the order of the Hiroshima bomb. Easily enough to devastate a city center in one shot.

>>8506131
Tsar Bombas