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Spacecraft Propulsion

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Spacecraft Propulsion SPACECRAFT PROPULSION Spacecraft propulsion .................................................................................................................................... 1 Rocket technologies .................................................................................................................................. 4 Cold gas rockets .................................................................................................................................... 7 Solid propellant rockets ........................................................................................................................ 7 Liquid propellant rockets .................................................................................................................... 10 Electrothermal rockets ........................................................................................................................ 15 Electrodynamic rockets ....................................................................................................................... 16 Rocket propulsion modelling .................................................................................................................. 18 Tsiolkovsky rocket equation ............................................................................................................... 18 Delta-v budget ..................................................................................................................................... 19 Rocket exit speed ................................................................................................................................ 24 Chamber pressure equation ................................................................................................................. 26 Rocket cooling .................................................................................................................................... 28 Sub-orbital spaceflight ............................................................................................................................ 30 Sounding rockets ................................................................................................................................. 31 Air drag: ballistic coefficient .............................................................................................................. 34 Descent and reentry ................................................................................................................................. 37 Deorbiting and reentry angle ............................................................................................................... 41 Reentry phases .................................................................................................................................... 44 Landing ............................................................................................................................................... 47 Launchers ................................................................................................................................................ 48 Launcher trajectory ............................................................................................................................. 50 Launch windows and entry windows .................................................................................................. 53 Type of launchers and propellants used .............................................................................................. 53 Ariane 5 engines.................................................................................................................................. 54 Soyuz 2 engines .................................................................................................................................. 55 Vega engines ....................................................................................................................................... 57 Long March engines............................................................................................................................ 57 The Space Shuttle.................................................................................................................................... 57 Lift-off and ascent ............................................................................................................................... 59 Engines: SRB, SME+ET, OMS, RCS ................................................................................................ 63 Reentry events ..................................................................................................................................... 66 Other spacecraft propulsion systems....................................................................................................... 68 ATV propulsion .................................................................................................................................. 68 Meteosat and AlphaBus propulsion .................................................................................................... 69 Galileo system propulsion ................................................................................................................... 71 A trip to Mars (MLS-Curiosity) .......................................................................................................... 71 Rocket emissions and other environmental effects ................................................................................. 73 SPACECRAFT PROPULSION The unique characteristic of space propulsion is the absence of a material medium (i.e. vacuum conditions), which prevents the throwing back of environmental matter for the vehicle to accelerate forward, with the following major consequences: 1. Propulsion under vacuum requires the throwing back of on-board mass. We call 'propellants' the materials to throw, and 'rocket' the engine to force the ejection; the energy to power the rocket Spacecraft propulsion 1 engine may come from inside the vehicle (e.g. combustion) or from outside (e.g. solar power); see Propulsion fundamentals, aside. 2. Propulsion under vacuum requires the carrying of both fuel and oxidiser aboard. This is a huge penalty in space propulsion, when we recall that in the burning of most fuels, stoichiometry dictates that every kilogramme of fuel requires 15 kg of air. Yes, we do not need to transport air but only oxygen, or any other oxidiser; and we might totally forget about combustion, and use other physical process to accelerate the propellants backwards to achieve propulsion. 3. Propulsion under vacuum requires the throwing of on-board mass to decelerate and brake, since there is no air drag. But, before we go on, we should specify what 'space' means in Space propulsion. By default, we understand 'outer space' where vacuum prevails, say beyond the 100 km altitude Kármán line on Earth until another planetary atmosphere is encountered; see Space environment. Besides this vast genuine outer space, we are also including under Space propulsion the atmospheric flight of space vehicles (e.g. launchers and descenders). Contrary to aircraft flight, which must be continuously propelled (sailplanes considered aside), spacecraft flight is most of the time unpowered (ballistic motion dominated by gravity forces), with some periods of propulsion based on rocket engines, i.e. on high-speed ejection of some stored mass (the propellant), accelerated by internal energy sources (e.g. chemical or nuclear reactions) or by external energy sources (e.g. natural radiation from the Sun, or radiation coming from a 'power station' spacecraft, originating in a nuclear reactor or stored solar radiation, being aimed to the recipient spacecraft in a laser or microwave beam). Another distinct feature of space propulsion is that, for the time being, there is no refuelling possibilities, and the end of a space missions is often dictated by fuel run out. We only deal here with space-related rockets (launchers and space thrusters, including sounding rockets), but rockets are not only used in spacecraft propulsion, but in some aeronautical applications (notably in missiles). Rockets for military and recreational uses (fireworks) date back to at least 13th century China. Relative motion under the outer-space vacuum must be created by ejecting own mass backwards. A rocket is the 'engine' to achieve that, although it may simply be a gas reservoir with a hole (like when an inflated balloon-toy is released open-mouth). Other means of spacecraft propulsion without mass ejection can be conceived, by making use of environmental material and electromagnetic flows in outer space (e.g. solar- sail propulsion), or the ejection of electromagnetic radiation (a flow of energy without rest-mass but with momentum), but the forces involved are too small for present applications. Space propulsion is needed for launching from a planet surface to orbit (suborbital flights included), orbit acquisition and orbit keeping against perturbations, orbit changes (including interplanetary transfers), deorbiting (descent and landing on the surface of a planet or moon), and attitude control in all phases of space flight (launch, orbiting, and deorbit). The first rocket theory is due to K.E. Tsiolkovsky (a Russian teacher, reader of Jules Verne's 'From Earth to the Moon', who developed it in 1880s and published it in 1903). He derived the rocket equation (presented Spacecraft propulsion
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