SPACECRAFT PROPULSION - KTH

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- 3 -The main features of jet propulsion are:a) LAUNCH PROPULSION for launching rockets with thefollowing characteristics:- high velocity increment capability (7 - 11 km/s)- very high thrust levels (ratio thrust/launch vehicle weight: 1.3)- low fraction of launch vehicle take-off mass for payload (1 - 5%)- powerful chemical rocketsb) SPACECRAFT PROPULSION is characterised in general by itscomplete integration within the spacecraft. Its function is toprovide forces and torques to:- transfer the spacecraft: orbit transfer incl. interplanetary travel- position the spacecraft: orbit control- orient the spacecraft: attitude controlWhile jet propulsion systems for launching rockets are also calledprimary propulsion systems, spacecraft, e.g. satellites, are operatedby secondary propulsion systems.In order to fulfil attitude and orbit operational requirements,spacecraft propulsion systems are characterised in particular by:- low thrust levels (1 mN to 500N) with low acceleration levels,- continuous operation mode for orbit control,- pulsed operation mode for attitude control,- predictable, accurate and repeatable performance (impulse bits),- reliable, leak-free long time operation (storable propellants),- minimum and predictable exhaust plume impingement effect.
- 4 -3 PROPULSION FUNDAMENTALS3.1 Basic Propulsion EquationsThe essence of space propulsion is to modify the velocity vector of aspacecraft either in magnitude or in direction so as to modify theorbit or attitude. However, an isolated body, like a spacecraft, canmodify its momentum only if external forces act on it, since allinternal forces cancel each other in action-reaction pairs. This isexpressed by Newton's law of motion: d(mv)dv dmF m v , (1)dt dt dtUnfortunately, there are no such external forces in space (except veryweak perturbation forces which have to be compensated by thespacecraft onboard propulsion system) and Eq. (1) becomes:dv dmm vdt dt 0(2)Therefore, the only and obvious way out is, that the spacecraft mustbe split up such, that a part of the spacecraft can modify its velocitythrough the effect of action-reaction forces.In fact, this is realised by the ejection of mass in form of propellantfrom the spacecraft. If we assume a spacecraft with a mass m, ejecting propellant with a rate of dm/dt at constant velocity v veatnozzle outlet, Eq. (2) can be written with the action and reactionforces in balance:dv dmm ve(3)dt dt
Page 6 and 7: -iv -Standard NotationsStandard not
Page 8 and 9: - 1 -1 INTRODUCTIONThis booklet sum
Page 12: - 5 -This expresses that the spacec
Page 17 and 18: - 10 -3.2.3 Evaluation of Mass of P
Page 19 and 20: - 12 -With regard to the system-spe
Page 21 and 22: - 14 -According to Fig. 3 and with
Page 23 and 24: - 16 -Historically, chemical propul
Page 25 and 26: - 18 -gases leave the outlet of the
Page 27 and 28: - 20 -The vaporising liquid system
Page 30 and 31: - 23 -Further, for vaporising liqui
Page 32 and 33: - 25 -ConclusionAlthough of moderat
Page 34 and 35: G- 27 -4.2.3 MonopropellantMonoprop
Page 36 and 37: - 29 -System-specific Impulse, I ss
Page 38 and 39: - 31 -Table 4: Ranges of typical Pr
Page 40 and 41: - 33 -4.2.4 BipropellantBipropellan
Page 42 and 43: - 35 -management devices), propella
Page 44 and 45: - 37 -From Eq. (41) it is obvious t
Page 46 and 47: - 39 -4.2.5 General System Design C
Page 48 and 49: - 41 -System-specific Impulse, I ss
Page 50 and 51: - 43 -4.3 Electric Propulsion4.3.1
Page 52 and 53: - 45 -To the above described catego
Page 54 and 55: - 47 -4.3.2 Propulsion System Desig
Page 56 and 57: - 49 -Fig.17, has to be considered
Page 58 and 59: - 51 -The term of an optimal exhaus
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- 53 -resulting in a maximum value
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- 55 -Table 8 notes the differences
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- 57 -5 PROPULSION SYSTEMS SELECTIO
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- 59 -m PS/m S/C1,0I ssp=193 Ns/kg(
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- 61 -In considering the merits of
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- 63 -Table 11: Survey: Typical Can
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- 65 -6.1 Potential Improvement of
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- 67 -6.2 Potential Improvement of
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- 69 -6.3 New ApproachesNew approac
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- 71 -Extensive research has been p
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- 73 -8 MISSION SURVEILLANCE OFPROP
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- 75 -[9 W. Inden; “Development R
Page 84:
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SPACECRAFT PROPULSION - KTH

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