Post on 26-Mar-2018
Spacecraft Design :Propulsion Systems
Olivier Leonard
University of LiegeTurbomachinery Group
October 2009
October 2009 à áá à ' n ? 6
Spacecraft systems
ControlBalistic
PayloadPropulsion
Telecommunications
Structures
Energy
October 2009 Slide 1/33 à áá à ' n ? 6
Spacecraft propulsion systems
n Introduction : missions and performance
n Thrust generated by a rocket engine
n Specific impulse and velocity increment
n Cold gas systems
n Mono- and bi-propellant systems
n Solid propellant systems
n Electric systems
October 2009 Slide 2/33 à áá à ' n ? 6
Rocket engines : various missions and performance
n From the ground to low orbit⇒ ∆V ≥ 9500 m/s
n From low orbit to high orbit⇒ ∆V ≈ 4200 m/s
n From high orbit to Mars⇒ ∆V ≈ 3400 m/s
n Escaping solar system requires an additional ∆V ≈ 8500 m/s
n On orbit control and positioning⇒ ∆V ≈ 20...400 m/s
n Launch vehicles engines providing huge thrust levels for extended periods(200 tons during 8 min for the SSME)
n Apogee and perigee engines providing moderate thrust levels(a few tons during a few seconds)
n On orbit control and positioning providing small thrust levels(mN to 10 N, pulsed operation for the whole vehicle lifespan)
October 2009 Slide 4/33 à áá à ' n ? 6
Rocket engines : Thrust, power, acceleration
T = qmVe = Mαg0 P =1
2qmV
2e =
1
2TVe
P
M=
αg0
2Ve
October 2009 Slide 6/33 à áá à ' n ? 6
Rocket engines : non chemical engines
n An external source (nuclear, solar energy) provides energy to the propellant
n The propellant may be directly or indirectly heatedand accelerated through a nozzle
n Ionized propellants are accelerated through an electrical field
n Electric rocket engines have high exhaust velocities but low specific power
n Nuclear rocket engines offer high power levels but have limited exhaustvelocities
n Solar energy is unlimited but offers a very low effective power density
⇒ Restricted to small accelerations : orbit control, spacecraft attitudes
October 2009 Slide 7/33 à áá à ' n ? 6
Rocket engines : chemical engines
n A chemical reaction provides the energy
n Liquid propellants are the most energetic
n Turbopumps pressurize the combustionchamber but limit the available power
n Solid propellant engines (boosters) are simpleand compact but are energy limited
n Chemical engines are powerful but provide ratherlow Ve due to chemical and temperature limitations
n Well suited for launch vehicles
n Instabilities (chocks in the nozzle, pogo effects)
October 2009 Slide 8/33 à áá à ' n ? 6
Thrust generated by a rocket engine
Thrust is the result of all internaland external forces due to pressureand viscous effects developedby the fluid on all componentsof the the engine
T =
ZΣ
p nfpax dS − F
fpv,i − F
fpv,e
T =
ZΣi
(pi − pa) nfpax dS +
ZΣe
(pe − pa) nfpax dS − F
fpv,i − F
fpv,e
At the test bench :
T =
ZΣi
(pi − pa) nfpax dS − F
fpv,i
October 2009 Slide 9/33 à áá à ' n ? 6
Thrust generated by a rocket engine
Momentum balance yields(a contribution is positivewhen exerted from left to right) :
−Fpfv,i − (pe − pa)Ae +
ZΣi
(pi − pa) npfax dS = (ρV
2A)e
reulting in
T = qmVe + (pe − pa)Ae Tsl = qmVe + (pe − psl)Ae
Th = Tsl + (psl − ph)Ae T0 = Tsl + pslAe
October 2009 Slide 10/33 à áá à ' n ? 6
Specific impulse
Effective ejection velocity C
T = qmC C = Ve +
»pe − pa
qm
–Ae = Ve
»1 +
1
γM2e
„1−
pa
pe
«–
Specific impulse
Isp =
Z τ
0T (t)dtZ τ
0qm(t)dt
≈T
qm= C [m/s]
Isp =
Z τ
0T (t)dt
g0
Z τ
0qm(t)dt
≈T
g0 qm=
C
g0[s]
October 2009 Slide 11/33 à áá à ' n ? 6
Velocity increment
Force balance
mdV
dt= T −D −mg = C qm −D −mg
dV = −Cdm
m−
D
mdt− g dt with dh = V dt
Velocity increment
∆V
C= ln
m0
m0 −mp−
Z τ
0
D
Cmdt−
Z τ
0
g
Cdt
Neglecting gravity and viscous effects :
∆V
C= ln
m0
m0 −mp
m0
m0 −mp= e
∆V/C
October 2009 Slide 13/33 à áá à ' n ? 6
Secondary spacecraft propulsion
Typical functions of a secondary propulsion system:
n final orbit acquisition from the orbit established by the launch vehiclen orbit controln attitude control
Main options:
n cold gas systemsn monopropellant hydrazinen bi-propellant systemsn solid propellantsn electric systems
October 2009 Slide 14/33 à áá à ' n ? 6
Cold gas systems
n Cold gas systems are based oniinert gas : nitrogen, argon, freon, propane
n Typical thrust level : 20 mN
n Typical specific impulse : 50 s
n Typical functions : high pointingaccuracies (0.1 degree)
n Gas is stored at high pressureand fed to small thrusters
n Propellant are selected for their storagesimplicity and plume compatibilitywith sensitive surfaces
October 2009 Slide 15/33 à áá à ' n ? 6
Monopropellant and bi-propellant systems
n Hydrazine is stored as a liquid pressurized by an inert gas (N2 or He)
n Storage properties are similar to water
n Anhydrous hydrazine N2H4 decomposes through an exothermic process
n Decomposition is enhanced by a resistively heated metal catalyst(Pt-Ir-Al2O3)
n Hot gas products N2, H2 and NH3 expands through a nozzle
October 2009 Slide 16/33 à áá à ' n ? 6
Monopropellant and bi-propellant systems
n Typical thrust level > 10 N
n Typical specific impulse : 200 s
n Typical functions : attitude control and station keeping(geostationary spacecrafts)
n Bi-propellants such as N2O4/MMH offer higher performance (Isp = 300)and mass reductions
October 2009 Slide 17/33 à áá à ' n ? 6
Monopropellant systems
n Astrium CHT
n Thrust : 1 N
n Specific impulse : 210 s
n Propellant : Hydrazine
n Burn time : 50 hours
n Length : 17 cm
n Attitude control, orbit control and station keepingof small satellites and deep space probes
n Herschel, Globalstar
October 2009 Slide 18/33 à áá à ' n ? 6
Monopropellant systems
n Astrium CHT
n Thrust : 400 N
n Specific impulse : 220 s
n Propellant : Hydrazine
n Burn time : 30 minutes
n Length : 32 cm
n Attitude control
n Arianne V
October 2009 Slide 19/33 à áá à ' n ? 6
Bipropellant systems
n Astrium S
n Thrust : 10 N
n Specific impulse : 291 s
n Fuel : MMH
n Oxidizers : N2O4
n Attitude control and orbit control of large satellitesand deep space probes
n Venus Express, Arabsat
October 2009 Slide 20/33 à áá à ' n ? 6
Bipropellant systems
n Astrium S
n Thrust : 400 N
n Specific impulse : 318 s
n Fuel : MMH
n Oxidizers : N2O4
n Apogee orbit injectionof GEO satellitesand for planetary orbitmaneuvers of deep spaceprobes
n Venus Express, Artemis
October 2009 Slide 21/33 à áá à ' n ? 6
Solid propellant systems
n Typical mission : from apogee of an elliptical transfer orbit to a circulargeostationary orbit, ∆V ≈ 2000 m/s
n Example : Intelsat V, on station mass ≈ 1000 kg, fuel mass ≈ 900 kg,engine mass ≈ 1000 kg
n Typical performance : 70 kN during 40 s, Isp ≈ 280 s
October 2009 Slide 22/33 à áá à ' n ? 6
Solid propellant systems
n ATK Star
n Thrust : 27 kN
n Specific impulse : 288 s
n Burn time : 34 s
n Length : 1.3 m
n Mass : 361 kg
n Apogee motor
n GOES, GPS
October 2009 Slide 23/33 à áá à ' n ? 6
Electric systems
n Total spacecraft mass M = Mpay + Mpp + Me
n Power plant output W = qmV 2e /2
n Power plant output and weight are proportional Mpp = β W
n Exhaust mass flow is constant Me = qm tb
Me =M −Mpay
1 +βV 2
e
2tb
Mpp =M −Mpay
1 +2tb
βV 2e
Vc =
s2tb
β
∆V
C≈
∆V
Ve= ln
266641 +
„Ve
Vc
«2
Mpay
M+
„Ve
Vc
«2
37775October 2009 Slide 24/33 à áá à ' n ? 6
Electric systems
n For any payload the optimum is close to Ve ≈ Vc
n Low propellant mass requires high Ve, high Vc, long burn time and highspecific power
n Example :l payload ratio Mpp/M = 0.5l orbit raising maneuver with ∆V = 5000 m/sl Ve ≈ Vc ≈ 17000 m/sl electric engine powered by solar arrays : β ≈ 20 kg/kWl burn time tb ≈ 30 daysl thrust acceleration α ≈ ∆V/tb ≈ 2 10−4 g0
October 2009 Slide 26/33 à áá à ' n ? 6
Electric systems : the resistojet
n The propellant is heated bypassing over a (tungsten)heating element
n Propellant : H2 (difficult to store),N2, NH3 (corrosive),hydrazine, teflon
n Exhaust velocity is limited bytemperature to ≈ 10 km/s
n Typical thrust : 1 N
October 2009 Slide 27/33 à áá à ' n ? 6
Electric systems : electrostatic thrusters
n A cathode extracts electrons from the propellant which is ionized
n The ions are accelerated by an electric field
n Propellant : Hg, Ar, Xe
n Exhaust velocity is limited by temperature to ≈ 10 km/s
n Typical performance : T = 10 mN, Ve = 30 km/s
October 2009 Slide 28/33 à áá à ' n ? 6
Low-Thrust systems
n Astrium RITA
n Thrust : 150 mN
n Specific impulse : 4000 s
n Propellant : Xenon
n Beam voltage : 1200 V
n Brun time : > 20000 h
n Mass : 154 kg
n Station keeping, orbit transfer,deep space trajectories
n Artemis
October 2009 Slide 30/33 à áá à ' n ? 6
TOC
n Spacecraft systems v
n Spacecraft propulsion systems v
n Flight envelope v
n Rocket engines : various missions and performance v
n Rocket engines : classification v
n Rocket engines : Thrust, power, acceleration v
n Rocket engines : non chemical engines v
n Rocket engines : chemical engines v
n Thrust generated by a rocket engine v
n Specific impulse v
n Velocity increment v
n Secondary spacecraft propulsion v
n Cold gas systems v
n Monopropellant and bi-propellant systems v
n Solid propellant systems v
n Electric systems v
n Electric systems : the resistojet v
n Electric systems : electrostatic thrusters v
October 2009 Slide 33/33 à áá à ' n ? 6