Download Rocket Groups: Chemical versus Electrical

CHEMICAL vs. ELECTRIC ROCKET PROPULSION
CHEMICAL
•
Always thermal
•
ELECTRIC
Some are thermal (resistojet, arcjet)
– Some are non-thermal (ion, hall effect, MPD)
•
Energy / propellant initially together
•
Energy source / propellant separate initially
•
Energy source is combustion
•
Energy source onboard or external
– Solar, Nuclear
– Energy conversion equipment onboard (heavy)
•
Energy limited
– Best propellants, Ue ~ 4,500 m/s
– Isp ~ 100-500 s
– Thrust ~ 0.1 N-10 MN
•
‘Unlimited energy’
– Very high Ue (10,000-100,000 m/s)
– Isp ~ 1,000-10,000 s
– Thrust ~ mN-N
•
Propellant and Energy decrease with time
•
•
Propellant decreases with time
Energy remains constant with time
•
High Thrust, Low Isp, High mdot, Fast ao, Short tburn
– Thrust independent of tburn
– tburn ~O(seconds)
•
Low Thrust, High Isp, Low mdot, Slow ao, Long tburn
– Thrust inversely proportional to tburn
– tburn ~O(days-months-years)
•
Earth to orbit missions, low DV
•
Station keeping, deep space exploration, high DV
Origin of Thrust: Eject Stored Mass Backwards → Use Reaction Force to Propel Vehicle
Rocket Equation is Always True