Presentation on theme: "Low-thrust trajectory design ASEN5050 Astrodynamics Jon Herman."— Presentation transcript:
Low-thrust trajectory design ASEN5050 Astrodynamics Jon Herman
Overview Low-thrust basics Trajectory design tools Real world examples Outlook
Low-thrust Electric propulsion –Solar electric propulsion (SEP) –Nuclear electric propulsion (NEP) –SEP is mature technology, NEP not exactly Solar sails –Comparatively immature technology –Performance currently low All very similar from trajectory design stand point
Electric Propulsion About 0.2 Newton About 4 sheets of paper Engine runs for months-years 10 times as efficient Chemical propulsion Up to ~17 000 000 N About 4 000 000 000 sheets of paper Engine runs for minutes
Hall thrusters (University of Tokyo, 2007) Exhaust velocity: 10 – 80 km/s
Why is a higher I SP not always better? (Elvik, 2004)
Implications for optimal trajectories The optimal transfer properly balances Specific impulse Spacecraft power Mission ΔV Unique optimum for every mission ΔV no longer a defining parameter! (arguably: ΔV no longer a limiting parameter)
Trajectory example What is difficult about low-thrust? –Trajectory is “continuously” changing –No analytical solutions –Optimal thrust solution only partially intuitive Specialized, computationally intensive tools required!
Example Method JPL’s MALTO –Mission Analysis Low Thrust Optimization –Originally: CL-SEP (CATO-Like Solar Electric Propulsion) Source: Sims et al., 2006 Forward integration Backward integration Match Points Small impulsive burns Fly by, probe release, etc... (discontinuous state)
MALTO-type tools Optimize... Trajectory Subject to whatever desired trajectory contraints Specific impulse (Isp) Spacecraft power supply Using solar power Using constant power (nuclear) Possible: solar sail size, etc.
Strengths Fast Robust Flexible Optimizes trajectory & spacecraft!
Weaknesses Ideal for simple (two-body) dynamics Limited to low revolutions (~8 revs) –No problem for interplanetary trajectories –~Worthless for Earth departures/planetary arrivals
Electric propulsion developments Boeing Four GEO satellites, 2 tons each Capable of launching two-at-a-time on vehicles as small as Falcon9 Private endeavor ESA/SES/OHB Public-Private partnership One “small-to-medium” GEO satellite Possibly the second generation spacecraft of the Galileo constellation NASA 30kW SEP stage demonstrator (asteroid retrieval?)
Conclusion Electric propulsion rapidly maturing into a common primary propulsion system This enables entirely new missions concepts, as well as reducing cost of more typical missions Very capable trajectory design tools exist, but not all desired capability is available or widespread