2. Advanced Spacecraft Propulsion Systems 1 Ted Spitzmiller Advanced Spacecraft Propulsion Systems

3. 2 Exploring the Problem Space travel involves confronting the Genisis Factors: –Time, Force, Distance, and Mass Large quantities of equipment, people and consumables Must be accellerated Over limited periods of time To travel great distances

4. Advanced Spacecraft Propulsion Systems 3 Parts of the Problem Propelling the spacecraft –Getting the spacecraft to LEO –Accellerating to escape velocities Available materials (lunar mining) Generating electricity Recycling consumables –water –oxygen –Food

5. Advanced Spacecraft Propulsion Systems 4 The Solution Great distances involved in traveling to the outer limts of the solar system (and beyond) demands new sources of energy far greater than can be obtained from chemical systems for upper stages and for the ‘cruise’ period.

6. Advanced Spacecraft Propulsion Systems 5 Aerospike Engines Conventional chemical propulsion rockets have limited energies (430 Isp) Aerospikes technique seeks to improve the efficiency. Provide “Single Stage to Orbit” (SSTO) Lockheed Martin X-33 Venture Star

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9. 8 Ramjet Uses air ‘rammed’ into its intake by speed of vehicle and sprayed with fuel. On ignition, expanding combustion ‘pushes’ (Newton’s third law) against ‘wall’ of incoming air to provide thrust. Ramjet requires initial movement through air to get required volume of intake to begin productive combustion—typically a speed approaching Mach 1. Second conceptual shortcoming –loses efficiency above Mach 6, combustion process defeated by shockwave of incoming air. Ramjet performs best at a specific altitude for which its intake has been configured.

10. Advanced Spacecraft Propulsion Systems 9 Supersonic Combustion Ramjet; Scramjet Improve ability to accelerate heavy payloads to LEO. Most advanced propulsion units are relatively low-thrust and cannot get themselves into orbit. Need to use oxygen in Earth’s atmosphere to reduce weight of propellants carried during the early part of powered flight (Pegasus) Jet engine limited to speeds of up to Mach 3— the top speed of the SR-71.

11. Advanced Spacecraft Propulsion Systems 10 X-43 SCRAMJET Modified ramjet that uses supersonic combustion of hydrogen fuel Supersonic Combustion ramjet unmanned X-43 achieved a world-record Mach 10 flight for an air-breathing vehicle in November 2004. parallel development project by (DARPA) and the (ONR) successfully flew a hypersonic scramjet-powered vehicle in December 2005. first free flight of a scramjet-powered vehicle using conventional JP-10 liquid hydrocarbon jet fuel. explore speeds up to Mach 10.

12. Advanced Spacecraft Propulsion Systems 11 Ion; Plasma Electronic propulsion EP Very promising technology Goddard metioned 1906 Tsiolkovsky in 1911, “It is possible that in time we may use electricty to produce a large velocity for the particles ejected from a rocket device”. Popular with science fiction writers Uses charged particles— nucleus of an element that lost or gained a net charge of electrons.

13. Advanced Spacecraft Propulsion Systems 12 Ion thruster - EP Beams of accelerated charged particles High velocities (300,000 fps vs 16,000 fps) High Specific Impulse (3000 seconds). Uses much smaller reaction mass for power generated compared to chemical rockets Much lower volume than chemical engines –thrust derrived measured in ounces not 100,000 of pounds. –High efficiency reduces propellant mass by up to 90 percent Current energy sources tens of kilowatts Current technology provide only extremely modest forces resulting in milli-G accelleration. Not practical for initial take-off from the Earth.

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15. Advanced Spacecraft Propulsion Systems 14 Primary use On-orbit attitude control Station keeping Long duration missions to outer planets – engine provides power for weeks or months at a time.

16. Advanced Spacecraft Propulsion Systems 15 Developed in the 1960’s by NASA Thrust generated by reactive force (Newton’s third law) of electrically repelling ions. Engine requires –a significant souce of electrical power (nuclear power) –quanitity of a fuel (argon or xenon) Current EP produce about 6-pounds of thrust for each million watts of power. –EPs referred to more by their electrcal power consumption than by thrust produced.

17. Advanced Spacecraft Propulsion Systems 16 Solar Electric Propulsion Technology Application Readiness (NSTAR) 1995 first ion engine as primary propulsion in a deep space mission. 200 pounds of xenon propellant, 20 months of continuous thrusting, Accelerated 1,000 pound spacecraft by 10,000 mph.

18. Advanced Spacecraft Propulsion Systems 17 Ion Powered NSTAR Spacecraft

19. Advanced Spacecraft Propulsion Systems 18 Xenon Ion Propulsion System Japanese Space Agency's Hayabusa spacecraft powered by two xenon ion engines. Rendezvoused with asteroid ‘Itokawa’ and performed station keeping with it for several months.

20. Advanced Spacecraft Propulsion Systems 19 Electron Cyclotron Resonance (ECR) Thruster called the High Power Electric Propulsion, or HiPEP. Consumes 20-50 kW of power Produces a Specific Impulse of 6000-9000 seconds. Goal is to achive a practical application unit by 2008.

21. Advanced Spacecraft Propulsion Systems 20 Ion engines offer significant utility But… Lacking dramatic break-throughs in electrical power generation in space, too limited in thrust generation for very large spacecraft.

22. Advanced Spacecraft Propulsion Systems 21 Nuclear Thermal Rockets — NTR Working fluid (hydrogen) heated to high temperatures by nuclear reactor Efficiency typically twice that of chemical engines. Shuttle’s SSME 420 seconds Isp — NTR 800 to 1200 seconds

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24. Advanced Spacecraft Propulsion Systems 23 NTR Categorized by Reactor Construction Solid-core engines only for upper-stages –weight of flight ready reactor would probably not achieve a thrust-to-weight ratio of 1:1 –unable to overcome the weight of the rocket at launch.

25. Advanced Spacecraft Propulsion Systems 24 Gas Core Reactor –More complex but efficient –Similar to liquid-core design –Fuel placed in containers ‘float’ inside the working fluid (hydrogen or water)

26. Advanced Spacecraft Propulsion Systems 25 ‘Liquid-core’ Engines –Operated at temperatures beyond melting point of fuel and provide Isp in the range of 1300 to 1500 seconds. –Greater efficiencies achieved by mixing nuclear fuel with working fluid –Allows nuclear reaction to take place in liquid mixture itself. –Nuclear fuel not retained, but discharged resulting in large quantities of radioactive waste –Practical only well outside the Earth's atmosphere.

27. Advanced Spacecraft Propulsion Systems 26 Only ‘solid-core’ Actually Tested Atomic Energy Commission’s Project Rover, begun in 1956. Kiwi first NTR tested in July 1959 concluded in 1964 –Not a flight rated reactor (thus its name). Larger reactor Phoebus fired in June 1965 for over 10 minutes.

28. Advanced Spacecraft Propulsion Systems 27 Atomic Energy Commission’s Project Rover, begun in 1956

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30. Advanced Spacecraft Propulsion Systems 29 NERVA (Nuclear Engine for Rocket Vehicle Applications). 75,000 lb. thrust for upper stages of Saturn V. Cancelled in 1972 –NASA abandoned manned mission to Mars. –Space race assumed lower priorties in 1970’s –Significant safety issues became parmount. –Dispersal of radioactive material should a launch fail catastophically.

31. Advanced Spacecraft Propulsion Systems 30 Prometheus Project 2003, ‘Nuclear Systems Initiative’, –‘Bimodal’ uses reactor to create electrical power when not being used to produce thrust. –‘Tri-modal’ provides an afterburner-like operation liquid oxygen (LOX) injected into exhaust nozzle for increased thrust.

32. Advanced Spacecraft Propulsion Systems 31 Project’s Objectives Provide both forms of spacecraft power systems –electrical power for ion engines –spacecraft electrical power. NASA evaluating a scaled down system Prometheus budget reduced from $430 million to $100 million in 2006, Nuclear energy still meeting with opposition, Represents most powerful energy producing capability in mankind’s possession.

33. Advanced Spacecraft Propulsion Systems 32 Mass Drivers Exotic means of escaping the Earth’s gravity. Simplest of electronic mechanisms—a linear electric motor. –Conventional electric motor uses magnetic lines of flux to generate a rotating motion. –Mass driver uses ‘in-line’ arrangement of ‘stator’ component of motor rather than circular; –An electromagnetic catapult.

34. Advanced Spacecraft Propulsion Systems 33 Two Design Categories Low-acceleration applications include magnetic levitation transportation systems implemented in futuristic rail lines (18 mile segment built in Shanghai with speeds up to 270 mph) High-acceleration applications directed towards weapons that hold promise for spacecraft. Relatively short segment of linear accellerator propels a mass to high velocity to orbital or escape velocity. Electrical energy expended in such as device is significant

35. Advanced Spacecraft Propulsion Systems 34 Mass Driver Problem Typical Electrical Generators not sufficient. Capacitor banks would be extremely large and not practical. Possible use of ‘homopolar’ generators –large conducting flywheel spun up to a high speed over a long period of time (hours or even days) in a magnetic field. –Commutator energized to convert kenetic energy of spinning mass into electricity generated by magnetic lines of flux. Efficiencies of mass driver relatively poor but use of superconducting coils could increase by 50%. Isp 3000 seconds but efficiencies drop off at higher velocities. No theoretical limits to size of a mass driver

36. Advanced Spacecraft Propulsion Systems 35 Future of Mass Drivers Effective for relatively small payloads of up to one ton. Earth’s atmosphere and gravitation limit application Hybrid application uses mass driver for an initial accelleration and then a ‘second stage’ such as nuclear power. Mass driver on moon more practical. –Electrical energy from solar arrays or reflectors Nuclear power for deep space missions.

37. Advanced Spacecraft Propulsion Systems 36 Beam Power; You Can Leave Home Without It Virtually all propulsion systems considered require that mass (fuel) be carried along (or picked up along the way) during the journey to provide for Newton’s third law. For high velocity flight, this imposes a significant weight penalty for some forms of propulsion.

38. Advanced Spacecraft Propulsion Systems 37 Beam Powered Spacecraft Source of propulsive mass remains behind Only a high intensity beam of energy is directed to spacecraft. Energy is converted into a reactive force by the spacecraft.

39. Advanced Spacecraft Propulsion Systems 38 Solar Energy Stream of protons ejected from Sun by fusion process. Solar sail — a large expanse of light weight material unfurled in space acts like a traditional ‘wind’ sail of a boat. Mass of protons impacting on sail provides reactive force, moving the sail (spacecraft) away from Sun. Positioning sails relative to beam of protons, ‘vectors’ desired course as a sailing ship ‘tacks’ with the wind. Because of relatively small force of each proton, a very large sail would be needed— many square miles.

40. Advanced Spacecraft Propulsion Systems 39 Sun’s Radiant Heat Create a high working temperature in a fluid. Use to drive a turbine for generating electrical power –used in an ion drive –fluid recovered for reuse However, both solar sail and radiant heat collector become less efficient as spacecraft moves into outer solar system Sun energy dissipates to unusable level towards the outer planets

41. Advanced Spacecraft Propulsion Systems 40 Directed Beam Energy Use directed beam of energy –laser light –microwave radiation. Provides high concentration of energy. Power generating station in space (or on Moon) –Atmosphere would attenuate the beam. Cost of generating intense beam dictates that system part of a high use corridor –Commuting between two points in the solar system.

42. Advanced Spacecraft Propulsion Systems 41 Warp Drive and Anti-gravity Requires breakthrough in physics to understand principle

43. Advanced Spacecraft Propulsion Systems 42 Summary Chemical propulsion systems (LH2) and storable fuels, will be primary means to LEO for the next 25-50 years Travel to Other Galaxies (intergalactic/interstellar) requires a complete paradeigm shift of the Genesis Factors