Powered Space Flight

Transcription

1 Powered Space Flight KOIZUMI Hiroyuki ( 小泉宏之 ) Graduate School of Frontier Sciences, Department of Advanced Energy & Department of Aeronautics and Astronautics ( 基盤科学研究系先端エネルギー工学専攻, 工学系航空宇宙工学専攻兼担 )

2 Scope of Today s Lecture Purpose of today s lecture to learn Powered Space Flight using electric propulsion by actual orbit examples Contents 1. Introduction 2. Fundamentals of orbit 3. Examples of powered flights 3.1 HAYABUSA 3.2 DAWN 3.3 Boeing 702SP

3 Scope of Today s Lecture Purpose of today s lecture to learn Powered Space Flight using electric propulsion by actual orbit examples Contents 1. Introduction 2. Fundamentals of orbit 3. Examples of powered flights 3.1 HAYABUSA 3.2 DAWN 3.3 Boeing 702SP

4 What is Powered Space Flight?

5 How to change orbits? Adding energy (or velocity) changes the orbits JAXA Energy: depends on the mass Velocity: as specific energy Velocity increment, Delta-V (ΔV), is the index of Powered Space Flight

6 Powered space flight is flight using a propulsion device to control the trajectory by ΔV maneuvers

7 Propulsion is a device to provide ΔV

8 Chemical & Electric Propulsion Propulsive device = Device exhausting propellant by adding energy on it = Energy converter (from any source to kinetic energy) Chemical propulsion Chemical E (inside propellant) Kinetic E Exhaust V:1 4 km/s Electric Propulsion Electrical E (Solar, Nuclear) Kinetic E Exhaust V:10 50 km/s

9 Chemical & Electric Propulsion ΔV: 4 5 km/s M Propellant V M Payload exp 1 v Exhaust Chemical propulsion Exhaust V:3 km/s Propellant = % Payload 1 ton Car + 3 ton gas Electric Prouplsion Exhaust V:30 km/s Propellant Payload = 14 18% 1 ton Car kg gas

10 Merit of EP 1) Saving propellant Low cost by decreasing S/C weight High quality by increasing equipment

11 Merit of EP 2) Excessive propellant Chemical propulsion Your journey (orbit) is pre-fixed Electric propulsion You can freely change the journey as you do in the journey on the ground Flexibility & Redundancy are increased

12 My opinion: True powered space flight needs Electric Propulsion

13 Scope of Today s Lecture Purpose of today s lecture to learn Powered Space Flight using electric propulsion by actual orbit examples Contents 1. Introduction 2. Fundamentals of orbit 3. Examples of powered flights 3.1 HAYABUSA 3.2 DAWN 3.3 Boeing 702SP

14 Motion in space on the ground in space JAXA Free-form path governed by celestial bodies

15 Equation of Motion Position of the S/C Standard gravitational parameter: GM d 2 dt r = μ F t r + 2 r2 m Thrust Massive body M>>m r M F(t) Spacecraft m : thrust

16 Two-body Problem w/o thrust Three types Ellipse Parabola Hyperbola

17 Orbit Terminology Apoapsis Periapsis Focus Peri Apo Sun Perihelion Aphelion Earth Perigee Apogee Semi-minor axis Moon Perilune Apolune ea a: Semi-major axis e: Eccentricity

18 Initial velocity and its orbit V: small V: middle Ellipse (from apoapsis) Circle V: large Ellipse (from periapsis)

19 Typical trajectory by CP Orbital period >> Thrusting time JAXA Impulse approximation Connect the analytical solutions of I.C. problem of Momentum eq.

20 Typical Trajectories of EP ; Spiral Tangential thrust Gradual orbit raising/lowering Spiral orbit T = 25 mn Msc = 500 kg 1000 days

21 Typical Trajectories of EP ; Deform. Constant Thrust Orbit raising and lowering Eccentricity change Earth gravity assist Ellipse to/from Circle T = 25 mn Msc = 500 kg 1000 days

22 Scope of Today s Lecture Purpose of today s lecture to learn Powered Space Flight using electric propulsion by actual orbit examples Contents 1. Introduction 2. Fundamentals of orbit 3. Examples of powered flights 3.1 HAYABUSA 3.2 DAWN 3.3 Boeing 702SP

23 HAYABUSA JAXA Mission: Sample return of a small asteroid Feature: Return trip using electric propulsion

24 ITOKAWA (small asteroid) ITOKAWA; the asteroid JAXA 500 m 35,000,000 ton Orbit specifications Semi-major axis: Aphelion: Perihelion: Eccentricity: Inclination: 1.32 AU 1.70 AU 0.95 AU deg

25 HAYABUSA s journey Delta-V for Earth Gravity Assist Delta-V for rendezvous with ITOKAWA ITOKAWA touch down Some troubles Delta-V for reentry to the Earth

26 Trajectory from Earth to ITOKAWA ITOKAWA Earth HAYABUSA Sun Departure (2003, May 9 th ) Earth gravity assist (2004, May 19 th )

27 In the case of free flight HAYABUSA was launched with hyperbolic excess velocity: 3.2 km/s Sun orbital velocity: 29.8 km + Initial ΔV 3.2 km/s Earth Departure Spacecraft Unit is AU (astronomical unit) 1 AU = Sun-Earth distance = 150 Million km

28 In the case of free flight HAYABUSA orbit on Earth Sun direction Spacecraft does not meet with the Earth Spacecraft Unit is AU (astronomical unit) 1 AU = Sun-Earth distance

29 In the case of free flight HAYABUSA orbit on Earth With thrust (18 mn average) Sun direction Thrust off Thrust on Spacecraft meets with the Earth Gravity assist

30 Real HAYABUSA orbit JAXA

31 Dec. 3 rd Oct. 29 th Oct. 2 nd Sep. 3 rd Aug. 4 th July 29 th June 24 th in 2003 JAXA

32 Earth Gravity Assist Required accuracy is Position: 1 km Velocity: 1 cm/s JAXA Alt km Velocity increment: 4 km/s

33 Gravity Assist; Principle Moving wall

34 Hyperbolic Trajectory u f = R(θ*)u i Hyperbola θ* Scattering angle Collision parameter b tan 2 * u 2 b u i

35 GA = Velocity Rotation Red arrows: S/C inertial velocity Black arrows: S/C relative velocity Green arrow: Planet inertial velocity u i = v sc,i - V p v sc,f u f u i v sc,i θ* β V p

36 Accurate Trajectory Control for GA Collision parameter: b Scattering angle: θ* Planet scale To get 90 deg scattering b = 4,4000 km (relative V : 3 km/s, Earth) Planet velocity Spacecraft velocity Gravity assist Orbit scale 1 AU = 150,000,000 km Accurate Orbit Control is required

37 Trajectory from Earth to ITOKAWA ITOKAWA Earth HAYABUSA Sun Departure (2003, May 9 th ) Earth gravity assist (2004, May 19 th ) JAXA

38 Toward the ITOKAWA Rendezvous Position & Velocity must be matched Orbits of two objects must be matched

39 Toward the ITOKAWA Earth: 1.00 AU The semi-major axes Hayabusa :1.37 AU (after the GA) Aphelion matching Ion thruster Delta-V : reducing the perihelion (deceleration) ITOKAWA: 1.32 AU

40 Return to Earth Outward journey Rendezvous with ITOKAWA Position & velocity must be exactly matched Homeward journey Reentry to the Earth Only position must be matched Delta-V requirement is lower Troubles

41 Scope of Today s Lecture Purpose of today s lecture to learn Powered Space Flight using electric propulsion by actual orbit examples Contents 1. Introduction 2. Fundamentals of orbit 3. Examples of powered flights 3.1 HAYABUSA 3.2 DAWN 3.3 Boeing 702SP

42 DAWN DAWN by NASA JPL Weight:1250 kg Mission: rendezvous with asteroids Propellant: 400 kg ΔV : 11 km/s (Ion propulsion) NASA NSTAR 90 mn ion thruster 3 kw 3100 s

43 NSTAR ion engine (NASA) Deep Space 1(1998): Flyby of comet Single NSTAR Demonstration of NSTAR (16 k-hours operation) DAWN(2007-): Asteroid probe Three NSTARs NSTAR engine Thrust Isp Power 93 mn 3100 s 2550 W Efficiency 62 % Beam D. 29 cm NASA NASA

44 530 km Vesta The second most massive NASA Ceres The most massive 950 km NASA

45 Spiral orbit raising Earth Vesta Ceres Launch, 2007 Sept. Spiral orbit raising Thrust on Thrust off

46 Spiral orbit raising Tangential thrust to the orbit Assuming the circular orbit E mv m μ r m μ 2 r de dt FV JAXA mμ dr μ V V1 V2 F 2 2 r dt r V F( t t ) / m) ( 2 1 Spiral orbit raising requires ΔV equal to the difference between the initial orbit and the final orbit

47 Let s estimate the thrust of DAWN Spacecraft momentum change = given impulse M SC V FT M SC 1000 kg DAWN wet mass = 1250 kg Xenon propellant = 425 kg V 11.9 km/s T? Get from the orbit and events

48 Phase-1; from Earth to Mars Three thrusting phases 1. Earth departure Mars gravity assist Earth 600 days = Mars GA (Feb 2009) - Launch (Oct 2007) - Mars period/6 687 days

49 Phase-2; from Mars to Vesta Three thrusting phases 2. Mars gravity assist Vestra arrival Earth 550 days = Vesta arv. (July 2011) - Mars GA (Feb 2009) - Mars period/6

50 Phase-3; Vesta to Ceres Three thrusting phases 3. Vesta departure Ceres arrival Earth 950 days = Vesta dept. (July 2012) - Ceres arrv. (Feb 2015)

51 Let s estimate the thrust of DAWN M SC V FT ΔV:11.9 km/s S/C mass (average):1000 kg Thrusting time:2100 days ( ) Estimate: 65 mn Actual: 91 mn John R. Brophy et al.,j. Propul. Power 25(2009)

52 Solar power is decreasing Earth:1 AU Ceres: 2.8 AU Estimated: 65 mn Solar power at Ceres is 1/2.8 2 (= 13%) of Earth Solar power averaged from Earth to Ceres is 57% of Earth Actual: 91 mn 70% Good estimation!

53 Very low power near Ceres Phase 1+2 (Earth to Vesta) Spiral ΔV = 10.4 km/s Period = 1150 days Estimated F = 105 mn Over 90 mn is caused by initial dv & Mars GA Earth Phase 3 (Vesta to Ceres) Spiral ΔV = 1.5 km/s Period = 950 days Estimated F = 18 mn

54 Scope of Today s Lecture Purpose of today s lecture to learn Powered Space Flight using electric propulsion by actual orbit examples Contents 1. Introduction 2. Fundamentals of orbit 3. Examples of powered flights 3.1 HAYABUSA 3.2 DAWN 3.3 Boeing 702SP

55 GEO: Geostationary Earth Orbit 24 hrs/cycle 90 min/cycle Communication satellite Broadcasting satellite JAXA 600 km km

56 Disturbances from Sun and Moon GEO:on equatorial plane Sun, moon, planets: on ecliptic plane Sun and Moon gravity forces are disturbances to GEO S/C

57 North South Station Keeping Maintaining the orbit plane requires ΔV of 50 m/s per year (NSSK: north south stationkeeping) 3 ton+10 year operation Eelectric(3000 s) Chemical (200 s) Propellant: 50 kg Propellant: 850 kg

58 Orbit transfer from GTO to GEO GEO ΔV (GTO GEO) =1500 m/s JAXA GTO: GEO Transfer Orbit (insertion by a rocket)

59 By all EP, mass becomes half ΔV = m/s M sat = 2.0 ton M Propellant M Propellant = 1.9 ton V M exp 1 Sat u e by Chemical M Propellant = 0.14 ton by Electric

60 Disadvantage-1; long time GEO longer time JAXA Time (GTO GEO) CP:half day EP:half year

61 Disadvantage-2; radiation Electron belt Proton belt Passing Van-Allen belt damage to electronics JAXA

62 Scope of Today s Lecture Purpose of today s lecture to learn Powered Space Flight using electric propulsion by actual orbit examples Contents 1. Introduction 2. Fundamentals of orbit 3. Examples of powered flights 3.1 HAYABUSA 3.2 DAWN 3.3 Boeing 702SP