Solar-Electric Ion Engines Using Molecular Nanotechnology

Transcription

1 Solar-Electric Ion Engines Using Molecular Nanotechnology Dr. Thomas L McKendree Engineering Fellow 4 May 2013 Copyright 2013 Raytheon Company. All rights reserved. Customer Success Is Our Mission is a registered trademark of Raytheon Company.

2 Agenda Overview of Molecular Nanotechnology (MNT) and Application to Space Transportation Simple MNT Solar Power Complex and Most Advanced MNT Solar Power Concentrator Assembly Mass Total Mass Specific Power Solar-Electric Ion Engine System Performance References and Questions 5/19/2012 2

3 Technology Levels No MNT Current Technology Simple MNT Any Stable Simple Pattern of Atoms Complex MNT Any Molecular Machinery, Except Molecular Manufacturing in the Field Most Advanced MNT Any Molecular Machinery Molecular Manufacturing in the Field Enables Bootstrapping, Self-Repair, and Very Low Manufacturing Costs TL McKendree, 20 APR 01

4 Performance of Technology Levels No MNT Simple MNT Complex MNT Most Advanced MNT Material Strength (Pa) c: 9.3 x 10 8 t: 4.0 x 10 9 c: 5.0 x t: 4.5 x Material Density (kg/m 3 ) c: 4540 t: 971 c: 3510 t: 1300 Vehicle Cost $5000/kg of dry, empty vehicle mass $0.5/kg of GLOM Very Small Machinery No Yes Systems Capable of Self Repair No Yes Safety Factor Manufacturing Doubling Period (Given Proper Inputs) (Not Used) ~1 Hour TL McKendree, 20 APR 01

5 Emitter Accelerating Electrode Some System Architectures for Space Transportation All Other Mass Propellant Rockets Payload V V=0 0 J q M 50 µm x a Ion Engine Accelerates Charged Ions Across a Voltage Gap Small, High Specific TL McKendree, 30 OCT 00

6 More MNT-Based System Architectures for Space Transportation Solar Sail Skyhook Throw Trajectory Tower Rotating Tether (Not to Scale) Planetary Orbit [Optional] Synchronous Height Planet TL McKendree, 30 OCT 00

7 Applications of Technology Levels to Space Transportation TL McKendree, 20 APR 01 Most Advanced MNT Complex MNT Simple MNT No MNT High Strength to Mass Very Small Machinery Very Low Cost Manufacturing Robust On-Board Repair Allows Long Term Use of: Unshielded Diamond Low Design Margins Current Capabilities Low Parasitic Mass High Payload Low Cost per Payload Low Vehicle Costs Very Low Cost per Payload Chemical Rockets Ion Engines Solar Power High Specific Power Small, Steered Reflectors for Higher Specific Power Highest Specific Power More Specific Power = More Performance Skyhooks, Towers and Tethers Much Lighter Structures Very Much Lighter Structures Lighter Sails = Higher Acceleration Solar Sails

8 Simple MNT Performance Specific Power Feasible with MNT-Based Solar Panels The key to high-performance from ion-engines is to have very high specific power {see Equation (19)}. GaInP/GaAs tandem solar cells can achieve ~25% efficiency in vacuum at one solar constant of light, with an active thickness of ~5 µm (Bertness et al. 1996). GaAs has a density of kg/m3, yielding a specific power of ~13 kwe/kg at 1 AU, if only the active thickness of the solar cell is provided. With a safety factor for overhead, ~10 kwe/kg should be achievable with Simple MNT, given the ability to build simple structures to atomic precision, and thus provide a thin sheet composed almost entire of the active layer. M c Kendree, Thomas Technical and Operational Assessment of Molecular Nanotechnology for Space Operations, Ph.D. dissertation, University of Southern California, p /19/2012 8

9 How to Get High Specific Power If one had a design goal of 1 MWe/kg at a solar distance of 1 astronomical unit (AU), where the solar constant is 1370 W/m 2, the mass per unit area budget would be kg/m 2. If the entire system were made of diamond, which has a density of 3510 kg/m 3, then the allowable solid thickness would be less than 400 nm. If the solar cell efficiency is 25%, this drops to under 100 nm of allowable thickness. To develop a design with such low mass per unit area, one powerful technique suggested in (Drexler 1995b) is "The key idea is to focus sunlight to 1,000 times normal intensity." In other words, trade higher mass per unit area solar cells for lower mass per unit area reflectors. By comparison, lenses (as used on Deep Space 1 (JPL 1999)) would have too much mass per unit area. M c Kendree, Thomas Technical and Operational Assessment of Molecular Nanotechnology for Space Operations, Ph.D. dissertation, University of Southern California, p /19/2012 9

10 Baseline MNT Solar Concentrator 50 µm Radius Primary Mirror 80 µm Radius Cooling Disk Struts for Secondary Mirror Not Shown TL McKendree, 20 APR 01

11 Cross Section of the Basic Optical Design All distances in mm [10-6 m] 5/19/

12 kg Primary Mirror Mass for Baseline Solar Concentrator 6.00E E E-12 1 m/s2 10 m/s2 100 m/s2 3.00E E E E00 Self Supporting Al Solid Diamond Diamond Spaceframe Reflective Surface (40 nm Al) TL McKendree, 20 APR 01

13 Mass of solar cell panels (in kg) per Solar Concentrator Structural Material Aluminum and Solid Diamond Carbon Fibre Diamond Spaceframe Acceleration Load 10 m/s2 10 m/s2 100 m/s2 Solar Concentrator Assembly 4.39 x x x Wiring 0.12 x x x Support Plates 0.47 x x x Support Beams ~0.00 x ~0.00 x ~0.00 x Total 4.98 x x x Specific Power at 1 AU (in We/kg) x x x /19/

14 Specific Power of MNT Solar Panel Designs Specific Power (We/kg) No MNT Aluminum and Carbon Fibre Solid Diamond Diamond Spaceframe m/s2 10 m/s2 100 m/s TL McKendree, 20 APR 01

15 Emitter Limited Thrust a f m 2 F ma x J em ittermax P s f p f f F ma x J em ittermax v 0 eng P s v 0 (20) F max = J emitter max = P s = f p = f f = v 0 = Maximum Electrostatic Field Strength (V/m) Maximum Current of Propellant Per Unit Area Possible With an Emitter (A/m 2 ) Specific Power [of Power Source] (W/kg) Ratio of Total Dry Mass with Payload to Total Fueled Mass with Payload Ratio of Engine and Power Source Mass to The Sum of Payload, Engine and Power Source Mass Exhaust Velocity (m/s) eng = Overall Density of an Engine (kg/m 3 ) Best Propellant Option for High P s is H 5/19/

16 Performance of Solar Electric Ion Engines Initial Acceleration (m/s2) 10 2 Most Advanced MNT Complex MNT 10-1 Simple MNT No MNT Exhaust Velocity (m/s) 10 7 TL McKendree, 20 APR 01

17 MNT-Based Solar Electric Ion Engine Performance No MNT Simple MNT Complex MNT Most Advanced MNT Specific Power 0.1 kwe/kg 10 kwe/kg 739 kwe/kg 1000 kwe/kg Acceleration (1/3 Mass Propulsion System, v 0 = 500,000 m/s) m/s m/s m/s m/s 2 v 0 at 1 m/s 2 acceler ation with 1/3 Mass Propulsion System 67 m/s 6,700 m/s 492,000 m/s 680,000 m/s Corresponding D V km/s 2.7 km/s 200 km/s 276 km/s 5/19/

18 Final Simplification Note, for the region of performance for Complex and Most Advanced MNT, the mass of the engines are negligible. If they are dropped from Equation (19), that equation simplifies to a f m f p f f 2 P s v 0 (21) M c Kendree, Thomas Technical and Operational Assessment of Molecular Nanotechnology for Space Operations, Ph.D. dissertation, University of Southern California, p /19/

19 References K. A. Bertness, D. J. Friedman, Sarah R. Kurtz, A. E. Kibbler, C. Kramer, and J. M. Olson High-efficiency GaInP/GaAs tandem solar cells, Journal of Propulsion and Power, Vol. 12, No. 5, pp Drexler, K.E. 1992a. Nanosystems: molecular machinery, manufacturing, and computation. New York:Wiley Interscience b. Molecular manufacturing as a path to space. In (Krummenacker and Lewis 1995), pp Fraas, L.M. and Avery, J.E Over 30% efficient tandem gallium solar cells for use with concentrated sunlight. Optoelectronics Devices and Technologies. Vol. 5 No. 2, pp , December Gray, D.E., ed American institute of physics handbook. New York:McGraw-Hill. Hughes Space & Communications, Hughes' ion engine serving as primary propulsion to nasa's deep space 1. nstar/ionengine.htm, accessed 13 September JPL (Jet Propulsion Laboratory), Solar concentrator arrays. Available at hppt://nmp.jpl.nasa.gov/ds1/tech/scarlet.htm, accessed 28 September Krummenacker, M. and Lewis, J., eds Prospects in nanotechnology: toward molecular manufacturing. New York:John Wiley & Sons. Lide, D.R., ed Handbook of chemistry and physics, 77th ed. Boca Raton:CRC Press, Inc. M c Kendree, T Technical and Operational Assessment of Molecular Nanotechnology for Space Operations, Ph.D. dissertation, University of Southern California. Particularly Section 3.2 Solar Electric Ion Engine (pp ) and Appendix G Small Scale Electrostatic Ion Engine (pp ) Sackheim, R.L., Wolf, R.S. and Zafran, S Chapter 17: space propulsion systems. In (Wertz and Larson 1991), pp Wertz, J.R. and Larson, W.J Space mission analysis and design. Space Technical Library. Dordrecht:Kluwer Academic Publishers. Yamaguchi, M Compound semiconductor solar cells, present status. Optoelectronics Devices and Technologies. Vol. 5 No. 2, pp , December /19/

20 QUESTIONS?