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Home , Air launch, Laser propulsion, Space elevator

An Overview of Advanced Concepts for Space Access Andrew Ketsdever Assistant Professor University of Colorado at Colorado Springs and Marcus Young Deppyuty Prog ram Manag g,er, Advanced Concep ts Group Air Force Research Laboratory

Distribution A: Approved for public release; distribution unlimited. Early Attempts to Defy

Dreams

Applications Ideas

Break- Research throughs

2 Advances in Flight

Turbojet c. 1940 Ramjet C. 1960 C. 1990

Advanced Turbofan 3 Rocketry

Hero Engine ~62 AD (?)

Chinese Rocketry ~First Century AD

1926 1976 4 Introduction

• Every man-made object launched to space has been by chemical combustion • Liquid propulsion systems (bi-) • Solid propulsion systems • Hybrid propulsion systems (suborbital) • Energy to reach low- (LEO) • 45 MJ/k g or 12. 5 kW-h/khr/kg • At current Colorado Springs Utilities rates: $1.75/kg • Room for improvement? YES Thrust Payload Mass Cost/kg Launch Cost/ Efficiency Fraction ($1000/kg) Energy Cost 97% (SSME) .025 10s~5500 Trillions spent to increase chemical propulsion efficiency have led to minimal advances – e.g. Isp increases of mere 10’s seconds out of 400. Æ Need a breakthrough 5 Today’s Launch Outlook: Dismal

• New vehicles coming on line are looking at advances in the business model of launch Æ not necessarily advancement • SXSpaceX (COTS pro ducti on) • Blue Origins • NASA has cut all funding for Advanced Concept development • Ares depends on existing and in many cases Apollo-era technology • Not necessarily a bad thing • The Air Force has minimal funding currently going into Advanced Propulsion technology for space access • Advanced Concepts Group, Edwards AFB, CA ($1M) • Hyperson ic V Vhilehicles B ranch hWihtPtt, Wright Patterson AFB AFBOH($5M), OH (<$5M) • Black programs (?) – probably not in space access directly • Department of Defense • DARPA – Falcon program

6 Essence of the Problem

7 Introduction

• AFRL Advanced Concepts Group performed critical review of advanced technologies for space access.

• Technologies Considered:

Using Propellantless •NlNuclear •Electromagneti c (R ail) •Space Tug • •Beamed Energy •Space Platforms and Towers •Advanced Chemical •Gravity Modification and Breakthrough Physics •Hypersonic Air Breathing •Launch Assist

• Analysis perffformed for advanced concepts (1 5-50)0 years) is not su fficiently accurate for more than semi-qualitative comparisons. • Qualitatively consider known missions: microsat to LEO and large comsat to GEO.

Distribution A: Approved for public release; distribution unlimited. 8 Existing State of the Art

• Advanced launch concept must be more than just a new solution. • Must yield system level performance improvements over SOA. Microsat to LEO Large Comsat to GEO Orbital Minotaur IV Boeing Delta IV Heavy •Reduces microsat launch costs by •Developed as part of EELV program. reusing Peacekeeper boosters. •Reduce costs by 25%. •4 stage all solid propellant . •Increase simplicity and reliability. •First flight scheduled for Dec. 2008. •Increase standardization. •7 successful Minotaur I flights… •Decrease parts count.

•Stage 1: 3 CBCs RS-68 (LH2/LO2). •Stage 2: 1 RL -10B-2 (LH2/LO2) . •First flight Nov. 20, 2002.

Performance: Performance: •Thrust: I: 2.2MN, II: 1.2MN, III: .29MN. •Stage 1: : 8.673MN @ 410s •1750kg to LEO. •Stage 2: At Altitude: 110kN @ 462s •Minotaur I ~ $30,000/kg. •22,950 kg to LEO. •~$10, 000/kg.

•“Advanced Concepts” have not aided most recent generation!

Distribution A: Approved for public release; distribution unlimited. 9 Launch Costs

• Technologically feasible to launch 130,000kg to LEO (Ares V). • What else is important? •Isp: Propppellant cost represents small fraction of overall… • Responsiveness: Years/months Æ Weeks/days? • Cost($/kg): Limitation on type and amount of payload.

• Major focus on reducing launch cost (1/10). • Improved performance (STS): Not successful. • Reduced performance (EELV): Not quite successful.

Distribution A: Approved for public release; distribution unlimited. 10 Other Considerations

• Reliability: Likelihood that launch vehicle will perform as expected and deliver payload into required orbit. •Typicall y 0.91-0.95 (Sauvageau,,) Allen JPC 1998). • 2/3 due to propulsion elements. • Upper stages less reliable. • Increasing decreases insurance costs, improve RLV competitiveness. • Availability: Fraction of desired launch dates that can be used. • Responsiveness: Time from determination of desired launch to actual launch. • Currently measured in months/years. • DtDesert Storm: Sept . 1990 Æ Launc h Fe b. 1992! • Ideal to have weeks/days/hours capability.

• EtExtreme MitdMagnitudes 2 2 • SSME: P=6GW dthroat=600cm Æ 10MW/cm . • Saturn V: Height: 116m, Diameter: 10m, Mass: 6.7 million pounds.

Distribution A: Approved for public release; distribution unlimited. 11 Propellant: Nuclear

• Nuclear materials have extremely high energy densities. • Fission: 7 x 1013 J/kg at 100% efficiency. • Fusion: 6 x 1014 J/kggy at 100% efficiency. •~107 –108 J/kg Æ chemical •Benefit practical launch systems?

Nuclear powered His tory upper stage •Nuclear fission first proposed in the late 1940s. •Variety of concepts exist with Isp from 800s to > 5000s. •Typically use hydrogen working gas. •Nuclear propulsion enabling for large interstellar Orion missions. •Launch concepts exist. •NERVA upper s tage. •Primary concerns: system mass, system cost, allowable temperatures, socio-political. •Larggppgpye size limits applications to large payloads.

Distribution A: Approved for public release; distribution unlimited. 12 Propellant: Nuclear Tug

• Nuclear fission propulsion can enable space tugs. • Reduce the requirements for launch systems?

• Example: mtug (no payload) of 22, 000kg, ΔV = 4 . 178km/s. Where is breakeven?

200000 Finert = 010.1 180000 Finert = 0.3 160000 Finert = 0.5 Finert = 0.7 140000 (kg) 120000 O EE G 100000 to

80000 Payload 60000

40000

20000

0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 (sec) Significant investments required to reduce specific mass of nuclear systems. Distribution A: Approved for public release; distribution unlimited. 13 Propellant: Beamed Energy

• Chemical Propulsion: energy and ejecta same material (neither fully optimized). • Beamed Propulsion: energy stored remotely so ejecta could be optimized. • and microwaves are both proposed for beamed energy launch. • Both lasers and microwave sources are under continuous development. • More emphasis on . • Laser propulsion was first introduced by Kantrowitz in 1972 1. Heat Laser Æ heat exchanger Æ flow Exotic heat exchangers are required. Exchange 2. Form plasma in a nozzle to reach high Have high accuracy pointing requirements. Formation operating temperatures. 3. Laser Removal and acceleration of pppropellant via More thrust than PLT,,y but must carry Ablation . propellant. 4. Photon Pressure from photons directly used for Bae’s PLT has shown 3000x amplification. Pressure propulsion. Still requires higher powered lasers.

Generation: 1MW Æ 1GW

Laser beamed propulsion will take significant money to develop and deploy and will only service μSat launches in foreseeable future due to required power levels.

Distribution A: Approved for public release; distribution unlimited. 14 Propellant: μwave Beamed Energy

Source: Parkin and Culick (2004): • 300 gyrotron sources (140GHz,1MW) Æ 1000kg to LEO. • Transmission: Frequency very important. • Atmospheric Propagation. • Breakdown. • Coupling Efficiency. • Generator Size. •Coupling • Plasma FtiFormation • (Oda et al, 2006) Gas discharge formed at focus of beam. Plasma absorbs beam energy. • Heat Exchanger • (Parkin and Culick) Heat exchanger & hydrogen propellant yield 1000s, payload mass fraction 5- 15%. • Both laser & microw av e beamed energy propu lsion sy stems requ ire significant sou rce (>1GW) and coupling development to yield viable systems for microsatellite launches. • Overlap with other source applications. Distribution A: Approved for public release; distribution unlimited. 15 Microwave Thermal LV

Parkin, 2006

16 Propellant: HEDM

• Performance of chemical rocket is critically dependent on propellant properties.

1000.0 10000 R ⎛ m ⎞ T 900.0 ⎜ i ⎟ 8000 R ΔV = I sp g ln I sp ∝ 6000 R ⎜ ⎟ 800.0 m f m ⎝ ⎠ 700.0 • Problem: High I typically low density. 600.0 sp 500.0 Impulse (sec)

• Goal: Find high Isp,,ypp density propellant cc 400.0

1. Strained ring hydrocarbons. 300.0 Specifi 2. Polynitrogen 200.0 Theoretical Isp Gamma = 1.15 3. Metallic Hydrogen (216MJ/kg). 100.0 P1/P2 = 750

000.0 0 5 10 15 20 25 30 Exhaust Molecular Weight Difficulties • Molecules containingggp high potential ener gy are t ypyypically less stable. • Dramatically more expensive (difficult to manufacture, less alternative uses). • Require new nozzle materials/techniques.

•Wide range of potential materials yielding both near-term and far-term potential improvements, but with similar technological challenges: less stable, higher operating temperatures. Distribution A: Approved for public release; distribution unlimited. 17 Propellant: Hypersonic Air Breathing Vehicles • Oxidizer mass fraction >> payload mass fraction for existing launch systems (30% vs. 1.2% for STS). • Can atmosppygheric oxygen be used instead?

Thrust-to-Weegight •SSME: 73.12 •Scramjet ~ 2

• Alternative technologies show significantly higher Isp, but over a limited range of Mach number. • Multi-stage systems are required. • Parallel systems suffer from volume and mass constraints. • Combined cycle systems require significant development to integrate flowpaths. Distribution A: Approved for public release; distribution unlimited. 18 Combined Cycle Launch Vehicles RBCC and TBCC

Rocket Based Combined Cycle (RBCC) Turbine Based Combined Cycle (TBCC) Rocket-ejectorÆRamjetÆScramjetÆRocket TurbojetÆRamjetÆScramjetÆRocket • Both technologies are under development at the component/initial integration stages. • Basic demonstration of has been shown, but survivable, reusable vehicles have not. • Development will probably require decades, but may yield a revolutionary launch technology. • Could be viable for both launch scenarios X-51 X-43A

Distribution A: Approved for public release; distribution unlimited. 19 Electromagnetic Launch:

•Multiple proposed EM launch technologies: , , maglev. Acceleration as a function of track length and launch velocity •Suffer from similar limitations… Only railguns will be discussed. 100000 10 m 100 m 1 km 10000 10 km 100 km km

1000

100 Acceleration (g)

10

1 Technical Challenges 0 2 4 6 8 101214161820 •Maintain rail integrity. Launch Velocity (km/sec) •Useful high gee payloads must be developed. •Pulsed power system must be developed. Now: Ei=10MJ,m=3.2kg,Vmuzzle=2.5km/s 64MJ (6MA) System Ready > 2020 •Aero-thermal loads Navy Direct Launch Requirements •Vmuzzle > 7.5km/s •E > 10GJ (35GJ muzzle, 44GJ input for 1250kg) •L > 1km •Estimated costs: System cost > $1B, 10,000 launches Æ $530/kg. •Potential for cost savings for microsatellites or small ruggedized payloads in the very far term. Distribution A: Approved for public release; distribution unlimited. 20

• Cable running from Earth’s surface to orbit. • Idea originated with Tsiolkovsky in 1895. Ribbon to • No stored energy re quired. • Technical hurdles: • Require extreme tensile strengths. • nanotubes? Beamed Climber • High power requirements. Power •Cost. • /orbital debris impact. • WthWeather itinterac tions. • Atomic oxygen/radiation belts. From Liftport

• Significant economic/technical challenges in the short term. • Long term possibility …

Distribution A: Approved for public release; distribution unlimited. 21 Space Platforms and Towers

• Physical structures reaching from the earth’s surface to 100km and above. • Idea has been around for awhile • More recently several different configurations have been proposed. • Solid • Inflatable • Electrostatic • Launching from 100km yields only a small amount of the total required mechanical energy • Going from <1km to >100km yields significant technological challenges World’s Tallest •Extreme materials properties. Structure 70 •Winds Circular Orbit Kinetic Energy 60 Potential Energy Total Mechanical Energy 50

40

/Mass [MJ/kg] /Mass 30 yy

20 Energ

10

0 1 10 100 1000 10000 100000 Altitude [km] •Energy benefit at 100km is small making the development costs Burj Dubai difficult to justify. (May 12, 2008: 636m of Distribution A: Approved for public release; distribution unlimited. 818m) 22 Gravity Modification and other Breakthrough Ideas • Large number of breakthrough physics concepts exist. • Some are based on unproven physics.

• Modification or comppgy(lete removal of gravity (reduce Ep). • Tajmar and Bertolami (J. Prop. Power 2005): “gains in terms of propulsion would be modest (from these concepts) and lead to no breakthrough” • Inertial mass modification: increase propellant mass as it is expelled out of vehicle for increased thrust. • Gravitational mass modification: lead to direct ΔV reduction. ~1.4km/s if mÆ 0. GEO 13km/s Æ 3 km/s. • GitGravitomagneti c fie lds: Loren tz force ana log for gravit y. I nt eract with Earth’s magnetic field to produce thrust. For most configurations very small thrust levels are produced. • Some proven physics yields currently unusable systems. • Casimir force: force is very small and not applicable for launch. • Antimatter: convert all mass to energy during annihilation. • density of ~ 9x1016 J/kg. Currently limited in production rate, cost, and storage. Energy return is ~ 10-10. • No viable systems based on proven physics.

Distribution A: Approved for public release; distribution unlimited. 23 Launch Assist: Effects

• Can reviewed concepts provide a fraction of required ΔV instead of all of it? ΔVdesign = ΔVburnout + ΔVgravity + ΔVdrag • Consider only first stage launch assist technologies. • Must provide system level performance benefit. 757.5-11km/s 101.0-15km/s1.5km/s

1. Potential Energy Assist Circular Orbit Kinetic Energy 70 • Launch from higher initial altitude. Potential Energy • LEO: mostly kinetic energy Total Mechanical Energy 60 • 100km Space Tower: Added 0.968 GEO MJ/kg (26% potential, 2.9% total). 50 2. Kinetic Energy Assist 40 • Launch with initial velocity s [MJ/kg] ss • Need several km/s to be worthwhile. 30 Pegasus • Encounter problems with high- Near 20 Space Space LEO speed low altitude flight. Energy/Ma Mount Dirigible To wer (400km) Everest 3. ΔVLV Loss Ass is t 10 • Launch from higher altitude. • Typically represents several % of 0 total energy. 1 10 100 1000 10000 100000 Altitude [km]

Distribution A: Approved for public release; distribution unlimited. 24 Launch Assist: Technologies

1. Both feasible only for μsat • Fixed Wing launch. • Balloon Pegasus launcher exists, isn’t any cheaper, possible other mission benefits. 2. Electromagnetic Launch Both gun technologies • Railgun potentially fffeasible only for μsat • Coilgun launch. Need to increase ΔE by • Maglev > 1000x.

3. Gun Launch HARP gun fired 180kg projectile • Gas Dynamic at 3.6km/s. Next gen could • Light Gas Gun place 90kg in LEO. SHARP gun 5kg projectile at 3km/s.

Distribution A: Approved for public release; distribution unlimited. 25 Conclusions

• Significant room for improvement in launch technology. • Wide range of concepts proposed and being investigated. •No obvi ous winn er s. μSat Æ LEO Comsat Æ GEO Challenges

Nuclear Mass, Cost, Socio-Political Space Tug Signifi can t re duc tion in spec ific mass oflf nuclear sys tem requi idred. Beamed Energy Generated power levels. Tracking. Coupling. HEDM Stability. Toxicity. Cost. Nozzle Materials. Hypersonics Scramjets: thermal load. Rapid combustion. Lifetime. High thrust-to-weight. Significant atmospheric flight. Electromagnetic Power source. Rail integrity. High gee payloads. Rail integrity. Aerothermal loads. Elevator Long defect free nanotubes, atomic oxygen, , weather, vibrations. Platforms Same as elevator. Must define mission benefit. Breakthrough No demonstrated pppphenomena with sufficient propulsive force. Launch Assist High gee payloads. Power sources. Aerothermal.

Distribution A: Approved for public release; distribution unlimited. 26 Conclusions II

• Significant number of remaining technical challenges.

• Solving any single challenge may not enable complete systems, but may have broad effects. • Hig h gee payld&loads & upper s tages. • High temperature nozzles. • Very high power instantaneous power levels. • Lightweight power systems.

• Additional concepts are required!

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