an overview of advanced concepts for space accessspace access

An Overview of Advanced Concepts for Space AccessSpace Access

Andrew KetsdeverAssistant Professor

University of Colorado at Colorado Springsandand

Marcus YoungDeputy Program Manager, Advanced Concepts Groupp y g g , p p

Air Force Research LaboratoryDistribution A: Approved for public release; distribution unlimited.

Early Attempts to Defy Gravity

Dreams

IdeasApplications

ResearchBreak-throughs

2

Advances in Flight

TurbojetTurbojetc. 1940 Ramjet

C. 1960 ScramjetC. 1990

3Advanced Turbofan

Rocketry

Hero Engine62 AD (?)~62 AD (?)

41926 1976

Chinese Rocketry~First Century AD

Introduction

• Every man-made object launched to space has been by chemical combustion

• Liquid propulsion systems (bi-propellants)

• Solid propulsion systems

• Hybrid propulsion systems (suborbital)

• Energy to reach low-Earth orbit (LEO)

• 45 MJ/k 12 5 kW h /k• 45 MJ/kg or 12.5 kW-hr/kg

• At current Colorado Springs Utilities rates: $1.75/kg

• Room for improvement? YES• Room for improvement? YESThrust

EfficiencyPayload Mass

FractionCost/kg

($1000/kg)Launch Cost/Energy Cost

97% (SSME) 025 10 5500

5

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. Need a breakthrough

Today’s Launch Outlook: Dismal

• New vehicles coming on line are looking at advances in the business model of launch not necessarily technology advancement

S X (COTS d ti )• SpaceX (COTS production)

• 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• The Air Force has minimal funding currently going into Advanced Propulsion technology for space access• Advanced Concepts Group, Edwards AFB, CA ($1M)

H i V hi l B h W i ht P tt AFB OH ( $5M)• Hypersonic Vehicles Branch, Wright Patterson AFB, OH (<$5M)

• Black programs (?) – probably not in space access technologies directly

• Department of Defense

6

• DARPA – Falcon program

Essence of the Problem

7

Introduction• AFRL Advanced Concepts Group performed critical review of advanced

technologies for space access.

• Technologies Considered:

Using Propellant PropellantlessN l El i (R il)•Nuclear

•Space Tug•Beamed Energy•Advanced Chemical

•Electromagnetic (Rail)•Elevator•Space Platforms and Towers•Gravity Modification and Breakthrough Physics

f f (1 0 ) ff

Advanced Chemical•Hypersonic Air Breathing

Gravity Modification and Breakthrough Physics•Launch Assist

• Analysis performed for advanced concepts (15-50 years) is not sufficiently accurate for more than semi-qualitative comparisons.

• Qualitatively consider known missions: microsat to LEO and large comsat to GEO.

8Distribution A: Approved for public release; distribution unlimited.

Existing State of the Art

Microsat to LEO Large Comsat to GEO

• 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 GEOOrbital Minotaur IV Boeing Delta IV Heavy

•Reduces microsat launch costs by reusing Peacekeeper boosters.

•Developed as part of EELV program.•Reduce costs by 25%.

•4 stage all solid propellant rocket.•First flight scheduled for Dec. 2008.•7 successful Minotaur I flights…

•Increase simplicity and reliability.•Increase standardization.•Decrease parts count.•Stage 1: 3 CBCs RS-68 (LH2/LO2).•Stage 2: 1 RL-10B-2 (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.•1750kg to LEO.•Minotaur I ~ $30,000/kg.

•Stage 1: Sea Level: 8.673MN @ 410s•Stage 2: At Altitude: 110kN @ 462s•22,950 kg to LEO.•~$10 000/kg

9

•~$10,000/kg.

Distribution A: Approved for public release; distribution unlimited.

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

Launch Costs• Technologically feasible to launch 130,000kg to LEO (Ares V).• What else is important?

• Isp: Propellant cost represents small fraction of overall…p p p• Responsiveness: Years/months Weeks/days?• Cost($/kg): Limitation on type and amount of payload.

• Major focus on reducing launch costreducing launch cost (1/10).

• Improved performance (STS): Not successful.

• Reduced performance (EELV): Not quite successful

10

Not quite successful.


Other Considerations• Reliability: Likelihood that launch vehicle will perform as expected

and deliver payload into required orbit.• Typically 0.91-0.95 (Sauvageau, Allen JPC 1998).yp y ( g , )• 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.D t St S t 1990 L h F b 1992!• Desert Storm: Sept. 1990 Launch Feb. 1992!

• Ideal to have weeks/days/hours capability.

E t M it d• Extreme Magnitudes• SSME: P=6GW dthroat=600cm2 10MW/cm2.• Saturn V: Height: 116m, Diameter: 10m,

11

Mass: 6.7 million pounds.


Propellant: Nuclear• Nuclear materials have extremely high energy densities.

• Fission: 7 x 1013 J/kg at 100% efficiency.• Fusion: 6 x 1014 J/kg at 100% efficiency.

Hi t Nuclear powered

g y• ~107 – 108 J/kg chemical

•Benefit practical launch systems?

History•Nuclear fission rockets first proposed in the late 1940s.•Variety of concepts exist with Isp from 800s to > 5000s.•Typically use hydrogen working gas

pupper stage

Typically use hydrogen working gas.•Nuclear propulsion enabling for large interstellar missions.•Launch concepts exist.NERVA t

Orion

•NERVA upper stage.•Primary concerns: system mass, system cost, allowable temperatures, socio-political.•Large size limits applications to large payloads.


g pp g p y

Propellant: Nuclear Tug

• Nuclear fission propulsion can enable space tugs.• Reduce the requirements for launch systems?• Example: m (no payload) of 22 000kg ΔV = 4 178km/s

200000

Finert 0 1

• Example: mtug (no payload) of 22,000kg, ΔV = 4.178km/s.Where is breakeven?

120000

140000

160000

180000

EO (kg)

Finert = 0.1

Finert = 0.3

Finert = 0.5

Finert = 0.7

40000

60000

80000

100000

Payloa

d to GE

0

20000

40000

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Specific Impulse (sec)


Significant investments required to reduce specific mass of nuclear systems.

Propellant: Laser Beamed Energy• Chemical Propulsion: energy and ejecta same material (neither fully optimized).• Beamed Propulsion: energy stored remotely so ejecta could be optimized.• Lasers and microwaves are both proposed for beamed energy launch.

Both lasers and microwave sources are under continuous development• Both lasers and microwave sources are under continuous development.• More emphasis on laser propulsion.• Laser propulsion was first introduced by Kantrowitz in 19721. Heat Laser heat exchanger flow Exotic heat exchangers are required. Exchange

2. Plasma Formation

Form plasma in a nozzle to reach high operating temperatures.

Have high accuracy pointing requirements.

3. Laser Removal and acceleration of propellant via More thrust than PLT, but must carry Ablation

p plaser ablation.

, ypropellant.

4. Photon Pressure

Pressure from photons directly used for propulsion.

Bae’s PLT has shown 3000x amplification.Still requires higher powered lasers.

Generation: 1MW 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.

Propellant: μwave Beamed EnergySource: Parkin and Culick (2004):

• 300 gyrotron sources (140GHz,1MW) 1000kg to LEO.g

• Transmission: Frequency very important.• Atmospheric Propagation.• Breakdown.• Coupling Efficiency.• Generator Size.

•CouplingPl F ti• Plasma Formation

• (Oda et al, 2006) Gas discharge formed at focus of beam. Plasma absorbs beam energy.

• Heat Exchangerg• (Parkin and Culick) Heat exchanger & hydrogen

propellant yield 1000s, payload mass fraction 5-15%.

Both laser & micro a e beamed energ prop lsion s stems req ire significant so rce


• Both laser & microwave beamed energy propulsion systems require significant source (>1GW) and coupling development to yield viable systems for microsatellite launches.

• Overlap with other source applications.

Microwave Thermal LV

Parkin, 2006

16

Propellant: HEDM

900.0

1000.010000 R8000 R6000 R

TIsp ∝⎟⎟⎞

⎜⎜⎛

=Δ isp

mgIV ln

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

500.0

600.0

700.0

800.0

c Im

puls

e (s

ec)

6000 RmIsp⎟

⎠⎜⎝ f

sp mgV

• Problem: High Isp typically low density.• Goal: Find high Isp, density propellant

0 0

100.0

200.0

300.0

400.0

Spec

ific

Theoretical IspGamma = 1.15P1/P2 = 750

g p, y p p1. Strained ring hydrocarbons.2. Polynitrogen3. Metallic Hydrogen (216MJ/kg).

0.00 5 10 15 20 25 30

Exhaust Molecular Weight

Difficulties• Molecules containing high potential energy are typically less stable.g g p gy yp y• 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.

Propellant: Hypersonic Air Breathing Vehicles

• Oxidizer mass fraction >> payload mass fraction for existing launch systems (30% vs. 1.2% for STS).

• Can atmospheric oxygen be used instead?p yg

Thrust-to-Weightus o e g•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.

Combined Cycle Launch VehiclesRBCC and TBCC

Rocket Based Combined Cycle (RBCC) Turbine Based Combined Cycle (TBCC)Rocket-ejector Ramjet Scramjet Rocket Turbojet Ramjet Scramjet Rocket

• Both technologies are under development at theBoth technologies are under development at the component/initial integration stages.

• Basic demonstration of scramjets has been shown, but survivable reusable vehicles have notsurvivable, reusable vehicles have not.

• Development will probably require decades, but may yield a revolutionary launch technology.

• Could be viable for both launch scenarios

X-43AX-51


Electromagnetic Launch: Railguns•Multiple proposed EM launch technologies: railgun, coilgun, maglev.•Suffer from similar limitations… Only railguns will be discussed.

Acceleration as a function of track length and launch velocity

10000

10000010 m100 m1 km10 km100 km

10

100

1000

Acc

eler

atio

n (g

) 100 km

Technical Challenges•Maintain rail integrity.•Useful high gee payloads must be developed

1

10

0 2 4 6 8 10 12 14 16 18 20

Launch Velocity (km/sec)

•Useful high gee payloads must be developed.•Pulsed power system must be developed.•Aero-thermal loads

Now: Ei=10MJ,m=3.2kg,Vmuzzle=2.5km/s64MJ (6MA) System Ready > 2020

Navy Direct Launch RequirementsNavy •Vmuzzle > 7.5km/s•E > 10GJ (35GJ muzzle, 44GJ input for 1250kg)•L > 1km•Estimated costs: System cost > $1B, 10,000 launches


$530/kg.•Potential for cost savings for microsatellites or small ruggedized payloads in the very far term.

Space Elevator• Cable running from Earth’s surface to orbit.• Idea originated with Tsiolkovsky in 1895.• No stored energy required.

Ribbon to Counterweightgy q

• Technical hurdles:• Require extreme tensile strengths.

• Carbon nanotubes?Climber

g

Beamed • High power requirements.• Cost.• Micrometeoroid/orbital debris impact.

W th i t ti

Climber Power

• Weather interactions.• Atomic oxygen/radiation belts. From Liftport

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


• Long term possibility…

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.

• SolidSolid• Inflatable• Electrostatic

• Launching from 100km yields only a small amount of the total required mechanical energy

60

70Circular Orbit Kinetic Energy

Potential Energy

mechanical energy• Going from <1km to >100km yields significant technological challenges

•Extreme materials properties.•Winds

World’s Tallest Structure

30

40

50

y/M

ass

[MJ/

kg]

Potential Energy

Total Mechanical Energy

0

10

20Ener

gy

22

1 10 100 1000 10000 100000Altitude [km]

Burj Dubai (May 12, 2008: 636m of 818m)Distribution A: Approved for public release; distribution unlimited.

•Energy benefit at 100km is small making the development costs difficult to justify.

Gravity Modification and other Breakthrough Ideas

• Large number of breakthrough physics concepts exist.• Some are based on unproven physics.

• Modification or complete removal of gravity (reduce Ep).p g y ( p)• 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 m 0. GEO 13km/s 3 km/s.G it ti fi ld L t f l f it I t t ith• Gravitomagnetic fields: Lorentz force analog for gravity. Interact with Earth’s magnetic field to produce thrust. For most configurations very small thrust levels are produced.

• Some proven physics yields currently unusable systems• 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.• Specific energy density of ~ 9x1016 J/kg. Currently limited in production


Specific energy density of 9x10 J/kg. Currently limited in production rate, cost, and storage. Energy return is ~ 10-10.

• No viable systems based on proven physics.

Launch Assist: Effects• Can reviewed concepts provide a fraction of

required ΔV instead of all of it?• Consider only first stage launch assist technologies.• Must provide system level performance benefit

draggravityburnoutdesign VVVV Δ+Δ+Δ=Δ

1 0-1 5km/s7 5-11km/sMust provide system level performance benefit.

70Circular Orbit Kinetic EnergyPotential EnergyTotal Mechanical Energy

1. Potential Energy Assist• Launch from higher initial altitude.• LEO: Orbits mostly kinetic energy

1.0-1.5km/s7.5 11km/s

40

50

60

ss [M

J/kg

] GEO

LEO: Orbits mostly kinetic energy• 100km Space Tower: Added 0.968

MJ/kg (26% potential, 2.9% total). 2. Kinetic Energy Assist• Launch with initial velocity

20

30

Ener

gy/M

as

Mount Everest

Pegasus Near Space

DirigibleLEO

(400km)Space Tower

y• Need several km/s to be

worthwhile.• Encounter problems with high-

speed low altitude flight.3 ΔV L A i t

0

10

1 10 100 1000 10000 100000Altitude [km]

3. ΔV Loss Assist• Launch from higher altitude.• Typically represents several % of

total energy.


Launch Assist: Technologies

1. Air Launch• Fixed Wing• Balloon

Both feasible only for μsatlaunch.Pegasus launcher exists, isn’t gany cheaper, possible other mission benefits.

2. Electromagnetic Launch Both gun technologies f f• Railgun

• Coilgun• Maglev

potentially feasible only for μsatlaunch. Need to increase ΔE by > 1000x.

3. Gun Launch• Gas Dynamic• Light Gas Gun

HARP gun fired 180kg projectile at 3.6km/s. Next gen could place 90kg in LEO.SHARP gun 5kg projectile at 3km/s.


Conclusions

• Significant room for improvement in launch technology.• Wide range of concepts proposed and being investigated.• No obvious winners.

μSat LEO Comsat GEO Challenges

Nuclear Mass, Cost, Socio-Political

S Si ifi t d ti i ifi f l t i d

o ob ous e s

Space Tug Significant reduction in specific mass of nuclear system required.

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, micrometeoroids, weather, vibrations.

Platforms Same as elevator. Must define mission benefit.

Breakthrough No demonstrated phenomena with sufficient propulsive force.

26

Breakthrough p p p

Launch Assist High gee payloads. Power sources. Aerothermal.


Conclusions II

• Significant number of remaining technical challenges.

• Solving any single challenge may not enable complete systems, but may have broad effects.

Hi h l d & t• High gee payloads & upper stages.• High temperature nozzles.• Very high power instantaneous power levels• Very high power instantaneous power levels.• Lightweight power systems.

• Additional concepts are required!

27

an overview of advanced concepts for space accessspace access

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