February 18, 2006HYPERION ERAU 1 Interstellar Travel Now

February 18, 2006 HYPERIONERAU

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Interstellar Travel Now


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Agenda

• RFP

• Proposal

• Sub-topics


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Request for Proposal

• Under current or near term technology what can be done to send a robotic probe to a nearby star?

• Define reasonable cost and flight time• What is the minimum probe and engine

mass?• How long from launch until stellar arrival?• How much will it cost?• Why is this preferred to telescopes?


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Issues

If this is done viapropulsive methodsthe following areissues

-Fuel Energy Density-Specific Impulse-Thrust/Acceleration


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Assumptions

• Consider a probe launched from a C3=0 orbit on a fly-by mission of α-Centari

• Consider vehicle mass fractions of 20000, 2000, and 200

• All probes with ΔV’s of less than 0.05c require 6 months of acceleration

• All probes with a ΔV of more than 0.05c require 18 months of acceleration

• Trip time is a function of Isp


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Flight Time (years) vs. Isp

Specific Impulse vs. Time of Flight to Alpha Centari

0

50

100

150

200

250

300

350

400

450

500

0 1 2 3 4 5 6 7

Specific Impulse (million seconds)

Tim

e of Flig

ht re

lative

to E

arth

(ye

ars)

MR 20000

MR 2000

MR 200

-Rapid interstellar flight requires millions of seconds of Isp

-This can only be accomplished via antimatter propulsion, laser accelerated proton propulsion or solar sails

-All of the above systems are out of current technical grasp


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Case Studies

Time of Flight (years) ΔV (%c) MR 20000 Isp (ks) MR 2000 Isp (ks) MR 200 Isp (ks)

500 0.91 28.189 36.729 52.692

200 2.28 70.581 91.962 131.927

100 4.58 141.516 184.386 264.518

75 6.16 190.281 247.924 355.671

50 9.3 287.364 374.417 537.134

25 19 586.702 764.435 1096.649

10 50.6 1564.539 2038.493 2924.398

6 91.2 2816.171 3669.28 5263.918

NEP

Fusion

Antimatter


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Investigated Propulsion Systems

• Plasma Core Nuclear Thermal Rocket (NTR)• Nuclear Electric Propulsion

- 10 MWe core or larger- Consider Ion, Hall Effect, MPD thrusters

• Nuclear Fusion- Different fuel cycles (D-T, D-D, D-He3+, pB, spin polarized fuels)- Magnetic Confinement Fusion (MCF)- Inertial Confinement Fusion (ICF)- Magnetically Insulated ICF (MICF)- Antiproton Initiated Fusion (AIF)

• Antimatter Propulsion (beamed core)- proton-antiproton- electron-positron- hydrogen-antihydrogen


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Plasma Core NTR

- Requires 106 K for 20,000 s + Isp

- Contamination a problem- Plasma containment a problem

-Probably not feasible


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NEP

-Fission Reactor produces electrical power-Electrical power runs electrostatic or electromagnetic thruster-Can run Ion, MPD, Arc Jets, and Hall Effect thrusters

-Very realistic

Problems include power processing, grid erosion, high temperature Materials, but it is feasible to build engines at 30,000-100,000 secondIsp’s


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NEP Thrusters

Ion MPD

~ 3000 – 100,000 s of Isp

Isp can depend on propellantIsp can depend on efficiencyIsp depends largely on input power


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30 ks NEP

• What input power is required to obtain 30 ks of specific impulse?

• How much waste heat does this produce?

• How do we dissipate the waste heat?


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100 ks NEP

• What input power is required to obtain 100 ks of specific impulse?

• How much waste heat does this produce?

• How do we dissipate the waste heat?


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Fusion

• Fusion of light elements provides propulsive source of energy

• Releases ~ 1014 J/kg


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Fusion Fuel Cycles

D-T: Low ignition temp. High neutron yield 1st generation fuel

D-D: Large energy yield Thermal radiation

D-He3+: Large energy yield Thermal radiation

Spin Polarized Fuels


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Magnetic Confinement Fusion

Tokomak-Torodial fields-Polodial field

Spheromak-Similar to Tokomak-Slightly higher Q-Slightly higher α

-Under Lawson’s criteria all MCF techniques require low ion densities and long burn times-All MCF techniques are very heavy and have no applications as an electrical power producing device

- Plasma is ejected as rocket exhaust


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Magnetic Confinement Fusion

Gas Dynamic Mirror

-Similar to a z-pinch

-Ions with precise θ escape

-Escaping ions produce thrust

-Potentially 50-100,00 s of Isp

-Very heavy

-Potentially near term if it burns D-T mixture


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Inertial Confinement Fusion

-Particle beams or lasers compress fusile targets

-Magnets must contain plasma for short time frames

-Drivers are very heavy must be ~1.6 MJ

-Higher Q’s than MCF

-Higher α than MCF

-High ion densities (neutron star), short confinement time- If weight can be negated this has serious potential in propulsion!!


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Magnetically Insulated ICF

-Tungsten or gold surrounds target pellet

-Low thermal impulse on tungsten shield

-Produces transient magnetic field

-Reduces need for magnets

-Ablated Tungsten reduces Isp

-Drastically reduces mass of drivers and electromagnets!!


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Antiproton Initiated ICF

Muon Catalyzed Fusion-Antiproton annihilation creates μ-mesons (muons)

-muons displace electrons around nucleus

-must occur at low energies (1200 – 1600 K)

-no or little need for drivers

-combined with MICF makes a lightweight engine

Requires nano-grams of antiprotons


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Antiproton Initiated ICF

Antimatter Initiated Micro-Fusion/Fission

-Antiprotons induce U238 fission

-Released neutrons help compress fusion fuel

-Larger α than muon catalyzed fusion

-Isp ~ 50,000 s – 1,000,000 s


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Antimatter Propulsion

-Highest performance under the laws of impulse and momentum

-Requires kilograms of antimatter which is not yet available

-Offers Isp near the theoretical limit (30.6 x 106 seconds

-The only hope for rapid robotic or manned interstellar propulsion


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Antiproton

-~35% of annihilation energy is lost to massive particles

-Requires 2 km long nozzle

-Large radiation levels due to pions and muons


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Positron

-Uses momentum from 0.511 MeV photons

-Requires reflection of high energy photons

-Positrons easier to produce than antiprotons

- Very high burnout velocities


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Investigation Questions

• Does the technology exist now?

• If not can it be developed in 15 years assuming unlimited funds?

• Or can the system not be developed with current physical understanding?


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Investigated Parameters

• What is the system mass?• What is the system thrust?

• What is the system Isp?

• What is the fastest the system can reach α-centari?

• What is the systems TRL now?• What is the cost of developing this system?• What is the cost of launching this system?


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Investigated Parameters

• What is the cost of transferring the craft from LEO to C3=0? (assume the use on an NTR)

• What the minimum engine mass?


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Probe Design

• What are the data transfer signal requirements for transmitting over 4.56 ly?- beam vs. isotropic signal- S/N ratio- Transmission Power- Pointing accuracy

• What are the thermal control, attitude control, and navigation requirements- The stars will not be in the same place to use star trackers

• What are the total power requirements for the probe?- Do we need an onboard fission reactor or can we shut down the craft during flight and use solar arrays when it arrives near its target, or even use batteries that only last 15 minutes?


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Probe Question

• How does the info. from the previous slide drive the probe mass?

• What is the craft dry mass when the probe mass is combined with the engine mass?

• At MR’s of 20,000, 2000, and 200 what is the total craft mass for each case, when propellant is added to the dry mass?


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Questions

• ???

Documents

February 18, 2006HYPERION ERAU 1 Interstellar Travel Now