Upload
isabella-lamb
View
244
Download
4
Tags:
Embed Size (px)
Citation preview
February 18, 2006 HYPERIONERAU
3
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?
February 18, 2006 HYPERIONERAU
4
Issues
If this is done viapropulsive methodsthe following areissues
-Fuel Energy Density-Specific Impulse-Thrust/Acceleration
February 18, 2006 HYPERIONERAU
5
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
February 18, 2006 HYPERIONERAU
6
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
February 18, 2006 HYPERIONERAU
9
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
February 18, 2006 HYPERIONERAU
10
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
February 18, 2006 HYPERIONERAU
11
Plasma Core NTR
- Requires 106 K for 20,000 s + Isp
- Contamination a problem- Plasma containment a problem
-Probably not feasible
February 18, 2006 HYPERIONERAU
12
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
February 18, 2006 HYPERIONERAU
13
NEP Thrusters
Ion MPD
~ 3000 – 100,000 s of Isp
Isp can depend on propellantIsp can depend on efficiencyIsp depends largely on input power
February 18, 2006 HYPERIONERAU
14
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?
February 18, 2006 HYPERIONERAU
15
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?
February 18, 2006 HYPERIONERAU
16
Fusion
• Fusion of light elements provides propulsive source of energy
• Releases ~ 1014 J/kg
February 18, 2006 HYPERIONERAU
17
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
February 18, 2006 HYPERIONERAU
18
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
February 18, 2006 HYPERIONERAU
19
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
February 18, 2006 HYPERIONERAU
20
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!!
February 18, 2006 HYPERIONERAU
21
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!!
February 18, 2006 HYPERIONERAU
22
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
February 18, 2006 HYPERIONERAU
23
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
February 18, 2006 HYPERIONERAU
24
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
February 18, 2006 HYPERIONERAU
25
Antiproton
-~35% of annihilation energy is lost to massive particles
-Requires 2 km long nozzle
-Large radiation levels due to pions and muons
February 18, 2006 HYPERIONERAU
26
Positron
-Uses momentum from 0.511 MeV photons
-Requires reflection of high energy photons
-Positrons easier to produce than antiprotons
- Very high burnout velocities
February 18, 2006 HYPERIONERAU
27
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?
February 18, 2006 HYPERIONERAU
28
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?
February 18, 2006 HYPERIONERAU
29
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?
February 18, 2006 HYPERIONERAU
30
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?
February 18, 2006 HYPERIONERAU
31
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?