Transcript The Three Choices for Apollo

Feasibility of Robotic
Investigations of Extra-Solar
Planets
Brice Cassenti
Mechanical Engineering
University of Connecticut
Feasibility of Robotic Investigations of
Extra-Solar Planets
• Extra-Solar Planets
• Solar System Robotic Exploration
– Some History
– Some Results
• Interstellar Missions
– Requirements
– The Propulsion Question
– Feasibility
Extra-Solar Planets
- Current Status
Extra-Solar Planets
• First ordinary extra-solar planet discovered in 1995
• Currently almost 350 have been confirmed
• Nearest
– Epsilon Eridani b 10.5 light years
– 1.2 to 1.8 times Jupiter’s mass
• Most Earthlike
– Gliese 581 at 20.5 light years
– Gliese 581 e is at least 1.94 times Earth’s mass
– Gliese 581 d is inside the “habitable” zone
Gliese 581
Credit ESO at http://www.space.com/scienceastronomy/090423-am-earth-mass-planets.html
Epsilon Eridani
http://www.solstation.com/stars/eps-erid.htm
Solar System Robotic Exploration
– A History
Solar System Observations
• 1800
– Sketches
• 1900-1960
– Telescopic Photography
• 1960-2010
–
–
–
–
Robotic fly-by probes
Robotic orbiters/landers
Manned lunar landings
Earth orbital telescopes
Mars Exploration
1800s
Proctor - 1867
Schiaparelli - 1888
Mars Exploration
1900 - 1960
Yerkes - 1909
Mars Exploration
1960-2010
Mariner 4
NASA
Mariner 7
NASA
Hubble
NASA
Mercury Exploration
Antoniadi 1929
Schiaparelli 1889
Mercury Messenger
NASA - 2004
Mariner 10
NASA - 1974
More and More and More …
Jupiter Pioneer 10 - NASA
Pluto Hubble- NASA
Conclusion?
Robotic Exploration
Works
Io Galileo- NASA
Distant vs. In-Situ Observations
of Extra-Solar Planets
• Near Term Distant Observations
• Long Term Distant Observations
• In-Situ Observations
Near Term Distant Observations
of Extra-Solar Planets
• Celestial Mechanics
– motion
• Photometric observations
– surface reflectivity
– atmosphere properties
• Spectral observations
– chemistry
Long Term Distant Observations
of Extra-Solar Planets
• Objective
– Solar System Hubble Telescope Resolution
– Mirror is 2.4 meters (~94 inches)
• Use Mars as example
– 6780 km nearest typically 0.52 AU
– At 10 light years requires 1000 times diameter
• 2.4 km (~1.4 miles)
– At least another 100 times for crater counts
• i.e., 240 km (~140 miles)
For In-Situ Observations We
Need Interstellar Missions
Astronomical Distances
Earth to Moon
4x105 km
Earth to Neptune
4x109 km
Earth to Alpha
Centauri C
4x1013 km
Design Criteria
• Crew trip time 40 years
– Manned crew uses on board ship time
– Unmanned crew uses Earth elapsed time
• Payload mass
– 500 tons for unmanned (Hubble is ~ 12 tons)
– 5000 tons outbound for manned
– 2500 tons inbound for manned
Performance Estimates
• Use Special Relativity
• Attach origin to spacecraft
Interstellar Rockets
• Low Speed
 Total speed change 
mass

 exp 
– Initial
Final mass
Exhaust
velocity


– Initial mass  Mass of propellent  final mass
– Exhaust velocity  Specific impulse  Acceleration of
• Relativistic Speed
gravity
– Replace velocities with rapidities
• Conclusion
– Speed change and specific impulse are key
Rocket Specific Impulse Today
• Chemical
– Solid: 350 seconds
– Liquid: 450 seconds
• Nuclear
– NERVA Program: 900 seconds
• Ion
– Typical: 2000 seconds
Interstellar Precursor Missions
Distance
AU
Kuiper Belt Objects
100
Solar Focus
550
Oort Cloud
5,000
a Centauri
270,000
Mission
*Mass Ratio 40 Year Fly-By
Specific Impulse - sec
200,000
600,000
1,000,000
1.01
1.00
1.00
1.03
1.01
1.01
1.34
1.10
1.06
7151803
192.67
23.49
*Mass Ratio 40 Year Round Trip
Distance
Specific Impulse - sec
Mission
AU
200,000
600,000
1,000,000
Kuiper Belt Objects
100
1.05
1.02
1.01
Solar Focus
550
1.29
1.09
1.05
Oort Cloud
5,000
10.36
2.18
1.60
a Centauri
270,000
6.84E+54
1.90E+18
92696819562
*Note: Mass ratio is initial mass / final mass
2,000,000
1.00
1.00
1.03
4.85
2,000,000
1.00
1.03
1.26
304462
The Question is Propulsion
Saturn F-1 Engine
Thrust: 1.5 million pounds
Specific Impulse: 350 seconds
Sutton, Courtesy of Rocketdyne
The Nuclear Option
Nuclear Fission Rockets
• Nuclear thermal rockets (NTR)
– Bimodal
– LOX Augmented NTR (LANTR)
• Gas core rockets (GCR)
– Vortex
– Nuclear light bulb (NLB)
• Nuclear pulse propulsion
– Orion
Fission Reaction
Nuclear Thermal Rocket
Vortex Contained
Gas Core Nuclear Rocket
Nuclear Light Bulb
Orion
Performance of Nuclear
Fission Rockets
minitial
MR 
e
m final
v
I sp g 0
minitial  m final  m propellant
Rocket
Chemcal
NTR
GCR
Orion
Specific
Impulse - s
450
910
1,900
10,000
Note: For a constant Isp energy efficient rocket v  1.6 I sp g 0
Nuclear Fusion Propulsion
• Nuclear Reactions
• Propulsion Concepts
• Solar System Missions
Nuclear Reactions
• Uranium Fission
N1
N2
238
1
1
n

U

X

X


n

0
92
k1
k2
0
• DT Reaction
2
3
4
1
H

H

He

n
1
1
2
0
• Lithium Fission
1
6
4
3
n

Li

He

H
0
3
2
1
Propulsion Concepts
• Critical Mass Systems
• Antiproton Triggered Systems
– Hybrid Fission-Fusion Pellets
– MICF Hybrid Pellets
• External Compression Systems
Medusa
http://en.wikipedia.org/wiki/File:MedusaNuclearPropulsionOperatingSequenceDrawing.png
Medusa
Specific Impulse:
500,000-1,000,000
http://en.wikipedia.org/wiki/File:MedusaNuclearPropulsionOperatingSequenceDrawing.png
Matter-Antimatter Annihilation
Positron-Electron Annihilation
e e  


p  p  m 0  n   n 
n  p  m  (n  1)  n
0


Antiproton-Uranium Nucleus
Annihilation
p  92 U 238  2 X  kn
+
p
p
n
Pellet Ignition
Tritium Fuel Considerations
• Tritium is naturally radioactive
– Beta decay
– Half-life ~12 years
• Tritium requires cryogenic storage
• Lithium-6 is not radioactive
• Lithium-6 does not require cryogenic
storage
Fusion Reactions
• The DT reaction
2
3
4
1
H

H

He

n
1
1
2
0
• And Lithium fission reaction
1
6
4
3
n

Li

He

H
0
3
2
1
• Are equivalent to
1H
2
6
4
 3 Li  2 He  2 He
4
Pellet Construction
Typical Pellet
Geometry
•
•
•
•
•
Core radius
Fuel Radius
Tungsten Shell Thickness
Antiproton Beam Radius
Uranium Hemisphere Radius
0.05 mm
1.00 cm
0.10 mm
0.10 mm
0.30 mm
Typical Pellet
Performance
•
•
•
•
Antiproton Pulse
Maximum Field
Pellet Mass
Specific Impulse
2x1013 for 30 ns
24 MG
3.5 g
– 600,000 s for 100% fusion
– 200,000 s for 10% fusion
– 3,000 s for contained fusion
Solar System Transit Times
One-Way
Isp: 200,000 sec
MR: 1.5
Accel: 0.07g0
Time
(days)
8
6
6
13
14
25
44
86
133
175
Limited
By
Mercury
Acceleration
Venus
Acceleration
Mars
Acceleration
Ceres
Acceleration
Vesta Specific Impulse
Jupiter Specific Impulse
Saturn Specific Impulse
Uranus Specific Impulse
Neptune Specific Impulse
Pluto
Specific Impulse
To
Daedalus Study
British Interplanetary Society
From Nicolson “The Road to the Stars”
Daedalus
http://www.grc.nasa.gov/WWW/PAO/images/warp/warp44.gif
Exotic Propulsion Alternatives
Sanger Electron-Positron
Annihilation Rocket
By G. Matloff
Proton-Antiproton Reaction
p  p  m  n  n
0


Proton-Antiproton Reaction
 
p  p  m  n  n
0


Proton-Antiproton Reaction
 
p  p  m  n  n
0


 m  m

 m  m

Proton-Antiproton Reaction
 
p  p  m  n  n
0


 m  m

 e  e  m

 e  e  m

 m  m

Proton-Antiproton Reaction
 
p  p  m  n  n
0


 m  m

 e  e  m
+  

 e  e  m

 m  m

Proton-Antiproton Reaction
 
p  p  m  n  n
0


 m  m

 e  e  m
+  

 e  e  m

 m  m

Pion Rocket
By R. Forward
a Centauri C Fly-By
• 40 years to arrive
Propulsion
• 4 light years distance System
Pellet Fusion
• 0.1c final speed
ICF
MCF
Antimatter
Photon
Isp
sec
500,000
1,000,000
2,000,000
10,000,000
31,557,600
Mass
Ratio
550.882
23.471
4.845
1.371
1.105
Pion Rockets
Minimum Energy Manned Missions
be = 0.95, h = 0.6
Constant Exhaust Velocity
Mssion
Sun ↔ a Centauri
Sun ↔  Reticuli
1 ↔ 2 Reticuli
Distance
Crew
Observer
l.y.
Time - yr. Time - yr.
4.1
37.5
0.083
40
40
40
41
86
40
Mass
Ratio
3.54
8010
1.49
AntimatterFinal Mass
Ratio
1.00
3150
0.19
Optimum Exhaust Velocity
Mssion
Sun ↔ a Centauri
Sun ↔  Reticuli
Distance
Crew
Observer
l.y.
Time - yr. Time - yr.
4.1
37.5
40
40
41
86
Mass
Ratio
4.9
5
AntimatterFinal Mass
Ratio
0.0052
1.5
Even More Exotic Propulsion
• Wormholes
• Warp Drives
• Interstellar Ramjet
Conclusions
• Interstellar robotic missions are hard but not
impossible.
• A 2.4 km telescope in the solar system can
significantly add to our knowledge and will
be much less expensive.
• But what about a 240 km telescope?
– We can send robots after picking out target
extra-solar planets with a 2.4 km telescopes.
Questions?