FUSION WILL WARM US.
Fusion reactors
will provide the power
(though not the propulsion)
for humans to live well and prosper
during multi-year journeys to the stars.
What Power?? On Earth, humanity gets life support power directly from Sol. It's likely that interplanetary habitats will also leverage Solar power.
HOWEVER, interstellar flights will spend long periods between stars; since power decreases per distance squared, vessels won't get much power from solar/stellar radiation. How will the onboard flora and fauna flourish without solar energy??
Without sunlight available to planetary habitats, interstellar habitat relies on fusion reactors to provide internal power. A helium isotope, Helium-3, is the best candidate for fusion fuel. Two most likely sources include: 
RECALL THREE PHASE PROFILE
of Thought Experiment's typical interstellar profile from Sol to AC. 
| PHASE-1. ACCELERATE AT G-FORCE FOR ABOUT ONE YEAR | |
 |
Previous work indicates that 365.26 days of g-force acceleration achieves cruise velocity, VCru, 63.8% c, light speed, for a distance of about .38 Light Year (LY). Einstein conducted thought experiments to determine Principle of Equivalence:"occupants will not distinguish between g-force accleration or being static on Earth's surface".
Thus, the g-force which accelerates the spacecraft will also impart near Earth gravity throughout the vessel. Our Thought Experiment (TE) assumes that fuel limitations will restrict acceleration duration to about one year. |
| PHASE-2. CRUISE AT 63.8% LIGHT SPEED (c) FOR SEVERAL YEARS. | |
| TE considers it impractical for an interstellar vessel to carry enough fuel to accelerate for entire interstellar flight; thus, the vessel needs to spend a long portion of flight at a constant velocity "cruise" phase. Fortunately, a year of g-force acceleration brings this constant velocity to a significant portion of light speed, c. For example, Sol's nearest stellar neighbor is Alpha Centauri, about 4 LYs away; .638c makes the cruise time about about 6 years (tCru= 4 LY / .638c = 6.3 years ). Cruise Phase. Having achieved a significant portion of light speed (.64 c), travel time between stars reduces from centuries to just years. Since g-force propulsion will be off for cruise phase, near Earth gravity is maintained by spinning the habitat section of the vessel just like asteroidal habitats will have done for centuries back at the Solar System. |  |
| PHASE-3. DECELERATE AT G-FORCE FOR ABOUT A YEAR. | |
| Deceleration Phase reduces ship's velocity down to operational speed at destination to orbit around the star and it's children such as planets, asteroids, etc.
Without this essential deceleration, interstellar vessel would stay imprisoned at two thirds light speed forever!! |  |
- A gas giant, perhaps Uranus, can be mined for huge quantities. (NOTE: See "To Uranus".)
- A large magnetic field might collect/fuse enough interstellar protons to fuel onboard fusion reactors. (NOTE: See "Interstellar Ramjets".)
|
Deuterium (D) and Tritium (T) fuse most readily; their nucleonic electrical charge is the lowest of all elements. A deutrerium nucleus fuses with a tritium nucleus to form an alpha particle (4He nucleus) and a neutron. This reaction produces about 17.6 million electron volts (MeV) of energy.
PROBLEM: Above neutrons have no electrical charge and can't be controlled by magnetic fields. Thus, as an unwanted byproduct of first generation fusion reactors, neutral neutrons disregard magnetic forces and fly off into the walls of a fusion chamber, making them radioactive. Destructive power of those neutrons is cumulative and eventually adds up. After several years, reactor walls irradiate beyond repair and must be replaced. Also, this process creates large volumes of high-level radioactive waste.
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Second generation fuels (Deuterium and Helium-3) generate more energy than first generation fuels, but they require much more stringent confinement methods. A Deuterium atom fuses with a Helium-3 isotope (3He) to produce a proton and 4He nucleus (also known as an "alpha" particle).
Sum of components going into the reaction weigh more then the reaction results, because the missing mass converts to energy. 
Fusion When we fuse Helium-3 with Deuterium, we get the following aneutronic fusion reaction,
2D + 3He → 4He (3.7 MeV) + 1p (14.7 MeV)
This is currently the most promising process for power generation; this is due to the nature of its reaction products. Most other fusion processes produce radioactive neutrons which bombard reactor components and eventually render them useless. In contrast, Helium-3 itself is non-radioactive. Fortunately, magnetic fields can contain high-energy protons and generate electricity.
PROBLEM: Inevitable side reactions (D-D fusion) result in minor low energy neutron production; thus, second generation fusion reactions will most likely never be completely 'clean'. |
|
Helium 3 fusion would be ideal for powering spacecraft during the long stints of interstellar travel. While offering fusion's high performance power, 3He-3He reactors would require less shielding then the 2nd generation process.
(3He-3He) "third generation" fusion power fuses many Helium-3 atoms, to produce only protons and alpha particles with total energy of 12.9 MeV; this eliminates stray neutrons and radioactive waste. Third generation fusion fuels produce only charged particles in the primary reactions. With almost no neutrons, there would be little induced radioactivity in the walls of the fusion chamber. This is often seen as the end goal of fusion research. 3He has the highest Maxwellian reactivity of any 3rd generation fusion fuel.
Thought experiment assumes 3rd Gen. fusion reactors will be essential for starship's auxiliary power needs. In this regard, Helium-3 (3He) might prove an essential resource for interstellar travel but not necessarily directly toward propulsion. This fusion process might provide essential power for the many power hungry life support processes as well as some components of the accelerator. In this aspect, 3He might someday become an essential part of the propulsion process. | |||||||||||||||||||||||
| PROTON + BORON-11 YIELDS 3 ALPHAS | |||||||||||||||||||||||
 Electricity could directly form via moving charged particles, bypassing the need for inefficient steam turbines. Energy Losses: High temp electrons release massive amounts of X-ray energy via bremsstrahlung radiation. This energy loss might exceed any gains from fusion reactions. CURRENT RESEARCH: TAE Technologies is pursuing p+B-11 fusion | |||||||||||||||||||||||
| CARBON, NITROGEN, OXYGEN (CNO) CATALYTIC CYCLE | |||||||||||||||||||||||
The CNO cycle commences once the stellar core temperature reaches 14 × 106 K and is the primary source of energy in stars of mass M > 1.5 M⊙. TE assumes no current commercial research into CNO fusion production. | |||||||||||||||||||||||
| Planet | Typical Distance to Earth | Planet Mass |
Escape Velocity |
Estimated Mass of Helium-3 | Estimated Energy Capacity |  |
|---|---|---|---|---|---|---|
Earth=
1.0 AU
| M⊕ = 1 Earth mass
| Earth's e = 11.2 km/sec
| mT = metric Tonne
| 1 yr = Earth annual consume
| ||
Jupiter
|
5 AU
|
318×M⊕
|
59.5 kps
|
350×1012 mT
|
65×109 yr
| |
Saturn
|
10 AU
|
95×M⊕
|
35.5 kps
|
104×1012 mT
|
19×109 yr
| |
Uranus
|
20 AU
|
15×M⊕
|
21.3 kps
|
16×1012 mT
|
3×109 yr
| |
Neptune
|
30AU
|
17×M⊕
|
23.7 kps
|
19×1012 mT
|
3.5×109 yr
|
BRIEF AFTER THOUGHT
Dr. Gerald Kulcinski, previous director of the University of Wisconsin's Fusion Technology Institute (FTI), managed the "inertial electrostatic confinement device," an experimental low-power reactor that has successfully used lasers to perform continuous deuterium-helium-3 fusion. May 2001, FTI researchers created fusion from steady-state deuterium-helium 3 plasma in a small reactor with a basketball sized chamber. While it produced some radioactive waste, it was much less than the standard deuterium-tritium fusion reaction.
"Proof of principle," says Dr. Kulcinski, "but the next generation of Helium-3 fusion reactors will perform better and be completely free of radiation. Pure Helium-3 fusion (3He-3He) is a long way off, but it's worth the effort," says Kulcinski, "You'd have a little residual radioactivity when the reactor was running, but none when you turned it off. It would be a nuclear power source without the nuclear waste."
NOTE: In addition to He-3, additional energy might come from an external source. See INTERSTELLAR RAMJET which leverages concepts from Bussard and Whitmire for harvesting enroute high speed particles.
posted by JimODell at 4:34 AM
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