NASA
(Advanced
Space
Transportation Program) and
Pennsylvania State University
(Laboratory
for Elementary
Particle Science -- more
images)
Interstellar version of a Matter-
AntiMatter rocket (with an Ion
Compressed Antimatter Nuclear
(ICAN)
engine that rotates
shielded habitation modules at
the end of four extended arms
to provide pseudo-gravity.
Introduction
Currently, interstellar travel is an extremely expensive proposition whose engineering solutions have yet to be resolved. Alpha Centauri 3, the closest neighboring star system, is located over four light-years away. To travel four light-years within 40 years -- inside a human lifetime -- requires an average travel speed of about 10 percent of the speed of light (0.1 C).
Marshall Space
Flight Center, NASA
Larger illustration.
Bussard ramjet fusion propulsion systems
still lack workable engineering solutions
to provide magnetic scooping and fusion
of interstellar hydrogen
(more).
Under those constraints, a single-stage rocket would need to have a specific impulse (Isp) of over four million seconds with over 97 percent of its total mass comprised as fuel. Multi-stage fusion and matter-antimatter rockets would require relative mass ratios between stages that exceed 1,000. While Bussard fusion ramjets have been proposed, no workable engineering solutions for magnetically scooping and fusing interstellar hydrogen "drag-free" (instead of carrying along propellant) have been developed thus far. Space sails (e.g., relying on laser-beamed power from the Solar System instead of carrying it along) require very large and low density sails that are difficult to deploy and control. (See NASA summary in pdf.)
Interstellar Propulsion Research : presentation by Les Johnson (Marshall Space Flight Center) of "realistic possibilities and idealistic dreams."
Robert Forward, NASA
-- larger B&W image
A space sail with detached inner sail
in deceleration mode. (For more
information, see
Solar
Sails, Paul
Woodmansee's discussion of
Light Sails,
and a NASA web link page on
Solar
Sails and its
Interstellar
Probe proposal.)
Current Propulsion Options : overview by Island One.
| Propulsion Type | Specific Impulse [sec] | Thrust-to-Weight Ratio |
| Chemical Bipropellant | 200 - 410 | .1 - 10 |
| Electromagnetic | 1200 - 5000 | 10-4 - 10-3 |
| Nuclear Fission | 500 - 3000 | .01 - 10 |
| Nuclear Fusion | 10+4 - 10+5 | 10-5 - 10-2 |
| Antimatter Annihilation | 10+3 - 10+6 | 10-3 - 1 |
Fusion Rockets : summary.
NASA
Larger and
largest images
Fusion rocket.
The existence of antimatter was predicted by physicist Paul A.M. Dirac in 1929. By 1953, however, Eugen Sanger (a German rocket scientist) had proposed its use for spacecraft propulsion because antimatter has the highest energy density of any material currently found on Earth. Under current proposals, the annihilation of matter with antimatter is 10 billion times more efficient than the oxygen-hydrogen combustion in the Space Shuttle's main engines, and about 100 times more than fission or fusion reactions. As shown in the table above, antimatter offers the greatest specific impulse of any propellant currently available or in development, and its thrust-to-weight ratio is still comparable with that of chemical propulsion. By comparison, it would take only 100 milligrams of antimatter to equal the propulsive energy of the Space Shuttle.
Courtesy of Laboratory for
Elementary Particle Science
at Pennsylvania State
University and NASA
Larger
image
Robotic interstellar vessel with
Matter-AntiMatter propulsion.
On the other hand, at a recently estimated cost of about $6.4 million per nanogram (about 1,000 antiprotons to the penny) through one productionproposal involving enhancements to the U.S. Fermi National Accelerator Laboratory, antimatter would be the most expensive source of energy known today. Hence, it's too expensive for use currently as a pure antimatter rockets. However, small amounts of antimatter would be useful for initiating and maintaining fission or fusion reactions in hybrid rockets.
Matter and antimatter destroy each other, efficiently converting matter to energy in a real-world application of Einstein's classic E=mc2 equation. Storing antimatter is a technical challenge that engineers at NASA's Marshall Space Flight Center and the Laboratory for Elementary Particle Science at Pennsylvania State University worked on through new designs for penning traps, sophisticated magnetic bottles that "pen" or suspend chilled antimatter and keep it from touching the walls of its container in 1999. Even more difficult, of course, is creating anitmatter, as high-energy particle accelerators currently can make only about 10 billionths of a gram of antiprotons per year (equivalent to a mere 10 grams of Shuttle propellants).