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Pulled from an old email...
><< >Dr. Chang-Diaz then presented a summary of his research on plasma
> >engines and the VASIMR (variable specific impulse magnetic resonance)
> >propulsion system.>>
>Chang-Diaz took me on a tour of his lab a couple of years ago, at which
>he gave me a copy of a paper on the VASIMR system so I could annotate it
>"Romance to Reality." He also checked my write-up for accuracy, so I think
>can safely claim that my description is better than the MIT PR. . .
>>>"Rapid Mars Transits with Exhaust-Modulated Plasma Propulsion," Franklin
>Chang-Diaz, et al, NASA Technical Paper 3539, March 1995.
>Veteran astronaut Chang-Diaz leads a team at NASA's Johnson Space Center
>developing an "advanced (nonchemical)" rocket engine using plasma
>heating and magnetic containment technologies derived from nuclear
>fusion research. Chang-Diaz commenced work on the design in the early
>1980s. Called VASIMR (Variable Specific Impulse Magneto-Plasma Rocket),
>the system features a modulated ("tunable") exhaust permitting
>high-thrust operation during departure from and arrival in planetary
>orbit and gradual shift to continuous low-thrust operation between
>planets. The practical upshot is a highly efficient, potentially very
>fast propulsion system. According to the authors, exhaust modulation,
>first proposed in the 1950s, permits both slow, high-payload cargo
>missions and fast, low-payload crew missions using the same rocket
>engine. Chemical rocket engines cannot be "tuned" in this manner.
>Modulation is made possible through use of a new-technology two-stage
>hybrid "magnetic nozzle" instead of a solid matter engine bell. The
>engine consists of three magnetic cells. An injector ionizes hydrogen
>gas into cold, dense plasma and places it into the forward cell. This
>"seed" plasma is heated in the central cell using radio-frequency
>radiation beamed by antennas. Upon achieving the desired temperature and
>density, the plasma is exhausted through the aft cell, which includes
>the hybrid magnetic nozzle. Three nuclear fission reactors provide
>redundant electricity for magnetic containment, hydrogen ionization, and
>plasma heating. The authors propose three possible mission profiles:
>•Cargo "slowboat" missions are one-way, 180-day automated cargo missions
>with payload making up 66 percent of total spacecraft mass.
>•The first piloted Mars mission is a "speedboat" mission profile with
>payload making up 2 percent of spacecraft mass, a 101-day outbound
>voyage, 30 days on Mars, and a 104-day inbound trip (total mission
>duration = 235 days). If difficulties occur within 15 days of Earth
>departure the spacecraft can abort back to Earth in 75 days, assuming a
>fully functional propulsion system. An abort scenario assuming
>accidental loss of all propellant returns the crew to Earth in 180 days.
>•Later Mars missions include a 90-day outbound trip, "winter over" 705
>days on Mars to permit the planets to align for optimum transfer, and a
>90-day inbound trip (total duration = 885 days). On the outbound leg
>payload can make up 18 percent of total spacecraft mass; on the inbound
>leg, payload can total 14 percent.
>The authors propose aerobraking and other techniques to further enhance
>the engine's already considerable capabilities.<<
>The *big* problem with this exciting prop tech is the three big fission
>reactors, given nuclear energy hysteria.
"They make a desert and call it peace."