-----Original Message-----
From: Daniel R. Zeigler, Ph.D. <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Monday, January 22, 2001 7:29 AM
Subject: Two weeks to Mars?!?
>
>Two weeks to Mars?!? Let's see...that would mean Jupiter in six
>months...Pluto in less than a year and a half... Is this technology
>feasible? If so, how long (best case scenario) would it take to develop
it?
>
>---------
>
>
>Nuclear engine promises to slash travel times to Mars
>BY JEFF FOUST
>SPACEFLIGHT NOW
>Posted: January 19, 2001
>A novel type of nuclear reactor could cut make it possible for spacecraft
to
>travel from the Earth to Mars in as little as two weeks, one Israeli
>researcher has found.
>Yigal Ronen, a professor of nuclear engineering at Ben-Gurion University of
>the Negev, believes that americium-242m (Am-242m), a little-known isotope
of
>an artificially produced element, could power future robotic or human
>spacecraft far more efficiently than chemical or other nuclear propulsion
>sources.
>Ronen found that Am-242m could sustain nuclear fission even when formed
into
>thin sheets less than a micron (millionth of a meter) thick. Such thin
>sheets would let the byproducts of the fission reaction to easily escape
>their fuel elements, allowing them to ionize and heat materials like
>hydrogen that could serve as a propellant.
>"The gas will be magnetically confined so temperatures of about 250,000
>degrees can be reached," explained Ronen. "With such temperatures a
velocity
>of 80 km per second can be obtained."
>Ronen estimates that such an engine on a typical robotic spacecraft would
>require only about 375 grams of Am-242m per day, or several kilograms for
>the trip from Earth to Mars. The material could be produced by irradiating
>another isotope, Am-241, with neutrons, a process that Ronen admits is
>expensive today but still feasible.
>The idea of using americium to power spacecraft is still in the earliest
>concept stages, Ronen emphasized. "We have not done an elaborate design,"
he
>said. "Actual reactor design, refueling, heat removal, and safety
provisions
>for manned vehicles have not yet been examined."
>Another issue that would have to be addressed by a mission using an
>americium or other nuclear-powered engine is strong opposition by many
>environmental and anti-nuclear activists to any spacecraft mission that
uses
>radioactive isotopes. In 1997 a small but vocal group of protestors staged
>rallies and made legal attempts to stop the launch of NASA's Cassini
>mission, which carries 32 kg of plutonium dioxide in heavily-shielded
>radioisotope thermoelectric generators (RTGs).
>Ronen shrugged off such political issues. "The controversy about using
>radioisotopes in space is not related to a real problem, it is mainly a
>political issue," he said. "I don't know how to deal with a problem which
is
>'no problem'."
>This proposal is not the only concept for propulsion systems that could
>shorten travel times to Mars. Another proposal, the Variable Specific
>Impulse Magnetoplasma Rocket (VASIMR), would use magnetic fields and
>electromagnetic waves to heat hydrogen, turning it into a high-velocity
>propellant like Ronen's americium engine. The VASIMR team, led by NASA
>astronaut and plasma physicist Franklin Chang-Diaz, believes such an engine
>could send a human mission from Earth to Mars in 90 days.
>Ronen believes that, given time, americium will prove to be a key fuel for
>future space missions, citing the support of, among others, Nobel laureate
>physicist Carlo Rubbia. "Rubbia has also recognized that this is the most
>probable fuel that will be getting us to Mars and back," Ronen said. "I
>think that we are now far enough advanced to interest international space
>programs in taking a closer look at americium-based space vehicles."
>
Before I cheerfully say that using this stuff in a spaceship is "no
problem", I'd like to know just how radioactive it is, thank you. (The nice
thing about uranium-235 is that -- unless it's piled up in a critical
mass -- it's virtually non-radioactive.)
Bruce Moomaw
==
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