The rest of the (long) article is also interesting, but the section on JIMO is of particular interest.....

http://www.spacedaily.com/news/spacetravel-05v.html

Washington DC (SPX) Apr 21, 2005

In addition to the Hubble debacle, discussed above, the gross managerial failures during this period included the Orbital Space Plane program, the Jupiter Icy Moon Orbiter program, and the loss of the space shuttle Columbia.

Next, the Jupiter Icy Moon Orbiter (JIMO) intended to use advanced technology to study the frozen moons of Jupiter.

This program was begun by O'Keefe himself, and could have been his greatest accomplishment-it would have been a significant scientific achievement and it would have made the essential capability of space nuclear power into a reality.

The merit of this proposal lay in the fact that replacing today's radioisotope generators with nuclear power would allow a probe sent to the outer solar system to employ active sensing instruments and to transmit back vastly greater amounts of scientific data.

Using nuclear power would also enable electric propulsion ("ion drive"), allowing the spacecraft to engage in extensive, highly efficient maneuvers among Jupiter's moons.

So far, so good. However, in order to get more funding, the electric propulsion community managed to insert a requirement into the program that the flight from Earth to Jupiter be accomplished using electric propulsion, and that the trip to Jupiter not use any planetary gravity assists ("the slingshot effect").

Suddenly, under these new rules, the power needed to propel JIMO grew to 150 kilowatts in order to reach Jupiter in nine years. This is not only absurd (in the 1970s, Voyager made the trip in less than three years; in the 1990s, Galileo did it in five) but disastrous, since the nuclear reactor cannot be rated in advance for nine years of operation.

In other words, JIMO would almost certainly fail before it reached the planet. Furthermore, as a result of the weight and the huge mass of the 150 kilowatt reactor and xenon propellant, the spacecraft couldn't be launched into space on any existing rocket.

In contrast, had these rules not been adopted, the reactor could have been scaled down to 20 kilowatts, all the interplanetary transfer xenon propellant been eliminated, and the spacecraft thus made light enough to be put on top of an existing rocket and thrown toward Venus for the first in a series of gravity assists.

These maneuvers would have allowed the spacecraft to reach Jupiter in five years on a Galileo-like trajectory, without needing to start burning the reactor until operations within the Jupiter system began.

In other words, JIMO done the easy way could have been accomplished with one-seventh the power, one-quarter the mass, half the flight time, and a much greater success probability as JIMO done the hard way.

Administrator O'Keefe apparently did not understand any of these issues. Instead, the former Secretary of the Navy wrongly equated nuclear electric propulsion for spacecraft to nuclear power for submarines, allowing them to transcend the limits of chemical propulsion and "go anywhere, anytime," without the need for such old-fashioned tricks as gravity assists.

Because of his naïveté on such matters, O'Keefe failed to see this bunk for what it was, and in fact promoted it as a programmatic mantra.

As a result, the program's cost ballooned to over $9 billion, and the White House declined to ask for further funding for Fiscal Year 2006. In the meantime, more money was spent studying JIMO than was spent designing, building, flying, and analyzing the data from the highly successful Mars Global Surveyor mission, from start to finish.

Robert Zubrin, an astronautical engineer, is president of Pioneer Astronautics, a research and development firm, and president of the Mars Society, a space advocacy group. He is the author of the nonfiction books The Case for Mars (1996), Entering Space (1999), and Mars on Earth (2003), and the science fiction political satire The Holy Land (2003).