It could cost $42 million or so to take a retired space shuttle and display it in a museum or other forum, according to John Shannon, space shuttle program manager.

Much of that expense is to completely rid the shuttle of the many toxic substances in its systems, he told space journalists in a briefing.

They include the auxiliary power system, control systems, and Freon-filled radiators.

Every last bit of the toxic materials must be removed, he said. "Even if you drain [the dangerous substances] and let it vent" by leaving a system open, that won’t suffice, he said.

If that is all that is done, then when the system is resealed, even a film of toxic substances remaining in a system will cause toxic fumes to build up in the sealed space, he explained.