moonsky_485.jpg:

In July, the space shuttle Discovery is slated to deliver two tons of hardware and supplies to the partially built International Space Station. This mission is paid for. As for the 16 more needed to finish assembly, as mandated by President George W. Bush two years ago in his Vision for Space Exploration policy, NASA is short by as much as $5 billion. On top of that, the agency needs an estimated $15 billion to build its new Crew Exploration Vehicle to reach the moon by 2020 (another Vision mandate).

To come up with the cash, in February NASA proposed a staggering $3 billion in cuts from its space-science budget over the next five years. Among the endangered missions is the Terrestrial Planet Finder, two telescopes intended to hunt for Earth-like planets around nearby stars, and the Europa Orbiter, a probe designed to find alien life on Jupiter´s moon. If Congress approves the bud-
get this summer, these and many others face extinction. Below, four projects on the chopping block.

THE ENDANGERED PROJECTS:

• What We'd Lose:The chance to find habitable planets. Slated to launch by 2020, two space telescopes would look for signs of life around nearby stars.
• Money Saved: Up to $1.7 billion over
  15 years.
• The Rationale: Costly technical challenges still remain for the second telescope, a fleet of small infrared scopes that must be flown in precise formation.

• What We'd Lose: Insight into our planet's birth. If launched later this year, Dawn would study two rare asteroids containing building blocks of the early universe.
• Money Saved: $40 million, which is the cost to complete the project. (NASA has already spent $371 million to build the orbiter.)
• The Rationale: Dawn´s ion engine is weaker than it should be, and the processing units that provide power to the orbiter´s thrusters are not functioning properly.

• What We'd Lose: The ability to reach Mars in two months instead of six. The program would build nuclear reactors to power and propel spacecraft.
• Money Saved: $2.1 billion over five years. (NASA has already spent about $900 million on the project since its inception in 2003.)
• The Rationale: NASA hopes to share the cost of the research by partnering with countries including France, Russia and Japan, all of which are investing in nuclear propulsion.

• What We'd Lose: The potential discovery of alien life on Jupiter´s moon Europa. If launched in 2015, the probe would search for a subterranean liquid ocean.
• Money Saved: Up to $700 million over
  10 years.
• The Rationale: NASA plans to focus on more-promising targets, such as Saturn´s moon Enceladus, where geysers of water may have been detected in March.