NASA has given the green light to development of a robotic spacecraft mission that reads more like a story line from a science fiction movie script. Imagine intercepting a comet in deep space and using a heavy projectile to blow a hole in the celestial body, some seven stories deep and about the size of a football field.

In a space exploration first, NASA's Deep Impact Mission will attempt to use a probe to collide with a comet in an attempt to peer beneath its surface. Scheduled for launch in January 2004, the unique spacecraft is expected to arrive at comet Tempel 1 in July 2005.

Artist's concept shows Deep Impact's flyby spacecraft and the impactor already dispatched to comet. Photo: NASA

Researchers hope the impact will allow them to measure freshly exposed material and study samples hidden deep below the surface of the comet, which could yield dramatic scientific breakthroughs.

The 770 pound impactor, equipped with a camera, will separate from the flyby spacecraft and slam into the comet at an approximate speed of 22,300 miles per hour, blasting material from the comet into space with the force of its impact. A camera and infrared spectrometer on the flyby spacecraft, along with ground-based observatories, will study the resulting icy debris and exposed pristine interior material.

The total cost of Deep Impact to NASA is $279 million. The principal investigator, Dr. Michael A'Hearn, University of Maryland, College Park, will lead a team consisting of NASA's Jet Propulsion Laboratory in Pasadena, CA, and Ball Aerospace Technology Corp., Boulder, CO, which will build the spacecraft.

Comet Tempel 1 was discovered in 1867. Orbiting the sun every five and a half years, it has made many passages through the inner solar system. This makes it a good target to study evolutionary change in the mantle, or upper crust, of the comet.

Scientists are eager to learn whether comets exhaust their supply of gas and ice to space or seal it into their interiors. They would also like to learn how a comet's interior is different from its surface. The controlled cratering experiment of this mission could provide those answers.

NASA's Discovery Program emphasizes lower-cost, highly focused scientific missions within the Space Science enterprise. NASA has developed six other Discovery Program missions. Three have completed their missions, one is operational and two others, in addition to Deep Impact, are under development:

• In 1997, the Mars Pathfinder lander, carrying a small robotic rover named Sojourner, landed successfully on Mars and returned hundreds of images and thousands of measurements of the Martian environment.
  
  
• The Near Earth Asteroid Rendezvous (NEAR) spacecraft orbited the asteroid Eros for a year, ending with a successful landing on February 12, 2001.
  
  
• The Lunar Prospector orbiter mapped the Moon's composition and gravity field and completed its highly successful mission in July 1999.
  
  
• The Stardust mission to gather samples of comet dust and return them to Earth was launched in February 1999, and is on its way to comet Wild-2.
  
  
• The Genesis mission to gather samples of the solar wind and return them to Earth is scheduled for launch on July 30, 2001.
  
  
• The Comet Nucleus Tour (CONTOUR) mission to fly closely by three comets is scheduled for launch in June 2002.