NASA officials said Tuesday they were a year away from making the final decision whether to send a robot spacecraft to service the Hubble Space Telescope.

We will be looking at summer 2005 for the (Critical Design Review), said Al Diaz, NASA's associate administrator for the agency's Science Mission Directorate. Diaz said NASA was evaluating several types of robots that could

accomplish the servicing task, but is mainly focused on a system called Dexter, a highly advanced robotic arm that could handle tools and equipment and install the necessary replacement instruments, batteries and gyroscopes while docked to the craft.

Diaz declined to identify the potential costs of the robot servicing mission option, but did not dispute reports the cost could reach $1 billion or more.

We have about three and a half years in which to develop a robot flight, decide to de-orbit the Hubble to a watery grave, or fly a crew of astronauts aboard the space shuttle, as has been done four times previously.

NASA administrator Sean O'Keefe last January canceled the remaining planned shuttle trip to Hubble for safety concerns. But Diaz told reporters during a teleconference Tuesday the space agency was doing nothing that would

make a shuttle service call impossible.