Dextre has a central "torso" with two 10-foot arms that can pivot, turn, reach and grab in seven different ways. In repose, it is a 2,220-pound, Rube Goldberg-style titanium stick figure, but in action it can readily choose a mix of intricate movements to execute the commands of its operator.
Dextre's future changed dramatically in January, after NASA Administrator Sean O'Keefe canceled a scheduled shuttle servicing mission to Hubble, citing safety concerns after last year's Columbia tragedy.
Goddard Director Edward Weiler, reflected in a copy of the Hubble's photo of Eagle Nebula, calls the mission almost as difficult as landing on Mars twice.
(Preston Keres -- The Washington Post)
Public outrage greeted this decision, which essentially sentenced Hubble to a watery grave once its batteries give out, but O'Keefe left open the possibility of robotic repair, and NASA sent out a bulletin asking for proposals.
Burch, who oversees Hubble from Goddard's Greenbelt labs, said the cancellation did not come as a surprise: "We knew it was going to be a long time before a shuttle mission, and if that day never came, what could we do?"
MD Robotics responded to the bulletin, and Goddard asked to see Dextre perform. "We were able to demonstrate a lot that astronauts had done," said Dan King, MD Robotics' director for orbital robotics. "We opened doors, gained access, changed an existing connector, that kind of thing."
After Goddard and MD Robotics engineers dazzled the NASA brass in last April's demonstration, excitement started to build, climaxing in August, when O'Keefe traveled to Goddard to tell the Hubble team to get to work on a robotic mission to fly by the end of 2007.
Late last month, NASA awarded MD Robotics a $144 million preliminary contract to provide Dextre and the grappling arm, and gave a $330.6 million contract to Lockheed Martin for the de-orbit module. Goddard will build the ejection module and assemble the package, which will weigh about 24,000 pounds, fully fueled.
NASA set 2007 as the deadline, at first suggesting that Hubble's batteries would give out by then and cause the telescope to shut down within hours. But Weiler said a second set of test batteries on the ground show that Hubble's power should last until 2009. Still, engineers are sticking with an early launch in case the schedule slips.
Each of the contemplated jobs is complicated but doable, Massimino said. "The main thing is to move very slowly." There is a time lag of 1.5 seconds between the command sent by the operator on the ground and Dextre's ability to execute it as it orbits with Hubble 360 miles above the Earth, but Massimino said he and another astronaut were able to handle the delay "pretty well" during a recent practice run, "as long as we took our time."
The Hubble Robotic Vehicle will be built from scratch, giving the United States a robotic rendezvous and docking capability for the first time in the history of space travel.
The spacecraft will use the 39-foot grappling arm to grab Hubble, then swing down until the de-orbit module can lock to the telescope's underside. Executing this maneuver -- which is routine for the shuttle -- will require precision sensors that Lockheed Martin must develop.
The de-orbit module will have six new batteries inside and will feed power to the telescope through the same "umbilical" cable that the shuttle used, an arrangement that will survive for the rest of Hubble's life. The robot will jettison the tool-carrying ejection module at the end of the servicing mission, but the de-orbit module will stay with Hubble until the end, eventually steering it into the sea.
The trouble with the new alignment is that power can only move in one direction, so the batteries cannot be recharged through the umbilical cable. Instead, Dextre will rig jumper cables from the telescope's solar arrays to the batteries.
Next, Dextre will unlatch the fastener holding Hubble's Wide-Field and Planetary Camera 2 in place and remove it from the telescope, like pulling out a drawer. Wide Field Camera 3, one of four imaging instruments on the telescope, will then be inserted to replace it.
This would also be a relatively straightforward task, except engineers will attach six new gyroscopes to the camera, thus avoiding the hazards involved with opening the difficult-to-handle doors that guard the compartment where the original gyros are mounted.
To make it work, Dextre will have to run a cable from the new gyroscopes out the compartment door, back to control units in the de-orbit module, then up to the telescope's computer, so Hubble can receive the information it needs to aim the telescope and stay stable in space.
Next comes the Cosmic Origins Spectrograph, another swap-out requiring Dextre to disconnect and reconnect four electrical cables. After that, Burch would like to have it install a new Fine Guidance Sensor, a pointing device, and he has also asked for ideas on robotic repair of the nonfunctioning Space Telescope Imaging Spectrograph.
"The concern of headquarters" is that "these crazy people at Goddard" want to do too much, Burch acknowledged. "And it's true, we don't want to lose sight of the main objectives."