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Satellite pair reunites from afar

News Team



Publicat Vineri, 6 Iulie 2007, ora 09:14

      A 'mechanic' satellite has successfully latched onto a target satellite after being separated by 7 kilometres in one of the final tasks of the Orbital Express mission, which was designed to test autonomous docking technologies.
     
      The US Defense Advanced Research Projects Agency (DARPA) launched the mission on 9 March 2007.
     
      Despite some glitches, the mission has demonstrated the ability of a mechanic satellite, called ASTRO (Autonomous Space Transfer and Robotic Orbiter), to rendezvous with a target satellite, called NextSat, in space, grab it with its robotic arm, and perform basic maintenance on it – with little or no help from ground controllers.
     
      The technology required to perform these manoeuvres should lay the groundwork for future autonomous robotic missions to the Moon and Mars, where communications delays with Earth would make it more efficient for robots to do some things on their own. The technology would also allow future spacecraft to be repaired or refuelled in space.
     
      Since the mission launched, ground controllers have been stepping up the challenges for ASTRO (watch an animation of a separation, fly-around and docking test carried out on 16 June). On 22 June, ASTRO autonomously separated from NextSat to a distance of 4 kilometres before returning and catching hold of NextSat with its robotic arm.
     
      Now, ASTRO has completed the mission's most challenging rendezvous of all.
      Ground intervention
     
      It undocked from NextSat on 27 June, separated to a distance of 7 kilometres, then used onboard cameras to track its partner and move back towards it. ASTRO circled NextSat at a distance of 120 metres, then closed in and seized NextSat with its robotic arm.
     
      "This scenario marks the second successful grapple and capture of the NextSat by the ASTRO using its robotic arm," reads a statement posted on DARPA's Orbital Express website.
     
      Unfortunately, the manoeuvre was not completely autonomous. After ASTRO grabbed NextSat with its robotic arm, mission controllers noticed the two spacecraft were misaligned. So they sent commands to move the satellites so they could dock together successfully.
     
      So far, NASA has not had much luck with autonomous docking. In April 2005, its Demonstration of Autonomous Rendezvous Technology (DART) mission crashed into a satellite (see Spacecraft collision due to catalogue of errors). It achieved only 11 of its 27 objectives before putting itself in a retirement orbit.
     
      Jonathan How, who does research on autonomous navigation and formation flying of spacecraft at MIT in Cambridge, Massachusetts, US, says Orbital Express has been crucial to demonstrating autonomous abilities that could be incorporated into future spacecraft.
      Mission success
     
      He thinks the fact that the ground crew had to intervene to make the spacecraft mate should not detract from the achievements of the mission. "That seems relatively harmless in my opinion," he told New Scientist.
     
      The mission succeeded in the more difficult and crucial task of getting the spacecraft to autonomously rendezvous in space after being separated, he says. Spacecraft mating is relatively easy to test and refine on the ground, he says. "I think they'll be able to get all the bugs out."
     
      ASTRO is in the process of completing its final tasks. It transferred fuel and installed new batteries on NextSat and is now removing and reinstalling one of its own flight computers using its robotic arm.

© Copyright News Team
Sursa :   NewScientist.com
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