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NASA has used Voyager 1's trajectory correction maneuver (TCM) thrusters in place of its attitude control thrusters. The move could extend the amount of time NASA can communicate with Voyager 1 by two to three years:
NASA scientists needed to reorient the 40-year-old Voyager 1 -- the space agency's farthest spacecraft -- so its antenna would point toward Earth, 13 billion miles away. But the "attitude control thrusters," the first option to make the spacecraft turn in space, have been wearing out.
So NASA searched for a Plan B, eventually deciding to try using four "trajectory correction maneuver" (TCM) thrusters, located on the back side of Voyager 1. But those thrusters had not been used in 37 years. NASA wasn't sure they'd work.
Tuesday, engineers fired up the thrusters and waited eagerly to find out whether the plan was successful. They got their answer 19 hours and 35 minutes later, the time it took for the results to reach Earth: The set of four thrusters worked perfectly. The spacecraft turned and the mood at NASA shifted to jubilation.
Also at Space.com.
(Score: 3, Informative) by inertnet on Tuesday December 05 2017, @09:18AM (3 children)
That's the one way time. They had to wait twice as long after sending their commands.
(Score: 5, Interesting) by isostatic on Tuesday December 05 2017, @01:35PM (2 children)
They knew the thrusters wouldn't ignite until Tuesday 04:14. At 04:13 they knew the thrusters were off and hadn't been turned on. Then from 04:14 they had no idea if the thrusters had turned on or not, and didn't until 23:49.
The question I suppose is what does 'now' mean. Did they fire up the thrusters at Tuesday 04:14, when the command reached the ship, or did they fire them up the Monday at 09:39 when they issued the command on their keyboard.
(Times changed to protect the innocent)
(Score: 2) by crafoo on Tuesday December 05 2017, @06:06PM
In terms of relativity, now means whatever it means from your reference frame. There is no "prime" reference frame. Now means different things depending on your reference frame.
In terms of voyager and the distances involved: just think of it as really bad display lag. like, really pretty bad. about as bad as a Sony, not quite as bad as Samsung.
In terms of Voyager 1, it fired it's thrusters when the signal was received telling it to do so. We found out about it some time later, at approximately distance/c later in voyager's frame (voyager isn't traveling at a significant fraction of c).
(Score: 2) by inertnet on Tuesday December 05 2017, @10:22PM
The context is that the engineers fired up the thrusters and started waiting. The clock started ticking when the command was sent and stopped when the answer was received. To me that's a round trip.