onward, Voyager!

As of this week, Voyager 2 is 37 years old, having launched on August 20, 1977.  That makes it the longest-running space probe mission, easily surpassing the solar observatory Pioneer 6, launched in 1965 and last contacted in December 2000 (it’s not clear if they’ve tried since). Despite what Wikipedia says on its page on space probes, Voyager 2 is older than Voyager 1; Voyager 1 was launched two weeks later on September 5, on a more optimal trajectory that got it to Jupiter and Saturn first.

At launch, the Voyager mission (until six months earlier considered part of the Mariner program, where the probes would have been Mariner 11 and 12) was only supposed to go to Jupiter and Saturn, because it was deemed too expensive to build a spacecraft to do the Grand Tour NASA initially wanted. However, NASA kept the option open for Voyager 2’s flight path, and after an extremely successful visit to Saturn and Titan by Voyager 1 (which prevented it from going on to Pluto), Voyager 2’s flightpath was altered to send it to Uranus and Neptune.

Voyager’s extended mission gives us practically all we know about Uranus and Neptune, their moons, and is the closest look we’ve had at outer solar system objects.  That includes everything from the appearance of Miranda, the mixed-up moon of Uranus, and Neptune’s crazy captured moon Triton, which orbits Neptune backwards, at an angle, and has volcanoes and an atmosphere.  (Seriously). If that’s what awaits us at Pluto, we’re going to have a very fun year in 2015.

The Voyager space probes benefitted greatly from software upgrades en route.  Voyager camera platforms rotate to track objects and take longer exposures, but for Uranus and Neptune, Voyager 2 had to be reprogrammed to rotate the entire spacecraft to get images. It apparently worked well enough that NASA no longer builds probes with rotating camera platforms (except for the Mars rovers). Right now, the camera software has been removed from the probes to make room for its current mission, charting the edge of the heliopause and the beginnings of interstellar space.

Despite its fame and incredible bounty of results, Voyager 2 has suffered some problems.  Shortly after launch it suffered a technical fault that meant it had to find itself again (locating the Sun, Canopus, and Earth while spinning). It has also been operating on its backup receiver since 1978, its magnetometer was accidentally destroyed by a misinterpreted command in 2006, and in 2010, it suffered some sort of computer glitch probably caused by a cosmic ray hit flipping a crucial bit in its memory, which has now been repaired.  But it continues.

And yes, they do make them like that nowadays – The NEAR spacecraft was only meant to orbit 433 Eros, which it did, and then it LANDED on the asteroid in 2001.  The Mars Rovers Spirit and Opportunity landed in 2004 and were meant to last 90 days, but we only lost contact with Spirit in 2010, and Opportunity is still going.  Cassini’s initial mission (launched 1997, arrived at Saturn in 2004) was supposed to last four years – ending in 2008.  The current mission extension keeps it operational through 2017, and its final fate largely depends on how much propellant remains in 2017 to control the probe.

And some day, we will go back to Uranus and Neptune – the New Horizons probe flies by Pluto next year.  It will be going slow, compared to the Voyager probes, and will never pass them… which is good for imaging Pluto, but bad for setting distance records.  Until we launch something else, Voyager 1 and 2 will be at the head of our interstellar lineup for a long time to come.

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