Requiem for a Space Probe


Just over a month ago, the MESSENGER space probe crashed into Mercury. It wasn’t a surprise, of course, MESSENGER was always going to crash into Mercury, and the date was fairly well known. MESSENGER completely ran out of fuel, and even after it ran out of fuel it was kept operating for a few more days using the helium that pressurized the tanks as a last-minute source of thrust*. At 11:15 AM EDT on April 30th, they began communicating with the spacecraft for the last time; at 3:25 PM EDT they lost contact for the final time as MESSENGER swung around the far side of the planet, and it spent its last minutes prior to destruction alone and out of contact with Earth.

Around the same time, the various twitter accounts associated with MESSENGER sent out very sad tweets:

Why do we anthropomorphize spacecraft? I think it’s because we care about people, and the things we care about become people. The road to MESSENGER was long, starting with the 1974-1975 flybys of Mariner 10 (which remains the only other spacecraft to ever visit Mercury), continuing up through 1998 when the Mercury Orbiter mission was selected by NASA using a very clever orbital approach that would take a long time but allow a small and cheap spacecraft to reach Mercury*. And then it took 6 years to build the spacecraft, 7 years to reach Mercurian orbit, and the actual meat of the mission was going to be 1 year of Mercury orbits.

This was actually extended twice to bring the final mission up to 4 years (if you’ve expended 13 years of effort to do the hard work of building a spacecraft and sending it to Mercury, why WOULDN’T you want to keep using it as long as it works?). The extended missions allowed scientists to watch the effects of the Sun during the recent 2012-2013 Solar Maximum, and also push the spacecraft into more extreme close passes of Mercury so they could get better images of the surface. Meanwhile, the Sun’s gravity pulled rather strongly on the spacecraft, meaning that it had to expend a lot of fuel to maintain its orbit and keep from hitting Mercury. When the fuel ran out, well…

At the time of the spacecraft’s demise, the actual craft had spent 11 years in space, and the project had been running for (at least) 17. That’s 17 years of pouring your heart and soul into something, only to have it suddenly be gone. Sure, it leaves behind mountains of data, but there will be no more from that instrument that you guided all the way to Mercury.

Machines aren’t forever, any more than people are. The Space shuttles are gone. The Spirit rover is gone (2210 days into its 90 day mission). The Mars Phoenix Lander is gone. Pioneer 10 and 11, our first eyes on the outer reaches of the Solar System, are gone (in 2003 and 1995, respectively), and some day fairly soon the Voyager space probes will join them, drifting off into an endless unpowered night.

Those are sad days. The robotic explorers are extensions of ourselves. They are our eyes and arms in exploring outer space, and testaments to our ability to create and interest to explore. And eventually, like all things, they break down or run out of power.

MESSENGER’s story isn’t quite over, though. It’s left one last scientific treasure behind: a fresh crater excavating the surface of Mercury, that’ll be only nine years old when the BepiColumbo orbiters arrive in 2024 to pick up where MESSENGER left off.

* Why is it so hard to get to Mercury? Well, the Earth orbits the Sun at 1 AU with an orbital period of 1 year, and anything launched from it will have basically the same orbit size and time. You could somewhat quickly alter an orbit to go in to Mercury’s distance from the Sun (0.38 AU) but the craft would then swing past and shoot out rather far beyond the Earth’s orbit, such that your average distance was still 1 AU. If you want to actually ORBIT Mercury, you have to lose a LOT of energy. That either requires a big rocket, or the series of complicated slingshot maneuvers MESSENGER used.


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