Mercury Minus Ten, Pluto Minus Eighty-five



As of 2015/04/20 there are 10 days until the MESSENGER spacecraft goes splat somewhere in Mercury’s northern regions, and just under three months until the-little-spacecraft-that-could, New Horizons, flies by our last commonly accepted outpost, planetoid Pluto.


Image credit: NASA–NSSDC/New Horizons


These two missions bookend our solar system, innermost and outermost, if you disregard the billions of tiny bodies stretching farther out in the Kuiper belt and Ort cloud, farther than the eye can see and with more Pluto-sized bodies than the schoolchildren can memorize (which is probably one practical reason Pluto was demoted from planethood in the first place).

MESSENGER has been spaceborne since 2004, New Horizons, 2006. New Horizons was pretty much a straight shot to Pluto; MESSENGER was a complicated mess, the equivalent of a 6 bank shot in billiards, flying by Earth once after launch, Venus twice, and Mercury three times before dropping into the pocket—that is, going into orbit—on the fourth Mercury encounter in 2011.

Now MESSENGER is out of hydrazine and quite literally running on fumes, squirting the helium gas that used to pressurize the fuel straight out of the tanks and through the thrusters. Not as efficient as the hydrazine, but sufficient to delay the inevitable a few maneuvers and days at a time as the orbit closest approach altitude inches (kilometers!) toward an inevitable rendezvous—a kiss of death with the Mercury surface somewhere in the North-polar region, the final splatt. One more planned maneuver on April 24th should stave it off until about the 30th of April, and then it’s bye-bye MESSENGER.

New Horizons was the fastest ever spacecraft at launch, peaking at a blistering 43 kilometers per second relative to the Sun. The inexorable hand of gravity slowed it so that—even though a distant flyby of Jupiter gave it a boost—today it glides at a more leisurely pace, 14.5 kilometers per second through the deeps and darks of space. When it gets to Pluto it’ll fly by that remote outpost—more than 30 times the distance from Sun to Earth—at a tad under 14 kilometers per second.

Interestingly, the distance New Horizons has traveled all the way out to Pluto is less than MESSENGER traveled in its pinball encounters with the inner solar system planets to lose enough energy to get into orbit at Mercury. Gee, Mr. Wizard, you have to lose a lot of energy to get to Mercury.


Image credit: NASA–APL

Too bad MESSENGER’s demise can’t be delayed two more months. Then the Deep-Space Navigators of both spacecraft, who work for KinetX Aerospace, would be able to say they’re navigating simultaneously to the extremes of the solar system. Nevertheless, to do them both within a few months of each other is pretty noteworthy.

Important science was done at Mercury and more knowledge comes from Pluto in July, but the purpose of this blog is to celebrate the art and science of deep-space navigation—and particularly the two KinetX Navigation Teams (both of which I was once a member)—that guided us there, for truly the journey is more than half the fun …

And we almost always get you there!


2 thoughts on “Mercury Minus Ten, Pluto Minus Eighty-five

  1. Michael Mello

    Great blog Brian. “Mercury Minus Ten, Pluto Minus Eighty-five” is very well-written and loaded with far more information than most of us will ever get about these missions from the standard news agencies. Great stuff!

  2. Black Sky Voyages Post author

    Thanks, Michael. It was my great privilege to be aboard this mission (metaphorically, of course!) from launch through the 1st Mercury flyby. Still doing some data processing for it.

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