Time to say goodbye to the Messenger, 5 miles up at 8,000 mph

Posted: April 27, 2015 by tchannon in Uncategorized


Sodium gas tail, image from http://messenger.jhuapl.edu/image_highlights.html

Executes Last Orbit-Correction Maneuver, Prepares for Impact
MESSENGER mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., conducted the last of six planned maneuvers on April 24 to raise the spacecraft’s minimum altitude sufficiently to extend orbital operations and further delay the probe’s inevitable impact onto Mercury’s surface.

With the usable on-board fuel consumed, this maneuver expelled gaseous helium — originally carried to pressurize the fuel, but re-purposed as a propellant. Without a means of boosting the spacecraft’s altitude, the tug of the Sun’s gravity will draw the craft in to impact the planet on April 30, at about 8,750 miles per hour (3.91 kilometers per second), creating a crater as wide as 52 feet (16 meters).

At the start of yesterday’s maneuver, at 1:23 p.m. EDT, MESSENGER was in an orbit with a closest approach of 8.3 kilometers (5.1 miles) above the surface of Mercury. With a velocity change of 1.53 meters per second (3.43 miles per hour), the spacecraft’s four largest monopropellant thrusters released gaseous helium to nudge the spacecraft to an orbit with a closest approach altitude of 18.2 kilometers (11.3miles).


The crater will be out of sight. The next Mercury mission is expected maybe 2018 will take a look.

Post by Tim

  1. Alan Poirier says:

    Will it determine if Mercury is a planetary core? That’s what I’d like to know.

  2. tchannon says:

    Good question.
    If we had seismometers on the surface, maybe. Don’t think we do, wee bit too hot.

  3. Brian H says:

    The sun’s tug will crash it? Not Mercury’s?

  4. tchannon says:

    Ah yes Brian, well, an object in orbit will stay there permanently unless there is an additional force.

    I read that and thought the same as you. The web site is kind of the horse’s mouth, so a typo is possible but unlikely.

    I don’t know.

    Drag from whatever gas or particles are there will be one thing. Electrodynamic drag another. Neither are solar tug. Only thing comes to mind is the orbit gets pulled out of shape. Wonder who actually knows?

  5. oldbrew says:

    ‘an object in orbit will stay there permanently unless there is an additional force’

    There’s orbital decay due mainly to atmospheric drag.

  6. tchannon says:

    An atmospheric pressure of 1 nanopascal is not a lot.

  7. oldbrew says:

    ‘Satellite Orbital Decay Calculations’ – Australian BoM

    Click to access SatelliteOrbitalDecayCalculations.pdf