[meteorite-list] MESSENGER Executes Last Orbit-Correction Maneuver, Prepares for Impact

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun, 26 Apr 2015 14:40:11 -0700 (PDT)
Message-ID: <201504262140.t3QLeBLg009656_at_zagami.jpl.nasa.gov>

http://messenger.jhuapl.edu/news_room/details.php?id=282

MESSENGER Mission News
April 25, 2015

MESSENGER 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).

The previous maneuver, completed on April 14, raised MESSENGER's minimum
altitude above Mercury from 6.5 kilometers (4.0 miles) to 13.3 kilometers
(8.3 miles). But because of progressive changes in the orbit over time,
the spacecraft's minimum altitude continued to decrease.

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).

Mission controllers at APL verified the start of the maneuver 9.4 minutes
later, when the first signals indicating spacecraft thruster activity
reached NASA's Deep Space Network (DSN) tracking station in Goldstone,
California. This was the third MESSENGER maneuver designed to adjust the
course of the spacecraft using just helium gas.

Since MESSENGER's launch in 2004, mission engineers have been working
in lockstep with KinetX Aerospace to conduct such maneuvers. KinetX, based
in Simi Valley, California, is the first commercial company to navigate
any spacecraft to distant planetary bodies. The team processes radiometric
tracking measurements from NASA's DSN antennas to perform orbit determination
for MESSENGER.

The KinetX team was key to successfully navigating the spacecraft to arrive
at the planet, and then for maintaining precise knowledge of the spacecraft's
position while in orbit, including these last two months during MESSENGER's
"hover campaign."

"Navigating a spacecraft so close to a planet's surface had never been
attempted before, but it was a risk worth taking given mission success
had already been met, and the novel science observation opportunities
available only at such very low altitudes," said Bobby Williams, who leads
the KinetX Space Navigation and Flight Dynamics group. "The MESSENGER
mission presented new technical challenges for mission design and navigation
that were successfully met through close cooperation and innovation of
the APL and KinetX flight operations teams."

MESSENGER Principal Investigator Sean Solomon, Director of Columbia University's
Lamont-Doherty Earth Observatory, commented on yesterday's maneuver on
behalf of the project's Science Team as the end of the mission draws near.

"Operating a spacecraft in orbit about Mercury, where the probe is exposed
to punishing heat from the Sun and the planet's dayside surface as well
as the harsh radiation environment of the inner heliosphere, would be
challenge enough," he said. "But MESSENGER's mission design, navigation,
engineering, and spacecraft operations teams have done much more. They've
fought off the relentless action of solar gravity, made the most of every
usable gram of propellant, and devised novel ways to modify the spacecraft
trajectory never before accomplished in deep space. They've extended the
duration of MESSENGER's orbital observations by more than a factor of
four over the original plan, and an amazing set of scientific discoveries
has been enabled by their creative efforts. This latest maneuver is icing
on a multi-tiered cake of spectacular accomplishment. The MESSENGER mission
will soon end, but its legacy of scientific knowledge and technical innovation
will endure for as long as we study the planets and explore the Solar
System."
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MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging)
is a NASA-sponsored scientific investigation of the planet Mercury and
the first space mission designed to orbit the planet closest to the Sun.
The MESSENGER spacecraft was launched on August 3, 2004, and entered orbit
about Mercury on March 18, 2011, to begin a yearlong study of its target
planet. MESSENGER's first extended mission began on March 18, 2012, and
ended one year later. MESSENGER is now in a second extended mission, which
is scheduled to operate through April 2015. Dr. Sean C. Solomon, the Director
of Columbia University's Lamont-Doherty Earth Observatory, leads the mission
as Principal Investigator. The Johns Hopkins University Applied Physics
Laboratory built and operates the MESSENGER spacecraft and manages this
Discovery-class mission for NASA.
Received on Sun 26 Apr 2015 05:40:11 PM PDT