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Messenger at the planet Mercury

NASA image from their "Messenger" probe on its approach toward Mercury, approximately 17,000 miles out.
Click image to enlarge to 1000 pixel width.

About NASA Messenger with some history
The last time anything man-made got this close to the planet Mercury was the NASA probe Marinar 10 back in 1974 through 1975. Marinar used the gravitational pull of Venus to enable it to visit both planets and take pictures that were sent back to earth. That mission also allowed NASA to improve upon the "gravitational assist" method of using competing celestial gravity fields to maneuver. "Gravity assist" is also called "gravity sling-shot" among other things, and it is based upon mathematical theories developed at the Steklov Institute of Russia in 1959.¹ Using this method has its problems, though, because while it cuts down on the need for fuel, it is a slower method of travel, and also it has to accomodate the change in position of planets and other objects that are in constant orbital motion.

Messenger was launched August 3, 2004 at the Cape Canaveral Air Force Station in Florida, atop a Boeing Delta II rocket. Because the planet Mercury is so close to the gravitational pull of the Sun, Messenger is piloted by NASA using "gravitation sling-shot" maneuvers to control Messenger's velocity. Otherwise, it would simply increase speed until it plunged into the sun, and so goodbye $446 million.²

Messenger is propelled by a main biopropellent engine that uses "dual-mode" liquid chemical (combinations of hydrazine, nitrogen tetroxide and helium). This engine is used for course correction and its fuel load takes up 55% or the entire Messenger weight of 2,410 pounds (or 1093 Kg). Messengr is also equipped with sixteen thrusters to allow minute position alterations. This is necessary because the recording instruments on Messenger are rigidly fastened to the body of the craft. These thrusters use battery power which is recharged using the vehicle's solar array panels that collect and store energy from the sun.

The four onboard computers all use radiation-hardened IBM RAD6000 processors, and two solid-state data storage units are used for recording info from the onboard science instruments. (A Mercury Dual Imaging System, a Gamma-Ray and Neutron Spectrometer, an X-ray Spectrometer, a Mercury Laser Altimeter, and a Atmospheric and Surface Composition Spectrometer (MASCS), all fixed to the bottom deck of the main unit.Also onboard is an Energetic Particle and Plasma Spectrometer mounted to the side and top deck. A magnetometer is on the end of a 12 1/2 foot boom pole.

What the NASA Messenger space probe looks like.

This NASA probe is called 'Messenger' based upon contracting this mission summary: MErcury Surface, Space ENvironment, GEochemistry and Ranging.

Timeline of development and
mission goals for NASA Messenger:

Preliminary:
July 1999 -- MESSENGER approved as the 7th Discovery Program mission
December 1999 -- Preliminary design started
July 2001 -- Final design approved and construction begins
December 2003 -- Space-environment testing starts at Goddard facility
March 2004 -- Pre-launch preparations at Astrotech Space Operations
July 15, 2004 -- Media briefing at NASA Headquarters

Launch:
August 3, 2004 -- MESSENGER Launched
August 2005 -- Earth flyby
October 2006 -- Venus flyby
June 2007 -- Venus flyby
January 2008 -- Mercury flyby
October 2008 -- Mercury flyby
September 2009 -- Mercury flyby
March 2011 -- Yearlong science orbit of Mercury to begin

The NASA probe "Messenger" recorded this image of the surface of Mercury in January 2008. From the nasa.org site.

FOOTNOTES
1. Steklov Mathematical Institute web site is here.
2. The price for the cost of the NASA Messenger program is from this news story "Messenger space probe to visit Mercury" from thursday, January 10, 2008 at cbc.ca online here.

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