Saturday, 19 March 2011

Mission profile

The MESSENGER probe was launched on August 3, 2004 at 06:15:56 UTC by the National Aeronautics and Space Administration from Space Launch Complex 17B at the Cape Canaveral Air Force Station in Florida, aboard a Delta II 7925 launch vehicle. The complete burn sequence lasted 57 minutes bringing the spacecraft into a heliocentric orbit, with a final velocity of 10.68 km/s (6.64 miles/s) and sending the probe into a 7.9 billion-kilometer trajectory that took 6 years, 7 months and 16 days before its orbital insertion on March 18, 2011.[8]

Traveling to Mercury requires an extremely large velocity change (see delta-v) because the relative closeness of Mercury's orbit places the planet deeper in the Sun's gravity well. As MESSENGER traveled to Mercury, it was constantly being accelerated as it fell toward the Sun. For planets such as Venus and Mars, a technique known as aerobraking is used to slow a spacecraft to orbital speed. However, the tenuous atmosphere of Mercury is far too thin for this maneuver to work for MESSENGER. Instead MESSENGER made extensive use of gravity assist maneuvers to gradually slow the spacecraft. This process greatly reduced the amount of propellant necessary to slow the spacecraft, but at the cost of prolonging the trip by many years and to a total distance of 5.9 billion miles. To further minimize the amount of necessary propellant, the spacecraft orbital insertion targeted a highly elliptical orbit around Mercury. The elongated orbit has two other benefits. It allows the spacecraft time to cool after the times it is sandwiched between the hot surface and the sun, and it allows the spacecraft to measure the effects of solar wind and the magnetic fields of the planet at various distances while still allowing close-up measurements and photographs of the surface and exosphere.

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