NASA satellite goes where no other spacecraft has gone before: Mercury orbit

NASA MESSENGER satellite achieves Mercury orbit

NASA has sent the very first spacecraft into an orbit around Mercury, the closest planet on our solar system to the Sun.

Now that it is there, NASA's satellite MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) will orbit Mercury about 730 times in the next 12 months, beaming back pictures and never-before-available pictures and data on the planet.   

The $446 million MESSENGER will orbit the planet once every 12 hours for the duration of its mission. The spacecraft will orbit Mercury at about 200 kilometers (124 miles.  At the time of orbit insertion, MESSENGER will be 46.14 million kilometers (28.67 million miles) from the Sun and 155.06 million kilometers (96.35 million miles) from Earth, NASA stated.

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According to NASA, MESSENGER's equipment will be checked out in the first few days after orbit is achieved and then on March 24 its instruments will be turned on and checked out.  Then on April 4 the science phase of the mission will begin and the first data from Mercury will be beamed to Earth. 

A quick look at MESSENGER:

Size: Main spacecraft body is 1.44 meters (57 inches) tall, 1.28 meters (50 inches) wide, and 1.85 meters (73 inches) deep; a front-mounted ceramic-fabric sunshade is 2.54 meters tall and 1.82 meters across (100 inches by 72 inches); two rotatable solar panel "wings" extend about 6.14 meters (20 feet) from end to end across the spacecraft.

Launch weight: Approximately 1,107 kilograms (2,441 pounds), including 599.4 kilograms (1,321 pounds) of propellant and 507.6 kilograms (1,119 pounds) of "dry" spacecraft and instruments.

Power: Two body-mounted gallium arsenide solar panels and one nickel-hydrogen battery. The power system generated about 490 watts near Earth and will generate its maximum possible output of 720 watts in Mercury orbit.

Propulsion: Dual-mode system with one bipropellant (hydrazine and nitrogen tetroxide) thruster for large maneuvers; 4 medium-sized and 12 small hydrazine monopropellant thrusters for small trajectory adjustments and attitude control.

The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft for NASA. 

MESSENGER has a variety of tools at its disposal. For example, MESSENGER has two cameras -- one wide-angle, and one narrow-angle -- to help the "two-eyed" Mercury Dual Imaging System (MDIS) create a map of the planet's landforms, NASA said.   It will also trace different features on the surface. A special pivoting platform will let scientists point the MDIS in whatever direction they choose, NASA said. 

The Mercury Laser Altimeter (MLA) will create topographic maps of the planet's surface in unprecedented detail, NASA stated. When the laser shines down and reflects off Mercury's surface, a sensor will gather the light, allowing scientists to track variations in the distance from the surface to the spacecraft. A Radio Science experiment will use the Doppler Effect to track the changes in MESSENGER's velocity, and translate them into clues to how the planet's mass is distributed and where the crust is thicker or thinner, NASA said. 

Three instruments will rely on a process called spectroscopy to tell scientists what elements are present in the rocks and minerals around the planet. The X-ray Spectrometer (XRS) will detect X-rays emitted by certain elements in Mercury's crust. The Gamma Ray and Neutron Spectrometer (GRNS) works in much the same way, detecting gamma rays and neutrons emitted by various elements. GRNS may also help to determine if water ice really exists in permanently-shadowed craters at the planet's north and south poles -- as previous observations suggest. The Mercury Atmospheric and Surface Composition Spectrometer will be able to determine Mercury's atmosphere and also detect minerals on the surface. The instrument is extremely sensitive to light from the infrared to the ultraviolet, NASA said. 

To get into its proper orbit, MESSENGER has taken a six-year scenic route through the solar system, including one flyby of Earth, two flybys of Venus, and three flybys of Mercury. 

Some other Mercury facts from NASA:  

  • Mercury has a diameter of 3,032 miles, about two-fifths of Earth's diameter. Mercury orbits the sun at an average distance of about 36 million miles (58 million kilometers), compared with about 93 million miles for Earth.
  • Because of Mercury's size and proximity to the brightly shining sun, the planet is often hard to see from the Earth without a telescope. At certain times of the year, Mercury can be seen low in the western sky just after sunset. At other times, it can be seen low in the eastern sky just before sunrise.
  • Mercury travels around the Sun in an oval-shaped orbit. The planet is about 28,580,000 miles from the sun at its closest point, and about 43,380,000 miles from the sun at its farthest point. Mercury is about 48,000,000 miles from Earth at its closest approach.
  • Mercury moves around the Sun faster than any other planet. The ancient Romans named it Mercury in honor of the swift messenger of their gods. Mercury travels about 30 miles per second, and goes around the sun once every 88 Earth days. The Earth goes around the sun once every 365 days, or one year.
  • As Mercury moves around the Sun, it rotates on its axis, an imaginary line that runs through its center. The planet rotates once about every 59 Earth days -- a rotation slower than that of any other planet except Venus. As a result of the planet's slow rotation on its axis and rapid movement around the Sun, a day on Mercury -- that is, the interval between one sunrise and the next -- lasts 176 Earth days.
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