Thursday, August 30, 2007


Credit: MIC onboard NOZOMI / ISAS

The 1998-99 launch window was an ambitious one, with three spacecraft launched toward Mars; unfortunately, all three suffered failures.

The first of the three to be launched was Nozomi ("Hope"), the first (and, to date, only) Japanese spacecraft to be sent toward Mars.

Its mission was to conduct long-term investigations of the planet's upper atmosphere and its interactions with the solar wind, and to track the escape trajectories of oxygen molecules from Mars' thin atmosphere. The spacecraft also was to take pictures of the planet and its moons from its operational orbit of 300 x 47,500 kilometers. During perigee, Nozomi was to perform remote sensing of the atmosphere and surface; while close to apogee, the spacecraft would have studied ions and neutral gas escaping from the planet. Although designed and built by Japan, the spacecraft carried a set of fourteen instruments from Japan, Canada, Germany, Sweden, and the United States.

Nozomi was launched by an M-V (M-5), a Japanese solid fuel rocket, on July 3, 1998. After entering an elliptical parking orbit around Earth, Nozomi was sent on an interplanetary trajectory that involved two gravity-assist flybys, once around the Moon on September 24th, and once around the Moon and the Earth on December 18th and December 20th, respectively. However, on the December 20th flyby, a malfunctioning valve resulted in a loss of fuel and left the spacecraft with insufficient acceleration to reach its planned trajectory. Two course correction burns were made on December 21st, but the burns used more propellant than planned, leaving the spacecraft short of fuel.

A new mission was then devised, whereby Nozomi would remain in a heliocentric orbit for an additional four years, including two Earth flybys in December 2002 and June 2003, and encounter Mars at a slower relative velocity in December 2003. On April 21, 2002, as Nozomi was approaching Earth for the gravity-assist maneuver, powerful solar flares damaged the spacecraft's onboard communications and power systems. An electrical short was caused in a power cell used to control the attitude control heating system, allowing the hydrazine fuel to freeze. The fuel thawed out as the craft approached Earth and maneuvers to put the craft on the correct trajectory for its Earth flyby were successful.

The second Earth flyby occurred on June 19, 2003. The fuel had completely thawed out for this maneuver because of the spacecraft's proximity to the Sun. However, on December 9, 2003, efforts to orient the craft to prepare it for a December 14, 2003 main thruster orbital insertion burn failed, and efforts to save the mission were abandoned. The small thrusters were fired on December 9, moving the closest approach distance to 894 km so that the probe would not inadvertently impact on Mars and possibly contaminate the planet with Earth bacteria, since the orbiter had not been intended to land and was therefore not properly sterilized. Nozomi flew by Mars on December 14, 2003 and went into a roughly 2-year heliocentric orbit. Though its mission has been abandoned the spacecraft is still active.

The above photograph, of the Earth and Moon, was the first picture taken by Nozomi, on July 18, 1998.

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