Nozomi at Mars
|Launch date||July 4, 1998, Uchinoura Space Center|
|Mission duration||December 9, 2003|
|Homepage||Nozomi official site|
|Mass||258 kilograms (569 lb)|
Nozomi (のぞみ) (Japanese for "Wish" or "Hope," and known before launch as Planet-B) was planned as a Mars-orbiting aeronomy probe, but was unable to achieve Mars orbit due to electrical failures. Operation was terminated on December 31, 2003.
It was constructed by the Institute of Space and Astronautical Science, University of Tokyo and launched on July 4, 1998 at 03:12 JST (18:12 UTC) with an on-orbit dry mass of 258 kg and 282 kg of propellant.
Nozomi was designed to study the upper Martian atmosphere and its interaction with the solar wind and to develop technologies for use in future planetary missions. Specifically, instruments on the spacecraft were to measure the structure, composition and dynamics of the ionosphere, aeronomy effects of the solar wind, the escape of atmospheric constituents, the intrinsic magnetic field, the penetration of the solar-wind magnetic field, the structure of the magnetosphere, and dust in the upper atmosphere and in orbit around Mars. The mission would have also returned images of Mars' surface.
The spacecraft used a lunar swingby on September 24, 1998 and another on December 18, 1998 to increase the apogee of its orbit.
It swung by Earth on December 20, 1998 at a perigee of about 1000 km. The gravitational assist from the swingby coupled with a 7 minute burn of the bipropellant rocket put Nozomi into an escape trajectory towards Mars. It was scheduled to arrive at Mars on October 11, 1999 at 7:45:14 UT, but a malfunctioning valve during the Earth swingby resulted in a loss of fuel and left the spacecraft with insufficient acceleration to reach its planned trajectory. Two course correction burns on December 21 used more propellant than planned, leaving the spacecraft short of fuel.
New mission plan
The new plan was for Nozomi to remain in 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.
First Earth flyby
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 occurred 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.
Second Earth flyby
Another Earth flyby within 11,000 km 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 1000 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.
The spacecraft flew by Mars on December 14, 2003 and went into a roughly 2-year heliocentric orbit.
Intended Mars mission
Nozomi was to be inserted into a highly eccentric Mars orbit with a periareion 300 km above the surface, an apoareion of 15 Mars radii, and an inclination of 170 degrees with respect to the ecliptic plane. Shortly after insertion, the mast and antennas were to be deployed. The periareion would have been lowered to 150 km, the orbital period to about 38.5 hours. The spacecraft was to be spin stabilized at 7.5 rpm with its spin axis (and the dish antenna) pointed towards Earth. The periapsis portion of the orbit would have allowed in-situ measurements of the thermosphere and lower exosphere and remote sensing of the lower atmosphere and surface. The more distant parts of the orbit would be for study of the ions and neutral gas escaping from Mars and their interactions with the solar wind. The nominal mission was planned for one martian year (approximately two Earth years). An extended mission might have allowed operation of the mission for three to five years. The spacecraft was also to point its cameras at the martian moons Phobos and Deimos.
Spacecraft and subsystems
The Nozomi orbiter is a 0.58 meter high, 1.6 meter square prism with truncated corners. Extending out from two opposite sides are solar panel wings containing silicon solar cells which provide power to the spacecraft directly or via NiMH (nickel metal hydride) batteries. On the top surface is a dish antenna, and a propulsion unit protrudes from the bottom. A 5 m deployable mast and a 1 m boom extend from the sides, along with two pairs of thin wire antennas which measure 50 m tip to tip. Other instruments are also arranged along the sides of the spacecraft. Spacecraft communications are via X-band at 8410.93 MHz and S-band at 2293.89 MHz. The 14 instruments carried on Nozomi are an imaging camera, neutral mass spectrometer, dust counter, thermal plasma analyzer, magnetometer, electron and ion spectrum analyzers, ion mass spectrograph, high energy particles experiment, VUV imaging spectrometer, sounder and plasma wave detector, LF wave analyzer, electron temperature probe, and a UV scanner. The total mass budgeted for the science instruments was 33 kg. Radio science experiments were also possible using the existing radio equipment and an ultrastable oscillator. The total mass of Nozomi at launch including 282 kg of propellant was 540 kg.