The Martian Chronicles
Issue 9, Spring 2001

The Nozomi Mission to Mars
by Anthony M. Schilling


The Japanese Institute of Space and Astronautical Science (ISAS) launched Nozomi/Planet B towards Mars on July 4th, 1998 from the Kagoshima Space Center. After launch, the $80 million dollar, 535 kg (1,177lb) Planet B probe was renamed ďNozomiĒ (Hope). Japan became the third country, after the US and Russia, to launch a Mars probe.

Saving the Mission

Nozomiís original trajectory involved orbiting the Earth for 4 months, then 2 lunar swingbys and a powered Earth swingby. The December 20, 1998 powered Earth swingby was to put Nozomi on a transfer orbit with a scheduled arrival at Mars for October 11, 1999. Unfortunately, a thruster valve malfunction during the Earth swingby put the spacecraft into an incorrect trajectory. To correct the error, the Mission Control team decided on a second firing, which placed Nozomi back on a trajectory toward Mars.

Nozomi's Launch  
Nozomi's Launch

As a result of the second maneuver, Nozomi no longer had enough fuel to place itself into orbit around Mars. The mission analysis team found an alternative trajectory to would save the mission. Nozomi would perform two more swingbys of Earth - in December 2002 and another in June 2003. This low fuel consumption trajectory would put the spacecraft into orbit around Mars during January 2004. Upon arrival, Nozomiís orbit will range from a low of 96 miles to 27,000 miles.

The mission science

Nozomiís 2 year primary mission is to investigate the motion and structure of the upper atmosphere and ionosphere of Mars. The probe will also study the interaction of the atmosphere, ionosphere, and solar wind. There are 14 experiments on the Nozomi from 5 different countries, including a NASA neutral mass spectrometer. Other countries contributing experiments include Canada, Germany, and Sweden.

NASAís Neutral Mass Spectrometer (NMS) will study the vertical and horizontal density variations of the major neutral constituents in the upper atmosphere of Mars. The measurements will determine the existing dynamic, chemical, and thermal state. The highly elliptical orbit will allow data to be taken in the low altitude atmospheres and ionosphere as well as the solar wind interaction regions.

  Planet-B/Nozomi getting ready for launch  
Planet-B/Nozomi getting ready for launch
Nozomiís NMS results will be compared to results from the 1960ís Pioneer Venus mission, which used similar type of instrument.

Other instruments onboard include a Mars Imaging Camera from Kobe University and a Mars Dust Counter which will search for a dust ring along the orbit of Phobos. Nozomiís orbit is designed to permit very close passes of Phobos and Deimos to observe the shape and surface in detail. A Thermal Plasma Analyzer from Canada will investigate the components, structure, temperature, and plasma waves of the ionosphere. Other instruments from Japan will study the ionosphere, magnetic field, and atmosphere of Mars.

Current status

Despite its initial fuel problem, Nozomi has recovered well and is midway through its long journey. Nozomi is providing measurements of the interplanetary medium as it travels towards Mars. The spacecraft and its instruments are in excellent health, and they are expected to enter orbit around Mars during January 2004.