Integrated by NEC Corp under the direction of the Institute of Space and Astronomical Science (ISAS) the Planet-B mission has been a low cost affair, with a budget of 11.3 billion yen ($85 million) for the mission.

"ISAS has worked hard to lower weights and balance fuel with scientific payloads, as well as developing techniques to enable Japan to conduct an interplanetary program within the limits of its 2-ton class launcher, the M-5," said ISAS' Ichiro Nakatani, who is the project's engineering manager.

To get to Mars, ISAS shift the probe into a 400,000 by 7,000 km orbit that will enable the probe to make a fuel-saving lunar swing-by maneuver to propel itself on a 10-month voyage to Mars, arriving mid-October 1999.

"While NASA has established these technologies, the orbit definition and planning have been a big challenge considering the limited propellant budget, along with the 40 minute-plus time delay," he said.

To survive and communicate Planet-B will use Nickel Metal Hydride (Ni-MH) batteries that are 20 percent lighter than previous battery systems used by ISAS. The spacecraft will also make use of silicon solar cells that are 23 percent lighter and capable of converting up to 18% of incoming radiation. The onboard computer will use a 128bit processor and weigh less than 1.0 kg. Such streamlining will allow the mini-probe a fuel budget of 278 kg which will be just enough to get it to Mars.

Lastly, the spin-stabilized probe will be able to autonomously self-correct its attitude to an accuracy of 0.7 degrees for up to a week without contact with NASA's deep space network.

"The spacecraft will be pretty smart...you can call it a kind of engineering test satellite for planetary missions," said Nakatani, adding that the lunar swing-by technique solution will be used by ISAS�' 2001-scheduled asteroid sample return probe, Muses-C. Further, Planet-B may form a standard bus option for ISAS as it develops a second wave of planetary probes next decade, said Nakatani.

On arrival at Mars, the probe's main task will be to measure how the solar wind depletes the planet's upper atmosphere. While NASA's Mars Surveyor, currently undergoing aerobreaking, has discovered the planet has a magnetic field and is examining the planet's lower atmosphere, scientists lack data on reading back the depletion of oxygen from the Martian atmosphere to when it may have been possible to sustain life in the open.

To do this, the probe will conduct a two-year orbital mission dipping into the outer fringes of the Martian aeronomy, or outer atmosphere, using 15 micro instruments in a 35 kg package featuring a large international component. Of this, NASA's Goddard Space Flight Center is providing a mass spectrometer, John Hopkins University a radio science equipment and Calgary University a thermal plasma analyzer. From Europe, Sweden is providing an ion mass spectrometer, Germany a dust counter from the Munich Technical University, and in France CNES will supply a data compression kit for the probe's CCD camera.

In addition to its main planetary mission, ISAS will swing Planet B�s cameras on to the tiny Martian satellites Phobos and Deimos, added Nagatani.