Japan's Mars probe
in final tests
Tokyo - Nov, 26, 1997 - Japan's first Mars probe,
Planet-B, is now undergoing flight model systems and
integration tests this month in preparation for launch in August
1998. On arrival at Mars the probe will continue Origins-style
work where Mars Global Surveyor leaves off. Masaki Adachi, a
manager of Tokyo-based NEC Corp.'s scientific satellite systems
department said, "Right now we're having no problems. There have
been some minor delays getting some components, but this is
normal," he told Japan Space Net.
Following integration, the probe's scientific instruments will
begin complete systems testing in December. Environmental,
vibration and mechanical shock tests come in February, thermal
vacuum tests in March and a final inspection is scheduled in
mid-April before packing and shipping to Kagoshima launch center,
in Kyushu, southern Japan, said Adachi.
All tests will be at the Sagamihara campus of the Institute of
Space and Astronomical Science (ISAS), outside Tokyo. NEC is
integrating the 11.3 billion yen ($100 million) 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.
Firstly, after a four-month 400,000 km apogee, 7,000 km perigee
parking orbit above Earth, the probe will use a fuel-saving lunar
swing-by maneuver to propel itself on a 10-month voyage to Mars,
arriving mid-October 1999.
"While NASA have 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 20 percent lighter. The spacecraft will also
make use of silicon solar cells that are 23 percent lighter and
capable of converting 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 in the middle of next
century, said Nakatani.
NEC also considered the manufacture of light, compact
communications and command systems for the probe as reinforcing
its status as ISAS' preferred contractor, said Adachi.
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. The process of
depletion is ill-understood, according to ISAS' Planet B science
mission manager, so Planet-B's work will compliment NASA's
Origins-style investigations of the planet.
"We think the evolution of life on Mars is an important part of
Martian history, and this depletion will enable us to better
understand the planets evolution," he said October 30.
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.