SPACE scientists have been forced to radically redesign Japan鈥檚 first lunar
probe after a simple fault delayed its launch.
The redesign has stripped the Lunar-A mission of one of its three
moonquake-measuring devices, called penetrators, which would have helped to
determine the size and composition of the Moon鈥檚 core (鈥淲atch this space鈥�,
快猫短视频, 25 November 1995, p 46). The scientists will now have to
fall back partly on data from the Apollo missions.
Lunar-A was to have been launched in February, but a leaking battery set this
back. The timing was crucial because Japan鈥檚 Institute of Space and
Astronautical Sciences planned to use a period in which the Earth would cast
less of a shadow over Lunar-A鈥檚 orbit. The probe will now have to spend more
time in darkness as it orbits the Moon, so it will require more battery power to
compensate for the loss of energy from its solar panels.
Advertisement
Instead of waiting years for the next ideal astronomical configuration, ISAS
has decided to redesign the craft and launch it in August 1999. The rebuilt
Lunar-A will be fitted with an extra battery to survive longer in the Earth鈥檚
shadow. But the addition means the loss of a vital component.
鈥淭he new battery weighs 15 kilograms,鈥� says Yasunori Matogawa, director of
the Kagoshima Space Centre. 鈥淓ach penetrator weighs 13 kilograms. So one of the
penetrators had to go.鈥�
Lunar-A鈥檚 penetrators are rocket-powered capsules containing seismometers and
other instruments. They will slam into the Moon鈥檚 surface at up to 300 metres
per second and bury themselves to a depth of between 1 and 3 metres. The
monitoring instruments are designed to withstand an impact of around 50 000
times the force of gravity on Earth.
The seismometers will measure moonquakes which occur at depths of 500 to 900
kilometres. The quakes are believed to originate at the same locations at
monthly intervals, indicating that they result from tidal stresses as the Moon
orbits the Earth.
Comparing the shockwaves will determine the size and composition of the core.
ISAS intended to use recordings from seismometers left on the Moon by Apollos 12
and 14 only to supplement its own data.
鈥淭he core measurement will not be affected by having just two penetrators,鈥�
says chief mission scientist Mizutani Hitoshi. 鈥淏ut we鈥檒l have to place them
differently, on opposite sides of the Moon. And we鈥檒l have to rely more on the
Apollo data.鈥�
ISAS hopes to determine whether the core is iron or some other material such
as siderite, an iron-rock mixture commonly found in meteorites. That information
could give clues about the origins of the Moon鈥攚hether it was created
after a glancing collision between the Earth and an object the size of Mars or
was dragged into Earth鈥檚 orbit from another part of the Solar System.