Lunar-A mission: Outline and current status |
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| Authors: | H Mizutani A Fujimura S Tanaka H Shiraishi T Nakjima |
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| Institution: | (1) Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Yoshinodai 3-l-l, Sagamihara, 229 8510 Kanagawa, Japan |
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| Abstract: | The scientific objective of the Lunar-A, Japanese Penetrator Mission, is to explore the lunar interior by seismic and heat-flow
experiments. Two penetrators containing two seismometers (horizontal and vertical components) and heat-flow probes will be
deployed from a spacecraft onto the lunar surface, one on the near-side and the other on the far-side of the moon. The data
obtained by the penetrators will be transmitted to the earth station via the Lunar-A mother spacecraft orbiting at an altitude
of about 200 km.
The spacecraft of a cylindrical shape, 2.2 m in maximum diameter and 1.7 m in height, is designed to be spin-stabilized. The
spacecraft will be inserted into an elliptic lunar orbit, after about a half-year cruise during which complex manoeuvering
is made using the lunar-solar gravity assist. After lunar orbit insertion, two penetrators will be separated from the spacecraft
near perilune, one by one, and will be landed on the lunar surface.
The final impact velocity of the penetrator will be about 285 m/sec; it will encounter a shock of about 8000 G at impact on
the lunar surface. According to numerous experimental impact tests using model penetrators and a lunar-regolith analog target,
each penetrator is predicted to penetrate to a depth between l and 3 m, depending on the hardness and/or particle-size distribution
of the lunar regolith. The penetration depth is important for ensuring the temperature stability of the instruments in the
penetrator and heat flow measurements. According to the results of the Apollo heat flow experiment, an insulating regolith
blanket of only 30 cm is sufficient to dampen out about 280 K lunar surface temperature fluctuation to < 3 K variation.
The seismic observations are expected to provide key data on the size of the lunar core, as well as data on deep lunar mantle
structure. The heat flow measurements at two penetrator-landing sites will also provide important data on the thermal structure
and bulk concentrations of heat-generating elements in the Moon. These data will provide much stronger geophysical constraints
on the origin and evolution of the Moon than has been obtained so far.
Currently, the Lunar-A system is being reviewed and a more robust system for communication between the penetrators and spacecraft
is being implemented according to the lessons learned from Beagle-2 and DS-2 failures. More impact tests for penetrators onto
a lunar regolith analogue target will be undertaken before its launch. |
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| Keywords: | Lunar-A penetrator lunar exploration lunar interior lunar seismology heat flow |
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