The discovery, which will now push the launch back until August or September 1999, has already forced redesigns of the probe and dramatically altered mission capabilities, said to Yasunori Matogawa, director of ISAS-B external Affairs Division.
Originally composed of a barrel shaped 520 kg mothership and three 13 kg penetrators designed to smash below the lunar crust to collect seismic data, Lunar-A should have been launched in early 1997. However integration problems and leaking lithium batteries discovered during tests last summer by the penetrators builder Nissan Motors, which will have to withstand an impact speed of 300 meter per second, have delayed the mission to this year.
While these problems have been "fully resolved," according to Matogawa, the institute's mission analysis group realized late last year that the 520 kg mothership needed more primary battery power to survive up to five hours of lunar shadowing incurred during the orbiting mother probe-B’s mission. Weight restrictions have meant adding a third 15 kg primary battery, forcing ISAS to strip one of the penetrators and change the solar panel configuration to rebalance the probe.
"Our strategy has been to keep the changes to the minimum and we are planning to start final assembly and checks of the flight model this September," ISAS-B Lunar-A project manager Takashi Nakajima said, June 12.
While ISAS has yet to calculate the extra costs incurred, according to Nakajima, ISAS would "find the money from internal resources," and refrain from asking the Ministry of Education, which runs ISAS, or the regulatory Science and Technology Agency, which controls budget requests, for extra cash, he said. Lunar-A was originally budgeted at 19.2 billion yen and has no extra money allocation for this year's delay.
Mitsugi Chiba, Director of the space policy division at the at the Science and Technology Agency told Japan Space Net that ISAS would find it difficult to get extra funding. "The development budget for Lunar-A has already been set and they may need to take funds from other programs," he added.
The loss of a penetrator also posed questions whether the probe's science mission, an extensive study of moonquakes to determine the fundamental structure of the body, its core size and possibly discover its origin, were in doubt, said Matogawa. Three penetrators, including one on the far side, were deemed minimal to lay a network to research these themes, building on data collected from Apollo 17 and other studies conducted by NASA.
"The space science committee has discussed intensely about the effect of the loss of a penetrator.., but eventually we concluded that it was still worthwhile," he said.
One near and one far side penetrator, both placed near the moon's equator, will incorporate Apollo data in their measurements, making most of the original scientific objectives reachable, but with some reduced accuracy in measuring core size, according to Matogawa.
ISAS now expects to be able to estimate core size to within 50 kilometers, which will be vital to determining whether the moon was born with the Earth either from the original proto-planet cloud or ejected by a huge impact billions of years ago, or a completely separate body captured by the Earth's gravity.