The redesign and associated costs pose new challenges for the project and the Earth Observation Program of the National Space Development Agency (NASDA) of Japan, ADEOS-2 project manager Tadaaki Kurosaki told Japan Space Net. The redesign and associated costs may lead the project and NASDA's earth observation program into more trouble.

"We must change the paddle tension control system, which also means adjusting the attitude control and reaction control systems..." said Kurosaki.

ADEOS' flexible array collapsed June 30 because a minute layer of epoxy resin sandwiched along the middle of the 0.6 millimeter thick 26 meter paddle expanded and contracted beyond the means of the blanket's tension control mechanism to control it, breaking the system and then the paddle, according to an August 29 report submitted to the Space Activities Commission.

In an informal report relayed to NASDA on September 8, Kurosaki's team is consulting with engineers from Toshiba and Mitsubishi Electric on how many of four options to increase the new paddle's durability can be implemented.

Of the recommendations under consideration, the first asks for peer review of the tension control system mechanism design and the studying of changes in orbital operation to relieve stress on the paddle. The second looks at the possibility of rearranging the hinge and pressure board structure. The third suggests improvement of validation tests including more and better vacuum chamber and fatigue loading tests. The last calls for the possibility of adding an on-board monitoring system either from the ground, through a CCD camera or through improved telemetry monitoring.

"These options are only under discussion, it's only a technical study," said Kurosaki who emphasized that it was too early to comment on which ones would be adopted.

Carrying five major missions, including the NASA/JPL-developed Sea Winds sensor, the 3.7 ton ADEOS-2 is intended to build on the global earth observation duties carried out by its predecessor. ADEOS-2 was also to have deployed an array identical in size, weight and subsystems to the original ADEOS, but with more advanced silicon cells delivering around 14 percent more power.

ADEOS-2 will also be inserted in a sun-synchronous sub-recurrent 800km orbit. Attaining global coverage over a series of 585 sweeps in 41 days, it will have to survive the same stresses subjected on ADEOS, rapidly passing from sun to shade and back some 16,000 times over its 3 year operational lifespan.

Rather than redesign the new paddle completely, ADEOS-2 engineers initially plan to strengthen the array's tension control system by reducing internal friction within the wire and pulley assembly perched at the paddle's tip, said ADEOS-2 associate senior engineer Takashi Tamura, September 9. The moves also come on top of previous decisions to strengthen the array's pin-hinges following the demise of ADEOS-1, he said.

"Even before the ADEOS failure we noticed unusual vibrations in its array and we supposed they were caused by problems in the tension control system, we didn't think it was working properly, we also had report of similar problems on Hubble," he said.

"We were lucky," said Kurosaki, who pointed out ADEOS' failure came just before last July's scheduled critical design review and not later. As it is Kurosaki said the redesign would require rebalancing of several other systems and he could not rule out a launch delay, which has already been held back from February to summer 1999.

"This is very critical. The users have put us under a lot of pressure to launch before 1999 and then we have to find a launch window before the H-2A program begins with the launch of ARTEMIS in 2000," he said.

Kurosaki and NASDA officials say it is too early to estimate redesign costs until the proposals are discussed by the Space Activities Commission at the end of September. With ADEOS-2 already due to increase its budget from 9.5 billion to 15.6 billion next year, officials are skeptical whether all of the options for ensuring the paddles' credibility will be accepted. Among the most controversial might be asking for the whole series of rechecking and peer reviews when NASDA is under pressure to strip away such stages to cut development costs.

"It's necessary to struggle with this problem. Project managers will have to decide which points are most important," Nobuo Saki of NASDA's earth observation engineering department, said September 8. Saki had been one of the chief investigators into ADEOS' failure.

However Ryuichi Sekita, deputy director of the Science and Technology Agency (STA) put the chances of a launch delay at "50/50."

"Right now STA is not preparing for a delay and we will not begin any discussions about rebudgeting yet, but the National Space Development Agency and STA may propose asking for an additional budget this financial year...redesigning will cost a lot of money," he said.

The problems on ADEOS and ADEOS-2 will not cause NASDA to discontinue developing flexible paddles in the future, especially for large buses requiring lightweight and compact systems, said officials.