February 1982:the Solar Max rescue mission

A study has been performed at the Johnson Space Center to determine the feasibility of an in-flight repair by the Space Shuttle of the malfunctioning Solar Maximum Mission (SMM or simply “Solar Max”) spacecraft. If the plan is approved, the repair mission could take place during one of the early flights.

Solar Max

Solar Max was launched into orbit on 14 February 1980 by a Delta launch vehicle from the Kennedy Space Center. The satellite was designed to observe the Sun with seven precise instruments sensitive to wavelengths from far-infrared to gamma rays. The launch was timed in such a way that the bulk of its observations would be made in 1980, the most active year of the current 11-year solar cycle. The spacecraft had a design lifetime of one year, but it was hoped that it would continue to make useful observations for much longer. The spacecraft functioned extremely well for the first eight months of its mission. It observed the birth and development of several strong solar flares and provided solar physicists with a wealth of new and exciting information about processes going on inside the Sun.

But in November 1980, the $77 million observatory was crippled by the failure of an attitude control module which provides the fine-pointing capability for four of the instruments. The failure was eventually traced to faulty fuses in the module. The spacecraft itself and all of its scientific instruments were in fine shape, but the precision pointing capability so< essential to the success of the mission was lost. It was at this point that the question of a possible Shuttle mission to repair Solar Max was raised.

Solar Max is the first of a new generation of standardised satellites specifically designed to be serviced by tfie Space Shuttle. Most of the components are modular in nature for easy pop-in/pop-out replacement, and most are designed in such a way that they can be replaced in flight with little difficulty. This allows relatively easy repair of minor malfunctions, such as the fuse failure, because such repairs can be done on-orbit without the added expense of bringing the satellite back to Earth, repairing it down here, and then re-launching it.

Well before Solar Max was launched, NASA had had plans to retrieve it from orbit on STS-15 in 1984. It was to be returned to Earth in the Orbiter's payload bay and was to be the first demonstration of the Shuttle’s satellite retrieval capability. But with the attitude control module failure, the opportunity has arisen to provide an even earlier and somewhat more ambitious demonstration of the Shuttle’s versatility as a satellite service station.

To the rescue

The Solar Max repair mission required no new hardware development and it is presently technically feasible to accomplish. For the Orbiter to achieve the nearly 550 km orbital altitude required to reach Solar Max, the payload bay would have to be almost devoid of anything not directly required for the repair mission.

The repair mission would be launched from the Kennedy Space Center into an orbit inclined at 28.5 degrees. The Orbiter would perform several burns of the Orbital Manoeuvering System (OMS) engines to achieve a rendezvous with the ailing spacecraft, which by that time is expected to be in a circular orbit of 540 to 515 km. When the Orbiter gets close enough, the Remote Manipulator System (RMS) would be deployed from the open payload bay and used to snare Solar Max on one of the satellite’s special RMS-compatible grappling hooks. The RMS would then manoeuvre the captured spacecraft to a special collar in the payload bay called the Flight Support System (FSS). The Solar Max satellite would be fastened to the FSS during the actual repair work.

While the module replacement itself is a fairly simple operation, there are several possible methods being studied that could be used to accomplish it. Most of these centre around using the RMS from inside the Orbiter, an extravehicular activity (EVA) by a crewman outside the spacecraft, or the most popular method being looked at, which is a combination of both.

Under this procedure, one of the Shuttle crewmen would don an EVA pressure suit and backpack and go out into the open payload bay through the airlock in the Orbiter’s middeck. Once outside, the EVA astronaut would climb onto a special “cherry picker” platform mounted in the payload bay. The cherry picker would have attachments to allow the RMS to pick the platform up with the EVA crewman on it and move it to the FSS collar on which Solar Max would be mounted.

Attached to a rack on the cherry picker within easy reach of the astronaut would be the tools required for the module replacement as well as the new attitude control module. To remove the old unit, the astronaut would be required to loosen only two bolts and then he would be able to pull it free. The replacement module would be installed in just the same way. The old module would then be attached to the rack on the cherry picker so that it could be returned to Earth for study. The astronaut would then go back inside the Orbiter after an EVA excursion lasting probably three to four hours.

After a checkout to ensure that the new module is functioning properly, the RMS would be used once again to detach Solar Max from the FSS and release it back into space. A second checkout would also be done with the satellite in free flight and the Orbiter station-keeping in its vicinity. Once it is apparent that Solar Max is again in operation, the Orbiter would move away from it and prepare for landing.