April 30, 2009 Vol. 2, Issue 4
On April 9, 1984, astronauts aboard Space Shuttle Challenger on mission STS-41C successfully captured the ailing Solar Maximum spacecraft, serviced it on orbit, and released it back into operation.
Solar Max’s date with the Space Shuttle was not a planned part of its mission when the spacecraft was launched in February 1980. It was, however, the first spacecraft built using the Multi-mission Modular Spacecraft (MMS) design, which meant it could be serviced if necessary. When the spacecraft’s reaction wheels began to fail roughly a year after launch, NASA had the opportunity to put the spacecraft’s design to the test.
The concept for on-orbit servicing of a multi-mission modular spacecraft was the brainchild of Frank Cepollina of Goddard Space Flight Center. Cepollina conceived of serviceable modules as a cost-effective way for NASA to fix problems in space rather than having to rebuild and launch an entire spacecraft when a failure occurred.
Anticipating the difficulties that astronauts would face working with hand tools while wearing spacesuits and gloves, he and others concluded that servicing would work best with subsystem modules that had a minimum of interfaces. “We said to ourselves we can’t do circuit board and black box replacement,” he recalled. “It has to be at the subsystem level.” (He noted that there have been tremendous gains in on-orbit servicing capability, comparing the planned final servicing of the Hubble Space Telescope to “neurosurgery” on the telescope.)
In the early 1970s, Cepollina contributed the idea for modular instrument design to the Large Space Telescope (LST), which later became the Hubble Space Telescope. He continued to pursue the opportunity to build the MMS, and received permission to develop modules for Solar Max, Gamma Ray Observatory (GRO), Landsat 4, Landsat 5, and UARS. He also worked closely with the Space Shuttle Program to ensure that the Shuttle would have the capability to service a MMS on orbit. This required equipping the Shuttles with a grappling arm to capture and repair a free-flying spacecraft, and cradles to facilitate docking, berthing, and power transmission.
During STS-41-C, astronauts attempted to capture the Solar Max spacecraft on Day 3 of the mission but failed to grasp it after three attempts. On Day 4, they successfully secured the spacecraft on the first attempt. The servicing required two separate spacewalks. They returned Solar Max returned to operation the following day, and brought the faulty module back to Earth for repair.
Solar Max marked a number of firsts, including:
- The first use of the Shuttle to capture and repair a free-flying spacecraft and return it to operation;
- The first operational use of the multi-mission modular spacecraft; and
- The first return to Earth of spacecraft hardware that had been in space for several years.
“Solar Max led to something,” said Cepollina. “It was the application of a dream.”
A decade later, it led to a new lease on life for the Hubble Space Telescope. Having proved the capture-and-repair concept with Solar Max, Cepollina was tapped to lead the efforts for Hubble’s on-orbit servicing.
Suggested reading: “Repairing Solar Max: The Solar Maximum Repair Mission,” by Tracy McMahan and Valerie Neal (Document ID 19840020814), archived on the NASA Technical Report Server.
View an image of the on-orbit repair of Solar Max by a STS-41-C crewmember.
