Saving Skylab

May 26, 2023

As graceful as it looked during flight, the Saturn V was a powerful, violent rocket. Some astronauts described their experience riding this launch vehicle as feeling like "a small dog being shaken by a much bigger dog!" Instead of carrying astronauts, however, the thirteenth and final flight of the Saturn V was to place the Skylab space station into Earth orbit. Largely consisting of a modified Saturn S-IVB (or third stage) that would serve as the Orbital Workshop, Skylab was much lighter than any payloads that had flown on the Saturn V before. With a large fairing fitted on top of the modified S-IVB to protect the docking adaptor, Apollo Telescope Mount, and Airlock Module, Skylab was also a much different-looking payload than any previous Saturn V launch.

Saturn V SA-513 rocket launches the Skylab space station into orbit on May 14, 1973.

Surrounding the Skylab Orbital Workshop was a micrometeorite shield that had the dual purpose of protecting both the space station and its astronauts from the heat of the Sun. There were also two solar array panels folded up on either side of the workshop that were to be deployed once the space station reached orbit. During the launch on May 14, 1973, however, a design flaw allowed air to rush under the micrometeorite shield, causing it to peel away from the workshop. In the process, the shield became partially entangled in one of the solar array panels while completely tearing away the other. What was left of the shield rolled down the side of the Saturn V, cutting a strip of explosive charges that were to help separate the interstage ring from the second stage. This caused the interstage ring to remain attached to the second stage, and temperatures surrounding the five J-2 engines began to soar. A crewed Apollo mission would probably have aborted the launch, but flight controllers allowed the Saturn V to continue its flight, and ten minutes after launch it placed the badly damaged Skylab into orbit.

A diagram illustrating how within a few seconds the micrometeorite shield tore away from the Skylab Orbital Workshop during launch. The numbers following "SITUATION AT" are the seconds following liftoff. Astronaut Russell Schweickart, the backup commander to the first Skylab mission, likens the loss of the shield to, "… running your fingernail down the label on the outside of an old soup can."

Without a micrometeorite shield to protect the interior from the Sun, temperatures inside Skylab rose to over 130°F. In places, the temperatures even reached about 150°F. Although the four windmill-like solar array panels on the Apollo Telescope Mount successfully folded out into space, the remaining large, wing-like solar array panel on the side of the workshop was in bad shape and unable to provide much-needed electricity to power the space station. NASA would need to find a way of repairing Skylab if astronauts were to live and work on board. And time was critical. High temperatures inside the space station had the potential of damaging instruments, equipment, food, and photographic film while releasing toxic gases that would be dangerous for the astronauts. To save Skylab, the first crew would need to arrive and attempt a repair mission. And to keep the high temperatures from destroying everything, they had just ten days to do it.

To replace the missing shield, NASA considered three different ideas, including having the astronauts attach a sunshade to Skylab while standing in the hatch of the Apollo command module, which was quickly abandoned. A second idea was a twin-boom "solar sail" sunshade that would be attached to the Apollo Telescope Mount. The idea they eventually went with for the first mission came from Jack Kinzler, an engineer at NASA's Johnson Space Center and chief of their Technical Service Center. He suggested a parasol device constructed of aluminum poles and fabric made of nylon, mylar, and aluminum. Folded up like an umbrella, this parasol could be deployed through an 8-inch instrument port in the workshop so that it covered most of the damaged area that faced the Sun. His idea had the added benefit of being able to be put into place without having the astronauts perform an extravehicular activity (EVA). Meanwhile, special tools would also have to be found and tested to allow the astronauts to safely cut away the remaining debris from the micrometeorite shield and free the remaining solar array panel.

The job of testing the different solutions and developing procedures for deploying the devices in space became the responsibility of Russell L. (Rusty) Schweickart. A veteran of Apollo 9 and the backup commander to this first Skylab mission, Schweickart explained:

"We (led by me!) at MSFC started immediately on doing the job externally via EVA. I led the effort since I was "Mr. EVA" for the Skylab (nominal) operations and had done all that development work in the MSFC WIF. Meanwhile, NASA's Johnson Spaceflight Center (JSC) came up with and developed the "parasol" that was stuck out through the sunny side airlock. We were ready (sort of) by the first launch opportunity (five days - launch window every four days… so five, nine, thirteen…) but JSC wasn't ready with the parasol. Mission Control figured they could limit the temps for another four days, so we waited for the day nine launch window. Because the twin pole solar sail could go over the parasol, but the parasol could not go over the solar sail, the JSC parasol went first and lasted (just) for the first mission."

After designing a protective parasol to cover the Skylab Workshop, crews needed to practice using specially designed tools and materials to facilitate the repair procedure. Marshall Space Flight Center's Neutral Buoyancy Simulator (NBS), was used to practice these maneuvers. Pictured here are the astronauts in the NBS deploying the "twin pole" solar sail protective cover on the Apollo Telescope Mount, and solution that was eventually replaced the solar parasol after the success of the Skylab 2 mission.

Engineers at NASA’S Marshall Space Flight Center (MSFC) examine tools considered for use in freeing the solar array wing of Skylab. Enhanced television pictures showed that the wing was being held to the side of the Skylab by a strip of metal from the micrometeorite shield. The device at the center is a cable cutter that clipped an identical strip of metal in a test at MSFC, requiring 90 pounds of force. The cutter is one of several heads which could be attached to extension rods. At right is the handle end of a rod. The small object at left is the attachment head for a two-prong "rake" device for use on the end of a pole made up of one, two, or more five-foot sections of extension rods. The tools were tested in underwater EVA tasks in the MSFC Neutral Buoyancy Simulator.

On May 25, 1973, the first Skylab crew with commander Charles C. (Pete) Conrad Jr., pilot Paul J. Weitz, and scientist Joseph Kerwin were on their way. To be safe, the crew carried all three of the devices devised to replace the micrometeorite shield. They also carried along special tools they hoped could be used to fix the damaged solar array panel. It was a long day for them. After taking six hours to rendezvous and dock with Skylab, the crew ate their first meal. They then undocked and began investigating the damage the space station had received during launch. Conrad brought the Apollo command module near the damaged solar array panel, and Kerwin performed an EVA in an attempt to pry it free but was unable to. The crew attempted to dock with Skylab again so that they could rest and get some sleep, but the docking mechanisms would not work. After many different attempts, they had to manually modify the command module's docking port, which finally worked. Because it was still too hot inside Skylab to board, the crew slept inside the command module. It had been a long 22-hour day.

This image, taken during a fly-around inspection by the Skylab 2 crew, shows the damaged meteoroid shield being held by a thin aluminum strap entangled with green-hued remnants of the lost heat shield.

The next day, Weitz entered Skylab to determine if the high temperatures had generated any dangerous fumes. Fortunately, it was safe, and the crew was able to enter the workshop and deploy the parasol. The preparations they made on the ground were helpful, and once installed the parasol immediately began cooling the laboratory. The temperature inside Skylab dropped to a warm, but livable, 90°F, allowing the crew to begin working on their scheduled experiments. However, the power levels were still too low to support all the experiments they needed to conduct. The astronauts would have to make another attempt to fix the damaged solar array panel. NASA needed a new plan.

Schweickart was also in charge of a team assigned to devise another method for deploying the stuck solar array panel. Schweickart and his team came up with the idea of using a 25-foot-long cable cutter to free the panel and a tether to maneuver it, once freed, into its fully deployed position. Ground control relayed instructions on the procedure to the crew, and on June 7, 1973, astronauts Conrad and Kerwin began an EVA to make another attempt.

Astronauts Rusty Schweickart (right) and Edward Gibson (left) test emergency procedures to free jammed solar array panels on the Skylab workshop. A metal strap became tangled over one of the folded solar array panels when Skylab lost its micrometeoroid shield during the launch. The astronauts are in the Marshall Space Flight Center (MSFC) Neutral Buoyancy Simulator (NBS) using various cutting tools and methods developed by the MSFC to free the jammed solar wing. This huge water tank simulated the weightless environment that the astronauts would encounter in space.

Not everything went according to plan. Conrad found that he could only attach the tether to the solar array panel in one place, and he was worried that it wouldn't provide enough leverage to open the panel. Kerwin found it difficult to position himself on the space station where Schweickart had suggested, as cables kept him from getting the proper footing, making it difficult to use the cable cutter. Instead, Kerwin moved into a different position where he was finally able to cut the cable and free the solar array panel. It still needed to be leveraged into its fully opened position, however, and even though both astronauts pulled on the tether the panel refused to budge. To provide some additional leverage, Conrad placed the tether over his shoulder and both astronauts pulled again. The solar array panel suddenly popped into position, sending both astronauts cartwheeling into space. Conrad laughed as he went flying into space. Fortunately, umbilical cables kept them attached to the space station where they were able to safely return. Within a few days, the power in Skylab doubled and America's first space station was saved.

"Many people on the team I led beginning the night of the tragic lab launch, never slept for 48 and some 72 hours," Schweickart remembers. "Getting what was called the "spinnaker" or "twin-pole sail" conceived, designed, manufactured, tested, and crew trained… and ready for launch in four days! I’m not sure there's ever been a more intense all-hands engineering effort as that. Ultimately, we converted what was a ($2.2 billion) total failure into a 120% success. We actually got more done than planned over the three [Skylab] missions."

An image of Skylab taken by the third and final crew of astronauts. The original parasol sunshade installed by the first crew, which is a slightly darker color, can be seen under the twin pole sunshade that was installed by the second crew.

Many thanks to Rusty Schweickart for his comments and input to this blog.