|astronautix.com||Skylab's Untimely Fate|
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Credit: NASA. 28,885 bytes. 380 x 282 pixels.
by James Oberg
First appeared in Air & Space, February/March 1992, pp. 73-79
Reproduced by permission of the author
It was one of the more bizarre proposals offered in response to the funding and design crises surrounding NASA's space station Freedom. In June a shadowy organization calling itself the "Center for Strategic Space Studies" suggested that instead of building Freedom, NASA should take the back-up Skylab on display in the National Air and Space Museum in Washington and launch that.
The disgruntled NASA employees who suggested this idea did it anonymously, perhaps feeling that the space agency has come to enforce unanimity of thought not by encouraging superior ideas but by imposing bureaucratic discipline. And while many were quick to dismiss the proposal as impractical, it did briefly succeed in stirring debate throughout the space community. After all, with Skylab the United States once had a successful manned space station. Yet NASA let it slip through its fingers and fall to Earth in 1979.
In the late 1970s NASA had considered saving Skylab by sending an early space shuttle mission to boost it into a higher, more stable orbit, where astronauts could have studied how it had been affected by its years in space. Even more ambitious studies concluded that Skylab could have been repaired, reopened, and expanded. Had that happened, the history of the US space program might have been very different.
NASA could have begun the shuttle program with an embryonic space platform, a destination to shuttle to. Experiments still in the planning stages in the 1990s might have been carried out in the 1980s, and NASA could have accumulated the experience necessary to advocate, design, and construct a permanent space station.
"It was a very serviceable, useful facility," recalls Jack Lousma, an astronaut who lived aboard it for two months and was later assigned to a shuttle flight that was supposed to rescue it. "It would have made a good follow-on set of missions, a nucleus for expansion."
That would have been a grand role for a spacecraft that started out as a modified propellant tank from a Saturn rocket's upper stage. Refitted as the Orbital Workshop, or OWS, the large tank was given two solar panels and a pair of small modules (an airlock module and a multiple docking adapter) at one end and a solar telescope assembly that swung out to one side. During 1973 and '74, a trio of three-man crews studied the sun and Earth from the space station on missions lasting 28, then 59, and finally 84 days.
For a time, though, Skylab's fate was in doubt. During the launch a meteoroid shield tore off, taking one of the solar panels with it. Then the other panel jammed, and the first crew had to make an emergency spacewalk to deploy it and save the station. The lost meteoroid shield was supposed to double as a sunshade, so the astronauts also had to rig up a replacement shade to bring the workshop's internal temperatures down to tolerable levels. It was an inauspicious beginning, but Alan Bean, who commanded the second mission, recalls, "It got better with time. More things were working at the end of the mission than at the start."
The station, never designed to be resupplied, was retired after the third mission ended on February 8, 1974. On the remote chance somebody else would venture aboard, the departing astronauts left a bag of food, clothing, film, and camera filters near the front hatch, tied securely to the telescope control panel. As they left the station, they removed the inside locking pin from the airlock hatch -- in effect, putting out the welcome mat.
In the end, it was the sun that spelled doom for Skylab. The final crew used their Apollo spacecraft to nudge Skylab high enough to keep the station in orbit until sometime in 1983. But in the late 1970s solar activity intensified, heating and expanding the upper atmosphere enough to increase the drag on the space station. As Skylab's orbit decayed and its life expectancy decreased, the shuttle program encountered more and more delays. Early plans had called for the reboost mission to be undertaken on the sixth shuttle launch, but schedule pressures pushed it as far ahead as the second mission. However, STS-2 wasn't launched until November 12, 1981, more than two years after Skylab's charred remains had dropped across western Australia when the spacecraft fell on July 11, 1979.
Many at NASA were glad to see the end of Skylab. "It could well have been a snare and a delusion," says Joe Loftus, Johnson Space Center's advanced planning director. "It might have confused us, diverted us." That is, he elaborated, the energy expended on the rescue and repair mission might ultimately have been wasted, deflecting attention from more profitable investments in more promising projects.
Alan Bean disagrees: "I think we should have kept it up there. It wouldn't have detracted from anything. Maybe it would have had the opposite effect; we could have really demonstrated space station operations."
When plans to launch a second Skylab were scuttled in 1975, some preliminary thought was given to reopening the first one. With shuttle orbital missions due to start in 1979 and Skylab's orbit thought to be stable at least through the early 1980s, John Yardley, NASA's associate administrator for manned spaceflight, initiated a study to demonstrate what the shuttle could do on a Skylab visit. At the very least, the crew could attach a rocket stage to the station to ensure that when it did return to Earth, it would come down in an ocean.
Over the next year NASA worked to determine the likely condition of the ageing spacecraft. Engineers at the Skylab project office in Huntsville, Alabama, and Skylab contractors such as Martin Marietta were convinced the station would be in surprisingly good shape. More than just a handy target for a shuttle mission, Skylab was potentially a resource of great value.
Granted, the long exposure to space would have taken its toll. The hatch seals would have become brittle, gas pressure would have slipped (particularly within high-voltage components protected by high-pressure gas insulation), contamination would have built up on windows, mirrors, and filters, and mechanical parts would need lubrication. In addition, cosmic radiation and extreme temperature cycling would have degraded electronics and electrical parts.
But the wear and tear was in fact one of Skylab's most attractive traits. The information about effects of long-term space exposure would be vital to the design and construction of a new, permanent space station.
The engineers also catalogued the Skylab systems expected to be operable. These included refrigeration, oxygen/nitrogen distribution, carbon dioxide control (which used a molecular sieve more advanced than anything that has flown since), waste management, medical monitoring, trash disposal, ventilation, and the hatches (spare seals were aboard).The thermal control system would require servicing with cooling fluid. The power, communications, and data management systems would need augmentation. "All other systems should require minor flight activities for reactivation," concluded the final report to NASA headquarters.
Of the 6,000 pounds of water launched in 1973, nearly 2,000 pounds remained (about 180 man-days' worth). "Probably potable, but may taste bad," the engineers concluded. No live organisms were expected, but the water "may be off color." Taste and' color problems might make it useful only for washing (or, later, for electrolysis into breathing oxygen). The water system had valves within the workshop for eventual refilling.
There was an estimated 1,700 pounds (420 man-days) of oxygen in the tanks. Since the refill valves were near the airlock, it would be fairly easy for astronauts to replenish the oxygen during a shuttle visit.
The station's atmosphere did present one basic engineering problem for shuttle missions: Skylab's atmosphere was pressurized at 5 pounds per square inch, but the shuttle's was three times that, equal to sea level on Earth. An astronaut moving from the shuttle to Skylab would have to undergo three hours of pre-breathing in a transfer chamber to adjust to the change. Skylab's workshop could later be raised to 15 psi with no safety problems, but the airlock module and its extravehicular activity hatch could tolerate only 8 or 9 psi. Either these small modules would have to be replaced (or lined with a flexible airtight inner layer) or shuttle pressure could be temporarily reduced, as it is today prior to EVA.
And off-the-shelf shuttle equipment would need extensive modification to be installed in the old station. Merely getting it aboard would have been a problem: Skylab's hatch was only 30 inches in diameter-- half the size of the shuttle's.
Although only a third of Skylab's trash tank had been filled, the latches on the trash airlock had jammed. Alternate systems would probably be needed. But microbiologists were excited at the prospect of studying microbes that had been reproducing in the trash for hundreds of generations in a spacecraft. They also expected to find interesting fungal spores on the walls and in the air (something not expected to excite visiting astronauts).
Skylab's communications system was operable but already obsolete. The shuttle would use higher frequencies than Apollo missions, and already the old ground sites were being phased out. New monitoring sensors would eventually have to be set up in the station and shuttle-compatible radios installed.
Although the solar cells were ageing and good for only a few kilowatts of electrical output, the power buses and batteries were in good shape for reactivation. More power would be needed, however.
Probably the most serious problem in reactivating Skylab would have been the state of the station's attitude control system. One of three momentum wheels necessary to keep the station stable had already failed, and the nitrogen supplies in the thruster system were low. They could be replenished, but that would require an astronaut with a manned maneuvering unit to get to the feed valves. The star tracker (a vital component for attitude control): had also failed.
On the plus side, Skylab rescuers would get their shuttle repair missions "free," since the rescue was considered a good exercise for testing the new spaceship's capabilities. And the needed power and attitude control could be provided by an unmanned vehicle already in development, the Power Extension Package. The PEP was designed to be a space powerhouse, waiting in Earth orbit for those visits when the shuttle needed more electricity for missions with the portable laboratory it sometimes carries called Spacelab. Attracted by the hefty 25 kilowatts generated by the PEP's solar panels, the Skylab rescuers suggested attaching the PEP to the station and using its power, while the PEP's attitude control sensors and thrusters kept the station lined up properly.
In late 1977 NASA headquarters completed a four-phase rescue plan. During the first phase, shuttle astronauts would boost Skylab to a higher orbit to give it an additional five years of life. Various shuttle-based boosting techniques were proposed, including pushing (the off-balance Skylab structure would have been a huge dynamic challenge) and towing (on a cable). Martin Marietta started developing the Tele-operated Reboost System, a cluster of rocket engines that could be attached to Skylab.
Astronauts Fred Haise and Jack Lousma were assigned to the mission and began training to use the TRS.
Once Skylab was high and stable, phase 2 would commence. Engineers would develop refurbishment kits with the necessary tools and parts, and shuttles would make two visits, during which astronauts would enter the station. On the first visit, scheduled for January 1982, they would attach a modified version of the docking adapter built for the Apollo-Soyuz mission. Then they would test the thermal control system, install valves for repressurization, and reactivate all power buses. During the second visit, in August 1983, astronauts would install thermal and electrical units, service the thermal system, and conduct more extensive inspections and checkouts to assess the effects of exposure on solar cells, insulation, windows, seals, paints, film, lubricants, and other materials.
In March 1984 the shuttle crews for phase 3 would attach the PEP to Skylab, refurbish the station's scientific equipment, and operate the station in both tended (30 to 90 days) and unattended modes. They could use the Apollo Telescope Mount (all it required was more film) and the earth resources experiments. Other simple experiments could be taken up and installed as well.
When operations intensified, a large docking/interface module would be attached to the front end of Skylab, with ports for the PEP, the shuttle, and an additional logistics module launched full of supplies. Additional ports would also be available for Spacelab modules. The old Skylab would begin to expand, piece by piece.
Phase 4 would be a five-year plan of growth, with the addition of Spacelab modules and pallets and perhaps a construction platform based upon the shuttle's external tank. There was talk of eventually giving Skylab a larger power module (150 kilowatts) or a large dish antenna (or both) for radio astronomy or power transmission tests.
Once modified to accommodate six to eight astronauts, Skylab could serve as a space depot, experiment hangar, general-purpose laboratory, and habitat for construction crews working on more advanced structures. Equipment for the first three phases was estimated to cost about $60 million, not including launch costs or the power module, which were funded from different budgets.
But NASA, fixated on the shuttle program, wasn't really interested. Neither were those who controlled the purse strings in Washington. "I'd met with House and Senate staffers," recalls Joe Loftus. "In the end it was admitted that there was an argument to preserve Skylab, but it lost out to the fact of the high cost on immediate assets."
Besides, everything in the plan depended on getting Skylab boosted to a safe orbit, and that looked less and less likely as time passed. "It was nothing dramatic." recalls John Rivers, a NASA engineer who worked on the project. "But month by month the overlap between Skylab dying and the shuttle being born just dwindled into negative numbers."
As it became clear that a shuttle boost wasn't going to happen, alternate methods were considered, including expendable rockets. "We offered to fly (the TRS on a Titan III," says Robert J. Molloy, the projectís director at Martin Marietta. "That was seen as a bit self-serving, since Martin Marietta manufactured the Titan." It also would have taken two launches to get the entire booster into orbit. An Air Force Atlas Agena also might have done the job. Some even considered going to the Soviets for help, but their manned Soyuz clearly didn't have enough power. (An unmanned space tug named Cosmos- 929 did, but its existence was a secret at the time.)
The main drawback to all the schemes, however, was money. All of them would have diverted funds that were needed for the shuttle. "It was certainly feasible," says Robert Allen, one of the Skylabís manager's, about the rescue plans. "We were making some pretty good studies. It just cost more than we had ever considered."
The proposal finally died. There had been no obvious oversights, just a creeping conspiracy of circumstances that left a problem with no real solution. Besides, NASA hall great hopes for a future beyond Skylab, one that included more advanced stations constructed from three or four space shuttle loads deployed in the 1980s. For some, Skylab's continued existence threatened those plans. 'There was considerable resistance within NASA," says Martin Marietta's Molloy.' "The enthusiasts were those who had worked on Skylab and were quite proud of it, but it interfered with the more global vision of glory shared by the later generation at NASA." Given a risky cheap way and an expensive fancy way, NASA (not for the first or last time) opted for spending a lot of money in the future rather than a little money immediately.
But could Skylab really have been revived? Most likely, yes. When it was turned on briefly by ground command in 1978, the station's power, command and control, and attitude systems all functioned adequately. Years later, when the Soviet Salyut 7 station died and froze, it was revived from conditions far more extreme--and then operated normally. NASA's Long Duration Exposure Facility satellite, retrieved in 1990 after almost a decade in orbit, showed wear and tear but no serious damage.
Would it have been worth the effort? Visits and brief experiments were possible, but the grandiose plans for converting the old station into a space city by small steps would have encountered serious problems. "Whether it was something to build upon was doubtful," says Robert Allen. "Skylab was '60s technology and I seriously doubt that anyone would have wanted to build onto that."
Originally, plans for long-term shuttle visits required the shuttle to shut off its fuel cells and use energy from the station. Later NASA decided that the shuttle would have to keep its fuel cells on line--there was too much danger that once shut off, a fuel cell might not restart properly in space. The long manned missions to Skylab originally envisioned probably wouldn't have been possible.
Perhaps the most damning argument against Skylab was something any real estate agent can appreciate: location. The high-inclination orbit (tilted 50 degrees from the plane of the equator) was not convenient for shuttle missions. To reach Skylab, a shuttle would have to be launched more to the north than usual, sacrificing some of the boost offered by Earth's eastward spin. That wasn't a major penalty for expendable spacecraft and boosters (about 10 percent of maximum payload weight), but because the shuttle carries its heavy wings and engines back to Earth, the weight sacrifices would have to come from the payload. (To avoid this unacceptable loss, Freedom is to be built in an easterly orbit from Florida, with an inclination of 28 degrees.) (NOTE ADDED IN 1999: Now isn't this ironic, that in the end we chose to build the International Space Station at an even higher inclination, 52 degrees, in order to make it accessible to the Russians, and we wound up paying the performance penalty anyway).
But even with its drawbacks, a revived Skylab would have been a tremendous temptation to mission planners. Each incremental improvement--and all the expensive refurbishment and maintenance that would have become necessary year by year--would have seemed only a little bit more to spend. NASA would have been in the position of a poker player unwilling to walk away from the money he had in the pot even as the stakes went higher and higher. Would NASA ever have abandoned a revived Skylab to develop a newer design in a convenient orbit? Bureaucratic inertia might have made that unlikely.
Today the "what ifs" still tease, but the history is already written. Yes, operating a revived and refurbished Skylab would have provided valuable experience in space operations. It would have been better than nothing, which is what NASA has today--ironically, because the very sacrifice of Skylab was thought to be necessary to ensure future programs. One thing Skylab taught is that we should glance back from time to time to avoid old mistakes and gain inspiration from old successes. But to move forward into the future, we don't need to revive the past.