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Reviving & Reusing Skylab in the Shuttle Era: NASA Marshall's November 1977 Pitch to NASA Headquarters
14 November 2015 David S. F. Portree

The Skylab Orbital Workshop as seen by the Skylab 4 crew, the last astronauts to live on the station. Image credit: NASA

On 14 May 1973, the last Saturn V rocket to fly, designated SA-513, launched the Skylab Orbital Workshop (OWS) space station into a 435-kilometer-high orbit about the Earth. Flight controllers soon realized that the 85-ton space laboratory was in trouble. Although they did not know it at the time - Skylab climbed rapidly into dense clouds, so could not be imaged during most of its ascent - 63 seconds after liftoff a design flaw caused Skylab's meteoroid shield to rip away. Shield debris jammed one of the workshop's two main electricity-producing solar arrays. The other array remained attached to Skylab's side only at its hinge (forward) end.

Shield debris also pummeled SA-513, tearing at least one hole in the tapered interstage adapter that linked its S-II second stage with the Skylab station. Debris also apparently damaged the system for separating the cylindrical adapter that linked the S-II to the S-IC first stage. The adapter, meant to separate shortly after the spent S-IC, remained stubbornly attached to the S-II all the way to orbit.

Skylab 1 launch, 14 May 1973. Image credit: NASA

After the S-II's five J-2 engines shut down, forward-facing solid-propellant rockets ignited to push the spent stage away from Skylab. Their plumes blasted open and tore away the loose solar array. Ironically, the jammed array probably survived because it was tied down by meteoroid shield debris.

Without the protection of the reflective meteoroid shield, temperatures within Skylab's 11,303-cubic-foot pressurized volume soon soared, raising fears that its air would become tainted by outgassing from materials on board, film would be ruined, and food and medicines spoiled. Flight controllers soon found to their dismay that maneuvers designed to cool Skylab's interior tended to starve it of electricity, for they turned away from the Sun the four "windmill" solar arrays on the Apollo Telescope Mount (ATM), the beleaguered space laboratory's only functioning sources of electricity.

NASA immediately began a Skylab salvage effort. Engineers developed deployable sunshields and tools for freeing the stuck main solar array, flight controllers carefully maneuvered Skylab to maximize the amount of electricity the ATM arrays could produce while reducing temperatures on board as much as possible, and the first crew meant to board Skylab (their mission was designated Skylab 2) hurriedly trained to become the world's first orbital repairmen.

Skylab 2 astronauts Joseph Kerwin, Charles "Pete" Conrad, and Paul Weitz. Image credit: NASA

On 25 May, the Skylab 2 crew of Pete Conrad, Paul Weitz, and Joe Kerwin lifted off in an Apollo Command and Service Module (CSM) atop a Saturn IB rocket. After a failed attempt to pull open the one remaining main solar array with a hook extended from the open CSM hatch, they docked with and entered Skylab, then deployed a sunshield through an experiment airlock. Temperatures began to fall, but the Orbital Workshop remained starved for electricity. On 7 June, Conrad and Kerwin succeeded in forcing open the surviving main solar array, saving not only their own 28-day mission but also the planned Skylab 3 and Skylab 4 missions.

The Skylab 3 crew of Alan Bean, Jack Lousma, and Owen Garriott lifted off on 28 July. During their 6 August spacewalk, Lousma and Garriott deployed an improved sunshield. The lived and worked on board the station for 59 days.

The Skylab 4 crew of Jerry Carr, William Pogue, and Ed Gibson boarded Skylab on 16 November. Carr and Gibson mounted a meteoroid collector on an ATM strut during their spacewalk on 3 February 1974, in the hope that a Space Shuttle crew might retrieve it as early as 1979. When the Skylab 4 crew undocked on 8 February 1974 after a record-breaking 84 days in space, Skylab was expected to remain aloft until 1983, when atmospheric drag would cause it to reenter Earth's atmosphere. They left Skylab's airlock hatch closed but not latched so that it could provide entry for future visitors.

This pre-launch cutaway illustration of Skylab shows the station as it would have appeared if it had reached Earth orbit undamaged. In addition to two large main solar array, it includes the micrometeoroid shield which tore free during Skylab's ascent through the atmosphere. Image credit: NASA

During the solar-minimum years of the mid-1970s, the Sun was more active than had been anticipated at the time of Skylab's launch. Solar activity heated and expanded Earth's upper atmosphere, subjecting the first U.S. space station to more aerodynamic drag than had been expected. In March 1977, the NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama, lead center for the Skylab station, asked NASA Headquarters to grant it permission by mid-1977 to begin work on a mission to raise Skylab's orbital altitude.

On 10 June 1977, former Skylab Deputy Director John Disher, by then NASA's Director of Advanced Programs, requested that MSFC conduct a preliminary in-house study of the feasibility of reusing Skylab in the Space Shuttle era. At about the same time, NASA Headquarters directed NASA Johnson Space Center (JSC), lead center for the Space Shuttle, to study an early Shuttle mission to either boost Skylab to a higher, longer-lived orbit or cause it to safely reenter over an unpopulated area.

In September 1977, JSC informed NASA Headquarters and MSFC that the earliest it could reboost or deboost Skylab was September 1979, as part of the fifth Orbital Flight Test (OFT) Shuttle mission. At the time, NASA envisioned a total of six OFT missions before the Shuttle was declared operational. NASA Headquarters then gave the go-ahead for MSFC and JSC to begin work toward a September 1979 Skylab reboost/deboost mission.

On 16 November 1977, MSFC engineers J. Murphy, B. Chubb, and H. Gierow presented to NASA Associate Administrator for Space Flight John Yardley results of the study they had begun in June. They were speaking to a Skylab expert: before coming to NASA in 1974, Yardley had managed Skylab work at McDonnell Douglas, the prime contractor for the OWS.

The MSFC engineers first described Skylab's condition. They reported that when the Skylab 4 crew returned to Earth, the Orbital Workshop's water system contained 1930 pounds of water (enough to supply three men for 60 days). The water, they said, probably remained potable, but might have developed a bad taste. If it was no longer potable, then it might be used for bathing. In any case, the Skylab water system included resupply points, so a Space Shuttle crew could refill it with fresh water if water transfer equipment were developed.

The oxygen/nitrogen supply remaining on Skylab was probably sufficient to supply three men for 140 days at Skylab's standard operating pressure of five pounds per square inch, the MSFC engineers estimated. The station's ventilation and carbon dioxide-removal systems were almost certainly functional. Even if they were not, their most important components were designed to be replaceable in space.

The MSFC engineers also assessed Skylab's electrical power system. They estimated that the main solar array Conrad and Kerwin had freed could still generate between 1.5 and 2.5 kilowatts of electricity, and that the batteries it had charged, located in Skylab's Airlock Module, were probably still usable. The batteries for the four ATM arrays, located inside the ATM, were, on the other hand, almost certainly frozen. The team recommended that controllers reactivate the main array electrical system from the ground before the first Shuttle visit, and that any effort to revive the ATM electrical system be left for a later time.

More problematic than the electrical system was Skylab's attitude control system, which relied on a trio of Control Moment Gyros (CMGs) to turn Skylab so that, among other things, it could reliably point its solar arrays at the Sun. At the time the Skylab 4 crew departed, one CMG had already failed and another showed signs of impending failure. In addition, Skylab's guidance computer was probably dead after being subjected to "extreme thermal cycling" as Skylab passed between daylight and night. The Orbital Workshop's thruster system, on the other hand, was probably operational with about 30 days of propellant remaining.

Finally, the MSFC team looked at Skylab's cooling system, which had leaked while the astronauts were on board and had probably frozen and ruptured since the last crew returned to Earth. They called "serviceability of [the] cooling system. . .the most questionable area" as far as Skylab's reusability was concerned, but added that "any inflight 'fixes' should be well within the scope of crew capability."

The MSFC engineers then proposed a four-phase plan for reactivating and reusing Skylab. The target date for their first Phase I milestone had already passed by the time they briefed Yardley: though it was already mid-November, they made a point of calling for an October 1977 decision on whether Skylab should be reboosted to a higher orbit, extending its orbital lifetime until about 1990, or deboosted so that it could reenter safely over an unpopulated area.

Assuming that NASA decided to reboost Skylab, then a ground-controlled Skylab reactivation test would occur between June 1978 and March 1979. If the test was successful, then the fifth OFT Space Shuttle mission would rendezvous with Skylab. As already mentioned, in September 1977 JSC estimated that the fifth OFT would fly in September 1979. Two months later, when the MSFC team briefed Yardley, the mission had already slipped to February 1980.

Artist concept of Teleoperator spacecraft. Image credit: NASA

The MSFC team anticipated that the Space Shuttle crew would conduct an inspection fly-around of Skylab, then would deploy an unmanned Teleoperator spacecraft from the Shuttle Orbiter's payload bay. Using a control panel on the Orbiter flight deck, the astronauts would guide the Teleoperator, which would carry an Apollo probe-type docking unit, to a docking with the drogue-type docking unit on the front of Skylab's Multiple Docking Adapter. The Teleoperator would fire its thrusters to raise Skylab's orbit; then, its work completed, it would detach, freeing up Skylab's front docking port for Phase II of MSFC's plan.

Astronauts in a nearby Space Shuttle Orbiter stand by as the Teleoperator ignites its thrusters to raise Skylab's orbit and extend its orbital lifetime. Image credit: NASA

Phase II would begin in March 1980, when NASA would initiate development of Skylab refurbishment kits, a 10-foot-long Docking Adapter (DA) module, and a 25-kilowatt Power Module (PM). The DA would include at one end an Apollo-type probe docking unit for attaching it to Skylab's front port and at the other end an Apollo-Soyuz-type androgynous unit with which Shuttle Orbiters and the PM could dock.

The first refurbishment kit and the DA would reach Skylab on board a Shuttle Orbiter in January 1982, almost two years after the reboost mission. During the 1982 mission, spacewalking astronauts would fold two of the four ATM solar arrays out of the way to improve clearance for visiting Orbiters and would retrieve the meteoroid experiment the Skylab 4 astronauts had left on the ATM. As time allowed, this and other Phase II crews would perform unspecified "simple passive experiments" on board Skylab and would collect samples of its structure for engineering analysis on Earth.

The third Shuttle visit to Skylab would not take place until August 1983.The astronauts would install additional refurbishment kits and would tackle the daunting job of repairing Skylab's damaged cooling system.

The refurbished Skylab station after the start of Phase III of the NASA MSFC reactivation program. The Power Module, Docking Adapter, and Shuttle-carried Spacelab are clearly visible. Image credit: Junior Miranda

The MSFC engineers told Yardley that Phase III of the Skylab reactivation program would begin in March 1984 with delivery of the PM and any remaining refurbishment kits. Using the Shuttle's Remote Manipulator System robot arm, astronauts would lift the PM from the Orbiter's payload bay and turn it 180° so that it protruded forward well beyond the Orbiter's nose. They would then dock one of the PM's three androgynous docking units to an identical unit at the front of the Orbiter's payload bay. The Shuttle would use another of the PM's docking units to dock with the DA on Skylab.

Following docking with Skylab, the astronauts would deploy the PM's twin solar arrays and thermal radiators, link the PM to Skylab's systems using cables extended through open hatchways or installed on the hull during spacewalks, and power up the PM's three CMGs to replace Skylab's crippled attitude control system. The Orbiter would then undock from the PM, leaving it attached permanently to Skylab. Shortly thereafter, NASA would declare the revived and expanded Orbital Workshop to be fully habitable.

Phase III would continue with the first in a series of 30-to-90-day missions aboard Skylab. During these, a Shuttle Orbiter carrying a Spacelab module in its cargo bay would remain docked with the Orbital Workshop. The astronauts would work in the Spacelab module, take advantage of Skylab's large pressurized volume to perform "simple experiments" requiring more room than Shuttle and Spacelab could provide (for example, preliminary trials of space construction methods), and begin building up stockpiles of food, film, clothing, and other supplies on the revived station.

Another 30-to-90-day mission would see the astronauts refurbish and use selected Skylab science equipment, install new experiments based on Spacelab experiment designs, and stockpile more supplies. Between these missions, the new and improved Skylab would fly unmanned under control from the ground.

The view from the Sun: all of the solar arrays deployed for Phase III of the Skylab reactivation program are visible in this image by Junior Miranda

The MSFC engineers told Yardley that the volume available to a crew on board a Shuttle Orbiter without a Spacelab module in its payload bay would total only 1110 cubic feet. Adding a Spacelab would increase that to about 5100 cubic feet. This would, however, amount to less than half the pressurized volume of Skylab. For a mission including a Shuttle Orbiter, Spacelab module, and Skylab, the total volume available to the crew would exceed 16,400 cubic feet.

They were not specific about what Skylab would be used for when Phase IV of their program began in mid-1986, though they did offer several intriguing possibilities. Shuttle Orbiters might, for example, attach modified Spacelab modules and experiment pallets to the third docking port on the PM.

A Shuttle External Tank might be joined to Skylab to serve as a strongback for large-scale space construction experiments using a mobile "space crane." These experiments might include construction of a large space solar power module or a multiple beam antenna.

A new "floor" might be assembled within Skylab, enabling it to house up to nine astronauts. As NASA developed confidence in the revived space laboratory's health, manned missions on board Skylab without a Shuttle Orbiter present might commence, leading to permanent manning and "support [of] major space operations."

The MSFC engineers did not estimate the cost of Phases I and IV of their plan, though they did provide (perhaps optimistic) cost estimates for Phases II and III. Their estimates did not include Space Shuttle transportation and contractor study costs.

In Fiscal Year (FY) 1980, NASA would spend $2 million each on Phases II and III. This would increase to $5 million for Phase II and $3.4 million for Phase III in FY 1981. FY 1982, their plan's peak funding year, would see $4.5 million spent on Phase II and $10.2 million spent on Phase III. In FY 1983, NASA would spend $2.5 million to close out Phase II and $12 million to continue Phase III. The following year it would spend $9.1 million on Phase III. Phase III closeout in FY 1985 would cost $4.5 million. Phase II would cost a total of $14 million, while the more ambitious Phase III would total $41.2 million.

In November 1977, the month the MSFC engineers briefed Yardley on their study, NASA awarded Martin Marietta Corporation a small ($1.75-million) contract to begin development of the Teleoperator. The remote-controlled spacecraft was envisioned as a small space tug made up of modular components.

No decision was taken at that time as to whether the Teleoperator would reboost Skylab to make it available for possible future use or would deorbit it in a controlled manner; that decision would await assessment of Skylab's condition and additional study of potential applications. McDonnell Douglas and Martin Marietta subsequently commenced more detailed and extensive Skylab reuse studies under supervision of JSC and MSFC, respectively.


Skylab 1 Investigation Report, Hearing Before the Subcommittee on Manned Space Flight of the Committee on Science and Astronautics, US House of Representatives, Ninety-Third Congress, First Session, 1 August 1973

"Skylab Reuse Study Presented to Mr. Yardley by MSFC," 16 November 1977

Living and Working in Space: A History of Skylab, NASA SP-4208, W. David Compton & Charles D. Benson, 1983, pp. 361-372

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