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  • Subject area(s): Engineering
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  • Published on: 7th September 2019
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1. Abstract:

On May 14th 1973, NASA launched Skylab; their first experimental space station. However, by late afternoon on May 14th it was confirmed that Skylab had lost its micrometeoroid shield[1]. The main reason for this was the discrepancies between the design criteria and the actual manufacturing of Skylab, this was debatably due to a lack of sound engineering judgement[2] or a lack of governmental funding[3].

1.

Introduction

Between its launch on May 14th 1973 and the return of the third and final crew on February 8th 1974, Skylab fulfilled both its main goals: to prove humans could survive in zero-gravity for an extended periods of time and to complete experiments in unique conditions[5]. On Earth, Skylab weighed 169,950 pounds[6] including enough food, water and medicine for all three of the crews. It mostly contained numerous scientific and engineering equipment, mainly for making observations of the surrounding sky[7]. The Skylab experiment initially started a decade before the original launch. It was set to be the first truly habitable station launched by the Americans into space, partly as an attempt to remain in space longer than that of the Soyuz 11 crew. Each of Skylab’s missions overtook the Soviet’s record of 23 days[8] with Skylab 2 lasting 28 days, Skylab 3 lasting 59 and Skylab 4 lasting 84[4]. The original design of Skylab consisted of a “wet workshop”, in which the workshop would be filled with a propellant in the propulsive phase and once empty of the propellants a liveable atmosphere would be introduced. However, after the success of the Apollo 11 lunar landing, launch vehicles became a feasible option and so the design was changed to a “dry workshop” concept and so was equipped for immediate occupancy[2]. Skylab was expected to receive the first three man crew just 24 hours after take-off[9]. However, only 63 seconds after lift-off[6] at an altitude of 28,600 feet and a velocity of Mach 1[2], erratic signals received by NASA led flight director Donald Puddy to determine that the micrometeoroid shield had been prematurely released. The Earth’s atmosphere had ripped the shield loose and the debris caused the solar array wing no. 2 to dismount and propel itself into space[10]. The other solar array which was still attached was prevented from deploying by material left when the micrometeoroid shield was torn off[4]. Temperatures in Skylab reached 52 degrees Celsius[11] after NASA had to rotate the station to a 45 degree angle to stabilise thermal relief whilst ensuring a minimum power of 2,800 watts to maintain altitude control and communications with NASA[2]. Skylab 2 was postponed for 10 days whilst a make-shift micrometeoroid shield was manufactured and the astronauts were trained how to install and deploy it[11].

2.

Analysis

During the testing phase, Skylab performed as expected and all problems had been resolved so NASA expected the launch to go off without a hitch[12]. However, it was clear after take-off that NASA had failed to take into account aerodynamic loads in Skylab’s design, this is due to them assuming the micrometeoroid shield would be structurally integrated as shown in the design criteria[2], yet NASA allowed a gap that exceeded design specifications by half a centimetre[1]. This created internal pressurisation of the auxiliary tunnel because it had not been constructed as designed[1] and so allowed the end of the shield to be forced away from the body of Skylab and into the supersonic air stream. Many panels were used in the construction to achieve a tighter fit between the components and the body. A discrepancy report outlined the areas where there were gaps that hadn’t been included in the design criteria: this was met with a response from the Material Review Board to “use as is”[2]. The flight differential pressure was said to be substantially higher than 8psi[2] and so engineers deduced that the contact area during flight would be anything above 95 percent[2], meaning the meteoroid shield was cleared for take-off with no other changes made. The failure to recognise the dangers of allowing the ship to launch without adhering to design criteria was due to a lack of sound engineering judgement and no alert engineering leadership regarding the construction and attachment of the shield and surrounding panels. When investigated, the board found no evidence that the design and manufacturing process of the micrometeoroid shield had been compromised due to NASA’s significant cut in funding[3]. The testing that was done to ensure the station would survive launch, however, omitted aerodynamic, vibration, acoustic and flutter tests as they were not considered necessary under the “tight to tank” design criteria[2]. This criteria, however, was not met during the manufacturing process and so the aforementioned tests should have been involved in the initial testing phase, and would have been had there been any competent managerial presence. It appears that the reason the aerodynamic loads were overlooked is because the shield was viewed as a structural component rather than a complex system involving multiple technical disciplines, all different from one another[2].

Although the board suggested that the lack of funding had no real effect on the problems during take-off, it is hard to ignore that NASA did receive massive funding cuts during this time[3]. In January of 1967, a fire in a Apollo command module resulted in the death of 3 astronauts[13]. This resulted in the government losing trust in NASA’s ability to produce results and with the ever-growing financial burden of the Vietnam war, appropriated only $300million dollars of the previously promised $457million that NASA had asked for[13]. Many within the agency then believed that Skylab would fail as transforming a spent booster stage into a working laboratory whilst in space, a “wet workshop” design, was too difficult under a restricted budget[13]. The transformation to a “dry workshop” did not occur until July 22nd 1969, after Apollo had successfully completed its mission and a Saturn V rocket could be used to propel Skylab into space. By September 1970, however, the Nixon administration promised to cut NASA’s funding substantially[13]. Skylab’s funding was saved from immense cuts but changes to design and scheduling were still necessary to adhere to the new budget[13]. This could have quite easily resulted in the loss of the micrometeoroid shield due to a lack of funds to correctly fix the shield to the body of the station, and the instruction to “use as is” despite a lack of testing for anything other than the “tight to tank design”. Had funds been available, NASA could’ve executed the aerodynamic, vibration, acoustic and flutter tests that were needed due to the inconsistencies between design and manufacturing. Or the components could’ve been manufactured “tight to tank” as the design indicated.

3. Discussion

The moment NASA knew Skylab had lots its micrometeoroid shield a team was assembled to devise a plan to rectify the problem. As previously mentioned, Skylab was rotated to a 45 degree[11] angle to reduce the sun’s glare but was then not receiving enough power to accommodate the astronauts and so the micrometeoroid shield had to be replaced. NASA’s original ideas included paint and wallpaper, but both were eliminated as paint had too much of a high contamination risk and wallpaper relied too heavily upon the condition of the workshop’s exterior[1]. Three realistic solutions emerged: extending a shade from a rod attached to the end of the telescope mount, deploying a shade from the Apollo spacecraft or extending a device through the scientific airlock situated on the solar side of the workshop[1]. The most feasible solution was to extend the shade from the scientific airlock as the astronauts could do this from within the workshop. However, the opening was only twenty centimeters square and had to inflate to cover an area seven meters square[1]. After extensive testing of thermal barriers, which included thermal coatings and plastic and fabric shades, engineers preferred a parasol-type design made from a fabric awning[2]. However, the nylon included in the fabric was proven to deteriorate under ultra-violet rays, losing half its pull strength in 100 hours of solar vacuum testing[1], and so a two-pole awning was sent up as a precaution[2]. The task of releasing the partially deployed solar array was left for Skylab 2.

The review boards for the Skylab disaster included three recommendations that directly affected NASA’s management. The first called for a project engineer for any element of the design that included more than one engineering discipline, meaning any complex element of the design had to have its own leader. The second tried to lead NASA away from its clear emphasis on documentation and formal details, and ensure all engineers are familiar with the actual materials and can use flight data effectively.[2] Finally, they encouraged experienced engineer to be given the task of overseeing major elements of the design. They would be permitted full control, without being hindered by administrative duties, and so could focus on the subtle incorporation of all components under his observation.[1]

4. Conclusion

To conclude,

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