Skylab (short for Sky Laboratory) – an American space station that operated from May 14, 1973, to July 11, 1979.
The purpose of placing the laboratory in orbit was to prove the possibility of human survival for an extended period in outer space. The opportunities to conduct the experiment arose after NASA cancelled further Apollo missions and decided to use the equipment for the Skylab project.
Scientific Apparatus
Apollo Telescope Mount (ATM)
Coronagraph (special telescope for observing the solar corona)
X-ray spectrograph (for studying the spectrum of solar X-ray radiation that does not reach the Earth’s surface)
Spectroheliometer (for studying the solar radiation spectrum)
X-ray telescope
Two ultraviolet spectrographs
Two solar telescopes observing in the $H\alpha$ spectral line (wavelength of 656 nm)
A separate set of observation instruments named EREP (Earth Resources Experiments Package) consisted of:
Six observation cameras (eighteen filters) for various spectral bands
Infrared spectroscope – camera, filter wheel system, cryogenic cooler
Multispectral scanning spectroscope – rotating mirror at 6000 rpm, 13 channels with HgCdTe detectors
L-band radiometer in the range of approximately 21 cm – 1 m antenna system
Microwave radiometer
„Television” scanning observation camera
Skylab Station Parameters
Project, adaptation, and construction using Apollo program elements: 1969–1973
Launch mass: 88,830 kg
Mass in satellite orbit (with Apollo spacecraft): 91,030 kg
Mass of components:
Apollo (+ propellant mass 2300 kg): 14,000 kg
ATM Astronomical Observatory: 11,100 kg
MDA Docking Adapter: 6,200 kg
AM Airlock: 22,230 kg
IU Instrument Unit: 2,060 kg
OWS Orbital Workshop: 35,380 kg
Station capacity: total 369 m³, usable 324 m³
Total length: 36.2 m
Wingspan: 27 m
Electric power: nominal 22.9 kW, actual 16.7 kW
Atmosphere: oxygen (72%) + nitrogen (28%), pressure 0.34 atm
Stabilization: system with three flywheels, each 181 kg, 9000 rpm; axis $Z \pm 10”$, axes $X$ and $Y \pm 2.5”$
Skylab Program Timeline
SL-1
The Skylab station was launched on May 14, 1973, using a Saturn INT-21 carrier rocket.
Technical problems appeared immediately after launch in the form of heavy vibrations.
Sixty-three seconds after launch, the laboratory’s micrometeoroid shield and one of the solar panels were torn away.
Debris from the shield jammed the opposite solar panel, preventing its automatic deployment after reaching orbit.
To manage power issues, the station maneuvered in orbit to point the solar panels of the ATM module toward the Sun.
However, this setting caused the laboratory, stripped of its shield, to heat up to over 180°C.
The station was not repositioned until the SL-2 mission was sent to reduce the temperature in that module.
SL-2
Flight duration: May 25 – June 22, 1973; 28 days, 49 min.
Crew: Charles Conrad – Commander, Paul Weitz, Joseph Kerwin.
Number of Earth orbits: 404.
Time spent outside the station: 5.7 hours.
Photos from ATM: 30,242.
Photos from EREP: 8,886.
Skylab Program Timeline (Continued)
SL-2 Mission Details
The first crewed mission was initially delayed by 10 days due to technical problems.
During this time, NASA specialists prepared a plan for urgent repairs.
The mission began on May 25, 1973, and lasted 28 days and 50 minutes.
The crew consisted of Charles Conrad (Commander), Paul Weitz (Pilot), and Joseph Kerwin (Scientist).
Essential repairs were completed, including shielding the laboratory with a „parasol” and lowering its internal temperature to 24°C.
SL-3
Flight duration: July 28 – September 25, 1973; 59 days, 11 hours, 9 minutes.
Crew: Alan Bean (Commander), Jack Lousma, Owen Garriott.
Number of Earth orbits: 858.
Time spent outside the station: 13.7 hours.
Photos from ATM: 77,600.
Photos from EREP: 14,400.
Skylab Program Timeline (Continued)
SL-3 Mission Details
The mission began on July 28, 1973, and lasted 59 days, 11 hours, and 9 minutes.
The crew consisted of Alan Bean (Commander), Jack Lousma (Pilot), and Owen Garriott (Scientist specializing in ionospheric physics).
Upon arrival, they inspected the base from the outside before entering Skylab to continue previous research.
On August 6, Lousma and Garriott performed an EVA to install a proper protective screen, which successfully lowered the internal temperature to 21°C.
The crew spent 305 hours on solar observations, capturing many solar flares during a period of high solar activity.
Earth resource studies were conducted over Western Europe, Japan, Australia, West Africa, and the Americas.
Observations included avalanche threats in Switzerland, earthquake effects in Mexico, and atmospheric pollution in West Germany.
Biological experiments had mixed results: experimental mice and fruit flies died, and fish struggled to adapt to zero gravity.
Two spiders, named Anita and Arabella, successfully adapted and began weaving proper webs (a project proposed by 17-year-old student Judith Miles).
SL-4
Flight duration: November 16, 1973 – February 8, 1974; 84 days, 1 hour, 14 minutes.
Crew: Gerald Carr (Commander), William Pogue, Edward Gibson.
Number of Earth orbits: 1214.
Time spent outside the station: 22.3 hours.
Photos from ATM: 75,000.
Photos from EREP: 17,000.
Skylab Program Totals & Failures
Program Totals
Total stay for 3 crews: 171 days, 13 hours, 14 minutes.
Total Earth orbits: 2476.
Total time spent outside the station (EVAs): 41.7 hours.
Total photos from ATM: 182,842.
Total photos from EREP: 40,286.
Major Failures
The tearing away of the micrometeoroid and thermal shield of the OWS during launch, causing the station to overheat and reducing electrical power by over 6 kW.
Disturbances in the stabilization system (gyroscopes).
Mission SL-4
The mission began on November 16, 1973, and lasted 84 days, 1 hour, and 16 minutes. The crew consisted of Gerald Carr (Commander), William Pogue (Pilot), and Edward Gibson (Pilot/Scientist-Physicist). Originally intended to last 59 days, it was ultimately decided that the mission would last 84 days. The new crew worked slowly and without enthusiasm, was constantly late in performing tasks, and became involved in conflicts with ground control when urged to work more efficiently. Interestingly, despite being less committed to their tasks, they were in significantly better physical condition than their predecessors. Nevertheless, they completed the planned research program and gathered a vast amount of scientific information. They performed four EVAs: November 22 for 6 hours and 34 minutes, December 25 for 7 hours and 3 minutes, December 29 for 3 hours and 29 minutes, and finally February 3 for 5 hours and 19 minutes.
A very important result of their work was conducting research on solar flares and observing and photographing Comet Kohoutek using five different instruments. The astronauts photographed it in visible and ultraviolet light during their stays outside the base. While it approached the Sun, they observed it through telescopes designed for solar research. In total, they took 75,000 photographs of the comet and the Sun. Research was hindered by a shortage of electricity caused by worsening solar panel orientation toward the Sun, due to the depletion of nitrogen supplies used for the thruster nozzles. The astronauts returned to Earth on February 8, 1974. After returning to Earth, it turned out that they were 2 cm taller.
Station Construction
The Saturn V rocket was used for the construction of the station. The station’s hull was made from its third stage, the S-IVB, while the first two stages, the S-IC and S-II, were assembled into the two-stage Saturn INT-21 carrier rocket. The S-IVB hull had a diameter of 6.6 m, a length of 14.6 m, and was divided by a transverse partition into two tanks: a larger one for liquid hydrogen and a smaller (lower) one for liquid oxygen. The lower tank, left unchanged, was intended as a waste container (deposited through a special airlock), while the upper one was divided into two floors. The lower floor, 2 m high, was designated for living and utility quarters, and the second, 6 m high, was designated for laboratories. Each of these floors was further divided into many smaller rooms. The entire structure had a volume of 292 m³ and, with complete equipment, had a mass of 35,400 kg.
The 17% mass fraction of yttrium oxide (Y₂O₃) was used to stabilize the zirconia structure, which shows the highest density among the examined samples. The highest density was achieved thanks to the use of nanoscale powder, which after sintering at 1600°C reached 5.97 g/cm³ (96.5% of theoretical density). The material exhibits low porosity of 3.5%, and the average grain size is 0.55 µm.
The material obtained shows a good set of functional properties. The Young’s modulus is 209 GPa, and the hardness is 780 HV10. The material also shows high fracture toughness of 1.7 MPa√m. The obtained material shows resistance to hydrothermal aging – after 25h exposure in an environment of 134°C/2bar steam, the phase transformation did not exceed 24%.
The material was subjected to detailed tribological tests. The coefficient of friction against alumina is 0.28, and against steel 0.35. During the tests, no material transfer to the counter-sample was observed. The wear coefficient is 3.5×10⁻⁶ mm³/Nm against alumina and 1.00×10⁻⁵ mm³/Nm against steel.
For communication purposes with Earth, 15 transmitters and 5 receivers were used, operating in the 230–450 MHz and 2100–2270 MHz bands. Television cameras operated in a 525-line system. For orientation and stabilization changes, 6 motors powered by compressed nitrogen and three gyroscopes were used. In addition, the telescope had its own orientation system with an accuracy of about 10″. Equipment for gymnastic exercises, biomedical research, and materials science experiments (melting and welding of metals, casting, and crystallization of materials) was placed in the base.
Termination of the program
There were plans to maintain Skylab in orbit for at least the next eight years and to send space shuttles to it. For this purpose, remote tests were conducted: the station was placed in a stable orbit, and then all systems were turned off. In the fall of 1977, it turned out that increased solar activity and the associated expansion of the atmosphere caused a faster than predicted orbital decay. NASA had no way of boosting the Skylab station to a higher orbit because the Apollo program had ended, and the shuttle missions had not yet begun. The station entered the dense layers of the atmosphere on July 11, 1979, and its debris fell into the Indian Ocean and Western Australia, between the towns of Esperance and Rawlinna. The largest piece, weighing about 500 kg, fell on a certain farm 900 km east of Perth. Many elements of the station (e.g., a series of tanks) survived the fall from space to Earth unexpectedly well. Fortunately, this area was relatively sparsely populated, and the only victim of the disaster was an Australian cow. By the time of its destruction, the Skylab station had orbited the Earth 34,981 times and traveled a distance of about one and a half billion kilometers. It turned out that during disintegration, the station was subjected to lower thermal and aerodynamic stresses than expected; therefore, the disintegration occurred 16 km lower than anticipated. The dimensions of the debris footprint ellipse also turned out to be much smaller than expected, measuring 64 by 3860 km.
Shortly before the launch of the Skylab station, NASA also planned to send a second module in 1975 or 1976 named Skylab B, which was to serve as an addition to the Soyuz-Apollo mission (International Skylab), and then be expanded by the space shuttle into an orbital station (Advanced Skylab); however, due to a lack of funds, the launch of Skylab B was canceled, and the station hull itself was handed over to a museum in 1976.
Summary
The experiments conducted on board the station mainly concerned astronomy (24%), Earth surface reconnaissance (48%), engineering and technology (10%), and medicine and biology (10%). These studies were completed successfully. They were the result of both careful preparation of the equipment and experiments as well as the excellence of the technology, work organization, and the activities of the astronauts themselves. Important information was obtained in the fields of physics, materials science, and technologies for obtaining products of significant industrial importance. Medical and biological studies were also completed successfully. Regarding astronomy, the research concerned the Sun. Each of the instruments located in the station had been previously used in satellites. For example, a white-light coronagraph was on board the astronomical satellite OSO 7 in 1971, and earlier on rockets and stratospheric balloons. However, on Skylab, the instruments were larger and significantly improved. The six main instruments were about three meters long, and their total mass was over a ton. The stability of the ATM astronomical observatory was comparable to the stability of instruments placed on the Earth’s surface (sometimes better than one second). In the absence of an atmosphere, a spatial and spectral resolution was achieved that was sometimes orders of magnitude better compared to previous achievements. At the same time, research conducted at the station was supported by parallel observations on the surface of our planet through the headquarters at the Johnson Space Center in Houston.
During its nine months of operation, Skylab encountered many complex technical problems that threatened the entire program. At the same time, this first American space station became famous as a real-life laboratory orbiting the Earth. During 3,896 orbits, the three crews that visited Skylab confirmed that outer space can create a new, unique quality for scientific and technological research, as well as change the way we look at Earth and our Universe. During their stay at the station, the astronauts traveled a total of about 115 million kilometers over the course of 171 days on board. Nine crew members went into space ten times, spending over 42 hours outside the station. During this time, they performed repairs, maintenance, collected experimental kits and film canisters from telescopes, and photographed celestial objects. They conducted experiments in various fields lasting over two thousand hours. At the same time, they proved that humans can safely adapt to life and long-term work in microgravity conditions in space.
Because work on the space shuttle was already advanced, there was a possibility that the shuttle could reach Skylab during its first flights and boost it to a higher orbit, which would allow for the recovery of results from several experiments and perhaps house several more crews on the station. However, the space shuttle plans changed, which caused these and other ideas for saving the station to be abandoned – the decreasing distance from Earth gradually brought Skylab closer to its inevitable entry into the Earth’s atmosphere.
