Castle in the Sky- Remembering NASA's Spacelab.

With leftover hardware from the Apollo program but absent funding for further lunar landing missions, NASA shifted its resources to embark on a plan to construct an orbiting laboratory. This concept had been introduced in the early 1960s during the Gemini program (which was under Air Force sponsorship at the time) with an unmanned prototype launched in late 1966, but it was felt that reconnaissance functions could be adequately served by unmanned cameras. Nonetheless, interest grew towards a long-term human presence in space.

A Novel Design Made with Repurposed Parts

Thus, NASA repurposed a majestic Saturn V launch vehicle designed to propel astronauts to the moon. Its third stage, weighing 85 tons and enclosing 460 cubic yards in volume – nineteen times that of the Apollo spacecraft that ferried three astronauts to their orbiting home- was reconfigured to serve for habitation. The orbiting behemoth was subdivided into modules – the orbital workshop (for occupancy and experiments), an airlock module, a docking adapter and a telescope mount. Both the workshop and the telescope mount included photovoltaic arrays to provide electrical power from solar radiation.

Atop the Saturn V’s second stage, the Skylab space station launched into low earth orbit about 270 miles above the surface on May 14 fifty years ago – a mere five months after Apollo’s last walk on the moon. Unfortunately, the micro-meteoroid shield and port side photovoltaic solar array had ripped away from premature deployment, while the remaining starboard solar array jammed in an unfurled position. These conditions caused internal overheating and left the station bereft of electrical power. NASA quickly designed and fabricated a parasol of nylon and mylar attached to aluminum poles for deployment via an airlock.

Trios of astronauts would be launched aboard Saturn 1B launch vehicles. Each three-man crew boarded an Apollo command module attached to its service module, as had been conducted during the Apollo program. NASA conducted three such missions in order to dock and ingress Skylab. At the conclusion of their mission, the astronauts would return to their command module, undock from Skylab, jettison the service module and reenter the atmosphere for retrieval at sea by the United States Navy.

Eleven days after Skylab station entered orbit, the first mission crew (officially SL-2) aboard an Apollo spacecraft rendezvoused with the orbital behemoth. These astronauts included the late Pete Conrad (Apollo 12 commander), the late Paul Weitz (subsequent commander of Space Shuttle STS-6) and Joseph Kerwin. Despite docking complications, the crew boarded Skylab.

Life and Work Aboard the Castle in the Sky

After conducting a spacewalk to deploy the improvised parasol shade and the remaining solar array, the crew began their scheduled science experiments during their 27 days in space, accompanied by three spacewalks. Upon return after atmospheric reentry, the astronauts were recovered by the carrier USS Ticonderoga (CV-14), which had also retrieved the crews of Apollo 16 and Apollo 17 from their moon landing missions.

The second Skylab mission (SL-3) launched in July 1973 for 59 days in orbit, accompanied by three spacewalks. This crew included the late Alan Bean (Apollo 12 lunar pilot), Jack Lousma (subsequent commander of STS-3) and the late Owen Garriott (mission specialist on STS-9). As an aside, Garriott’s son Richard flew aboard Soyuz TMA-13 to the International Space Station in 2008.

Experiments included medical evaluation of the astronauts exposed to prolonged weightlessness, along with ultraviolet photography of the sun’s photosphere, galactic X-ray mapping and visual observation of Hurricane Ellen. The amphibious assault ship USS New Orleans (LPH-11), which had previously rescued the crew of Apollo 14 two years before, dispatched the command module from the sea after its splashdown.

The third and final Skylab mission (SL-4) launched in November 1973 for a record-breaking 84 days in orbit and four spacewalks. This all-rookie crew included the late Gerald Carr, the late William Pogue and Edward Gibson. Mission control had assigned the astronauts burdensome assignments for unloading and stowing long-duration items. One gyroscope for orbital maintenance failed from inadequate lubrication, and a second one required monitoring and load reduction to maintain operation.

Celestial observations included the first recording of the beginnings of a solar flare. In addition to that, the crew also conducted numerous other astronomical recordings, undertook earth terrain photography, as well as student experiments, including cosmic X-ray measurements. The crew’s cabin returned from orbit and was retrieved from the Pacific Ocean by USS New Orleans. The mission’s duration record stood for four years until surpassed on Salyut 6.

The remaining Apollo spacecraft was assigned to join with Soyuz 19 in 1975 as the first international manned space venture. NASA expected to use Skylab as a node for future long-duration missions after the completion of these three manned flights. Unfortunately, overoptimistic projections about the Skylab’s orbital decay and delays in the first launch of the Space Shuttle forced their abandonment. Skylab re-entered the atmosphere and disintegrated in July 1979 over the Indian Ocean. Afterwards, the Space Shuttle, which  first flew in April 1981, was used for research purposes. It became the first partially reusable manned orbiting spacecraft – and thus far the only contender that landed on a runway instead of thumping to the surface via parachute.

Orbital Innovations Around the World

By way of geopolitical comparison and historical perspective, the Soviet Union flew their first orbiting station Salyut-1 in April 1971. Lifted by their Proton booster, this payload provided its cosmonauts a 20-ton laboratory with 130 cubic yards of internal volume – about a third of the volume and a quarter of the mass of Skylab three years later. Soyuz 10 was unable to latch, and unfortunately, the crew of Soyuz 11 died of asphyxiation upon their departure after 23 days in orbit.

As a result of this tragedy, the Soyuz descent module was redesigned, reducing its crew from three to two to ensure sufficient space to don spacesuits for launch and reentry.  Eventually, the Soviets resumed their program with the military version Salyut 3 in June 1974, visited by Soyuz 14 to test the first cannon in space. Salyut 4 launched in December 1974 and hosted Soyuz 17 and Soyuz 18 two-man crews. A final military Salyut 5 launched in June 1976 received Soyuz 21 and Soyuz 24 crews. All these stations were eventually destroyed upon de-orbiting.

The Soviets further improved their station’s second generation design with docking ports at either end, enabling supplies from Progress supply freighters and visiting crews to exchange Soyuz spacecraft. Salyut 6 lifted into orbit in September 1977, and over its five years received crews from fourteen Soyuz and four Soyuz T spacecraft, as well as adding Kosmos 1267 as a test of modular expansion. Launched in April 1982, Salyut 7 sported multiple docking ports and received crews from ten Soyuz T spacecraft, as well as intermittently joining with modules Kosmos 1443 and later Kosmos 1686, remaining in orbit almost nine years.

Finally Mir launched in February 1986 with a core platform. This was later followed by modules Kvant-1 for astrophysics, Kvant-2 to provide an airlock and water storage, Kristall for experiments, Spectr for power, Priroda for remote sensing over the following years. A total of one Soyuz T and twenty-nine Soyuz TM vehicles visited, thirty crewed Soyuz vehicles visited Mir – with more than half including international crews. The improved TM spacecraft enabled the reintroduction of a third crew member. In addition, improving relations enabled visits from the Space Shuttle.

In addition to the unmanned Progress supply flights, from March 1995 through June 1998, nine Space Shuttle missions docked with Mir: Atlantis seven times, with Endeavour and Discovery once each.  The combined orbiting mass of Mir with its modules and the shuttle orbiter yielded 280 tons at those intervals. Following the launch of early components for the International Space Station (or ISS), Mir was de-orbited in March 2001.

Meantime, China has pursued its ambitious manned space ambitions independently from the world community using boosters from the Long March family of boosters. The first Chinese manned mission Shenzhou 5 rose in October 2003, with the spacecraft derived from Soyuz designs. Its first space station, Tiangong-1 was launched 2011 with a mass of nine tons, receiving visits by Shenzhou 9 and Shenzhou 10 mission crews over the next two years. Its successor, Tiangong-2 was launched in 2016 and hosted the crew of Shenzhou 11.

In April 2021, China launched Tianhe as the core module for its third generation station, which has been visited by Shenzhou 12 and Shenzhou 13 over the subsequent twelve months. Meanwhile, Tianhe incorporated Wentian and Mengtian modules last year 2022 during the stay of the Shenzhou 14 crew, and thereby expanded the station’s capabilities.

Current Innovations and Moving Forward

From 1998 through 2021, assembly of the International Space Station (ISS) continued apace. Modules from Russia, Japan, Europe and ourselves were brought either by the Space Shuttle (until its retirement in 2011) or Proton. Suspended from American trusses, these components receive power from enormous solar panels, accompanied by thermal radiators. With meticulous planning and intricate execution, this multi-faceted platform extends 358 feet in length and with a mass of 495 tons. ISS remains in orbit and crewed operation, with Soyuz MS-23 and Crew-6 (SpaceX Dragon), to be joined by Axiom Mission 2 (Dragon) on May 17th.

The need for eventual replacement of the aging ISS has led to proposals from Axiom for detachable modules to ISS, Blue Origin with Orbital Reef, Airbus with its wide body Loop and Northrup Grumman, which received a contract for the habitation module for lunar Gateway. Ever so gradually, humans are gathering the resources and determination to escape the confines of our world. Skylab presented an outstanding initiation towards this avid endeavor, as we stand on the shoulders of such giants.

Photo Credit- Space Flight Insider