Designing the Largest Human-Made Object in Space to Date: The International Space Station

by #LizPublika

Illustration of Tsiolkovsky's spacecraft (1883)

Earth is the cradle of humanity, but one cannot live in a cradle forever.

This quote by Russian space visionary Konstantin E. Tsiolkovsky (1857 - 1935), whose words and works, including his book Free Space (1883) that features sketches of what he imagined a manned spaceship orbiting Earth might look like, inspired many future space engineers and scientists world-wide.

The largest international construction project in space to date officially kicked off on the steppes of Kazakhstan in 1998, when Zarya (also known as the Functional Cargo Block or FGB), thundered off its launch pad at the Baikonur Cosmodrome. And so, the first module of the International Space Station was deployed atop its proton rocket.

Launch of Zarya, the first ISS on-orbit element (1998)

Built by the Khrunichev State Research and Production Space Center, a Moscow-based manufacturer of spacecraft and space-launch systems, the FGB would provide crucial electrical power, storage, propulsion, and guidance to the International Space Station (ISS) during the initial stage of its assembly.

Plans for the ISS date back to 1984, when President Ronald W. Reagan gave NASA the green light to develop a space station for low-Earth orbit. Canada, Japan, and the European Space Agency (ESA) were invited to join the project four years later, and five years after that (in 1993) then President Bill Clinton extended an invitation to Russia to join the partnership.

This artist's concept is a cutaway illustration of the Skylab with the Command/Service Module being docked to the Multiple Docking Adapter (1972)

As a result, former adversaries on Earth became colleagues, working together to build a huge collaborative space laboratory. But before this historic partnership had formed, the United States had launched Skylab, the only American space station launched by NASA to date. And even though it was occupied for just 24 weeks, between 1973 & 1974, it helped scientists learn a lot.

Astronauts who worked on Skylab — including Gerald Carr, Bill Pogue, and Ed Gibson — were consulted on the design of habitable spaces for the new station. And they had invaluable feedback. For one, engineers were surprised to learn that astronauts were fine with being weightless and floating around in Zero G, but not with an inconsistent up-and-down orientation.

Skylab in orbit in 1973 as flown, docking ports in view

The Skylab workshop had an up-and-down orientation but the multiple docking adapter with two docking ports didn’t; astronauts found this to be thoroughly disorienting. And because early space programs, like Mercury and Gemini, focused on the significant challenges of safety and survivability, concerns of this nature were often wrongly dismissed as irrelevant.

The fact that the ISS would consist of multiple modules in a configuration that required multiple exits from a single module coupled with the fact that Skylab astronauts found the division of a module into vertical decks claustrophobic and visually confining, led to scientists settling on a longitudinal orientation for the module interiors.

A portion of the ISS and the docked space shuttle Endeavour is featured in image taken by a spacewalker, using a fish-eye lens attached to an electronic still camera. (2011)

And, since each participating country would build their own laboratories, the interior designs for these modules were guided by four specific principles: modularity, maintainability, reconfigurability, and accessibility. For that to happen, utilities and certain hardware components had to be standardized, so that they could be used in different modules.

A surprising number of options were analyzed to configure the interior space of the modules while maximizing and optimizing the volume devoted to habitation, storage, and utilities. Scientists settled on the “four stand-off” design: in cross-section, a square corridor running the length of the module, with four rows of standardized racks for storage and workstations.

This image is among the initial series taken through a first of its kind "bay window" on the International Space Station, the seven-windowed Cupola (2010)

At the time, computers had little capacity for video, so astronauts in the station wouldn’t be able to see what was happening outside. Skylab astronauts insisted that direct observation was crucial for conducting space operations, so European engineers eventually agreed to construct a Capula, if the US agreed to transport European crew on the Space Shuttle, which they did.

In International Space Station: Architecture Beyond Earth (2016), architect David Nixon goes into the details pertaining to the earliest designs conceived by the Johnson Space Center study group in 1983. But, in 1985, the team began work on something new. After 13 years of design, redesign, revision, and renaming of the project, the assembly of the ISS was ready to begin.

Graphic showing the assembly of the International Space Station

The process would take place in space. “The Russian Zarya and Zvezda modules were selected to be the first functional modules sent into orbit because of their self-sufficiency: Each could maneuver and power itself using self-deployed solar arrays, and they would be relied upon to keep the rest of the ISS in orbit. But the historic day in 1998 was just the first step.

“Assembling modules and components manufactured by multiple countries, often in different parts of the world, and launching them to match up perfectly while touching each other for the first time hundreds of miles above Earth presented ISS partner space agencies with an unprecedented logistical challenge.”

Because Russians had years of experience building space stations, their streamlined process proved to be helpful for the new project. The idea was that before anything was sent into space, a full mock-up of the space station modules would be created on the ground, with all components brought in, plugged in, and thoroughly tested to make sure everything worked.

“The pressurized modules of the U.S. segment relied on the use of Common Berthing Mechanisms (CBMs), roughly analogous to the Russian docking ports, developed by Boeing at the Marshall Space Flight Center. At locations where U.S. segment modules linked up with the Russian Segment, or with Russian vehicles, Pressurized Mating Adapters (PMAs) were attached to the Common Berthing Mechanisms to enable connection.

“Another key difference between the assembly of the Russian and U.S. Segments was the ability of Russian modules, based on the design of self-sufficient Mir and earlier Salyut orbital station modules, to navigate, maneuver, and dock automatically. Modules of the U.S. segment were “berthed” – guided into place with the use of the Space Shuttle’s robotic arm, the Canadarm2, and the Mobile Servicing System, once it had been attached to the station.”

ISS configuration as of 2022

“The penultimate module delivery by the Space Shuttle to the ISS was achieved in May 2011, when Endeavour delivered the Alpha Magnetic Spectrometer (AMS-02) — a particle physics experiment module —and ExPRESS Logistics Carrier to the station.” This monumental moment marked the beginning of the station’s “utilization” phase, or operating at the height of its power.

It took 40+ missions, some including space walks, to complete the assembly of the largest human-made object ever to orbit our planet. Now, weighing 900,000 pounds, and stretching as far as a football field; the International Space Station is enabling research that improves life on Earth as well as informs the future of long-term space exploration.

The International Space Station pictured from the SpaceX Crew Dragon 5 (2021)