The history of human spaceflight to the International Space Station (ISS) is a story of international cooperation, technological achievement, and resilience in the face of challenges. For many years, the Russian Soyuz spacecraft served as the sole means of transporting crews to and from the orbiting laboratory after the retirement of the American Space Shuttle in 2011. However, the advent of commercial crew vehicles developed by SpaceX and Boeing under NASA’s Commercial Crew Program has marked a new era in ISS operations and reduced reliance on Russia for access to space.
The Soyuz Spacecraft
The Soyuz spacecraft has been a workhorse of the Russian space program since the late 1960s. Evolved from the early Vostok and Voskhod capsules that carried the first Soviet cosmonauts into orbit, the Soyuz has undergone numerous upgrades and modifications over its long service life. The basic design consists of three modules: the spherical orbital module that provides living space for the crew during their mission; the small, aerodynamic descent module that returns the crew to Earth; and the cylindrical service module housing the spacecraft’s propulsion, power, and life support systems.
Soyuz spacecraft are launched atop Soyuz rockets from the Baikonur Cosmodrome in Kazakhstan. After reaching orbit, the spacecraft typically spends two days chasing down the ISS before docking to one of the station’s ports. At the end of the mission, the crew boards the Soyuz, undocks, and jettisons the orbital and service modules. The descent module fires its thrusters to deorbit and reenters the atmosphere, deploying parachutes and landing in the Kazakh steppe.
Reliance on Soyuz After Shuttle Retirement
The Space Shuttle was the United States’ primary means of transporting astronauts to the ISS from the station’s inception in 1998 until the fleet’s retirement in 2011 after 30 years of service. The winged, reusable orbiters carried crews of up to seven along with large payloads in their capacious cargo bays. However, the Shuttle’s complexity and high operating costs, along with the loss of two orbiters and their crews in tragic accidents, ultimately led to the decision to end the program.
In the absence of the Shuttle, NASA was left without a domestic means of launching astronauts and had no choice but to purchase seats on Russian Soyuz flights to maintain a continuous American presence on the ISS. This arrangement was not without precedent; American astronauts had flown on Soyuz missions to the Russian Mir space station in the 1990s as part of the Shuttle-Mir program that helped pave the way for the ISS partnership. However, sole reliance on Russia for crew transport was a new and uncomfortable position for NASA.
Soyuz seat prices rose sharply after the Shuttle’s retirement, reaching over $80 million per round trip by 2018. This represented a significant expense for NASA and a financial boon for the Russian space agency Roscosmos. There were also concerns about the potential for geopolitical tensions between the United States and Russia to disrupt the fragile space partnership, particularly after Russia’s annexation of Crimea in 2014 led to international sanctions.
The Commercial Crew Program
Recognizing the need to restore America’s human spaceflight capability and reduce reliance on Russia, NASA initiated the Commercial Crew Program in 2010. The goal was to leverage private industry to develop new spacecraft capable of safely and cost-effectively transporting astronauts to and from the ISS. In 2014, NASA awarded contracts to Boeing and SpaceX to develop their Starliner and Crew Dragon vehicles, respectively.
SpaceX, founded by entrepreneur Elon Musk, adapted its cargo Dragon capsule that had been supplying the ISS under NASA’s Commercial Resupply Services program since 2012. Crew Dragon features a sleek, conical design with large windows, touchscreen controls, and a reusable propulsion system. It launches atop SpaceX’s Falcon 9 rocket and can carry up to seven astronauts, although NASA missions typically fly with four. After docking with the ISS, Crew Dragon remains attached to serve as a lifeboat in the event of an emergency.
Boeing’s Starliner capsule shares some design heritage with the company’s Apollo-era command modules and the Orion spacecraft being developed for NASA’s Artemis lunar program. It launches on United Launch Alliance’s Atlas V rocket and, like Crew Dragon, can carry up to seven astronauts and dock to the ISS for the duration of the crew’s mission. However, Starliner has faced technical issues during its uncrewed test flights that have delayed its schedule compared to SpaceX.
SpaceX’s Crew Dragon Takes Flight
After years of development and rigorous testing, SpaceX’s Crew Dragon became the first commercial spacecraft to launch astronauts when it carried NASA’s Doug Hurley and Bob Behnken to the ISS on the Demo-2 test flight on May 30, 2020. The mission was a complete success, with the spacecraft performing flawlessly from launch through docking, undocking, and splashdown.
Following Demo-2, NASA certified Crew Dragon for operational crew rotation missions. The first of these, Crew-1, launched four astronauts to the ISS on November 15, 2020 for a six-month stay. Subsequent Crew Dragon missions have settled into a regular cadence, with new crews launching roughly every six months to replace those completing their deployments on the station.
The advent of Crew Dragon has allowed NASA to increase the size of the ISS crew from six to seven, enabling a greater amount of scientific research to be conducted on the orbiting laboratory. It has also ended NASA’s sole reliance on Soyuz for crew transport, although the agency continues to fly astronauts on the Russian spacecraft under a “seat swap” agreement with Roscosmos that sees Russian cosmonauts flying on Crew Dragon in exchange.
Starliner’s Delayed Development
Boeing’s Starliner has faced a rockier path to operational readiness than Crew Dragon. During its first uncrewed Orbital Flight Test (OFT) in December 2019, Starliner suffered a mission clock error that caused it to burn too much propellant to reach the ISS. Although the spacecraft was able to return safely to Earth, the failure to achieve the primary objective of docking with the station was a significant setback.
After investigating the cause of the anomaly and implementing corrective actions, Boeing prepared Starliner for a second OFT in August 2021. However, just hours before launch, the mission had to be scrubbed due to stuck propellant valves in the spacecraft’s service module. The capsule was returned to the factory for repairs, and the OFT-2 mission finally got underway on May 19, 2022.
This time, Starliner successfully reached orbit and docked with the ISS, achieving the objectives that had eluded it on the first OFT. However, two of the spacecraft’s main thrusters failed during the orbital insertion burn, and the capsule’s thermal cooling system also malfunctioned during the flight. Although these issues did not prevent the completion of the mission, they underscored the technical challenges Boeing continues to face with Starliner.
Following the OFT-2 mission, NASA announced that the first crewed flight of Starliner, known as the Crew Flight Test (CFT), would be delayed to allow time for investigation of the thruster and cooling system problems. The CFT mission is currently scheduled to launch on May 17, 2024. Assuming the CFT mission is successful, NASA will then work to certify Starliner for operational crew rotation flights to the ISS alongside Crew Dragon.
The Future of ISS Crew Transport
With Crew Dragon now flying regular missions and Starliner on the cusp of crewed flight, NASA has successfully achieved its goal of restoring America’s human spaceflight capability and ending sole reliance on Russia for access to the ISS. However, this does not mean the end of the ISS partnership or flights on Soyuz.
Under the seat swap agreement between NASA and Roscosmos, Russian cosmonauts will continue to fly on Crew Dragon and Starliner, while American astronauts will still have the opportunity to fly on Soyuz. This arrangement helps ensure that there is always at least one American and one Russian on the ISS to operate their respective segments of the station, even if there are disruptions to either country’s launch systems.
Looking ahead, NASA has already awarded additional crew rotation missions to SpaceX and Boeing that will keep the ISS staffed through at least 2030. The agency is also looking to bring on additional commercial crew providers to increase redundancy and competition in the market. Sierra Nevada Corporation, which developed the Dream Chaser spaceplane for cargo missions, has expressed interest in adapting it for crew transport.
Summary
The story of human spaceflight to the ISS is one of international cooperation, technological achievement, and perseverance in the face of challenges. For many years, the Russian Soyuz spacecraft served as the sole lifeline to the station, ensuring a continuous human presence in low Earth orbit. However, the success of NASA’s Commercial Crew Program and the advent of new American spacecraft like SpaceX’s Crew Dragon have ushered in a new era of ISS operations and reduced reliance on Russia for access to space. Seapot
