Butch Wilmore and Sunita Williams stranded in space: What next?

On June 22, 2024, NASA astronauts Butch Wilmore and Sunita Williams were supposed to return to Earth. However, the Boeing Starliner, the spacecraft they used for their trip to the International Space Station, experienced a problem with its thrusters. This issue could impact the spacecraft’s ability to manoeuvre and its safety. As a result, their return has been delayed multiple times, and NASA has announced that the next attempt will likely be in the middle of July.

Boeing’s plan to receive NASA certification for full crew rotation missions to the ISS by completing the Crew Flight Test has hit a snag due to this mission’s setbacks.

What the International Space Station is

The International Space Station, or ISS for short, is a marvel of human ingenuity, a space platform orbiting Earth at around 370–460 km. It orbits at a 51.6° inclination to the Equator, allowing it to fly over nearly 90% of inhabited Earth. It takes almost 90 minutes to circle the Earth once, a testament to our ability to conquer the vastness of space.

The station was established as a joint initiative of the Canadian Space Agency, the European Space Agency, the Japan Aerospace Exploration Agency, the National Aeronautics and Space Administration, and the State Space Corporation “Roscosmos”. Construction began in 1998 and has hosted at least one human being since November 2000. More than 280 individuals from 23 countries have visited the International Space Station. The ageing ISS is proposed to be decommissioned in 2030.

With all its solar panels, the ISS is as large as a football field, and the living and working space available to the crew members is as ample as a six-bedroom apartment. There are seven sleeping quarters, two bathrooms, a gym, and a 360-degree view bay window. The ISS hosts between 3 and 13 crew depending upon the rotation schedule.

The ISS crew is responsible for conducting experiments in the unique space environment and performing essential housekeeping tasks. One of the most notable experiments aboard the ISS is the Alpha Magnetic Spectrometer (AMS), designed to detect dark matter, a crucial component of our understanding of the universe.

The space platform provides a microgravity environment that eliminates gravity's effect. Without gravity, for example, flames behave differently and become spherical. The absence of surface tension and capillary movements allows a more detailed study of fluid behaviour. Critical scientific experiments in the space lab include studying biological processes such as seed germination and shoot development in the absence of gravity. Nearly 3,000 experimental studies have been conducted on various topics and disciplines, including space manufacturing techniques, space botany, and algae-based life support systems.

Boeing Starliner

The ISS was initially serviced by the Russian Soyuz spacecraft and NASA's space shuttles, transporting crew members and supplies. NASA's fleet of five space shuttles—Endeavour, Discovery, Atlantis, Challenger, and Columbia—played a crucial role in ferrying crew to the ISS and aiding in its construction. This fleet completed 135 missions to the ISS, starting with the first test flight conducted by Space Shuttle Columbia on April 12, 1981, and concluding with the landing of Space Shuttle Atlantis on July 21, 2011, marking the end of the space shuttle era.

On its tenth flight in January 1986, Challenger broke up just 73 seconds after liftoff, killing the seven-member on the launch pad. The Space Shuttle Columbia disintegrated as it re-entered the atmosphere on February 1, 2003, killing all seven astronauts on board, including Kalpana Chawla, Indian born American crew. These led to the pullout of the space shuttles from service.

2011, after the retirement of the space shuttles, NASA began relying on the Russian Soyuz to transport American crew members and cargo to the ISS. The agency initiated the Commercial Crew Program to encourage American aerospace companies to participate in building and operating space vehicles for NASA. In 2010, NASA selected Boeing's CST-100 Starliner and SpaceX's Crew Dragon as the Commercial Crew Transportation providers.

Boeing developed the CST-100 Starliner spacecraft to carry seven passengers and transport crew and cargo to the ISS. Boeing constructed three crafts, one of which has been retired, while the remaining two, S2 and S3, are still operational. S2, which carried Sunita Williams to space, is currently docked at the ISS.

The spacecraft is partially reusable and consists of a conical Crew Module for the crew and a cylindrical Service Module at its base. The service module houses the fuel tank, engines, and cooling system.

In space, the spacecraft's thrusters help with navigation and docking with the ISS. After the mission, the crew module and service module are detached from the ISS, and the engines in the service module provide the thrust needed for de-orbit. The service module is detached and allowed to burn up in the Earth's atmosphere just before re-entry. The crew module, which can be used ten times with a six-month turnaround time, makes a safe touchdown using parachutes.

Boeing and other firms plan to build a space station called Orbital Reef to serve as a space tourism destination. Boeing aims to utilize the Starliner as a commercial spacecraft to transport tourists and crew to this station and support NASA crew in travelling to the ISS.

Crew Test Flight

Boeing conducted the first unmanned Orbital Flight Test on December 20, 2019, which was a partial failure. A second Orbital Flight Test took place on May 19, 2022. The craft successfully docked with the ISS on May 25, 2022, and returned safely to Earth despite technical glitches. Two Orbital Manoeuvring and Attitude Control System (OMACS) and Reaction Control System (RCS) thrusters failed during orbital insertion.

Before NASA accepted the vessel for regular missions, Boeing had to undertake a Crew Flight Test. Launched on June 5, 2024, the Crew Test flight carried Butch Wilmore and Sunita Williams aboard. This flight was a crucial step in the certification process, allowing the astronauts to test the spacecraft's systems and capabilities in a real-world scenario.

During this test flight, Starliner purposely took about 26 hours to dock with the ISS after launch. The crew operated the craft in manual mode to test its capabilities. The craft can fly automatically using the onboard computer, like a self-driving, hands-free space cruise. It is designed to detect, isolate, and respond to faults and can autonomously navigate any demanding situation. The crew also tested manual control of the craft under various challenges.

Helium leak

After spending a week aboard the ISS, the crew was scheduled to return on June 14. However, the mandatory pre-flight systems checkouts indicated that one of the reaction control thrusters, B1A3, had developed a helium leak. During the test, the thruster gave only 11 per cent of the thrust it was designed to. In the second 'hot fire' test, it produced zero thrust.

The fuel tank in motor vehicles is typically positioned above the engine to allow gravity to draw and supply fuel to the engine. However, in space, the craft is in free fall and does not experience the pull of gravity. This means the fuel from the tank must be pushed to reach the engines. Helium is used to assist in this process. The helium is released into the fuel tank to move the fuel to the engines. If the helium leaks, the pressure drops, and the proper amount of fuel does not flow to the engine, causing a loss of power.

NASA initially planned for the craft's return date to be June 22, 2024, but this was later revised to June 28, 2024. However, it was discovered that more issues had arisen. Five of the 28 vital reaction control thrusters suffered from helium leaks. As a result, NASA has announced that the return will be delayed by a 'couple of weeks' until the thruster issues are resolved or better understood.

Reaction control thrusters

The reaction control thrusters are small rockets fired to control, navigate, and maintain the desired orientation of the craft. For example, when the craft needs to undock from the ISS and back away before taking a flight path for de-orbit and returning to Earth, the thrusters help achieve these manoeuvres.

The rockets operate based on Newton's third law, which states that every action has an equal and opposite reaction. When a missile is fired, thrust is developed opposite to the rocket exhaust. In the frictionless environment of space, the craft will continue moving in the same direction indefinitely. However, to stabilize the craft at a specific point, we must apply a braking force to stop its movement. This is done by firing the rocket in the direction opposite to the motion of the capsule. The inertial force of the craft in the forward direction and the force generated by the rocket exhaust in the opposite direction cancel each other out, halting the movement of the capsule. This manoeuvre requires the two thrusters to be fired precisely for a specific duration with a predetermined gap.

Boeing spokespeople claim that the remaining 23 reaction control thrusters are sufficient to safely bring the craft back home. However, NASA is not convinced. It has been announced that the capsule will not be approved to fly until its thruster issues are resolved or at least better understood.

Stranded in space

Currently, the crew members are safe and sound aboard the ISS. The crew comprises US and Russian members, including Oleg Kononenko, Tracy Dyson, Mike Barratt, Matthew Dominick, Jeanette Epps, Nikolai Chub, and Alexander Grebenkin. They are part of Expedition 71, which started on April 5, 2024. They are expected to remain on the station until the next rotation crew arrives in September 2024. Butch Wilmore and Sunita Williams have recently joined the team. The space station is well-stocked with food and other supplies. Additionally, apart from Boeing's Starliner, there are five other spacecraft docked at the space station, including SpaceX Dragon Endeavour, Northrop Grumman's Cygnus space freighter, the Soyuz MS-25 crew ship, and the Russian Progress 87 and 88 resupply ships, all of which are available for emergency evacuation if needed.

The extended delay in the capsule's return will allow the joint NASA-Boeing team to test similar thrusters currently used in space at the White Sands Test Facility in New Mexico. The aim is to understand why the systems failed. The preliminary testing will take about two weeks, starting from July 2, 2024.

Meanwhile, the Starliner crew is conducting a test firing of each thruster for 1.2 seconds and measuring the acceleration from the impulse in the ISS flight control system to assess the thrusters' performance.

Recently, Boeing has faced controversy over alleged quality and safety issues. Numerous insiders have reported safety concerns at the plants manufacturing Boeing 787 aircraft.

There are reports of a helium leak being detected at launch and disregarded. Despite the helium leak, the Crew Test Flight was launched. Allegedly, it was claimed that the helium supply was one hundred times more than required, and a small leak was deemed unimportant. Boeing's embarrassing delay in the return of the crew members due to the malfunction of the reaction control thruster has been a setback for the company.

(The story was first published on July 2)