Ms Williams and Butch Wilmore also participated in vein scans using an ultrasound device.
Having taken off on Boeing Starliner's maiden flight for what was supposed to be a 10-day mission, Indian-origin astronaut Sunita Williams has now been in space for 50 days and counting.
The Starliner has faced glitches in the propulsion system following a series of helium leaks but NASA has said Ms Williams and her fellow astronaut, Barry "Butch" Wilmore are safely aboard the International Space Station (ISS), where they have been assisting the Expedition 71 crew of seven astronauts with maintenance as well as various experiments since June 6.
The US space agency said Ms Williams, who is a veteran and is on her third space mission, investigated using fluid physics, such as surface tension, to overcome the lack of gravity when watering and nourishing plants being grown in space. This is akin to gardening in space and is a very vital step towards understanding how plants grow and respond to microgravity conditions. The research will be crucial when humanity looks to establish various bases in the solar system and beyond.
Ms Williams and Mr Wilmore also participated in vein scans using an ultrasound device. Doctors on the ground monitored in real-time as the pair took turns imaging veins in each other's neck, shoulder, and legs. Ms Wilmore also scanned the veins of fellow NASA astronaut Matthew Dominick, helping researchers understand how microgravity affects the human body.
Advanced biology research is also underway aboard the orbiting lab with astronauts exploring how living in space affects the human body and mind. Ms Williams extracted DNA to identify microbe samples collected from water systems aboard the ISS, which is like a mini-city in space and has been flying for 25 years. Results from the genetic biotechnology experiment may improve ways to keep crews healthy and spacecraft systems clean on future missions.
Return Date?
Back on terra firma, Boeing engineers have been testing replicas of thrusters on Earth to try and figure out what went wrong with the Starliner and how to safely bring back the spacecraft and its crew.
In an update, NASA said, "Engineering teams with NASA and Boeing recently completed ground hot fire testing of a Starliner reaction control system thruster at White Sands Test Facility in New Mexico, USA. The test series involved firing the engine through similar in-flight conditions the spacecraft experienced during its approach to the space station, as well as various stress-case firings for what is expected during Starliner's undocking and the deorbit burn that will position the spacecraft for a landing in the southwestern United States. Teams are analysing the data from these tests.'
The engineers are expected to give an update on these tests on Thursday and may also announce the likely date of Ms Williams and Mr Wilmore's return.