The International Space Station is our home in low-Earth orbit. Humans have been living and working continuously on the station for more than 20 years. Astronauts and cosmonauts visiting the space station have arrived on the space shuttle, the Russian Soyuz, and now, the SpaceX Crew Dragon, with Boeing's CST-100 Starliner to be added to the mix. With these new flights on U.S. commercial spacecraft, the station is transitioning from indirect to direct crew handovers.

What does this mean? Read below to find out.

What's the difference between a direct and indirect handover?
A handover is the period between the start of one space station crew's time on the station, and the end of a separate crew's time. From the end of the Space Shuttle Program in 2011, until the first Commercial Crew flights with astronauts in 2020, teams typically performed an indirect handover. All crews traveled to and from the orbiting laboratory on the Russian Soyuz spacecraft. with one Soyuz crew departing the space station before a new crew launched and arrived.

When one crew of three reached the end of their mission, they would undock their Soyuz and return to Earth, temporarily leaving the station with three crew members aboard. A new crew of three would launch days or weeks later, returning the space station to a total number of six crew members.

Now that the Commercial Crew Program has begun flying crews of four on U.S. commercial spacecraft, the full crew of the station has expanded to seven people. We now see what is called a direct handover. To ensure that the station is continuously staffed with astronauts and cosmonauts, a new crew launches and arrives at station before the prior crew returns to Earth. This results in a short period of time when there are more crew than usual aboard the station.

What's the most amount of people who have stayed on the International Space Station at one time?
During the Space Shuttle Program, the International Space Station had a total of 13 people aboard three different times, when a shuttle launched with seven astronauts aboard and docked with the space station with six crew aboard for a long duration mission: STS-127 in July 2009, STS-128 in August 2009, and most recently STS-131 in April 2012. That's the largest number of crew members at one time living on station, which is about the size of a five-bedroom home.

The launch and arrival of four astronauts on NASA's SpaceX Crew-2 mission resulted in 11 people living aboard the station during the direct handover period before the departure of Crew-1. This direct handover is the first time 11 long-duration crew members have lived aboard station. The last time exactly 11 people were aboard was in 2010; the station's crew size was temporarily reduced to five during Expedition 22, and the six-person space shuttle Endeavour crew on the STS-130 mission came for a visit from Feb. 9-19.

What do crew members do during handovers?
Crew activities are largely the same whether the handover is direct or indirect. When a new crew arrives in space, they spend several days doing orientation tasks to familiarize themselves with their new home. They also take part in data collection for several Human Research Program studies, to establish baseline data to help scientists track how their bodies adapt to living and working in space. Crew members preparing to return to Earth spend time packing cargo for the flight home, doing refresher training for landing or splashdown operations, and collecting any final samples for human research projects. The combined crew continues to support science and maintenance, and all crew members continue to exercise approximately two hours every day.

Where do astronauts sleep while on the International Space Station during handover periods? As of April 2021, the International Space Station has seven permanent crew quarters, or personal spaces for astronauts to sleep and work during their stay on station. Each location provides a small pocket of privacy for astronauts and cosmonauts during their stay on orbit.

There are currently:

+ Four crew quarters in the U.S Harmony Module (also known as Node 2)
+ One crew quarter in the European Columbus Module
+ Two crew quarters in the Russian Zvezda Module (also known as the Service Module)

When there are more astronauts aboard station than crew quarters, the crew members work with flight controllers to identify temporary "campout" locations for crew to sleep during the short handover period. These are typically located in modules with the least activity during the handover period, like the U.S. Quest Airlock or the Japanese Kibo Module, and can include docked spacecraft. For example, NASA's Mike Hopkins slept inside the Crew Dragon Resilience during his entire six-month stay aboard the station.

How often could we see crew handovers on the space station?
With NASA's Commercial Crew Program now regularly delivering astronauts to the space station, in conjunction with continued flights of the Russian Soyuz spacecraft, we expect to see four handovers a year. This will include two Soyuz handovers spaced approximately six months apart, and two U.S. commercial spacecraft handovers spaced approximately six months apart.

Video: Crew Quarters Tour Inside the Space Station

Related Links
Commercial Crew at NASA
Space Tourism, Space Transport and Space Exploration News

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Alpha: Second Space Station mission for ESA's Thomas Pesquet begins
Paris (ESA) Apr 24, 2021
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