CRS-21 Dragon brings science and a new airlock to the ISS

CRS-21, in the distance, approaches the ISS with Crew-1 Dragon seen in the foreground. Credit: NASA

Just three weeks after launching its first operational Crew Dragon to the International Space Station, SpaceX sent a cargo variant of that capsule design to the orbiting outpost.

Called CRS-21, this vehicle is designed to send more cargo to the ISS than it’s older predecessor and it’s even more reusable than the first-generation Dragon spacecraft.

Liftoff atop a Falcon 9 rocket from Kennedy Space Center’s Launch Complex 39A in Florida took place at 16:17 UTC Dec. 6, 2020. Docking with the space station’s space-facing International Docking Adapter 3 occurred a day later at 18:40 UTC Dec. 7.

“I’d just like to say a huge congratulations to all of the teams that worked on SpaceX-21,” said NASA astronaut Kate Rubins over the space-to-ground radio loop from the space station. “It’s pretty amazing to think that less than a month ago you docked four crew members to the International Space Station, and now you are bringing a vehicle full of world-class science for us to execute. Thank you.”

Rubins is one of seven members of the space station’s Expedition 64 crew. Four members — NASA astronauts Mike Hopkins, Victor Glover, Shannon Walker, as well as Japanese astronaut Soichi Noguchi — arrived Nov. 17, 2020, aboard SpaceX’s Crew-1 Dragon. The other three — Russian cosmonauts Sergey Ryzhikov and Sergey Kud-Sverchkov, as well as Rubins — flew to the ISS on Oct. 14.

Expedition 64 is expected to continue until the spring of 2021.

CRS-21 Dragon carried about 3,000 kilograms of supplies and equipment to the ISS. This included a new commercial experiment airlock — the Nanoracks Bishop Airlock Module.

Bishop is the first commercially-funded airlock module to be launched to the ISS. It was designed by Nanoracks and is being built by that company with the help of Thales Alenia Space and Boeing, both of which have ample experience in designing, building and flying space station modules.

The Bishop airlock is located in Dragon’s trunk and will be removed and transferred to its final location via the space station’s robotic arm. Credit: NASA

The purpose of this commercial airlock is to allow Nanoracks the ability to increase satellite deployment capabilities at the ISS. Currently, those are typically done via the Japanese Experiment Module’s equipment airlock. It’s use is limited, however, prompting the company to seek a longer-term solution.

Bishop can not only be used to deploy objects, it can also host external payloads via mounts on the airlock and can be used to expose experiments to the vacuum of space for long periods of time.

According to NASA, it can even be used for jettisoning large pieces of unneeded equipment from inside the ISS as well as bring inside large orbital replacement units for potential repair in a pressurized environment.

Overall, Bishop has a mass of about 1,090 kilograms. It’s about 1.8 meters tall and just over 2 meters wide. It has an internal volume of nearly 4 cubic meters, which can be accessed by ISS crew members via a common berthing mechanism door.

While it can be located at many spots across the outpost, its primary home is expected to be the port side of the Tranquility module.

The inside of CRS-21 as seen before liftoff. Credit: NASA

In addition to the new airlock, the capsule carried 317 kilograms of vehicle hardware, 364 kilograms of crew supplies, 120 kilograms of spacewalk equipment, 46 kilogram of computer resources and 24 kilograms of Russian hardware.

But perhaps critically, CRS-21 included 953 kilograms of science investigations, including experiments to help better understand the infrastructure needed to mine and process material at extraterrestrial destinations, to evaluate an off-the-shelf white blood cell counter, as well as a study designed to better understand brain disorders.

CRS-21 is slated to remain attached to the ISS for about a month. During that time, its contents will be unloaded before being re-loaded with equipment and science designated to return to Earth. This includes a failed treadmill data avionics unit, a degraded carbon dioxide removal assembly air selector valve as well as live rodents from the Rodent Research-23 mission, according to NASA.

Once CRS-21 leaves the ISS, it will perform a deorbit burn, jettison its trunk section and re-enter Earth’s atmosphere, splashing down in the Atlantic Ocean, or Gulf of Mexico, just off the coast of Florida.

After its mission is complete, this capsule is expected to be refurbished and used for another resupply mission in the future. SpaceX has said it’s intent is to fly these upgraded capsules at least five times.