Our last launch of the week was a SpaceX Falcon 9. On December sixth at 16:17 UTC, CRS-21 started its journey to the International Space Station from historic LC-39A at Kennedy Space Center, Florida.

CRS-21 marks the first flight of a Dragon 2 as a cargo resupply ship. Cargo Dragon 2 features a different pressure vessel than Crew Dragon, so although the two craft share a name, they aren’t the same — Cargo Dragon 2 doesn’t carry people, so there’s no need for things like windows or an abort system. As far as upgrades from Cargo Dragon 1, the newer craft has twenty percent more volume and ditches the extendable solar panels for wrap-around panels on one side of the trunk. On the other side of the trunk are radiators. Additionally, Cargo Dragon 2 docks itself to the space station without assistance from Canadarm2. The IDA-3 docking adapter CRS-21 docked to was itself brought up in the trunk of the CRS-19 Dragon in July 2019.

The primary payload for CRS-21 was the Bishop airlock — the very first commercial airlock on the ISS. Built by NanoRacks, Thales Alenia Space, and Boeing, it will be used to deploy CubeSats from the ISS more efficiently.

The current method involves using an equipment airlock in the Japanese Kibo module, but it is low capacity. That particular airlock only opens ten times a year, with half of those instances reserved for JAXA, Japan’s space agency, and the other half allotted to NASA and commercial partners.

Bishop will be attached to Node-3 port. Also on Node 3 is the Cupola module and the Bigelow Expandable Activity Module. Also onboard were supplies for the crew and new science experiments.

For those of you keeping score at home, this was the fourth flight for B1058. There were two firsts for NASA with this mission: this booster previously flew a non-NASA mission and it has flown more than once. It had a successful landing on Of Course I Still Love You. Unlike a Falcon 9 with a satellite payload, there were no fairings used for this Dragon launch and therefore none were recovered.

This new version of Cargo Dragon, like the Crew Dragon it is based on, has a hinged cover to protect its docking port that is retracted once on orbit to allow docking. The four Draco thrusters used for deorbit are also under this cap. It is folded back after this burn and before it enters the atmosphere, to protect the docking port.

More Information

SpaceX press release 

NASA Spaceflight article