CRS-21 | Falcon 9 Block 5

Lift Off Time
December 06, 2020 – 16:17:08 UTC | 11:17:08 EST
Mission Name
Launch Provider
(What rocket company launched it?)
(Who paid for this?)
Falcon 9 Block 5 B1058-4
Launch Location
Launch Complex 39A (LC-39A), Kennedy Space Center, Florida, USA
Payload mass
Around 15,000 kg (33,000 lbs) (~12,000 kg dry mass + cargo)
Where did the Dragon go?
Dragon C208 rendezvoused with the International Space Station (ISS) for 37 days
Did they recover the first stage?
Where did the first stage land?
623 km downrange on Of Course I Still Love You (OCISLY)
Did they attempt to recover the fairings?
There are no fairings on Dragon 2
This was the:
1st SpaceX launch under the CRS 2 contract
1st launch of Cargo Dragon 2
Fastest a booster has reached 4 flights, by far, at 190 days (Previous record: 269)
1st time two Dragons will be docked to the ISS at once
– 2nd to last Cargo Dragon that will stay docked to the ISS for 1 month. (CRS-23 and later will stay docked for 3 months)
100th successful Falcon 9 launch
101st Falcon 9 launch
47th re-flight of a booster
19th re-flight of a booster in 2020
7th 4th flight of a booster
68th booster landing
– 41st landing attempt on Of Course I Still Love You
18th consecutive landing (SpaceX record: 19)
24th launch for SpaceX in 2020
1st SpaceX launch on December 6
28th SpaceX launch from LC-39A
61 day turnaround of the booster
102nd orbital launch attempt of 2020
Where to watch
Official replay

Everyday Astronaut replay

How did CRS-21 go?


SpaceX successfully launched Cargo Dragon C208 to the International Space Station on their CRS-21 mission. CRS-21 launched on SpaceX’s Falcon 9 Block 5 rocket, and marked the first SpaceX launch under the CRS 2 contract. The Falcon 9 lifted off from Launch Complex 39A, at the Kennedy Space Center in Florida.

After Dragon deploy, Dragon performed a number of phasing burns to adjust its orbit and catch up to the ISS. Just over 26 hours after launch, at 18:40 UTC, Dragon docked with the ISS. Docking marked the first time that two Dragons were at the ISS at once, as C207 is docked at the station with the USCV-1 crew. Once docked, and after the completion of hatch opening, the astronauts aboard the ISS started unloading cargo.

In the following weeks the teams aboard the ISS conducted the time-sensitive research experiments, and deployed the payloads. After this, they began packing Dragon for its flight home. Along with some of the experiments that went up with Dragon, Dragon will be bringing home 2,360 kg of payload, including a treadmill avionics unit; a Carbon Dioxide Removal Assembly Air Selector Valve; Thermal Amine Bulk Water Save Valve; Minus Eighty Laboratory Freezer; and a Rodent Research Habitat and Transporter.


After being docked to the ISS for 37 days, Dragon undocked from the ISS on January 12, 2021 at 14:05 UTC. Undocking was pushed back a day due to the weather in the recovery zones; the primary landing location was changed to Tampa due to unfavorable weather in the Cape Canaveral, Daytona Beach, and Jacksonville landing zones. Dragon then performed a number of phasing burns to lower its orbit, then jettisoned its trunk and performed a deorbit burn.

Dragon under its parachutes during the DM-1 mission. (Credit: SpaceX/NASA)

After reentering the Earth’s atmosphere, Dragon deployed its drogue chutes followed by the 4 main parachutes in a reefed configuration. The parachute reef limits the area of the parachute, which helps lessen the jerk experienced by the spacecraft, which ensures that the parachutes and spacecraft is not damaged. It then softly splashed down in the Gulf of Mexico and was recovered by GO Navigator. The CRS-21 payloads are now being sent to NASA.

CRS-21 mission payloads


Bishop is a commercially funded airlock module for the ISS, built by NanoRacks, Thales Alenia Space, and Boeing. The airlock is relatively small with a mass of 1,059 kg (2,300 lbs) and a pressurized volume of 4 cubic meters, and will be used to deploy cube sats and smallsats. Bishop attached to the Tranquility module of the ISS, allowing for the Canadarm 2 to be used to deploy payloads.

CRS-21 payload
Bishop being prepared for launch (Credit: NanoRacks)


Hemocue will be used to test white blood cell counting systems, which have been used and validated in 1g, but not 0g.

The Brain Organoid Experiment

This experiment will study how masses of cells organize and grow into the start of a functional brain. Researchers are hoping this experiment will be able to help them better understand cell migration, interaction, division, and death in 0g. Scientists hope that a better understanding of these cellular alterations will allow for a better model of the brain’s formation; this will allow them to more effectively treat neurodegenerative disorders.


The University of Edinburgh developed the BioAsteroid experiment which will investigate how gravity affects the interaction between microbes and rock in reduced gravity. BioAsteroid includes two bio-mining reactors, which will allow researchers to research how microbes develop a biofilm on the surface of a rock. This research will be used to develop techniques to mine on other celestial bodies.

CRS-21 payload
BioAsteroid (Credit: ESA)

Cardinal Heart

The Cardinal Heart experiment was designed with the intent to study how changes in cardiovascular cells and tissues are different in 0g. Cardinal Heart aims to research how long-term 0g exposure affects cardiovascular tissue. Scientists hope studying these differences will allow them to better understand how cardiovascular problems arise on Earth. This study is also hoping to establish ways to predict heart and cardiovascular risk prior to an astronaut launching to space. Cardinal Heart will use engineered heart tissue (EHT), which is essentially a 3D chip of cardiovascular tissue.


This experiment aims to find better methods to braze two alloys to each other in 0g. Researchers hope these methods will be used for repairing the ISS and building human habitats in space.

What’s new on Cargo Dragon 2?

CRS-21 marks the first launch of SpaceX’s upgraded Dragon spacecraft. Cargo Dragon 2 is essentially a Crew Dragon, without an abort system, so it has all of the upgrades from Crew Dragon. Most importantly, Dragon 2 is designed to be reused up to 5 times, with a turnaround time of under 6 months, which is significantly lower than Dragon 1; Dragon 1’s fastest turnaround time was 418 days, with most turnaround times being significantly longer.

CRS-21 Dragon
Cargo Dragon 2 undergoing final assembly in Hawthorne (Credit: SpaceX)

Unlike Dragon 1, Dragon 2 is able to dock with the International Space Station. This means that Dragon 2 autonomously attaches to the ISS, as opposed to berthing, like Dragon 1, where Dragon 1 would hold a position away from the ISS. In this position the Canadarm would capture the spacecraft, attaching it to the ISS. CRS-21 will mark the fourth fully autonomous docking SpaceX has completed (DM-1, DM-2, Crew-1 and CRS-21).

Trunk Differences

Cargo Dragon 2’s trunk is also different from both Dragon 1’s and Crew Dragon’s. Dragon 2 has its solar panels integrated into its trunk, while Dragon 1 had a deployable solar array from its trunk. However, unlike Crew Dragon, Cargo Dragon 2’s trunk has 2 fins, while Crew Dragon’s has 4.

Cargo Dragon 2 is also significantly more massive, with a dry mass of ~12,000 kg. With this mass increase Dragon 2 is able to carry ~50% more science to the ISS than Dragon 1. Because of this, missions past CRS-22 will sty docked to the ISS for 3 months, rather than the 1 month that they stay docked to now.

Dragon 1 (left) and Dragon 2 (right). Note differences in nosecone and trunk (Credit: SpaceX and NASA)

Dragon 2’s nosecone is also significantly different as it opens instead of being jettisoned on ascent.

At a press conference after Crew-1, Gwynne Shotwell said SpaceX is expecting to have a fleet of 8 dragons: 5 Crew Dragons and 3 Cargo Dragons. This will allow SpaceX to conduct up to 25 crewed missions and 15 resupply missions.

What is Falcon 9 Block 5?

Falcon 9 Block 5 is SpaceX’s partially reusable two-stage medium-lift launch vehicle. Block 5 is the final iteration of the Falcon 9; the goal is to apply all the lessons learned from 56 previous Falcon 9 pre-Block 5 flights into a human-rated reusable rocket. The Falcon 9 contains 3 main components: a reusable first stage, an expendable second stage, and a reusable fairing or Dragon spacecraft.

Falcon 9 launching
Falcon 9 Block 5 launching on the GPS Block III SV03 mission (Credit: SpaceX)

Block 5 Updates:

SpaceX introduced a lot of changes on Block 5, allowing it to become the crew-launching reusable rocket that we know today. To start, the Composite Overwrapped Pressure Vessels (COPVs) had to undergo a complete redesign. NASA mandated the COPV redesign, as it had been the cause of both of the Falcon 9 failures: AMOS-6 and CRS-7.

Along with certification for human spaceflight, Block 5 came with a number of other major changes. To increase the amount of flight each booster could handle, and decrease the turnaround time, SpaceX reinforced the landing legs, upgraded the grid fins, and added a carbon fiber interstage. They also added heat resistant external paint and upgraded the engines. For more information about the changes in Block 5, and the other Blocks of the Falcon 9, check out this video by the Everyday Astronaut:

Tim Dodd explains the differences between the Falcon 9 versions. (Click image to watch) (Credit: Andrew Taylor)

Falcon 9 B1058

The booster that supported this mission is B1058. This had flown three times; its maiden flight was the SpaceX Demonstration Mission 2, which launched on May 30, 2020. The booster’s second flight was on ANASIS-II, which launched on July 20, 2020. The booster’s third flight was on SpaceX’s Starlink V1.0 L12 mission, which launched on October 6, 2020. As CRS-21 was B1058’s fourth flight, its designation will change to B1058-4.

CRS-21 Full Mission Profile

Hr/Min/Sec              Event

– 00:38:00                 SpaceX Launch Director verifies go for propellant load.
– 00:35:00                 RP-1 (rocket grade kerosene) loading underway.
– 00:35:00                 1st stage LOX (liquid oxygen) loading underway
– 00:16:00                 2nd stage LOX loading underway
– 00:07:00                 Falcon 9 begins engine chill prior to launch
– 00:01:00                 Command flight computer to begin final prelaunch checks
– 00:01:00                 Propellant tank pressurization to flight pressure begins
– 00:00:45                 SpaceX Launch Director verifies go for launch
– 00:00:03                 Engine controller commands engine ignition sequence to start
– 00:00:00                 CRS-21 Liftoff

Launch, Landing, and Dragon Deployment*

Hr/Min/Sec              Event

00:01:18                    Max Q (moment of peak mechanical stress on the rocket)
00:02:30                    1st stage main engine cutoff (MECO)
00:02:34                    1st and 2nd stages separate
00:02:41                    2nd stage engine starts (SES-1)
00:06:37                    First stage entry burn begins
00:08:38                    2nd stage engine cutoff (SECO-1)
00:08:38                    1st stage landing
00:11:49                    Dragon separation
00:12:35                    Dragon nose cone sequence begins

* All times are approximate

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