A unique robot, dubbed “OctaGrabber”, was first spotted in March 2017 when it was photographed aboard the droneship Of Course Of Still Love You (OCISLY) where it serves to this day.
Last Updated: May 5, 2019
Elon Musk later explained that the robot is used to stabilize the Falcon 9 and Falcon Heavy rockets after landing on the Autonomous Spaceport Droneship (ASDS) to prevent them from sliding around the deck in choppy seas. For example, during the Thaicom-8 mission, the sea was so choppy that the rocket slid across the deck before it could be tied down, and the only thing that prevented it from sliding off the droneship was a lip around the deck:
Additionally, using the robot to secure the rocket is safer than tying it down manually. Normally, the SpaceX personnel boards the platform as soon as possible after landing and buttresses the rocket up with jacks to take some of the weight away from the composite landing legs. Subsequently, metal stoppers are welded to the deck beneath the rocket, and the rocket is basically tied down with chains that attach to the heavy Octaweb (the sturdy structure that houses the engines at the bottom of the rocket).
According to SpaceX president Gwynne Shotwell, the robot is officially dubbed OctaGrabber. It is assumed to be remote-controlled and running on electricity supplied by a cable. Currently, there is no video of the robot in action, but the available information gives us a good idea of how it works. When a rocket booster is landing, the robot is hidden away in a safe place on the ASDS (sometimes called a garage) so it does not get damaged by the rocket’s exhaust or by an explosion in the event of an unsuccesful landing.
However, if the landing is successful, SpaceX workers can presumably control the robot equipped with tank treads remotely from a nearby ship and drive it directly under the landed rocket. Subsequently, the robot lifts four hydraulic jacks, grabs the rocket, and thus secures it against inadvertent slipping during the ASDS’s voyage back to port. In addition to saving time, the big advantage this robot provides, is that the SpaceX personnel is safe on another ship while the rocket is secured, so the risk of injury is significantly reduced compared to securing the rocket manually.
— Stephen Marr (@spacecoast_stve) March 5, 2019
You might wonder how can this relatively small robot actually prevent such a big rocket from sliding. Remember:
- The rocket is mostly hollow and almost empty after landing as almost all fuel had been used to launch and land. After landing, the rocket weighs only about 25 tons.
- The rocket has a very low center of gravity, as almost all of its weight is concentrated at the bottom of the rocket where the heavy engines are
- The robot is pretty large and heavy (it’s hard to tell from the photos but OCISLY is the size of a football field)
- The combination of the robot’s weight, low center of gravity, increased traction provided by the treads and large contact area (compared to the small contact area between the deck and Falcon’s landing legs) results in a sufficiently secure fit
OctaGrabber was first used in June 2017 during the BulgariaSat-1 mission when it supported the landed stage on its way back to port. The robot was then supposed to be used again on the SES-11 mission 4 months later, but there was a small fire onboard after landing which resulted in the robot being damaged. All the circumstances of the fire are not known, but according to NASA Spaceflight, a portion of the remaining RP-1 fuel from the rocket had leaked after landing which has subsequently accumulated near the containers at the back of the ASDS. Then it ignited, supposedly as a result of an automatic safing procedure in which the landed rocket burns off the remaining pyrophoric substance TEA-TEB used to ignite the engines. The water hoses on deck extinguished the fire quickly, but not before it engulfed the “garage” in which OctaGrabber was stored. The robot was damaged as a result and then had to spend several months in Port Canaveral being repaired. It was finally used again in April 2018 during the TESS mission.
Currently, OctaGrabber is only compatible with Falcon 9, which proved fatal to the Falcon Heavy center core during the Arabsat 6A mission in April 2019. Although the booster successfully landed on OCISLY, bad weather prevented the crew from securing it to the deck. Rough sea conditions then damaged the booster after it tipped over. Falcon Heavy center core has different mechanical interface from Falcon 9, but OctaGrabber should be upgraded for Falcon Heavy in time for the STP-2 launch, according to Spaceflight Now.
SpaceX currently has only one such robot, and it serves on the droneship Of Course I Still Love You in Florida. Hans Koenigsmann said that SpaceX is still tweaking on the robot. It is expected, however, that once OctaGrabber is perfected and all bugs are squashed, additional robots will be made, to be used on other SpaceX droneships Just Read the Instructions and A Shortfall of Gravitas.
OctaGrabber has been used on these missions so far:
- BulgariaSat-1 (July 2017)
- TESS (April 2018)
- Bangabandhu-1 (May 2018)
- Telstar 19V (July 2018)
- Merah Putih (August 2018)
- Telstar 18V (September 2018)
- Es’hail-2 (November 2018)
- Nusantara Satu (February 2019)
- Crew Dragon DM-1 (March 2019)
- CRS-17 (May 2019)
- May 5 – OctaGrabber was used on the CRS-17 mission
- April 16 – Updated with information about OctaGrabber not being compatible with Falcon Heavy
- March 23 – Article first published