It Appears CAPSTONE Is Healthy Again

A couple of days ago, after mentioning that the Japanese HAKUTO-R M1 satellite that SpaceX is launching in early November will have a longer trip to the moon than the mid-60s era, three-day direct flights, but not as long as CAPSTONE is having, it got me thinking of that program.  While there have been a handful of problems since launch, the loss of control and communication CAPSTONE went through back in mid-September (second part of that post) were what came to mind.  That naturally led me to wonder "what's up with that, now?"  Did they get the spacecraft back under control?

It turns out they did, back on Friday, October 7th.  

Following a planned trajectory correction maneuver on Sept. 8, CAPSTONE suffered an issue that caused the spacecraft to spin beyond the capacity of the onboard reaction wheels to control and counter. Data from the spacecraft suggests the most likely cause was a valve-related issue in one of the spacecraft’s eight thrusters. The partially open valve meant the thruster produced thrust whenever the propulsion system was pressurized. The mission team extensively reviewed telemetry and simulation data and conducted multiple tests on the spacecraft in order to formulate a plan to stop the spacecraft’s spin despite this issue.

The recovery commands were uploaded to the spacecraft on Thursday and executed Friday.  Both the initial telemetry and all observation data indicates it was a successful maneuver.  The spacecraft has stopped its spin and regained full 3-axis attitude control, meaning CAPSTONE’s position is controlled without unplanned rotation. Following that, CAPSTONE oriented its solar arrays to the Sun and adjusted the pointing of its antennas to provide a better data connection to Earth.   

The problem valve is apparently still partially open, or considered to be, which implies that there's a risk of the same uncontrollable rotation issue the next time they need to pressurize the propulsion system.  The mission leader, Advanced Space, posts 

... the spacecraft status will be monitored while the team works to evaluate subsequent changes to the spacecraft operating procedures so that upcoming critical events can be conducted in the possible presence of a valve that remains partially open. In parallel, the mission team will work to design possible fixes for this valve related issue to further reduce the risk of future propulsive operations.

Considering how deep in space it is, it feels silly to say it's not out of the woods yet, but it's looking much better.  The vehicle is on path to insert into it's Near Rectilinear Halo Orbit at the Moon on November 13th. 

CAPSTONE revealed in lunar Sunrise: CAPSTONE will fly in cislunar space – the orbital space near and around the Moon. The mission will demonstrate an innovative spacecraft-to-spacecraft navigation solution at the Moon from a Near Rectilinear Halo Orbit slated for Artemis’ Gateway. Credits: Illustration by NASA/Daniel Rutter.  

As I mentioned back in June, this is the first mission to try to achieve the NRHO, which has been purely theoretical to this point.  As that picture caption points out, the orbit is intended for Artemis' Gateway - essentially a miniature space station that will host crews and vehicles headed for the moon.  Testing out that the orbit behaves as theory says it should makes CAPSTONE essentially the first launch in the Artemis program. 

The NRHO follows an interesting concept and there are some videos worth watching about them. The topic could be a long post by itself.  The video shows how the NRHO can be derived from a Lagrange point L2 orbit, and becomes essentially stable in a lunar polar orbit.  "Essentially stable" means the orbit requires periodic corrections but those aren't as hard to implement as other orbits.