Capsule: the story so far

After decades of delays and false starts, so is NASA finally Back to the moon. The world is eagerly awaiting the launch of Artemis I, the first test flight of both the Space Launch System and the Orion Multi-Purpose Crew Vehicle, which together will send humans out of low Earth orbit for the first time since 1972. But it’s overdue.

While the first official Artemis mission naturally gets all the attention, the space agency is planning to do more than just put a new set of shoes on the surface — its long-term goals include the “Lunar Gateway” space station that will be the rallying point for the ongoing exploration of its nearest celestial neighbor.

But before launching humanity’s first deep space station, NASA wants to make sure that the unique near-rectilinear corona orbit (NRHO) in which it will operate is as stable as computer modeling predicted. Enter Cislunar Autonomous GPS Technology Operations and Navigation Experience, or CAPSTONE.

CAPSTONE in the clean room before launch.

The CubeSat was launched on an electronic rocket in June, and it is hoped that the CubeSat will become the first spacecraft to enter the NRHO. By positioning itself in such a way that gravity from the Earth and the Moon affect it equally, maintaining its orbit should only require periodic corrections of position. This will not only reduce the maintenance burden for tuning the lunar gate orbit, but also reduce the station’s propellant requirements.

CAPSTONE is also set to test an experimental navigation system that uses the Lunar Reconnaissance Orbiter (LRO) as a reference point in place of ground stations. In the future, as spacecraft regularly orbit the Moon, it will be important to create a navigation system that does not depend on terrestrial inputs to operate.

So despite costing a relatively small $30 million and being the size of a microwave oven, CAPSTONE is a very important mission to NASA’s grand lunar ambitions. Unfortunately, things have not gone as planned so far. The problem started just days after quitting, and as of this writing, the outcome of the mission is still very much in jeopardy.

From the rocky start

Rocket Lab’s Electron rocket performed perfect during launch on June 28, after which a third stage of the boosted “kick” began with a series of engine burnouts to gradually raise its orbit. After firing the engine six times in as many days, the kick stage implemented the Burning Moon Final Injection (TLI) before launching CAPSTONE on July 4. This placed the craft on a low-energy ballistic trajectory toward the Moon, which would be refined with a series of small trajectory correction maneuvers over the course of its four-month journey.

After entering the mission’s free-flight phase, CAPSTONE expanded its solar arrays to begin charging its batteries and stabilized itself in preparation for the first trajectory correction burn that was scheduled for the next day. But shortly after making contact with NASA’s Deep Space Network (DSN) ground station in Madrid, contact with CAPSTONE was lost.

Communications were re-established after about 24 hours, and the analysis eventually concluded that a distorting command from operators on the ground had put the spacecraft’s radio into an unexpected state, which in turn triggered the onboard fault-detection procedures. The vehicle automatically resets itself and clears the fault condition, as well as independently performing the necessary maneuvers to keep itself on the intended flight path.

While CAPSTONE got away from that first anomaly unharmed, and the ground controllers felt they could prevent the problem from happening again, the first lane correction maneuver window was a long time ago. This meant that a new maneuver had to be planned given the vehicle’s updated position and speed, a delicate process that took extra time.

On July 7, CAPSTONE successfully performed a revised trajectory correction burn (officially referred to as TCM-1), placing itself on a trajectory within 0.75% of the calculated cycle.

worrying stumble

After the initial communication difficulties were resolved, the expedition continued without problems. A small course correction was made on July 12, and the larger TCM-2 maneuver was carried out on July 25 without incident. On August 26, CAPSTONE reached its peak of 1,531,949 kilometers (951,909 miles), the furthest from Earth in its ballistic trajectory.

But on September 8, when the TCM-3 maneuver was about to end, the spacecraft’s position began to drift. For reasons yet unknown, the CAPSTONE reaction wheels could not cope with the wobble, and the car went into an uncontrolled stumble. With the antenna not pointing at the ground, the connections were lost again.

Mission controllers that evening declared an operational emergency, giving them access to additional capabilities for the DSN. Through this they were finally able to receive a weak telemetry signal from CAPSTONE the next day, but the data looked grim. Because of its rotation, the spacecraft’s solar arrays were not producing enough power to charge the batteries, causing the spacecraft to reset frequently due to a lack of power. Even worse, without power to operate the heaters on board, the thrusters that would eventually be needed to stop the fall were now rigidly frozen.

But it wasn’t all bad news. It was determined that the TCM-3 burn had advanced far enough that CAPSTONE was on its intended orbital path – so while the spacecraft may technically be out of control, it is still bound for the Moon.

advanced mode

Currently, our last update from the CAPSTONE team was made on September 15th. The big news is that even though the craft is still spinning, the solar panels are getting enough light to charge the batteries. There was enough energy in the budget to run the heaters, although they were apparently operating at a reduced duty cycle. However, getting rid of the cold is enough, and it is hoped that the propulsion system will soon reach a high enough temperature to evaluate its functionality. Assuming they can be brought back online, firing the thrusters against the direction of rotation should restore control of CAPSTONE.

Several more maneuvers must be performed before CAPSTONE reaches the Moon.

But we haven’t gotten there yet. The update shows that task monitors are still analyzing the data to determine why CAPSTONE got out of hand in the first place, and how to prevent it from happening again. The original mission schedule shows that a number of additional burns were planned to put the spacecraft into its intended orbit, and even then, that was just beginning of her mission.

Fortunately, CAPSTONE will not need to make another course correction for a few weeks, giving engineers on the ground more time to assess the situation. However, the fact that two of the three major maneuvers caused the car to become unresponsive is concerning, especially when several engine burns are still on schedule.

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