NASA’s Lucy mission team has decided to suspend further solar array deployment activities. The team determined that operating the mission with the solar array in the current unlatched state carries an acceptable level of risk and further deployment activities are unlikely to be beneficial at this time. The spacecraft continues to make progress along its planned trajectory.
Shortly after the spacecraft’s Oct. 2021 launch, the mission team realized that one of Lucy’s two solar arrays had not properly unfurled and latched. A series of activities in 2022 succeeded in further deploying the array, placing it into a tensioned, but unlatched, state. Using engineering models calibrated by spacecraft data, the team estimates that the solar array is over 98% deployed, and it is strong enough to withstand the stresses of Lucy’s 12-year mission. The team’s confidence in the stability of the solar array was affirmed by its behavior during the close flyby of the Earth on Oct. 16, 2022, when the spacecraft flew within 243 miles (392 km) of the Earth, through the Earth’s upper atmosphere. The solar array is producing the expected level of power at the present solar range and is expected to have enough capability to perform the baseline mission with margin.
The team elected to suspend deployment attempts after the attempt on Dec. 13, 2022, produced only small movement in the solar array. Ground-based testing indicated that the deployment attempts were most productive while the spacecraft was warmer, closer to the Sun. As the spacecraft is currently 123 million miles (197 million km) from the Sun (1.3 times farther from the Sun than the Earth) and moving away at 20,000 mph (35,000 km/hr), the team does not expect further deployment attempts to be beneficial under present conditions.
Due to the energy boost that the spacecraft received during last October’s Earth gravity assist, the spacecraft is now on an orbit which will take it over 315 million miles (500 million km) from the Sun before returning to Earth for a second Earth gravity assist on Dec. 12, 2024. Over the next year and a half, the team will continue to collect data on how the solar array behaves during flight. Most significantly, the team will observe how the array behaves during a maneuver in Feb. 2024, when the spacecraft operates its main engine for the first time. As the spacecraft warms up during its approach to Earth in the fall of 2024, the team will re-evaluate if additional steps to reduce risk will be needed.
UPDATE AS OF DECEMBER 15, 2022: The Lucy team updated the spacecraft’s attitude controller on Dec. 6, resolving the previously observed vibration interaction between the controller and the solar array structural modes. As previously reported, the vibration was too small to pose a risk and the spacecraft continues to operate safely.
The team resumed solar array deployment activities, with an attempt on Dec. 13 that did not result in a latch. Since the estimated progress in deployment has decreased to minimal levels, the likelihood of a latch in the current thermal environment is very low. The team has therefore made the decision to suspend additional re-deployment activities through 2022. Future opportunities may be considered after careful analysis of the data and as the thermal environment changes.
Now that NASA’s Lucy spacecraft has successfully carried out its first Earth gravity assist, it has resumed high-data-rate communication with Earth. The Lucy spacecraft continues to operate safely and progress toward its mission goals.
Earlier this year, the team executed a series of commands to further deploy the spacecraft’s unlatched solar array. While deployment attempts were paused during a period of low-data-rate communications, the team continued to analyze the spacecraft’s telemetry and carry out ground-based tests. Based on these analyses, the team decided to continue attempts to further deploy the solar array. The likelihood of mission success in the current unlatched state is high, however the team expects that additional deployment—or potential latch—only improves confidence in performance without jeopardizing the spacecraft’s safety.
On Monday, Nov. 7, the spacecraft was instructed to point toward the Sun and operate the array deployment motors for a short period of time. As expected, the latest attempt deployed the wing incrementally forward, but it did not latch. The operation did succeed in providing the team with data to evaluate the array’s status and ascertain any changes since the last deployment attempt on June 16. During this analysis, the team identified that a small vibration occurred as the unlatched array interacted with the spacecraft’s attitude controller while the array was pointed toward Earth and at a cold temperature. The vibration did not occur as a result of the deployment activity itself. While this vibration is too small to pose a risk to the spacecraft in its current state, further array deployment attempts have been paused while the attitude controller is updated to resolve this issue. In the meantime, the spacecraft was reoriented so that the array is warmer, and the team found that the vibration is not present. The team will re-evaluate further redeployment activities once the updates to the controller are checked out on the spacecraft.
All of Lucy’s instruments functioned as expected during the gravity assist and provided an excellent test of the spacecraft’s systems and mission procedures. The team is continuing to analyze the images of the Earth and Moon collected during the flyby.
From May 6 to June 16, NASA’s Lucy mission team carried out a multi-stage effort intended to further deploy the spacecraft’s unlatched solar array. The team commanded the spacecraft to operate the array’s deployment motor for limited periods of time, allowing them to closely monitor the response of the spacecraft. As a result of this effort, the mission succeeded in further deploying the array and now estimates that the solar array is between 353 degrees and 357 degrees open (out of 360 total degrees for a fully deployed array). Additionally, the array is under substantially more tension, giving it significantly more stabilization. The mission team is increasingly confident the solar array will successfully meet the mission’s needs in its current tensioned and stabilized state.
Further deployment attempts will be paused as the Lucy spacecraft enters a planned period of limited communications. Due to thermal constraints caused by the relative positions of the Earth, spacecraft, and Sun, the spacecraft will be unable to communicate with the Earth via its high-gain antenna for several months. Throughout this period, the spacecraft will remain in contact with Lucy’s ground team via its low-gain antenna. The spacecraft will emerge from this partial communications blackout after its Earth gravity assist maneuver on Oct 16. At that time, the mission team will have more opportunities to attempt further deployment efforts if deemed necessary.
On June 21, the spacecraft successfully carried out a trajectory correction maneuver, which is the second in a series of maneuvers to prepare the spacecraft for its Earth flyby.
UPDATE AS OF JUNE 20, 2022: The Lucy team executed another deployment attempt on June 16. Although there was still no latch, the attempt reeled in additional lanyard and further stabilized the array. Future opportunities still exist to repeat the deployment commands if necessary.
UPDATE AS OF JUNE 14, 2022: The Lucy team executed another deployment attempt on June 9 with no latch. The attempt continued to further stabilize the array, and there are future opportunities to repeat the deployment commands if necessary.
NASA’s Lucy mission team is in the midst of a multi-stage effort to further deploy the spacecraft’s unlatched solar array. On May 9, the team commanded the spacecraft to operate the array’s deployment motor using both the primary and back-up motor windings simultaneously to generate more torque, i.e. a harder pull. The motor operated as expected, further reeling in the lanyard that pulls the solar array open. After running the motor for a series of short intervals to avoid overheating, the team paused to analyze the results. Data from the spacecraft showed that the deployment was proceeding similarly to engineering ground tests, allowing the team to move forward with the second stage of the attempt. Analysis of the data also suggested that there was still additional lanyard to be retracted. The team sent the same commands again on May 12. Although this series of commands did not latch the solar array fully open, it did advance the deployment enough to increase the tension that stabilizes the arrays as was hoped.
On May 26, the spacecraft was again commanded to deploy the solar array. As in the first two attempts, both motor windings were operated simultaneously for short periods of time to avoid overheating. Afterwards the team again analyzed the data from the event, which again showed that the array was continuing to open. The team repeated the deployment command sequence a fourth time on June 2. While the array still did not latch, the data indicates that it continued to further deploy and stiffen throughout the attempt.
The team has several more opportunities to repeat these deployment commands. While there is no guarantee that additional attempts will latch the array, there is strong evidence that the process is putting the array under more tension, further stabilizing it. Even if the array does not ultimately latch, the additional stiffening may be enough to fly the mission as planned.
The spacecraft completed a trajectory correction maneuver on June 7. This was the first in a series of maneuvers the spacecraft will take in preparation for the mission’s first Earth gravity assist scheduled for October 16, 2022.
On May 9, NASA’s Lucy team executed the first of two planned steps in its efforts to complete the deployment of the spacecraft’s unlatched solar array. This first step was time-limited and was intended to validate that the team’s ground testing adequately represented the flight system’s performance, rather than to latch the solar array. Analysis is currently underway to determine if the results are consistent with ground testing. After reviewing the data, the team will determine the next steps for the deployment effort. The second step is tentatively scheduled for about a month after the first one.
On April 18, NASA decided to move forward with plans to complete the deployment of the Lucy spacecraft’s stalled, unlatched solar array. The spacecraft is powered by two large arrays of solar cells that were designed to unfold and latch into place after launch. One of the fan-like arrays opened as planned, but the other stopped just short of completing this operation.
Through a combination of rigorous in-flight solar array characterization and ground testing, Lucy engineers determined the unlatched solar array is nearly fully open, positioned at approximately 345 out of the full 360 degrees, and is producing ample energy for the spacecraft. Nonetheless, the team is concerned about potential damage to the array if the spacecraft conducts a main engine burn in its present configuration.
After launch, the arrays were opened by a small motor that reels in a lanyard attached to both ends of the folded solar array. The team estimates that 20 to 40 inches of this lanyard (out of approximately 290 inches total) remains to be retracted for the open array to latch.
The solar array was designed with both a primary and a backup motor winding to give an added layer of reliability for the mission-critical solar array deployment. Lucy engineers will take advantage of this redundancy by using both motors simultaneously to generate higher torque than was used on the day of launch. Ground tests show that this added torque may be enough to pull the snarled lanyard the remaining distance needed to latch.
The team is now preparing to complete the solar array deployment in two steps. The first step, tentatively scheduled for the week of May 9, is intended to pull in most of the remaining lanyard and verify that flight results are consistent with ground testing. This step will also strengthen the array by bringing it closer to a fully tensioned state. Because this step is designed to be limited in duration, the array is not likely to latch at that point.
If this step goes as planned, the second step will continue the array deployment with the intent to fully latch. Information gleaned from the first part will help fine-tune the second. The second step is currently planned for a month after the initial one, giving engineers enough time to analyze the data seen in the first attempt.
The Lucy spacecraft, launched on Oct. 16, 2021, is now over 30 million miles, or 48 million kilometers, from Earth and continues to operate safely in “outbound cruise” mode. Besides a solar array that didn’t latch after deployment — an issue the mission team is working to resolve— all spacecraft systems are normal. The arrays are producing ample energy, charging the spacecraft’s battery as expected under normal operating conditions.
The current plan supports a latch attempt in the late April timeframe; however, the team is continuing to study the possibility of leaving the array as is. In the meantime, in the lab, they are testing a dual motor solar array deployment using both the primary and backup motor. The testing aims to determine if engaging both motors at the same time applies enough force to complete the deployment and latch the solar array.
In addition to the solar array activity, the team continues to run routine operations on the spacecraft. The next activity is calibrating guidance, navigation & control hardware to ensure pointing accuracy of the spacecraft.
On January 5, Lucy completed a test to look at the dynamics of the spacecraft in order to characterize the solar array.
NASA plans to conduct additional ground tests on an engineering model of the Lucy solar array motor and lanyard prior to potentially attempting full deployment of one of the probe’s solar arrays.
A project team completed an assessment Dec. 1 of the ongoing solar array issue, which did not appear to fully deploy as planned after launch in late October. Initial ground tests determined additional motor operations are required to increase the probability of the latching Lucy’s array in place as intended, and the team has recommended additional testing.
Spacecraft operations included discharging and charging the battery while pointed at Earth, moving the spacecraft to point to the Sun, operating the solar array motor with the launch day parameters, moving back to pointing at Earth, and then another battery discharge and recharge. The solar arrays charge the batteries, then the batteries are deliberately discharged, and the solar array circuits are used to recharge the batteries; performing these charging and discharging processes gives the team more information about the solar array circuits.
The team gathered information on two of the 10 gores – the individual solar array panel segments that make up the full array — that previously had no data. NASA now has data on all 10 gores confirming they are open, producing power as expected, and not stuck together.
These activities are helping the agency create a robust plan for attempting to fully deploy the array. Additional ground tests using the engineering model setup will validate a two-motor attempt for full deployment. NASA currently is creating a schedule and the resources needed to support that effort, as well as continuing to study the possibility of leaving the array as is.
NASA’s Lucy spacecraft continues to operate in cruise mode – the standard mode for its orbit away from Earth.
Checkouts for the Lucy instruments were successfully completed Nov. 8, and all instruments are working normally. Following checkout completion, the instruments were powered off, and the remaining spacecraft subsystem commissioning activities are continuing as scheduled.
Lucy’s Solar Array Anomaly Response Team has made progress searching for the cause of the solar array’s incomplete deployment. The team has used an engineering model of the solar array motor and lanyard to replicate what was observed during the initial solar array deployment. The test data and findings suggest the lanyard may not have wound on the spool as intended. Testing continues to determine what caused this outcome, and a range of scenarios are possible. The team isn’t planning to attempt to move or further characterize the current state of the solar array deployment before Wednesday, Dec. 1, at the earliest.
The Lucy spacecraft continues to operate in cruise mode – the standard mode for outbound orbit. The team has begun turning on instruments. L’TES and L’Ralph have been powered on and are working normally. Turning on L’LORRI is scheduled for Nov. 8, 2021. Other than the solar array, all subsystems continue to work normally.
The joint Anomaly Response Team has been studying the array using an engineering model. Initial tests indicate that the lanyard that pulls out the solar array may not have completed the process successfully; however, it is still uncertain what caused this condition. The team is conducting more tests to determine if this is indeed the case, and what the root cause might be.
An attempt to characterize the array deployment by attempting to move it would occur no earlier than Nov. 16.
The response team continues its analysis on using the solar array in its current configuration and how that might affect upcoming spacecraft maneuvers.