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.
The Lucy spacecraft remains in cruise mode, which is the standard flight mode for outbound flight and allows for substantial autonomy for the spacecraft. The spacecraft has successfully executed several small planned maneuvers, which have had no adverse effect on the one solar array that is not fully deployed. On Oct. 29, NASA will adjust Lucy’s position to point toward Earth in preparation for instrument checkout.
Most recently, the spacecraft’s position was adjusted on Oct. 26 to allow the team to measure how much electric current is moving through the partially deployed solar array and thus understand how close that array is to the fully latched position. Analysis indicates that the array is between 75% and 95% deployed. It is currently being held in place by a lanyard, specifically designed to help unfurl the arrays during deployment.
An anomaly response team continues to work on establishing what caused the solar array to not fully deploy. NASA and SwRI are evaluating a range of options, including the possibility of leaving the array in its current state. Any attempt to safely redeploy the array would occur no earlier than Nov. 16.
All other systems are functioning normally.
NASA’s Lucy spacecraft successfully transitioned to cruise mode Oct. 20, which is the standard configuration for flight. The following day, the instrument pointing platform was deployed after temporarily being postponed earlier in the week. Both events were normal and raised no concerns. The spacecraft remains stable, power positive, with all other subsystems working, with the exception of one solar array.
The Lucy team is working to understand the current state of the array before attempting to complete deployment. NASA is reviewing spacecraft data, including using techniques to measure how much electric current is produced by the array during various spacecraft positions and attitudes. This will allow the team to understand how close the array is to the latched position. These techniques are well within the capabilities of the system and pose no risk. Any plans for re-deployment will be considered after completing this latest assessment.
The spacecraft continues to travel along its expected trajectory –track its path online.
After successful separation from the rocket on Oct. 16, NASA’s Lucy spacecraft deployed both solar arrays. Soon after deployment, NASA received confirmation that one of the solar arrays was fully deployed and latched. Analysis currently shows the second solar array is partially unfurled. The team continues to look at all available engineering data to establish how far it is deployed. That solar array is generating nearly the expected power when compared to the fully deployed wing. This power level is enough to keep the spacecraft healthy and functioning.
The Lucy spacecraft has remained in safe mode and is transitioning to cruise mode today. This mode has increased autonomy and spacecraft configuration changes, which is necessary as Lucy moves away from Earth. The team continues its assessment and an attempt to fully deploy the solar array is planned no earlier than the end of next week.
Lucy has successfully fired thrusters to slew the spacecraft with the current array configuration and will safely continue with desaturation maneuvers — small thruster firings to manage the spacecraft’s momentum — as planned.
The operations team has temporarily postponed the deployment of the instrument pointing platform to focus on resolving solar array deployment. The operations team continues to execute all other planned post-launch activities. The ULA Atlas V rocket delivered Lucy precisely to the target point at separation, and so a backup maneuver called the Trajectory Correction Maneuver (TCM-1) is unnecessary and has therefore been canceled. The first maneuver will now be what’s known as TCM-2, currently scheduled for mid-December.
The project is evaluating whether there are any long-term implications to other scheduled activities.
Following a successful launch on Oct. 16, 2021, analysis of NASA’s Lucy spacecraft systems show the spacecraft is operating well and is stable. Lucy’s two solar arrays have deployed, and both are producing power and the battery is charging. While one of the arrays has latched, indications are that the second array may not be fully latched. All other subsystems are normal. In the current spacecraft attitude, Lucy can continue to operate with no threat to its health and safety. The team is analyzing spacecraft data to understand the situation and determine next steps to achieve full deployment of the solar array.