HRC Update

Grant Tremblay, Ralph Kraft, Paul Nulsen, Dan Patnaude, Tom Gauron, Almus Kenter, Ken Gage, Brad Bissell, Josh Model, Gerald Austin, Tom Aldcroft, Sabina Hurley, & Megan Lin

As we approach the three-year anniversary of the first two HRC anomalies on A-side electronics, and following a year of intense work recovering from the 2022 B-side anomaly, the HRC Team is delighted to report that the instrument has returned to normal science operations on a newly recovered A-side electronics board. More than twenty successful HRC-I and HRC-S observations have now been completed following our official return-to-science on April 10, 2023, and both instrument performance and science data quality have been nominal. With no known effects as a result of either the A-side anomalies, or the more than two-year A-side shutdown while we were in B-side operations, the HRC is once again fully available to the community to pursue the cutting-edge science that the instrument has long enabled.

Astronomical image of a central bright source with a fainter cloud around it, displayed in a purple-to-yellow colormap. Labels at the top and bottom state that this is a calibration observation of supernova remnant G 021.5 minus 00.9 with the A-Side power supply bus on HRC-S.

Figure 1: SNR G021.5−00.9, a calibration observation with HRC-S taken as part of our new normal science operations mode. All instrument performance and scientific data since return to science have been nominal.

The return to science is thanks to a major joint effort—ongoing since the very first anomaly on August 24, 2020—by the HRC Science and Flight Operations teams, the HRC Anomaly Working Group, and indeed the Chandra team as a whole, including our partners at the Marshall Space Flight Center, Northrop Grumman, and NASA Headquarters. The HRC Anomaly Working Group is close to completing a community report that will present conclusions from an extensive fault tree investigation that spans all encountered anomalies on the A- and B-sides. They have made major progress in understanding the root cause of the anomaly, and their findings have informed planning for the new operational paradigm for the HRC.

A graph labeled ‘An example week of nominal HRC operations’. Bus voltages are plotted against Date, covering May 14, 2023 to May 22, with a plotted voltage range of minus twenty to twenty volts. Four lines are shown; two are horizontal, while the other two are horizontal except for five square spikes. At that time, one line moves to plus 15 volts and the other to minus 15 volts. A second y label on the right lists those voltages as on and off, respectively, for the plus 15 volt state.

Figure 2: An example plot from one of our HRC telemetry monitoring systems developed in the wake of the anomalies. The plot shows five successful HRC observations with nominal performance by the +/− 15 V A-side power supply bus. Our new operations mode for the HRC includes shutting down the 15 V power supply between observations, leaving the instrument powered only by the +5 V supply, keeping the mean temperature of the central electronics assembly between ∼0–10 °C.

While we will leave it to the HRC Anomaly Working Group’s report to present the detailed findings of this years-long analysis, we can share that the main culprit for the A- and B-side anomalies is believed to be contained within the MTR28D15 DC-to-DC converter on both electronics boards, and that there is great reason to believe that keeping the instrument cool can help to prevent the re-occurrence of another anomaly. To that end, the updated operational paradigm for the instrument includes the following new guidelines and constraints, none of which should impact the Chandra user directly:

The HRC’s return to science with our new operational paradigm is one of the most major milestones since that first 2020 anomaly, reflective of the enormous amount we have learned about the cause of the anomalies in the past three years. This has been a total team effort, with input from the HRC science, engineering, and operations teams, as well as support from Flight Operations Team (FOT) engineers, FOT operations, ACIS operations, Chandra calibration, and the CXC Data Systems operations group. We remain grateful to our colleagues at the Chandra Project at Marshall Space Flight Center, as well as our continued partnership with NASA Headquarters, who have been supporting the mission and cheering for our beloved observatory all these years. Chandra's voyage of discovery continues, and HRC is again along for the ride.