A Letter to the Chandra Community

Dear Chandra Community:

As many of you are aware, the NASA budget for FY25 and beyond was released on 11 March 2024, and plans for major reductions for Chandra were announced. As described below, these reductions compromise the ability to continue the Chandra mission.

The budget document states that

"The reduction to Chandra will start orderly mission drawdown to minimal operations."

NASA has a long-existing plan from the Chandra Project for activities to be invoked should a mission-ending failure be encountered. These include, among many other items, closeout of flight operations, final preparation of the data archive and source catalog, final documentation of calibration and other products, placing software into repositories, and producing detailed spacecraft and instrument documentation from the mission. The funding levels provided in the new budget plan are consistent with levels for these closeout activities, but lower than can accommodate operation of the Chandra science mission; the minimal operations referred to in the budget document would actually be decommissioning activities.

The rationale provided in the budget language is:

"The Chandra spacecraft has been degrading over its mission lifetime to the extent that several systems require active management to keep temperatures within acceptable ranges for spacecraft operations. This makes scheduling and the post processing of data more complex, increasing mission management costs beyond what NASA can currently afford."

While all spacecraft degrade over the lifetimes of their missions, most Chandra observers are aware that the temperatures of spacecraft and instrument components on Chandra have indeed been increasing, and that these make the scheduling of observations complicated. This has been the case since at least 2005. Our teams have developed thermal models and processes to manage this situation and have done so with amazing success – experiencing little or no decrease in observing efficiency, which far exceeds the initial requirements for the mission. This is all managed through advanced planning. Schedules and command loads with thermally-balanced observing and maneuver parameters are developed in advance and sent for autonomous operation on the spacecraft. "Active management" isn't done with Chandra, given that the Chandra Operations Control Center is only in contact with the spacecraft through one-hour communications every 8 hours.

The thermal properties of the instruments (e.g., spectral response) are encoded into our analysis software and calibration database, so there is nothing about Chandra’s evolving temperature behavior that makes "post processing of data more complex."

The statement that there are "increasing mission management costs" needs clarity. There has been only one instance in which the cost has increased to help manage temperatures. In our Senior Review (“NASA’s highest form of peer review”) in 2022, which resulted in a highly favorable appraisal of Chandra by an independent panel of prestigious scientists, we provided a request for two additional people on our flight team. This was approved and corresponds to about a 1% increase in cost. Every other budget change has been to decrease the staff (by more than 40% over the history of the mission) or to provide occasional modifications to cover either cost-of-living increases or a small increase in GO funding.

The NASA budget document states the following as additional rationale:

"The 2022 Senior Review of Operating Missions recommended continuing Chandra operations through FY 2025 but noted that temperature issues are reducing the ability to provide uninterrupted extended observing time and have greatly increased complexity of mission planning."

For context, this text was provided by the Senior Review Committee in support of the request to provide the extra two members to the flight team. This was in the section to address "Technical Capability and Cost Reasonableness" for which their rating was "Excellent/Very Good."

As part of the budget reduction process, Chandra (along with Hubble) is going through a review in April to discuss options for continuing to operate the observatory within the new budget guidelines. As noted, the current budget guidelines do not appear to provide for a robust science mission, let alone continued support for the X-ray community. The draft guidelines for the review state that the resulting actions

"could include authorizing a mission to; maintain the status quo; restructure the project; or terminate an ongoing science mission."

Taking this at face value, we will continue to strongly make the case for the continued full support of Chandra, which the astrophysics community recognizes as a highly functioning facility that provides transformational science and crucial support to many of NASA's primary astrophysics goals.

Dr. Patrick Slane
Director, Chandra X-ray Center