Report from Project Science

Steve O'Dell, Steven Ehlert, Doug Swartz

In 1977, Martin C. Weisskopf moved from Columbia Astrophysics Laboratory to NASA Marshall Space Flight Center (MSFC) to serve as Project Scientist of what was to become the Chandra X-ray Observatory—née Advanced X-ray Astrophysics Facility (AXAF)—the X-ray component of NASA’s Great Observatories. Pursuing Riccardo Giacconi’s vision of a high angular resolution X-ray telescope, Harvey Tananbaum, Leon Van Speybroeck, and Martin worked tirelessly and skillfully to realize this magnificent cathedral. Last year, after nearly 45 years of service, Martin retired as a NASA employee and as Chandra Project Scientist. However, he remains active in astrophysics as a NASA Emeritus.

By 1980, Martin began building an MSFC project science team that comprised 7 civil servant and 3 contractor scientists at maximum staffing—which came during calibration at MSFC’s X-Ray Calibration Facility (XRCF). At various times prior to launch, MSFC Project Science (PS) included Robert A. Austin, Charles R. Bower, Roger W. Bussard, Ronald F. Elsner, Marshall K. Joy, Jeffery J. Kolodziejczak, Brian D. Ramsey, Martin E. Sulkanen, Douglas A. Swartz, Allyn F. Tennant, Alton C. Williams, and Galen X. Zirnstein. Steve O’Dell joined PS shortly after his 1987 arrival at MSFC, was named Deputy Project Scientist in 1994, and became Project Scientist upon Martin’s retirement in 2022. Doug Swartz joined PS in 1995, becoming Assistant Project Scientist in 2020. To round out the PS leadership, Steven Ehlert joined PS in 2019, becoming Assistant Deputy Project Scientist in 2020 and Deputy Project Scientist in 2022.

After 23 years of operation, perhaps the biggest challenge for the Observatory is dealing with continued degradation of its thermal insulation. The resulting overall increase in temperatures requires careful scheduling of observations to efficiently balance science objectives against thermal control and momentum management. The most noticeable impact to users is that deep observations must be segmented into multiple pointings of limited dwell time, intermixed with pointings that provide more favorable attitudes for thermal control of specific Chandra subsystems.

In terms of scientific performance, the focal plane temperature of the Advanced CCD Imaging Spectrometer (ACIS) affects that instrument’s energy resolution due to charge transfer inefficiency (CTI) increasing with increasing temperature. Ideally set at −120 °C, the focal plane can be operated at a warmer temperature; this somewhat alleviates the scheduling burden, albeit at the cost of somewhat worse energy resolution. However, for imaging and grating-readout purposes, the spectral resolution of the CCDs is not critical. Accordingly, the ACIS Calibration Team is currently performing observations to determine a temperature-dependent CTI correction applicable to temperatures up to −105 °C.

At the other end of the Observatory, the increased operating temperature of the Aspect Camera Assembly has adversely impacted acquisition of faint guide stars. Consequently, a new proposal tool is now available to assess the quality of the star field for a selected celestial target. Notwithstanding the higher temperatures, the aspect system continues to provide better absolute celestial pointing and aimpoint stability than originally required.

In its 24th year of operations, Chandra continues to perform remarkable and cutting-edge research across a diverse range of sources. Press releases since the last newsletter include solid detection of the warm-hot intergalactic medium (WHIM) between two colliding galaxy clusters, documentation of the influence of hot Jupiter-like planets on the X-ray activity of their host stars, and discovery of new populations of active galactic nuclei using joint catalogs from the Chandra Source Catalog and the Sloan Digital Sky Survey. This last project demonstrates one way as to how the Chandra data archive will continue the scientific legacy of Chandra for decades.

Thanks to everyone who has made Chandra the outstanding success it is!