Paul P. Plucinsky

Modeling Contamination Migration on the Chandra X-Ray Observatory - III

During its first 14 years of operation, the cold (about -60°C) optical blocking filter of the Advanced CCD Imaging Spectrometer (ACIS), aboard the Chandra X-ray Observatory, has accumulated a growing layer of molecular contamination that attenuates low-energy x rays. Over the past few years, the accumulation rate, spatial distribution, and composition have changed. This evolution has motivated further analysis of contamination migration within and near the ACIS cavity. To this end, the current study employs a higher-fidelity geometric model of the ACIS cavity, detailed thermal modeling based upon temperature data, and a refined model of the molecular transport.

Lessons we learned designing and building the Chandra telescope

2014 marks the crystal (15th) anniversary of the launch of the Chandra X-ray Observatory, which began its existence as the Advanced X-ray Astrophysics Facility (AXAF). This paper offers some of the major lessons learned by some of the key members of the Chandra Telescope team. We offer some of the lessons gleaned from our experiences developing, designing, building and testing the telescope and its subsystems, with 15 years of hindsight. Among the topics to be discussed are the early developmental tests, known as VETA-I and VETA-II, requirements derivation, the impact of late requirements and reflection on the conservatism in the design process.

Analysis of the AXAF HRMA+ACIS effective area measurements from the XRCF

We describe the analysis of effective area measurements for the AXAF High Resolution Mirror Assembly (HRMA) and the AXAF CCD Imaging Spectrometer (ACIS). The measurements were obtained at the X-ray Calibration Facility (XRCF) in Huntsville, AL, during April 1997. Measurements obtained with two frontside-illuminated (FI) charge-coupled devices (CCDs) in the imaging array and the backside-illuminated (BI) CCD located on-axis in the spectroscopic array are considered. We compare the XRCF effective area measurements to independent, semi-empirical model predictions constructed using the product of the efficiencies of the AXAF components. The XRCF measurements, in general, confirm the reliability of the model at most energies, but only after correcting the data for several effects related to event pileup. However, after applying the corrections, the uncertainties in the XRCF measurements remain uncomfortably large. We suggest several future avenues of investigation that should improve our knowledge of the HRMA + ACIS effective area.

Modeling contamination migration on theChandra X-ray Observatory: III

During its first 16 years of operation, the cold (about -60°C) optical blocking filter of the Advanced CCD Imaging Spectrometer (ACIS), aboard the Chandra X-ray Observatory, has accumulated a growing layer of molecular contamination that attenuates low-energy x rays. Over the past few years, the accumulation rate, spatial distribution, and composition have changed. This evolution has motivated further analysis of contamination migration within and near the ACIS cavity, in part to evaluate potential bake-out scenarios intended to reduce the level of contamination.

X-ray observations of the vela supernova remnant ejecta fragments

The Vela Supernova remnant (SNR) is one of the nearest SNRs. At an estimated distance of ∼250 pc, it is likely just beyond the edge of the local bubble and there seems to be no direct evidence of interaction with the bubble. The SNR is in a complex environment, though. It is notably brighter and more sharply defined to the east and north, but much fainter and less ordered in the west and south. The age of the SNR is estimated to be ∼11000 years, based on the spin‐down rate of its associated pulsar, but ages as large as 20000–30000 years have also been argued. This SNR is also notable for a number of protrusions extending well beyond its rim, which were suggested to be fragments of ejecta from the supernova explosion. X‐ray spectroscopy has since confirmed several of these protrusions to indeed be strongly enriched with ejecta. We present initial results based on the XMM‐Newton and Suzaku X‐ray observations of two these ejecta fragments.

ACIS Door Failure Investigation: Technical Details and Mitigation Procedures

NASAs Chandra X-ray Observatory (formerly AXAF) was launched on July 23, 1999 and is currently in orbit performing scientific studies. Chandra is the third of NASAs Great Observatories to be launched, following the Hubble Space Telescope and the Compton Gamma Ray Observatory. One of four primary science instruments on Chandra, and one of only two focal plane instruments, is the Advanced CCD Imaging Spectrometer, or ACIS. The ACIS focal plane and Optical Blocking Filter needed to be launched under vacuum, so a tightly sealed, functioning door and venting subsystem were implemented. The door was opened two and one-half weeks after launch (after most out-gassing of composite materials) and allowed X-rays to be imaged by the ACIS CCDs in the focal plane. A failure of this door to open on-orbit would have eliminated all ACIS capabilities, severely degrading mirror science. During the final pre- flight thermal-vacuum test of the fully integrated Chandra Observatory at TRW, the ACIS door failed to open when commanded to do so. This paper provides a somewhat technically expanded description of the efforts, under considerable time pressure, by NASA, its contractors and outside review teams to investigate the failure and to develop modified hardware and procedures which would correct the problem.