UC Berkeley's Space Sciences Laboratory (SSL) currently operates a fleet of seven NASA satellites, which conduct research in the fields of space physics and astronomy. The newest addition to this fleet is a high-energy X-ray telescope called the Nuclear Spectroscopic Telescope Array (NuSTAR). Since 2012, SSL has conducted on-orbit operations for NuSTAR on behalf of the lead institution, principle investigator, and Science Operations Center at the California Institute of Technology. NuSTAR operations benefit from a truly multi-mission ground system architecture design focused on automation and autonomy that has been honed by over a decade of continual improvement and ground network expansion. This architecture has made flight operations possible with nominal 40 hours per week staffing, while not compromising mission safety. The remote NuSTAR Science Operation Center (SOC) and Mission Operations Center (MOC) are joined by a two-way electronic interface that allows the SOC to submit automatically validated telescope pointing requests, and also to receive raw data products that are automatically produced after downlink. Command loads are built and uploaded weekly, and a web-based timeline allows both the SOC and MOC to monitor the state of currently scheduled spacecraft activities. Network routing and the command and control system are fully automated by MOC's central scheduling system. A closed-loop data accounting system automatically detects and retransmits data gaps. All passes are monitored by two independent paging systems, which alert staff of pass support problems or anomalous telemetry. NuSTAR mission operations now require less than one attended pass support per workday.
Accurate calibration of the Chandra Low Energy Transmission Grating (LETG) higher-order (|m|>1) diffraction efficiencies is vital for proper analysis of spectra obtained with the LETG's primary detector, the HRC-S, which lacks the energy resolution to distinguish different orders. Pre-flight ground calibration of the LETG was necessarily limited to sampling a relatively small subset of spectral orders and wavelengths, and virtually no higher-order data are available in the critical region between 6 and 10 Å. In this paper, we describe an analysis of diffraction efficiencies based on in-flight data obtained using the LETG's secondary detector, the ACIS-S. Using ACIS, the relative efficiency of each order can be studied out to
|mλ| ~ 80 Å, which is nearly one-half of the LETG/HRC-S wavelength coverage. We find that the current models match our results well but can be improved, particularly for the even orders just longward of the Au-M edge at 6 Å.
We present the in-flight effective area calibration of the Low Energy Transmission Grating Spectrometer (LETGS), which comprises the High Resolution Camera Spectroscopic readout (HRC-S) and the Low Energy Transmission Grating (LETG) aboard the Chandra X-ray Observatory. Previous studies of the LETGS effective area calibration have focused on specific energy regimes: 1) the low-energy calibration for which we compared observations of Sirius B and HZ 43 with pure hydrogen non-LTE white dwarf emission models; and 2) the mid-energy calibration for which we compared observations of the active galactic nuclei PKS 2155-304 and 3C 273 with simple power-law models of their seemingly featureless continua. The residuals of the model comparisons were taken to be true residuals in the HRC-S quantum efficiency (QE) model. Additional in-flight observations of celestial sources with well-understood X-ray spectra have served to verify and fine-tune the calibration. Thus, from these studies we have derived corrections to the HRC-S QE to match the predicted and observed spectra over the full practical energy range of the LETGS. Furthermore, from pre-flight laboratory flatfield data we have constructed an HRC-S quantum efficiency uniformity (QEU) model. Application of the QEU to our semi-empirical in-flight HRC-S QE has resulted in an improved HRC-S on-axis QE. Implementation of the HRC-S QEU with the on-axis QE now allows for the computation of effective area for any reasonable Chandra/LETGS pointing.
The Chandra X-ray Observatory (CXO) High Resolution Camera (HRC) is a
microchannel plate (MCP) based X-ray detector with heritage from
similar detectors flown on the Einstein and ROSAT missions. The HRC
consists of two detectors in a common housing. Improvements from the
previous instruments include: fabricating the MCP from 'low-noise'
glass (glass that contains a reduced level of radioactive isotopes)
and surrounding the detector housing on five sides with an active
coincidence detector. Both of these improvements help to maximize the
X-ray signal to background noise ratio. The on-orbit background is
dominated by cosmic ray and solar-wind particles. The temporal
behavior of the background has two parts: a quiescent level and a
flaring component. The quiescent level slowly changes with time and is
correlated with the high-energy particle flux as measured by the
Electron Proton Helium Instrument (EPHIN), the CXO radiation
detector. The flaring component is associated with times of elevated
low-energy particle flux, primarily from the Sun. A combination of
on-board vetoing and filtering during ground processing provides a
substantial rejection of the non-X-ray background. This work was supported by NASA contract NAS8-39073 to the Chandra X-ray Center.
In this paper we present and compare flight results with the latest results of the ground calibration for the HRC-I detector. In particular we will compare ground and in flight data on detector background, effective area, quantum efficiency and point spread response function.
The Chandra X-ray Observatory was successfully launched on July 23, 1999, and subsequently began an intensive calibration phase. We present preliminary results from in- flight calibration of the low energy response of the High Resolution Camera Spectroscopic readout (HRC-S) combined with the Low Energy Transmission Grating (LETG) aboard Chandra. These instruments comprise the Low Energy Transmission Grating Spectrometer (LETGS). For this calibration study, we employ a pure hydrogen non-LTE white dwarf emission model (Teff equals 25000 K and log g equals 9.0) for comparison with the Chandra observations of Sirius B. Pre-flight calibration of the LETGS effective area was conducted only at wavelengths shortward of 45 angstroms (E > 0.277 keV). Our Sirius B analysis shows that the HRC-S quantum efficiency (QE) model assumed for longer wavelengths overestimates the effective area on average by a factor of 1.6. We derive a correction to the low energy HRC-S QE model to match the predicted and observed Sirius B spectra over the wavelength range of 45 - 185 angstroms. We make an independent test of our results by comparing a Chandra LETGS observation of HZ 43 with pure hydrogen model atmosphere predictions and find good agreement.
The High Resolution Camera (HRC) is one of two focal plane instruments on the NASA Chandra X-ray Observatory which was successfully launched on July 23, 1999. The Chandra X-ray Observatory was designed to perform high resolution spectroscopy and imaging in the X-ray band of 0.07 to 10 keV. The HRC instrument consists of two detectors, HRC-I for imaging and HRC-S for spectroscopy. Each HRC detector consists of a thin aluminized polyimide blocking filter, a chevron pair of microchannel plates and a crossed grid charge readout. The HRC-I is an approximately 100 X 100 mm detector optimized for high resolution imaging and timing, the HRC-S is an approximately 20 X 300 detector optimized to function as the readout for the Low Energy Transmission Grating. In this paper we discuss the in-flight performance of the HRC-S, and present preliminary analysis of flight calibration data and compare it with the results of the ground calibration and pre-flight predictions. In particular we will compare ground data and in-flight data on detector background, quantum efficiency, spatial resolution, pulse height resolution, and point spread response function.
The Advanced X-Ray Astrophysics Facility High Resolution Camera was calibrated at NASA's X-Ray Calibration Facility during March and April 1997. We have undertaken an analysis of the effective area of the combined High Resolution Mirror Assembly/High Resolution Camera using all data presently available from these tests. In this contribution we discuss our spectral fitting of the beam-normalization detectors, our method of removing higher order contamination lines present in the spectra, and the corrections for beam non- uniformities. Using an approach based upon the mass absorption cross-section of Cesium Iodide, we determine the quantum efficiency in the microchannel plates. We model the secondary electron absorption depth as a function of energy, which we expect to be relatively smooth. This is then combined with the most recent model of the telescope to determine the ensemble effective area for the HRC. The ensemble effective area is a product of the telescope effective are, the transmission of the UV-Ion shield, and the quantum efficiency of the microchannel plates. We focus our attention on the microchannel plate quantum efficiency, using previous result for the UV-Ion shield transmission and telescope effective area. We also address future goals and concerns.