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.

Extensive X-ray and EUV photometric observations of the eclipsing RS CVn system AR Lac were obtained over the years 1997-2013 with the Chandra X-Ray Observatory Extreme-Ultraviolet Explorer (EUVE). During primary eclipse, High Resolution Camera count rates decrease by similar to 40%. A similar minimum is seen during one primary eclipse observed by EUVE but not in others owing to intrinsic source variability. Little evidence for secondary eclipses is present in either the X-ray or EUV data, reminiscent of earlier X-ray and EUV observations. Primary eclipses allow us to estimate the extent of a spherically symmetric corona on the primary G star of about 1.3 R-circle dot, or 0.86 R-star, and indicate that the G star is likely brighter than the K component by a factor of 2-5. Brightness changes not attributable to eclipses appear to be dominated by stochastic variability and are generally non-repeating. X-ray and EUV light curves cannot therefore be reliably used to reconstruct the spatial distribution of emission assuming that only eclipses and rotational modulation are at work. Moderate flaring is observed, where count rates increase by up to a factor of three above quiescence. Combined with older ASCA, Einstein, EXOSAT, ROSAT, and BeppoSAX observations, the data show that the level of quiescent coronal emission at X-ray wavelengths has remained remarkably constant over 33 yr, with no sign of variation due to magnetic cycles. Variations in base level X-ray emission seen by Chandra over 13 yr are only similar to 10%, while variations back to pioneering Einstein observations in 1980 amount to a maximum of 45% and more typically about 15%.

THEMIS, a constellation of five spacecraft, referred to as probes, was launched in 2007 to study the physical processes leading to the aurora. In 2009, THEMIS successfully completed its primary mission phase. As an ambitious mission extension, the constellation was then split into two new missions - THEMIS-Low and ARTEMIS. THEMIS-Low refers to three of the five probes that continued magnetospheric observations in Earth orbits while the remaining two probes started a new lunar mission called ARTEMIS. The two ARTEMIS probes were transferred from Earth to lunar orbits via low-energy trajectories with Earth and lunar gravity assists. The complex mission design and navigation operations took the two probes on trajectories along weak stability boundary manifolds, venturing out as far as 1,500,000 km and 1,200,000 km from Earth, respectively. Upon arrival in the lunar environment, both probes were first inserted into libration point orbits where they spent up to ten months collecting science data. Periodic stationkeeping maneuvers were executed to ensure the two probes would not be ejected from these unstable orbits. In 2011, both probes were successfully inserted into stable, retrograde and prograde lunar orbits, respectively. We report on the challenges with executing the complex navigation plans, discuss experiences and lessons learned from operating two spacecraft in lunar libration point orbits for the first time ever, and finally cover mission planning and science operations in the lunar environment.

The University of California, Berkeley has conducted flight operations for multiple NASA-funded spacecraft from its multi-mission operations center at Space Sciences Laboratory for more than a decade. All ground systems were designed and implemented by members of the multi-mission operations team who are involved in all phases of mission life cycles from the early proposal stages through mission design and development, integration, launch and on-orbit operations. Operational task areas include mission and science operations, mission design and navigation, ground station operations, and hardware and software systems support. Team members are trained across missions and across support disciplines to provide a breadth of knowledge and redundancy within the team. This paper describes the ground system design and summarizes experiences, challenges, and lessons learned with conducting complex multi-mission spacecraft operations in an academic environment.

We present an interim report on Chandra HRC-S calibration observations of Vega, an Xray–dark and UV-bright star. The purpose of the observation s is to monitor the UV response of the detector, and recently it has acquired further importan ce as a means to track the effects of increased radiation dosage on the UV/ion-shield of the dete ctor. We find no conclusive evidence that leaving the HRC door open during radiation-zone passag e is adversely affecting the UVIS. In order to spot any degradation early, we recommend continu i g the higher frequency schedule of observations.

We present 348 X-ray-emitting stars identified from correlating the Extended Chandra Multiwavelength Project (ChaMP), a wide-area serendipitous survey based on archival X-ray images, with the Sloan Digital Sky Survey (SDSS). We use morphological star/galaxy separation, matching to an SDSS quasar catalog, an optical color-magnitude cut, and X-ray data-quality tests to create our catalog, the ChaMP Extended Stellar Survey (ChESS), from a sample of 2121 matched ChaMP/SDSS sources. Our cuts retain 92% of the spectroscopically confirmed stars in the original sample while excluding 99.6% of the 684 spectroscopically confirmed extragalactic sources. Fewer than 3% of the sources in our final catalog are previously identified stellar X-ray emitters. For 42 catalog members, spectroscopic classifications are available in the literature. We present new spectral classifications and H alpha measurements for an additional 79 stars. The catalog is dominated by main-sequence stars; we estimate the fraction of giants in ChESS is similar to 10%. We identify seven giant stars (including a possible Cepheid and an RR Lyrae star) as ChaMP sources, as well as three cataclysmic variables. We derive distances from similar to 10 to 2000 pc for the stars in our catalog using photometric parallax relations appropriate for dwarfs on the main sequence and calculate their X-ray and bolometric luminosities. These stars lie in a unique space in the LX-distance plane, filling the gap between the nearby stars identified as counterparts to sources in the ROSAT All Sky Survey and the more distant stars detected in deep Chandra and XMM-Newton surveys. For 36 newly identified X-ray-emitting M stars we calculate L(H alpha)/L(bol). The quantities L(H alpha)/L(bol) and L(X)/L(bol) are linearly related below L(X)/L(bol) similar to 3 x 10(-4), while L(H alpha)/L(bol) appears to turn over at larger L(X)/L(bol) values. Stars with reliable SDSS photometry have an similar to 0.1 mag blue excess in u - g, likely due to increased chromospheric continuum emission. Photometric metallicity estimates suggest that the sample is evenly split between the young and old disk populations of the Galaxy; the lowest activity sources belong to the old disk population, a clear signature of the decay of magnetic activity with age. Future papers will present analyses of source variability and comparisons of this catalog to models of stellar activity in the Galactic disk.

THEMIS, a five-spacecraft constellation mission to study magnetospheric phenomena leading to auroral outbursts was launched on February 17, 2007 on a single Delta II rocket into a 31.4-hour, low-inclination insertion orbit. After an initial on-orbit check-out and science instrument commissioning period, the five spacecraft called probes were maintained in temporary coast phase orbits to control orbital dispersions. Beginning in early September 2007, four of the five probes were maneuvered into their highly elliptical, synchronized mission orbits with 1, 2 and 4-day periods in preparation for the primary winter observing season. The fifth probe, acting as an on-orbit spare, was maneuvered into its 4/5-day period orbit, once the four primary probes were completely deployed. This paper describes the concept of constellation operations including a description of the flight and ground systems, as well as mission, science and flight dynamics operations, and discusses challenges encountered and lessons learned during the first year of on-orbit operations.

We have analyzed Chandra calibration observations of Betelgeuse (α Ori, M2 Iab, mV = 0.58, 131 pc) obtained at the aimpoint locations of the HRC-I (8 ks), HRC-S (8 ks), and ACIS-I (5 ks). Betelgeuse is undetected in all the individual observations as well as cumulatively. We derive 3σ upper limits to its X-ray count rates and compute the corresponding X-ray flux upper limits for isothermal coronal plasma over a range of temperatures, T = 0.3 − 10 MK. We place a flux limit at the telescope of fX ≈ 4× 10−15 ergs s−1 cm−2 at T = 1 MK. The upper limit is lowered by a factor of ≈ 3 at higher temperatures, roughly an order of magnitude lower than that obtained previously. Assuming that the entire stellar surface is active, these fluxes correspond to a surface flux limit that ranges from 30 − 7000 ergs s−1 cm−2 at T = 1 MK, to ≈ 1 ergs s−1 cm−2 at higher temperatures, five orders of magnitude lower than the quiet Sun X-ray surface flux. We discuss the implications of our analysis in the context of models of a buried corona and a pervasive magnetic carpet. We rule out the existence of X-ray emission at the quiet Sun levels, but the presence of low-level emission on the scale of coronal holes remains plausible. Subject headings: stars: individual (Betelgeuse, α Ori) — stars: MIab — X-rays: stars

We have analyzed Chandra calibration observations of Betelgeuse (alpha Ori, M2Iab, m_V=0.58, 131 pc) obtained at the aimpoint locations of the HRC-I (8 ks), HRC-S (8 ks), and ACIS-I (5 ks). Betelgeuse is undetected in all the individual observations as well as cumulatively. We derive upper limits to the X-ray count rates and compute the corresponding X-ray flux and luminosity upper limits for coronal plasma that may potentially exist in the atmosphere of Betelgeuse over a range of temperatures, T=0.3-10 MK. We place a flux limit at the telescope of fx ~ 4x10^(-15) ergs s^(-1) cm^(-2) at T=1 MK. The upper limit is lowered by a factor of ~3 at higher temperatures, roughly an order of magnitude lower than that obtained previously. Assuming that the entire stellar surface is active, these fluxes correspond to a surface flux limit that ranges from 30-7000 ergs s^(-1) cm^(-2) at T=1 MK, to ~1 ergs s^(-1) cm^(-2) at higher temperatures, five orders of magnitude below the quiet Sun X-ray surface flux. We discuss the implications of our analysis in the context of models of a buried corona and a pervasive magnetic carpet. We rule out the existence of a solar-like corona on Betelgeuse, but cannot rule out the presence of low-level emission on the scale of coronal holes.

We present X-ray observations of Vega obtained with the Chandra High Resolution Camera and Advanced CCD Imaging Spectrometer. After a total of 29 ks of observation with Chandra, X-rays from Vega remain undetected. We derive upper limits to the X-ray luminosity of Vega as a function of temperature over the range of 10(5) - 10(7) K and find a 99.7% upper limit as low as similar to 2 x 10(25) ergs s(-1) at T = 10(6.2) K. We also compare these new deeper observations with the limit derived from a reanalysis of ROSAT PSPC data. Our X-ray luminosity limit for Vega is still greater than predictions of post-Herbig Ae phase X-rays from the shear dynamo model proposed by Tout & Pringle for a Vega age of 350 Myr. If the age of Vega is closer to 100 Myr, as suggested by some indicators, our X-ray limit is then similar to Tout-Pringle model predictions. Current X-ray observations of Vega are therefore unable to discriminate between different scenarios explaining the X-ray activity of the convectively stable Herbig Ae/Be stars. Further progress is more likely to be achieved through X-ray observations of younger main-sequence early-type A stars, whose conjectured residual post-Herbig Ae phase X-ray activity would be significantly higher.

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.

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.

Getting reliable estimates of coronal metallicity (Z) from X-ray spectra obtained with instruments such as ASCA/SIS and Chandra/ACIS is very difficult, because the sole determinant of Z is the ratio of line to continuum fluxes, which is not well-determined for low-resolution spectra. Here we propose new Bayesian methods which directly model the Poisson nature of the data. Our model also accounts for the Poisson nature of background contamination, blurring due to instrument response, and the absorption of photons in space. The resulting highly structured hierarchical model is fit using the Gibbs sampler, data augmentation, and Metropolis-Hasting. We demonstrate our methods with the X-ray spectral analysis of several apparently coronal metal abundance deficient (”MAD”) stars.