Bryce A. Roberts

On-Orbit Performance of the Far Ultraviolet Spectroscopic Explorer Satellite

The launch of the Far Ultraviolet Spectroscopic Explorer (FUSE) has been followed by an extensive period of calibration and characterization as part of the preparation for normal satellite operations. Major tasks carried out during this period include the initial coalignment, focusing, and characterization of the four instrument channels and a preliminary measurement of the resolution and throughput performance of the instrument. We describe the results from this test program and present preliminary estimates of the on-orbit performance of the FUSE satellite based on a combination of these data and prelaunch laboratory measurements.

On-orbit performance of the Far Ultraviolet Spectroscopic Explorer (FUSE)

The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched into orbit on June 24, 1999. FUSE is now making high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 angstroms). Its high effective area, low background, and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. In this paper, we describe the on- orbit performance of the FUSE satellite during its first nine months of operation, including measurements of sensitivity and resolution.

FUSE in-orbit attitude control with two reaction wheels and no gyroscopes

The Far Ultraviolet Spectroscopic Explorer is a NASA Origins mission launched in June 1999 to obtain high-resolution spectra of astronomical sources at far-ultraviolet wavelengths. The science objectives require the satellite to provide inertial pointing at arbitrary positions on the sky with sub-arcsecond accuracy and stability. The requirements were met using a combination of ring-laser gyroscopes, three-axis magnetometers, and a fine error sensor for attitude knowledge, and reaction wheels for attitude control. Magnetic torquer bars are used for momentum management of the reaction wheels, and coarse sun sensors for safe mode pointing. The gyroscopes are packaged as two coaligned inertial reference units of three orthogonal gyroscopes each. There are four reaction wheels: three oriented along orthogonal axes, the fourth skewed at equal angles (54.7°) with respect to the others. Early in the mission the gyroscopes began showing signs of aging more rapidly than expected, and one failed after two years of operation. In addition, two of the orthogonal wheels failed in late 2001. The flight software has been modified to employ the torquer bars in conjunction with the two remaining wheels to provide fine pointing control. Additional new flight software is under development to provide attitude control if both gyroscopes fail on one or more axes. Simulations indicate that the pointing requirements will still be met, though with some decrease in observing efficiency. We will describe the new attitude control system, compare performance characteristics before and after the reaction wheel failures, and present predicted performance without gyroscopes.

Ground Systems and Flight Operations of the THEMIS Constellation Mission

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.

Multi-Mission Flight Operations at UC Berkeley - Experiences and Lessons Learned

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.

THEMIS Mission Networks Expansion - Adding the Deep Space Network for the ARTEMIS Lunar Mission Phase

THEMIS is a five-spacecraft constellation launched in 2007 to study magnetospheric phenomena leading to the aurora borealis. During the primary mission phase, completed in the fall of 2009, all five spacecraft collected science data in synchronized, highly elliptical Earth orbits. For an ambitious mission extension, the Project proposed to split the constellation into two parts - THEMIS-Low and ARTEMIS. THEMIS-Low includes the three spacecraft on the inner orbits with approximately one-day periods, continuing their study of the magnetosphere in a tighter formation. ARTEMIS involves transferring the outer two spacecraft from their Earth orbits with two and four-day periods into lunar orbits to conduct measurements of the interaction of the Moon with the solar wind and of crustal magnetic fields. This transfer was initiated on July 21, 2009 and follows low-energy trajectories with Earth and lunar gravity assists. The THEMIS mission is controlled from the highly automated multi-mission operations center at the University of California, Berkeley and was originally designed to be supported by 11-m class ground stations and NASAs Space Network. To increase the telemetry bandwidth for science data return at lunar distances, the mission network was expanded to also include the 34-m subnet of NASAs Deep Space Network (DSN). This paper discusses all aspects of the process to seamlessly integrate the new DSN interfaces into the THEMIS/ARTEMIS mission control network, and describes challenges and lessons learned with the implementation of real-time telemetry and command data transfer using the CCSDS Space Link Extension protocol. It also includes on-orbit characterization of the transponder ranging channels, orbit determination results using two-way Doppler and range data from a combination of conventional ground stations and DSN stations, as well as pass scheduling via the DSN Resource Allocation Planning Service and via automated, electronic data exchanges. All of these tasks were accomplished within a compressed schedule of one year, with very limited staffing resources, and on a tight budget.

Spectroscopy and Photometry of EUVE J1429-38.0:An Eclipsing Magnetic Cataclysmic Variable

EUVE J1429-38.0 was originally discovered as a variable source by the Extreme Ultraviolet Explorer {EUVE) satellite. We present new optical observations which unambiguously confirm this star to be an eclipsing magnetic system with an orbital period of 446. The photometric data are strongly modulated by ellipsoidal variations during low states which allow a system inclination of near 80 degrees to be determined. Our time-resolved optical spectra, which cover only about one-third of the orbital cycle, indicate the clear presence of a gas stream. During high states, EUVE J1429-38.0 shows ~ 1 mag deep eclipses and the apparent formation of a partial accretion disk. EUVE J1429-38.0 presents the observer with properties of both the AM Herculis and the DQ Herculis types of magnetic cataclysmic variable.

Extreme Ultraviolet Explorer Optical Identification Campaign. IV. A Northern Hemisphere Sample of Active Late-Type Stars and Typical EUV Sources

We present new optical identifications of previously unidentified faint extreme ultraviolet sources. Our total sample of 30 identified sources, of which 22 are new identifications, includes 24 late-type stars, three white dwarfs, two cataclysmic variables (CVs), and one active galactic nucleus. These sources are joint detections of the faint sources from the all-sky surveys of the Extreme Ultraviolet Explorer (EUVE) in the 58–174 A (0.071–0.214 keV) EUV band and of the ROSAT Position Sensitive Proportional Counter in the 5–120 A (0.1–2.4 keV) X-ray band. We obtained medium-resolution spectra of the possible optical counterparts with the Shane 3 m telescope at Lick Observatory using the Kast double spectrograph covering a bandpass of 3600–7500 A. Our sample of active late-type stars is dominated by K and M stars showing strong Balmer and Ca II emission lines. The white dwarfs are fairly typical for those detected in the EUVE survey with Teff and log g ranging from 35 to 53 kK and 7.6 to 8.7, respectively. We found strong H and He emission lines typical of cataclysmic variables (CVs) for EUVE J0854+390 and EUVE J1802+180. EUVE J0854+390 is a newly identified cataclysmic variable showing radial velocity shifts to the red as large as ≈400 km s-1. We associate EUVE J1802+180 with the previously identified CV, V884 Her (RX J1802.1+1804). Including the present work (22 new identifications), EUVE optical identification campaigns have identified ≈28% of the presently cataloged NOID sources.

Highly automated on-orbit operations of the NuSTAR telescope

UC Berkeleys 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 MOCs 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.

Operations planning and mission readiness testing for the THEMIS spacecraft constellation

THEMIS - a five-spacecraft constellation - is a NASA Medium Explorer mission that was launched in 2007 and maneuvered into synchronized, highly elliptical Earth orbits to study magnetospheric physics leading to the appearance of the aurora borealis. THEMIS operations are conducted from the multi-mission control center at the University of California, Berkeley. After a successful completion of the prime mission phase in fall of 2009, all five spacecraft and the ground systems are still performing very well. The excellent flight and ground systems performance can in part be traced back to a carefully designed and meticulously executed mission readiness test program, as well as operations planning and extensive operator training. This paper describes the methodology of the mission readiness test program, its organization from box level to full systems level end-to-end testing, and includes lessons learned that may be directly applicable towards future missions. 1 2