Ronnie Killough

The Swift Ultra-Violet/Optical Telescope

The Ultra-Violet/Optical Telescope (UVOT) is one of three instruments flying aboard the Swift Gamma-ray Observatory. It is designed to capture the early (∼1 min) UV and optical photons from the afterglow of gamma-ray bursts in the 170–600 nm band as well as long term observations of these afterglows. This is accomplished through the use of UV and optical broadband filters and grisms. The UVOT has a modified Ritchey–Chrétien design with micro-channel plate intensified charged-coupled device detectors that record the arrival time of individual photons and provide sub-arcsecond positioning of sources. We discuss some of the science to be pursued by the UVOT and the overall design of the instrument.

The Swift ultra-violet/optical telescope

The UV/optical telescope (UVOT) is one of three instruments flying aboard the Swift Gamma-ray Observatory. It is designed to capture the early (~1 minute) UV and optical photons from the afterglow of gamma-ray bursts as well as long term observations of these afterglows. This is accomplished through the use of UV and optical broadband filters and grisms. The UVOT has a modified Ritchey-Chretien design with micro-channel plate intensified charged-coupled device detectors that provide sub-arcsecond imaging. Unlike most UV/optical telescopes the UVOT can operate in a photon-counting mode as well as an imaging mode. We discuss some of the science to be pursued by the UVOT and the overall design of the instrument.

The IMAGE Observatory

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission will be the first of the new Medium-class Explorer (MIDEX) missions to fly. IMAGE will utilize a combination of ultraviolet and neutral atom imaging instruments plus an RF sounder to map and image the temporal and spatial features of the magnetosphere. The eight science sensors are mounted to a single deckplate. The deckplate is enveloped in an eight-sided spacecraft bus, 225 cm across the flats, developed by Lockheed Martin Missiles and Space Corporation. Constructed of laminated aluminum honeycomb panels, covered extensively by Gallium Arsenide solar cells, the spacecraft structure is designed to withstand the launch loads of a Delta 7326-9.5 ELV. Attitude control is via a single magnetic torque rod and passive nutation damper with aspect information provided by a star camera, sun sensor, and three-axis magnetometer. A single S-band transponder provides telemetry and command functionality. Interfaces between the self-contained payload and the spacecraft are limited to MIL-STD-1553 and power. This paper lists the requirements that drove the design of the IMAGE Observatory and the implementation that met the requirements.

SCORPIO: the Gemini facility instrument for LSST follow-up

We present the current status of the SCORPIO project, the facility instrument for Gemini South designed to perform follow up studies of transients in the LSST era while carrying out with unique efficiency a great variety of astrophysical programs. SCORPIO operates in the wavelength range 385-2350 nanometers, observing simultaneously in the grizYJHK bands. It can be used both in imaging (seeing limited) and spectroscopic (long-slit) mode, and thanks to the use of frame-transfer CCDs it can monitor variable sources with milli-second time-resolution. The project has recently passed PDR and is on schedule to be commissioned at the time of the LSST first light.

Observing modes for the new SCORPIO imager and spectrograph at Gemini South

SCORPIO (Spectrograph and Camera for Observation of Rapid Phenomena in the Infrared and Optical) is the new workhorse instrument for the Gemini South Telescope in Chile. Originally proposed in response to the Gen4#3 solicitation, SCORPIO is a unique fast-multicolor imager and ultra-wide band spectrograph capable of rapid exposures for high time-resolution images and spectra. SCORPIO consists of 8 separate channels (corresponding to the standard wavebands g, r, i, z, Y, H, J, K) that can operate with different exposure times. Each channel can be used in imaging or long-slit mode, with independent readout timing. In this report we illustrate the detectors, the control systems, and the observing modes that will be available with SCORPIO.

Juggling Spacecraft: Similarities and differences of eight microsatellites for the CYGNSS mission

The goal of any system in which there is a large set of components that are mostly similar, but have a non-negligible set of differences, is to find the balance between a “one-size-fits-all” approach, and a “unique-per-system-and-customizable” approach. This paper discusses how the balance between these two extremes is achieved as part of the ground segment and flight segment that will support the eight microsatellites of the National Aeronautics and Space Administration (NASA) Cyclone Global Navigation Satellite System (CYGNSS) mission. The NASA CYGNSS mission aims to understand the coupling between ocean surface properties, moist atmospheric thermodynamics, radiation, and convective dynamics in the inner core of Tropical Cyclones (TCs). The mission is comprised of eight microsatellites in Low-Earth Orbit (LEO) at an inclination of 35 degrees. As discussed in “The CYGNSS Ground Segment: Innovative Missions Operations Concepts to Support a Micro-Satellite Constellation” [1], previously presented at IEEE Aerospace 2013, the ground segment system must take into account the unique aspects of each microsatellite, including unique Spacecraft Identification (SCID) schemes, setup of multiple ground system consoles, definition of telemetry limits unique to a microsatellite, and any unique table or command loads. This paper expands upon the previously presented paper on the ground segment, and discusses how each of these details has been addressed in the implementation of the CYGNSS mission. This includes discussion of how Spacecraft I/Ds are defined onboard via the avionics, how the FSW table configurations vary between microsatellites, and whether or not a “one-size-fits-all” approach of FSW images is necessary for each microsatellite. The CYGNSS mission completed Preliminary Design Review (PDR) in 2014, Critical Design Review (CDR) in 2015, and is expected to launch in late 2016.

Simulators, software and small satellites: Testing in tight spaces

In the world of spacecraft integration and test, “Test As You Fly” (TAYF) is the mantra. This is sometimes easier said than done since methods to stimulate the various sensors can be difficult, and commanding many flight actuators while the spacecraft is sitting on the ground is impractical. As such, a mixture of sensor stimulation, sensor emulation and other environment simulations are used to dupe the spacecraft into believing it is flying, thus enabling the flight software (FSW) and control algorithms to be tested in their final flight configurations. When building and testing very small satellites, some additional obstacles are present. For example, installing external simulators and emulators necessary for activities such as attitude determination and control (AD&C) testing and mission simulations late in the integration schedule may be precluded due to a lack of physical access. Using special electrical ground support equipment (EGSE) interfaces to stimulate the spacecraft may introduce other challenges - no one wants to stand before a launch readiness review board and say that one set of FSW was used during final mission tests and simulations, but that another version will be loaded just prior to launch! The Cyclone Global Navigation Satellite System (CYGNSS) mission is a constellation of eight microsatellites that is currently in the integration and test phase. The CYGNSS payload is comprised of a set of Global Positioning System (GPS) receivers, which compare direct and ocean-reflected signals to measure surface wind speeds. Each microsat has a suite of AD&C sensors and actuators that must be simulated or stimulated during test. Designing a simulation and test environment that was cost-effective for a NASA Class D mission and dealt with the limitations of size, while maintaining a TAYF philosophy, presented significant challenges. This paper discusses how satellite size translated into challenges in the design of the FSW and EGSE, and how this impacted the overall test and simulation approach. Unique and creative solutions developed will be described, such as the use of “man-in-the-middle attack” techniques (commonly used by cyber hackers) to allow the FSW to execute normally even while communicating over non-flight interfaces. Finally, the pros and cons of the various design choices will be discussed.

Onboard science processing on a microsatellite with limited resources

The National Aeronautics and Space Administration (NASA) Cyclone Global Navigation Satellite System (CYGNSS) mission aims to understand the coupling between ocean surface properties, moist atmospheric thermodynamics, radiation, and convective dynamics in the inner core of tropical cyclones (TCs). The mission is comprised of eight microsatellites (μSats) in low-earth orbit (LEO) at an inclination of 35 degrees. The mission faces unique challenges in hardware and software design to satisfy mission restrictions: the small size of the μSats implies a low power budget for telemetry downlink bandwidth, science data processing, and Attitude Determination and Control (ADC) processing. Additionally, the LEO path of each μSat implies shorter ground passes that limit the downlink time. To accommodate these constraints, creative and efficient hardware and software designs are required. This paper discusses how downlink and power limitations will be accommodated by the design of the CYGNSS Spacecraft hardware and software. Each μSat contains a Delay Doppler Mapping Instrument (DDMI) which receives direct signals from Global Positioning System (GPS) satellites as well as GPS signals scattered by the ocean surface. The direct signals pinpoint the location of the μSat, while the scattered signals respond to ocean surface roughness from which wind speed is derived. The science data derived from these direct and scattered GPS signals, Delay Doppler Maps (DDMs), will be used to provide information about and improve forecasts of the intensity of TCs.

Software engineering processes for Class D missions

Software engineering processes are often seen as anathemas; thoughts of CMMI key process areas and NPR 7150.2A compliance matrices can motivate a software developer to consider other career fields. However, with adequate definition, common-sense application, and an appropriate level of built-in flexibility, software engineering processes provide a critical framework in which to conduct a successful software development project. One problem is that current models seem to be built around an underlying assumption of “bigness,” and assume that all elements of the process are applicable to all software projects regardless of size and tolerance for risk. This is best illustrated in NASA’s NPR 7150.2A in which, aside from some special provisions for manned missions, the software processes are to be applied based solely on the criticality of the software to the mission, completely agnostic of the mission class itself. That is, the processes applicable to a Class A mission (high priority, very low risk tolerance, very high national significance) are precisely the same as those applicable to a Class D mission (low priority, high risk tolerance, low national significance). This paper will propose changes to NPR 7150.2A, taking mission class into consideration, and discuss how some of these changes are being piloted for a current Class D mission—the Cyclone Global Navigation Satellite System (CYGNSS).