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Forrest, David J.

Publications and source records attributed to Forrest, David J..

Challenges and lessons learned in the application of autonomy to space operations

NASA's Space Operations Management Office (SOMO) is working toward a goal of providing an integrated infrastructure of mission and data services for space missions undertaken by NASA enterprises. A significant portion of this effort is focused on reducing the cost of these services. We are interested in the potential of autonomy to reduce operations costs. Some attempts have already been made to apply autonomy and automation in these areas in the past with varying degrees of success. We present brief case histories and the lessons inferred from them. Combining this past experience with anticipated future needs, we attempt to clarify the challenges that must be met in order to realize the benefits of autonomy.

challenges↗

Challenges and Lessons Learned in the Application of Autonomy to Space Operations

NASA's Space Operations Management Office (SOMO) is working toward a goal of providing an integrated infrastructure of mission and data services for space missions undertaken by NASA enterprises. A significant portion of this effort is focused on reducing the cost of these services. We are interested in the potential of autonomy to reduce operations costs. SOMO services support space missions, but are not part of the mission objectives; therefore the level of acceptable risk is very low. In fact, SOMO could be effective ly prevented from applying autonomy if customers merely perceive it as adding risk to their mission(s). We are interested in this workshop from the standpoint of understanding what can be done to realize the potential cost savings due to autonomy while maintaining acceptable risk and serving the needs of our customers. We would like to present our lessons learned so far in adopting autonomy and automation, which we think will contribute to clarifying the challenges facing the use of such technology. SOMO provides services to a diverse and ambitious set of mission customers. Many of these missions are groundbreaking missions for which communications, data, and other operations requirements sometimes cannot be clearly articulated early in the program. This motivates a need for systems that are robust in the face of unanticipated situations so that customer missions are not unreasonably constrained or impacted by "shortcomings" in SOMO services. One of SOMO's primary goals is to realize a paradigm in which SOMO acts as a service provider to organizations that fly space missions for NASA, other government agencies, and even the commercial sector. These organizations purchase SOMO services "by the pound" as customers. We have to provide systems that are not experiments themselves, but rather stable bases from which to do bold experiments. To this end, SOMO also seeks to work closely with industry to see that robust autonomy technology gets infused into products and services for the space industry and beyond. The potential for application of these technologies spans space-based communications networks (e.g. TDRSS) and ground-based assets including communication and tracking antenna systems, data networks, and control centers. There are several problems that are candidates for the application of autonomy, if it can be made reliable enough, including: antenna control, antenna scheduling, communication link scheduling and operation, navigation, attitude determination, fault detection, isolation, and reconfiguration (for spacecraft or ground assets), and mission-level planning and scheduling. Some attempts have been made to apply autonomy and automation in these areas in the past with varying degrees of success. We will present relevant case histories and the lessons inferred from them. Combining this past experience with anticipated future needs, we can clarify the challenges that must be met in order to realize the benefits of autonomy.

Forrest, David J.↗

Study of the Polarization Properties of the Crab Nebula and Pulsar with BATSE

Activities carried out under this proposal included: 1) development and refinements of Monte Carlo simulations of the atmospheric reflected albedo hard x-ray emissions, both unpolarized and polarized, 2) modeling and simulations of the off-axis response of the BATSE LAD detectors, and 3) comparison of our simulation results with numerous BATSE flare and cosmic burst data sets.

Forrest, David J.↗

Evidence for a spatially extended component of gamma rays from solar flares

We present gamma-ray measurements of a large solar flare that occurred beyond the western solar limb on September 29, 1989. The gamma-ray spectrum shows a neutron capture line which is much stronger than predicted by limb-darkening curves that fit the measurements for flares on the visible hemisphere. We show that this strong neutron capture line can be explained if, in addition to the compact impulsive phase component that normally dominates the total fluence, there is a spatially extended component. For the September 29, 1989 flare we find that such a spatially extended region must subtend more than about 30 deg on the solar surface. We suggest that the extended component could be powered by particles that diffuse from a compact impulsive region or by particles that diffuse into the lower solar atmosphere from a large-scale acceleration site.

Vestrand, W. T.↗

Man-made transients observed by the gamma-ray spectrometer on the Solar Maximum Mission satellite

Since launch in early 1980 the gamma-ray spectrometer (GRS) on SMM has monitored the sun at gamma-ray energies. In addition to observations of solar flares, cosmic gamma-ray bursts, and precipitating radiation-belt electrons, the instrument has detected a new class of high-energy transient events that cannot be attributed to any of these phenomena. The duration of these transients can range from 1 sec to more than 10 min. The average event rate between 1980 and 1986 was about five per month. However, in February 1987 this rate increased by more than a factor of 25 and continued at this high level until June 1988. These transients can be subdivided into three classes: 511-keV annihilation-line events, particle events, and broad-band photon continuumlike events. It is found that the most likely sources of these events are reactors in earth-orbiting satellites.

Rieger, Erich↗

Flare observation during Max 1991 balloon campaigns

A brief overview is presented for some of the large flare properties as observed during the prime SMM flare observation interval, 1980 to 1984. Two of these properties, namely their tendency to occur in groups and the strong effects of the 154 day periodicity, can be used to increase the probability of detecting large flares during the limited observing duration of Max 1991 balloon campaigns provided the solar flare characteristics of the 1991 solar cycle follows that observed in 1980 to 1984.

Forrest, David J.↗