Radioprotection by metals: selenium.

The need exists for compounds that will protect individuals from high-dose acute radiation exposure in space and the agents that might be less protective but less toxic and longer acting. Metals and metal derivatives provide a small degree of radioprotection (dose reduction factor < or = 1.2 for animal survival after whole-body irradiation). Emphasis is placed here on the radioprotective potential of selenium (Se). Both the inorganic salt, sodium selenite, and the organic Se compound, selenomethionine, enhance the survival of irradiated mice (60Co, 0.2 Gy/min) when injected IP either before (-24 hr and -1 hr) or shortly after (+15 min) radiation exposure. When administered at equitoxic doses (one-fourth LD10; selenomethionine = 4.0 mg/kg Se, sodium selenite = 0.8 mg/kg Se), both drugs enhanced the 30-day survival of mice irradiated at 9 Gy. Survival after 10-Gy exposure was significantly increased only after selenomethionine treatment. An advantage of selenomethionine is lower lethal and behavioral toxicity (locomotor activity depression) compared to sodium selenite, when they are administered at equivalent doses of Se. Sodium selenite administered in combination with WR-2721, S-2-(3-aminopropylamino)ethylphosphorothioic acid, enhances the radioprotective effect and reduces the lethal toxicity, but not the behavioral toxicity, of WR-2721. Other studies on radioprotection and protection against chemical carcinogens by different forms of Se are reviewed. As additional animal data and results from human chemoprevention trials become available, consideration also can be given to prolonged administration of Se compounds for protection against long-term radiation effects in space.     

Protocol for the treatment of radiation injuries.

Despite adequate precautionary measures and high-quality safeguard devices, many accidental radiation exposures continue to occur and may pose greater risks in the future, including radiation exposure in the space environment. The medical management of radiation casualties is of major concern to health care providers. Such medical management was addressed at The First Consensus Development Conference on the Treatment of Radiation Injuries, Washington, DC, 1989. The conference addressed the most appropriate treatment for the hematopoietic and infectious complications that accompany radiation injuries and for combined radiation and traumatic/burn injuries. Based on the evidence presented at the conference, a consensus statement was formulated by expert physicians and scientists. The recommended therapies, including a suggested algorithm incorporating these recommendations for the treatment of radiation injuries, will be discussed.     

Stability of motion of a space vehicle under constantly acting disturbances

The attitude stability of an Earth-orbiting satellite experiencing aerodynamic torque is studied. This is accomplished by applying the theory of total stability (or, stability under constantly acting disturbances) to the equations of motion. The satellite is gravity-gradient stabilized and a damping torque is incorporated. The aerodynamic torque results from the presence of two flat panels attached to the cylindrical body of the vehicle. This perturbing torque is treated as an additive disturbance in Euler's equations of motion. A Lyapunov function is constructed and then used in an appropriate theorem on stability under constantly acting disturbances. Explicit expressions are thereby found for bounds on a hypothetical initial condition (a rotation from the Earth-pointing equilibrium) and on the aerodynamic torque, so that if these disturbances are less than their respective bounds then the resulting attitude motion of the satellite will not exceed a pre-assigned value. These bounds depend on that pre-assigned value, and on the physical parameters of the satellite. The design implications of these bounds are then discussed.     

Efficient dynamic programming in presence of nuisance parameters

The dynamic programming approach for maximum a posteriori (MAP) estimation of Markov sequences is frequently proposed for problems in control theory, communications, and signal processing. It is usually assumed that the observation sequence is a perfectly known function of the Markov sequence of interest, except for some additive noise with known statistics. However, often the observation is not only a function of the Markov sequence but also of a vector of unknown nuisance parameters. It is shown how the dynamic programming methodology can be extended to estimate both the nuisance parameters and the Markov sequence, using a combined maximum-likelihood and MAP framework. The technique is efficient relative to other possible solutions. The problem of detecting and tracking moving targets observed by imaging sensors is used to demonstrate the efficiency of the procedure     

Social and cultural issues during Shuttle/Mir space missions.

A number of interpersonal issues relevant to manned space missions have been identified from the literature. These include crew tension, cohesion, leadership, language and cultural factors, and displacement. Ground-based studies by others and us have clarified some of the parameters of these issues and have indicated ways in which they could be studied during actual space missions. In this paper, we summarize some of our findings related to social and cultural issues from a NASA-funded study conducted during several Shuttle/Mir space missions. We used standardized mood and group climate measures that were completed on a weekly basis by American and Russian crew and mission control subjects who participated in these missions. Our results indicated that American subjects reported more dissatisfaction with their interpersonal environment than their Russian counterparts, especially American astronauts. Mission control personnel were more dysphoric than crewmembers, but both groups were significantly less dysphoric than other work groups on Earth. Countermeasures based on our findings are discussed which can be applied to future multicultural space missions.     

Human interactions during Shuttle/Mir space missions

To improve the interpersonal climate of crewmembers involved with long-duration space missions, it is important to understand the factors affecting their interactions with each other and with members of mission control. This paper will present findings from a recently completed NASA-funded study during the Shuttle/Mir program which evaluated in-group/out-group displacement of negative emotions; changes in tension, cohesion, and leader support over time; and cultural differences. In-flight data were collected from 5 astronauts, 8 cosmonauts, and 42 American and 16 Russian mission control personnel who signed informed consent. Subjects completed a weekly questionnaire that assessed their mood and perception of their work group's interpersonal climate using questions from well-known, standardized measures (Profile of Mood States, Group and Work Environment Scales) and a critical incident log. There was strong evidence for the displacement of tension and dysphoric emotions from crewmembers to mission control personnel and from mission control personnel to management. There was a perceived decrease in commander support during the 2nd half of the missions, and for American crewmembers a novelty effect was found on several subscales during the first few months on-orbit. There were a number of differences between American and Russian responses which suggested that the former were less happy with their interpersonal environment than the latter. Mission control personnel reported more tension and dysphoria than crewmembers, although both groups scored better than other work groups on Earth. Nearly all reported critical incidents came from ground subjects, with Americans and Russians showing important differences in response frequencies.     

Cyclicality or volatility? The satellite insurance market

The history of the satellite insurance market indicates that this market experiences crises and booms in profitability and prices that repeat in a manner suggestive of cycles. The purpose of this article is to rigorously investigate cyclicality of these and other features of the satellite insurance market and assess their volatility formally. Using data from 1968 to 2008, volatility and cyclicality are analyzed for satellite insurance market capacity, rates, and underwriting results, among other measures. The coefficient of variation for the various satellite insurance market metrics is used to assess volatility. Standard underwriting analysis is used to determine whether a cycle exists for various insurance metrics. The results indicate that some aspects of the satellite insurance market are volatile (e.g. claims) or cyclical (e.g. rates), while capacity is both volatile and cyclical.     

Kalman filtering for matrix estimation

A general discrete-time Kalman filter (KF) for state matrix estimation using matrix measurements is presented. The new algorithm evaluates the state matrix estimate and the estimation error covariance matrix in terms of the original system matrices. The proposed algorithm naturally fits systems which are most conveniently described by matrix process and measurement equations. Its formulation uses a compact notation for aiding both intuition and mathematical manipulation. It is a straightforward extension of the classical KF, and includes as special cases other matrix filters that were developed in the past. Beyond the analytical value of the matrix filter, it is shown through various examples arising in engineering problems that this filter can be computationally more efficient than its vectorized version.     

Performance Evaluation of Postdetection Integrators with Partially Correlated Noise

A simple procedure for calculating receiver operating characteristics (ROC) for postdetection integration of arbitrary partially correlated noise samples is presented. The approach is based on the application of the ?effective number of independent integrated noise samples? to the classical theory of Marcum and Swerling and has been justified by Monte-Carlo simulation.