SPHERES flight operations testing and execution

Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) is a formation flight testing facility consisting of three satellites operating inside the International Space Station (ISS). The goal is to use the long term microgravity environment of the ISS to mature formation flight and docking algorithms. The operations processes of SPHERES have also matured over the course of the first seven test sessions. This paper describes the evolution of the SPHERES program operations processes from conception to implementation to refinement through flight experience. Modifications to the operations processes were based on experience and feedback from Marshall Space Flight Center Payload Operations Center, USAF Space Test Program office at Johnson Space Center, and the crew of Expedition 13 (first to operate SPHERES on station). Important lessons learned were on aspects such as test session frequency, determination of session success, and contingency operations. This paper describes the tests sessions; then it details the lessons learned, the change in processes, and the impact on the outcome of later test sessions. SPHERES had very successful initial test sessions which allowed for modification and tailoring of the operations processes to streamline the code delivery and to tailor responses based on flight experiences.     

Determination of attitude motion of the <Emphasis Type="Italic">Foton M-3</Emphasis> satellite according to the data of onboard measurements of the Earth’s magnetic field

The results of reconstruction of rotational motion of the Foton M-3 satellite during its uncontrolled flight in September 2007 are presented. The reconstruction was performed by processing the data of onboard measurements of the Earth’s magnetic field obtained by the DIMAC instruments. The measurements were carried out continuously throughout the flight, but the processing technique dealt with the data portions covering time intervals of a few orbital revolutions. The data obtained on each such interval were processed jointly by the least squares method with using integration of the equations of satellite motion relative to its center of mass. When processing, the initial conditions of motion and the used mathematical model’s parameters were estimated. The results of processing 16 data sets gave us complete information about the satellite motion. This motion, which began at a low angular velocity, had gradually accelerated and in five days became close to the regular Euler precession of an axisymmetric solid body. At the end of uncontrolled flight the angular velocity of the satellite relative to its lengthwise axis was 0.5 deg/s; the angular velocity projection onto the plane perpendicular to this axis had a magnitude of about 0.18 deg/s.     

RFI suppression for ultra wideband radar

An estimate-and-subtract algorithm is presented for the real-time digital suppression of radio frequency interference (RFI) in ultrawideband (UWB) synthetic aperture radar (SAR) systems used for foliage- and ground-penetrating imaging. The algorithm separately processes fixed- and variable-frequency interferers. Excision of estimated targets greatly reduces bias in RFI estimates, thereby reducing target energy loss and sidelobe levels in SAR imagery. Performance is demonstrated on data collected with the Army Research Laboratory's UWB rail SAR.     

On the Effective Single Trial Probability of Success

Define the cumulative probability Pn of occurence of some event as the probability that it occurs at least once in n trials. If the single trial probabilities are not fixed, but are drawn from a distribution of their own, or are dependent on some other nonfixed variable, then it would be convenient to have an ?effective single trial probability (esp)? for use in the simple Bernoulli model which would give the same cumulative probability of occurence as actually observed. We show here that the esp can be interpreted as a kind of average, and that its value is given by 1 minus the geometric mean of 1-d(p), where d(p) is the probability density function of the single trial probabilities, the p's. We further define this geometric mean for both discrete and continuous distributions and evaluate the esp for several cases. These results are compared with earlier ones which suggest that the esp is given by the (arithmetic) average or expectation of the single trial probabilities, and we determine under what conditions this simpler result can be used.     

The atmosphere of the primitive earth and the prebiotic synthesis of organic compounds.

The prebiotic synthesis of organic compounds using a spark discharge on various simulated prebiotic atmospheres at 25 degrees has been studied. Methane mixtures contained H2 + CH4 + H2O + N2 + NH3 with H2/CH4 molar ratios from 0 to 4 and pNH3 = 0.1 torr. A similar set of experiments without added NH3 was performed. The yields of amino acids (1.2 to 4.7% based on the carbon) are approximately independent of the H2/CH4 ratio and the presence of added NH3, and a wide variety of amino acids are obtained. Mixtures of H2 + CO + H2O + N2 and H2 + CO2 + H2O + N2, with and without added NH3, all give about 2% yields of amino acids at H2/CO and H2/CO2 ratios of 2 to 4. For the H2/CO and H2/CO2 ratios less than 1, the yields fall off drastically to as low as 10(-3)%. Glycine is almost the only amino acid produced from CO and CO2 atmospheres. These results show that the maximum yield is about the same for the three carbon sources at high H2/carbon ratios, but that CH4 is superior at low H2/carbon ratios. In addition, CH4 gives a much greater variety of amino acids than either CO or CO2. If it is assumed that amino acids more complex than glycine were required for the origin of life, then these results indicate the need for CH4 in the primitive atmosphere. The yields of cyanide and formaldehyde parallel the amino acid results, with yields of HCN and H2CO as high as 13% based on the carbon. Ammonia is also produced from N2 in experiments with no added NH3 in yields as high as 4.9%. These results show that large amounts of NH3 would have been synthesized on the primitive earth by electric discharges. The amount of ammonia formed by hydrolysis of HCN and various nitriles may have exceeded that formed directly in electric discharges.     

ATS-6 Satellite Instructional Television Experiment

The Satellite Instructional Television Experiment (SITE) is scheduled for the second year of satellite operation. Applications Technology Satellite (ATS-6) will receive C-band video signals frorn Abmedabad and Delhi, India, and will retransmitt the video and two audio sub-carriers at 860 MHz to 6 clusters of 400 direct-receive stations for a total of 2400 direct-receive stations. Morning programs of 1.5 hours per day are designed for classroom use, and evening programs of 2.5 hours duration are designed for village adult education. Indian production antennas and television sets have been tested and found to meet specifications, and a successful experiment is anticipated.     

The Challenger accident and public opinion : Attitudes towards the space programme in the USA

This article reports on a major survey of American attitudes towards the space programme in general, and the Shuttle in particular. The survey was carried out in three waves: before the January 1986 Challenger accident, immediately afterwards, and five months later. It was found that the net effect of the accident was a strong shift of public sentiment in favour of the space programme and the Shuttle. Expectation was high for a timely resumption of Shuttle flights, although there was a delayed recognition that the impact of the accident on the space programme was more significant than originally thought by most Americans. There was a shift towards a more positive assessment of the benefits and costs of space exploration. Positive attitudes towards funding increased even more markedly. These shifts were of a magnitude rarely found in studies of public attitudes.     

Spatial and temporal variations of the ion velocity measured in the venus ionosphere

The average velocity of the Venus ionosphere is nightward and approximately symmetric about the sun-Venus axis. We report here on temporal and spatial deviations from this average flow and their effects on the ionosphere. Temporal variability of the ion flux affects the main ionization source on the nightside. The influence of the solar wind is seen in the correlation between nightside ion density and ionopause height. Spatial asymmetries include a low-altitude superrotation (v-dawn < v-dusk) component related to superrotation of the neutral atmosphere, and a high-altitude prograde (v-dawn > v-dusk) component that is shown to be the result of asymmetric pressure gradients on the dayside.