SIGMA: Projet d'Observatoire spatial a haute resolution angulaire pour les sources de rayons gamma

(SIGMA: Project of a high resolution space observatory for gamma rays sources)—The SIGMA space observatory is designed to obtain images of the sky in the hard X-ray/low energy gamma-ray domain (30–2000 keV range), with an angular accuracy of a few are min, within a field of ～7° × 7°, and a sensitivity for point sources down to a level of a few 10^?6 photons cm^?2s^?1keV^?1 (exposure 24 hr). The instrument is designed using the principle of the coded aperture mask telescope with a position sensitive detector derived from the Anger gamma-camera which is used in nuclear medicine. The pseudo-images of the sky are accumulated on board and transmitted to the ground stations for decoding processing. The gross weight of the instrument is 750 kg and its overall dimensions are 3 m long and 1.2 m in diameter.     

Advanced materials for space applications

Since NASA was created in 1958, over 6400 patents have been issued to the agency—nearly one in a thousand of all patents ever issued in the United States. A large number of these inventions have focused on new materials that have made space travel and exploration of the moon, Mars, and the outer planets possible. In the last few years, the materials developed by NASA Langley Research Center embody breakthroughs in performance and properties that will enable great achievements in space. The examples discussed below offer significant advantages for use in small satellites, i.e., those with payloads under a metric ton. These include patented products such as LaRC SI, LaRC RP 46, LaRC RP 50, PETI-5, TEEK, PETI-330, LaRC CP, TOR-LM and LaRC LCR (patent pending). These and other new advances in nanotechnology engineering, self-assembling nanostructures and multifunctional aerospace materials are presented and discussed below, and applications with significant technological and commercial advantages are proposed.     

A Comparison of Second, Third, and Fourth Order Phase-Locked Loops

This paper presents data describing various performance characteristics of phase-locked loops, which were obtained for the purpose of determining an optimum selection of system order in view of typical operating conditions. With the functions optimized with respect to particular performance characteristics, calculations of the integrated square error and peak error with polynomial inputs are presented in terms of the noise bandwidth; and the generalized error coefficients are also provided in terms of the bandwidth with consideration for the use of both perfect and imperfect integrators. With specific input functions as provided by signals transmitted from earth satellites, an improved performance is demonstrated with the use of the higher order loops, and experimental results verify the calculations and also demonstrate the feasibility of the fourth order loop design.     

Current barriers and factors of success in the diffusion of satellite services in Europe

Satellite services benefit civil society by helping tackle challenges such as climate change, the digital divide, etc. They have the potential to deliver concrete benefits to European society through innovative services supporting economic, societal and environmental policies. Such benefits can trigger increased public support for space in Europe. However, this potential has yet to be achieved. This paper argues that technological bias, the diversity of interests and initiatives among stakeholders and their individual actions do not always serve their collective objective to ensure wide diffusion of satellite services. It draws on theories of diffusion of innovation and on its authors' participatory work with the space and the user communities and at their interface in an effort to help diffuse satellite services within civil society. One of the major causes of insufficient service diffusion is the weakness of the interface between the space and user communities; some of factors that currently contribute to this state of affairs are the space community's over-reliance on publicly financed, technical demonstration projects as solutions to service diffusion; insufficient coordination by public authorities of innovation policies and programmes with other public policies and objectives; and an insufficient integration of satellite services within users' culture, traditional tools and services. The discussion allows for conclusions to be drawn on how the system of stakeholders could function better in order for satellite services to be successfully diffused in Europe.     

Refraction Error in Measurement of Angle of Arrival with the Radio Interferometer

The ``extra-path' error in the measurement of angle of arrival with the radio interferometer is analyzed as a function of target coordinates and baseline B for an exponential atmosphere. By treating the error rather than the measurement and by formulating the error in terms of well-known radar refraction parameters, the necessity for numerical integrations characteristic of earlier approaches is avoided. The table of computed errors shows that angle of arrival can be measured to an accuracy of 0.01 mrad for B?500 meters.     

Instrument Boom Mechanisms on the THEMIS Satellites; Magnetometer, Radial Wire, and Axial Booms

The five “Time History of Events and Macroscale Interactions during Substorms” (THEMIS) micro-satellites launched on a common carrier by a Delta II, 7925 heavy, on February 17, 2007. This is the fifth launch in the NASA MeDIum class EXplorer (MIDEX) program. In the mission proposal the decision was made to have the University of California Berkeley Space Sciences Laboratory (UCB-SSL) mechanical engineering staff provide all of the spacecraft appendages, in order to meet the short development schedule, and to insure compatibility. This paper describes the systems engineering, design, development, testing, and on-orbit deployment of these boom systems that include: the 1 and 2 meter carbon fiber composite magnetometer booms, the 40 and 50 m tip to tip orthogonal spin-plane wire boom pairs, and the 6.3 m dipole stiff axial booms.     

Benefits from incorporation of combined cycle propulsion

The X-33 program was initiated to develop a testbed for integrated RLV technologies that pave the way for a full scale development of a launch vehicle (Venture Star). Within the Nasa Future X Trailblazer program there is an Upgrade X-33 that focuses on materials and upgrades. The authors propose that the most significant gains can be realized by changing the propulsion cycle, not materials. The cycles examined are rocket cycles, with the combustion in the rocket motor. Specifically, these rocket cycles are: turbopump, topping, expander, air augmented, air augmented ram, LACE and deeply cooled. The vehicle size, volume, structural weight remain constant. The system and propellant tank weights vary with the propulsion system cycle. A reduction in dry weight, made possible by a reduced propellant tank volume, was converted into payload weight provided sufficient volume was made available by the propellant reduction. This analysis was extended to Venture Star for selected engine cycles. The results show that the X-33 test bed could carry a significant payload to LEO (10,000 Ib) and be a valuable test bed in developing a frequent flight to LEO capability. From X-33 published information the maximum speed is about 15,000 ft/sec. With a LACE rocket propulsion system Venture Star vehicle could be sized to a smaller vehicle with greater payload than the Venture Star baseline. Vehicle layout and characteristics were obtained from: http:// www.venturestar.com.     

Exposure of Arabidopsis thaliana to hypobaric environments: implications for low-pressure bioregenerative life support systems for human exploration missions and terraforming on Mars

Understanding how hypobaria can affect net photosynthetic (P (net)) and net evapotranspiration rates of plants is important for the Mars Exploration Program because low-pressured environments may be used to reduce the equivalent system mass of near-term plant biology experiments on landers or future bioregenerative advanced life support systems. Furthermore, introductions of plants to the surface of a partially terraformed Mars will be constrained by the limits of sustainable growth and reproduction of plants to hypobaric conditions. To explore the effects of hypobaria on plant physiology, a low-pressure growth chamber (LPGC) was constructed that maintained hypobaric environments capable of supporting short-term plant physiological studies. Experiments were conducted on Arabidopsis thaliana maintained in the LPGC with total atmospheric pressures set at 101 (Earth sea-level control), 75, 50, 25 or 10 kPa. Plants were grown in a separate incubator at 101 kPa for 6 weeks, transferred to the LPGC, and acclimated to low-pressure atmospheres for either 1 or 16 h. After 1 or 16 h of acclimation, CO(2) levels were allowed to drawdown from 0.1 kPa to CO(2) compensation points to assess P (net) rates under different hypobaric conditions. Results showed that P (net) increased as the pressures decreased from 101 to 10 kPa when CO(2) partial pressure (pp) values were below 0.04 kPa (i.e., when ppCO2 was considered limiting). In contrast, when ppCO(2) was in the nonlimiting range from 0.10 to 0.07 kPa, the P (net) rates were insensitive to decreasing pressures. Thus, if CO(2 )concentrations can be kept elevated in hypobaric plant growth modules or on the surface of a partially terraformed Mars, P (net) rates may be relatively unaffected by hypobaria. Results support the conclusions that (i) hypobaric plant growth modules might be operated around 10 kPa without undue inhibition of photosynthesis and (ii) terraforming efforts on Mars might require a surface pressure of at least 10 kPa (100 mb) for normal growth of deployed plant species.     

Determination of Angular Distribution Models for Indian desert scene: Comparison with other desert models

In this paper, the shortwave and longwave anisotropy for clear sky Indian desert scene has been estimated using long-term surface data, radiative transfer calculations and Helmholtz reciprocity for missing values. This study is important in the perspective of the low inclination satellites like Megha–Tropiques (MT) mission, carrying Scanner for Radiation Budget (ScaRaB) payload, which will provide broadband radiative fluxes at the top of the atmosphere (TOA). Due to low inclination angle, the angular models for clear sky land scenes for the MT-ScaRaB orbits will be dominated by desert points.The Angular Distribution Models (ADMs) determined in this study were compared with existing desert models. It is observed that for longwave radiation, the largest disagreement is observed for higher values of viewing zenith angle, especially for the summer season, where the difference in flux can reach up to 13 W/m². For the shortwave radiation, higher values of both solar zenith angle and viewing zenith angle cause largest incongruity in the computed albedo from the different models, suggesting the need of caution in interpretation of the flux computations from these bins. In fact at the higher solar zenith angle bin, the disparity in albedo can go up to 6.4%.