A search for narrow band signals with SERENDIP II: a progress report

Commensal programs for the Search for Extraterrestrial Intelligence (SETI), carried out concurrently with conventional radio astronomical observing programs, can be an attractive and cost-effective means of exploring the large multidimensional search space intrinsic to this effort. Our automated commensal system, SERENDIP II, is a high resolution 131,072 channel spectrometer. It searches for 0.49 Hz signals in sequential 64,700 Hz bands of the IF signal from a radio telescope being used for an astronomical observation. Upon detection of a narrow band signal with power above a preset threshold, the frequency, power, time, and telescope direction are recorded for later study. The system has been tested at the Hat Creek Radio Astronomy Observatory 85 ft telescope and the NASA-JPL Deep Space Station (DSS 14) 64 m telescope. It is currently collecting data at the National Radio Astronomy Observatory 300 ft telescope.     

Stabilization of a Reentry Vehicle by a Partial Spin-up during Uncontrolled Descent

Stabilization of a reentry vehicle (RV) by a partial spin-up of it is considered for the case of uncontrolled descent into the atmosphere. In this case, the vehicle is a composite construction consisting of two rigid bodies, a return capsule and a stabilizing block, which is put in rotation. A model is developed for the spatial motion of the reentry vehicle considered as a system of coaxial rigid bodies rotating about a common axis of symmetry. The free motion is studied, and the stability of steady-state regimes is analyzed. The spatial motion of the system is considered for the case of a small asymmetry due to displacement of the axes of dynamic symmetry of the bodies with respect to the spin axis, and approximate solutions for the motion parameters of the free system are found.     

Sputnik fever — again?

The author offers some comments on the drawbacks of another US-Soviet space race. She compares the relative positions of the USA and the USSR in various areas of space science and technology, and concludes that the USSR does not lead in all areas. More importantly, she argues that it is distressing still to be portraying the superpowers as in a race in space. ‘Sputnik fever’ the first time round showed that a space race does not lead to a strong, long-term US space programme. She argues that cooperation in some areas — perhaps a trip to Mars — could b an alternative.     

Pathophysiology of motor functions in prolonged manned space flights.

The influence of weightlessness on different parts of the motor system have been studied in crew members of 140 and 175 days space flights. It has been shown that weightlessness affects all parts of the motor system including (i) the leg and trunk muscles, in which severe atonia, a decrease of strength and an increase of electromyographic cost of contraction have been observed, (ii) the proprioceptive elements and the spinal reflex mechanisms in which decreased thresholds accompanied by decreases of maximal amplitude of reflexes and disturbances in cross reflex mechanisms have been found. and (iii) the central mechanisms that control characteristics of postural and locomotor activities. The intensities and durations of disturbances of different parts of the motor system did not correlate to each other, but did correlate with prophylactic activity during space flight. The data suggest a different nature of disturbances caused by weightlessness in different parts of the motor system.     

Stability of dynamic algorithms of determination of quasi-stationary satellite orbits

A method of estimating the stability of the problem of orbit determination under disturbances caused by finite accuracy of calculation and geographical siting of observation stations is proposed.     

Future earth observation missions for oceanographic applications: Indian perspectives

Significant progress has been achieved in India in demonstrating the utility of remote sensing data for various oceanographic applications during the last one decade. Among these, techniques have been developed for retrieval of ocean surface waves, winds, wave forecast model, internal waves, sea surface temperature and chlorophyll pigments. Encouraged from these results as well as for meeting the specific and increasing data requirements on an assured basis by oceanographers, India is making concerted efforts for developing and launching state-of-the-art indigenous satellites for ocean applications in the coming years.

The first in the series of ocean satellites planned for launch is Oceansat-1 (IRS-P4) by early 1999. Oceansat-1 carries on-board an Ocean Colour Monitor (OCM) and a Multi-frequency Scanning Microwave Radiometer (MSMR). OCM will have 8 narrow spectral bands operating in visible and near- infrared bands (402–885 nm) with a spatial resolution of 360 m and swath of 1420 km. The MSMR with its all weather capability is configured to have measurements at 4 frequencies viz., 6.6, 10.65, 18 & 21 GHz in dual polarisation mode with a spatial resolution of 120, 80, 40 & 40 km, respectively with an overall swath of 1360 km. The Oceansat-1 with repetitivity of once in two days will provide global data for retrieval of various oceanographic and meteorological parameters such as chlorophyll (primary productivity), sea surface temperature and wind speed, besides a host of other parameters of relevance to meteorology.

A full fledged satellite for ocean applications known as Oceansat-2 (IRS-P7) is also planned for launch during 2002. This satellite with payload mix of microwave (Scatterometer, Altimeter & Passive Microwave Radiometer), Thermal (TIR) and Optical (OCM) sensors, will provide greater in-sight into the global understanding of ocean dynamics/resources. This mission is expected to provide a complete set of oceanographic measurements, which are useful for providing operational oceanographic services.

Efforts are also on towards development of missions having multi-frequency, multipolarisation and multi-look angle microwave payloads including Synthetic Aperture Radar (SAR) and advanced millimeter wave sounders, besides development of imaging spectrometers by 2005.

A well-knit plan has been initiated in India for utilisation of planned Oceansat data. Important efforts initiated in this direction include SATellite Coastal and Oceanographic Research and Ocean Information Services, which are being carried out on an integrated basis aiming at providing services to the down stream users. The paper highlights these efforts in India towards providing an operational ocean information services in the coming years.     

The Mode of Gravitational Orientation for the International Space Station

The results of the determination of the uncontrolled attitude motion of the International Space Station during its unmanned flight in 1999 are presented. The data of onboard measurements of three components of the angular velocity are used for this determination. These data covering an interval of slightly less than one orbit were jointly processed by the least squares method, by integrating the equations of motion of the station relative to its center of mass. As a result of this processing, the initial conditions of the motion and the parameters of the mathematical model used were estimated. The actual motion of the station has been determined for 20 such intervals during April–November. Throughout these intervals, the station rotated about the axis of the minimum moment of inertia, the latter executing small oscillations relative to the local vertical. Such a mode, known as the mode of gravitational orientation of a rotating satellite or the mode of generalized gravitational orientation, was planned before the flight. The measurements were made to verify it. The quasistatic component of the microaccelerations aboard the station is estimated for this mode.     

Low-Frequency Microaccelerations onboard the Foton-11 Satellite

We analyze the microacceleration measurements carried out onboard the Foton-11 satellite with the three-component accelerometer BETA. The microaccelerations were recorded virtually throughout the entire orbital flight of the Foton-11 satellite. The data obtained were analyzed in the following way. First they were used to determine the actual rotational motion of the satellite for several arbitrarily selected time intervals 4 h long. This problem was solved by constructing the approximation of the microacceleretation low-frequency component (previously determined from the data) by its calculated analog computed along the solutions to differential equations of rotational motion of the satellite. The approximation was made by the least squares method. As a result, those mathematical model parameters and the solutions to equations of motion were found that gave the best consistency of the microacceleretation low-frequency component and its calculated analog. Then the spectral analysis of the low-frequency component and its calculated analog was made. It was shown that, although basic harmonics of these functions coincided sufficiently well, some harmonics of the low-frequency component failed to be interpreted in terms of the satellite's rotational motion.     

Delayed gratification habitable zones: when deep outer solar system regions become balmy during post-main sequence stellar evolution

Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >10(5) objects > or =50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, approximately 10(9) Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy.     

Design feasibility via ascent optimality for next-generation spacecraft

This paper deals with the optimization of the ascent trajectories for single-stage-sub-orbit (SSSO), single-stage-to-orbit (SSTO), and two-stage-to-orbit (TSTO) rocket-powered spacecraft. The maximum payload weight problem is studied for different values of the engine specific impulse and spacecraft structural factor.The main conclusions are that: feasibility of SSSO spacecraft is guaranteed for all the parameter combinations considered; feasibility of SSTO spacecraft depends strongly on the parameter combination chosen; not only feasibility of TSTO spacecraft is guaranteed for all the parameter combinations considered, but the TSTO payload is several times the SSTO payload.Improvements in engine specific impulse and spacecraft structural factor are desirable and crucial for SSTO feasibility; indeed, aerodynamic improvements do not yield significant improvements in payload.For SSSO, SSTO, and TSTO spacecraft, simple engineering approximations are developed connecting the maximum payload weight to the engine specific impulse and spacecraft structural factor. With reference to the specific impulse/structural factor domain, these engineering approximations lead to the construction of zero-payload lines separating the feasibility region (positive payload) from the unfeasibility region (negative payload).