NanoSail-D: A solar sail demonstration mission

In the early to mid-2000s, NASA made substantial progress in the development of solar sail propulsion systems. Solar sail propulsion uses the solar radiation pressure exerted by the momentum transfer of reflected photons to generate a net force on a spacecraft. To date, solar sail propulsion systems were designed for large robotic spacecraft. Recently, however, NASA has been investigating the application of solar sails for small satellite propulsion. The NanoSail-D is a subscale solar sail system designed for possible small spacecraft applications. The NanoSail-D mission flew on board the ill-fated Falcon Rocket launched August 2, 2008, and due to the failure of that rocket, never achieved orbit. The NanoSail-D flight spare is ready for flight and a suitable launch arrangement is being actively pursued. This paper will present an introduction solar sail propulsion systems and an overview of the NanoSail-D spacecraft.     

Extragalactic origin of antiprotons

We have studied the effect of Galactic modulation on cosmic rays entering the Galaxy from outside for two different models for the confinement of cosmic rays, using one dimensional transport equation. From this study, the role of extragalactic cosmic rays has been examined critically in the context of the recent data on antiprotons. We have arrived at the conclusion that they are not a significant source of cosmic ray antiprotons. However, determination of the energy spectrum of Ps at least up to a few tens of GeV would provide information on the modulation of cosmic rays, while entering the Galaxy from outside.     

Recent advances in surrogate-based optimization

The evaluation of aerospace designs is synonymous with the use of long running and computationally intensive simulations. This fuels the desire to harness the efficiency of surrogate-based methods in aerospace design optimization. Recent advances in surrogate-based design methodology bring the promise of efficient global optimization closer to reality. We review the present state of the art of constructing surrogate models and their use in optimization strategies. We make extensive use of pictorial examples and, since no method is truly universal, give guidance as to each method's strengths and weaknesses.     

Resolution Performance of Pulse Trains with Large Time-Bandwidth Products

The coherent pulse train has good clutter suppression performance because the energy in its matched-filter response is essentially concentrated within sharp ambiguous spikes. However, this is so only when the Doppler distortions are neglected, so that the Doppler effect is taken as a simple translation of the carrier frequency. This paper analyzes the consequences of Doppler distortions on the resolution performance of pulse trains. It is found that Doppler distortions widen the Doppler ambiguities of the pulse train response, with the widening factor proportional to the order of the Doppler ambiguity. This reduces the interval between Doppler ambiguities, and hence the Doppler width of a clutter space that can be accommodated without severe clutter interference. For an operation in a Doppler-ambiguous mode, it also degrades nominal Doppler resolution performance. A detailed analysis of the effects is presented, and numerical results on the widening of the Doppler ambiguities are obtained.     

Multi-cell satellite for the communications of year 2000

The multi-cell communication satellite concept allows an efficient use of the geostationary orbit and a large reduction of the bit transmission cost, as a Bell-type (phased array), multiple mobile narrow beams arrangement with SS-TDMA.It has a flat hexagonal flying-saucer shape, being erected in a low altitude orbit, through an automatic assembly process of a large number of quasi-identical hexagonal cells. Each cell has independent power supply, thrusters, RF modules etc….Total assembly requires 10 ARIANE V or 4 SHUTTLE launches. An automatic tooling assembly using simple iterative manoeuvers is used to obtain the final shape, from initial cylindrical packages.Transfer into geostationary orbit is provided by low-thrust bi-propellant units attached to the cells, and released after burn-out. Assembly and transfer duration is about 6 months.Total traffic to 1000–2000 towns being 100 Gbits/s, the expected reduction of bit-transmission cost relative to year 1981 is 75–100 fold.     

A Note on the Effects of the Ionosphere on Satellite Orbital Corrections in Near-Real Time

The influence of ionospheric irregularities,e.g., sudden increase of electron content, onthe accurate determination of the position ofa satellite is being investigated. In this note amethod is presented whereby these effects areeasily accounted for in near-real time withoutthe need to know their detail structure.