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.     

An extensive phase space for the potential martian biosphere

We present a comprehensive model of martian pressure-temperature (P-T) phase space and compare it with that of Earth. Martian P-T conditions compatible with liquid water extend to a depth of ～310?km. We use our phase space model of Mars and of terrestrial life to estimate the depths and extent of the water on Mars that is habitable for terrestrial life. We find an extensive overlap between inhabited terrestrial phase space and martian phase space. The lower martian surface temperatures and shallower martian geotherm suggest that, if there is a hot deep biosphere on Mars, it could extend 7 times deeper than the ～5?km depth of the hot deep terrestrial biosphere in the crust inhabited by hyperthermophilic chemolithotrophs. This corresponds to ～3.2% of the volume of present-day Mars being potentially habitable for terrestrial-like life.     

Planetary parks—formulating a wilderness policy for planetary bodies

Building on an earlier article, establishment of a planetary park system for other planetary bodies is further developed. Reasons are elaborated for such a system to protect representative regions of other planetary bodies. Although a parks system might seem supererogatory, and an over-reaction to the currently very limited environmental impact of robotic and human exploration and settlement activities, four arguments are provided that suggest that such a system does have a value, even in advance of robotic and human missions. Planetary parks incorporate concepts of planetary protection, but they extend the reasons for practical protection policies beyond the utilitarian protection of scientific resources emphasized by planetary protection, into other utilitarian and intrinsic value arguments. Planetary parks might still allow for the development of non-park areas by commercial enterprise.     

Viscous-type processes in the solar wind-magnetosphere interaction

A debate of long standing concerns the role viscous interactions play in magnetospheric dynamics. Is it minor or is it central to, e.g., drive the low latitude boundary layer on closed field lines and account for the substantial level of wave activity seen on the flanks? Newer data and theoretical considerations leave little doubt that viscous coupling is important. The Kelvin-Helmholtz instability is a major protagonist in fostering momentum transfer. Closer studies of the state of the flank magnetosphere will help to resolve the issue.     

A Planetary Park system for Mars

The increasing robotic exploration of Mars and eventual human exploration and settlement of that planet threatens to have a significant environmental impact on scientifically important sites and sites of natural beauty in the form of contamination with micro-organisms and spacecraft parts. By definition, the sites that we might wish to preserve are likely to be those to which robots and humans will be sent. An interventionist step to protect pristine regions of Mars with the formation of a Planetary Park system is proposed. Possible locations for the first seven Planetary Parks are suggested. Landing of unmanned craft in these parks would be forbidden. Although global dust storms can carry microorganisms across the planetary surface, the regulations suggested for these parks will allow for the maximum level of preservation. We also suggest that the Planetary Park system could be applied to the Moon.     

Adaptive Main-Beam Nulling for Narrow-Beam Antenna Arrays

Narrow-beam, low-sidelobe antennas may be used to enhance communication in the presence of sidelobe interferers. Protection against main-beam interferers as well can be obtained through the use of an adaptive multibeam antenna. Such an antenna, suitable for time-multiplexed, multichannel signals is described here. The objective is to permit successful communication and signal direction-of-arrival tracking in the presence of a large number of sidelobe interferers and a small number of main-beam interferers.     

Particle code simulations with injected particles

As problems we are interested in become more complex, we often find our simulations stretching the limits of available computer resources. For example, an interesting problem is simulation of dissipation processes in sub-critical collisionless shocks. To simulate this system our simulation box must contain the shock and its upstream and downstream regions over the entire length of a run. If the shock moves with any appreciable speed the box must then be considerably larger than the shock thickness making it hard to resolve the shock front itself with a reasonable number of grid points. A solution to this problem is to run the simulation in the frame of reference of the shock. Particles are injected upstream of the shock and leave the simulation box downstream. With the shock stationary in the simulation box, we only need to contain enough of the up and downstream regions for the fields, etc., to settle down and separate the shock from the box boundaries. In this tutorial we consider some basic algorithms used in a practical particle injection code, such as the two dimensional WAVE code used at Los Alamos. We will try to present these ideas in a simple format general enough to be easily included in any particle code. Topics covered are:

1. Smoothly Injecting Particles.
2. Generating the Distribution Functions.
3. Time Dependent Injection Density.
4. Boundary Conditions on Fields and Particles.

(Flux and Charge Conservation)