The US civilian space programme : Charting a new course

The US space programme continues to face difficulties in restructuring to meet existing political and fiscal conditions, in part because the basic structure and focus of the programme derive from the tensions of the Cold War. This paper argues that the world's new, more complicated political and economic conditions present a challenge for US policy makers that can be met with a renewed focus on the pursuit of science and the public good, within the context of international economic competition and political and scientific cooperation.     

Strange star Equation of State with a modified Richardson potential

Richardson potential is an phenomenological interquark interaction taking care of two aspects of QCD, namely the asymptotic freedom and the confinement. The original potential has a scale parameter having value 400 MeV and is well tested in hadronic property calculations. This potential was then used in strange star calculation. Strange stars are very compact stars composed of strange quark matter, i.e. a very high density strange quark phase consisting of deconfined u, d and s quarks. Here the value of the scale parameter was taken as 100 MeV. The argument was that for a deconfined quark system like a strange star, the scale parameter may have a value quite different from that used in hadronic sector. To remove this discrepancy we introduced two scale parameters in the potential, one for the asymptotic freedom part and the other for the confining part. With suitable values of the parameters, this modified potential has been successfully used in both baryonic property and strange star calculations. The Equation of States obtained with the modified potential are also used to obtain mass–radius relations for the strange stars.     

An evaluation of the radio frequency susceptibility of commercialGPS receivers

The radio frequency (RF) susceptibility characteristics of two commercial Global Positioning System (GPS) receivers were evaluated. A first-order analysis was performed to predict the receiver susceptibility thresholds based on the receiver sensitivity and processing gain. The receiver susceptibility thresholds in the post-acquisition mode were then measured for various interference signal frequencies and modulations. Both receivers exhibited very low susceptibility thresholds to in-band continuous wave (CW) signals. In addition, both receivers could be over-driven with an out-of-band signal. In this state the receivers indicated acceptable figures of merit despite loss of satellite signal lock     

Production of high fidelity lunar agglutinate simulant

As space faring nations consider manned and unmanned missions to the Moon, there is a growing need to develop high fidelity lunar regolith simulants that can accurately reproduce the properties and behavior of lunar regolith. Such simulants will be employed to verify the performance of equipment, mechanisms, structures and processes to be used on the lunar surface. One of the significant limitations of current terrestrial-based simulants, such as the popular mare simulant, JSC-1A, is the lack of agglutinates. This paper investigates the production of a lunar mare agglutinate simulant based on JSC-1A. A modified plasma processing technique was used to expose the JSC-1A regolith simulant to high temperatures and transform it to predominantly a glassy phase. Detailed characterization results are presented to confirm that the agglutinate simulant material produced during this investigation reasonably satisfies the primary requirements of an agglutinate simulant such as amorphous/crystalline content, particle size, morphology, vesicular structure, chemistry, and presence of nanophase elemental Fe.     

Impact of loading effects on determination of the International Terrestrial Reference Frame

The International Terrestrial Reference Frame (ITRF), as a realization of the International Terrestrial Reference System (ITRS), is represented by a set of station positions and linear velocities. They are intended to be used as regularized coordinates to which some corrections should be added to access instantaneous coordinates. The latest ITRS realization is the ITRF2005, which has integrated time series of station positions to form long-term solutions for the four space geodetic techniques. Currently, a purely linear model is used to parameterize station displacements in the estimation process, plus occasional discontinuities in case of earthquakes or equipment changes. However the input data have been derived without applying surface loading models and so surface loading effects are supposed to be embedded in the coordinates as measured quantities. We evaluate the effect of applying a posteriori loading corrections, which include the effect of atmospheric, non-tidal ocean, and continental water loading, to time series of positions estimated from Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Global Positioning System (GPS) data. We notice that they reduce about 50% or more of the annual signals in the translation and scale parameter time series of the SLR and VLBI techniques, except in SLR Z translation. In general, the estimated secular frame definition is negligibly affected and estimated positions and velocities are not significantly modified for stations that have accumulated a large number of observations. A multi-technique combination of such derived frames allows concluding that, for some cases, loading model corrections might degrade co-located station coordinates almost as much as they benefit them. However, most significant improvement of the estimated secular coordinates is observed for stations with less than 100 estimated positions as demonstrated with a multi-technique combination.