Control and reconfiguration of satellite formations by electromagnetic forces, Journal of Telecommunications and Information Technology, 2007, nr 1

Current concept of interferometric missions assume that they employ formations of spacecraft. The cooperation between members of a multisatellite formation is a challenging problem. One of the main difficulties is to implement a reliable system for position control and actuation. A precise control of the position and orientation of each satellite in the array is a key factor in obtaining high quality images of distant objects. The controlling system should frequently collect data about geometry and kinematics of all array elements and use actuators to keep them as close as possible to their nominal positions. Forces that are required for actuation or array reconfiguration in space can be produced by engines of various types. In most cases chemical propulsion is used, with a drawback of limited fuel resources and a danger of polluting optical elements. In our work, we analyze dynamics of satellite formation flight, in which interaction forces result from electromagnetic fields generated by coils with current. We use simple controller equation proposed by members of MIT team to control a formation of two or three aligned satellites rotating around the array’s mass center

Thermal conductivity measurements of road construction materials in frozen and unfrozen state

A series of thermal conductivity measurements for various materials was performed in a large climate chamber. The size of the chamber allowed the preparation of relatively large samples in a controlled thermal environment. Three types of thermal sensors were used: (1) two needle probes; (2) a grid of temperature sensors, evenly distributed inside the sample; (3) two additional thermal probes, which were simplified versions of an instrument originally developed for measuring thermal properties of the ice/dust mixture expected to exist at the surface of a comet nucleus. They consist of a series of individual temperature sensors integrated into a glass fibre rod. Each of these sensors can be operated in an active (heated) or passive (only temperature sensing) mode. The following sample materials were used: fine-grained reddish sand, coarse-grained moist sand, gravels with various grain size distributions from < 1 cm up to about 6 cm, and for comparison and calibration pure water (with convection suppressed by adding agar-agar), compact ice, and compact granite. Of particular interest are the measurements with composite samples, like stones embedded in an agar-agar matrix. We describe the evaluation methods and present the results of the thermal conductivity measurements

“Pi of the Sky” Detector

“Pi of the Sky” experiment has been designed for continuous observations of a large part of the sky, in search for astrophysical phenomena characterized by short timescales, especially for prompt optical counterparts of Gamma Ray Bursts (GRBs). Other scientific goals include searching for novae and supernovae stars and monitoring of blasars and AGNs activity. “Pi of the Sky” is a fully autonomous, robotic detector, which can operate for long periods of time without a human supervision. A crucial element of the detector is an advanced software for real-time data analysis and identification of short optical transients. The most important result so far has been an independent detection and observation of the prompt optical emission of the “naked-eye” GRB080319B

In situ methods for measuring thermal properties and heat flux on planetary bodies

The thermo-mechanical properties of planetary surface and subsurface layers control to a high extent in which way a body interacts with its environment, in particular how it responds to solar irradiation and how it interacts with a potentially existing atmosphere. Furthermore, if the natural temperature profile over a certain depth can be measured in situ, this gives important information about the heat flux from the interior and thus about the thermal evolution of the body. Therefore, in most of the recent and planned planetary lander missions experiment packages for determining thermo-mechanical properties are part of the payload. Examples are the experiment MUPUS on Rosetta's comet lander Philae, the TECP instrument aboard NASA's Mars polar lander Phoenix, and the mole-type instrument HP3 currently developed for use on upcoming lunar and Mars missions. In this review we describe several methods applied for measuring thermal conductivity and heat flux and discuss the particular difficulties faced when these properties have to be measured in a low pressure and low temperature environment. We point out the abilities and disadvantages of the different instruments and outline the evaluation procedures necessary to extract reliable thermal conductivity and heat flux data from in situ measurements