Mumbai University > EXTC > Sem 8 > Satellite Communication and Networks

Marks: 5M

Besides planets, natural and artificial satellites, many other particles like cosmic rays, protons, electrons, meteoroids and manmade space debris exists in space.

These particles collide with the satellites causing permanent damage to it and sometimes degrading the solar cells.

Space debris, also known as orbital debris, space junk and space waste, is the collection of objects in orbit around Earth that were created by humans but no longer serve any useful purpose. These objects consist of everything from spent rocket stages and defunct satellites to explosion and collision fragments.

The debris can include slag and dust from solid rocket motors, surface degradation products such as paint flakes, clusters of small needles, and objects released due to the impact of micro meteoroids or fairly small debris onto spacecraft. As the orbits of these objects often overlap the trajectories of spacecraft, debris is a potential collision risk.

The vast majority of the estimated tens of millions of pieces of space debris are small particles, like paint flakes and solid rocket fuel slag. Impacts of these particles cause erosive damage, similar to sand blasting. The majority of this damage can be mitigated through the use of a technique originally developed to protect spacecraft from micrometeorites, by adding a thin layer of metal foil outside of the main spacecraft body.

Impacts take place at such high velocities that the debris is vaporized when it collides with the foil, and the resulting plasma spreads out quickly enough that it does not cause serious damage to the inner wall. However, not all parts of a spacecraft may be protected in this manner, i.e. solar panels and optical devices (such as telescopes, or star trackers), and these components are subject to constant wear by debris and micrometeorites.

TWTA consists of cathode, electron gun, tube structure and collector plate. Cathode is the source of electrons. This cathode is heated at approx. temperature of 1000oC. High voltage bias application results into generation of electrons down the tube structure. As cathode has finite source of electrons, TWT will have certain life time. TWTs tend to be less efficient than klystrons because of the necessity for loading the structure for stability and because relatively high RF power is present in an appreciable fraction of the entire structure. One important technique for improving the efficiency of high-power TWTs is called velocity tapering.