There are no "bare bones notes" in this section.  The key points are:

• Satellites give a good advantage point.
• Much radiation from space is blocked by the atmosphere, so can only be studied from a satellite.
• Communications satellites can beam images around the Earth in a fraction of a second.  Before satellites, news-reek film had to be flown to the studio, the developed; this process took many hours.  Or weeks if they were sent by ship.
• Satellites have to work in extreme conditions.  Either very hot (+ 180 ^oC) or very cold (-270 ^oC or 3 K).  This has important implications for the structure and the machinery.
• There have to be suitable power supplies to run the satellite's systems.  They include a battery to store electrical energy made by solar panels.  They have to work in very hot or very cold conditions.
• The satellites have to cool themselves by radiation; there are no materials in space to allow cooling by conduction or convection.

Satellites have stayed in space for many years.  The Voyager satellite started its journey in 1976.  We can still pick up the signals from its transmitter, the power of which is equivalent to a weak torch bulb.

Although this unit is set in the context of satellites, the basic physics involved is true for all sorts of situations.