[1]This is obtained from _k_ = _gR_², where _g_ is the acceleration due
to gravity and _R_ is the radius of the earth. (Here, we can use _k_
= 96,500 miles³ per second².)
[2]Donald R. Herriott of Bell Labs had suggested using plane reflectors
on satellites as long ago as 1957—although his idea was that this
would increase their visibility, rather than aid in determining
their attitude.
[3]This method was developed by D. W. Hill of Bell Telephone
Laboratories.
[4]We will not attempt to go into all the details of semiconductor
physics here. If you would like to know more about how solar cells
work, refer to the Suggested Reading on page 88.
[5]See pages 42 and 43.
[6]Published as part of the Bell System Aid to High School Science
Program.
[Illustration: Wraparound cover image]