\<COLOUR 1> SIZE: \<COLOUR 0> Sphere, diameter 16 cm
\<COLOUR 1> WEIGHT: \<COLOUR 0> 1.5 kg
\<COLOUR 1> COUNTRY: \<COLOUR 0> USA
\<COLOUR 1> COMMENTS: \<COLOUR 0> The second US and the world's fourth satellite, launched by a US Navy team; it is the first satellite powered by solar cells; it discovers that the Earth is slightly pear-shaped.