<a class="mw-redirect" href="https://en.wikipedia.org/wiki/Explorer_program" id="mwyA" rel="mw:WikiLink" title="Explorer program">Explorer program</a>: <a href="https://en.wikipedia.org/wiki/Explorer_9" id="mwyQ" rel="mw:WikiLink" title="Explorer 9">Explorer 9</a> (S-56a) is launched.