Solrad 1
... that Solrad 1 was the first satellite to successfully observe solar X-rays?
... that <b id="mwIw"><a class="mw-redirect" href="./Solrad_1" id="mwJA" rel="mw:WikiLink" title="Solrad 1">Solrad 1</a></b> was the first satellite to successfully observe <a href="./Astrophysical_X-ray_source" id="mwJQ" rel="mw:WikiLink" title="Astrophysical X-ray source">solar X-rays</a>?