His credentials in the field are pretty good, and his books are always hard-science (no elves or wizards, and very little hand-wavy stuff).<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Robert_L._Forward" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Robert_L._Forward</a><p>If I recall the design correctly (forgive me - it&#x27;s been over 15 years since I read it), there&#x27;s a significant size difference in the sails. The larger sail collects photons from the distant laser and focuses them on the smaller &quot;backwards facing&quot; deceleration sail.