&gt; The main goals are efficiency and pollution, and eliminating the supersonic boom is a secondary goal.<p>The supersonic boom should be one of the top priorities, also. Just look at this well-known video: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=annkM6z1-FE" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=annkM6z1-FE</a> , you can&#x27;t have that happening over populated territory, meaning land.<p>Adding to that, just wanted to say that airplanes&#x27; sound pollution is a real and damaging thing. My parents live in a remote Eastern European village but, apparently, the skies over their house is a commercial airplane highway, as there were moments when I could count 6 or 7 of them up in the sky at the same time, including a big, white whale which looked like an A380. Anyway, it&#x27;s not fun when it&#x27;s 5 in the morning, you&#x27;re surrounded by the four thick walls of your parents&#x27; house but you can still hear the airplane flying above your house at 30,000 feet.