Thank you. Good points, but I think we&#x27;ll have to do a full blown calculations to decide. In aerospace margins are usually thin and it&#x27;s easy to have the sign error.<p>1) I fully agree that air-breathing engines are heavier per unit of thrust. Merlins - pretty good rocket engines by that parameter - lift, as you say, 150 times their weight; for air-breathing engines it&#x27;s 5-10.<p>2) Aircraft engines usually don&#x27;t need to be particularly thrusty; wings generate lift, so you can take off even with T&#x2F;W &lt; 1.<p>3) Liquid oxygen has density about 1.1 that of water. Kerosene, in comparison, is about 0.8. Difference less than 1.5 times, but the mass ratio is more like 2.5:1, so ditching oxygen tanks - especially at the start, when the system is relatively heavy - can save quite a bit. And why engines&#x27; T&#x2F;W is relevant here?