It is always interesting to see square wheels re-invented. Nevertheless, I am surprised you published the letter by Mr. Dale Lawrence Jensen [“Update Shuttle Rocket Engines,” March 27, page 24 ]. It shows complete ignorance on the issue of the optimum mixture ratio for liquid oxygen/liquid hydrogen engines. That excess hydrogen is required to reach optimum specific impulse and therefore payload mass fraction has been known for nearly 40 years.

Claudio Bruno

Roma, Italy