In response to the commentary by Arnold D. Aldrich [ “Space Shuttle Past and Future,” Aug. 29, page 19], Mr. Aldrich is indeed correct that liquid fuel boosters have been investigated several times since the start of the shuttle program. I participated in the first such study by the (former) Rockwell International Corp. under contract to NASA’s Marshall Space Flight Center.

The study, “Shuttle Growth Study, ” published in May 1977, evaluated several liquid booster concepts . The final selected booster was the LO2/LH2 version, which was sized for an orbiter carrying a fictitious 100-kilogram payload. The principal focus was on the booster, so we did not investigate the changes in the orbiter design that would have been necessary for that payload. However, we did study that, and more, in later in-house studies.

Today, I would recommend that booster coupled with the Rocketdyne RS-2100 engine that was defined for the (then) Rockwell X-33 vehicle. It was to be a greatly improved version of the highly successful space shuttle main engine and was to have incorporated some 20 years of applied advanced development into the current space shuttle main engine

Carl Ehrlich, Associate Fellow AIAA