Blue Origin is planning some major design changes for the next version of its New Shepard suborbital vehicle, according to MSNBC’s Alan Boyle.

Boyle reports that the new New Shepard will use a single liquid-hydrogen rocket engine, instead of five kerosene rocket engines. He quotes Blue Origin’s business-development manager Brett Alexander saying, “It’ll look a little different, but it’s essentially the same size.”

That statement is somewhat odd, because liquid hydrogen has a much lower density than liquid kerosene. Hydrogen is lighter and more energetic, so a smaller weight of propellant is required for the same mission but the volume is normally larger. That implies larger tanks. (This is one of the reasons why hydrogen-fueled airliners have never gotten past the drawing board. The fuselage always ends up being huge and filled mostly with fuel rather than passengers.)

In addition, the size of engine pumps scales with the volume of propellant to be pumped, rather than the weight. Hydrogen-fueled engines generally have a lower thrust-to-weight ratio than kerosene engines. That could be offset, though, by lower thrust requirements since the hydrogen weighs less than an equivalent amount of kerosene. There might also be some weight savings from replacing five smaller engines with one larger engine.

Also see Blue Origin Had a Great Day in West Texas.

Written by Astro1 on October 22nd, 2012 , Blue Origin

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