Blue Origin changes engines for New Glenn second stage

Behind the Black ^ | March 30, 2018 | Robert Zimmerman

[Voption]

"Capitalism in space: In order to maintain its goal of launching its orbital New Glenn rocket by 2020, Blue Origin has changed the engine it will use in the rocket’s second stage from a version of its main BE-4 engine to new version of their already developed BE-3 engine, used in their reusable New Shepard suborbital spacecraft...This quiet change, which the company made with no fanfare, carries with it some significant information as well as important ramifications."

[Ozark Tom]

Based on energy per kilogram, combined with density for each liquefied fuel, LH would likely need about two-point-five times the tank volume as for NG. Liquid hydrogen (RS-25) delivers better ISP than super-cooled slush Natural-gas, about 450 versus 375 (Raptor) for a vacuum optimized engine design; and, 366 (RS-25) versus 330 (Raptor Sea Level optimized) for first stage operation. BE-4 design for natural gas should be roughly equivalent to the Raptor.

[TexasBarak]

I drive by that place from time to time. “Middle of nowhere” doesn’t begin to describe it!

[Ozark Tom]

Pitch-over of trajectory results in a deviation from vertical of about 30 to 45 degrees at first-stage cutoff. First stage shut-down often occurs at about 40 miles altitude and 5000 mph for a two-stage configuration. There is still air resistance in addition to the gravity load. Orbit will require adding 60 miles altitude and about 12,000 mph to achieve a minimal stable orbit at 100 miles altitude.

Two BE-3U (vacuum optimized) engines in combination deliver about fifty percent of the thrust projection for a single vacuum optimized BE-4. Can a half-thrust second stage reach orbit by doubling the burn time?

Apollo 13 lost 1 out of 5 engines of the second stage, and would have aborted the mission if any more were lost. This Blue Origin substitution doesn’t seem an equitable engine swap, even given a higher performance fuel.