Lets see who gets to Mars first.
On Sun, Aug 9, 2020 at 3:06 PM Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
On Sun, 9 Aug 2020, ken mason wrote:
Let's not get carried away. Atlas has been flying...
...with throttlable closed-cycle high-efficiency-and-Isp engines,
really truly routinely, for two decades now.
Not 40% deep throttle and methane...
The RD-180 was tested to 40% (with no significant Isp penalty), although
the production engine is only rated to go down to 47%. I don't think
normal Atlas flight profiles go even that low, but the engine can do it.
The RL10 in the Atlas second stage isn't normally throttled at all, but
small changes to one valve give throttling to 30% (flown on DC-X) and even
lower is possible with bigger hardware changes.
As for methane, why does that matter? It's not a miracle fuel. There's
no major performance advantage over kerosene, and a substantial density
penalty. The hype greatly exaggerates the benefits. (Methane's one big
win is if you hope to someday refuel from extraterrestrial sources: if
you don't have a local petroleum industry to support you, methane is a lot
easier to find or make than anything approximating kerosene.)
If you really must have methane, experimental variants of the RL10 ran
successfully on methane half a century ago. (Also on propane, which is
probably a better choice if you want to use a light hydrocarbon and don't
care about extraterrestrial sources.)
Henry
