NASA: We Have Ignition
How do you test a new kind of rocket engine? To start
with, bolt it to a trailer in the middle of the Mojave
Desert.
In this case, NASA is firing up the 5M15, which runs on
compressed liquid methane. The odorless substance has multiple
advantages over conventional rocket propellants: It's cheaper,
it requires much less insulation, and it exists on several
planets NASA hopes to travel to. That means astronauts could
collect their own fuel for the trip home.
Those glowing figure eights in the blast stream are called
Mach disks, after the guy who lent his name to the speed of
sound. They're shock waves, created as the expanding fuel hits
the higher atmospheric pressure outside the nozzle. If part of
this blast weren't obscured, you could take the number of Mach
disks (we count seven) and multiply by the speed of sound —
about 758 mph at the 1,300-foot altitude of this test — to
estimate the speed of fuel exiting the engine. Just don't get
too close now.
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