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The XLR99 engine was the first large,
throttleable, restartable liquid propellant rocket engine. Development
began in the 1950s by the Reaction Motors Division of Thiokol Chemical
Company to power the X-15 research aircraft. It could deliver up to
57,000 pounds force (254 kN) of thrust with an Isp of 279 seconds (239
seconds sl). Thrust was variable from 50 to 100 percent, and the restart
capability allowed it to be shut down and restarted during flight when
necessary.
The engine was propelled by liquid oxygen
and anhydrous ammonia, pumped into the engine by turbines at a flow rate
of over 10,000 lbs (4,500 kg) per minute.
After one hour of operation, the XLR99
required an overhaul. Operating times nearly twice that were recorded in
tests, but declared largely unsafe. The basic X-15 aircraft carried
about 83 seconds of fuel for full-powered flight, while the X-15A-2
carried fuel for just over 150 seconds. Therefore each XLR99 was
capable, in theory, of between 20 and 40 flights before an
overhaul.
Like many other liquid-fuel rocket engines,
the XLR99s used regenerative cooling, in that the thrust chamber and
nozzle had tubing surrounding it, through which the propellant and
oxidizer passed before being burned. This kept the engine cool, and
preheated the fuel. The basic engine weighs 910 lb, or 413
kg.
Nikon D7000 cha cha, Sigma 10-20mm lens (-at-)
16mm (24mm equiv.) ISO 4500, f5, 1/30 sec handheld, SPM, PS
CS6.
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