Pintle injector
The pintle injector was reduced to practice and developed by Space Technology Laboratories (STL), then a division of Ramo-Wooldridge Corp., later TRW, starting in 1960.
[2] Pintle-based engines were first used on a crewed spacecraft during the Apollo Program in the Lunar Excursion Module's Descent Propulsion System,[4][2][5] however, it was not until October 1972 that the design was made public.
[2][7] While pintle injectors have been developed for applications in rocket propulsion, due to their relative simplicity, they could easily be adapted for industrial fluid handling processes requiring high flowrate and thorough mixing.
In order to keep the device from blowing itself apart during high energy tests, the outer tube was retracted, thus constituting a primitive pintle injector.
[2] Peter Staudhammer, under the supervision of Program Manager Elverum, had a technician cut multiple slots across the end of an available inner tube and subsequent tests of this new configuration showed a substantial improvement in mixing efficiency.
[2][3] By 1960, Elverum, Grant, and Staudhammer had moved to the newly-formed Space Technology Laboratories, Inc. (Later TRW, Inc.) to pursue development of monopropellant and bipropellant rocket engines.
[2] In 1963, TRW introduced the MIRA 150A as a backup for the Thiokol TD-339 vernier thruster to be used in the Surveyor probes, and started development of the Apollo Lunar Excursion Module's Descent Propulsion System.
[2] In parallel with those projects, TRW continued development of other pintle engines, including by 1966 the URSA (Universal Rocket for Space Applications) series.
[2] In 1972 the Apollo Descent Propulsion System ended production, but starting in 1974, and continuing through 1988, the TR-201, a simplified, low cost derivative of it, featuring ablative cooling and fixed thrust, was used in the second stage of the Delta 2914 and 3914 launch vehicles.
[2] In the early 1980s, a series of design refinements were applied to the pintle injector obtaining exceptionally fast and repeatable pulses on command and linear throttling capability.
[2] Starting in 1981, a very compact, 8,200 lbf N2O4/MMH engine employing this feature was developed as a pitch and yaw thruster for the army's SENTRY missile program.
[2] A further refinement of the face shutoff injector was used on the Army Strategic Defense Command's Exoatmospheric Reentry-vehicle Interceptor Subsystem (ERIS).
This feature, called FSO (Face Shutoff Only) greatly improved overall thruster response and significantly reduced engine size and mass.
As part of the Air Force Brilliant Pebbles program, TRW developed a very small 5 lbf (22 N) N2O4/hydrazine thruster using a pintle injector.
This radiatively-cooled engine weighed 0.3 lb (135 grams) and was successfully tested in August 1993, delivering over 300 seconds Isp with a 150:1 nozzle expansion ratio.
[2] The preceding technology innovations enabled the first exoatmospheric kinetic kill of a simulated reentry warhead off Kwajalein atoll on 28 January 1991 on the first flight of ERIS.
For gelled propellants to be used on a rocket, face shutoff is mandatory to prevent dry-out of the base liquid during off times between pulses, which would otherwise result in the solids within the gels plugging the injector passages.
