LOX-kerosene, LOX-Methane or LOX-Alcohol

The XCOR XR-5K18 is the LOX-Kerosene main rocket engine which will power the XCOR Lynx to the edge of space. The first iteration of the 5K18 was test fired on December 15th, 2008 at XCOR's facilities in Mojave, California.

Like all of XCOR's engines, the XR-5K18 has demonstrated the ability to safely and reliably stop and restart using XCOR’s proprietary spark torch ignition system.  Its regenerative cooling system allows it to run for indefinite periods without maintenance and disassembly.

Our 5K18 engine produces between 2900 lbf thrust while burning a mixture of liquid oxygen and kerosene. It has design and performance characteristics similar to a previous XCOR engine, the 4K14, which had a full test and flight history as the X-Racer engine. This made the 4K14 an ideal model on which to base the Lynx engine. 

4K14 engine on test stand

4K14 engine in the X-Racer

The primary differences between the 5K18 and 4K14 design are:

  • The 5K18’s chamber pressure and thrust are approximately twice the power of the 4K14
  • The 5K18 has a nozzle extension to optimize specific impulse and thrust at higher altitudes
  • While both engine chambers are regeneratively cooled by kerosene, the 5K18 has additional coolant loops for the nozzle extension.

Based upon prior XCOR intellectual property, XCOR and Alliant Techsystems Inc. (ATK) Tactical, Propulsion and Controls Division, GASL Operations was awarded a NASA contract to design, build, and test a 33 kN (7,500 lbf) LOX/methane pressure-fed engine. This engine was subsequently designated the XR-5M15.

In total, the XR-5M15 demonstrated a series of forty three hot fire tests at our Mojave facilities. Applications for the 5M15 include returning manned space vehicles from Lunar orbit and Mars to the Earth, and performing in-space maneuvering.

The approach was a rapid design, build and test of a workhorse main engine based closely on relevant design features from our previous engine programs. The 5M15 program built upon XCOR's existing 3M9 LOX/methane engine, as well as our 1,800 lbf 4K5, 10,000 lbf 5M12 design, and 400 lbf 4A3 EZ-Rocket engines.

This main engine development uses several features from the 3M9, including the same augmented torch electrical ignition system and the propellant combination.

Relevant features of the 4K5 engine include the igniter geometry, the torch spark igniter, and the fuel cooling configuration. While the 5M15 uses many of the same 4K5 component designs, we changed the fuel, lowered the chamber pressure, and increased the size.

The XCOR 5M12 engine study was the closest configuration of the main engine. It was developed for a DARPA program through to layout design, but not built. The DARPA contract enabled XCOR to develop the methane cooling analysis tools, which have also been used with the 3M9 engine runs.

The 5M15 engine has many relevant features that are shared with XCOR’s FAA licensed manned vehicles, the EZ-Rocket and the X-Racer.
The regeneratively cooled “workhorse” engine served several purposes. It validated the key engine design elements, including the regen-cooled chamber/throat assembly, the stability and performance of the injector, and the reliability of ignition. It incorporated a number of design features for safety and reliability, critical for human-rated application that were demonstrated on previous XCOR engine designs. Finally, it is a modular design, which facilitated rapid test of new components during development, and enabled modification for future NASA Exploration applications.

In June of 2000, after we had concluded tests of our proprietary oxygen/alcohol igniter, we began work on a 160 lbf liquid oxygen and isopropanol engine, which we ran in October of the same year. Following successful tests of this engine, known as the XR-3A2, in November 2000 we started to design and build the regeneratively cooled 400 lbf LOX/alcohol engines that we eventually integrated into a Long-EZ airplane, which became our EZ-Rocket aircraft.

400 lbf LOZ-Alcohol firing

The XR-4A3 engines went through multiple acceptance tests before the first flight of the EZ-Rocket on July 21, 2001.  Early flights on engines 101 and 102 quickly lead to design improvements, and serial numbers 103 and 104 powered 20 of the 26 flights of the EZ-Rocket.

EZ-rocket in air

The flight test program passed its first milestone by flying with both engines for an engine run time of 96 seconds, and a total flight time of five minutes and twenty seconds. Later flights achieved burn times of up to 2.5 minutes, altitudes to 11,500 feet, and the point-to-point distance record for a rocket-powered vehicle.

Specific impulse of this engine is higher than either LOX/alcohol engines in the Bell X-1 and the Redstone.

The fact that two 4A3 engines powered an aircraft safely, reliably, and routinely multiple times proved the viability of civilian rocket-powered aviation. Routine operations must be the primary criterion for rocket engine development. The XCOR approach is to build safer and more reliable rocket engines first, then progress to the higher performance needed for orbital launch vehicles.

Dock with

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