Northrop Grumman test fires first GEM-63XL motor for ULA’s Vulcan

by Justin Davenport

The first GEM-63XL motor for the ULA Vulcan Centaur’s strap-on boosters was successfully test-fired for approximately 90 seconds, sending 449,000 lbs of thrust along with bright fire, loud noise and vibration into the sunny desert sky on Thursday at Northrop Grumman testing facility in Promontory, Utah.

The QM-1 was the first of two test firings required before the GEM-63XL is used in operational missions on the new ULA Vulcan Centaur, which has recently won a number of critical US Space Force launches under the National Security Space Launch contract, and which will replace the long-serving Atlas V beginning with its scheduled first flight in 2021.

The GEM-63XL fired today was conditioned to a temperature of 40 degrees Fahrenheit to test the motor’s performance in cold conditions. Ballistic, insulation, nozzle plug, igniter insulator performance and ablative nozzle performance, erosion and plug measurements were taken with 192 instrumentation channels, and these were the main qualification objectives.

Additional objectives included vibration, acoustic, and heat data, motor axial elongation and radiative heat monitoring data. The cold conditioned test was done first as it is the most taxing test of the motor and its systems, including the fixed, non-steerable nozzle.

The GEM-63XL ahead of its test – via NG

The next test firing, VM-1, will be the validation motor and it will be hot-conditioned to a temperature of 90 degrees Fahrenheit. Its objective will be risk mitigation for the US Space Force by finishing a second test before the GEM-63XL flies.

The GEM-63XL at 865 inches in length is longer than the GEM-63 qualified for flight one year ago, and the XL will use a pointed nosecone as opposed to the blunt curved nosecone that is currently used on the AJ-60A and that will be used on the GEM-63.

The XL’s nozzle exit cone diameter is 60 inches and its propellant mass is 105,497 lbs as opposed to a 58 in exit cone and 97,195 lb propellant mass for the GEM-63 tested previously. Also as Northrop Grumman Vice President of Propulsion Systems Charlie Precourt stated, “The GEM 63XL increases thrust and performance by 15-20 percent compared to a standard GEM 63.”

The GEM-63 family is not only 3 inches wider than the GEM-60 (used on the Delta IV), it is also much longer, and the GEM-63XL tested today is the largest monolithic composite solid rocket casing that NGSS has ever produced. The biggest challenge that the widened and lengthened GEM booster posed for NGSS was building a new casting pit which was required due to the length of the booster.

The casing is spun at the NGSS facility in Clearfield, UT, which is south of Promontory and Ogden, and other prep work is done at the Promontory and Bacchus facilities (in Magna near the Oquirrh Mountains, well south of Clearfield) before the final assembly is done and the rocket booster is sent on its way to the launch site, using a large wheeled transporter as part of the process.

The GEM-63 and GEM-63XL have been developed as a response to SpaceX’s disruption of the space launch market, to help lower costs and increase performance for the ULA Atlas and Vulcan launch vehicles, as ULA and others need to control costs to stay competitive in the new era.

Sixty GEM-63/63XL rockets have been ordered, 30 for each program, as of 2018. One booster per day will be shipped to launch sites when the process is in full swing, and production has already begun. Configurations of two, four, and six GEM-63XL boosters are planned for Vulcan Centaur launches, along with the base rocket with no solid boosters.

Vulcan heading uphill with four boosters – as envisioned by Nathan Koga for NSF/L2

The Northrop Grumman Space Systems unit and its Propulsion Systems Division have drawn on a heritage of six decades of work on solid rocket motors ranging from the Sidewinder to the Minuteman, the Shuttle, the Castor and earlier GEM graphite-epoxy motors and are one of two solid rocket production companies in the United States now.

The GEM-63 and GEM-63XL are some of the latest solid rocket motors to be built and tested at the Promontory facility in the Utah desert, and these boosters will help power Atlas and Vulcan launch vehicles into the next decade.

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