Northrop Grumman is set to conduct the first test firing of its Booster Obsolescence and Life Extension (BOLE) five-segment solid rocket motor at its Promontory production and test site in Utah. The DM-1 test is scheduled for Thursday, June 26, at 11:00 AM MDT (17:00 UTC) and will last for just over two minutes, burning over 1.4 million pounds of propellant.
The BOLE motor is intended for use on the Block 2 version of NASA’s Space Launch System (SLS) rocket, beginning with the Artemis IX mission. Featuring unpainted composite casings with copper wiring wrapped around them for protection against lightning, the booster will generate over 3.9 million pounds of thrust upon ignition and will burn for approximately two minutes and 20 seconds. Sensors will monitor hundreds of parameters using 757 channels of data, and a water quench system will help to save the booster after its firing.
The motor, mounted on its side, is held down by a large concrete block, which prevents it from moving forward. All test motors for the program are processed in an assembly building enclosure that is moved away from the motor prior to the test.
The motor differs from the flight booster in that it does not contain the flight avionics, recovery system, and separation devices that the flight booster will utilize. In addition, while the unpainted casings have a bluish cast due to the copper wiring, the flight boosters will be painted white.
Northrop Grumman’s test objectives for the DM-1 test firing are to demonstrate the full-scale ballistic performance and characteristics of the BOLE design, including pressure, thrust vs. time, ignition characteristics, erosive burning, pressure drop, and burn rate. Motor insulation and nozzle ablative performance will also be studied, along with thrust vector control, composite case, case joints, joint seal performance, and environmental conditions.
After the firing is complete, regardless of the result, engineers will thoroughly analyze all the data obtained. This is the first of two development motor tests scheduled for BOLE. The DM-1 test will see the motor cooled to 60 degrees Fahrenheit to test response in ambient conditions. Other tests will assess BOLE’s performance in cold and hot conditions, assuming SLS Block 2 remains a part of the Artemis program.
Graphic detailing improvements in BOLE boosters compared to legacy RSRMV boosters SLS currently uses. (Credit: Northrop Grumman)
The BOLE booster’s casings are made out of carbon-fiber composites rather than steel, which is used for the existing Shuttle-era SLS booster casings. BOLE is not simply an existing SLS booster with carbon-fiber casings, however; in many ways, it is a new booster.
For one thing, the BOLE booster is slightly larger than the SLS’s legacy Redesigned Solid Rocket Motor-V (RSRMV) boosters, standing 47.5 m tall and 3.8 m in diameter as opposed to RSRMV’s 46.9 m height and 3.7 m in diameter.
The nozzle is redesigned, with a diameter of 4.4 m, as opposed to the 3.9 m diameter of the RSRMV nozzle. The BOLE nozzle, made of composite material with brown glass phenolic material, also includes a 0.6 m extension.
The first composite case wound for the BOLE process simulation article. (Credit: NASA)
BOLE boosters were designed to increase specific impulse by 3.9% and total impulse by 11% compared to existing five-segment boosters, allowing Block 2 to add three metric tons of payload capacity compared to the upcoming Block 1B version of SLS.
To offer higher performance, BOLE boosters will utilize upgraded hydroxyl-terminated polybutadiene (HTPB) propellant, as opposed to the polybutadiene acrylonitrile (PBAN) propellant currently used on solid boosters. BOLE boosters will also operate at a maximum operating pressure of 1330 pounds per square inch absolute (psia), compared to the RSRMV’s 1016 psia. The changes give BOLE boosters more thrust compared to the RSRMV’s 3.6 million pounds of thrust.
In addition, while the BOLE DM-1 test motor’s casings are made of IM7/T300 carbon fiber used in the company’s prior projects, future BOLE casings, starting with the DM-2 motor, will be made out of newer T1100 fiber.
Artist’s impression of the Block 2 SLS launching with the BOLE boosters. (Credit: NASA)
This change enables the casings to be thinner, reducing mass and enhancing vehicle performance. Northrop Grumman offered NASA two paths for BOLE: use fiber and production methods the company was familiar with from past experience, or use the new T1100 fiber. NASA opted for the latter path.
BOLE boosters will also utilize electronic thrust vector control (TVC) mechanisms to steer the motor’s nozzle, rather than the current hydraulic TVC system, reducing complexity and eliminating the use of hazardous materials. A new systems tunnel, improved booster-to-core stage attachment and separation systems, new internal insulation, and other enhancements are also included with the new booster.
A new aft skirt will be compatible with the cylindrical launch mount on the under-construction Mobile Launcher 2 (ML2) at the Kennedy Space Center. The skirt will be lighter, as it will not need to support loads through four vehicle support posts, unlike the current SLS boosters.
Artist’s depiction of Northrop Grumman’s now-canceled OmegA rocket. (Credit: Northrop Grumman)
The BOLE booster’s improvements are an outgrowth of the canceled OmegA program, which was started when Orbital ATK was competing for business in the National Security Space Launch (NSSL) program. SpaceX’s Falcon family and United Launch Alliance’s Vulcan were ultimately selected by the U.S. Space Force, eliminating the need for OmegA.
The OmegA program advanced as far as solid motor tests at Promontory, using the same infrastructure as SLS boosters, before the NSSL winners were announced. OmegA was designed to utilize composite casings, and the composite casing motors were tested alongside the eTVC and several other improvements now being incorporated into BOLE.
The BOLE motor’s first segment was finished in early 2024, and the other segments were finished earlier this year. The next BOLE motor will start production using the same factory infrastructure involved in producing Shuttle and SLS hardware. Legacy booster hardware for Artemis IV and V is also under production in these same buildings.
The first segment of the first BOLE test motor after being finished in early 2024. (Credit: Northrop Grumman)
As for the BOLE program’s future, there is uncertainty due to the Trump Administration’s planned budget cuts for NASA. One of these cuts involves ending the SLS program after Artemis II and III, meaning that SLS Block 1B and Block 2 would never fly.
Congress recently proposed reversing enough of the cuts to allow, at least, Artemis IV and Artemis V to fly, thereby allowing Block 1B to fly. Since the BOLE boosters are not needed until Artemis IX, it is unlikely BOLE will fly before the 2030s, if at all. BOLE’s continuation as a program depends on enough of a reversal of budget cuts to continue with all planned Artemis missions.
Regardless of what happens to NASA’s budget in the coming months, the BOLE test will enable Northrop Grumman to gain more insight into its design and maintain the option for future SLS flights after the program exhausts its previously produced steel casings.
(Lead image: The BOLE DM-1 motor before its scheduled test firing on Thursday, June 26, 2025. Credit: Northrop Grumman)
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