Northrop Grumman’s Propulsion Systems Division has completed the first of a series of Flight Support Booster (FSB) tests of the NASA Space Launch System’s solid rocket motors, a series that will last as long as the SLS program exists. The FSB-1 booster will help NASA and Northrop Grumman evaluate new materials for use in future boosters and new manufacturing processes as well as current manufacturing quality, to support missions beyond the Artemis 3 human lunar landing scheduled for 2024.
The test, completed at the T97 test area at Northrop Grumman‘s facility in Promontory, Utah, took place on Wednesday, September 2, 2020, at 1:05 PM Mountain Daylight Time (19:05 UTC). A single five-segment SLS solid rocket motor with a thrust of up to 3.6 million pounds was ignited, and burned for approximately two minutes.
One new material being tested is a new cleaning solvent that is being evaluated for use on future SLS booster nozzles. On August 6th of this year, a sub-scale 24 inch solid rocket motor with a representative nozzle using the solvent was test-fired at the Marshall Space Flight Center in Huntsville, Alabama, and the program used the test results to confirm that it will be tested on a full scale SLS booster. As the manager for motor and booster separation motor systems at Marshall, Tim Lawrence, noted “This 24-inch motor test is to evaluate the material in a solid rocket motor environment and make sure that we don’t get any unexpected changes in how it performs”.
As rocket programs continue, product refinements are often developed and introduced, and new processes and technologies are tested on sub-scale solid motors first. If test data supports continued development, the next step is testing on a full flight support booster like the one tested on Wednesday. Depending on the results of the FSB test, the new process or technology can be used on future flight boosters. The Space Shuttle program used similar tests to refine the SRB over time from the early 1980’s to nearly the end of the program, and to test modifications to the system after the 1986 Challenger disaster.
The Flight Support Booster is cast and produced on the same production line as the Artemis boosters, using the same methods and personnel. The booster’s propellant, a mixture with fuel and oxidizer particles mixed in to a substance with a rubber-like consistency, is cast in large mixers at the Promontory site. The steel SRB casings, which have flown on Shuttle missions in the past, are cleaned and prepared to receive the propellant mixture, and the propellant is poured in and cured in a large autoclave. Once the segments are finished, they are stored until Northrop Grumman is ready to stack them for the test.
Preparations for the FSB-1 test firing began in March. The first segment was placed in the test bay in April, and the fifth and final segment was installed in June. The booster is assembled in a building at the test stand and readied for the FSB test, with hundreds of channels of telemetry available to record data and parameters.
The FSB-1 booster was then conditioned to cold temperatures desired for the test in the weeks leading up to the test. Targeting between 60 and 70 degrees Fahrenheit, this stresses the system more than a warm test. After a siren sounds at T-1 minute the booster is fired in a horizontal position with the plume climbing up a hillside, turning the nearby soil into glass. The sound and shockwave can be heard and felt for miles. After the booster shuts down, a Carbon Dioxide system quenches the fire to preserve the state of the booster at burnout, and the test data is evaluated.
Ignition! SLS booster static fire test. Two minute test.
Earth's rotation about to get a boost. pic.twitter.com/dig2WbVHPu
— Chris Bergin – NSF (@NASASpaceflight) September 2, 2020
The FSB-1 test is the sixth ground test of a full scale SLS solid rocket booster, following three development test firings and two qualification test firings. Meanwhile, at the Kennedy Space Center in Florida, the boosters for the maiden flight of SLS, Artemis 1, are being assembled in the Vehicle Assembly Building. That mission will launch an uncrewed Orion spacecraft to lunar orbit.
The SLS solid rocket motor and booster is based on the Space Shuttle SRBs, but with five 300,000 pound segments weighing instead of four segments as used on the Shuttle boosters. Two SRB’s generate 75 percent of the thrust the SLS needs to launch its payload into orbit, with the other 25 percent is provided by four liquid fueled RS-25 engines, better known as the Space Shuttle Main Engine (SSME). These SRB’s are not equipped with parachute recovery systems due to cost and weight considerations, and are disposed of in the ocean at the end of their flight.
The SLS booster is the most powerful solid rocket booster developed to date, and NASA has issued a contract to Northrop Grumman to purchase long lead items for six sets of SLS SRB’s beyond Artemis 3, with the contract lasting through 2030, to allow for up to nine SLS missions to be flown. The Artemis lunar landing and Europa Clipper programs are currently scheduled to use the Space Launch System to launch their respective spacecraft in the coming decade, including the first human lunar landing since Apollo 17 in 1972.