SLS upper stage test article arrives at NASA Marshall
NASA’s Space Launch System (SLS) has taken another step in its preparation for a projected 2018 launch with the arrival of the rocket’s upper stage Structural Test Article (STA). The United Launch Alliance (ULA)-built Interim Cryogenic Propulsion Stage (ICPS) STA arrived at NASA’s Marshall Space Flight Center (MSFC), after a short barge trip from ULA’s facility in Decatur, Alabama.
The STA will undergo a battery of structural load tests later this year to validate the hardware can tolerate launch stresses, with certain stresses being measured at 125 percent of design requirements. The unit will be placed in a vertical stress stand, which will be capable of applying flight-like loads on the hardware, simulating conditions the STA is expected to encounter from launch through stage jettison.
Though seemingly similar in appearance to the Delta Cryogenic Second Stage (DCSS), which is used on ULA’s Delta IV rocket, there are some significant differences between it and the ICPS.
Firstly, the stage’s liquid hydrogen (LH2) tank has been extended by 18 inches, giving a capacity of 19,250 U.S. gallons (11,300 pounds) of the cryogenic fuel. The liquid oxygen (LOX) tank remains unchanged in volume, as it had enough overhead in its DCSS configuration to support the necessary 5,700 U.S. gallons (54,000 pounds) of the cryogenic oxidizer required for the ICPS.
During the testing and validation process, the tanks will be filled with liquid nitrogen (LN2)—rather than the more volatile LH2 and LOX—to approximate the sub-zero temperatures the hardware will encounter on an actual flight without unnecessarily risking personnel or hardware.
Other differences from the DCSS go beyond the basic structure: the ICPS will have its own flight control software and avionics hardware, which will integrate with the SLS’ overall flight control package. However, since the avionics and software packages aren’t germane to a structural load test, they were not included on the STA.
Additionally, the stage’s propulsion unit—Aerojet Rocketdyne’s RL10B-2 engine—is also not included on the STA.
The ICPS will provide the thrust required to push NASA’s Orion spacecraft to destinations beyond low-Earth orbit. Once spent, the ICPS will be jettisoned and Orion will make use of its own service module (SM) propulsion for other maneuvers.
Though other structural test articles for SLS hardware have been built, the ICPS STA is the first to be fully-fitted with a suite of test instrumentation and is ready for its testing as-is.
Once testing begins, NASA’s Cataldo Mazzola said that each suite of tests will generate greater than one terabyte of data from the more than 800 channels being analyzed.
Beyond gearing up to test the ICPS, MSFC is also preparing to test every major SLS assembly: the LH2 and LOX tanks from the core stage, the Orion Stage Adapter (OSA), the intertank, and the Launch Vehicle Stage Adapter (LVSA), just to name a few. Data from these tests will be integrated into computer models, providing a high fidelity—albeit simulated—testing environment.
While the ICPS may be subjected to a multitude of stress tests, it may only fly on a single mission: EM-1. Congress has stipulated that NASA not spend any funds to crew-rate the ICPS and instead focus on preparing the Exploration Upper Stage (EUS) for the first crewed mission, EM-2, which currently targeting launch in the 2021–2023 time frame.
Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.