SLS ‘racing stripes’ replaced with photogrammetry targets
Dulles, Virginia-based Orbital ATK has cast 10 solid rocket booster (SRB) segments for NASA’s Space Launch System (SLS). Four of those segments have been completed at the company’s facilities in Promontory, Utah, and painted with photogrammetric markings. Two five-segment boosters will be used to help power the super-heavy-lift vehicle into orbit as early as 2019 – but what happened to the rocket’s “racing stripes”?
Ultimately, all completed motor segments will be shipped to NASA’s Kennedy Space Center in Florida to be integrated with the forward and aft booster structures and SLS core stage.
The black-and-white, checkerboard-like targets on the outside of the structure will be used as “targets” for cameras to locate the distance between the spacecraft and another target. This procedure is called photogrammetry, which is the science of using photography to help measure distances between objects.
Targets will also be located on Orion, the SLS core stage, the interim cryogenic propulsion stage, the interior of the launch vehicle stage adapter, and on the mobile launcher to easily track the vehicle’s position by fixing on black-and-white checkerboard targets.
Engineers are also interested in measuring the booster nozzles’ clearance from the mobile launcher and the entire vehicle’s clearance from the mobile launch tower after liftoff.
“Booster separation is influenced by several factors – their length, the configuration of the separation motors and the timing of separation,” said Alex Priskos, SLS systems engineering and integration manager, in a news release. “The longer separation is delayed, the greater the clearance will be. However, waiting longer adversely impacts performance. Our job is to balance these factors.”
If everything continues as NASA plans, the SLS and Orion will integrate diverse types of checkerboard patterns for photogrammetry onto the rocket’s upcoming flights.
“The big squares will be used to measure general vehicle motion and ground clearances,” said David Melendrez, Orion’s lead for imagery integration at NASA’s Johnson Space Center. “Smaller checkerboards and elongated markings will be used to measure more complicated three-dimensional motions of the boosters relative to the core stage during their separation, about two minutes into the spaceflight.”
Engineers designed the SLS using 3-D software models and analysis. However, Beth St. Peter, SLS imagery integration lead, said that as accurate as those models are, photogrammetry will provide what she calls “truth data” on separation events and other key points of the mission.
“For the first flight of SLS, gathering this real-world data on how the vehicle performs compared to the models is crucial,” St. Peter said.
Although NASA has used this type of technology since the days of the Saturn V rockets in the 1960s and 1970s, and during the Space Shuttle era, the technology has advanced to be able to place digital imagery systems on launch vehicles.
“Designing and building these deep space exploration vehicles is an evolutionary process,” Priskos said. “In the beginning, you define a mission and basic architecture to take you where you want to go. The details might be a little fuzzy at first, but gradually, like a camera zooming in closer and closer, those details are revealed. This is where we are with SLS and Orion.”
Heather Smith's fascination for space exploration – started at the tender age of twelve while she was on a sixth-grade field trip in Kenner, Louisiana, walking through a mock-up of the International Space Station and seeing the “space potty” (her terminology has progressed considerably since that time) – she realized at this point that her future lay in the stars. Smith has come to realize that very few people have noticed how much spaceflight technology has improved their lives. She has since dedicated herself to correcting this problem. Inspired by such classic literature as Anne Frank’s Diary, she has honed her writing skills and has signed on as The Spaceflight Group’s coordinator for the organization’s social media efforts.