A Closer Look at SLS Avionics
Lifting off the launch pad with over 8 million pounds of thrust and reaching space soaring at speeds of almost 25,000 miles per hour in just over 8 minutes requires more than power — it requires brains.
The huge hardware being built for NASA’s new 322-foot-tall deep space rocket, the Space Launch System (SLS), often grabs the spotlight, but the “brains” of the rocket — the avionics and software that will guide the rocket’s flight — direct all that power.
Avionics are the electrical systems necessary for flight and are driven by software to tell the rocket where it should go, and how it should pivot the engines to keep on the right trajectory. To achieve this, a spacecraft actually has several “brains” distributed throughout its various components. All systems communicate with each other as well as with the Orion spacecraft avionics and command systems.
Flight Computers – During SLS’s first eight minutes from liftoff to separation of the 212-foot-tall core stage from the in-space stage and NASA’s Orion spacecraft, the main brains controlling the world’s most powerful rocket are the flight computers located in the core stage. The three flight computers guide the rocket’s flight and each processes data to decide what the rocket will do. Two of the three computers must work perfectly at all times — one cannot function alone. The SLS flight computers communicate with other avionics for the four RS-25 engines and the two solid rocket boosters, which provide the thrust to launch SLS and Orion
Engine Flight Controllers – Each RS-25 engine has a new “brain,” a flight controller that communicates with core stage flight computers to ensure engines are performing at needed levels. Aerojet Rocketdyne qualified the new engine controllers during hot-fire testing and assembled the four engines, which are ready to be installed on the core stage.
Booster Avionics – At liftoff, two five-segment rocket boosters will provide 80 percent of the thrust for the first two minutes of flight. The booster avionics, receiving commands from the flight computers, provide 80 percent of the control authority for the rocket during the first 2 minutes of flight.
Core Stage Avionics – The avionics units on the SLS core stage work with the flight software to perform various functions during the first 8 minutes of flight. Some control the navigation, some communicate with Orion and some control how the engines perform. These other parts of the rocket’s “nervous system” include the redundant inertial navigation unit, responsible for the rocket reaching its destination, the power system that serves as the “heart and blood” of the rocket body, and the sensors and effectors that tell the rocket what to do — much like your sensors tell you to pick up a pen or remove your hand from a burning stove.
Final Assembly and Testing Before Launch
The engines and boosters have completed qualification testing and testing is underway for the core stage. Qualification signifies crucial electronic components have been tested to operate through the harsh lift-off and flight environments with system margin. Key interactions confirmed during booster qualification testing included the ability to initiate booster ignition, control the booster during flight, and terminate flight, and triggering core stage separation.
For the core stage, technicians at NASA’s Michoud Assembly Facility in New Orleans are testing the flight computers and all the SLS avionics after they are placed in parts of the stage. Later, these will be tested along with the engine controllers during a full-up test of all four RS-25 engines. The booster avionics will be delivered to NASA’s Kennedy Space Center where they will be installed in the booster and functionally checked out before launch.
Technicians at Marshall’s systems integration laboratory are currently checking out the avionics systems for the entire rocket to verify they can all “talk” to each other, to Orion and to ground control computers and work properly to give SLS the direction it needs for a successful first mission. Almost identical avionics boxes in the lab simulate the flight computers and other avionics in the booster and in the core stage. The flight software that runs the systems is checked out by flying thousands of simulated flights in a variety of expected and abnormal conditions that put both the software and the rocket’s avionics through the paces to confirm it is ready for spaceflight.
Meanwhile, Orion and ground systems in Kennedy Space Center’s firing room are checking out electronics and power systems and working with SLS on integrated testing, so that on launch day, all the brains are synched up and ready for the first mission: Exploration Mission-1.
