A spectacular test is scheduled for today at Orbital ATK’s Utah rocket facility where the world’s largest solid rocket booster (SRB) will be fired. NASA has all the pieces in place for its return to human spaceflight in the coming years with the Space Launch System (SLS), but all those pieces still need to be tested before any people will be strapped in. This will be the second such test, the first having taken place back in 2015.
The test is expected to happen at 10:05 AM eastern time today, June 28th. The NASA live feed is embedded below so you can catch all the action when the Qualification Motor 2 (QM-2) lights up.
The SLS boosters are based on the SRBs that flew on the Space Shuttle missions. Like those boosters, these are designed to be jettisoned from the craft after they’re spent. The QM-2 has a fifth segment that wasn’t present in the Shuttle boosters, allowing it to carry more fuel. The 177-foot rocket can put out 3.6 million pounds of thrust, which is more than 75% of the SLS’ total power at liftoff.
Solid rocket boosters like the QM-2 are required for heavy lift vehicles like the SLS. This differs from a rocket like the standard Falcon 9, which is designed to deliver small payloads into low-Earth orbit — it can manage that with just liquid fuel. SRBs can provide a huge amount of thrust for a short time, but unlike liquid-fueled engines, they can’t be turned on and off. Once they ignite, they burn until all the fuel is gone. The QM-2 engine has a way to vary power output even without a throttle, though. Each segment is cast in a different shape that changes the burn rate, thus altering the thrust.
NASA says there are 82 design objectives for today’s launch, and more than 530 instrumentation channels will be monitored to make sure the QM-2 booster hits all of them. The test will last two minutes, the length of time the SRBs will fire for a SLS launch. This will all take place on the ground, with the SRB locked into place so it can be studied after.
One of the main goals of this test is to validate the booster’s operational temperature range. The 2015 test checked how the SRB worked at the top of that rage — 90 degrees F. Today’s test requires the booster be cooled to 40 degrees F with giant air conditioning units. It took weeks to cool the booster to the necessary temperature, and Orbital ATK took it past that to just 25 degrees F. The cooling will stop shortly before launch, allowing the temperature to come up to the desired 40 degrees.
If this and other SLS-related test go as planned. The first unmanned flight of the full launch vehicle could take place in late 2018. The Space Launch System should carry astronauts in the early 2020s.