It wasn't a big headline story, but the SLS program ran a couple of tests in the last week in an effort to keep the program alive. We know from talk essentially since Trump's inauguration that he has not been a fan of the program. During talk about how the Artemis moon landings ought to happen, we learned that the administration wants to end SLS after just three launches, while the preliminary text of a bill making its way through Congress would extend it to five flights.
For the second time in less than a week, NASA test-fired new propulsion hardware Thursday that the agency would need to keep SLS alive. Last Friday, a new liquid-fueled RS-25 engine ignited on a test stand at NASA's Stennis Space Center in Mississippi. The hydrogen-fueled engine is the first of its kind to be manufactured since the end of the Space Shuttle program. This particular RS-25 engine is assigned to power the fifth flight of the SLS rocket, a mission known as Artemis V.
Then, on Thursday of this week, NASA and Northrop Grumman test-fired a new solid rocket booster (SRB) in Utah. This booster features a new design that NASA would use to power SLS rockets beginning with the ninth mission, or Artemis IX. The motor tested on Thursday isn't flight-worthy. It's a test unit that engineers will use to gather data on the rocket's performance.
The new SRB is referred to as BOLE for Booster Obsolescence and Life Extension. While the test of the new production liquid fueled RS-25 apparently went as planned, the solid rocket booster self-destructed in under two minutes, less time than it's supposed to run. You can watch it in this video that's set to start within 10 seconds of the explosion. A strange appearance before the engine bell disappears is visible at 22:12 on the time line. Few seconds later a large blast is visible.
We've covered this material many times, but the RS-25 engines leftover from the Shuttle era are running out and the replacements are prohibitively expensive (a two-word description of the entire SLS).
Recognizing that shuttle-era parts will eventually run out, NASA signed a contract with Aerojet Rocketdyne to set the stage for the production of new RS-25 engines in 2015. NASA later ordered an initial batch of six RS-25 engines from Aerojet, then added 18 more to the order in 2020, at a price of about $100 million per engine. NASA and its contractor aim to reduce the cost to $70 million per engine, but even that figure is many times the cost of engines of comparable size and power: Blue Origin's BE-4 and SpaceX's Raptor.
Some old data that I've posted before says the BE-4 engines cost less than $20 million each while SpaceX is working to push the similarly powerful Raptor rocket engine costs even lower, to less than $1 million per engine. Yes that means for four engines of the same power as the RS-25, SLS is running $400 million, BE-4s cost $80 million and I'll just say SpaceX is cheaper still and I won't go with the $4 million number implied there.
An engineering evaluation booster exploding is not an indictment of the SLS program, but it's not a very good thing, either.
An uncontained plume of exhaust appeared near the nozzle of an SLS solid rocket booster moments before its nozzle was destroyed during a test-firing Thursday. Credit: NASA
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