Saturday, August 15, 2015

Mars is just a little bit closer now...

What follows is a tale told by an idiot, full of sound and fury, signifying...well...quite a lot, actually.

On a hot August day in coastal Mississippi, NASA and Aerojet Rocketdyne tested an engine which will help power America's next great rocket - the Space Launch System (SLS) - to destinations beyond low Earth orbit...something that no crewed vehicle has accomplished in more than 40 years. But first, a bit of exposition is in-order.

After the retirement of the Space Shuttle in 2011, and the cancellation of the nascent Constellation program shortly after that, many considered NASA to be 'dead'. In fact, I've spoken with several people who ardently believe that NASA was shut-down after the Shuttle program ended. Nothing could be further from the truth.

While it is true that no crewed launches have occurred from US soil since the Shuttle was 'put to pasture' (which is a shame...and perhaps a topic for a later blog entry), lack of manned flights does not equate to NASA being a moribund agency. The dynamics of spaceflight have changed in a relatively short time. No longer are rockets the domain of deep-pocketed governments - private companies are now competing to take cargo and crew to low Earth orbit and the Internal Space Station (ISS) is now host to many non-governmental experiments.

Where does that leave NASA if not to launch astronauts to the ISS? Exploration, that's where...and that's the purpose of SLS - to be an exploration-class vehicle to take humans back to deep space, and to destinations which were the domain of fanciful dreams just a few generations ago. In order to do that, hardware must be tested...and re-tested...and tested again. That testing and validation were the driving forces behind Thursday's test.

Complete RS-25 assembly.
Photo courtesy Aerojet Rocketdyne.
Not your grandfather's rocket engine
Though the RS-25 engine is essentially the same as the Space Shuttle Main Engine (SSME), there are some significant differences, key of which is the engine's "brain" - the controller. Many years have passed since the initial design of the SSME...and while it may have received an occasional update over the life the Shuttle, SLS required something a bit...'smarter'.

Aerojet Rocketdyne had been testing a modernized variant of the Saturn-era J-2 engine (the J-2X), which was to be used in the now-canceled Constellation program...and was in contention to be used as the upper-stage engine for SLS. Though down-selected in favor of the RL10, the modern controller from the J-2X could be modified to work on the RS-25.

Beyond testing the new controller, the engine will also be running at higher thrust levels than it did during the Shuttle's tenure...and the cryogenic propellants will reach the engine at a colder temperature and higher pressure. Though fully capable of pushing more power than it did on a Shuttle flight, engineers desired to not do so as the engine would be subject to greater 'wear and tear'...and since it was meant to be a reusable engine, that additional stress would result in higher costs.

However, since SLS isn't going to be reusable (other than, perhaps, the Orion crew capsule), engineers are comfortable pushing the engine harder, with each of the four engines producing approximately 550,000 pounds of thrust.

RS-25 in testing conditions on the stand.
Photo courtesy Aerojet Rocketdyne.
These go all the way to '111'
With the engines now projected to deliver 111% of the original design's thrust, a mighty roar was sure to be heard across the bayou of southern Mississippi. To quote a good friend: "Any day that NASA gives you ear plugs is pretty much guaranteed to be a good day."

This was to be my second static engine test, the first of which was for the upgraded Solid Rocket Booster (SRB) in Utah earlier this year. At that event, we were warned to not look directly at the exhaust plume. Thinking that the 2.5 kilometers between us and the booster should be sufficient to attenuate the blinding brightness, I chose to look at the exhaust. Ouch - the light...IT BURNS! I think I had spots on my vision for the next hour or so.

So, since NASA had seen fit to provide us with earplugs, I was not going to question the need for hearing protection - the plugs were inserted as soon as ignition time neared. Though I heard no countdown, certain visual clues indicated the time was near...well, that and the clock inched towards 4:00 PM, which was when the test was supposed to occur.

I guess you just had to be there
Through the cushioned protection of the earplugs, the engine roared to life with a mighty 'WHOOSH!' followed by a loud, sustained crackle and roar and cloud of steam. Nothing I've ever done in life could've prepared me for the visceral experience this engine test would be. Even the SRB test in Utah paled in comparison to the symphony of sight, sound, and feeling from the RS-25. While the SRB was a distant 2.5 kilometers away (about 8,200 feet), the RS-25 would be a scant 1,200 feet away.

While my expectations for sight and sound from the event were easily surpassed, I was wholly unprepared for the FEELING of the engine. Every crackle and thump from the engine was accompanied by a tangible pressure wave. I could feel it in my chest...I actually *saw* shirts flutter in concert to the waves...and this was only one engine! Imagine the cacophony which will accompany the four engines from core stage's full-burn test in two year's time.

I don't know if you watched the event live, or if you have since seen replays like the one below, but there is nothing - NOTHING - that can compare to the experience of being there. I am truly sorry that I lack the skill to convey the wash of emotions and feelings that I felt with this test. Yes, it was that impressive.

What's next?
NASA and Aerojet Rocketdyne will analyze the data from the test, and perform a few more tests and should wrap-up design validation before the end of this year. After that, the next big event will be the core stage 'green fire, which will be all four flight engines firing at once - something that hasn't happened at Stennis Space Center since the days of Apollo.

SLS is a big deal. It's big for's big for America...and, yes, it's big for humanity. The successful test brings us one step closer to the moon, to Mars, and beyond. I don't know about you, but I'm excited. The rumors of NASA's death have been greatly exaggerated. Not only that, but I think the agency's most incredible accomplishments may still be ahead of us.