It’s ALIVE!!!!! For the very first time, the Falcon Heavy has successfully lit all 27 of its mighty Merlin engines in preparation for its maiden launch. Once it flies, the Falcon Heavy will be the most powerful rocket currently in operation.
SpaceX does a hold down test of all their rockets called a static fire and today we’re going to give you a quick rundown on what that is, how it works, and why they do it.
Let’s get started!
Now that Falcon Heavy has successfully gone through static fire, hopefully we’ll have a more concrete date on the calendar for it’s maiden launch. Elon Musk even tweeted “Falcon Heavy hold-down firing this morning was good. Generated quite a thunderhead of steam. Launching in a week or so.”
But meanwhile, I’ve had a lot of questions about static fires.
SpaceX likes to test stuff. Like, all of the stuff. As a matter of fact, SpaceX avoids using anything that can’t be tested beforehand, like pyrotechnics or explosive bolts and tends to rely on hydraulics and things that can tested out before the launch.
This philosophy is repeated throughout the company and testing their engines and rockets as a whole is no exception. SpaceX has fired their workhorse Merlin engines over 5,600 times to date. That’s a lot of a data.
Considering they’ve built hundreds of these engines, SpaceX has learned the limits of the Merlin very well and feels confident that testing ensures no errors in manufacturing and doesn’t cut into the lifespan of the engine any more than planned.
Don’t forget, the Merlin engine is designed to eventually be reused for several launches, and SpaceX has continually evolved the engine to last longer and be more powerful as well.
They first test fire each engine on its own at a test stand in McGregor, Texas to make sure there are no issues in manufacturing. They will often test the single engines for the full duration of the mission, so about 2 and a half minutes for the Merlin 1D and 6 to 8 minutes for the Merlin 1D vacuum engine.
Then they take the engines back to their headquarters and manufacturing plant in Hawthorne, CA to be integrated onto the bottom portion of the rocket, known as the octaweb.
The octaweb is then mated to the rest of the first stage core which is then shipped back out to McGregor, Texas via a semi for a long duration static test fire. They hold the rocket down via massive hold down clamps and perform around a one minute test fire. Occasionally you may see them use a cap with cables for additional support if they need to test the vehicle longer.
Remember, the rocket weighs a lot when fully fueled! So at first, the clamps only need to hold the difference between the weight of the rocket and the thrust of the rocket engines. But as the rocket burns up fuel, it gets lighter and the load on the clamps increases.
Once they’re sure everything is in good working order, they then ship the core out to its launchpad, either launch pad 39A at Kennedy Space Center in Florida, Space Launch Complex 40 at nearby Cape Canaveral Air Force Station or at Space Launch Complex 4 at Vandenberg Air Force Base in California.
Once the rocket is at the launch site, they mate the first stage with the upper stage and do one more shorter static fire on the launch pad to ensure everything is in good working order, including ground systems, the vehicle and the procedures. These static fires tend to last anywhere from 3 seconds to 7 seconds. And although the video from SpaceX’s official tweet made it appear as though the static fire was only around 6 seconds, more continual shots make it appear to be closer to 11 seconds.
This practice is fairly unique to SpaceX, but some other vehicles have done static fire tests such as the Space Shuttle and Orbital ATK’s Antares. Other companies, occasionally perform a wet dress rehearsal which is everything but the firing of the engines.
The Falcon Heavy went through several wet dress rehearsals leading up to its actual static fire. Remember, there’s a lot of new things at play here, so practicing how to synchronize loading three first stage cores, and checking the alignment and loads probably took a decent amount of tweaking to get to where they’re very confident with the procedure.
Testing hardware this often is a little different philosophy than others in the space industry. As a matter of fact, there’s some things that just simply can’t be tested before they’re used in space because they can only be used once.
My favorite and most terrifying example, is the engine that got astronauts off of the moon. That’s right, the ascent engine on the Lunar Module Ascent Stage known as the APS could only be used once because the fuel and oxidizer were so corrosive the engines had to be rebuilt after each firing.
That means every engine that got astronauts off the moon had not been test fired before flight!!! It’s one and only use was the life or death ignition on the surface of the moon. YIKES.
So in regards to the Falcon Heavy static fire, there’s a few things we need to note. First off, each of the three cores of the Falcon Heavy were already tested at McGregor on its own, just like a standard Falcon 9. But seeing as there’s three times as many things to fuel, check and ignite, there’s a lot of new procedures taking place.
One of these procedures is the fact that the Falcon heavy doesn’t actually light all 27 engines simultaneously.
It was assumed that the Falcon Heavy would stagger the ignition of its engines, similar to how the Space Shuttle staggered ignition of its RS-25 main engines. Something you could only see in high speed film. But that’s yet to be confirmed and they may have performed a different procedure during for the static fire.
It appears as though the side cores were actually first followed soon after by the center core as a way of staggering the ignition.
They do this so the engines don’t create too much torque thrust along the octawebs. The engines are lit two at a time a few milliseconds apart from one another.
After static fire, the remaining fuel is then pumped out of the vehicle, rechilled and recycled for next time.
With SpaceX having static fired and launched so many vehicles, they’re continually trying to speed up the process to be both more automated and quicker. Since the Falcon 9 and Falcon Heavy uses super chilled propellants, there’s only a short window of time where the vehicle will operate within its full potential. As the fuel and oxidizer warm up, they decrease in density which in turn decreases the performance of the rocket.
The desire to speed up propellant loading, and decrease preparations is what led to the AMOS – 6 pad anomaly on September 1st, 2016. SpaceX used to do the static fires with the payload on top, which was seen as a good way to reduce launch preparation times since they didn’t have to integrate the payload after static fire.
If you want to know more about what went wrong during the Amos 6 pad anomaly, I suggest you watch Scott Manley’s awesome summary on the event.
Static fires have a time window just like a launch and nearby roads are blocked off. Personnel are kept miles away in case of an accident. The eastern range run by Cape Canaveral Air Force Station makes sure there are no boats and planes within the exclusion zone for a static fire as well.
Static fires. Like a launch, minus the let go part. One step closer to the first flight of Falcon Heavy! I CANNOT WAIT!
Just a quick one today. Let me know what questions you may have leading up to the inaugural launch of Falcon Heavy! Will you be at the Cape to see it fly? You’d better believe I’ll be there!
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That’s gonna do it for me, I’m Tim Dodd, the Everyday Astronaut, bringing space down to Earth for everyday people.