Falcon Heavy

December 22, 2017 In Featured NEWS SPACEX

Written by Tim Dodd The Everyday Astronaut, With contributions from Everyday Astronaut Patreons

Edited by Allyson Cornish

Falcon Heavy. It’s ALMOST HERE! When it flies, it will be the most powerful and highly anticipated rocket of the 21st century.

SpaceX will be attempting the ultimate feat in rocketry, strapping three orbital class boosters together to form a heavy lift vehicle. As if that weren’t enough, the Falcon Heavy will be attempting to land ALL THREE of its massive first stages boosters, 2 by land one by sea.

SpaceX first announced the Falcon Heavy in 2011 saying the vehicle would be ready to launch in 2013… So why exactly has it taken 5 additional years to develop a rocket that’s essentially just 3 Falcon 9’s strapped together?

Well, we’re going to dive into what all has changed since the 2011 announcement including what specific hardware and technology had to be developed. We’re also going to compare the Falcon 9 to the Falcon Heavy in a side by side comparison and explain just why exactly there’s so much more to the Falcon Heavy than just strapping three Falcon 9’s together. Let’s get started!

 

Now that we’re closer than ever to seeing the Falcon Heavy fly, the excitement is THROUGH THE ROOF. For the past four years, SpaceX has been claiming the Falcon Heavy is only 6 months away, but for once, we’re WELL within that!

In case you didn’t know, all the hardware for Falcon Heavy is sitting inside the hanger at Launch Pad 39A at Kennedy Space Center. YES. This means Falcon Heavy exists. For the first time in its long history, it’s not a paper rocket!  Elon Musk even revealed the payload of the Falcon Heavy, and I have to rub it in, I WAS RIGHT!!!!

 

Although I’ve kind of been half-joking for the past couple years, it still blows me away that this truly is the payload. A midnight cherry Tesla Roadster… And not just any Tesla Roadster, but Elon’s personal roadster at that! And to top it off, it’s not just going to space, it’s going to MARS.

Let’s give you a quick history rundown of how the Falcon Heavy came to be and how it’s changed over the years.

Despite Elon mentioning a Falcon 9 Heavy at the Mars Society way back in 2008, SpaceX didn’t reveal their official plans for Falcon Heavy until April 5th, 2011 at a news conference in Washington, DC. Here, Elon Musk announced his ambitious timeline for Falcon Heavy…

At the time, SpaceX’s plans were to have three Falcon 9 cores put together to form a heavy lift launch vehicle. The Falcon Heavy would be able to put 53,000 KG or 117,000 pounds into orbit. This is enough to launch a fully loaded 737 into space! It would have 16,900 KNs or 3.8 million pounds of thrust coming from 27 of their Merlin engines…

The Falcon Heavy was also to be touting propellant cross-feed which means the outer cores were to be continually topping off the center core, so once the side boosters were empty, the center core would still be full which maximizes Delta V and payload mass.

Elon also announced the price, a shocking $80 million to $125 million dollar price tag per mission. This would be the cheapest ride to space, beating out the competition by 4 to 10 times when it comes to dollar per kg ratio.

An interesting note was how often Elon foresaw the Falcon Heavy flying, claiming it would be flying about as often as Falcon 9, with each of the vehicles hopefully seeing about 10 launches per year. According to their estimates, the Falcon Heavy filled a gap in the market that the Falcon 9 was currently unable to fulfill. More on that later…

Before we continue with how the Falcon Heavy wound up changing so much beyond this, we need to look at how the Falcon 9 evolved since then to gain some insights on how SpaceX’s continual evolution of their Falcon family is a different philosophy than traditional aerospace companies.

I don’t want to get super deep into the history of specific changes to the Falcon 9 since I’ll be covering that in another post, but let’s just do a quick rundown on the major changes the Falcon 9 has experienced since the announcement of the Falcon Heavy.

When Falcon Heavy was announced in April 2011, the Falcon 9 had only flown twice. Back then, the Falcon 9 was a much smaller vehicle. The entire version 1.0, including the 1st stage, 2nd stage, and payload, was almost exactly the same size as only the first stage of today’s Falcon 9, version 1.2.

Version 1.2 has almost 50% more thrust than version 1.0, they’ve added landing legs, grid fins, nitrogen thrusters, super chilled propellant and stretched the tanks of both stages… SpaceX was very busy tweaking the Falcon 9 in just 20 flights!

So already, just by looking at how much the Falcon 9 has evolved, two things become clear. First off, some of the missions Falcon Heavy was slated to fly could now fly on the much upgraded Falcon 9 such as Inmarsat-5 F4 and Intelsat 35e which both flew in 2017.

The other thing is SpaceX realized the Falcon 9 still had so much maturing to do, it seemed silly to put all the research and development into the Falcon Heavy if the core of the vehicle wasn’t mature yet. Obviously, the SpaceX team knew about the future of the Falcon 9, something that in hindsight clearly led to delaying the Falcon Heavy from becoming concrete early on.

This pivot is the opposite of the sunk cost fallacy. This is perhaps the biggest paradigm shift in SpaceX’s philosophy compared to more traditional aerospace companies. This approach allows SpaceX to be nimble enough to evolve with their rocket and not say “well we’ve already put this much effort into Falcon Heavy, let’s just fly it as is.”

Imagine if they had invested in committing to launching a Falcon Heavy based on version 1.0 of the Falcon 9… All of the engineering development on the loads and stresses would be out the window, let alone recovery hardware would’ve been non-existent. So it’s clearly the right move to wait until their Falcon 9 was more mature.

So let’s move on to what things actually had to be developed for Falcon Heavy. What exactly do we know is new with Falcon Heavy that’s unique compared to the Falcon 9?

First off, we keep saying the Falcon Heavy is essentially 3 Falcon 9’s strapped together… so what exactly holds the three cores together? Well here’s a fun word for you, LONGERONS! The Falcon Heavy is held together by 8 relatively thin rods that hold the entire vehicle together. Four at the top of the boosters and four at the bottom of the boosters.

There are also 4 additional supports that tie the centers of each core together, again, 2 at the top and 2 at the bottom for a total of 12 supports.

Longerons might be more commonly known as struts…. Especially if you’re familiar with Kerbal Space Program! MOAR STRUTS!!!! A few common examples of rockets with obvious longerons are the Space Shuttle and ULA’s awesome Delta IV Heavy.

Back to the Falcon Heavy, the four Longerons let go of the tops of the boosters first and then tuck in tight against the fuselage of the center core while the two side boosters begin to peel away from the center core.

The four longerons at the base are tied into the octawebs of all 3 cores which means they carry the bulk of the load. They will release after the top of the side cores tilt away from the center core. SpaceX is against using pyrotechnics since they can’t be tested before the launch. They want things to be testable, repeatable and most importantly, reusable. This means SpaceX tends to rely on hydraulics for all these moving parts, so get ready to see some awesome shots of them in work.

Another fairly obvious aspect is the loads the center core will encounter. Don’t forget, the Falcon Heavy can loft a payload around three times heavier than a standard Falcon 9, so this means the stresses through the core of the vehicle, including the second stage and the payload adapter could be three times as high too.

SpaceX had to carefully redesign the entire center core to deal with these heavier loads. It’s fairly safe to say there’s not as much in common with the center core of the Falcon Heavy and a standard Falcon 9 as you may think. Consider the center core has an entirely different interstage, a different octaweb, and the fuselage needs to handle much higher loads, there’s a lot more engineering involved than just swapping out a few parts.

Another thing that might not be as obvious is the grid fins. The side boosters of the Falcon Heavy have a more aerodynamic nose cone compared to the interstage of the Falcon Heavy center core or a standard Falcon 9. This means the grid fins actually have less control authority due to the aerodynamic properties of having less drag at the tail end of the falling rocket… remember when it comes back down, the nose cone is now the tailcone.

 

We first saw the next generation titanium grid fins on the Iridium NEXT launch which took place June 25th, 2017? To date, that was the only launch SpaceX launched with an upgraded titanium grid fins so far. Beyond preparing them for their upcoming block V version of Falcon 9, SpaceX was just testing their work to make sure these could be used for Falcon Heavy as well.

Here’s a shot of the two grid fins side by side. We can see there’s a much larger surface area to the titanium grid fins that are used on the outer cores. The titanium grid fins also feature “bear trap” serrated leading edges. These help break up the shockwave that would normally occur on the leading edge of the grid fin. Typically when the vehicle is transitioning from supersonic to subsonic, otherwise known as the transonic region, gridfins become less effective because a shockwave forms within the lattice structure and the air flows around it instead of through it. These serrated gridfins do the trick to allow for greater control during this otherwise dicey period.

In a funny side note, when researching this particular topic, I found out there’s ENTIRE BOOKS about the aerodynamic analysis of lattice grid fins in transonic flow, such as this book titled, “Aerodynamic Analysis of Lattice Grid Fins in Transonic Flow“!!!

One more fun aspect I wanted to make sure we mention is the fact that SpaceX essentially got nearly 2/3rds of the rocket for free in a sense. The two sidecore boosters are previously flown and recovered Falcon 9 boosters. One of the boosters is from CRS-9 which flew July 18, 2016 & the other from Thaicom 8 which flew on May 27th, 2016. The two side cores were lightly refurbished and outfitted with everything necessary to transition from being a Falcon 9 to a Falcon Heavy side core.

Since the side cores don’t have to deal with the same loads as the center core, they didn’t have have to make any major changes to the fuselages. Considering how risky the Falcon Heavy launch is, the fact that SpaceX was able to use two previously flown boosters is probably another reason they waited so long to make Falcon Heavy happen. Prior to December 22nd, 2015, there just simply hadn’t been any reflown boosters in existence… and now they have over  a dozen!

Remember how earlier I mentioned plans of propellant cross-feed in the initial announcement? Well, unfortunately, Elon mentioned that they are currently not pursuing cross-feed with Falcon Heavy, although they may pursue it later. This is most likely due to the 50% increase in thrust SpaceX has been able to squeeze out of the Merlin engines. They’re already increased the performance of the vehicle drastically and they just simply don’t need propellant cross-feed. Besides that, Falcon Heavy is plenty capable until SpaceX gets their next generation rocket, the BFR online.

Let’s move onto what the biggest risks Falcon Heavy encounters for its first launch.

Let’s start with the biggest elephant in the room… igniting 27 orbital class engines at once… Those of us familiar with spaceflight history may have flashbacks to the last time a rocket tried to fly with so many engines. The massive and ludicrous N1 rocket. The N1 was the Soviet Union’s counterpart the United States’ Saturn V moon rocket. The first stage had 30 NK-15 engines which were all lit simultaneously.

The N1 launched 4 times… All four ended with massive fireballs, and some blasts were so big, it shattered windows 6 miles away. So what’s changed since 1972 and today that ensures the Falcon Heavy can safely manage 27 engines?

Well, a lot. But take for example the fact that SpaceX has fired the Merlin engine over 1,000 times and they have only experienced one Merlin engine fail in flight… so they’re working with a much more mature and robust engine as well as much more advanced engine control systems.

Also, don’t forget, 27 engines, although a lot, isn’t that much more than the 20 engines on the Soyuz rocket. The Soyuz is one of the most reliable and most flown rockets in history. So… I don’t think they’re getting too far out there on this one.

While we’re talking about 27 engines lighting at once, we need to be pedantic for a minute. Technically, they won’t actually light simultaneously. They will need to stagger the ignition of the engines so the instant torque thrust doesn’t rip the octawebs apart. This might be something we can’t even see in real time, but on high speed, I’ll bet they’ll catch the staggering of the ignition. I’m excited to see if we can catch it on the maiden launch, or maybe we’ll get a sneak peak with footage from the static fire when it occurs!

Another major risk is the vibrations of having 27 engines chugging along at full thrust. The three cores have a total a total of 22,819 kilonewtons or 5.13 million pounds of thrust at liftoff. Shortly after liftoff the center core engines are throttled down. After the side cores separate, the center core engines throttle back up.

Despite being able to model these vibrations in highly accurate computer simulations, there’s nothing like the real thing. This is simply one of those where SpaceX hopes they over engineered the Falcon Heavy enough to compensate for the unknowns.

Another major unknown is the stresses the vehicle will experience at Max Q, or the point of maximum aerodynamic pressure. These forces, although fairly well understood, will be entirely new for Falcon Heavy. Again, there’s been wind tunnel testing, computer models and the like, but there’s nothing like the real thing. If the Falcon Heavy makes it through Max Q, I would consider it a success.

But there’s one more major portion of flight that will be unique to the Falcon Heavy compared to the Falcon 9. Booster separation. Now we’ve already talked about how the longerons that hold onto the side boosters will let go, but there’s still a lot of unknowns here. This will certainly be another major pucker moment. If the two boosters separate cleanly, I will be cheering so loud… I’m not sure I’ll be able to handle it.

Booster separation will happen a little earlier than stage separation of a standard Falcon 9. At this point the two side boosters will turn around and head back to LZ-1 and LZ-2 at Cape Canaveral where they’ll land virtually simultaneously. Again, when this happens, I’m going to have to try so hard to contain myself. This will be a sight to see.

Despite the lack of propellant crossfeed like we mentioned earlier, the center core will throttle down during ascent so it has propellant remaining to give an additional boost to the second stage. Most likely, depending on the profile of the mission, this means the center core will always be too far down range to ever do a return to launch site landing or RTLS as its known.

Mostly likely, the center core will be landing on a drone ship very far down range, potentially much further down range than a standard Falcon 9.

Once there’s stage separation of the center core and the second stage, the second stage will continue along much like a standard Falcon 9 and put the payload into its intended destination. And for the demo mission, the intended destination is Mars!

So what do you think about Falcon Heavy? Are you as excited as I am about it? Are you skeptical it will work and never fly again? Well I want to hear from you. First take the poll to let me know if you think it’s maiden’s flight will be a complete success, or a complete failure, or somewhere in between. Personally, I actually think it’ll be a complete success on the maiden flight, but hey, that’s me… forever an optimist…

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Thanks everybody that does it for me. I’m Tim Dodd, the Everyday Astronaut. Bringing space down to Earth for everyday people.






Allyson Cornish