The Falcon 9. The world’s FIRST reusable rocket. Wait. No it’s not. Do you remember the Space Shuttle? It had those solid rocket boosters and the orbiter, which were both reusable weren’t they?
Well, today we’re going to talk about why the Space Shuttle failed to actually be reusable and wound up being described with a more accurate word, refurbishable. People often cite the shortcomings of the Space Shuttle and are quick to point it to SpaceX’s claims of the Falcon 9 booster being reusable.
So today we’re going to look at what it took to get the space shuttle operational between flights, what it takes to get a Falcon 9 operational between flights, and why SpaceX’s first stage boosters take much less of a beating than the Space Shuttle.
We’ll also do a quick reminder of what technologies SpaceX added to their Block 5 booster to hopefully achieve their goal of making a rapidly reusable rocket that can truly be reused 10 times before needing serious refurbishment.
Let’s get started!
Reusable is definitely the hot buzz word in the new space industry. If you don’t know why a vehicle being reusable is such a massive game changer, may I suggest checking out my video “Why does Falcon Heavy matter” to help get a good perspective on why reusability matters.
But long story short, the margins to get stuff to space are so thin it takes a massive rocket to put anything substantial up there. So unfortunately there’s just little margin left over to add additional hardware to make a rocket reusable.
This makes spaceflight extremly extremly expensive. As in, so expensive we’re hoping to someday see costs come down to JUST $1,000 per KILOGRAM!!! Yeah… imagine those shipping costs in down here on Earth.
“Yes, hello, I’d like to order a new set of tires for my Hyundai Elantra, I’ve been way too busy doing some super cool drifting. Great, $400, what’s the shipping? $36,000?!?!?!? WHAT?!”
And that would be a STEAL compared to the historically astronomical prices of getting space hardware into space. Even the cheapest $ to KG ratio is around the $3,000 per KG thanks to the Falcon 9 and Falcon Heavy. It’s a good thing rocket delivery isn’t the standard here on Earth.
So, here’s where reusability comes in. It’s honestly fundamental. Of course! Why throw away super expensive multi million dollar engines and massive fuselages when you could just reuse it right? Well that was the original idea behind the space shuttle.
Believe it or not, NASA was seeking a reusable launch vehicle before we even put humans on the moon. The original studies began in 1968, some 10 months before Neil Armstrong famously took the first steps on the moon.
As a matter of fact, one of the first people to fly the space shuttle, John Young was walking on the moon when he got news of the shuttle. He was quite excited, proclaiming:
“The country needs that shuttle mighty bad.”
So with all the excitement leading up to the shuttle, fast forward 50 years to today and the space shuttle suddenly has kind of a bad taste in our mouths. It wound up being terribly expensive, dangerous, and actually more expensive than about any other rocket system, granted it could things that no other rocket system could do too.
So… with some of the greatest minds working on the shuttle, why did it fail its promise of bringing the cost down? Is SpaceX doomed to repeat history or has a lot changed in 50 years?…
So first, let’s look at the recovery methods of each system. They’re quite different…
The Space Shuttle utilized both parachutes and a lifting body to recover hardware. Let’s go in order of what was recovered, so starting with the Solid Rocket Boosters which were jettisoned around 2 minutes into flight.
The boosters separate while traveling around 4,800 km/h or 3,000 mph, at an altitude of around 45 kms or 30 miles. Due to their velocity, they do continue to coast upward to their highest point of around 65 kms or 40 miles. Just a fun note, that means the SRBs never actually make it to space… keep that in mind here.
The boosters fall back through the atmosphere and start popping a sequence of parachutes at exactly 4,786 meters or 15,704 feet. Eventually after a pilot chute, and a drogue chute the three main parachutes deploy and splish splash the booster down relatively softly in the ocean.
The orbiter on the other hand is traveling much much faster and its recovery, like all orbital things, is a lot uhhh hotter.
About an hour before touchdown, the orbiter turns around and faces away from its direction of travel or retrograde. It fires up its orbital maneuvering system or OMS and slows down 1%… yup. That’s it, 1% and that’s enough to lower its orbit from about 480 k/m or 300 miles down to just 45 kms or 28 miles!
The orbiter then turns back around so it can reenter at about a 40 degree angle. Now it’s time for the atmosphere to do its work. The orbiter is absolutely cruising at this point. Still traveling around 27,000 km/h or 17,000 mph, the orbiter begins to hit air molecules and starts to build up compressed air and a TON of heat.
The orbiter will reach temperatures of 1650 degrees celcius or 3,000 degrees fahrenheit!!! Ouch. Luckily, the orbiter is covered with 4 different types of thermal protection.
It has reinforced carbon-carbon on the leading edges, then there were between 24,177 and 31,088 tiles, depending on the orbiter, on the underside and front of the vehicle, white nomex blankets on the upper payload bay doors, the upper wing and fuselage, and a few white surface tiles for low temperature areas.
For 12 minutes, the shuttle had so much hot ionized gases surrounding the vehicle, it caused a full radio blackout. Eventually, after minutes of atmospheric drag and some computer guided S-turns, the shuttle bleeds off a lot of its velocity. Once it’s about 40 kms or 25 miles downrange, the commander drops the nose to minus 20 degrees, almost 7 times steeper than a commercial airliner and 20 times faster.
Finally the shuttle lands like a traditional jetliner, only a little quicker, touching down at 350 km/h or 220 mph on a 4.5 km or 2.8 mile long runway. So long in fact that there’s over 1 and a half meters or over 5 feet in relative height between the ends of the runway due to the curve of the Earth!
Wow, that’s quite the journey! Welcome home!!!
So now, let’s do a quick rundown on how a Falcon 9 is recovered. I’ve covered this topic a few times more in depth, so if you have any questions remaining, check out my video “How SpaceX lands the Falcon 9”
At around 2:40, the Falcon 9 shuts down its main engines called MECO or main engine cut off. It coasts for a moment and then the first stage lets go of the second stage for stage separation.
At this point, the Falcon 9 is traveling as fast as 8,000 km/h or almost 5,000 mph and at an altitude of 65 kms or 40 miles. Quick note, this is about twice as fast as the space shuttle’s solid rocket boosters. Again, more on this later.
The first stage quickly performs a flip maneuver with its nitrogen thrusters to point its engines prograde. Then, depending on the mission, the booster may ignite 3 of its engines and do a boost back burn if it’s going to land back land.
But there might not be enough margins left over to do the boost back burn. In that case it’s omitted and the Falcon 9 continues on its ballistic trajectory away from the launch pad and heads towards the drone ship that’s precisely placed based on each mission profile.
But in either case, the booster will coast up to its highest point, typically over the karman line or 100 kms or 62 miles. In other words, the booster gets to hang out in space for a minute or so! Lucky.
Around 55 kms or 34 miles in altitude, the Falcon 9 will light up three of its 9 merlin engines as it reenters the atmosphere. It does this to slow itself down AND to create a literal forcefield around itself so it can survive reentry.
After around 20 seconds of reentry burn, the booster scrubs off 30 to 40% of its velocity, which is enough to withstand the remaining heat as the atmosphere gets thicker and thicker.
The atmosphere will then take off another 60 to 70 percent of the remaining velocity until the booster is only traveling about 1,000 km/h or 620 mph. Then it lights up one or three of its merlin engines to perform the final landing burn which needs to be perfectly timed.
Even with just one of the 9 engines running at its minimum throttle, the booster still has too much thrust to hover. So if the vehicle stops before it’s on the ground, it will actually start going back up… uhhhh… yeah.
This needs to be perfectly timed in a maneuver called a hover-slam or suicide burn. Then the landing legs deploy and the Falcon 9 softly touches down. Well, hopefully.
YAY! So now we have a 15 story tall rocket out on a ship the size of an American football field. A little robot called the octograbber goes out, grabs onto it to secure it so this doesn’t happen… and it gets towed back to port to get ready to fly again. Or if it was a booster that landed back at the cape, they just lift it up, put it on a truck and get it ready to fly again.
So before we move on, let’s really quick remind you why the Falcon 9 doesn’t use parachutes like the Space Shuttle’s SRBs did. Well there’s a few reasons, and I’m just going to breeze through these since I’ve done a video about this and need to probably do a more dedicated video about it in the future.
So here’s Everyday Astronaut’s top 7 reasons why SpaceX doesn’t use parachutes to land the Falcon 9!!!
1: SpaceX tried to use parachutes on the first two Falcon 9 missions to recover the booster. Unfortunately, the booster is going about twice as fast as the SRBs and the parachutes couldn’t survive the extra forces.
2: The rocket already has engines capable of slowing down, why not use them? Does a helicopter need a parachute to land? NO it has an engine and propeller silly!
3: You can’t land a large rocket on Mars or the moon with a parachute, the atmosphere is too thin or non existent. So you’d better start practicing propulsive landings and get good at it now!
4: The rocket needs to slow down before it hits the atmosphere to survive reentry anyway. Remember that whole reentry burn thing? Yeah, a parachute can’t work before it’s in the atmosphere, so… rocket engines are the only way.
5: Parachutes and the supporting system would just add otherwise dead weight.
6: Parachutes, although steerable, are not nearly as precise as grid fins, cold gas thrusters and an engine gimbal. SpaceX is finding this out the hard way as they try to catch their fairings under steerable parafaoils.
7: Splashing down is bad mkay. Salt water and precise liquid rocket engine don’t mix very well…. So that’s actually a great place to transition…
Ok, so now that we recovered the reusable parts of the Space Shuttle and the first stage of a Falcon 9, what did they do to prepare them for reflight. Let’s start off with the Space Shuttle. What did it take to get one back to the launch pad?
After splashdown, the boosters were sealed up by scuba divers with a giant plug where they drained the water so it could be towed back to Kennedy Space Center.
Each booster required a crew of 18 for their ocean recovery. The Space Shuttle obviously had 2 boosters, so that’s 36 people on booster recovery.
Then the boosters are disassembled and sent to Promontory, Utah to be cleaned, paint stripped, repainted, inspected and reloaded with solid propellant.
Then they go back to Kennedy Space Center for assembly at the United Space Alliance Assembly and Refurbishment Facility. I like the name of that place.
The four segments in each booster are then mated to a new igniter, forward segment, nose cap, aft skirt and frustum. So basically just the casing was actually truly reused. *cough* I think refurbished is the right word considering they were stripped down to bare metal each time and taken to a place called the refurbishment facility…
So the boosters definitely weren’t what I’d call reusable… but how about the orbiter? What’s it look like to get that reflying?
After touching down, a highly trained crew of 150 people and 25 specially designed vehicles head out to intercept the vehicle. They do safety checks for explosive and toxic gases, helped the crew exit the orbiter and eventually tow it to the Orbiter Processing Facility.
Once inside the 2,700 square meter or 29,000 square foot hangar, the shuttle would be processed for approximately 125 days. More than 115 multi level platforms would surround the vehicle so engineers could check 6 MILLION PARTS. SIX MILLION PARTS!!!!
But first technicians would don hazmat suits to drain the vehicle of any remaining toxic and hypergolic elements. Then they would remove the Orbital Maneuvering System pods and the Forward Reaction Control Systems modules to be repaired and retested.
Then crews would take off all three of the space shuttle’s main engines, or RS-25’s. These babies are still incredible engines, some of the most efficient engines ever made. But they required a healthy amount of inspection and refurbishment between each flight.
Each engine had 50,000 parts and about 7,000 of which were life limited and occasionally replaced. In 2002, Kennedy Space Center took over assembly tasks of the engines instead of sending them out for refurbishment.
But perhaps the biggest and most daunting task of the Space Shuttle was inspecting the thousands and thousands of fragile silica tiles on the bottom of the orbiter. There were between 24,177 and 31,088 tiles, depending on the orbiter. Every single one was unique and had to be carefully inspected and if damaged, replaced.
And of course, all the avionics, payload bay, hydraulic control surfaces etc etc were carefully checked out between each flight as well. In total, the Space Shuttle required no less than 650,000 hours of labor between each flight.
650,000 HOURS. Say the average person made $25 an hour, which I’m sure is conservative for highly trained technicians, the cost of human labor to get a space shuttle ready for launch would be around 16 million dollars! And again, that’s being fairly conservative.
But it wasn’t always this way. Actually, before the challenger accident in 1986, the shuttle went through much less refurbishment and checks. So few in fact, it may have seen as little as 1% the amount of labor hours between flights…
But after the challenger accident, NASA changed the entire process of getting the space shuttle flight ready and wound up going over every inch with a fine tooth comb.
And lastly, after 1989, the shuttle was placed on the Orbiter Transfer System, a 76 wheel transporter to take it from the OPF to the Vehicle Assembly building to be mated with the external tank and solid rocket boosters.
Fun fact, SpaceX now owns the Orbiter Transfer System to transport their boosters!
Alright, now time for the big question. What does it take to get a Falcon 9 booster back to the launch pad?
Let me start off by saying a lot of this is speculation since SpaceX doesn’t make public exactly what goes into preparations, but let’s give a rundown on what they have done, and what things they will be doing.
Well first off, just like the SRBs on the shuttle or the orbiter itself, the Falcon 9 needs to be transported. If it landed at sea, it’s transported back by a support crew of around 10 and two ships.
If it’s landing on land, the booster is picked up by a crane and put onto their transporter.
For the first few years of Falcon 9 re-use, the boosters were shipped back to Hawthorne for the refurbishment. But SpaceX is building a booster refurbishment facility at the cape.
The first booster to ever land on December 21, 2015 for the OG2 mission, was extensively torn down and inspected. Since this was the first booster SpaceX “caught”, they had to check their work and see how it actually came out.
On the first 13 reused boosters, or non block 5 boosters, we know SpaceX changed out the heat shields and blankets behind the exhaust nozzles, we know they had to fix and repair the grid fins on “extra hot missions”, we know they have to do a full inspection of each vehicle. They also run an X-ray along the booster to ensure the fuselage is still good to go.
I’ve heard speculations between 5,000 to 10,000 human hours of labor for the turnaround of the Block 3 and block 4 boosters. Say this is terribly conservative. Say it’s actually 100,000 hours of labor, that’d STILL be over 6 times less labor than the Space Shuttle Orbiter.
The Falcon 9 has substantially less systems to check than the orbiter… so I think it’s very safe to assume there’s less labor hours required to prepare it for reflight. We know SpaceX has a goal with their new Block 5 Falcon 9 to see it land and refly within 24 to 48 hours with “Nothing but inspections and checks” between flights.
The overall goal of their new block 5 booster is to be reflown 10 times without any actual refurbishment, only inspections. They built Block 5 having learned lessons from the 24 recoveries leading up to block 5.
If you need a reminder of what’s new with block 5, I have this video all about what block 5 is and what changed.
A quick list of things that are new with block 5 is a thermal protective coating on the whole booster, a liquid cooled heat shield by the engines, a bolted octaweb, 8% increase in thrust on the first stage, upgraded retractable landing legs, titanium grid fins, an upgraded COPV 2.0 and a ton of tweaks that allow it to be more reusable and even most importantly, rated for human flight.
So how can the Falcon 9 booster actually be reflown without refurbishment? Can it? What’s so different about the Falcon 9 and the space shuttle?
Well let’s first compare it to the SRBs and see what it does differently.
First off, the SRBs splashed down in salt water. That’s not really a good thing. Solid Rocket Boosters are also basically giant empty canisters that are loaded up with a rubber like solid propellant between each flight.
This is different than a liquid rocket engine that has say tens of thousands of parts each. If a liquid engine were to be submerged in salt water, I don’t think it’d be a good thing.
So right there is probably the biggest thing, having a booster land on dry land or a dry ship deck, is a huge leg up as far as reusability and refurbishment goes.
As a matter of fact, the SRBs were so expensive to refurbish, in the long run, it was more expensive to bring them back, tear them down and all than it was to just build new ones.
So why is the Falcon 9 booster more reusable than the orbiter?
Well first off, the orbiter was not only a rocket, it was also a spaceship that carried up to 7 people. So a lot of work and check outs went into the cockpit, interior, payload bay etc etc, let alone the actual rocket engine portion of the orbiter.
The RS-25 engine, although amazing and eventually refurbished on-site, still required an awful lot of work to fly again.
The Merlin 1D engine that SpaceX has developed has been fired over 5600 times, and is designed to be reflown and reused over and over with minimal inspections. How much, we don’t really know… but more on that in a second
But perhaps the biggest difference between the Falcon 9 booster and the space shuttle orbiter is the velocity in which each one reenters.
Let’s compare the velocities of the SRB, the Falcon 9 first stage and the orbiter to help understand why each one uses their given reentry system.
The SRBs never exceeds 4,800 km/h and it also stays lower in the atmosphere so it doesn’t require any kind of slow down before it reenters, well because it never really exited in the first place.
The Falcon 9 on the other hand goes from up to about 8,000 km/h down to as low as 5,000 km/h in order to survive reentry using its retropropulsion. But it’s safe to say it will never see much more than 8,000 km/h.
The orbiter reenters at speeds of up to 27,000 km/h but it slowly bleeds a lot of speed off in the upper atmosphere.
Wow. Those are some pretty big differences in velocity…
Since the Falcon 9 booster reenters at “only” 8,000 km/h it experiences up to almost 40 times less heat compared to the orbiter. WHAT? How can this be?!
Well, since the first stage of the Falcon 9 only gets up to at most about 1/3rd of orbital velocity, it receives much less than just 1/3rd of the amount of heat.
The compressed gas on the leading edge of the vehicle will see heat increase by velocity squared but the thermal energy transferred to the rocket goes as velocity cubed!
So that means if a vehicle is traveling 4 times faster, the bow wave in front can get 64 times hotter! So that’s 4 times faster, times 4 (squared) times ANOTHER 4 (cubed) so 64!
This is an oversimplification BUT this is why the space shuttle needed those carbon carbon leading edges and the silica tiles all over the surfaces of the vehicle to protect it during reentry.
Not only that, but the Falcon 9 also does an a pretty significant retropropulsion burn before it reenters to ensure the vehicle can survive. The space shuttle didn’t do any of this because it relied on its large surface area to slowly bleed the speed off for several minutes.
As a matter of fact, the shuttle spent almost 10 times the amount of time radiating heat off through re-entry, which is the key to how its non-ablative heat shield worked.
So long story short. The first stage is going slow enough to not get crazy hot, so it doesn’t require nearly as much thermal protection. Therefore its safe to say it probably doesn’t require as much refurbishment consideration either…..
So some final thoughts on all this.
First off, the reason why I think the Falcon 9 will actually achieve reusability when the space shuttle didn’t is mostly due to the engineering philosophy of SpaceX.
They are constantly tweaking their rocket, to the point where according to SpaceX’s VP of production, Andy Lambert, SpaceX has “Never built any two vehicles identically, such is the pace of innovation at SpaceX”
This is pretty different than the Space Shuttle where there were only 5 operational shuttles ever made with very little physical design changes happening throughout its 30 year operation.
As a matter of fact, phase one of the Space Shuttle was only the first four flights of Columbia. After that, further development would be minimal.
But with the Falcon 9, if an idea doesn’t work out, they can literally implement that change on the next rocket being manufactured, or if it’s a large change, on the next block iteration.
The Space Shuttle’s design didn’t freeze, but it sure didn’t evolve nearly as much in 30 years as the Falcon 9 has in 8 years.
Some might consider this much change reckless, but considering the end goal is to actually have a reusable vehicle, I’m glad they’re pushing so aggressively. I can’t wait another 30 years.
And lastly to those who think SpaceX won’t’ be able to make it worth the cost of reflying or who question whether or not it will be worth it for them… luckily for us, it doesn’t matter.
SpaceX is a private company, they will only do it if it makes financial sense to do so. If after a few more years they look back and realize it’s more expensive to keep reusing boosters, then I’m sure they will stop doing so, so they don’t lose money.
They don’t owe it to anyone to reuse their rockets. It’s only in their best interest to figure out how to do so so they can maximize profits.
And that is just simply different than the Space Shuttle which had the weight of the entire nation’s expectations to be reusable. Whether or not the system put in place actually made sense, it was too late. There was no room for major changes per say since congress would probably frown upon “well this didn’t work, let’s scrap the entire idea.”
So personally, I think with this new age of innovation and materials, rapid evolution of hardware and software, and leadership that simply requires they keep trying until they figure it out, I think we’re finally entering a new era of reusable and airliner like rockets. Hopefully!
So what are your thoughts? Is actual reusability finally upon us or do you think we’re still going to be stuck in refurbishment land?
What other questions do you have? Let me know your thoughts, questions, and video requests in the comments below!
Thanks to Lukas from K-News for his amazing animations. I’ve always been a fan of his work and was so happy to work with him on some of these visuals. Be sure and check out his awesome channel where for updates on spaceflight news and great topics as well over at K-NEWS!
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