Adapted from a video by Tim Dodd the Everyday Astronaut. Web version by Andy Law.
Watching Starship come to life sure is addictive. Through the hard work of people covering this, the general public has never had access to a rocket’s development like this before. I love watching the updates roll in from Mary and the NASASpaceFlight crew, Spadre, Lab Padre, RGV aerial and Austin Barnard every single day. It’s so awesome what kind of access these dedicated people bring us!
Typically, prototypes come out of factories. However, SpaceX has spun this convention around by building their factory around their prototypes – turning Boca Chica into the Wild West of rocketry.
It should be noted that Starship is a system, and potentially a family, of vehicles – you could even call it the Starship Launch System, or SLS… But we will see different variants for different purposes. Generally speaking, this article will cover the generic crew version that is often seen in renders.
But there will also be a tanker variant that carries additional propellant as payload to refuel other Starships on orbit. We may someday see one-way bound Starships that are stripped down and only made to inject payloads to the outer solar system.
However, there will also be a cargo variant with a payload bay. Much like an alligator, this giant bay will open its jaws wide and release massive payloads.
There’ll also be a lunar lander version which will only stay in the Earth-Moon system. This variant won’t have the large flaps or heat shield needed to return to Earth and will also have additional landing engines positioned higher up such that they don’t kick up too much lunar regolith.
What’s the same?
Before we get deep into the differences, it might be best to lay out the similarities between Falcon 9 and Starship.
Firstly, they’re both rockets made by SpaceX. The two vehicles both have two stages that run on super-chilled liquid fuels and have a reusable first stage with legs and grid fins. And they probably have virtually the same avionics and software?
Maybe that’s why it’s not called the Big Falcon Rocket rocket anymore… Starship has almost no Falcon Heritage.
What’s different: Engines and Fuels
At the heart of every rocket is its rocket engine, or in this case, its rocket engines. The Falcon 9, as the name suggests, has 9 Merlin 1D engines on its first stage and a single vacuum-optimized Merlin (MVac) on the second stage.
The Merlin engines used on Falcon 9 are open cycle, meaning they contain a small baby rocket engine called a gas generator. The exhaust from which is then used to spin a turbine that drives the main propellant pumps.
In the case of the sea-level Merlin, this exhaust is then dumped overboard. However, the second stage’s vacuum engine reroutes the gas through the nozzle to provide a layer of cooler gas to keep the extended nozzle from melting.
However, with Starship development, SpaceX has cranked everything up to 11. In search of the best rocket engine ever made, they developed a full-flow staged combustion cycle engine known as Raptor.
The reason it is so complicated is that all of the exhaust gas that would normally be dumped overboard after spinning the turbine is instead routed into the main combustion chamber and used for thrust. Not only that, but there are two of those little rocket engines – each with their own turbines and pumps. The exhausts from which are pumped into the main combustion chamber. One of those is fuel-rich and the other is oxygen-rich.
Despite extremely hot gaseous oxygen wanting to turn every bit of the engine into soup, having the fuel and the oxygen arrive in the combustion chamber as a hot gas adds a huge boost in efficiency.
One little note here, if an engine is a closed cycle, we will call the gas generator a preburner since it’s just preburning the fuel or oxidizer, which is then routed straight into the combustion chamber.
Raptor is so advanced that there’s only ever been two attempts at building something similar – ever. Neither of which left the test stand.
As of the writing of this article, the Raptor has powered 4 short hops. Despite them never exceeding 150 m, it is the only time a full-flow staged combustion cycle engine has been used to perform work. But these hops were relatively simple, with only a single-engine. Some of which were even offset from the centre of the rocket-like prototypes SN5 and SN6, where they mounted only one engine on a mount that’s made to hold three in the centre.
But 3 engines is next for Starship for its first true flight, planning to reach 15 km to practice its crazy landing sequence. From there, the number of Raptors that Starship will utilize will just keep on increasing.
The orbital version of Starship will have 6 Raptors: 3 sea-level and 3 larger vacuum-optimized engines. The latter are currently in development and beginning their testing.
The Super Heavy booster will end up with over 2 dozen engines, eventually getting up to over 30 engines with some talk of over 40!!! Because of their relatively small size, SpaceX can squeeze many of them on the bottom of the large rocket.
And don’t worry, Starship shouldn’t suffer from “N-1 syndrome”. People are quick to point out how using so many engines on the first stage is dumb because the Soviet Union’s N-1 moon rocket developed in the 1960s failed on all four of its launch attempts.
Well first off, don’t forget the Falcon Heavy has had a perfect flight record and uses 27 engines, so clearly the number of engines doesn’t scare SpaceX, but also the N-1 failed for many other reasons, all having very little to do with the actual number of engines.
While we’re talking about engines, we should mention the fuels each engine runs on. The Falcon 9 runs on rocket-grade kerosene known as RP-1 along with liquid oxygen (LOX) – a combination often referred to as keralox. Whereas Starship and its Raptor engine run on liquid methane and liquid oxygen – otherwise known as methalox.
Liquid methane burns cleaner than RP-1, leaving behind virtually no soot in the engine. It also has the potential to be more efficient, but it is less dense than RP-1 which leads to slightly larger tanks by volume.
One thing unique to SpaceX is in the constant pursuit of performance, they began utilizing super-chilled propellants on Falcon 9 in 2015. With the introduction of their first “full thrust” iteration, they started chilling the RP-1 and LOX more than any other operational rocket.
SpaceX chills their RP-1 from almost ambient down by about 30 °C, which typically gets it below 0 °C. But that’s nothing compared to the liquid oxygen, which is chilled all the way down to -207 °C – that’s only 12 degrees away from freezing solid!
Although they haven’t yet gotten too far into super chilling propellants for Raptor, it is in the works. But by default liquid methane is very close in temperature to liquid oxygen since it’s boiling point is -161.5 °C and it becomes a solid at -182 °C.
Due to the closeness in boiling points, we’ll likely see SpaceX chill their methane down closer to -180 degrees Celsius as they continue to squeeze performance out of that beast.
But there’s more than just a fuel and oxidizer tank in each stage of these rockets – and here’s where the Falcon 9 is more complex than Starship, because it has three more consumables onboard stored inside smaller tanks.
Inside each tank of Falcon 9’s tanks are a set of composite overwrapped pressure vessels (COPVs). These black cylinders house compressed helium – we’re talking 380+ bar in those bottles!
They use these to maintain a constant pressure of about 3 to 4 bar in the propellant tanks. So as fuel drains out, they put helium – which is extremely… un-dense? – in its place. This is done to avoid negative pressure in the tanks and keeps the propellant flowing.
Starship will do away with these entirely. After all, if you’re landing on Mars, you can’t just refill your helium tank. Instead, SpaceX will use methane, as it can be produced on the surface of Mars through in-situ resource utilization.
Consequently, Starship will pressurise the propellant tanks autogenously. Meaning, while the engines are running they’ll be pumping some gaseous fuel and oxidizer back in their respective tanks.
They will maintain their pressure by allowing some of the fuel to boil, and release any excess pressure. This also helps maintain their temperature, as the boil-off cools the fuel – like your sweat evaporating on a hot day.
UPDATE: SN9 is in fact using helium to ensure the pressure on the methane header tank, after SN8’s failure to land successfully was blamed on low fuel pressure in the header tank. This is just an interim solution however.
The propellant is also stored in smaller tanks-inside-tanks. Since they’ll be inside another tank, the propellant will be receive almost no heat from the sun and therefore it will not boil off.
The header tanks serve as reserves for the landing phase. Starship will do some pretty intense maneuvers, and if it tried to light its engines from a partially empty tank, it would suck up air bubbles. So these header tanks just provide a source of propellant that’s on tap, no matter the orientation or G-load of the rocket.
Another thing the Falcon 9 has that Starship won’t have is ignition fluid. The Falcon 9 uses what’s known as TEA-TEB, or Triethylaluminum Triethylborane. The mixture is pyrophoric – meaning it ignites without the need of a spark when it comes in contact with oxygen.
As SpaceX gets the pumps spinning up on the Falcon 9, they inject TEA-TEB into the combustion chamber to initialize combustion while they begin to dump fuel and get it into a stable combustion state. This is crucial for the ability to restart the Merlin engines with an onboard starting fluid so they can relight some of the engines 2 or 3 times during its reentry process. Without TEA-TEB, the engines would fail to reignite.
And again, just like with helium, you can’t exactly refill up your TEA-TEB bottles on Mars, so for Starship and the Raptor engine, they’re utilizing a spark ignition. I think this is quite literally like a giant spark plug or an arc welder to begin the ignition process.
But there’s one more propellant that SpaceX uses on the Falcon 9 and that’s cold gas or compressed nitrogen. Basically just compressed air since nitrogen is 78% of the air we breathe.
They utilize compressed nitrogen for the cold gas thrusters on the interstage of the Falcon 9. There are 2 packs of 4 little thrusters sitting way up on the top of the booster stage. These are what help flip it around and continue to point and guide the booster as it coasts before reentry.
And just like before, there’s not as much nitrogen on Mars, but even more so, SpaceX doesn’t want to carry around fluids other than the main propellant. So instead, Starship will utilize hot gas thrusters powered by boiled off methane and gaseous oxygen.
We don’t know much about these new thrusters, but they’ll likely be named after a bird and probably be around the 20 kN mark for thrust.
So all in all, the different fuels, different cycle types, different sizes and all other considerations leads to pretty drastic upgrades in performance for the power plant of each rocket.
SpaceX’s Merlin reaches an impressive amount of thrust at 845 kN at sea level and 981 kN in a vacuum, but the Raptor engine is currently in its infancy running at around 1,650 kN at sea level and can achieve around 1,800 kN in a vacuum.
But they’re already achieving just above 2,000 kN of thrust on the test stand and that will be their operating thrust relatively soon, and there’s another more powerful variant coming.
Someday there’s going to be a non-deep throttling Booster Variant of Raptor that’ll be on the outer ring of the booster and they’re targeting closer to 3,000 kN of thrust at sea level and more like 3,200 kN of thrust in a vacuum. Wow.
After all, the Merlin has had every last drop of performance squeezed out of it after over a decade of continuously developing the engine, and the Raptor is just at its infancy.
Next up: efficiency. This is measured in specific impulse or ISP. The higher the number the better, kind of like the gas mileage or fuel efficiency of a car.
The Merlin is pretty darn efficient, achieving 282 seconds of impulse at sea level and 311 seconds in a vacuum. But the Raptor is even more efficient, currently achieving 325 seconds at sea level and close to 350 seconds in a vacuum!
A lot of this performance is due to the chamber pressure inside the main combustion chamber. The higher the chamber pressure, the more potential the rocket has to turn that high pressure into higher thrust and better efficiency too.
The Merlin achieves 116 bar of pressure while the Raptor is operationally at around 275 bar currently – but has hit 330 bar on the test stand and will likely reach their goal of 350 bar operationally before too long, knowing SpaceX.
But at the end of the day there is one metric where Merlin currently out performs the Raptor, and that’s thrust to weight ratio. The Merlin will be hard to beat because it has the highest thrust to weight ratio of any liquid-fueled rocket engine ever!
The Merlin engine has a nutty thrust to weight ratio of around 200:1 while the Raptor currently is around 107:1 but increasing to 130:1 and again, Elon thinks they can get it to match the Merlin someday.
But perhaps one metric that’s just as important, especially when you’re cramming dozens of engines inside a fixed area is thrust to engine footprint ratio… You may notice that the Raptor isn’t THAT much wider or take up THAT much more space than the Merlin.
If we look at just the nozzle exit area, the Merlin 1D has a nozzle area of 0.65 m2 while the Raptor has a nozzle exit area of 1.33 m2. This means the Merlin 1D and soon the operational version of Raptor will have about the same thrust to nozzle exit area ratio of around 1,500 kN/m2.
And especially when you factor in the entire footprint of the engine, not just the nozzle exit area. Notice that the Merlin has the large gas generator exhaust pipe sticking way off the side of the engine while the Raptor almost fits inside its own footprint. This stuff matters when cramming tons of engines together!
And again, I expect the Raptor engine to far exceed the Merlin in this regard and when you have hard limitation of how many engines you can squeeze in a space, the thrust to nozzle exit area ratio matters about as much as thrust to weight ratio.
So when it’s all said and done, the first stage of the Falcon 9 with its 9 engines achieves 7.6 MN of thrust. Falcon Heavy, which is currently the most powerful rocket flying, gets 22.8 MN and Starship’s SuperHeavy booster will end up with about 3 times the thrust of that at 65 MN.
That’s likely about the minimum thrust we’ll see for an operational orbital version, but it’ll probably increase when they start utilizing more engines or those more powerful booster variants on the outer ring. And that’s over twice as much thrust as the Saturn V – this rocket will be huge.
What’s different: Size, Capabilities and Construction
OK next: their sizes. Starship is massive. Like, really really big. Don’t get me wrong, Falcon 9 is actually quite a decent sized rocket and it’s really hard to appreciate how big it actually is until you’re standing underneath it. But at 9 m wide compared to the Falcon 9’s 3.7 m diameter, the Falcon 9 is narrow enough to be transported cross country by road, but Starship – not so much. Although, it does get transported by road, it only does a little tiny bit on a completely closed off highway in Boca Chica, Texas.
The Falcon 9 stands 70 m tall with its first stage at 45 m tall while the second stage and the nose cone, or fairing as we call it, comprise the other 25 m. Despite being pretty tall, the entire Falcon 9 will be able to fit inside just the SuperHeavy booster.
The SuperHeavy booster will stand over 72 m tall, likely closer to 75 m tall. Then put the Starship upperstage on top of the Super Heavy Booster and the entire stack will stand 122 m tall – that’s over 10 m taller than the monster Saturn V!
YUP… that’s right. It’ll be about as tall as a 35 story building. In fact, it’ll be pretty much exactly as tall as the tallest skyscraper-esque condominiums on nearby South Padre Island, the Sapphire South Padre, which stands 123 m tall.
And once you put Starship on its massive launch mount, it will be the tallest thing for hundreds of kilometres! Yeah, just wait until that thing takes off, I think it’ll melt a few brains and possibly break a few windows. I can’t wait to see that!
Couple this massive size with their different engines with different performance figures and different fuels and what it all means is Starship can put a lot bigger and heavier things into orbit.
The Falcon 9 can take 22,800 kg into LEO when expended or 15,600 kg when reused, like it does for the Starlink missions. It can send 8,300 kg on a geostationary transfer orbit when expended, or about 7,000 kg when reused.
Now let’s drop in Falcon Heavy, which can take between 63,800 kg when fully expended, and about 38,000 kg with a 2 core return to launch site landing and 1 core on a drone ship.
Falcon Heavy can even get about 25,000 kg to geostationary transfer orbit when fully expended, but can still get about 13,000 kg when doing the 2 x RTLS, 1 x drone ship landing.
But Starship will be able to take over 150,000 kg up to LEO… Yes, that will be more payload mass than any rocket ever made, even beating out the Saturn V which could “only” put 145,000 kg into LEO. It will do this while still being fully reusable…
Starship can also put a solid 21,000 kg out to a geostationary transfer orbit, despite having to lug its own huge dry mass out there. Yes, that is lower than an expendable Falcon Heavy, but if you expended a Super Heavy booster, it would easily exceed that.
And expending a Super Heavy booster is just simply not in the plans. Don’t forget, since the whole rocket is reusable, Starship has to take its heavy flaps, landing gear, the payload fairing and all 6 engines with it everywhere it goes.
So instead, here’s where Starship can make up for that with orbital refueling. If Starship is refueled with just one tanker, it can get that GTO payload capacity right back up to that 150,000 kg mark. And if you refuel it enough, it can take 150,000 kg all the way to the moon or Mars! That’s game changing.
Another huge upgrade for Starship is its massive payload bay. The Falcon 9 and Falcon Heavy share the same fairing which is about 5 m wide and 14 m tall with a total usable volume of 145 cubic meters.
Although there is an extended version coming soon that is taller that will get that volume closer to 200 cubic meters.
But Starhip’s payload bay is a whopping 9 m wide and 18 m high with a usable volume of around 1,000 cubic meters. Yup, that’s more pressurized volume than a 747! And there will be an extended payload version coming that is 22 m in height!
Another big change is what these rockets are made out of. The Falcon 9 is made out of 2219 aluminum alloy and some carbon composite, while Starship is made out of stainless steel 304L and will eventually be made out of a SpaceX in-house developed 30X stainless steel.
Aluminum is typically the lighter option, but only at cryogenic temperatures. But the reason for using stainless steel on Starship is because it not only needs to handle low cryogenic temperatures, but it also needs to handle reentry heat for both stages.
The Falcon 9 actually has some heat shielding on the octaweb which is the bottom of the booster that holds all the engines. This keeps the extreme heat of reentry from destroying the fuselage.
Because of Starship’s stainless steel construction, they are hoping to not require any additional heat shielding on the Super Heavy booster.
But the upper stage will need to employ additional heat shield tiles along its windward side or its belly when it is reentering from orbital velocity. We will discuss this a little bit more shortly, but had they gone with another material, it would have required even bigger and heavier heat shields.
Originally SpaceX wanted to use carbon composites for Starship, but maybe one of the biggest reasons they switched to stainless steel is so they could rapidly prototype the vehicle. They can construct, make changes to and iterate on a stainless steel Starship with simple construction methods, and cheaply too.
We’re not really going to get into the philosophy of this iterative and quick design, building, manufacturing and prototyping process in this article, because we have covered it very in depth in the SLS vs Starship article already.
But maybe the most unique bit of hardware are those giant flippy-flappy-finny, air-brakey things on Starship, or as I call them, “Elonerons”. Yes, these are something entirely new. They are a unique control scheme that will help the vehicle maintain control while reentering belly-first.
These Elonerons will basically be powered by some Tesla electric motors with a direct drive. Despite requiring insane amounts of torque, geared the right way, that’s something an electric motor has plenty of!
They’ll be powered by Tesla batteries, or derived from them at least, and for longer missions, Starship will have solar panels. We don’t have too much info on those yet, but they’ll eventually work their way into designs.
But this is all just a giant iterative phase, SpaceX is making a huge and powerful rocket. But what’s it all for? Forget the size of Starship, the economics of this rocket is probably the biggest thing.
Now we’re not really going to get too into this, since we’ve talked about this a lot in other articles, but I just wanted to talk about price generally to help put into perspective how game changing this could be, and really only time will tell what the true costs of everything will actually be.
Despite being able to take almost 10 times as much payload into orbit as the Falcon 9, Starship should cost less than the Falcon 9 to launch. In fact, because it’s fully reusable, it should basically only be the cost of fuel and personnel time.
But we’re talking potentially way less than Falcon 9, SpaceX is hoping it’ll cost less to launch than a Falcon 1 even! In fact, it very well might end up being the cheapest ride to orbit, period.
In other words, it could be so cheap to launch an entire Starship, that you could put just a small sat or a couple cubesats or something tiny on it, and it might be cheaper than launching on an Electron rocket or some smallsat launcher.
Now that’s why Starship is truly revolutionary compared to even the Falcon 9. But in order to fulfil that goal, Starship will HAVE to be reusable. Fully and rapidly. So just how exactly can it do that? What hardware is different that will make that dream happen?
What’s different: Reuse
And now for the coolest part, reusing. After all, there’s nothing more exciting than watching a rocket land in person, falling from the sky, igniting its engines at what feels like the last second possible, and landing under a precise column of flames. And Starship will take this up a notch.
After all, the Falcon 9 has set a new bar in the aerospace industry by propulsively landing the first stage booster and reusing it. As of the making of this video, nearly half of all Falcon 9 flights ever flown have used a booster that’s flown more than once.
And what SpaceX developed for the Falcon 9 and Falcon Heavy’s booster recovery is actually a very similar method that they will use for the Super Heavy booster. So let us follow the first stages and talk about the systems and hardware in play and how it all works.
Of course, at lift off, all engines will ignite on both rockets. As soon as the computer senses all engines are running smoothly and at full thrust, it will command the launch pad to let go so it can break free of Earth’s gravity.
Both rockets will ascend, mostly vertically at first to get out of the thickest parts of the atmosphere as quickly as possible, but shortly after take off, they will begin to pitch over horizontally, in the direction of their desired orbit.
Remember, in order to get to space you just need to go up. But to stay in space you have to go sideways – really really fast. So fast that your horizontal speed matches the rate at which gravity is pulling on you, so you’re basically continually falling, but also continually missing the horizon.
By stage separation, they’ll be pretty much entirely horizontal, giving the upper stage as much horizontal velocity as they possibly can spare. And the first thing that the first stages do next is important – they immediately flip over and will begin to slow themselves down to go right back where they came from.
Let us assume that both first stages are going to be heading back to the launch site, otherwise known as Return to Launch Site or RTLS. The Falcon 9 can only do this for fairly light-weight low Earth Orbit missions, but SuperHeavy will likely always return to the launch site – meaning the actual launch complex, not a separate landing complex!
In order to get back to the launch site, the boosters need to cancel out their horizontal velocity as quickly as possible, because at stage separation, they’re traveling at thousands of kilometers an hour away from the launch pad.
Boost back burn
This is called the boost back burn. The Falcon 9 lights up 3 of its 9 Merlin engines, but SuperHeavy will likely light up all of the center engines, so potentially 6 or 7 engines for this maneuver.
Not only do they need to cancel out the horizontal velocity, they need to keep burning until they have actually completely reversed course, heading backwards from the original velocity and make their ballistic trajectory end up at the landing site, or just short of it for safety reasons.
After the engines shut down, the boosters will be coasting back to the launch site, seeing as they are well above 100 km at this time, they have no air resistance to slow them down. During this period, the cold gas thrusters on the Falcon 9 home in and precisely target the landing site using little tiny puffs of nitrogen.
Starship will use its hot gas thrusters for any of these maneuvers. But the idea is basically the same. Small tiny impulses can help precisely point and guide the booster back home. During this phase, they will deploy the grid fins, although in the vacuum of space they obviously don’t provide any control, yet.
The boosters will follow their ballistic trajectory and eventually they will both begin to experience more and more of the Earth’s atmospheric pressure. Here is where the Falcon 9 does something that Super Heavy is hoping to avoid.
The air in front of the booster will heat up due to being compressed by the leading surface of the booster. Due to the laws of thermodynamics, as air is compressed, it is heated up. The air in the bow shock compresses so much it actually turns into a plasma. This plasma can be about half as hot as the surface of the Sun.
So in order to avoid having this burning hot plasma destroy the rocket, the Falcon 9 will again light up 3 of its 9 Merlin engines to slow itself down just as it begins to really experience those extreme atmospheric temperatures.
This not only slows the booster down, but it also basically creates a “force field” in front of the booster, providing a boundary of exhaust gas which is a lot cooler than the plasma. Without this step, the Falcon 9 booster would likely not survive the reentry process.
Parachute recovery attempts
After all, SpaceX tried to recover the Falcon 1 and Falcon 9 boosters using parachutes for the first few flights, which kept failing, likely due to a complete lack of additional heat shielding.
By the time the booster was supposed to deploy the parachutes it was too late. Because it is hard to deploy parachutes when you are in a million flaming pieces.
But again as we mentioned before, this is something that stainless steel should allow the SuperHeavy booster to forgo which will save fuel and thereby increase overall performance.
Because of its higher melting point, SuperHeavy is hoping to just grit its teeth through this process and survive this brutal regimen.
And I think they can do it – after all, Rocket Lab’s Electron rocket has survived this portion of flight that Peter Beck is calling “the wall” – and that rocket is made from carbon composite. So it is definitely possible, although comparing these two vehicles might not be fair.
From this point on, the grid fins have more and more control. Grid fins are basically just hundreds of small fins stacked side by side. This allows them to be tucked out of the air stream on ascent but deployed into an atmospheric cheese grater when coming back down.
People often think the grid fins are just an air brake or something to help keep the center of pressure behind the center of mass, but really, they steer just like an all-moving control surface, like the stabilators on the tail of the F-16. The entire thing rotates around a central point to induce control. For grid fins they can move opposite pairs in unison to provide pitch or yaw and they can all move opposite their pair for roll.
The grid fins now steer hard and point the booster towards the landing site. They can even pitch it in a way that creates lift along the booster’s fuselage and help it translate even further over.
I should point out that all of this is guided autonomously. No one is steering it. It is just aiming at a fixed GPS position and altitude.
By utilizing as much of the booster as possible to basically glide, it also allows the air to slow it down as much as possible which requires less fuel for the final landing burn. Unlike ascent where the air is fighting against the rocket, here, the atmosphere is helping to remove energy.
So eventually the booster will line itself up directly overhead of the landing site. At the last possible moment, they will light their engines. In the case of the Falcon 9, this has to be extremely precisely timed.
The nearly-empty Falcon 9 booster, even when only 1 of its 9 engines is running at its minimum throttle setting, still has too much thrust to just hover. So they have to perform what has been called a hoverslam or a less astronaut-friendly term, a suicide burn.
This is where you light up your engines as late as possible, so late that you do not have a second chance. And because of the high thrust to weight ratio, they have to reach zero velocity right at zero altitude, otherwise the booster will end up going right back up! Whoops!
The SuperHeavy booster on the other hand will land using only its inner engines. These are the only engines that can gimbal and eventually, they will be the only ones that can deep throttle, which is necessary for soft propulsive landings.
Hovering vs hoverslam
The outer ring of engines will someday be those Booster Variants of Raptor that are higher thrust but cannot deep throttle and are fixed in place with no ability to gimbal.
SuperHeavy could probably technically hover because it could turn off opposing pairs of engines until its thrust to weight ratio is at one, but you really do not want to do that. After all, hovering is just 100% a waste of fuel, all the fuel spent to hover is literally getting you nowhere.
It is best to do the burn as late as you can and with as much acceleration as you can. The shorter the burn, the more efficient. But the good news is, SuperHeavy has the option to do a slower less efficient burn if they want to.
From here, the Falcon 9 lowers its landing legs which are hydraulically pushed out and then locked in place. SuperHeavy will likely forgo this since its legs probably will remain fixed in place. But, those plans seem to change often.
But don’t be surprised if we end up seeing basically scaled-up Falcon 9 style landing legs on it someday because of course it’s still evolving.
Once the rockets land, they of course shut down the engine(s) and begin to lower the tank pressures to something safe enough for humans to approach the vehicle. For the Falcon 9, once it is clear to proceed, a crew will go out and pick it up and lay it flat on its side on a trailer.
From here, a process of check outs and refurbishment happen. The Merlin engines often need a good check over and potential clean out because of that soot build up. The quickest turn around to date is about 50 days before it can be re-flown, although that time is decreasing quickly! [UPDATE: current record is now down to 38 days.]
But this will all hopefully be unnecessary someday for SuperHeavy since the plan will eventually be to just pick it back up and put it right back on the pad. And thanks to the reusable nature of the Raptor engine and Methalox, this might become a reality someday.
Or maybe it will be similar to kicking the tires like a jetliner before each flight, doing a simple check out before re-flying.
What’s Different: Upper Stage Reuse
So, now let us take a look at the upper stages of the Falcon 9 and Starship. SpaceX is already pursuing reuse beyond the first stage. This is by catching and reusing the nose cone or fairings on the Falcon 9.
As of the date of this article, SpaceX has reused a fairing 3 times so far. This is great, considering that they cost several millions of dollars. It just makes sense. Their “wile-e coyote” scheme to catch them has been paying off – and even when they miss a catch, simply fishing them out of the water has proven worthwhile.
But despite all these efforts at reuse, the second stage itself is always discarded. After a Falcon 9 deploys its payload, it either does a de-orbit burn and discards the upper stage in a pre-planned exclusion zone on Earth, or else it kicks itself into what is called a graveyard orbit.
But here is where SpaceX is going absolute “next level” with Starship. Despite the upper stage being a smaller portion of the rocket, it’s substantially harder – maybe even an order of magnitude harder – to recover something going at orbital velocity when compared to recovering a suborbital stage.
This is the biggest paradigm shift that Starship is hoping to achieve. The hardest and most cumbersome problem is speed. Minimum low Earth orbital velocity is around 28,000 km/h. Yes, that is literally about 10 times faster than a bullet shot from a rifle. Which is 8 km or 5 miles every second.
So the booster imparts a decent amount of the sideways velocity. But a booster’s maximum velocity is only about 1/3 – 1/4 of the speed that the second stage reaches. Now you might be thinking, “oh well, 3 or 4 times faster, why is that any harder to return?”
A vehicle going at 28,000 km/h needs to slow back down to nothing in order to land safely. That means that all of that energy needs to be removed from the vehicle somehow.
Remember how the atmosphere slowed the booster down? Well, now we can use the atmosphere to slow the upper stage down too.
The temperature of the compressive heating in the vehicle’s bow shock doesn’t increase linearly with speed. It is not as if you go twice as fast and the resulting temperature gets twice as high.
It’s not even that heating goes up by velocity squared. In other words, go twice as fast and the heating is 4 times as much. No no, reentry heating goes up by the cube of velocity. So in fact if you go twice as fast, you create 8 times as much heat.
The upper stage is traveling at about 4 times faster than the first stage as it reenters. This means it can experience up to 64 times as much heat. That’s why recovering the upper stage is so hard.
This raises the following question. Why not just slow down before re-entry and get back down to similar velocities and temperatures as the booster? Unfortunately, slowing down using engines, would require exactly as much energy as on ascent.
So the rocket on orbit capable of slowing you down is as big as the one previously used for ascent. And this of course means the rocket to launch that would now have to be perhaps 10 times bigger too.
SpaceX’ solution is to use as much of Starship as possible to slow down in the atmosphere. They will enter the atmosphere belly-first. This exposes as much of the cross section of the vehicle to the wind stream as possible.
This is why SpaceX’s Starship will reenter more like a skydiver. It won’t go engines-first like the Falcon 9, or at a 40 degree angle like the Space Shuttle. It will basically be slamming on the brakes as much as possible.
In order to do this, it needs to be able to control and maintain stability. That is exactly what those “elonerons” we talked about earlier are for. They change their drag to control pitch, yaw and roll.
Reentering the atmosphere allows the vehicle to exchange all of that insane amount of kinetic energy it has for heat. This is similar to a giant brake pad which does the same thing. Namely, exchanging kinetic energy through heat from friction.
Only in this case it’s not air friction that causes the heat; as was mentioned before, it’s compression of the air in the bow shock that heats up the vehicle. And this again is why SpaceX switched to stainless steel so it can survive the reentry intact.
SpaceX has brilliantly unified the heat shield size and shape. It mostly is just a common diameter cylinder besides the nose and hinges and some other features. This makes for easy check outs, easy production, and easy manufacturing.
Not much is known about the heat shield. It is likely an in-house variant of a material called TUFROC. This is a material which touts high reusability by being able to handle high peak temperatures before ablating.
There might be some hotspots that will ablate a little on each launch. But because they’re uniform, they should be easy to swap out and replace when they get too low. Again, this is just like replacing a brake pad during a routine service.
These will eventually be mechanically mounted. This will likely be done by an automated robot for quick and easy manufacturing or replacement. These heat shield tiles might be the only thing that really wears down. So there should be minimal maintenance on the entire rocket. (In a perfect world anyway.)
So Starship eventually gets slowed down. From going 10 times faster than a bullet to a relatively slow terminal velocity of around 200 km/h. At this point it is falling straight down now, but still belly first.
But here’s the thing that’s truly going to be absolutely insane to see. Starship will still need to land using its sea level raptor engines. If you recall, those engines are on the bottom of the rocket. At this moment they are facing sideways, completely horizontal.
The “belly-flop” maneuver
So what is the solution to this situation? A wild, daring, and potentially hard to nail down “belly-flop to tail-down” maneuver. This is something that I’ve found to be just bonkers since the day we first saw it. I even asked Elon all about it at the 2019 Starship event.
This maneuver will make the Falcon 9 landing look like a walk in the park in comparison. It’s a maneuver that would make the best stunt pilots poop their pants.
The first attempts at this will look a little different than the eventual system. This is because the cold gas thrusters on early prototypes aren’t very powerful. As a result they can’t aid too much in the flip maneuver. Eventually, when they are replaced by the hot gas thrusters on later vehicles, this maneuver will look different.
For the initial prototype landings, the rear elonerons will tuck in to aid in the rotation. At the same time the 3 Raptors will light up while going horizontally. However they’ll be at maximum gimbal angle, pitching the rocket’s nose up as quickly as they can. [UPDATE: during SN8’s flight, only 2 Raptors were relit.]
Of course in doing so, it’s going to inject a large amount of horizontal velocity during this process. So, in order to negate that and land on target, it will need to over correct. This means swinging back over to the other side. In doing so, it will cancel out the horizontal velocity before straightening out and touching down softly.
Hot gas thrusters (future)
Eventually more production-ready and advanced versions will have hot gas thrusters. So, this maneuver should be able to be done completely by the gas thrusters and elonerons. Then it would just be a simple “hover slam” landing just like a Falcon 9.
This maneuver is important because this is how a vehicle of this size will need to land on Mars. There’s no runway, no way to glide softly and land on wheels. There is no alternative to nailing this maneuver. This has to be “easy-peasy” before we put humans on it and send them to Mars.
But there’s one more really big technology that will debut on Starship. And this will be required to get humans to Mars. That is on-orbit refueling. Remember that Starship didn’t necessarily have a huge payload to geostationary transfer orbit? This is because it has to lug around all its dry mass.
Well, Starship can make up for that by refueling in orbit. If this vehicle really is rapidly reusable, then this could be the most important technology. The Super Heavy booster can just land and grab a Starship tanker and launch again on the next orbit.
By refueling Starship on orbit, it would then have an astonishing amount of Delta V. It could easily get to the Moon or Mars with fuel to spare! But something like this has never really been demonstrated, not at this scale and certainly not with cryogenic propellants.
But luckily, SpaceX has even got NASA invested in this effort. For now it has a $53M contract to study transferring cryogenic oxygen between the header tanks and the main tanks. But eventually they will hopefully be interested in Starship-to-Starship refueling as well.
Alternatives to orbital refueling
At this point you might be asking this question.”How could it be cheaper to launch several full-stack tankers on SuperHeavys to refuel a ship? Why not just make a lighter Starship that’s only to be used in Space?”
Firstly, once the launch cost is reduced enough, a full stack launch potentially only costs a few million dollars. Literally just the cost of the fuel, the crews to run the launch operations, and range etc etc.
But secondly, look at the hardware elements required to get humans safely back down to Earth. They are also the same or similar technologies that work on Mars. So let’s say the mission is go to Mars and come back. You can’t really strip down a Starship too much for that.
So when all is said and done, Starship takes reuse up to the next level. Potentially, all the way to Elon’s ultimate goal of a rapidly reusable orbital rocket. As he says often, if you designed an expendable jetliner, you’d get laughed out of the room.
StarShip could truly usher in a new era of spaceflight.
Starship is simply a massively ambitious proposition. But there are few physical barriers which would make it impossible, other than it’s never been done. And just as with anything that has never been done before, the unknowns are unknown.
I fully expect Starship to have some stumbling blocks along the way and some valuable lessons will be learned too. There’ll likely be many more explosions along the path to orbit, and even once in operation. Remember the Falcon 9 history has not always been smooth sailing either.
Nothing is when you’re pushing the boundaries. But now the Falcon 9 is one of the most reliable and most flown rockets. What used to be an experimental landing is now expected and almost mundane.
After all, Elon has said in the past he hopes these landings become so routine, that they become boring. Although I’m personally not quite to that point yet, it is getting close.
Starship might have a rocky start. There are many people who critique it and say that it will never work. Those same critics have been around the whole time constantly saying SpaceX won’t be able to do something. Then they get proven wrong over and over and over.
“Falcon 1 will never get to orbit, oh wait…” “Why are they trying to make a Falcon 9? They’ve only made it to orbit once. They can never make a rocket that big. They don’t know what they’re doing… oh wait…”
“Ok, cool, it went to orbit, but they won’t be able to deliver goods to the ISS. It’s all a fraud and they’ll lose that NASA contract… oh wait…” “They’re trying to land the Falcon 9? That’s impossible, what a waste of time?… oh wait… “
“OK cool they landed one, but that’s just showing off, it’s probably beaten up and they’ll never refly one… oh wait…” “OK they reflew one once, but reusability will never pay off because of how much it cost to develop it. They’d have to refly it over and over and over… oh wait…”
By this time I think you get the point. Ludicrous, sure, impossible, of course not. Nothing that’s physically possible is impossible.
I would not bet against SpaceX. They have proven over and over their ability to do insanely difficult and never-before-accomplished things. Their ambitious promises might not happen on time, but they do happen, and that is what matters.
So yes, Starship is stupidly ambitious and it’s a huge leap in technologies and capabilities over the Falcon 9. But so was the Falcon 9 over the Falcon 1. And in hindsight, thankfully SpaceX jumped over to the Falcon 9 as soon as possible. After all they could have flown the Falcon 1 for a decade before doing so.
As soon as it goes online and is fulfilling its goals, it will make all other SpaceX rockets immediately antiquated. Also, it will make all other rockets ever made antiquated and antiques in comparison. This will be a new era of spaceflight. This is not hyperbole.
Falcon 9 taught SpaceX how to reuse a rocket. Now they are applying all those lessons learned and “cranking it all the way up to 11”. I for one am beyond excited to be living in this moment to witness it happening before my eyes!
So to summarize: Starship takes everything that SpaceX learned from the Falcon 9. It in a brand new super heavy lift rocket that is rapidly and fully reusable. It is going to be huge, the biggest and most powerful rocket ever made.
They are utilizing methane that burns clean and is efficient. SpaceX developed the Raptor engine which is a compact and efficient work horse. They are scaling the vehicle up to a huge degree so they can pursue full reuse without sacrificing performance.
And perhaps most importantly, they are trying out new landing techniques. There’s no question that these are absolutely bonkers by design. But these should potentially solve the problem of surviving reentry and land propulsively on a dime.
We’ll see lots of Starships, Starship tankers, Starship people carriers, Starship Lunar Versions, Starship Cargo versions, etc etc.
And all of this is in the pursuit of getting humans to Mars. When you solve that, it makes rockets a lot more capable and a whole lot cheaper here on Earth too. Starship will truly usher in a new era. And that is not hyperbole.