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At the end of 2018, the first Starship prototype began to take shape.
After taking over a dirt field in Texas, SpaceX started a long journey of development with the
hopes of taking humans to Mars. Two years later and the progress of Starship has been mesmerizing.
In almost every way, Starship is more ambitious than any other rocket in the
history of spaceflight. Not only is it powered by one of the most advanced rocket engines ever made,
it also has the added complexities that are needed to be the first fully reusable rocket.
Starship has been an incredible challenge to design and build, but according to Elon Musk,
figuring out how to actually manufacture the rocket has been way more difficult. Despite
these challenges, SpaceX seems to be progressing at an absurd rate. But one of the most challenging
problems that SpaceX will need to solve isn’t actually the rocket itself, but the launch pad.
On the 9th of November 2020, SpaceX performed a static fire with one of
their Starship prototypes. This was the first time a fully assembled Starship had produced thrust.
The test was completed using a single engine and was carried out to make sure the
header tanks could feed fuel to the engine during a landing. But the test didn’t exactly go to plan.
Shortly after the engine fired up, chunks of concrete were sent flying upwards from the base
of the launch pad. Although it looked spectacular, it turned out to be a lot more damaging than
it first seemed. The concrete pad beneath the rocket had an ablative coating called
Martyte, which was designed to protect the concrete during each test fire.
Up until this point, the Martyte had done its job. But after months of testing, it had finally
worn away and the exposed concrete was ripped up and thrown into the air. A chunk of concrete
flew into the engine bay and severed an electrical cable which ended up damaging one of the engines.
Despite this unusual sight of flying concrete, SpaceX came back the next day and decided to
perform another static fire, this time using two of their raptor engines. During the test,
the engines once again sent concrete flying into the air - but once the engines shut down,
a much bigger problem was observed. At the bottom of the vehicle, a glowing liquid was seen pouring
out onto the launch pad. As it turned out, the internal components of the raptor engine had
completely melted and the glowing liquid was in fact molten metal. The reason this kind of damage
was able to happen is because there was no flame diverter underneath the rocket. Instead, the force
of the engines was hitting the concrete at a 90 degree angle, creating an enormous pressure point
of heat and energy. But surely SpaceX with their years of experience could see this problem coming.
So it seems like the lack of any flame diversion did cause problems for Starship.
So why did SpaceX decide to skip this seemingly crucial part of a launch pad?
Realistically, the Starship launch mounts in Boca Chica are still at a very early design phase
and SpaceX are likely trying to see how much they can get away with. After all, there will be no
launch or landing pads on Mars, so Starship will need to be able to deal with debris all by itself.
Despite the current launch pads being very basic in their design, Starship’s launch
pad will always be extremely different to the traditional launch pads we’ve seen in the past.
Since Starship is designed to do in-orbit refueling, all of the fuel lines need to be
located at the bottom of the rocket. This will allow Starships to dock tail-to-tail in space
and transfer propellants. On most rockets, the fuel lines are placed on the side of the rocket.
This allows the rocket to have a simpler design in terms of plumbing but it requires a much
larger structure at the side of the rocket to feed the vehicle with fuel and power.
During a Falcon 9 launch, this structure also known as the “strongback”, quickly pulls away
from the rocket as soon as it leaves the launch pad. This allows the strongback and all of its
components to move out of the way of the rocket’s flame and minimize the amount of refurbishment
needed for the launch pad. This is yet another problem that SpaceX are looking to solve.
Not only are they trying to make Starship fully reusable, they are also trying to design a fully
reusable launch pad. They want the launch pad to be so reusable, that a Starship can
land and be placed back onto the launch pad in less than an hour. In order to achieve this,
the launch pad will need to be fully resistant to debris and the force of Starship’s engines.
But debris is not the only problem, the sound produced during a launch
can be extremely damaging to the rocket and the launch pad. When a rocket fires up its engines,
the hot gasses exceed the speed of sound and collide with the surrounding air.
This creates shockwaves which blast the launch pad with massive amounts of energy which reflect back
onto the rocket. During the launch of the first Space Shuttle flight STS-1,
the sound energy produced by the engines was powerful enough to damage some of the protective
thermal tiles on the solid rocket boosters. This is exactly why launch pads typically
use sound suppression systems to absorb most of that energy. The most common method is to spray
large amounts of water beneath the rocket. As the sound waves meet the water, they are absorbed by
bubbles of air which contract and heat up, turning the sound energy into heat energy.
But there are other methods used to fix the sound problem. In Kazakhstan, where the Russian Soyuz
rockets launch, the temperatures can be as low as -40 degrees - so a water deluge system would simply freeze.
Instead, the Russians suspend the rocket over a much larger flame trench
where there is very little in the way that could bounce shock waves back onto the rocket.
So why hasn’t SpaceX chosen one of these methods for their Starship launch pad? To answer this,
we have to look at SpaceX’s overall goal with their Starship rocket. They want Starship to
be able to land on the Moon and Mars and return with little to no refurbishment.
There are no launch or landing pads on Mars. That means landing on Mars will
likely throw up similar problems, with rocks and debris being thrown back at the rocket.
So, since this rocket is designed specifically for Mars, it doesn’t make sense for SpaceX to
cut corners now by taking off from pristine launch pads. Instead, they need to design the
rocket in such a way that it can handle the rough environments of the Martian and Lunar surfaces.
One way in which they plan to get around this issue for the Moon is by reducing the amount of
debris that’s kicked up during a landing. The Lunar version of Starship will have smaller
engines at the top of the vehicle which will ignite to slow the vehicle down during a landing.
These engines will be at least 50 meters above the Lunar surface, minimizing the amount of debris
that gets kicked up. For the Moon, this is a great solution. However, this solution would
not work on Mars. Since the gravity on Mars is much stronger than on the Moon, Starship will
need to use it’s more powerful raptor engines to land. Since these engines are so large,
they will remain at the bottom of the vehicle. SpaceX will therefore have no choice but to find
a way to protect the engine bay from debris. On the Falcon 9, all of the Merlin engines are
attached to a structure known as the “octaweb”. Here, the main engine components are shielded
behind an aluminium structure with only the engine bells sticking out. This is mostly to protect
the engines during reentry, since the rocket enters the atmosphere with its engines first.
Starship reenters the atmosphere belly first but it will likely adopt a similar design in order to
protect the raptor engines from debris upon launch and landing. As SpaceX’s test program continues,
it’s likely that they’ll try taking off and landing from rougher terrains, to simulate a
real landing on Mars. After the recent static fire damage, SpaceX has started to shield the wiring in
the engine bay behind steel pipes. This is likely the first of many developments that go towards
armoring Starship, so it can handle the worst case scenarios when it eventually lands on Mars.
So as SpaceX continues to develop Starship and expand their knowledge, many of us are looking
to do the same. 2020 is almost over and it’s time to start thinking of ways to improve ourselves
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