This video is supported by Surfshark VPN. Hey, Hey Marcus House with you here. Today,
we are talking the explosive potential of Starship and Super Heavy. Typically I don’t
like to stress anyone out with such questions and I’m sure SpaceX are doing everything
they possibly can to minimize any such issue from occurring in the first place.Thanks to
spacex's iterative design the chance of a catastrophic explosion is very low, all the
static fires and flight tests leave us feeling confident in starship's first orbital flight
test at least clearing the tower. However in an unlikely event of an Rapid Unscheduled
Disassembly on the pad we were thinking about what the damage potential could be and it
isn’t as easy to predict as you may think. This is a topic I’ve wanted to explore for
a while now, but the reason I’ve been hesitant is because it is quite difficult to really
determine explosive potential in real-world situations. The major goals of Starship are
lowering the cost of payload to space, carrying life-support systems, orbital refilling, and,
finally, deliveries and transport to the Moon and Mars . … But before any of that can
happen, we need to see the largest, most powerful, and fully reusable rocket in the world successfully
launch without taking out the launch facility with it. You might be surprised at some of
the explosive numbers so let’s get started. Now, I don’t want to jinx anything talking
about this, but it is an interesting topic. Blast security is something SpaceX would indeed
be considering carefully right now. Sure we’ve seen plenty of Ships explode already without
there being a great risk to the launch site. All that happened there were minor repairs
being needed after fairly minimal damage, annnnd a little debris rain. We had explosions
on site, [pause] on impact, [pause] the “late boomer” [pause], and the mystery explosion.
But what all those had in common was a maximum methane load of maybe 10 tons or so. A fully
filled stack will hold more than 1,000 tons of methane. Nearly 100 times as much! So,
avoiding a Rapid Unscheduled Disassembly, should be the highest priority, otherwise,
things are going to get ugly. This is SpaceX’s Falcon 9 being prepared
for the launch with the Amos 6 mission in 2016. This mission certainly did not go to
plan. The Falcon 9 here suddenly erupted during pre-flight tests and dropped the payload in
this secondary explosion. A big setback for them at the time. Assuming it was fully filled,
the Falcon 9 contains around 160 tons of RP1 as its fuel. Only 16 percent of the fuel mass
than the full starship stack and it combusted not all at once but during 2 explosions and
burning afterwards. The Proton in 2013 hit the ground with nearly a third of the first
stage’s propellant burned and the upper stages in flames due to the aerodynamically
induced break-up. So in the area of 120 tons of UDMH ignited at once when smashing into
the Kazakhstanian soil. One of the biggest rocket explosions ever was the N1 in 1969.
The blast there destroyed the launch complex and hurled debris up to 10 kilometers around
the impact point. There are stories of broken windows even 35 kilometers away. But of the
possibly remaining 600 tons of RP1, several scientists estimated after the accident that
only 15% actually ignited at once. You need to remember that all this is an estimate as
well and it is hard to know solid numbers on this stuff. An interesting point is that
in this situation the kerosene was at room temperature. The methane of Starship-Superheavy
is at minus 180 degrees Celsius. Dispersed into the warm air heated by a smaller explosion
in say, the downcomer, it could evaporate faster and have more explosive potential than
RP1 since gases mix much better. Already the N1 explosion was estimated to have the equivalent
of 1 kiloton of TNT. But before we cover the possible TNT equivalent
range of methane explosions, let’s get a short understanding of the TNT equivalent
itself. Aeneas built a little Excel tool, to estimate the damage happening relative
to the distance of the explosion. We’ve got that linked as a download in the description
below. You just type in the TNT equivalent, and you get the sudden pressure change and
respective damage types for different distances to the explosion. It is certainly true that
very close to the explosion, damage happens because of the extreme heat additionally to
the pressure change, but generally, the damage potential is measured by that change in pressure
due to the shockwave. The usual unit is millibar. It doesn’t sound much, does it? But 1 millibar
is the equivalent of 100 Pascals. 1 Pascal is defined as 1 Newton per square meter. So
100 Newton Per Square Meter works out to be just a little over 10 kg per square meter.
That is a reasonably substantial force just for that 1 millibar. 1 bar of course is 1000
times that and this is roughly the atmospheric pressure on Earth here at sea level. But wait…
that is a force of about 10 tons or 2 monster trucks pressing against a typical 1 by 1 meter
sized window. Last I checked, our windows here were all intact so why is that? This
is due to the fact that there’s the same pressure inside and outside. But if there
is a sudden pressure change approaching from one side of the window, things get messy very
quickly. Just 3 millibar of sudden pressure change is the equivalent of about 140 decibels
or 30 kg per square meter. That’s not only loud, that’s painful. That’s like a firework
going off right next to your ear which can deal serious damage to your eardrum. Usually
sound is a stream of pressure changes, but a single loud bang is just one shock wave.
In extreme cases, we can even see it. Here, a small military solid rocket stage was destroyed
in a controlled manner, and we can see the shockwave speeding towards the camera resulting
in a loud bang once it reached the microphone. It’s hard to really know the decibels here
but given the movement on the ground and the camera shaking, we’re likely hearing something
beyond 140 decibels. We can count about 6 seconds until the sound reaches the microphone
as well. Multiplying this with the speed of sound at about 340 meters per second, the
explosion is 2 kilometers away - at least. Those shockwaves tend to travel faster than
the speed of sound closer to the detonation. Apparently, about 17 tons of solid propellant
was detonated here. If that’s half as explosive as TNT, say 8.5 tons worth, the camera could
have experienced about 6 millibars of pressure change. This shouldn’t damage windows but
the bang at this distance would be very painful and would result in complete destruction expanding
out to a radius of about 50 meters. So yes, we just assumed this detonation was about
half the strength of TNT but is this correct? Well precise estimation of the TNT equivalent
is hard. We did a bit of research and found a study for high pressure gas tanks. No solid
propellant but we’re here to get an idea of a fully filled Starship stack exploding.
These topics are always so interesting to me as we research them, and thanks to you
watching, that allows us to present this information in a friendly way to everyone, so thanks for
the support that you all show here. This study came to the conclusion that gaseous
methane at 350 bar is roughly as explody as the same amount of TNT with its high combustion
efficiency. When comparing the energy content of methane and TNT, we see that methane holds
more than 10 times as much energy. But energy content does not equal explosive potential.
Detonation velocity is a major factor. It’s the velocity of the shockwave travelling within
the explosive. Mixed well with air, it’s less than a fourth of TNT. Uneven mixture
though will then reduce that potential even more. And this opens a wide range, since methane
can’t burn in the center of a gas bubble when only the surface is in contact with oxygen.
Therefore, in case of gas tanks, when comparing the energy content, dividing the energy by
10 to 100 gives you the proper ballpark figure. So this means about 1,000 tons of liquid methane
that will end up in a fully filled stack is comparable somewhere between 100 to 1,000
tons of TNT. But that is weird right!? The N1 explosion was estimated to be comparable
to 1,000 tons of TNT as well, while only one 6th of the 600 tons of RP1 actually exploded...
allegedly. The energy content of RP1 is around 82% that of methane as well. Fairly comparable.
So how can this be? Well, what the tool also shows us is that the damage radius just increases
by a factor of 2.2 when the TNT equivalent increases by a factor of 10. This is due to
the logarithmic nature of shockwave propagation. That’s why slight errors in measuring the
pressure change will lead to large errors in the estimate. Meaning, the N1 explosion
estimate comes with a wide margin of error. But even this might not explain everything.
This is all very confusing of course and we will explain why this might be in just a moment...
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Ok, so I think we can clear up some of the potential numbers here a little more. The
solution might be in the fact that pure methane in a gas tank reacts only with air which is
mostly nitrogen and explodes not by ignition but by overpressure which means dispersion
of the methane before actual ignition. In ideal settings, when mixed with pure oxygen,
the detonation velocity of methane is about close to a third of that of TNT. That might
increase combustion efficiency by an order of magnitude and that possibly also explains
the N1 explosion. Luckily we have another interesting example! An Antares rocket exploded
in 2014 quite close to the pad. This setback was quite costly with about 15 million US
dollars in damage. No one got injured of course given the typical evacuation procedures with
such a launch. Just look at these stunning colours of the mushroom cloud! Having burned
through just a few seconds worth of propellant, most of the 70 tons of RP1 and the solid rocket
fuel in the upper stage were likely burned in and around the explosion. An assessment
we found on this event estimated the larger blast to be equivalent to 200 tons of TNT.
This is nearly double the amount per ton of fuel compared to the N1 estimate. Ok, so we
now have more data to work with, allowing us to combine assumptions on the available
oxygen, the results of the N1 and Antares explosions, and the easier vaporization of
methane compared to RP1 due to the much lower boiling point at -162 ° Celsius. RP1 in comparison
is liquid at room temperature. Elon Musk himself doesn’t seem to be that worried. He said,
it would be more of a big fireball than an explosion. Could be if the architecture of
the downcomer, when exploding, might push the oxygen to the side and the methane skywards
before it fully ignites. Under most conditions only the liquid methane that has dispersed
into the air or oxygen will burn meaning this fuel, though rather energy rich, is not as
volatile as one might initially expect. But let’s consider the absolute worst case with
perfect mixture and thorough ignition. Looking at the energy per kilogram as seen before,
we see that methane holds about 13 times as much energy as TNT. The detonation velocity
is about 30% of that of TNT - when mixed with oxygen. Completely filled, the stack holds
1,067 t of methane. This results in about a 4,300 ton TNT equivalent explosion. Deriving
from the damage tool, this will result in certain death and complete destruction within
a 350 meters radius. Boca Chica village, 3 kilometers away, would see windows burst and
potential damage to buildings. Even in Port Isabel, at around 9 kilometers away, windows
might get damaged. Let's hope that such an explosion would be very unlikely with this
potential blast, but those dams seen here on images provided by RGV photography won’t
help much in that case. Given what we’ve learned before about uneven mixture which
will most likely be the case for such an event, the actual explosion is probably by a factor
of 10 smaller. But we also learned that because of the exponential nature of explosions, this
means, the damage radius only decreases by the factor of 2.2. Therefore, Port Isabel
is safe but pretty sure the tanks would be gone and serious damage to the pad and the
tower are most likely. Repairing and rebuilding all of that would set the testing campaign
back by several months. Ok, so based on all that the obvious thing
to say is that we don’t want to see an explosion on the ground right? Avoiding the explosion
in the first minute of the launch is key. By then, the rocket will be more than 10 kilometers
away from the site and at least 2 kilometers out over the Ocean having already burned through
300 tons of methane. Debris rain here might do some damage but nothing compared to what
could be seen on the pad. An explosion here just needs a new rocket, not a complete rebuild
of the site which Elon stated is at least equally as hard to build as Booster or Ship.
And the rockets have an advantage because SpaceX already has an assembly line already
in place for that with stunning production speed.
So what sorts of problems could cause a Rapid Unscheduled Disassembly? Let’s have a look
at this. Here, we can see not only the outer ring of engines being close but the inner
ones, too. All 9 of these need to move or gimbal to steer the vehicle. Imagine just
one of the thrust vector control systems, or TVC for short TVC, failing. In a sudden
correction, the engine next to it might smash its bell into the blocked engine. Leaks of
the cooling system, flow separation through deformation of the bells, or particles getting
flushed into the pumps might then destroy an engine which, if strong enough, leads to
a chain reaction with the ignition of the propellant plumbing above.
The hard start of Starship Number 11 might be fixed 6 ways to Sunday but we’re looking
at 29 engines now instead of just the 3. Unwanted vibrations during start-up might still rupture
propellant pipes, or particles in the tanks could get flushed into the turbines enabling
a less likely way of a hard start. Perhaps sudden emergency shut-downs during
start-up could produce a water hammer effect in the propellant supply. Could that rupture
a weak pipe, having it spill its content and start an intense fire around the plumbing?
Keep in mind that 29 engines will feast on a minimum of 16 tons of propellant per second.
3.6 tons of which will be liquid methane. The biggest N1 explosion was a result of an
all-engine shut-down due to a few failures. This of course resulted in the rocket dropping
back onto the launch pad. This is something the Soviets did correct by allowing the vehicle
to keep the working engines firing so that it could get away from the pad. If a number
of engine shut-downs send the rocket into an increasing pitch or yaw, it might get rammed
like this into the ground near the pad with still plenty of fuel to ignite. If hurled
far enough, it might spare the launch site though.
Another scenario!? Well with 29 engines burning through 3.6 tons of methane every second,
the flame hitting the concrete pad underneath might loosen up more things than expected.
If debris gets shot into the engine bay at high speed, things would get messy.
What if the extremely powerful sound suppression system has issues? Here we see the one for
the Space Launch System being tested. Imagine the pressures here. Could any part of it burst
and hurl debris into the tanks penetrating them, resulting in a leak that’s being ignited
by the flames? Perhaps we need to have a closer look at such systems in another video but
keep in mind that for the full Starship and Booster stack it’ll need to pump over 100
tons of water per second! We are talking about megawatts of installed pump power.
There are many ways a launch can fail and only one way that it can succeed.
So yes, those are just some things we came up with and I’m sure the SpaceX team has
considered all these factors and many more. But what do you think? Where do you see risks
that might trigger a large explosion during the first minute? Did we get something wrong
regarding the damage potential? Did we over or underestimate fully filled explosions?
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