Da quell‘articolo è passato un bel po’ di tempo senza novità significative.
SpinLaunch ha pubblicato alcuni video dei lanci suborbitali di prova che ha
effettuato, come questo, che si
riferisce a un test del 27 settembre 2022, in cui ha lanciato dei carichi
sperimentali di NASA, Airbus U.S., Cornell University e Outpost. Non è stata
indicata la quota raggiunta, ma le notizie (Space.com) parlano di accelerazioni di circa 10.000 g e di una dimostrazione della
realizzabilità di carichi utili in grado di sopportare queste sollecitazioni
usando componenti standard. I carichi sono stati recuperati con successo.
Questo è stato il decimo lancio di prova effettuato e il primo con carichi di
terze parti.
In questa illustrazione il coperchio della camera a vuoto è rimosso per
mostrare il braccio rotante interno.
Non è difficile notare che quello che Spinlaunch ha costruito e propone di
costruire è non solo un lanciatore di veicoli spaziali, ma anche in sostanza
un cannone elettrico, che spara proiettili ipersonici. Se li lanciasse
angolati, anziché verticalmente come sta facendo, avrebbero una gittata non
trascurabile, e sarebbero dei proiettili assai difficili da intercettare. La
soluzione di usare un braccio rotante, invece di un acceleratore lineare come
nei cannoni elettrici militari (railgun) attuali, riduce il picco di energia elettrica richiesto, dato che il
braccio può essere portato alla velocità di lancio gradualmente. Le
applicazioni e implicazioni militari, insomma, non sono trascurabili, anche se
le velocità di lancio raggiunte finora da SpinLaunch sono inferiori ai 12.000
km/h dei railgun lineari. Non a caso
Wired.com
nota che nel 2019 il Dipartimento della Difesa statunitense ha siglato un
contratto con SpinLaunch per lo sviluppo della sua centrifuga.
Inoltre un sistema del genere sarebbe molto interessante se installato sulla
Luna o su altri corpi celesti che non hanno un’atmosfera densa o non ne hanno
affatto: costituirebbe un metodo efficace per lanciare carichi senza dover
portare o fabbricare propellente, senza sollevare polvere superficiale al
decollo e senza contaminare la zona di lancio con il proprio scarico di gas
combusti, evitando la necessità di collocare il sito di lancio lontano dalle
strutture abitate (sarebbe sufficiente metterlo dietro una collinetta che
conterrebbe eventuali malfunzionamenti catastrofici). L’energia per
alimentarlo sarebbe elettrica, e quindi generabile in loco usando dei pannelli
solari e un sistema di accumulo.
Questo video è lungo ma contiene moltissime immagini e informazioni tecniche
molto utili:
Da qui in poi non ho avuto tempo di impaginare per bene, ma ho sistemato gran parte degli
errori:
Like holding a carbon fiber brick.
I don't think there's... I've never seen an
application where that much carbon fiber has
been laid up.
It's, it's rare to see carbon fiber this thick.
Yeah.
It really is rare. The final fully scaled
tether for SpinLaunch’s orbital system is
likely going to be the single strongest tensile
structure on earth. Let’s do the math on that.
SpinLaunch aims to [release?] its aeroshell, containing
the miniaturized rocket system, at about Mach
6, that’s roughly 2 kilometers per second. With a radius of 45 meters, the tether will
need to spin 450 times per minute to attain
that velocity. At that rate the g loading on the tether will
be 10,000 gs.
Meaning this aeroshell is going to exert a
force 10,000 times greater than its weight
due to gravity.
The aeroshell with the payload and rocket
is going to weigh approximately 10 metric
tonnes. So that means the tether, at the tip,
is going to need to be able support 100,000
metric tonnes, or 100 million kilograms. To put that into context, a fully loaded Falcon
9 weighs about 0.55 million kilograms, so
this tether is going to need to support the
equivalent weight of 182 Falcon 9s.
This is going to require a hefty piece of
carbon composite with cross-sectional area
of at least 0.23 meters squared.
That explains the brick of carbon fiber we
saw.
That brick could support about 4.1 million
kilograms. So the full scale tether will need to be 24.4
times this size at its tip, but that’s just
the tip.
This equation tells us why carbon fiber is
so vital to this endeavor.
Because each section of the tether has to
support the section above it, its strength
to weight ratio needs to be exceptional. If we calculate the tether area near the hub
for the same carbon composite, the tether only
needs to increase in area by 2.5 times, at
about 0.56 meters squared. We would of course need to add a safety factor
of at least 1.5 to this, increasing these
dimensions by 50%.
I have skimmed over this equation here, but
if you want to learn more about the engineering
of this system, and energy of getting to space
in general, I have created an entire course
on Brilliant to partner this video, and you
can sign up for it with the link in the description.
That design is perfectly feasible and is reflected
in SpinLaunch’s renders. We even have the manufacturing skills necessary
to build even larger composite structures, thanks to the wind industry.
So, this is all well and good, but spinning
a carbon fiber composite up to Mach 6 isn’t
possible in air. The aerodynamic heating would destroy it. So, to solve this issue,
SpinLaunch created a massive vacuum chamber
around its tether.
"You know, there's a bunch of things at the
beginning of SpinLaunch that were nonstarters
for a lot of people, like even just building
a large-diameter vacuum chamber.
You know, people were telling us, you know,
the one behind me here would cost tens of
millions of dollars to build. And we ended up doing it.
You know, we had this really, really kind
of scrap-heap mindset. And we ended up doing it for less than a couple
million dollars with ten people.
Right. Which is unheard of.
There's some large industrial
vacuum chambers out there.
But there's, you know, quite a few of the
really large chambers around the world are
for aerospace applications.
And so they're achieving extremely high levels
of not only vacuum, but cleanliness.
And so the cost is proportional to that.
And it's kind of exponential.
You know, they're achieving vacuums that are
on the order of ten to the negative 8 millibar torr. And, you know, typically we're operating at
about a million times worse than that."
SpinLaunch is breaking new ground with this
kind of vacuum chamber.
Typical large-volume vacuum chambers, like
the world’s largest one at the Space Power
Facility in Sandusky, Ohio, are designed to
simulate the vacuum of space.
Those require an extremely low pressure vacuum,
with tight tolerances and control of contamination.
They even need specialized tools like lamps
to simulate the radiation and heat emanating
from the Sun and cryogenic cooling to simulate
the heat of space. The people that built these facilities are
the industrial experts SpinLaunch had to draw
from, and most thought they would never be
able to build a vacuum chamber this large on
their budget.
But SpinLaunch had some things on their side.
They didn’t need that extreme of a vacuum,
as their goal is not to simulate the vacuum
of space. Their goal is to minimize drag and the power
required to overcome it, minimize the aerodynamic
heating that would destroy the tether, and
eliminate all those pesky aerodynamics effects
like flutter. That means SpinLaunch could use cheaper materials
like mild steel, where ultra high-vacuum chambers
need more expensive specialized processed
materials to avoid outgassing,
where gases within the metal in the form
of oxides, or simply dissolved within the
metal, are released into the vacuum.
It also makes the process of drawing a vacuum
much easier. Drawing a vacuum isn’t as simple as just
turning on a pump and leaving it on long enough. The more air you draw out, the harder it becomes, as you are not only working against a continually
growing pressure gradient, but statistical
probability.
The first stage of drawing a vacuum is to
remove the bulk gas. At this stage the gas
is a viscous fluid, and the molecules within
the chamber interact with each other often. Here we can use traditional fluid flow pumps,
like a positive-displacement pump,
that mechanically moves molecules out of the
chamber, and higher-pressure air at the back
of the chamber forces more air to fill the space
created, allowing more air to be pumped out.
But as gas is removed from the chamber, the
distance between the molecules increases. This is called the mean free path: the distance a molecule can travel without
colliding with another molecule.
Now, pressure is really just molecules colliding,
and as collisions become more infrequent,
the pressure gradients that are needed to
achieve equilibrium begin to vanish,
meaning it takes longer and longer for equilibrium
to be established, and the rate the pump can
remove molecules lowers, as there are simply
fewer and fewer molecules near the pump to
remove. At some point viscous flow stops entirely
and we enter a flow regime called molecular
flow, where the distance between collisions is actually
larger than the internal dimensions of the
vacuum chamber.
Meaning, the molecules are statistically more
likely to just bounce inside the chamber with
nothing forcing them towards the exit. At this stage it is impossible to actively
pump the molecules out.
The molecular pumps needed for this flow regime
instead act like some kind of Venus flytrap,
waiting for a molecule to enter it, and then
its job is to prevent the molecule from returning
to the original chamber. Turbomolecular pumps are basically multiple
levels of turbines that knock molecules in
one direction and prevent them from traveling
backwards. These pumps require insane rotation speeds,
anywhere from 36,000 rpm to 72,000 rpm, and
need incredibly tight tolerances too; they
are trying to pump individual molecules after
all. So, it goes without saying, these kinds of
pumps are expensive.
All the while, outgassing and other leaks
are actively working against the game of pure
chance. Creating a high vacuum requires extreme precision
in manufacturing and design. SpinLaunch didn’t need any of this.
Mark Sipperley, the director of Engineering
at SpinLaunch, walked me through the vacuum
pump station at the New Mexico site.
"Here in the vacuum plant the, the most familiar
thing would be the tube that came out of the
chamber and then runs underground in this
manifold.
So this is the very end of it.
So off of this vacuum manifold, we then have
a series of three different types of pumps. Up on top we first have roughing pumps, which
pull the atmosphere of like one atmosphere
down to about 30 millibar. Those are dry screw pump that are essentially
like overlapping lobes.
It's it's one form like a turbocharger.
Then the next stage is we have this Roots
pump, which is, which is like a yeah, another
shape of a turbocharger. It's like this the rotating twin screw pumps
okay.
So that kicks on at about 30 millibars.
So it's mostly only in it's 30 millibars below.
But you'll notice that each pump, it exhausts
into the pump like a pump, that's a slightly
higher pressure.
So this Roots pump only works in 30 millibars
below, but it can't exhaust all the way up
to one atmosphere.
So that's backed by another piston pump
So this this would also be like a great roughing
pump.
So when we turn on the first system, we have
nine Edwards GSX pumps up there, and then
this piston pump.
Sorry, both of these piston pops when we get
down to 30 millibars, which we turn on a series
of Roots pumps, which is this guy right here.
And we have another smaller one on this one.
These pistons are also running as well.
And then once we get down below one millibar
they're going to turn on these vapor diffusion
pumps, which only are really effective down
at the very low pressure.
Those work like oil jets.
So you vaporize oil, you shoot it down a series
of channels and it grabs onto the air molecules,
runs them down a series of tubes and then
you have these cooling loops that will then
condense out the oil and then the water, or
sorry, the air progressively makes its way
through like a long path, and it eventually
goes to a Roots pump, which can grab on
to it, and then it goes to a piston pump,
then all the way out.
So we talked before, you know, vacuum may not
be the best description. Most people think
of vacuum like a hard vacuum like in millibar, in
torr is what most people are used to like.
E to the minus -7 torr, like seven zeros are
six zeros.
And the number that's like true vacuum. That's hard vacuum, that's where you test
like, you know, like electric propulsion systems
and like high-end space features. That is nowhere near the atmosphere that we
need.
And that's that vacuum is also really expensive
to get to. We have to follow a lot of stringent rules
like you can't use steels, you have to use
aluminums and use coatings. You know, even like putting your fingerprint
in an atmosphere in a vacuum that low, will
take weeks to boil off. We only require the equivalent to the minus
3 torr or as a .01 millibar or .1 millibar. Today we're going to be running at like one
millibar.
We only pull the vacuum that we need, because a
vacuum is expensive. So it’s is closer to describing it like
a high atmospheric chamber than a vacuum chamber
specifically.
And then it will be the same.
And again, that's all driven by the aerothermal. That's all that's the only vacuum that we
needed to accomplish. So on the orbital system, we'll probably pull
a very similar vacuum, we don’t have to
go much deeper, there’s no benefit to going
lower."
This is another one of those technical issues
that the internet made a big deal out of,
without fully understanding what SpinLaunch
actually needed out of the vacuum chamber.
One of the other primary concerns expressed
on the internet was the tricky and unique
problem of a vehicle traveling at hypersonic
speeds from a vacuum into a thick sea level
atmosphere.
To begin with, we need to prevent air from
rushing into the vacuum chamber once the vehicle
is released. SpinLaunch is aiming to be a high-frequency
launch system, capable of launching multiple
satellites per day, holding the vacuum between
launches to decrease energy and time costs. However, the primary concern is the disastrous
effects that air would have as it meets the
tether spinning at hypersonic speeds. This would be an incredibly expensive single
shot system if this was allowed to happen.
To solve this problem, SpinLaunch needed a
way of sealing the chamber extremely quickly
after launch, so inside this long tube attached
to the vacuum chamber is a double-door airlock,
with doors on either end of the tube. This tube is also under vacuum during spin-up.
As the vehicle is released, using a release
mechanism that SpinLaunch kept hidden from
our cameras throughout the shoot, it passes
into the exit tunnel, where the first door
rapidly closes behind it. As this first door is closing, the second door
will begin to open. The atmosphere will begin rushing into the
tube and give the aeroshell its first taste
of the hypersonic flight regime it will be
flying in. The first and second door need to close quickly
enough to prevent air from entering the vacuum
chamber.
This is not an easy problem. Millisecond delays that may seem trivial in
most cases start to mount up when the vehicle
travels this quickly. The time it takes for an electrical signal
to propagate, the time it takes to overcome
the inertia of the door, the time it takes
for a proper seal to form. All these problems become matters of survival
at these speeds.
Once again, SpinLaunch are keeping their cards
close to the chest on this one, but they did
give me a demonstration of the door closing
in their factory and engineering hub in Long
Beach, California.
"Well, it’s it's moving really fast.
And so when the... when the you know, without
specifying, is he going to do a countdown?
You're ready for a countdown just let me know.
Yeah.
So basically what's going to happen is, you
know, this is going to be filled with, you
know, for lack of a better word, like a black
door which basically you'll see that like
you can pass through this with a vehicle and
then in an instant it's going to be close.
Okay.
So and again, it's like fast in the blink
of an eye.
So you'll see a little bit of settling as
a, as a after it closes.
But it's, you know, basically 95% close within,
you know, 30 milliseconds."
Oh wow, okay.
Closing the airlock.
[Static]
Speaker
Closing airlock in five, four, three, two,
one.
[LOUD BANG]
It's pretty fast.
Yeah that is not what I was expecting.
[Laughing]
Yeah, it's fast.
So that actually closes.
Like, it's actually hinged.
There's a pivot.
Yeah, there's a pivot involved.
Yeah I wasn’t sure if it was going to be
a sliding thing.
But the hinged one makes sense as well.
Yeah, that wasn't that what I was expecting.
Yeah.
So it’s 100% reusable, so you can set that
back up again and do it again and again and
again.
So that's a key aspect of it is that you don't
have any major consumables in the process.
So, so that's fast. Visceral.
All right.
[Laughter]
It’s a door closing.
I don't know what to ask.
It's really important not to let everybody
back in.
So that's you know, that's why we have it.
Oh, everybody jumps.
You can’t not.
Yeah, yeah.
"So, you know, the airlock is a really critical
subsystem of the overall, you know, of the
overall architecture as you travel from vacuum
into the atmosphere because the tether is
still rotating at high velocities, you want
to maintain the vacuum inside of the vacuum
chamber. And so the airlock is your first line of defense
for that. And so we have multiple redundant airlocks just like what you see here that the vehicle
passes through and it subsequently closes
behind the vehicle, you know, preventing the
air from in-rushing and reentering into the
vacuum chamber. And so that the exit tunnel is really the
only portion of the chamber that experiences
a rise in pressure."
I imagine that allows you to reset and like
increase frequency of launches as well.
If you're not having to re…like..
"Yeah, totally.
So you can, you can do, you know, you can
essentially provide a, you know, an airlocked
space for the end of the tether as well.
And so you can basically just re-pressurize
that space as you load in new vehicles.
It's possible you could do vehicle integration
in vacuum.
But currently we're... we're anticipating actually
repressurizing a small portion of, you know, interfacing
around the tether. Repressurising a small portion and integrating
the vehicle without it being in vacuum or."
What do you actually see the like how many
launches a day do you think you can manage?
I think that's like one of the advantages
of this that you can yeah.
"I think on the very high end, it's upwards
of ten. I think on the low end, it's, it's, it's about
five is a pretty good nominal target for us. We see viability there."
In SpinLaunch’s public videos, the secondary
air lock has simply been sheets of mylar. This is one of the few problems that becomes
easier as the launcher scales. As the exit tunnel grows in length, it will
take air longer to reach the door at the base
of the exit tunnel. SpinLaunch have only just begun these one-third scale
tests, with their fastest launch
to date at 1.6 Mach, slowing ramping up the
speed of launch as they test their systems. This prototype launcher features some other
simplifications compared to their final planned
configuration.
One of the most obvious problems to tackle
is the issue of vibration. When a spinning object's weight is not evenly
distributed it will vibrate. This is how rumble feedback works in gaming
controllers.
A simple electric motor with an uneven weight
attached. However, with a structure as large as SpinLaunch’s
tether, spinning several times per second,
any imbalance could shake the entire structure
to the ground. This is a major problem, because by design
the tether releases a 10-tonne weight right
as it hits its maximum velocity. SpinLaunch needs a way to balance the tether
after launch.
There is a very simple solution to this problem
though.
Release a balanced weight from the other side
of the arm at the same time. Right now they are simply releasing a counterweight
that slams into an armored section of the
vacuum chamber. We saw one of these counterweights being manufactured
out of fiberglass in the Long Beach factory; however, over the long term having to clean
up the mess this creates after each and every
launch is far from ideal.
The ideal solution would be to release a counterweight
in the form of another launch vehicle after
a single half rotation of the tether. The oil-filled journal bearing the massive
axle sits upon should be able absorb the force
of this imbalance over a period of time this
short.
The next issue we need to concern ourselves
with is the aeroshell punching into the atmosphere
at Mach 6. This, again, is a fairly unique problem. Typically weight is a restraining factor in
aerospace, but for SpinLaunch the energy required
to spin the aeroshell up to speed is actually
rather trivial.
"And I like to use the analogy of like a Tesla,
right? So the Tesla Model S Plaid is about 0.7 megawatt. So on the low end, it's about 100 Teslas but
it really comes down..."
Is that the full scale?
Yeah, for the full scale.
Yeah, yeah, yeah.
"For the orbital system you're talking about like on the low
end.
On a very low end. You know, it's probably about 65 to 70 megawatts.
And again, that really depends on where you
end up with the final orbital tether, you
know, whether or not you, you know, what,
what safety factor you
operate with.
What, what, you know, what tether strength
you end up with your effective tether, cross
sectional strength that all feeds back into
itself.
And then you have to kind of scale it accordingly.
I would say like really conservatively, like, you know, if you wanted to spin
up really fast, then you're talking about
higher power demand.
So whether you want to speed up in an hour
or 2 hours, you know, proportionately makes
a difference of of how much power that you
need.
So but, you know, on the high end, you're
talking about maybe 150 megawatts of
power, which is like...
I don't know, maybe in layman's terms, it
sounds significant, but, you know, you can
you know, there's, you know, there's motor
catalogs where you purchase you know, the
motor that that has that capacity.
Right. And so this is, you know, it's industrial
scale hardware and certainly, you know, mostly
off the shelf."
Do you need to worry about grid integration
at all when you're when you're suddenly drawing
that much power?
"For better or for worse, no, because you're typically, you know, particularly
for for early, you know, orbital accelerators
that we're building, we're expecting them
to be in really remote locations, kind of
remote coastal locations. Green field sites that don't have substantial
existing onsite, you know, resources or power. So you're you're basically, you know, bringing
your own power. You you know, and so you have to, you know,
decide on, you know, what is your energy source
or are you doing energy recapture, you know,
etc.."
SpinLaunch claims their total energy demand
per spin-up is about 100 MWhrs.
The cost per kilowatt hour for industrial
facilities is about 6 cent.
So that’s a cost of 6000 dollars in electricity
cost.
That’s insanely cheap. To put that into perspective, 100 megawatt
hours is equivalent to about 9600 litres of
kerosene, about 8 tonnes of fuel.
For reference, the Electron Rocket from New
Zealand's small-satellite launching company
Rocket Lab, capable of launching a similar
sized satellite, weighs a total of 12.5 tonnes, the vast majority of that weight being its
own fuel and oxidiser.
SpinLaunch claims their rockets will need
to carry about 30% of the fuel and oxidiser
compared to these competitors. They are essentially replacing the first stage
of a traditional rocket with an easily reusable
kinetic launch system.
SpinLaunch will also be able to recapture
a good deal of the electricity stored as kinetic
energy in the tether, using regenerative braking, even further reducing their electricity bill.
Because of all this, the limiting factor for
SpinLaunch in terms of weight is actually
the weight the tether can support, and as
a result, it actually makes sense to maximize
the density of the aeroshell, because it affects
a variable that will drastically improve its
ability to punch through the atmosphere: its ballistic coefficient.
Ballistic coefficient is essentially an object's
ability to resist air resistance. Think about how hard it is to throw a feather.
No matter how hard you throw it, it’s not
going to go very far.
It’s got a large surface area for air resistance
to act upon relative to its weight.
That’s a low ballistic coefficient.
Ballistic coefficient is found by dividing
the mass of the projectile by the drag coefficient
multiplied by the cross-sectional area. So SpinLaunch effectively wants to maximize
the mass relative to the cross sectional area.
This is obviously not typical for aerospace
vehicles.
"If you, if you look at reentry capsules whether
it's for something like the Stardust return
capsule where it's really, really high velocity
or you look at it reentry from orbit for a
manned capsule or something like the Space
Shuttle, they're typically using thermal protection
systems that are extremely low density, like
on the order of less than 300 kilograms per
cubic meter.
It's just basically foam.
And so... so typically that means you're making
like significant compromises, like.
The material often is,
You know, brittle or prone to fracture you
know, or really expensive or gets worn away.
And then you have to replace the tiles, kind
of in the infamous case of the Space Shuttle. So what we're dealing with is, you know, you're
on the tip of the vehicle you have, you know, materials like copper,
which, you know, not only are they, you know,
a significantly higher density, right?
You're talking about, you know, thousands
of kilograms per cubic meter, but they also
have really great thermal conductivity.
So basically, as you transition through the
atmosphere, you have a high heat load, but
then you're dumping that basically into heavy, dense materials
that have good thermal conductivity."
This is one of those unintuitive consequences
of this style of launch. When I first saw the full-scale aeroshell
on the SpinLaunch factory floor, I first asked
if I could ride it like a cowboy, but then
immediately noticed the bi-metallic nose cone. I knew from looking at it that it was made
from copper and aluminum, and that struck
me as extremely odd. Those metals would melt at the temperatures
I associate with hypersonic speeds. But, because SpinLaunch launches at Mach 6,
it actually transitions through the lower
atmosphere rather quickly, and as a result,
the heat generated can simply be absorbed
by these large heat sinks. Aluminum and copper's high thermal conductivity
means the heat is distributed through the
body of the aeroshell before it has a chance
to damage the vehicle.
The hefty carbon fiber shell is also incredibly
strong. SpinLaunch has already pulled their smaller
scale aeroshells out of the ground, buried
several feet deep from the force of impact,
and reused them with minimal refurbishment. With a parachute, these aeroshells will be
fully reusable with minimal maintenance, especially
as they serve no function other than to protect
the inner rocket’s stages. This isn’t an intricate mechanical machine.
Launching from the ground at these speeds
comes with advantages too. If we plot drag coefficient vs Mach number
for a bullet-like projectile, something rather
unintuitive occurs. The drag coefficient rises as you would expect
up until we hit Mach 1; at this point it starts
to fall as Mach number increases.
This is the equation for drag.
It’s proportional to drag coefficient, air
density and velocity squared. With drag coefficient being lower at hypersonic
speeds, it actually makes some sense to punch
through the thick lower atmosphere, where
the high-density air causes drag to rise,
as fast as possible.
Deceleration is a function of time after all,
meters per second square, meters per second
lost per second. Let’s calculate the dynamic pressure this
drag would create at launch, and the deceleration
it would cause. The dynamic pressure is found by multiplying
air density by the velocity squared and dividing
by 2.
At sea level, at Mach 6, the dynamic pressure
will be 2.6 megapascals.
The final aeroshell is 1 meter in diameter
and has a drag coefficient of about 0.1, which means the force applied to the aeroshell
at launch will be 205 kNs.
This sounds like a lot, but here's where the
ballistic coefficient comes in.
This drag force is being applied to a 10 tonne
body moving at mach 6.
That’s a lot of inertia.
Force equals mass by acceleration. Acceleration equals force divided by mass. That means high mass equals less deceleration. In this case, deceleration due to drag will
be about 19.8 m/s per second at launch, but
it will rapidly decrease as we move through
to thinner and thinner layers of the atmosphere
and lose velocity. In fact, with SpinLaunch’s planned trajectory,
we can plot the atmospheric density the aeroshell
will encounter over time: halfing in just 5 seconds, and dropping to
less that 10% of the original air density
in 15 seconds.
While gravity will remain more or less constant
at 9.8 m/s per second.
That means gravity losses form the majority
of energy losses in our transition to orbit. In total, SpinLaunch will lose about 150 m/s
of velocity to drag and 1000 m/s to gravity.
Satellites like Starlink orbit at 500 kilometers
with a velocity of about 7700 m/s, so even
if SpinLaunch maintained its 250 m/s velocity
from launch up until the aeroshell broke apart,
the two-stage rocket hidden within would still
have its work cut out for it.
However, now free of the mass of the aeroshell,
the substantially miniaturized rocket needs
only a fraction of the mass of fuel and oxidiser
to rapidly accelerate the 200-kilogram satellite,
the largest satellite this system can launch,
through the thin atmosphere at this altitude.
We can actually graph the relative velocity
of the spacecraft over time. Starting at Mach 6 at launch, and ending
up at about 1500 m/s when the aeroshell splits apart. The rocket motors then kick in to rapidly
accelerate the satellite to its 7700 m/s orbital
velocity.
The physics here absolutely checks out here,
but whether the economics and cost of development
will be viable is the big question to be answered. SpinLaunch has built a 1/3 scale prototype
at a relatively low cost, but the hardest
part of this technology is scale. They have reached 1.6 Mach thus far, have
tested their satellite components at 10,000 g
in their test facility in Long Beach, and
are continually upping their test parameters,
pushing further and further.
This is a comparison of SpaceX and SpinLaunch’s
proposed launch trajectory, but it doesn’t
tell the full story of the real driving issue
here, economics. A SpaceX launch to low Earth orbit costs about
67 million dollars. The heaviest Falcon 9 payload to date has
been 16,250 kg on a densely packed Starlink
mission. That equates to a launch price of about
4100 dollars per kilogram.
However, small satellite launch companies,
like RocketLab, who offer greater control
over orbit and launch schedules, charge about
15,000 to 25,000 dollars per kilogram. Dollars per kilogram is not a perfect metric,
but gives us some idea of the competition
SpinLaunch is facing.
SpinLaunch’s main competitive advantage
is in the decrease of expendable materials
like fuel while substantially miniaturizing
rocket components. They also have huge potential to launch far
more frequently than their competitors, helping
the economics of scale to kick in.
SpinLaunch claims to be targeting an ambitious
per-launch price in the range of half a million
dollars, placing them at 2500 dollars per
kilogram.
In my time in SpinLaunch, talking to their
engineers, it’s clear they are excited and
believe in this company. The basic napkin physics for SpinLaunch absolutely
check out, and they are well on their way
to solving the engineering challenges, but
scaling up this monstrous engineering effort
is going to require enormous amounts of investment,
and SpinLaunch could not disclose the answer
to many of my questions, as they seek patents
for their solutions.
I got little info on one of the most difficult
parts of the launch system, the release mechanism
for the aeroshell; even the 3D models SpinLaunch
provided for this video had the release mechanism
removed, so we had to model our own along
with the internal rocket structure. The design of the satellites is another problem,
due to the massive gs the satellites have
to survive, but g-hardening isn’t as large
an engineering challenge as the internet seems
to think.
"The most difficult part.
So besides the structure is, is also the reaction
wheel.
So the reaction wheel is, generates momentum
and basically steals the bus. And so it typically is a big mass that's cantilevered
up at a certain angle. So which is the one thing that we don't like,
you don't want having a big mass sticking
up on a can really."
This is what I assumed was going to be like
a difficult thing to because it inherently
has to be fairly high mass to control the
satellite.
Right.
"And so we've done a lot of work to instead
of re-engineering the wheel itself and figure
out different ways to do that, we basically
just took and created it took a clever way
of deploying the wheel. So we support the wheel in the flat orientation
and we spin. So when it's spinning, it's, it's well supported. The bearings are unloaded and so it can spin
and do its thing. And then we deploy the wheel for when it actually
used to operate.
So it's a it's a simple solution for what
could have been a really difficult problem."
And does the the axis of the actual wheel
cause any issues when it's like being loaded?
I imagine that's a fairly high weight to have
on the axle yeah.
"So we, what we do is we unload the bearings
and as part of the deployment mechanism we
actually move we reload the wheel into the
bearings."
Oh, okay.
So it's just taken off completely Okay.
"So again, trying to make simple solutions
for very difficult problems."
And like those are very simple answers, right?
Like I figured that the like the inertial
wheels would be difficult, not like you just
think about it as like, yeah, that's actually
a fairly easy thing to just not deal with.
You don't have to have it in the exact configuration
when you like launch, right? Same with the solar panels.You can have them,
like you said, loaded.
"Yeah.
So it's the problems aren't necessarily hard
to deal with.
It's just you have to think differently. We just have to change the way we think about
design.
So it's a little bit it's not a lot. The nice part is to that over the last 60
years, what people have been trying to do
with satellites actually has helped us because
they want to reduce mass. They want to make things stronger. So every bit that they're forcing them to
deal with shock and vibe already helps us. And it already inherently starts to make them
more hardened. Most components, we don't have to do anything
to them.
Maybe a little epoxy here but like we one
of the most surprising events that we have
here among the entire team is we took a board
that had a password stuck up, you know, maybe
a quarter of an inch.
And we all looked I was like, okay, that thing's
it's going to fly off the wall.
And we spun it and we brought it back and
it just went over and that was it.
And we are like, all right.
Our intuition is completely changing.
And yeah, and it's because it's, it's so little
mass and it's being held on by two pieces
of steel.
You know, the amount of force that that was
really imparting on those two piece of steel
was relatively small. So it just bent over and we all kind
of like, Oh, yeah, after you think about it,
it does make sense.
Okay. Yeah, that's right. So our intuition is starting to grow about,
yeah, this little connector of the sticking
up really isn't that big of a deal.
And so that has been in a positive way.
Very surprising."
Gs can only create force where there is mass,
and it turns out the satellite industry has
been finding ways to reduce mass for decades.
A simple aluminum can is capable of withstanding
10,000 gs with a basic redesign of its structure.
Minimizing weight located on unsupported surfaces
lowers the mass available to be multiplied
by the gs, and some simple corrugation can
help the aluminium absorb some of the loading
without buckling.
We spun up an off the shelf star tracking
camera using Spin Launch's in-house centrifugal
accelerator, which can already achieve 10,000
gs, and the camera worked perfectly fine just
moments later.
This is a really interesting engineering challenge,
that I think the internet is giving a hard
time for some bizarre reason, posing questions about basic physics calculations
without actually doing the math, and then
saying it’s impossible. Even missing the fact that kinetic energy
launch systems have already reached beyond
the Karman line 6 decades ago. [...]
The Soyuz rocket is launched with Expedition 70 NASA astronaut Loral O'Hara, and Roscosmos cosmonauts Oleg Kononenko and Nikolai Chub, Friday, Sept. 15, 2023, at the Baikonur Cosmodrome in Kazakhstan.Credits: NASA
