Overnight on Sunday April 26th, newest prototype
of SpaceX's Starship Mars-colonizing spacecraft
underwent a super cold pressure test in Texas
and remained intact on the test stand, likely
setting the stage for a test flight in the
near future.
SpaceX Starship SN4 became SpaceX’s first
full-scale Starship prototype to pass the
cryogenic proof test, one that had destroyed
three of its predecessors.
The Starship SN4 vehicle, on a pad at SpaceX’s
launch site in Boca Chica, Texas, was loaded
with liquid nitrogen, a test designed to confirm
its ability to hold cryogenic propellants
at pressure.
That test came a day after a pressurization
test where the tanks were filled with gaseous
nitrogen at ambient temperatures.
The cryogenic proof is one of the first tests
necessary to prove the vehicle’s flight-worthiness.
With the successful test, SpaceX teams will
now work towards a static fire test.
SpaceX CEO Elon Musk confirmed the cryogenic
pressurization test was a success.
“SN4 passed cryo proof!” he tweeted.
In this video Engineering Today will discuss
SpaceX’s latest Starship prototype which
passes a key test that puts it on track for
a first flight.
Let’s get into details.
This success marks an important moment in
the SpaceX Starship program.
Since November 2019, the company has lost
three full-scale Starship prototypes.
SN4 follows the Mk1, SN1, and SN3 full-scale
Starship prototypes.
These three previous full-scale Starship prototypes
failed that test in spectacular fashion.
In November 2019, a bulkhead in the SpaceX
Starship Mark 1 vehicle, which the company
showed off to the media two months earlier,
ruptured during a cryogenic pressurization
test, sending debris flying.
The company said at the time that the outcome
“was not completely unexpected.”
A second SpaceX Starship vehicle, SN1, was
also destroyed in a cryogenic tanking test
Feb. 28, this time with the vehicle bursting
near its base.
Musk said that the failure in that test appeared
to be with a “thrust puck” at the base
of the tank that takes the load from the vehicle’s
Raptor engines.
The company then stripped down the next SpaceX
Starship prototype in development, SN2, to
its tanks, which alone passed a pressurization
test in early March.
However, the SpaceX Starship SN3 vehicle collapsed
in another cryogenic pressurization test April
3.
With the prior setbacks, the pressure was
on SN4 both literally and figuratively to
make it past the cryogenic proof test.
There was optimism ahead of SN4’s proof,
as the most recent failure of SN3 was not
a result of a welding problem.
Welding issues had plagued the previous prototypes.
Instead, a simple test configuration mistake
caused a substantial pressure difference between
the liquid oxygen and methane tanks.
Consequently, the liquid oxygen tank collapsed
under the weight of a fully fueled methane
tank above it.
This mistake was not one that was likely to
be repeated with SN4.
In the end, SN4 passed the cryogenic proof
test – hitting 4.9 bar, or 4.9 times the
atmospheric pressure at the surface of the
Earth.
This pressure is not as high as SpaceX Starship's
fuel tanks and plumbing system are designed
to withstand, but it is enough for a basic
flight.
Elon Musk admitted in a tweet that this was
“kind of a soft ball…”
However, “that’s enough to fly,” he
added.
It is now expected to move on to raptor engine
testing within the coming days.
SpaceX Engineers will install SpaceX’s newly
developed Raptor engine onto the base of the
prototype this week.
The company will then ignite the Raptor while
restraining the vehicle to see if the engine
is working properly.
SpaceX developed the Raptor engine specifically
for Starship, and the final design of the
rocket calls for six of these engines to power
the vehicle.
But SpaceX will only use one Raptor on this
prototype, with plans to increase that number
on future vehicles.
SpaceX currently has three different flight-ready
Raptor engines that are all waiting for the
opportunity to participate in the upcoming
testing and one of these engines will eventually
be installed on the SN4.
A Raptor engine is not installed until after
the cryogenic proof test, as that test uses
hydraulic pistons to simulate the forces created
by Raptors during flight.
After the SpaceX has loaded up the Raptor
onto the SN4, the teams will then have to
conduct some checkouts of the engine's own
vehicle.
These will include gimbal, ignitor, and fuel
pre-burner tests, among others.
When all of these checks have been done and
everything is secured, SpaceX will then be
ready to attempt a certain static fire.
April 29 was originally the target for a static
fire test, but a one day delay with the cryogenic
proof test means that the static fire is now
likely targeting no earlier than April 30.
Just like the other static fire attempts with
SpaceX's previous smaller Starhopper, the
test might take a few tries until SpaceX is
able to successfully execute the perfect static
fire test.
After all, it will be the first time that
SpaceX fully fuels a Starship with cryogenic
methane and liquid oxygen.
Once the Raptor is tested properly on this
prototype, it’ll be time for this vehicle
to catch some air.
SpaceX intends to fly the prototype up to
an altitude of 492 feet, or 150 meters, and
then land it back down on the ground in one
piece, similar to a flight by a smaller “Starhopper”
vehicle in August 2019.
It’d be a short “hop” test, meant to
test the vehicle’s ability to take off and
then use its engine to touch down gently afterward.
This type of propulsive landing is how SpaceX
lands its Falcon 9 rockets after launch, and
it’s the same technique that the SpaceX
Starship is supposed to use when it lands
back on Earth after launch or when it lands
on other worlds — such as the Moon or Mars.
SpaceX has road closures optioned every day
from April 26th to May 1st, leaving plenty
of opportunities for a cryogenic proof test
whenever Starship SN4 is deemed ready.
If things go according to plan, Starship could
be “physically” ready for a hop test as
early as a “few weeks” from now, though
Musk says “approvals may take longer.”
That flight would require an experimental
permit from the Federal Aviation Administration’s
Office of Commercial Space Transportation,
as was the case for Starhopper’s test flight
last August.
What is certain is that SN4 will be limited
to only small hops that do not require a relight
of the Raptor engines, according to a tweet
from Musk.
Musk explained that this is because the vehicle
will not be outfitted with the control surfaces
necessary for the vehicle to perform flights
where the engines are shut down and then relit.
Meanwhile, SpaceX is still updating the design
of Starship and implementing changes on future
vehicles.
Production of the next SpaceX Starship prototype
is underway as the company continues to develop
this rocket at a rapid pace in Boca Chica.
The construction of the SN5 vehicle is already
well underway.
SpaceX already has fabricated most of the
parts for its SN5 vehicle.
Numerous sections have been spotted inside
of the large production tents at SpaceX’s
Boca Chica facility.
Musk said the SN5 vehicle will have three
Raptor engines and the vehicle’s distinctive
nose cone section, something that a Starship
prototype has yet to have with it at the pad.
Musk said in tweets earlier in the month that
the vehicle’s flaps and other aerodynamic
surfaces “are undergoing redesign for mass
reduction & simplicity.”
The flap design has been modified slightly
from what SpaceX most recently unveiled with
the Starship Mk1 vehicle.
The revised flaps would be installed on either
the SN5 or SN6 vehicles.
The nose cone will not only house the payloads
for the operational Starships, but it will
also include the liquid oxygen header tank.
The placement of the header tank in the tip
of the nose cone helps keep the center of
mass of the vehicle forward.
This is important for when a Starship is descending
through an atmosphere without a payload.
While SN4 will not be receiving a nose cone,
the vehicle has had several heat tiles installed
on its surface.
A cluster of tiles has been placed along both
the engine section and towards the top of
the tank section.
The production version of SpaceX Starship
will eventually have an entire side of the
vehicle covered in heat tiles to allow the
vehicle to safely reenter Earth’s atmosphere
and eventually enter the atmospheres of other
planets.
Including heat tiles on SN4 will allow SpaceX
to gain experience with the mounting process
and to verify that the tiles stay properly
secured to the Starship during testing.
SpaceX Starship is the "upper stage" of a
two-part, fully reusable launch system that
SpaceX is developing.
The company's goal is for the "Super Heavy"
rocket to boost SpaceX Starship into orbit,
where this vehicle can either carry cargo
to some destination or carry dozens of passengers.
For all the challenges SpaceX has had testing
the Starship prototypes, Musk said the biggest
challenge is developing the production line
for the vehicle.
“The thing that’s really hard is the production
system,” he said in an April 24 online discussion
hosted by Hack Club, a student group.
Musk said in the conversation that he was
at Boca Chica overseeing work on Starship.
“Designing a rocket is 1x hard, then building
one of it is 10x,” he said.
“Building the production system is at least
100x, possibly a 1000x.”
At its Boca Chica site, the company has taken
the build-test-fly-iterate process and put
it on steroids.
In a matter of months, SpaceX built what is
essentially a rocket factory in tents in the
dusty scrubland along the Texas-Mexico border,
hard by the Rio Grande River.
While the program has experienced several
failures to date, the ability of engineers
to learn from their failures and rapidly churn
out new prototypes within a month or less
appears to be allowing Musk and his coveted
Starship program to advance ever closer to the stars.
