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Starship SN4 is set for a crucial cryogenic test run on Saturday night at the SpaceX launch site in Boca Chica, Texas. The cryogenic test test is one of the first tests necessary to demonstrate the vehicle’s flight ability. If all goes well, SpaceX teams will work toward a static fire potentially followed by a small jump.
SN4 follows the prototypes of the large-scale spacecraft Mk1, SN1 and SN3. Previous large-scale versions have failed all cryogenic test tests. The cryogenic test test is when the spacecraft is filled with liquid nitrogen to verify that its tanks can withstand flight pressures.
To date, the only Starship prototype that passed the cryogenic test test was SN2. However, SN2 was only a partially assembled tank section rather than a large-scale vehicle.
With the setbacks above, the pressure is on SN4 both literally and figuratively to pass the cryogenic test test, which is one of the first tests the vehicle will face on the launch pad.
The good news for SN4 is that the most recent SN3 failure was not the result of another soldering problem. Soldering problems had affected previous prototypes. Instead, a simple test setup error 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 on it.
This error will almost certainly not be repeated with SN4.
At the time of writing, SpaceX teams are currently targeting Saturday night or early Sunday morning for two-part test trials.
First, the ship will be pressurized with nitrogen gas. The teams will then return to the platform to inspect the vehicle before continuing with the main event – the cryogenic test test. It should be noted that the testing times are extremely fluid and there are likely to be delays.
If SN4 becomes the first large-scale prototype to pass the test test, it will move on to the engine test in the coming days.
SpaceX currently has three flight-ready Raptor engines awaiting the opportunity to participate in testing.
Raptor engines are not installed until after the cryogenic test test, as that test uses hydraulic pistons to simulate the forces created by the Raptors during flight.
A Raptor engine in Boca Chica, Texas. Credit: BocaChicaGal for NSF
If SpaceX can perform Raptor installations on SN4, teams will need to perform controls on all three engines in the vehicle. These payments will include tests of gimbal pre-burner, lighter and fuel, among others.
SpaceX will be ready to attempt a static fire. It’s unclear whether SpaceX will start with a single-engine static fire or go straight to a three-engine static fire.
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As a result, there is a good chance that minor problems with ground support equipment may have to be resolved prior to static fire.
If SpaceX can finally run on a successful three-engine static fire, the company may choose to proceed with a small leap of the Starship SN4 prototype.
Until the SN3 test incident, SpaceX had planned to jump that vehicle to about 150 meters. SpaceX can perform a similar test with SN4. However, test plans are constantly evolving.
What is known is that SN4 will be limited to only small jumps that do not require re-starting Raptor engines, according to a tweet from SpaceX CEO Elon Musk.
SN4 will have no flaps, so you can only fly with the engine running. I just restarted this week on the fin, actuator and aero static design. SN5 or SN6 will get fins.
– Elon Musk (@elonmusk) April 16, 2020
Musk explained that this is because the vehicle will not be equipped with the necessary control surfaces for the vehicle to fly where the engines are turned off and then back on.
SN5 or SN6 vehicles will have fins installed, according to Musk. The flap design has been slightly modified from what SpaceX recently unveiled with the Starship Mk1 vehicle.
The upcoming SN5 and SN6 vehicles are also expected to get backpacks, something a Starship prototype doesn’t have with it on the platform yet.
The nose cone will not only house payloads for operational starships, but will also include the liquid oxygen header tank. Placing the header tank on the nose cone tip helps keep the vehicle’s center of mass forward. This is important for when a starship descends through an atmosphere with no payload.
Construction of the SN5 vehicle is already underway. Numerous sections have already been seen inside the large production tents at the Space Chica facility in Boca Chica. Additionally, a portion of the SN5 tank section moved to the high bay just hours after SN4 was rolled to the platform on Thursday afternoon.
While SN4 will not receive a nose cone, the vehicle has installed several heat tiles on its surface. A group of tiles has been placed along the engine section and towards the top of the tank section.
The Starship production version will eventually have an entire side of the vehicle covered in thermal tiles to allow the vehicle to safely re-enter Earth’s atmosphere and eventually enter the atmospheres of other planets.
The inclusion of thermal mosaics in SN4 will allow SpaceX to gain experience with the assembly process and verify that the mosaics remain properly secured to the starship during testing.
For daily updates on progress in Boca Chica, subscribe to the NASASpaceflight YouTube channel.
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