Starship SN15 | Medium Altitude Test Flight

Featured image: Trevor Mahlmann

Launch Window (Subject to change)	May 05, 2021 -~17:00 UTC – May 06, 2021 -~01:00 UTC May 05, 2021 -~12:00 CDT – May 05, 2021 -~20:00 CDT
Mission Name	Medium Altitude Test Flight
Launch Provider (What rocket company is launching it?)	SpaceX
Customer (Who’s paying for this?)	SpaceX
Rocket	Starship SN15
Launch Location	Sub-orbital Test Stand A, Starbase, Texas, United States
Payload mass	There is no payload on this test flight
Where are the satellites going?	There is no payload on this test flight
Will they be attempting to recover the first stage?	Yes. However in the Super Heavy/Starship stack this will be the second stage and will also be recovered.
Where will the first stage land?	On the landing pad about 360 meters (~1,000 feet) from Test Stand A, Starbase, Texas, United States
Will they be attempting to recover the fairings?	There are no fairings on Starship
Are these fairings new?	There are no fairings on Starship
How’s the weather looking?	N/A
This will be the:	– 1st flight of SN15 – 4th flight of a Starship prototype to 10 km – 7th flight of a Starship prototype (excluding three Starhopper hops) – 5th flight of Starship with a nosecone and aerodynamic control surfaces
Where to watch	Official Livestream, once available Tim Dodd, the Everyday Astronaut, will be streaming; come ask questions and join the conversation live! Live updates leading up to the flight of SN15

What’s all this mean?

For the 5th time in the Starship program, SpaceX will be attempting to launch, belly flop, flip, and land a Starship prototype. SN15 aims to reach a medium altitude in the neighborhood of 10 km (6.2 miles), just like its predecessors SN9, SN10, and SN11 did. Yet again, SpaceX will attempt to land and recover the SN15 prototype from the landing pad about 360 meters (~1,000 feet) away from Test Stand A at the Boca Chica launch complex.

Starship SN15 Flight Profile

Similarly to the previous prototypes, SN15 will fly up to an altitude of around 10 kilometers (~6.2 miles) before performing its belly flop maneuver and falling back down towards the landing pad. SpaceX is aiming to intentionally shut down its three Raptor engines during ascent and later reignite them during the flip maneuver. Under the power of its Raptor engines, it will flip from horizontal to vertical, shut down one engine and try to land. Below is a table of each event based on the previous flights of Starship prototypes. Due to the nature of the dynamic countdown leading up to liftoff, these events do not have specific time stamps.

Events Prior and During Launch

Event	Description
Road Closure	The road leading to the pad and beach closes to all non-SpaceX personnel.
Flight Termination System (FTS) Pins Removal	The safety pins are removed which arms the FTS. The FTS is a set of C4 charges that explode the vehicle if it were to go off course or have a malfunction.
Pad Clear	Everyone, including SpaceX employees, must be cleared from the pad and the surrounding area.
Recondenser On (between T-48 and T-35 minutes)	This signifies the start of pressurization of tanks on the ground in the tank farm.
Ground Tank Clouds (around T-30 minutes)	The ground farm has become pressurized and is preparing to load fuel and oxidizer into the vehicle.
LOx and CH4 Tank Load (around T-25 minutes)	All four tanks on Starship begin receiving their propellants from the ground tanks. This is shown by the frost accumulation on the outside of the vehicle and visible vents.
Methane Vent (around T-16 minutes)	A vent can be seen from the methane tank on Starship, which depressurizes the tank.
Engine Chill (around T-12 minutes)	Engine chill is evident when condensation appears from inside the skirt, followed by “Tri-vents” or three vents near each respective Raptor engine closer to liftoff. The engines must be chilled by liquid oxygen before they ignite.
Liftoff!	The clamps holding down Starship are released after the engines are at desired thrust and the vehicle lifts off from the pad.
First Engine Shutdown	On ascent, one engine is shut down intentionally to extend the time they need to reach apogee in order to maximize the time an engine can fire.
Second Engine Shutdown	On ascent, a second engine is shut down intentionally to extend the time they need to reach apogee in order to maximize the time an engine can fire.
Hover and Third Engine Shutdown	At the target altitude, Starship will hover on one engine before initializing the belly flop and shutting it down shortly after.
Belly Flop Maneuver	The vehicle uses its four aerodynamic fin surfaces (two forward, two aft) to turn belly side down and control its descent as it begins to fall back towards the ground.
Flip/Engine Relight	At an altitude of approximately 500 meters (~1,600 feet) Starship relights all three Raptor engines as the fins and engines force it to go vertical again.
Landing	The least healthy engine shuts down after correcting for any over rotation as it slowly descends on the landing pad with its landing legs deployed.
Depress	After Starship is on the pad, the vehicle will begin to depressurize by venting as a step toward making the vehicle safe for recovery personnel approach.

What is Starship?

SpaceX is developing their next generation rocket in Boca Chica, Texas, United States. The launch system consists of the first stage “Super Heavy” vehicle, which will boost the second stage “Starship” out of Earth’s atmosphere. When both are fully stacked, they are referred to as “Starship”. After the two separate, Starship, powered by six Raptor engines, will continue to orbit. This could involve staying in Low Earth Orbit (LEO) or moving on to the Moon and eventually Mars.

As of the development of SN15, four previous Starships have flown with aerodynamic surfaces, (SN8, SN9, SN10, and SN11) with all four exploding before, on, or shortly after landing.

Starship Internals

Starship uses liquid methane (CH₄) as its fuel and liquid oxygen (LOx) as its oxidizer. When the vehicle is vertical, the larger liquid oxygen tank is on the bottom and the smaller liquid methane tank is on the top. The reason for the different sizes in tanks is due to the mixture ratio between methane and liquid oxygen that the Raptor engine requires to run properly. However, Raptor can operate outside of this ratio.

At the very top of the vehicle, and in-between the CH₄ tank and the LOx tank, are the two header tanks. These tanks are required for the unique flip maneuver that Starship does just before landing on the landing pad. When an engine relights, it must not suck in any gasses. That could result in the loss or damage of an engine. The header tanks are designed to eliminate that, so propellant will always be taken in by the engine while the vehicle is on its side.

Starship Variants

The current Starship launch vehicle is fairly minimal compared to the complex human transport version to be built and flown in the upcoming years. Along with human transportation, Starship also plans to have cargo and tanker versions to perform other various functions.

The crew version of Starship will have the capability to carry humans. The exact number of which is still up for debate, however its capacity will be higher than any other crewed launch vehicle ever built. The tanker appears to be similar to the current version of Starship undergoing testing and development, like SN11. Its main purpose will be to take an extra amount of propellant and transfer it to another Starship already in orbit.

The cargo variant of Starship will carry various types of cargo to a variety of orbits. Current numbers estimate that this variant could take 150 metric tons (330,000 pounds) to Low Earth Orbit (LEO). The lunar and deep space versions are even further out in development but these variants will be able to reach the Moon and the outer planets respectively.

The Raptor Engine

Both Super Heavy and Starship will be powered by various numbers of Raptor engines. The Raptor engines are unique enough themselves and use the Full Flow Staged Combustion Cycle, which makes it one of the most complex engines ever designed and built.

The Raptor engine is still in development, which means that significant and minor changes will occur as the development process continues. One of the more visible changes is the removal of testing hardware which has resulted in the engine plumbing being more compact and streamlined. SN15 will be the first Starship to carry these major design changes. As the Raptor engine gets farther along in development and SpaceX gathers more data, more changes will be made.

Future Testing

Up next after the testing of SN15, SN16-20 will begin their line of testing and an orbital flight attempt has been targeted for July of 2021. SN20 is slated to have nearly full heat tiles on the windward side of the vehicle to further test the entry of Starship back into Earth’s atmosphere at 25 times the speed of sound.