Starship SN8

SN8: How 3 Raptor Engines will shape future Starship prototypes

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The SN8 Starship prototype is set to undergo its first static fire test soon. Worthy of note too is that it will be the first multi-Raptor static fire that will be attempted by SpaceX. 

On Sunday October 12, SpaceX engineers began installing three raptors that will power the Starship’s flight test. The SN8 will be the company’s first high-altitude iteration of the spacecraft. 

Previous prototypes, namely the SN4, SN5 and SN6, had only one Raptor engine installed.

SN8: A Crash Course in Rocket Science

Last September, SpaceX CEO Elon Musk confirmed the SN8 will be the first prototype to have functional aerodynamic control surfaces installed.  

In other words, it will be fitted with a nose cone and body flaps. No matter the size, all operational rockets must have a nose cone and flaps.

The nose cone is the forwardmost section of a rocket. It is the first point that meets the air. It is designed to reduce aerodynamic drag as the spacecraft elevates into orbit. Drag itself is the force that opposes an aircraft’s motion through the air. 

A spacecraft’s stability relies on its ability to keep flying through the air pointing in the right direction without wobbling or tumbling. Body flaps provide that stability and control direction.  

A Starship SN8 placed on the launch mount in SpaceX’s facilities in Boca Chica, Texas on September 26, 2020 / Image source: NASASpaceflight.com – @bocachicagal

All prototypes go through three types of tests: A cryogenic proofing, static fire, and ultimately, a flight test.

A cryogenic proof test is when a rocket is filled with ultra-cold liquid nitrogen. The test’s goal is to verify that fuel tanks and associated hardware can withstand flight pressures. Under normal atmospheric pressure, nitrogen exists as a liquid between the temperatures of  -210 °C and -196 °C (-410 °F and -384.8 °F).

A static fire test is the process of firing the rocket engines at full-thrust while the rocket remains tethered to the launch mount. Its purpose is to examine the countdown process and the performance of the Raptor engines. SN8’s static fire test will involve firing three Raptor engines at full-thrust.

A flight test’s goal is to test out controlled takeoff and landing of the launch vehicle. The primary goal of a hop test is to prove whether a prototype’s unproven design is reliable or not.

Starship SN8’s Timeline

On September 23, the SN8 had body flaps installed. Three days later on September 26, the prototype was rolled to the launch pad in SpaceX’s facilities in Boca Chica, Texas. The SN8 was then forced to sit at the pad for four days due to unfavorable weather conditions. 

On October 1, it was finally installed on the launch mount itself to begin its test campaign. On October 7, Musk confirmed on Twitter that the SN8’s cryogenic proof test was successful, despite a leak near the engine mounts. 

SpaceX is now set to initiate the triple-Raptor static fire test. Two static fires will be attempted in total. SpaceX will also proceed with the tests before installing the SN8’s nose cone. It reduces scheduling conflicts and potential costs incurred by a hypothetical failure.

Starship SN8 Prototype fitted with body flaps / Image Source: Elon Musk via Twitter – @elonmusk

Finally, assuming that both static fire tests are successful, SpaceX will be able to conduct the eagerly-anticipated 60,000-foot hop test. Experts believe that the SN8 will perform an unusual “belly-flop” maneuver once it begins its controlled descent. It will use its aerodynamic control surfaces to slow its descent in a horizontal position. Once it gets closer to the ground, it will turn itself upright again and use its three Raptor engines to slow it down even further. 

YouTube channel C-bass Productions uploaded a video rendition of the maneuver last August.

YouTube channel C-bass Productions uploaded a video rendition of the maneuver last August.

The final version of the Starship will vastly differ from the current prototypes. It will serve as the second-stage of the launch vehicle. The first-stage of the launcher, the Super Heavy, will be powered by more than 30 Raptor engines.

SpaceX is inching closer and closer towards a fully-operational iteration of the Starship! 

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