SpaceX prepares for key Starship “SN8” test

SN8 sits ready at the pad for its test flight with sunset behind it. (Credit: An Tran, for Space Scout)

DEC. 7, 2020– Over a year ago, SpaceX executed a much-anticipated flight test. Starhopper, a sub-scale prototype of SpaceX’s massive fully-reusable Starship rocket, flew 150 meters before coming back down to land propulsively. Shortly thereafter, CEO Elon Musk took to Twitter and began to detail his plans for the future of Starship’s developmental program at the SpaceX South Texas Launch Site. Musk claimed that SpaceX was targeting a “20km flight in Oct (2019) & orbit attempt shortly thereafter.” Now, several explosive delays later, SpaceX is finally taking a crack at that next step.

On September 27, SpaceX rolled out their SN8 prototype of Starship to the test pad. Standing about 30 meters tall and lacking a nosecone, Starship SN8 rode on the backs of its unsuccessful predecessors. The testing campaign then officially began on October 7th when SN8 was filled with liquid nitrogen for the first time, in order to certify its ability to hold its cryogenic fuels – liquid methane and liquid oxygen. Later, Musk confirmed that this test was successful. SpaceX moved forward with the testing program, ensuring that every system was operational prior to the final launch and landing test, and on October 19, SpaceX performed a short test of SN8’s pre-burners, which allow the engine’s turbopumps to function. This test was shortly followed by a full test firing of SN8’s engines the following day, certifying its engines for flight.

At this point, SN8 had progressed far enough into the test program that SpaceX began to make serious preparations for the much-delayed high altitude flight test. On October 22, SpaceX rolled out a massive Starship nosecone to the launch site where the previously flat-topped SN8 was standing. Within a few hours, SN8 officially became a full-sized Starship prototype. With the inclusion of this nosecone, SN8 gained header fuel tanks, small tanks located at the tip of the nosecone and bottom of the methane tank, that were necessary for landing burns, as well as the aerodynamic surfaces required for a controlled descent.

These systems are all necessary for SN8’s upcoming flight test and required extensive testing beforehand. Thus, SpaceX ran various tests to verify the header tanks and the aerodynamic surfaces. Throughout the past few weeks, the test crews have also been seen moving the canards and flaps back and forth to make sure the actuators work as intended, along with also performing various static engine fires in order to test the header tank’s ability to feed fuel to the engines.

However, SN8’s testing has been met with various degrees of success. On November 10, SN8 successfully fired its engines using fuel fed from the header tanks. Yet, when they attempted a follow-up test three days later, foreign object debris kicked up from the test site damaged one of SN8’s three Raptor engines beyond repair, forcing SpaceX to replace it. Despite this, SpaceX was able to successfully reattempt that engine test less than two weeks later. These complications have raised some doubts about the vehicle’s ability to complete the planned flight test, leading even Musk himself to state that “Lots of things need to go right, so maybe 1/3 chance (of a successful SN8 test flight)” when questioned by CNBC space reporter Michael Sheetz on Twitter. Regardless, the Starship development team has decided to take the risk and continue to pursue the flight test.

Starship SN8 during a wet dress rehearsal for its upcoming 12.5km flight test. Credit: An Tran, for Space Scout

With all of these milestones completed, SN8 has now begun preparations for the grand finale of this testing program. CEO Elon Musk has confirmed that SpaceX is aiming to complete a 12.5km flight test in order to test the launch, descent, and landing systems of the Starship spacecraft. Over a year has gone by since Musk initially introduced his plans for such a test, and now we’re finally approaching this pivotal moment in Starship’s development.

The test – which was originally supposed to be 15 km, will test multiple parts of Starship’s ascent and landing profile. According to a simulation done by Flight Club, the vehicle will fly under power for the first 30 seconds of flight, cutting its engines at an altitude of six kilometers and reaching a peak velocity of Mach 1.23. After reaching its peak altitude of 12,500 meters, SN8 will attempt the most challenging part of the test – the “skydiver” descent. It will have to not only stay stable while falling in an orientation with its wings parallel to the surface, but it will also have to glide almost six kilometers to its landing site. The most extreme part will be the “flip” – a quick re-orientation of the vehicle to an engines-downward position, requiring a double engine ignition with extreme stresses on the vehicle. If SN8 remains intact after all this, it will land on its six legs on a landing pad, touching down just about three minutes after liftoff.

SpaceX has obtained FAA-issued temporary flight restrictions around their launch site for attempts possible on December 8-10. Based on current information, it seems like SpaceX will attempt the flight sometime in this window, however, Starship’s development program has proven to be unpredictable in the past and this is definitely subject to change. This test, if successful, will help certify Starship’s reentry and landing design, allowing SpaceX to progress further into their development program and bring themselves one step closer to the Moon and Mars.

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