Starship SN5 conducts successful 150-meter flight test

by Michael Baylor

The Starship SN5 prototype has successfully conducted a 150-meter test flight on Tuesday from SpaceX’s Boca Chica test site in Texas. Monday’s opening attempt was scrubbed after the Raptor SN27 engine aborted at ignition. Following an abort early in the window on Tuesday, the attempt late in the window saw SN5 take to the air and land in one piece. The hop was the first flight of a full-scale Starship tank section, clearing the way for SpaceX to attempt higher altitude flights with Starship prototypes.

Tuesday’s livestream – second half of the day:

The launch window for Monday’s hop lasted from 8:00 a.m. to 8:00 p.m. Central (13:00 – 01:00 UTC). However, the hop was targeting liftoff during the later portion of the window.

Testing schedules are extremely fluid, with Elon Musk himself providing a countdown with about 30 minutes to go. This was followed by the T-10 minute police siren before counting down to ignition. However, the firing was aborted, likely at T-0, due to an issue with the Raptor.

The window on Tuesday opened at 8 a.m local time. The first attempt was aborted with a few minutes remaining before recycling efforts began for an attempt later in the day.

That second attempt of the day proved to be the one where SN5 took flight.

As per usual, the first sign that the teams were working towards a hop attempt was when the road to the launch site is closed to the general public. This always occurs well in advance of the test flight.

The pad is then cleared of all SpaceX personnel at least an hour or two before the hop. Finally, a siren is sounded ten minutes before the hop. The siren warns the residents at the nearby Boca Chica village that spaceflight activities are imminent.

Fans stayed up-to-date on the flight’s status, with updates posted on the @NASASpaceflight Twitter account. The NASASpaceflight YouTube channel also broadcasted the test flight live from Boca Chica, Texas.

For the successful attempt, SpaceX pushed through the countdown, with the police siren once again sounding. Then, at T-0, Raptor SN27 ignited, and – as expected – lofted Starship off the pad with a slew due to its off-center engine placement.

Rising into the air, Starship then – under the control of its Reaction Control System (RCS) thrusters, rotated slightly and began its descent to the landing pad.

As the smoke cleared, SN5 was seen to be still standing, allowing for the SpaceXers watching the test to break out into cheers.

SpaceX had not performed a flight from their Boca Chica facility since Starhopper – a smaller-scale Starship test vehicle – hopped to 150 meters in August, 2019.

Starship SN5 features a thrust section with liquid oxygen and methane tanks stacked on top. A nose cone and aero surfaces are the only significant components missing between SN5 and a full-size Starship vehicle.

While SpaceX has not released the official height of SN5, it is estimated to be in the ballpark of 30 meters.

An off-centered Raptor engine mounted on SN4 via Elon Musk. SN5’s Raptor is mounted in the same fashion.

To perform the 150-meter hop, SN5 used Raptor SN27. While SN5’s thrust section was built to support up to three Raptor engines in a triangle configuration, only one methane-fueled engine has been installed for the flight. This means that the thrust during the hop was asymmetric. The asymmetric thrust caused Starship SN5 to powerslide as it left the pad.

Attitude control thrusters also assisted with controlling the vehicle over the course of the hop.

Propellant loads were low for the flight – reducing the risk to surrounding infrastructure in the event of an anomaly. 

A mass simulator was also added to the top of the vehicle. Its presence is likely to compensate for the lack of propellant mass. The mass simulator was created by welding together two rolls of stainless steel. The rolls are of the same type used to construct the Starship prototypes. 

The profile of Starship SN5’s 150-meter hop was very similar to that of Starhopper’s. SN5 lifted off from its launch stand and worked its way up towards 150-meters. The vehicle then began to translate over to a nearby landing pad.

Six landing legs, located inside of SN5’s thrust section and folded up during launch, deployed before landing.

SpaceX’s development process leans heavily on rapid iteration, which would have allowed for a test failure. The company prefers to do tests like SN5’s hop sooner rather than later. The tests provide valuable data to inform future designs.

Had SN5’s hop not gone to plan, Starship SN6 was already standing by, and could have potentially been ready as a replacement for SN5 in short order. 

In the end, the 150-meter hop went to plan for SN5, like it did with Starhopper. Setbacks with previous Starship prototypes had delayed the 150-meter hop by several months.

Starships Mk1, SN1, and SN3 all failed cryogenic proof testing – where the tanks are pressurized with liquid nitrogen to ensure structural integrity. SN2’s testing was successful, but it was a smaller-scale tank prototype not intended for flight.

SN4 became the first full-scale vehicle to pass a cryogenic proof test and perform static fires. However, its fifth static fire resulted in an explosion shortly after engine shutdown.

SN4’s anomaly was caused by a problem with the quick disconnect umbilicals. As part of the test, the quick disconnects – which connect propellant lines to the vehicle – were detached as they would do for a hop. However, valves failed to shut, leaking large amounts of propellant. The propellant was eventually ignited, resulting in an explosion.

During SN5’s single static fire test, the quick disconnect system was once again tested. This time around, the system functioned as intended.

Common Dome Flip for SN8 – Via Mary (@bocachicagal) for NSF

With SN5’s flight attempt successful, SpaceX will likely proceed to higher altitude test flights. While the exact details of the next testing milestones have not been confirmed, they are expected to feature a more fully-fledged Starship design.

Starship SN8 – the prototype which is currently under construction – is expected to feature three Raptor engines, a nose cone, and aero surfaces. These features would allow the vehicle to perform flight tests to much higher altitudes. However, plans are very fluid with Starship testing, so until SpaceX has had a chance to review the data from Starship SN5’s hop, future testing activities remain very much in flux.

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