Space Sunday: Starship orbital flight test

April 20th, 2023: the Starship combination of Ship 24 and Booster 7: (l) approaching Max Q, intact but with several engines shut-down; (r) tumbling as control is lost. Credit: SpaceX

Thursday, April 20th saw SpaceX attempt the first orbital flight test of their Starship / Super Heavy launch vehicle combination. As most reading this article likely already know, things did not go entirely well with the vehicle’s flight termination system (FLS) being used to destroy it just under  four minutes into its ascent.

The flight was always going to be a risk; the Starship / Super Heavy programme has been an extraordinary public display of a rapid development cycle (some might say too rapid), with little in the way of comprehensive systems and integration testing to match that of the likes of NASA. In addition, and ahead of the launch attempt, SpaceX President Gwynne Shotwell went on record as stating the launch wasn’t a “focus” for the company; that lay in upping the production rate for starship vehicles and boosters – a rather surprising statement, all things considered, and one I’ll return to later.

Launch came at 13:33 UTC, after some two hours of propellant loading on both vehicles, and proceeded per the notes below:

T -00:02: 33 Engine ignition and hold on the Orbital Launch Mount (OLM) as trust builds.
T +00:04 Launch clamps release, and vehicle commences ascent, most likely with the failure of three Raptors, two forming a pair on the outer ring of engines, one within the steerable inner ring.
T +00:11 Ship 24 clears the launch tower.
T +00:15 Booster 7 clears the launch tower, first confirmation of three engine failures / shut-downs.
T +00:19 Vehicle exhibits diagonal vertical movement, potentially due to the off-centre thrust resulting from the failure of the two outer ring motors.
T +00:28 Visible flashes in exhaust plume followed by debris departing the base of the vehicle at high speed – thought to be one of the hydraulic pressure units (HPUs), used to gimbal the inner ring of Raptor motors and steer the vehicle.
T +00:40 Loss of 4th Raptor, the third for the outer ring.
T +01:01 Loss of 5th Raptor, the fourth for the outer ring, as vehicle enters Max-Q.
T+01:30 Vehicle exits Max-Q.
T +02:00 Vehicle starts to exhibit off-nominal exhaust plume.
T +02:23 In a split-screen view, vehicle is seen to start slewing in flight at the point it is expected to rotate, re-stabilise and allow the separation of Ship 24 from Booster 7.
T +02:46 Vehicle is clearly spinning / tumbling.
T +03:09 Ship 24 appears to start venting propellants (or possibly a reaction / attitude control thrusters firing).
T +03:12 Venting (or thruster exhaust plumes) visible on both Ship 24 and upper portion of Booster 7.
T +03:25 Vehicle now clearly caught in a flat spin, venting / thruster plumes still visible from the booster’s upper section and from Ship 24.
T +03:58 Flight termination system (FTS) automatically triggered. Vehicle is destroyed.

While the data is still being assessed, the most probable cause for the loss of vehicle is a combination of the loss of at least one of the HPUs and the loss (or partial loss) of two of the inner gimbaling motors, coupled with the off-centre thrust generated by the failure of two pairs of motors located in the same hemisphere of the outer ring of 20 engines leaving the vehicle unable to sufficiently compensate for the biased thrust, resulting in the start of the spin / tumble, which continued beyond the point of recovery, triggering the FTS.

Following the launch, social media was swamped with hails of the launch being either a “success” or a “failure” – with the former being based on statements by SpaceX that if the stack cleared the tower it would be a “successful flight”; hardly the highest of bars to clear for a vehicle intended to be “rapidly reusable”, and the latter based on the fact that the vehicle had to be destroyed – also hardly a fair assessment: rocket can fail – as evidenced earlier in the month by the loss of the smaller Terran-1 rocket on its maiden launch.

Two views of Booster 7, showing 6 failed Raptor motors (l), and what appear to be two more in the process of shutting down (r). Credit: SpaceX

Certainly, there was a lot of valuable data gathered on the performance of the Raptor engines – although not all of this was good. From images gathered, it appears a total of 8 Raptors failed either fully (6) or partially (2). That’s a potential loss of 25% of thrust; not something you’d want to see on a payload carrying mission. On the other hand, however, the uncontrolled spin / tumble showed the starship / booster combination was fully capable of passing through Max-Q and showed remarkable resilience in withstanding any break-up prior to the FTS being triggered.

In particular, the test proved – as many looking at the launch site objectively had long noted (including myself) – the Orbital Launch Mount (OLM), the so-called “stage zero” of the system, was far from up to snuff if it is to support multiple launches, thanks to the lack of any provisioning of a water deluge system or flame deflectors.

Both of these are essential elements within any high-thrust rocket launch system. Flame deflectors do pretty much what their name implies: deflect the heat and flame of engine exhausts away from the launch complete infrastructure and launch vehicle, working in concert with the water deluge system. This delivers hundreds of thousands of litres of water across the launch pad and under it, to both absorb sound to prevent it being reflected back up onto the vehicle as damage-inducing pressure waves, and to absorb the raw heat of the engine exhausts through flash vaporisation – seen as the white clouds of “smoke” erupting from the pads during SLS and former space shuttle launches.

NASA’s Pad 39b water deluge system delivers 1.8 million litres of water to the mobile launch pad when in place over the flame trench, to help protect it and the rocket from sound damage, and into the flame trench itself (the “waterfall” in the image centre), to quench the heat and flame of the rocket engine exhausts, thus protecting the launch infrastructure (including the flame trench) from heat damage. Credit: NASA

When you consider that in preparing to launch the Space Launch System (SLS), a vehicle that generates around 53% of the thrust of Super Heavy at lift-off, NASA upgraded the existing water deluge system at Pad 39B to deliver over 1.8 million litres of water under the pad, SpaceX’s refusal to design such a system, and the necessary flame deflectors into the overall launch infrastructure has long appeared to be nothing less than short-sighted corner-cutting.

In fact, it appears that – thanks to the various static fire tests make at the launch site – SpaceX had belatedly come to accept this, and were just “weeks” from installing a water-cooled deflection system under the OLM and were already planning to add an actual deluge system to the facility over and above the sound suppression water jets fitted to the ring of the OLM. As it is, the amount of damage done to the OLM and its surroundings potentially leaves SpaceX with a lot to feel sorry about. During the 8 seconds the vehicle was held on the OLM after engine ignition and throttle-up, the exhaust from the Raptors was sufficient to excavate a crater under the OLM, throwing up huge clouds of debris and massive chunks of concrete, some of which only narrowly missed the vehicle, whilst stripping the OLM foundations down to their steel rebar.

The orbital launch mount (OLM) showing the post-launch damage

Nor was the damage caused limited to just the OLM: images taken after the launch revealed the vertical tanks of the nearby propellant tank farm (none of them in use at the time, fortunately) to have been fairly hammered by debris, again revealing their overall vulnerability in the event of a launch mishap, and the inadequacy of the earth berm intended to protect them (despite the height of the latter being increased under requirements issued by the Federal Aviation Authority (FAA) as a part of their Programmatic Environmental Assessment.

And not even this was all: large pieces of concrete were hurled distances of 500 metres at an estimated 160 metres per second, giving rise to some stunning footage of a vehicle being used as a remote camera stand (and so parked well inside the range safety area) being totalled by impacts.

Whilst there is no guarantee the installation of the flame deflection system would have prevented all of this damage, it is not unreasonable to assume it would have potentially stopped much of it from occurring, rather than leaving SpaceX with – according to one company estimate – up to six months worth of repair work to carry out before flight testing can resume.

A image from the launch showing a strip of the high density concrete supposed to withstand the engine blast being thrown into the air and (inset) its likely point of origin. Credit: RGV Aerial Photography

All of which begs the question: was the launch worth it? On the one hand, data was gathered for the brief duration of the flight, as noted, and that is worth something. However, and on the other, lay the fact that by Musk’s own admission, Booster 7 was pretty much obsolete; the next  Super Heavy in line for a launch – Booster 9 – contains “hundreds” of improvements. Given that it is very close to being ready to commence testing and SpaceX have a flame deflector almost ready for deployment at the OLM, would it not have been better to have simply moved Booster 7 aside and waited another couple of months? Not only might this have limited the damage, it could have lead to more of the overall flight objectives being met without the launch site suffering so much damage and the loss of at least US $9.75 million in largely wasted Raptor engines.

There is also the question as to both the literal and metaphorical fall-out from the flight. Following the destruction of the booster and starship, residents of Port Isabel, some 12 km along the coast from Boca Chica, reported dust and debris falling on their properties. Whilst no harm was done to either residents or properties and was easily cleaned-up, the land along this area of coastline and surrounding the Boca Chica site is a wildlife refuge and home to a range of endangered / rare species. As such, contamination from a lost vehicle – to say nothing of the debris thrown out over the surrounding wetlands due the excavation under the OLM – might be enough to raise further concerns over wildlife safety in the area.

An anomaly occurred during the ascent and prior to stage separation resulting in a loss of the vehicle.  No injuries or public property damage have been reported. The FAA will oversee the mishap investigation of the Starship / Super Heavy test mission. A return to flight of the Starship / Super Heavy vehicle is based on the FAA determining that any system, process or procedure related to the mishap does not affect public safety. This is standard practice for all mishap investigations.

Federal Aviation Administration statement following the April 20th, 2023 Starship launch

As it is the FAA will be investigating the launch and subsequent events, which is standard practice, per the above statement; but concerns over the impact of this launch are already being raised by other communities in the area surrounding Boca Chica might result in the Administration re-visiting their environmental assessment of the facilities, despite statements made at the time the launch license was granted, that the FAA was “satisfied” SpaceX has taken all the required environmental mitigations required for launch operations had been taken. Given this, we could be at the start of an interesting point in time for SpaceX and their starship system.


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