SN8

SN8 is the first completely stacked ship (upper stage) prototype which has made a suborbital flight. Although destroyed upon landing due to a header tank pressure issue, the SN8 testing can be considered as a great success, as most of the planned goals have been achieved. For SN9, they installed helium pressurisazion in order to prevent the header tank issue, that lead to the RUD, which, in turn, led to problems with SN10.

## Timeline

To be added from General Timeline, when finished.

## Flight Outcome and Analysis

SN8's flight did better than many expected. Only partially fueled, it lit all 3 engines to lift off from the pad. Although some were concerned about the successive engine shutdown that then followed on ascent, it was later stated that this was intended in order to get into a hovering position at apogee. During ascent, SN8 used its raptor engine gimbeling to control it. SN8 then flipped in to horizontal position, using its aero surfaces to manoeuvre back to the pad. It then tried to relight two engines in order to switch back to vertical for landing and to decrease its speed. One engine however showed unhealthy, green combustion, indicating not enough propellant getting into the engines, causing engine rich exhaust as the engine burns its copper parts instead. This was caused by low pressure on methane header tank, leading to oxigen rich mixture that caused the issue.

SN8 however managed to flip to vertical, and even was able to correct back a little, but it didn't decrease speed with now only one engine producing no thrust anymore. Therefore, the starship made a very hard impact on the landing pad, immediately resulting in an explosion (RUD).

Despite the landing failure, SpaceX was able to gather a lot of data on the "bellyflop" manoeuvre, one of the main objectives of the test. SN8 was a success as it proved that it could use its flings and flaps to get back to the pad. Furthermore, the raptors were now proven during long duration burns.

Timeline according to SpaceX:

* -00:01.1 Ignition of all 3 engines
* -00:00.0 Lift off
* +01:42 Engine shutdown #1, some normal fire in the engine skirt
* +03:13 Engine shutdown #2; more or less howering and horizontal translation
* +04:38 Flip induced by remaining engine RSN 42
* +04:40 Engine shutdown #3, using RCS thrusters and aero surfaces to get to horizontal position
* +06:19 Engine chill (Tri vent)
* +06:31 Engine ignition (the engine shut down first reignited first)
* +06:32 Engine ignition (the engine shut down second)
* +06:37 Engine one beginning to produce green combustion
* +06:38 Engine two burn out
* +06:42 Impact, RUD

## FAA investigation

On Monday, 25 January 2021 SpaceX began readying SN9 for a first launch attempt which was scrubbed, mainly due to high winds and low visibility. Later on 26 January 2021, Elon Musk posted a message on twitter, making clear that they were still "waitng for FAA review". This day was used in order to test SN7.2 for a first time and to roll out the big crane. The road closure from 27 January was cancelled.

After making aborting another launch attempt with SN9 right before T-0 on 28 January 2021, Elon Musk made another statement:

> "Unlike its aircraft division, which is fine, the FAA space division has a fundamentally broken regulatory structure. Their rules are meant for a handful of expendable launches per year from a few government facilities. Under those rules, humanity will never get to Mars."
>
>

However, it was not yet clear as for why the FAA wouldn't approve the flight. (Be aware, TFRs are not the same as flight approvals). Another attempt on 29 January was scrubbed as well, the day was instead used for rolling out SN10.
Later this day, Joey Roulette published an article on the verge, linking the delay to the explosive landing of SN8. In this article it was revealed, that according to two people familiar with the incident the SN8 launch violatd the terms of the FAA test license issued to SpaceX. An investigation was opened in the week of the test flight, "focusing not only on the explosive landing but on SpaceX's refusal to stick to the terms of what the FAA authorized". An FAA spokesman specified to the verge:

> "The FAA will continue to work with SpaceX to evaluate additional information provided by the company as part of its application to modify its launch license [...]”. “While we recognize the importance of moving quickly to foster growth and innovation in commercial space, the FAA will not compromise its responsibility to protect public safety. We will approve the modification only after we are satisfied that SpaceX has taken the necessary steps to comply with regulatory requirements.”
>
>

According to another source, SpaceX made changes in its license application and the FAA officials were still in the process of reviewing this application, causing the delay of SN9. After the flight of SN9, also resulting in an explosion, CNBC reporter Michael Sheetz has published an article on 2 February 2021, in which the FAA specifies the statement about the SN8 test previously made. He also published the statements on Twitter:

"The FAA's top priority in regulating commercial space transportation is ensuring that operations are safe, even if there is an anomaly. The FAA will oversee the investigation of today's landing mishap involving SpaceX Starhip SN9 prototype in Boca Chica, Texas. Although this was an uncrewed test flight, the investigation will identify the root cause of today's mishap and possible opportunities to furhter enhance safety as the program develps."
Apparently, SpaceX has violated the license terms by proceeding with the launch of SN8 without having shown to the FAA that the risk of a RUD (referred to as a far field blast overpressure) was within the regulatory criteria. After the SN8 test, the FAA therefore required SpaceX to conduct an internal investigation and suspended all launch activities.

## References

1. ↑ https://www.youtube.com/watch?v=egHxiX40eJY
2. ↑ https://www.youtube.com/watch?v=oIm3zkRi2U8
3. ↑ https://twitter.com/elonmusk/status/1354174713103319043
4. ↑ https://twitter.com/elonmusk/status/1354862567680847876
5. ↑ 5.0 5.1 https://www.theverge.com/2021/1/29/22256657/spacex-launch-violation-explosive-starship-faa-investigation-elon-musk
6. ↑ https://www.cnbc.com/2021/02/02/spacex-starship-sn9-explodes-on-attempted-landing.html
7. ↑ https://twitter.com/thesheetztweetz/status/1356761131721912320