What to expect on the day of Starship's Orbital Test Flight

The day of Starship’s inaugural orbital test flight will be one for the history books, the liftoff of the world’s (currently) most powerful rocket, destined to take humans to Mars. Many people will be attending the launch in-person, and a multitude watching online. This article will provide an overview of the events we can expect to see on the day, as well as a brief look at the Starship and Superheavy vehicles.

TLP live coverage note: Zac and the TLP will be on location providing live views and updates as well as answering your questions from outside the exclusion zone during WDR and launch activities. You can watch these events by clicking the following links: WDR live stream; launch live stream. Please note that dates & times are highly subject to change as SpaceX progress towards launch.

Pre-Launch Day Timeline

Many notices and regulatory documents must be released ahead of the launch day, based on the current order of events, the NOTMAR (notice to mariners) is released first, which provides a hazard zone with a date and time - warning seafarers to keep out of an area provided by the notice. As Starship has two stages, splashing down in two different locations, there must be two different NOTMARS. A NOTMAR for Booster 7’s splashdown in the Gulf Of Mexico was first published, and later a NOTMAR for Ship 24’s splashdown in Hawaii.

The FAA Advisory is a catalog of current operations, advising aircraft to be aware of special events that they could interfere with. A section of this advisory is titled Space Operations, and provides a list of upcoming launches/re-entries. Starship’s primary launch date, and backup launch date(s) are published here next. At the time of writing, the current primary date is the 17th April - the advisory can be found here.

FAA Advisory showing Starship launch on the 17th April.

A Temporary Flight Restriction (TFR) that goes up to an unlimited altitude over Boca Chica, TX is likely to be next. This notice informs aircraft that they are not to enter the TFR zone, and they must abide to the specified altitude. An unlimited altitude means no aircraft can fly over the launch site at any altitude.

A road closure is required for launch operations, to prevent any tourists or residents from fouling the range. The closure will most likely cover the day before, assuming SpaceX target an early launch time, and also the day-of. You can check for road closures at https://www.cameroncountytx.gov/spacex/, and the flight closure will be noted as a flight testing closure.

An overpressure alert notice most likely will be released at the same time as an evacuation notice, as these both go out to the Boca Chica village to inform the remaining residents of flight testing activities. The overpressure alert notice is required to inform villagers that a fiery malfunction is possible, and to stay out of their house if possible incase of broken windows. The evac notice tells villagers that they must evacuate the village incase of falling debris if the full stack was to malfunction mid-flight. However, it is possible (happened during the last Wet Dress Rehearsal) that the overpressure alert notice is not delivered as the villagers will be out of their houses due to the evacuation notice anyways.

An example of an overpressure notice from the 20th January, 2021 from Mary - @BocaChicaGal

For the April 17th launch, as of time of writing, we have received both NOTMARS and the FAA Advisory.

Launch Day Timeline

The current FAA Advisory states no launch window time, but it previously opened at 7am local time.

Throughout the day before, and early morning of the launch day, many tests can be expected to be seen at the launch site. A couple would include Booster QD retraction tests, Ship QD retraction tests, which both ensure that the fuelling system can pull away for launch. A FireX test was observed in the early morning of the last Wet Dress Rehearsal - FireX, known throughout the aerospace industry as ‘Fire Extinguisher’, is a system composed of Nitrogen and Water, which can provide many configurations for different uses. Water on it’s own can be used to cool down the OLM following launch, Nitrogen on it’s own can be used to push oxygen out from under the OLM so that there’s no chance of an explosion, however, using both at the same time creates a much more efficient spray, and is much more effective for suppressing detonations. 

Image from SpaceX's 33 Engine Static Fire stream, arrow highlighting the FireX system active.

Anyways, the first indication of launch operations starting will be the road getting closed. The roadblock is much further back for launches as the hazard zone is greater, and is activated by one or two police cars blocking off the road to prevent non-employee access.

The next event will be the release of Ship 24 from the chopsticks. Having them attached provides support to the free-standing full stack, but they must move out of the way for launch. The chopsticks are opened wide and moved down from the load points, and stop roughly halfway down the Ship.

Next up, Pad Clear. This is confirmed when all SpaceX employees have left the launch facility, and there are no cars remaining at the pad, usually, all the gates are closed too.

Now we’re getting into the good stuff. The tank farm will next begin to spool up as the propellant begins to precondition, you can tell this as a lot of venting will begin, and the LOX (liquid oxygen) and CH4 (methane) subchillers will begin venting, which means prop load is close to becoming underway. 

A gridfin test has been known to be performed at this stage in the countdown, this doesn’t mean it can happen earlier or later, but it is often seen after tank farm venting and before the OLM begins venting. 

Anyways, the OLM venting is how to tell prop load is imminent. There are two main OLM vents, a LOX vent, and a CH4 vent. The CH4 vent is pretty much directly underneath the Booster QD, and the LOX vent is separated in an anticlockwise direction. These vents signify that propellant is nearing the BQD. When the vents begin “waterfall” (term used to highlight when the vents become liquid instead of gas), propellant has reached the BQD, and the vents are promptly turned off. This indicates propellant load is underway.

Engine chill will begin on the Booster. As of the 7th April, this engine chill is redirected through a ring on the OLM, which then pipes out to a redirection pond just outside of the orbital pad concrete area. It’s redirected to avoid any possible issues with venting methane out of the engine bells under the OLM, where there could possibly be ignition sources. 

The tower will also begin venting as the same process happens simultaneously to begin loading on the Ship. The propellant has to travel up the Tower to the Quick Disconnect Arm. Venting will also come out of the back of the QD Arm.

A frost line will now appear on either the CH4 or LOX tank of Booster 7. These can be simultaneous, or slightly delayed. After both tanks have been filled to a reasonable level (was around ⅓ for the last Wet Dress Rehearsal), a frost line will form on S24’s tanks too. All 4 main tanks on the full stack will be loaded with propellant at the same time. Shortly after S24 begins propellant load, engine chill will also begin on the Ship. The engine chill goes through two symmetrical pipes on two sides of the Ship’s non-tiled section, this pipe has a spray nozzle, which is aligned with a receiving pipe on Booster 7, meaning the ship’s engine chill cascades down the side of the Booster.

Image from SpaceX showing the aftermath of the first Wet Dress Rehearsal. The chopsticks have been reattached as the countdown was completed, and water can be seen on the ground under the OLM as FireX was activated at T-15 seconds.

Next, the header tanks of Ship 24 will have a noticeable frost line, as they begin loading of recovery propellants (still LOX and CH4 - just in a different location to keep reserves for the flip maneuver). 

At T-15 minutes, Booster 7’s methane tank will begin venting to a great extent. This is much like the T-20 minute vent on Falcon 9. Shortly after, propellant load on both vehicles will finish up, marking the end of loading as we rapidly accelerate towards launch.

At around T-15 seconds, the FireX system will activate to push oxygen out from under the table to prevent unwanted ignitions from the methane spin-up of the Raptor 2 engines. At around T-3 seconds, the ignition sequence should begin.

Assuming enough engines ignite for a successful launch (only 31 engines ignited for the 31  engine static fire, and Elon Musk confirmed that it was still enough for launch), the full stack will liftoff from the Orbital Launch Pad at Starbase, TX. Assuming it does indeed launch on the 17th April, this will mark the first flight from Boca Chica in 712 days, since SN15’s flight on the 5th May 2021.

The full stack will remain together through Max-Q, up until MECO (main engine cut-off). Following MECO, the two stages will separate through the release of the Ship hold down clamps, and ullage thrusters will move Ship 24 away from Booster. Around 9 seconds after MECO, Booster 7 will ignite its inner engines once more for the Boost-back Burn.

Booster 7 will splashdown in the Gulf of Mexico, and Ship 24 will continue to a very near orbital trajectory, will (hopefully) survive re-entry, and will also splashdown following a powered landing sequence around 100 km off-shore of Hawaii.

Final Notes

This timeline has been constructed by using patterns from previous testing activities and the last Wet Dress Rehearsal, and events are subject to change. While most are expected to remain the same, smaller items such as grid-fin testing or OLM venting times will change. The current target NET for the Orbital Test Flight of Starship is April 17th, and excitement is growing rapidly in the aerospace community! For such an historical event, let's hope that the flight goes mostly as expected.