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This statement from the FAA is quoted on https://wccftech.com/spacex-receives-faa-clearance-for-starships-third-test-5-indian-ocean-landings-planned

The need for (switching landing to the) Indian Ocean stems from the increasing complexity ... of the Starship mission objectives. The current operational constraints limit optimization of launch trajectories and decrease the probability of success for early mission objectives. Landing operations in the Indian Ocean would give SpaceX the flexibility to design and execute launch trajectories that meet mission objectives.

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SpaceX plans five Starship hard landings in the Indian Ocean, according to the NOAA's concurrence letter.

How does the change in landing area “give SpaceX the flexibility to design and execute launch trajectories that meet mission objectives.”? What objectives can be met with a shorter flight but not a longer flight?

To my uneducated eye, the shorter suborbital path would limit, rather than expand, flexibility. My string-and-globe measurements show the ground tracks are very similar, but the Indian Ocean landing gives only about 60% of the flight time.

Both ground tracks cross the continent of Africa (pop 50/km2), which gets little mention in discussions of debris danger as compared with Papua New Guinea (pop <10/km2).

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    $\begingroup$ Just a guess, but time in space probably isn't real valuable to them. They mainly need to test the launch and reentry capability, and 40 minutes of space-time is probably plenty to run any system checks they need. $\endgroup$ Commented May 12 at 17:50
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    $\begingroup$ @DarthPseudonym: I agree. They have three tests they run on orbit: the propellant transfer test, the payload door test / payload deploy simulation, and the engine relight. #1 and #2 are done in parallel at the beginning of the cruise phase, #3 is done right before reentry. On IFT-3, there was a lot of time in between those tests, where they were basically just waiting around. So, even with the shorter flight targeting the Indian Ocean, there was already a significant amount of time where nothing was happening. $\endgroup$ Commented May 12 at 18:23
  • $\begingroup$ @JörgWMittag Well, those were the tests they were running on IFT-3, but that isn't necessarily the sum total of all tests Starship will ever need to perform in space. But that said, anything that's going to take more than 40 minutes would probably want to wait until they have their launch and reentry sorted and then run as an on-orbit test rather than during a suborbital arc. $\endgroup$ Commented May 13 at 12:38

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The Indian Ocean site apparently provides a safer landing target for the planned deorbit burn test. According to a SpaceX commentator during the IFT-3 webcast,

We are intentionally flying this new steeper trajectory so that we can test things like engine relight without substantially changing where we expect to splash down.

This added to what had been previous posted on the SpaceX website for IFT-3:

It (Starship) will also fly a new trajectory, with Starship targeted to splashdown in the Indian Ocean. This new flight path enables us to attempt new techniques like in-space engine burns while maximizing public safety.

So far all Starship integrated (booster and ship) flight tests have had a planned second stage cut-off that is just short of orbital velocity. This is so that the ship will safely reenter in a planned remote ocean area without the need for a deorbit burn. For the first two flight tests, which apparently did not have a planned engine relight test, the planned landing was to be in the Pacific Ocean near Hawaii. However as it turned out neither ship made it that far since both ships were destroyed by the flight termination system within minutes of launch.

For IFT-3 an engine restart test was planned, although it was cancelled due to excessive roll rates of the vehicle. The reason for the engine restart test on IFT-3 (and now IFT-4) is to simulate a deorbit burn, as stated by Elon Musk at an event at Starbase on January 12, 2024, where he stated the goals for IFT-3 (timestamp 52:20):

We want to get to orbit and we want to do an in-space engine burn from the header tank and prove that we can reliably deorbit.

However this type of test creates a situation with three main possible outcomes, a failure to restart the engine, a successful restart but not reaching full duration, or a successful restart with full burn duration. Any of these outcomes will change the location of the landing, so they want to fly a steeper trajectory to keep the exclusion zone as small as possible within all of the various outcomes. This is being achieved by flying the test on a steeper trajectory, with the result being a landing in the Indian Ocean instead of Hawaii.

Interestingly the burn would be in a posigrade direction, not retrograde as many people were assuming since it was being done to simulate a deorbit burn. However since the test objective is to test engine restart, not an actual deorbit, this method apparently fits better with the goal to safely land regardless of the test outcome.

It should be noted that even though the launch license indicates that SpaceX plans to do five tests that will land in the Indian Ocean, this does not mean that the next four tests will all be suborbital. Once they have successfully conducted an engine restart test, it is likely that the next test after that would be an orbital flight. However even with the orbital tests they apparently plan to continue doing water landings of the ship for now, even though Elon Musk has indicated that they may begin attempts to bring the booster back for a return to launch site landing as soon as IFT-5. In the case of orbital tests the distance from the launch site will not matter, and it is presumably simpler to have one launch license that will work for both the suborbital and initial orbital tests.

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    $\begingroup$ I have this vague memory of some statement by SpaceX or Elon Musk that the posigrade burn is supposed to increase reentry velocity in order to collect more and better data. Not sure if that is true, though. Orbital mechanics still confuses me, though. $\endgroup$ Commented May 12 at 21:59
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    $\begingroup$ A steeper trajectory will result in a smaller debris field independent of what tests are done (or not done) during the suborbital flight. If SpaceX was choosing the trajectories to maximize safety, they would have used the Indian Ocean for ITF-1 as well. And if they were concerned about the African debris field, they would have used the South Atlantic. Methinks SpaceX's public statements make virtue of necessity. $\endgroup$
    – Woody
    Commented May 13 at 2:08
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    $\begingroup$ @Woody I think the point is that IFT-1 and IFT-2 may have been considered “safe enough”, and so it was only the additional uncertainty in IFT-3 with the engine relights that made it outside the margin of safety, necessitating the change of venue. $\endgroup$ Commented May 14 at 4:08
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    $\begingroup$ @Woody Very well said. The FAA's statement "The current operational constraints limit optimization of launch trajectories and decrease the probability of success for early mission objectives." also sounds deliberately vague. $\endgroup$
    – phil1008
    Commented May 14 at 16:05
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Question Summary:

How does the change in landing area “give SpaceX the flexibility to design and execute launch trajectories that meet mission objectives.”?

The part in quotes is from the last sentence in the "Purpose and Need" section. I think it refers more broadly to meeting mission objectives, some of which were stated in the first paragraph of that section. Specifically

SpaceX’s activities would continue to fulfill U.S. expectation that space transportation costs are reduced to make continued exploration, development, and use of space more affordable.

If SpaceX stuck with the original location and failed to reach it because "current operational constraints limit ... launch trajectories" that activity would not support the stated goal of fulfilling an expectation. The new location is possibly a strategic move. By being within the current operational constraints on launch trajectories, it is more likely to meet U.S. expectation.

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  • $\begingroup$ That seems like a lot of word fluffery to decipher from the FAA if it's just about landing in the Indian Ocean for what is most likely a very short term need to do an engine restart test. A test which is apparently best served by that particular location. There is a good chance that if the IFT-4 restart test is successful that all subsequent test flights will be orbital, in which case the splashdown site may not really matter that much as long as it's in a relatively remote ocean location that satisfies the FAA. Of course things could be more complicated than that, hard to say at the moment. $\endgroup$ Commented May 14 at 18:37
  • $\begingroup$ According to Tiered Environmental Assessment for SpaceX Starship Indian Ocean Landings "SpaceX’s proposed action is to conduct up to a total of ten nominal operations, including up to a maximum of five overpressure events from Starship intact impact and up to a total of five reentry debris or soft water landings in the Indian Ocean, within a year of issuance of a concurrence letter from National Marine Fisheries Service ." This suggests to me that they need to wait for a redesign to complete before they'll be able to try for orbit. $\endgroup$
    – phil1008
    Commented May 14 at 19:07
  • $\begingroup$ Or it could be that they thought it might take up to five attempts to do a successful restart test, as well as demonstrate the ability to control the ship in orbit. Considering that at the time they applied for the IFT-3 license they had not yet even made it past the Atlantic on the first two flights. And at the moment they have not yet demonstrated an ability to maintain control in orbit, or restart. Applying for five splashdowns in the Indian Ocean was presumably no harder than applying for two, even if they wind up only needing it for two attempts. $\endgroup$ Commented May 14 at 19:23
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    $\begingroup$ It's too late to edit my first comment but hopefully the first sentence isn't misinterpreted, it would have been better worded as "That seems like a lot of word fluffery on the FAA's part that has to be deciphered", I was not referring to what you wrote. $\endgroup$ Commented May 14 at 19:57
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    $\begingroup$ I did interpret your comment as you intended and I liked your insightful characterization of the FAA report as "word fluffery". $\endgroup$
    – phil1008
    Commented May 14 at 22:20

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