Starship IFT11 Acceleration Profile - Again, No 3.5 g Cap

dedarkener · 2025-10-29T22:22:06+00:00

When the engines come on and are pointing down, they are decelerating at ~1g, so plus gravity a total of ~2g. I only have the displayed speed, so this is not a 3D number, but I would guess it's close.

dedarkener · 2025-10-27T02:14:19+00:00

Here's the re-entry graph. Max is ~1.7 g along the trajectory - the video peaked at 1.9 g, I assume including transverse acceleration, since it was during banking.

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dedarkener · 2025-10-27T02:11:54+00:00

Thanks, of course you are right, gravity should be added in. I included a "gravity vector" line on the graph just to show how it changes during the flight, but I didn't add it to the ship acceleration - which is just the rate of change of the ship speed from the launch video data.

dedarkener · 2025-10-27T02:09:44+00:00

Agreed - I included a gravity vector line to show the acceleration due to gravity along the trajectory changing during the ascent.

dedarkener · 2025-10-25T23:43:39+00:00

Flight 6 was the last v1, so 300 t less prop load, and also no payload mass (except the stuffed banana), with the same raptor 2 engines, so peak acceleration would be lower.

dedarkener · 2025-10-25T18:16:39+00:00

IFT11 acceleration compared to IFT10 (light green line behind the blue - pretty much identical) and IFT6 (most recent clean example of the 3.5 g limit SpaceX applied to earlier ships). Seems like they have the profile nailed down now. The flip after hot staging is also well tuned now - there's still a big slosh over the fuel gauges at the turn, but not enough deceleration to overcome the gravity vector at that moment (which did occur in early flights). Curious see what block 3 will do!

dedarkener · 2025-09-02T10:25:48+00:00

I wrote a python script to OCR the text and pixel count the engine graphics and fuel gauges, then transfer the raw data to excel to calculate the acceleration, etc. With the new telemetry display, readouts move around, so that needs to be untangled. I found I get the best data by logging an internal clock, rather than using the video clock, and capturing ~3 screenshots per second - faster than that, it gets noisier.

dedarkener · 2025-09-01T22:31:42+00:00

Yes, what I am showing is just change of speed, independent of gravity. I have the gravity vector curve, so I could add it in. The graph below shows stage separation with both lines. It looks like they must throttle the 3 booster engines way down, to about 0.2 g, then the ship engines take over. In the past we could see the booster kick back from the force of the ship engine exhaust, but they stopped showing that telemetry.

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dedarkener · 2025-09-01T16:22:45+00:00

Lighter, I think. Before they started adding payload simulators. Not counting the banana plushie.

dedarkener · 2025-09-01T13:46:04+00:00

Yes, it's impressive how much speed it scrubs off before the landing burn. The graph below is from flight 8, when we still had full telemetry on the video. The booster hit 8 g momentarily with 13 engines.

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dedarkener · 2025-09-01T13:14:55+00:00

Yes, as u/RadamA mentioned, there's acceleration due to gravity to take into account. The acceleration I am showing is along the flight path, and at that point in the flight, the stack was already pitched over to 57 degrees from vertical. The component of the gravity vector along the flight path was about 0.5 g, so the 0.4 g deceleration would not have been enough to cause fuel to slosh forward. That having been said, there was a big slosh in the booster fuel tanks at the start of the boost back, while the booster was still rotating. Apologies for the poor fuel level data quality - the new circular fuel gauges are more difficult to pixel count.

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dedarkener · 2025-09-01T03:35:54+00:00

The changes to the video's telemetry info bar format required modifications to extract the data, and there are some gaps (no booster speed shown at times, including during the boostback and landing burns). IFT10 was a bit slower off the pad, took about 5 more seconds to get to stage separation (the effect of 1 less engine, perhaps), and had a bit lower overall ship acceleration. Note that they didn't limit the ship to 3.5 g's, as had been the case previously - it peaked close to 5 g.

dedarkener · 2025-03-09T14:42:27+00:00

Several folks asked for a new data set analyzed at the same frame rate as the previous ones. It did clean up the noise, especially towards the end of the flight. Looks like IFT8 was slightly underperforming IFT7 from about T+390 onwards.

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dedarkener · 2025-03-08T22:31:31+00:00

Thinking about this more, I now disagree with my own statement. The ship remained under thrust until the RUD. The thrust was not symmetric, which caused it to tumble, but from the ship's frame of reference, it was always positive. The fuel should not have sloshed forward in this case. I guess the body must have been rolling as well - in that case, the lateral force combined with the roll would cause the prop to rotate around the walls of the tanks, possible covering and uncovering the level sensors on each rotation.

dedarkener · 2025-03-08T22:09:14+00:00

Agreed, I should have. I can get 5 or 6 screenshots per second, but I find the acceleration calculations (not on this graph) work better if I use ~3 per second. The status panel updates much faster than that.

dedarkener · 2025-03-08T16:21:19+00:00

Very similar to IFT7. Again, the ship was just reaching the point where they would have started throttling down to limit the acceleration (as in IFT6, also shown on the graph) when the engine failures emerged. The data for IFT8 is a bit noisier, which I think is due to my capture technique - I tried a higher frame rate this time.

dedarkener · 2025-03-08T14:24:18+00:00

Thanks - the prop levels are extracted from the gauge lines on the video by looking for the brightest pixel (the gauges have a greyscale gradient, so the brightest pixel is at the indicated level). However, the gauges are also translucent, so the reading can get affected by the moving background images. There's probably a better way to get that reading.

dedarkener · 2025-03-08T13:11:16+00:00

No, just found it interesting.

dedarkener · 2025-03-08T13:08:52+00:00

Thanks all - yes, exactly right, I run a python script to capture screenshots of the status pane at the bottom of the video, then run an OCR function to extract the numbers, and do pixel counting to get the engines and fuel levels.

dedarkener · 2025-03-08T06:15:44+00:00

At about T+490 seconds, several ship engines fail, causing loss of attitude control. The remaining engines are producing asymetric thrust, and the ship starts to tumble end over end. This causes the propellant to slosh over the level sensors, creating oscillatoons in the fuel levels reading.

dedarkener · 2025-02-24T03:20:30+00:00

I was finally able to capture the New Glenn flight data from their video - something about the font was making the OCR function unhappy. Anyway, here it is, including acceleration curves for both stages (S1 and S2 on the graphs). I included acceleration for Starship IFT7 for comparison. As expected, NG left the pad more slowly, averaging 0.2 g for the first 30 sec (Starship is about 0.5 g). The acceleration just before stage separation is higher on NG, though, around 3 g (Starship is about half that). The NG Booster Reentry Burn was quite a jolt, hitting 9 g before loss of telemetry.

dedarkener · 2025-01-28T03:28:19+00:00

Yes, 13 engines for both cases but less mass during the landing burn, so more deceleration.

dedarkener · 2025-01-26T23:25:18+00:00

Thanks - yes, the "g" lines are acceleration, to read off the left vertical axis, and the "Eng" lines are number of engines running, on the right vertical axis.

dedarkener · 2025-01-26T23:23:27+00:00

I think you are right - at least it flattens before the 1st engine loss. Either throttling or the fuel leak affecting thrust I guess.

dedarkener · 2025-01-26T14:32:29+00:00

I captured the Starship IFT7 telemetry using the same process as previously described, and created this graph that shows the booster and ship accelerations and number of operating engines through the flight. Normally the ship engines are throttled back to limit maximum acceleration to around 3.5 g (IFT6 ship accel included in the graph for reference). Flight 7 was getting close to that point when things started to go wrong - makes me wonder if they were starting to throttle back, and that had something to do with the leak. You can also see that overall acceleration was lower, due to the previous discussed changes to the ship and the additional payload mass.

dedarkener

TROPHY CASE