SpaceX Starship - IFT-3 - Starbase TX - Launch Thread and Post Launch Discussion

Launch Date: March 14
Launch Window: 7:00 am CDT (9:00 am EST, 13:00 UTC)
Launch site: LC-1 - Starbase, Boca Chica Beach, Texas
Core Booster Recovery: Expended in Gulf with a landing burn
Starship Recovery: A controlled reentry through the atmosphere to a terminal velocity splashdown in the Indian Ocean
Booster: Super Heavy Booster 10
Starship: Starship 28
Mass: No mass simulator mentioned
Orbit: LEO-ish
Yearly Launch Number: 26

A SpaceX Super Heavy and Starship launch vehicle will launch on its third not quite orbital integrated flight test designated IFT-3. The mission will attempt to place Starship into a nearly orbital trajectory that will attempt a controlled reentry through the atmosphere to a terminal velocity splashdown in the Indian Ocean . The Super Heavy booster will attempt a landing burn in the the Gulf of Mexico where it will likely be destroyed. This is a further test of Stage 0, the booster, full power ascent, Max-Q, stage separation using the new hot staging, a booster stage test of a hard turn and boostback, full burn boost of Starship to space and sub LEO, Starship will do one partial orbit, simulate a de-orbit burn, test tiles and heating from atmospheric reentry, until it has a splashdown in the Indian Ocean.

It has also been determined that for this test flight there will be a fuel transfer test done on Starship for NASA's Tipping Part contract. The Starship will also test its payload bay door in zero-G for a test of future Starlink 2.0 deployments.

 

[JB47394]

...and RGV Aerial Photography showing a rendition of what they believe happened during reentry. Renders by The Space Engineer.

It suggests to me that there was enough atmospheric drag to stop the roll, but the flap control software wasn't able to use that drag to keep the ship oriented for reentry. I wonder if the flaps could have done the job with 0.01-0.05%% of sea level pressure. The Shuttle apparently didn't get aerodynamic control until around 48 km, and SpaceX lost telemetry on Ship 28 around 65 km.

I guess an alternate theory is that heating of the ship resolved whatever problem plagued the roll thrusters and they were used to cancel the roll.

 

[Electroman]

I find it odd that there are no videos of booster reentry have surfaced so far, taken from a ship or a plane or a drone from outside of the safety zone, even some 100 miles away.

 

[JB47394]

I find it odd that there are no videos of booster reentry have surfaced so far, taken from a ship or a plane or a drone from outside of the safety zone, even some 100 miles away.

I saw mention that the WB-57 was up for the launch. I assume that it would track the booster, but we may never see much of the footage because REDACTED.

 

[Ben W]

Note that during staging, there is a brief negative acceleration (-0.4g) induced by the Starship engines, then a brief positive acceleration (0.4g) while the engines are running but the booster hasn't turned around yet, then an extended negative acceleration (3g) as the booster cancels out its downrange speed.

Note that as long as the acceleration in this reference frame doesn't drop to -1.0g (which would be equivalent to no thrust applied, falling at 1g), the propellant will stay at the bottom of the booster tank, rather than sloshing forward. It may be more helpful to think about that dip (to -0.4g in Earth's reference frame) as a dip to +0.6g in the booster's reference frame, with thrust still applied forward but not quite strongly enough to counteract gravity, so the booster begins slowing down but is still experiencing net forward thrust in its own frame.

Is that couple of seconds of positive acceleration the ship dragging the booster with it before it detaches? If so, I wouldn't have expected the side-vented exhaust to impart much thrust....

It depends on the angle the exhaust is leaving the vents, and at what speed. Its nominal speed is about 3750 m/s (corresponding to vacuum ISP of 382s); suppose the exhausts vents from the interstage ring at an average 45-degree downward angle, at 70% of that speed. That would work out to about a 50% reduction of forward thrust, applied to ship + booster. The near-empty booster masses around 300T at stage separation (200T dry + 100T propellant), and the ship masses around 1300T (100T dry + 1200T propellant), so the effective forward thrust on the whole stack would be around 40% of Starship's thrust after separation. (These numbers are all guesses, but hopefully in the ballpark.) Starship's initial thrust with 6 raptors is around 1.5g (in the ship's frame), so it's reasonable that lighting its first 3 raptors while still attached would provide the connected stack with around 0.3g forward acceleration, and all 6 raptors lit would double that to 0.6g.

I did have another thought regarding hot staging (versus the wonky IFT-1 flip maneuver), which is that it plausibly gives Starship a means of safely escaping, Super-Draco-style, in the event of a booster RUD on the pad or during ascent. I'm not sure if this has been analyzed or investigated as a serious option, but it would give me a lot more confidence in using Starship+Super Heavy for crew launches.

 

[scaesare]

Note that as long as the acceleration in this reference frame doesn't drop to -1.0g (which would be equivalent to no thrust applied, falling at 1g), the propellant will stay at the bottom of the booster tank, rather than sloshing forward. It may be more helpful to think about that dip (to -0.4g in Earth's reference frame) as a dip to +0.6g in the booster's reference frame, with thrust still applied forward but not quite strongly enough to counteract gravity, so the booster begins slowing down but is still experiencing net forward thrust in its own frame.


It depends on the angle the exhaust is leaving the vents, and at what speed. Its nominal speed is about 3750 m/s (corresponding to vacuum ISP of 382s); suppose the exhausts vents from the interstage ring at an average 45-degree downward angle, at 70% of that speed. That would work out to about a 50% reduction of forward thrust, applied to ship + booster. The near-empty booster masses around 300T at stage separation (200T dry + 100T propellant), and the ship masses around 1300T (100T dry + 1200T propellant), so the effective forward thrust on the whole stack would be around 40% of Starship's thrust after separation. (These numbers are all guesses, but hopefully in the ballpark.) Starship's initial thrust with 6 raptors is around 1.5g (in the ship's frame), so it's reasonable that lighting its first 3 raptors while still attached would provide the connected stack with around 0.3g forward acceleration, and all 6 raptors lit would double that to 0.6g.

I did have another thought regarding hot staging (versus the wonky IFT-1 flip maneuver), which is that it plausibly gives Starship a means of safely escaping, Super-Draco-style, in the event of a booster RUD on the pad or during ascent. I'm not sure if this has been analyzed or investigated as a serious option, but it would give me a lot more confidence in using Starship+Super Heavy for crew launches.

The safety abort (basically a staging maneuver on the ground) idea is cool... I wonder if you could test that and land the ship (once they get the belly flop working)...

Thanks for the calcs on the ship thrust.... with the center raptors gimbaled out to their limit of 15 deg (?) , and the slope of the dome in the ring, I suppose the exhaust angle is significantly less than 90 degrees....

 

[scaesare]

That dip before lighting the engines is interesting. I was going to say that it's the Starship's thrust pushing on the body of the booster, but it's probably just the change in orientation compromising its absolute speed.

Do you mean that you believe the speed display is calculated relative to the orientation of the ship's axis though it's nose? Thus if it rotated 90 degrees (without thrusting) it's speed would = 0?

 

[mongo]

Do you mean that you believe the speed display is calculated relative to the orientation of the ship's axis though it's nose? Thus if it rotated 90 degrees (without thrusting) it's speed would = 0?

The speed readout is non-directional. Which makes calculating the acceleration vector difficult.

 

[scaesare]

The speed readout is non-directional. Which makes calculating the acceleration vector difficult.

Trying to understand what @JB47394 meant by " but it's probably just the change in orientation compromising its absolute speed" ...

Or is this simply presenting a larger surface area in the direction of travel, thus incurring more drag?

 

[scaesare]

...and RGV Aerial Photography showing a rendition of what they believe happened during reentry. Renders by The Space Engineer.

It suggests to me that there was enough atmospheric drag to stop the roll, but the flap control software wasn't able to use that drag to keep the ship oriented for reentry. I wonder if the flaps could have done the job with 0.01-0.05%% of sea level pressure. The Shuttle apparently didn't get aerodynamic control until around 48 km, and SpaceX lost telemetry on Ship 28 around 65 km.

I guess an alternate theory is that heating of the ship resolved whatever problem plagued the roll thrusters and they were used to cancel the roll.

This was a cool watch... the render with the plasma is great...... it seems that the ship never got oriented that the non-tiled surface was leading into the atmosphere... but a couple of times it got pretty @ss-first (e.g. starting at about 6m), allowing a lot of heat up the non-protected side... and a huge plasma ball going up the engine skirt...

 

[JB47394]

Note that as long as the acceleration in this reference frame doesn't drop to -1.0g (which would be equivalent to no thrust applied, falling at 1g), the propellant will stay at the bottom of the booster tank, rather than sloshing forward.

If it were vertical and not turning, I'd agree. It's at a pretty good angle relative to the gravity vector (it looks like it's about 30 degrees off horizontal), and then it does that hard turn to get away from Starship. The propellant is certainly going to slosh, and I assume that the negative acceleration only makes it more pronounced.

My reason for even bringing this up is that they didn't appear to care about limiting sloshing. Instead, they reinforced the interior to tolerate it. The inability to relight for landing suggests that they might still have a problem with the consequences of propellant movement. Or it's something new, related to the stresses of descent.

It depends on the angle the exhaust is leaving the vents, and at what speed.

And throttle during staging.

I did have another thought regarding hot staging (versus the wonky IFT-1 flip maneuver), which is that it plausibly gives Starship a means of safely escaping, Super-Draco-style, in the event of a booster RUD on the pad or during ascent. I'm not sure if this has been analyzed or investigated as a serious option, but it would give me a lot more confidence in using Starship+Super Heavy for crew launches.

That would be a sight to see, and I hope I never see it.

I wonder what they'd do with a fully loaded Starship after a pad abort. Hover the thing until it's light enough to be caught by the chopsticks?

 

[mongo]

Trying to understand what @JB47394 meant by " but it's probably just the change in orientation compromising its absolute speed" ...

Or is this simply presenting a larger surface area in the direction of travel, thus incurring more drag?

It looks like booster goes near vertical for relight. That would increase drag and also put a bunch of the thrust into countering gravity resulting in minimal net acceleration.

 

[scaesare]

It looks like booster goes near vertical for relight. That would increase drag and also put a bunch of the thrust into countering gravity resulting in minimal net acceleration.

But the dip being talked about is before the ship lights it's engines for hot-stage, and therefore the booster is still attached? So no orientation change at that point, right?

 

[scaesare]

If it were vertical and not turning, I'd agree. It's at a pretty good angle relative to the gravity vector (it looks like it's about 30 degrees off horizontal), and then it does that hard turn to get away from Starship. The propellant is certainly going to slosh, and I assume that the negative acceleration only makes it more pronounced.

My reason for even bringing this up is that they didn't appear to care about limiting sloshing. Instead, they reinforced the interior to tolerate it. The inability to relight for landing suggests that they might still have a problem with the consequences of propellant movement. Or it's something new, related to the stresses of descent.


And throttle during staging.


That would be a sight to see, and I hope I never see it.

I wonder what they'd do with a fully loaded Starship after a pad abort. Hover the thing until it's light enough to be caught by the chopsticks?

(emphasis mine)

I was thinking about this... Elon some time back talked about the fact that the startup process for a FFSC engine like Raptor is a bit complex... you have to wonder what supersonic super-heated air rushing up the engine nozzles is going to do to that... It would be interesting to know what kind of pressurization the air past the throat induces in the combustion chamber...

 

[mongo]

But the dip being talked about is before the ship lights it's engines for hot-stage, and therefore the booster is still attached? So no orientation change at that point, right?

I though we were talking before booster relights. Are we talking big dip at 2:49 or little at 2:53?
Booster and ship did maintain orientation through staging release.

 

[scaesare]

I though we were talking before booster relights. Are we talking big dip at 2:49 or little at 2:53?
Booster and ship did maintain orientation through staging release.

View attachment 1030276

This was my comment that @JB47394 replied to:

It appears that the final 3 engines that remain lit bring acceleration to 0 and the stack actually slows down for a couple of secs before the stack lights it's engines....

So, I was talking about the acceleration starting to plateau at 2:43, I assume when he subsequently replied, "That dip before lighting the engines is interesting." and the subsequent conversation was regarding the same.

 

[mongo]

This was my comment that @JB47394 replied to:



So, I was talking about the acceleration starting to plateau at 2:43, I assume when he subsequently replied, "That dip before lighting the engines is interesting." and the subsequent conversation was regarding the same.

Ah, thanks! That's due to TWR being <<1 and losing vertical velocity.
From a propellant point of view, everything is fine and settled since engine thrust is still forward.

 

[scaesare]

Yup.. wasn't questioning that. I was simply pointing out that even though the stack "never stops thrusting" (thanks to hot-staging) it actually does start to slow down, obviously just not as much as if there was total M(ain)ECO and a delay before ship engine light.

It was @JB47394 's reply that it was "probably just the change in orientation compromising its absolute speed" that I questioned, as there is no change in ship orientation at that point.

 

[ecarfan]

I wonder what they'd do with a fully loaded Starship after a pad abort. Hover the thing until it's light enough to be caught by the chopsticks?

Yes, the problem with a pad abort that blasted the ship up and away from the booster is that currently the ship has no legs. And since the abort could be triggered by a malfunctioning booster on the OLM that could damage the tower and the chopsticks system, a hover and chopsticks catch may well not be an option.

So…could four minimalist emergency landing legs be incorporated into the base of the booster so the ship could do a controlled propulsive descent onto a flat, firm surface? The legs would add weight and complexity but they would only be designed for a single use so do not have to be to robust.

That said, can all 6 ship engines propel a fully loaded (props plus cargo) ship rapidly away from the booster starting from 0kph at sea level? And, how quickly can the engines ignite after a pad abort is triggered? The engines would have to be pre-chilled and ready for ignition at around T-0, and then presumably kept in that state up to staging. What problems would that present?

It seems to me there are a lot of potential obstacles to be overcome, but it’s an idea seriously worth considering.

 

[mongo]

That said, can all 6 ship engines propel a fully loaded (props plus cargo) ship rapidly away from the booster starting from 0kph at sea level? And, how quickly can the engines ignite after a pad abort is triggered?

That's iffy currently. 1,500 tf vs 1,200 t of propellant, 150t of cargo, and 160 - 200t dry mass.
HLS landing/ ascent engines may be an option with a breakaway cargo section.

Could possibly ditch into the gulf and tip over.

 

[TunaBug]

And, how quickly can the engines ignite after a pad abort is triggered?

I would think that the startup sequence would be the hard part of using the raptors for an abort story. Aren't abort motors usually something that can ignite instantly, and not a few seconds later? How long is the raptor startup sequence? I don't know, but I have been assuming it is multiple seconds.