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SpaceX Starship - Integrated Flight Test #2 - Starbase TX - Including Post Launch Dissection
- Thread starter Grendal
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Incredible videos. It appears staging in Starship happens at a much lower altitude and lateral distance than F9, as the ground based videos of MECO and staging are much clearer than those we have seen from F9.
Question: Why would the booster's engines ignite so quickly right after MECO? in F9 the engines are lit only after the booster's attitude is reversed and is oriented towards the launch base. Here though I see they are lit even as the boosters are only about 50 degrees rotated with another 130 degrees to go
Still no onboard videos yet ? Don't tell me they forgot to install cameras 
I'm assuming that it's to keep the propellants seated during the turn. Falcon 9 has thrusters to seat the propellants prior to engine restart, while Starship's booster does not. So they attempt to maintain forward acceleration at all times. It would have worked great if they had been running with more thrust during staging. Well, barring the problem of sloshing in the methane tank while pitching through the turn. I wonder if, in the end, they'll have to go with some baffles at the bottom of the methane tank.
Well I’ve watched that about 20 times.
Fascinating to see how the inner ring of booster engines come on after stage sep, but one fails to ignite, seemingly on the side nearest the ship (?). First sign of a problem.F9 staging is 65-75km
Starship staging was 70km
The footage may be from the WB-57 which flys at up to 18km (60k feet), both closer and with less atmospheric distortion
Booster engine difference:
Short answer: because they can.
Long answer: F9 booster is in full engine shutdown with only thrusters for orientation. Staging itself pushes it rearward as does the second stage exhaust. After staging, they kick the stage over, zero rotation, and also give it forward thrust to settle the propellant. Only then do they restart the engines.
Super Heavy never stops thrusting. So, theoretically, they should be able to restart engines at any point. The timing of when it is most efficient to do so is unknown to me. Turn slower but use less fuel? More thrust initally in the wrong direction?
They need a Falcon 9 chase booster to get better footage.
10 years ago this would have been nothing more than science fiction. Today SpaceX can do it so easily without breaking sweat.
Although I would think strategically placed cameras and sensors inside and outside the booster and ship is more than enough to get all the data needed.
Good analysis. Although he didn't speculate the root cause/trigger of Ship's failure.
You've gotten some good answers already but I'll take a shot at it too.
F9 is pressurized internally with helium in COPVs to keep the fuel at the bottom for engine intake. Obviously this system works well as they have never had an engine go out in an F9 from the fuel not reaching the intakes.
Starship and booster are intentionally trying to do away with this from what Elon has said. If I remember correctly, Elon wants less complexity because it's a lot of extra steps (or next to impossible) getting helium fueled onto a Starship on Mars or the Moon.
I agree with others here (and Scott Manley) that the burning turn of the booster caused fuel to slosh in some way which caused a flaw in the mixing which was way too much for the very sensitive Raptors to handle. Remember that Raptors are the most complex, and efficient because of it, engines to ever be created. They are very touchy compared to a Merlin. I speculate that the correction is to let the 3 already burning center engines to do the complete turn, and make it less dramatic, before re-igniting the outer engines. Or not re-ignite them at all. I would compare this to the original landings that F9 booster did at the last second: the hover slam. That landing worked and saved some fuel but put too much strain on the booster. SpaceX eventually went with a single engine landing burn. I'm not an engineer but re-lighting all those engines is absolutely necessary? Maybe just let the already active three engines do everything up to landing.
It sure looked like everything went well with the hot staging. I suppose it is possible that something was damaged in a minor way that led to the loss of Starship five minutes later. I doubt it though. I expect that there was some minor fault in the plumbing that happened at five minutes into the burn that led to a cascading issue. Much like what happened on the booster during IFT-1.
All speculation but my conclusion is that SpaceX came close. So close that I'm confident that they will eventually get it right. My bigger question now is how much payload will they get to orbit? Are they using the full thrust? If I remember correctly, Elon said they weren't using full power on the engines for IFT-1. Did they do it this time? It sure looked like they did.
The fact that SpaceX got 33 Raptors successfully up and running and got the Booster to hot staging is a huge win. These were Raptor 2s. I wonder what 33 Raptor 3s will do!
EDIT: I just watched the video. Wow. I seem to agree with this guy.
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Unfortunately, pressurization won't prevent movement of the propellant. The Helium serves to keep the pressure in the tank high enough to feed the propellant into the engines at the correct rate. Starship uses autogenous pressurization, which is a controlled conversion of the propellant into gas in order to keep the right pressure levels. If the fuel sloshes on Falcon 9, the engines run the risk of ingesting some of that Helium gas, which would be bad.
Interestingly, that Wikipedia link mentions that most new rockets plan to use autogenous pressurization.
Absolutely. I'm pretty shocked at their success there given that they haven't even done that on static fires. Perhaps the more recent batches of Raptor 2 engines are of higher quality. That may be why IFT-1 didn't run at full power.
That was the point I was trying to make earlier.
I understand the inner most 3 engines are not shutoff the entire time to keep a minimal level of thrust going during staging, but then why light the other engines before the 180 degree flip maneuver is fully completed, and the rocket is oriented towards the launch site? I am sure SpaceX has a reason..
Ben W
Chess Grandmaster (Supervised)
Deceleration is fine, as long as it doesn't decelerate below zero. ("Deceleration" is not technically the correct term; more "reduced acceleration".) To find the balance point, all that's needed is to total up the forces acting on the booster: the forward thrust provided by Booster's center 3 Raptors, and the backward thrust applied from Ship's Raptor exhaust, which is some fraction (~half at separation?) of the thrust applied to Ship itself. At MECO, I believe Booster still has about 10% of its fuel, implying a total mass around 500T. (Closer to 1/3 Starship's mass than 1/10; fully fueled Starship is around 1400T.)
Booster needs to maintain some small positive forward acceleration (say 0.1g) to avoid the fluid hammer effect. Starship should be able to slightly decrease its initial thrust at hot staging to allow this; its TWR at full power is around 1.0, which is far more than what's needed to separate from Booster. It could probably fire only its vacuum engines initially to separate, then light the sea-level Raptors a few seconds later. (That's particularly the case for future Starship designs that have 6 vacuum Raptors instead of 3; is that still the plan?) In any case, fine-tuning the relative throttle of Booster and Ship engines during hot staging should be more than enough to prevent the negative acceleration. Preventing lateral sloshing during the flip maneuver is a separate issue, but keeping positive acceleration during hot-staging may be enough to solve this as well.
FAA launch license is for Orbital Flight Test 2.
https://www.faa.gov/media/69476
Which is an integrated flight test.
Of course. However, this Starship test was never going to reach full orbit. There was a whole thread here discussing this. The FAA probably considers it close enough that they are going to call it that.
The NSF livestream shows workers at the OLM right now, a bit surprising considering what day it is and that the next flight is surely over a month away.
Sure...but that's not the point. I was replying to a post that took the stance "Surprised that Ars would make an error like that." When Ars used the official identification.
Also, it's mot a 'close enough' thing.. Federal definition does not classify the planned 50x250km (approximate) trajectory as suborbital.
Did the booster slow down when Starship lit up its engines?
I seem to remember seeing a graph put together by someone that showed that it did, in which case negative acceleration was definitely occurring and maybe screwed up the fuel feed.
I am not trained in these sciences
Yes. We were discussing that a few pages back, including a post of the graph that you mention.
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