Me too, but as far as I know it’s not been done before with a rocket. Possibly the N1; I’m not sure. Of course, once the clamps release you need to just go for it.
That said, I think they’ll roll this feature back once they reach commercial flights. Eventually the Raptors will become reliable. The Merlin has thousands of flights with only a tiny number of failures. Even if the Raptor “only” reaches 99.9% reliability, that’s enough that a single failure is an unusual enough situation to call things off. But they aren’t there yet, and test flights can take more risk.
It absolutely is. This came up specifically in the interview; it takes about 5 seconds now, and they hope to cut that in half.
I think it just wasn’t well optimized. You can’t just start up all engines at once and crank them to 100%. You have to stagger the startup to minimize various shocks, and wait a bit before throttling to 100%. But it’s definitely something they can improve.
Well, I don’t think those are coincident events. It may have been “out of control” in a TVC sense. But it keeps going in a straight line for a while. Maybe it had some tiny degree of control with differential thrust. Maybe it just got a little lucky and the vectoring that got frozen in happened to be pretty good. So it takes a while for it to really start spinning, but the FTS still isn’t going to fire until it meets whatever criteria it was set for. Which might just be position based, not velocity.
It’s hard to be sure because the there are some other venting gases already, but it looks to me like there are some distinct puffs at T+3:12. The venting gets more significant after that, so I think that was when the charges went.
I think it only makes sense if the failure of the engines is from a known and predictable effect. If you don’t know why they failed, you are launching a rocket with an unknown issue that could easily get worse fast.
I’m armchair quarterbacking here, but if the rest of the engine failures had happened a couple of minutes earlier, that thing could have come down on the facility, and the FTS would have taken too long to prevent a disaster.
Also, if failure of at least one of 33 engines is almost certain, the system isn’t ready for prime time. That’s a completely unacceptable failure rate, especially for new engines at startup. I suspect the engines weren’t the issue, but perhaps FOD damage or some system issue. They lost six engines in two minutes. Those Raptors have to be more reliable than that.
I think the interval between ignition and liftoff was probably due to lower thrust to weight because of the engine losses. That’s a huge rocket, with immense inertia and a fairly low thrust to weight initially. The start of liftoff can be S-L-O-W.
The Saturn V took 7.5 seconds to clear the tower after liftoff. It had a thrust-to-weight ratio of 1.2. Starship took 10 seconds, and has a full thrust TWR of 1.5. With three engines out, it would have been closer to SV’s 1.2, but it’s a bigger rocket and a taller tower. So not measurably different.
The engines did ignite, and remained responsive, but the system didn’t think they were healthy enough to bring to full power. This wasn’t a situation where they exploded or something and you have no idea what’s going on.
No, the first 5-6 seconds are absolutely due to the rocket still being held down at that time. Musk confirmed this in the interview and they plan on reducing it.
Well, all rockets are held down for a time. Was Starship unusual that way? Saturn V had a 8.9 second delay between ignition and liftoff, according to Wikipedia.
It’s unusual for rockets without a flame diverter .
In any case, it’s both wasteful and causes unneeded wear on the pad (even if they had protected it adequately). They didn’t optimize it perfectly on this first test flight, but they’ll improve things for the next one.
I thought it was pretty obvious, and said so several days ago in the thread (to some pushback). I even linked to the point in the video where it happened. You can see the two holes from the FTS very clearly with fuel jetting out of them. It took a long time between those holes appearing and the rocket coming apart. I counted close to a minute.
I’m guessing what happened is that the FTS charges were not designed for a rocket this large, and instead of ripping oppen both fuel and oxidizer for a big boom, they just vented one of the tanks without puncturing the other, leaving either oxidizer venting out with no fuel to burn, or fuel venting out with no oxidizer.
Had that anomaly happened anywhere within the first few thousand feet of launch, the FTS wouldn’t have stopped the rocket from crashing back down into a spectacular explosion somewhere close to the pad.
Hey, that was me I guess. I was just amazed at your (apparently correct!) assertion that that pathetic display of poking two tiny holes in the rocket was the extent of the FTS. Surely SpaceX can afford some kablooey charges, thought I. Silly me. As you say, the tower could have been consumed for lack of some oomph, but I’d bet this is reasonably easily corrected.
Question: the SpaceX (and apparently everyone’s) approach to flight termination is to breach the tanks, boom. So what do you do about a vehicle that’s a danger but the tanks are dry? Is that, um, unmitigatable? I mean, I guess if a vehicle has no fuel, the danger is somewhat minimal.
That’s not entirely clear. The aerodynamic loads are not trivial. A transcript of the interview here, where this comes up:
So the aerodynamic forces that I was experiencing were would be less than if it was at a lower, you know, lower down in the atmosphere.
And so the aerodynamic forces would have, I think, at lower point in the atmosphere aided in the destruction of the vehicle.
And in fact that’s kind of what happened when the vehicle got to a low enough altitude that the atmospheric density was enough to cause structural failure.
Musk emphasizes that it needs to be fixed. But it’s probably not true that it would have taken the same 40 seconds had it been triggered at a lower altitude.
It should never be on a trajectory like that in the first place. The main goal is to terminate thrust in a way that prevents it from reaching a populated area. The federal requirements are here:
None of this actually requires destruction of the vehicle. The charges are there to satisfy element (a).(4), but that’s irrelevant if the tanks are dry.
Scott Manley has a new video on the subject of FTSs here:
Was just skimming the comments of Scott Manley’s video–and what do you know, the Tory Bruno, the CEO of ULA, shows up with this comment:
Great job as always Scott. One simplified way to look at this is to start with the objective of an FTS system. It is NOT to blow up the rocket (although that is a frequent side effect). The primary objective is to keep it on the range by rendering it non-propulsive. When liquid propellants are present, we would also like to disperse them. Burning is not generally required, it’s just another common side effect.
To that end, most FTS designs cut the SRM’s dome or sidewall so it will tumble and not have a significant net thrust vector. The resulting “unplanned” burn surfaces sometimes, but not always, also result in some spectacular rapid combustion… As you said, liquid propellant tanks are also cut and vented.
When do we want this to occur? Three circumstances: 1) The rocket has left the safe corridor. 2) The rocket is obviously about to leave the safe corridor, or 3) The rocket is clearly out of control and/or breaking up.
How do we know this is happening? Three common ways: 1) Skin tracking, via RADAR of the rocket’s position. 2) Autonomous tracking of the rocket’s position via on board GPS receivers and/or conveying the GPS signal from the rocket to the ground, typically via a GPS solution or “bent pipe” translator, and 3) On board monitoring of critical systems. This data is also sent the ground. All 3 of these are usually present on any given rocket.
Then what? Three ways it get’s started: 1) Command destruct from the ground by the Range Safety Officer. Usually based on the skin track or the on board GPS, but this can also be prompted by the other data based on his/her judgement. 2) Auto Destruct, where the rocket initiates its own destruct based on violating pre-programmed parameters, including position. 3) Self Destruct, where a departing stage or SRM, during a breakup, detects that it’s no longer attached (when it should be, ie: this function is “inhibited” during planned staging) and initiates destruct to render itself non-propulsive. It is not uncommon for all of these to happen. Auto goes off during a break up, the individual stages self destruct, and the Range Safety Officer slams the button.
Off board command destruct and skin tracking is being phased out in favor of autonomous flight safety systems (AFSS), to reduced the burden on the Ranges going forward as launch rates increase and USSF infrastructure ages.
The systems above are at least dual redundant, extremely reliable, able survive “abnormal” environments (ie the kind of thermal and mechanical loads that would only happen during a bad day) and must be certified by the Range who is generally involved in the disposition of any anomalous behavior or observations.
I think it’s worth emphasizing the first paragraph. Blowing up the rocket is just a common side effect of an FTS trigger. It’s not a goal in and of itself.
I was initially surprised that they sued the FAA rather than SpaceX, but I guess it makes sense–no evidence that SpaceX broke their license; the complaint is that the FAA granted it at all. We’ll see if anything comes of it.
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As you say, the tower could have been consumed for lack of some oomph, but I’d bet this is reasonably easily corrected.
