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SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

latimes.com

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Re: SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

#111

Post by Already__Taken »

mulmen wrote: post #74
cremp wrote: post #46

Earlier quoted context omitted.

If I'm not mistaken, the SR-71 and A12 had enough TEB for 15 restarts. After doing an aerial refueling, they had to use TEB to get back to afterburner.

They also had to use TEB to re-light after an unstart [1]. I think 15 is abount right but it seems like a very small margin to deal with considering how common unstarts were. [1]: https://en.wikipedia.org/wiki/Unstart

Once they learned about that they worked around unstarts with software to control the engine spikes to keep the shockwave inside.

Re: SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

#112

Post by mikeash »

rwmj wrote: post #20
huhtenberg wrote: post #3

Has anyone seen any updates on how their fairing recovery attempt went? They had the ship done and seemingly ready back in December - https://imgur.com/gallery/MQcEE

Isn't the fairing just a simple pair of metal casings. Why bother to recover it?

Imagine building a shell big enough to hold a school bus, capable of withstanding hypersonic flight through the upper atmosphere, and protecting an extremely delicate payload from outside noise so loud it causes the waveform to clip because the troughs become vacuum.

They’re not quite simple.

Re: SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

#113

Post by JshWright »

inamberclad wrote: post #83

That engine uses tetraethyl borane (TEB), right? Do they have to first ignite the turbopump and then ignite the main engine?

This is not a definitive answer (a quick googling failed to turn up a solid source), but presumably they have to ignite both the gas generator (that powers the turbopump) as well as the main combustion chamber. You certainly see the green flash of TEA/TEB lighting underneath the rocket (inside the combustion chambers) just before liftoff.

Re: SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

#114

Post by mikeash »

meteor333 wrote: post #25

> Those two boosters, which were used in previous launches of SpaceX's workhorse Falcon 9 rocket, will not be reused again, Musk said in a post-launch news conference last week. Why did SpaceX spend resources to get them to safe landing then? I presume, they rather maintain their routine and maintain the success of landing the booster. It would probably be expensive to change their standard procedure. Does any know h…

Recovering the boosters on land is practically free. Landing at sea is less so, but they want to ensure they can recover the center booster in the future, so they probably want to start testing right away so they can find problems like this one before they start losing boosters they actually want to reuse.

Re: SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

#115

Post by bigiain »

jccooper wrote: post #47
meteor333 wrote: post #25

> Those two boosters, which were used in previous launches of SpaceX's workhorse Falcon 9 rocket, will not be reused again, Musk said in a post-launch news conference last week. Why did SpaceX spend resources to get them to safe landing then? I presume, they rather maintain their routine and maintain the success of landing the booster. It would probably be expensive to change their standard procedure. Does any know h…

Demonstrating that the system can work as intended is the point of the test, and that includes recovery. The boosters in particular have different aero. Even though these won't be reused, they serve to demonstrate that future vehicles can be.

Probably worth having done just for that beautiful video of the two of them landing together... You want credibility in the marketplace? You just can't buy the things that imagery says about your business/capability.

Re: SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

#116

Post by aerophilic »

jccooper wrote: post #43
ashleyn wrote: post #17

Perhaps some rocket scientist can explain why this seemingly-obvious error even happened? Shouldn't it be possible to calculate the precise amount of fuel used, and therefore required?

They probably used a simple model (and experience) to determine the needed amount. But the model was wrong because, well, it encountered the real world. So they'll adjust in the future. Probably they could have analyzed the heck out of it for years, and gotten it right, but then that would take years and cost buckets.

This reminds me of a phrase: “All models are wrong; Some models are useful”. https://en.m.wikipedia.org/wiki/All_models_are_wrong

Re: SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

#117

Post by InclinedPlane »

rwmj wrote: post #20
huhtenberg wrote: post #3

Has anyone seen any updates on how their fairing recovery attempt went? They had the ship done and seemingly ready back in December - https://imgur.com/gallery/MQcEE

Isn't the fairing just a simple pair of metal casings. Why bother to recover it?

No, they are carbon composite.

The fairings are troublesome for several reasons. They have to be very large because they have to be larger than the payload, they have to be very strong because they have to protect the payload through the atmosphere at supersonic speeds, and they have to be very light because they ride on the upper stage, and their weight takes away from payload weight (not quite at a 1:1 ratio but not too far from it). So they are expensive because expensive fairings allow you to launch even more expensive payloads.

And in principle they are not terribly difficult to recover. The re-entry speeds are fairly low since they are only ever sub-orbital, and they are very light for their size so re-entry heating isn't a major challenge. But aerodynamically controlling them in a reliably manner to a precise location seems to be a problem.

Re: SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

#118

Post by Stratoscope »

quadyeast wrote: post #39

Is that also why the video feed was not working? SpaceX commentators said it was possibly due to vibration.

The video feed didn't stop working, or if it did, it was only for a brief moment.

If you watch this part of the YouTube stream, after it cuts back to the two hosts there is a monitor at the far right center of the video that shows the continuing camera feed of the drone ship landing pad. Only part of the monitor is visible, but after the smoke clears over the next few minutes you can see the empty pad:

https://www.youtube.com/watch?v=wbSwFU6tY1c&t=30m33s

You can also see the surprised reactions of the hosts during these few minutes, and how relieved they were when John Insprucker joined them to wrap things up. It would have been interesting to be a fly buzzing around their earpieces to hear what the producers were telling them!

People have speculated that with everything else in the mission being so spectacularly successful, they wanted the initial news reports to be about that success instead of the one core that failed to land.

Knowing how the news works - "Here's what's wrong with the world today!" - I can sympathize with that.

Re: SpaceX's Falcon Heavy center booster lacked ignition fluid to re-light engines

#120

Post by nickparker »

Footkerchief wrote: post #53
Cacti wrote: post #40

Earlier quoted context omitted.

It says right there in the article that it used up the fuel while attempting to re-lights the engines (without success).

> Musk said Monday that there wasn't enough ignition fluid to light the outer two engines of the booster "after several three engine relights." I don't see a mention of whether the previous relights succeeded or not. I'm guessing they did succeed, but the center booster had to perform a higher number of relights than a Falcon 9 booster due to its higher speed.

By my reading, the center core was using three engine burns for more efficient boost-back and re-entry burns. The side cores and typical F9 boosters (afaik) always use single engines for those and occasionally three-engine burns at landing, so three engine-ing all three burns would be 4 more relights than any previous core.

So, an equal number of "relights" of the entire rocket but more engine relights, and engine relights are the relevant unit for ignition fluid consumption.

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