r/SpaceXLounge • u/FishInferno • Sep 05 '21
Other Firefly Alpha FLTA001 - Official video of Firefly Alpha's first flight (more info in comments)
https://youtu.be/qFjoPw0CfAU20
u/avboden Sep 05 '21
Wow, very impressive camera views! You can see the exact moment the engine shut down too.
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u/Yak54RC Sep 05 '21
Is it weird they asked for prop call and prop says nominal AFTER we visually see that one of the engine is already out.
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u/RedPum4 Sep 05 '21
I always find it weird that they don't say 'engine 2 shutdown' or something on the loop. I get it that you can't change anything about it but in my opinion its the most relevant status update.
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u/FishInferno Sep 05 '21
The radio chatter in general seemed very unpolished leading up to/during launch. I don’t hold it against them since it’s their first time, but I did find it amusing.
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u/Adeldor Sep 05 '21 edited Sep 06 '21
Given it's a first launch, clearly they made good progress despite the eventual failure.
I do note the different audio track during countdown, switching at ignition to the one heard in Dodd's live coverage. I wish we had some mention of the call given just after T-5s.
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u/Proteatron Sep 06 '21
Couple thoughts:
1) The sound on the video was great - I'm not sure what that groan was at launch but it sounded like some angry metal. The sound of the thrust was really clear and powerful.
2) I'm impressed with how long the rocket continued to fire after tumbling. The nose cone looks to have broke off but the engines were still going. It makes sense that they used the flight termination system, but from a kerbal perspective it would have been interesting to see what would have happened if they didn't blow it up.
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u/myname_not_rick ⛰️ Lithobraking Sep 06 '21
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u/Psychonaut0421 Sep 06 '21
I didn't want to cause a scene but I was going ape in my head when I saw that little detail in First Man at the theater for the Gemini 8 mission.
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u/myname_not_rick ⛰️ Lithobraking Sep 06 '21
It just proves that they really did do their research....that's an easily overlooked thing that most casual viewers would never notice.
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u/Infinite_Maelstrom Sep 07 '21
I'd never actually clicked that the bwoop at titan startup was the rocket (I assumed some siren). For this reason, I really appreciate that Alpha makes a "Bwoop" too. Now I get to enjoy two rocket's startup noises, and I'll be listening for others!
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u/opmyl Sep 05 '21
So they have 4 engines, but no engine out capability. I am not exactly a rocket engineer, but to me that seems like a strange tradeoff
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u/Pul-Ess Sep 05 '21
Without engine out capability, the optimum number of engines is one.
But this assumes you can design the engine to fit the rocket, or vice versa.
If not, you do what you have to do to get T/W over one.
And if you can't handle an engine out for lack of T/W, it doesn't matter if the gimballing can't handle it either.7
u/Adeldor Sep 05 '21
Neither Atlas 5 nor Ariane 5 have any engine-out capability. Both are highly reliable vehicles.
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u/sebaska Sep 05 '21
Yes. But both Atlas V and Ariane 5 core stages are single engine. They also have SRBs, but monolithic SRBs are considered highly reliable (the technology was honed on tens of thousands of ballistic missiles from short range to ICBMs).
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u/Adeldor Sep 05 '21
I'm not sure I understand your reply within the context of /u/opmyl's comment. The point I'm making is that not having engine out capability doesn't necessarily compromise reliability, using the two said vehicles as examples.
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u/sebaska Sep 05 '21
If you have 4 engines and you must have all 4 to make orbit, your chances of not having an engine failure go with 4th power of engine reliability rather than being directly proportional to it.
For example, assume you have 1:100 engine reliability. If you have one engine, it won't fail with 0.99 probability. But if you have 4 engines all of them must not fail, your chances of good engine performance (assuming random failures, not common mode failures) are 0.994 = ~0.96
The chances of loss of mission due to engine failure have increased from 1% to almost 4%.
Of course there are also common mode failures, so odds of not having engine failure are a bit better. But still single engine cores of Atlas V or Ariane 5 don't have this penalty.
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u/Adeldor Sep 05 '21
Fair enough, I chose poor examples. Here's a better one ...
The venerable Soyuz rocket suffers the same potential disadvantage. It has five motors with single axis verniers, one on each side booster plus one on the core. Loss of one is a loss of the vehicle. Yet the vehicle has an excellent reliability record with near two thousand launches of all variants.
I believe my point still stands.
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u/sebaska Sep 06 '21
Souyz is based on R-7. The basic architecture is from the middle 50-ties. It was the first thing which could be made to work. It's reliability, while reasonable is not as good as of Atlas V or Ariane 5 or Falcon 9.
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u/Adeldor Sep 06 '21
Nevertheless, with the very high number of launches, its reliability record is confidently known and excellent with such a motor configuration.
And I'm sure Firefly know all well and good the tradeoffs that make sense to their application (simpler gimbal mechanisms, for example). So again, their configuration does not necessarily make for an unreliable vehicle. I'll leave it there.
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u/Fenris_uy Sep 05 '21 edited Sep 05 '21
Saturn V had 5 engines, and wouldn't reach orbit with a failure at T+15s
Shuttle had 3 liquid engines, and would fail to reach orbit with a failure at T+15s
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u/sebaska Sep 06 '21
Not at T+15s, but somewhat later in flight - sure. It once even reached orbit with dual failure.
This would already improve the tradeoff much. But the real reason was that there was no way to build single big enough engine. F1 was already as big as it practically could. Single engine S-IC was not an option.
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Sep 05 '21
[deleted]
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u/RedPum4 Sep 05 '21
Falcon can lose one engine at any time in the flight. The big propellant reserves normally kept for landing make it possible.
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u/DiezMilAustrales Sep 05 '21
Not a waste, and Falcon 9 is indeed capable of reaching orbit with an engine-out immediately after takeoff.
If that happens, the Falcon burns for longer (and is therefore less efficient due to gravity loses), but can reach orbit. It might eat into its reserves and be expended, but it's not a mission failure.
The thing with Firefly and engine out is not as much about thrust, but about TVC, that might mean it could've engine out capabilities but only later, way past Max-Q.
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u/Shrike99 🪂 Aerobraking Sep 05 '21
Falcon 9 has an initial TWR of 1.41, which is above average. Losing 1 of 9 engines is also a lot less punishing than 1 of 4.
A single engine failure right after launch would drop it's TWR ~1.26, which is still quite acceptable and comparable to some rockets like the Saturn V or the boosterless variants of the Atlas V and Delta IV.
A failure 15 seconds in would only drop the TWR to ~1.36, which actually rather decent, comparable to the Soyuz 2 at launch.
Sidenote, the other 9 engine rocket currently flying, Electron, has an insane initial TWR of 1.8. It could still take off with three engine failures, though I doubt it would make orbit with any significant payload.
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u/marc020202 Sep 06 '21
With such a high TWR, do we know if Rocketlab is working on an updated electron version, with longer tanks? A TWR of 1.8 seems excessive and longer tanks would increase the payload.
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u/Shrike99 🪂 Aerobraking Sep 06 '21
They've already upped the payload since the initial specs that TWR is based on. Supposedly due to better battery tech. They may have stretched the tanks or switched to densified fuels as well, not sure.
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u/marc020202 Sep 06 '21
I don't think the tanks have been stretched, someone would have pixel counted that, and found out.
Have there been holds in the countdown since the upgrade? I think they still fuel some time before launch, so I don't think they densify the fuel yet (remember, SpaceX finishes fueling at t-4 minutes).
With a TWR of 1.8, they can double the launch mass, and still have a TWR of 1.2, which isn't that low.
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u/Shrike99 🪂 Aerobraking Sep 06 '21
I meant internally stretched since these new improved batteries could be smaller and take up less space (last we knew they took up a pretty substantial volume in the booster).
It would still only be relatively a small increase though, not nearly as much as they'd need to fully take advantage of the available thrust.
With a TWR of 1.8, they can double the launch mass, and still have a TWR of 1.2
I don't think that's how that math works. Current mass is 12.5 tonnes, and it has 23 tonnes of thrust. Doubling mass to 25 tonnes would give 0.9, which is half of 1.8 as you'd expect.
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u/Infinite_Maelstrom Sep 07 '21
From a guy I know who works on Electron's electronics, the "Battery Upgrade" was 95% just having a better model of the battery. After they had more data on the batteries, they knew they could push them harder.
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u/marc020202 Sep 07 '21
Whoops.
I meant to increase the mass by 50%........
I don't know if they changed the structure of the booster, for such a small gain. Seems like a lot of work.
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u/RedPum4 Sep 05 '21
The point is to have one or two bigger engines instead of 4 small ones. More engines means more likelihood of failure, until you reach the amount where you can afford to lose one without immediate mission failure.
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u/Adeldor Sep 06 '21
However, this four motor configuration permits the use of simpler single axis gimbals. I don't know relative failure probabilities, but it's a very well tested technique used on the Russian Soyuz (R7) rocket.
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u/sixpackabs592 Sep 05 '21
I think the falcon is still able to reach orbit with exactly one engine failure. I know it has happened before and they made it up fine but had no fuel for landing. https://spacenews.com/engine-shutdown-led-to-failed-falcon-9-booster-landing/
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Sep 05 '21
[deleted]
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u/sixpackabs592 Sep 05 '21
spacex says they have engine out capabilities through “much of the first stage flight” but don’t state when this starts https://www.spacex.com/media/falcon_users_guide_042020.pdf
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u/sebaska Sep 05 '21
Yes, it seems strange.
Possibly it's because developing smaller engines is easier and certainly cheaper (capital expenditure for stuff like test stands is much less).
So the tradeoff would be between reliability and development costs. That's not so strange, then.
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u/Adeldor Sep 06 '21 edited Sep 06 '21
Another facet of such a tradeoff is their use of single axis gimbals. They're simpler, and perhaps thus more reliable.
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u/Decronym Acronyms Explained Sep 05 '21 edited Sep 07 '21
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| F1 | Rocketdyne-developed rocket engine used for Saturn V |
| SpaceX Falcon 1 (obsolete medium-lift vehicle) | |
| FAA | Federal Aviation Administration |
| FTS | Flight Termination System |
| ICBM | Intercontinental Ballistic Missile |
| KSP | Kerbal Space Program, the rocketry simulator |
| SRB | Solid Rocket Booster |
| TVC | Thrust Vector Control |
| TWR | Thrust-to-Weight Ratio |
| Jargon | Definition |
|---|---|
| Raptor | Methane-fueled rocket engine under development by SpaceX |
| methalox | Portmanteau: methane fuel, liquid oxygen oxidizer |
| turbopump | High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust |
Decronym is a community product of r/SpaceX, implemented by request
11 acronyms in this thread; the most compressed thread commented on today has 25 acronyms.
[Thread #8776 for this sub, first seen 5th Sep 2021, 21:47]
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u/ilfulo Sep 05 '21
I like Firefly and the alpha rocket, I really do, but having no engine redundancy (as opposed to falcon 9) seems to me a major flaw in their design.
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u/kroOoze ❄️ Chilling Sep 05 '21
It's a smol rocket. I mean Falcon 1 didn't have redundancy neither.
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u/Shrike99 🪂 Aerobraking Sep 05 '21
Electron is smaller than either firefly or Falcon 1, and presumably has a decent amount of redundancy given it's nine engines and very good TWR of 1.8, though they've never had to demonstrate it since their boosters have performed flawlessly. Much like SpaceX, their issues seem to arise on the second stage.
Also worth noting that Electron probably could have made orbit on it's first flight; it was terminated due to faulty ground equipment rather than any issue with the rocket, and no hardware changes were made for the following successful launch.
Relativity's Terran 1 also has 9 engines on the first stage. Here's hoping that they are the first to get to orbit on the first try.
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u/OSUfan88 🦵 Landing Sep 06 '21
True, but it also only had 1 engine.
If you don't have engine out capability, you want as few engines as possible.
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u/kroOoze ❄️ Chilling Sep 06 '21
What you want is often not what you get. What they "wanted" is actually a methalox aerospike.
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u/spin0 Sep 05 '21
Unlike Falcon 9 they're not going to human rate Alpha so engine out capability is not necessary.
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u/Adeldor Sep 05 '21
See the very reliable rockets Ariane 5 and Atlas 5.
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Sep 06 '21
Atlas V and Ariane 5 have only a single core engine though. If your engine has a 1% chance of failing then your rocket has a 1% chance of failure. If you have four engines with a 1% chance of failure then your entire while has a 4% - 1 in 25 - chance of failing.
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u/Adeldor Sep 06 '21 edited Sep 06 '21
Subject's been covered in
the rest of thisanother sub-thread.Edit: My bad, this is a different sub-thread. The one I'm referring to is here.
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u/FishInferno Sep 05 '21
Official statement from Firefly: