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Dragon
So watching the Starliner scrub tonight it's an odd feeling seeing people there getting in and out while the rocket is fully fueled. They're going to offload the whole crew before detanking. Now this used to be the ONLY way it was done, but spaceX got approval for the load and go back in 2018 from NASA. After getting so used to Dragon this old-school method just feels weird now.
I get the argument that the most dangerous phase is during fueling or detanking, and once it's full it's actually a pretty static system. Still though....ya know?
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If I were an astronaut I would feel a lot safer in a load and go rocket. You spend 100% of your time on the rocket strapped into an armed abort system
Sorry if im kissing something simple but why can’t they arm the capsule if it’s not a load and go?
you can, once you're in the capsule and closeout is complete. but you have to walk up to and get in to a fully fueled rocket, which is the problem.
And the ground crew has to both walk up to it and walk away from it.
They do arm it when the astronauts are strapped in, the hatched is closed, and the ground crew gets to safety. During those ground operations though if anything goes wrong the crew has to be ready to zipline away from a potentially exploding rocket
the zipline is a nice idea but i feel like it's kind of theater. I'm not aware of any pad explosion where it would have made any difference, and really, i think pretty much every failure mode of that sort is going to go from everything's fine to full nedelin faster than you can say double decker cheeseburgers.
Wasn't Amos 6 a RP-1 + oxygen explosion?
A side-by-side video simulation at the time demonstrated that a crew Dragon could have escaped but with a small margin in the order of a hundred milliseconds. I found this video but it wasn't the one I was looking for, which put the launch escape test literally at the same level as the Amos 6 payload.
In an imaginary situation where ground crew were to be loading astronauts into Dragon sitting atop a fueled Falcon 9, there would clearly be no survivors on Dragon or the crew bridge.
It also seems fair to imagine that any survivors in the launch tower would be better remaining where they were than spending several seconds outside on the zip line with an ongoing fire.
BTW sorry about my quoted reply order, but it seems to get the gist of what people meant.
In the example of (something like) the Amos-6 anomaly the zip lines could have been useful for anyone who survived the blast to get away from the hydrazine explosion.
"full nedelin'
TIL about the Nedelin Disaster.
Are you joking or do they actually zip line away from the rocket?
https://www.space.com/36347-ula-zip-line-astronaut-escape-system-in-photos.html
The zip line is very very real. They even have a little tank at the bottom of the zip line to take cover in
SpaceX is changing it for a slide, instead of a basket zipline.
Yes, fuel loading and unloading is short enough that it not much mission time anyway.
Yeah, putting the pad crew at risk is nuts.
The astronauts only get a bit more risk between starting fueling and the launch abort system arming, while there isn't that much fuel in the tanks.
They arm launch escape before fueling starts.
Yep. I confused the poll for fueling and the fueling itself.
When do they disarm the launch escape system?
it's not armed at all until the arm is retracted (I think)
Load then faround a bunch then go is basically relic of the first rockets. It does seem that load and go seems to be the better fueling strategy. Source: I've seen a lot of scrubs.
This is good example of old school aerospace industry doing what traditionally has been done, instead of innovating in terms of safety.
Yes, there are lots of trade-offs. Launch escapes are always going to be risky - Dragon's escape system detonated during a test - and load-and-go leaves the crew reliant on launch escape for a long time, and there is risk during the loading procedure - refer AMOS-6.
You are trading launch escape risk during the whole loading procedure, for higher risk of having no active escape system for a shorter time while the loaded rocket is as static as they can make it as the crew enters.
We're not talking about the safety of escape systems. We're talking about if your rocket starts to combust under you, a launch escape system of any sort, no matter its safety, is preferable to blowing up with the rocket.
But the risks of the launch escape system is key to the safety of the whole system. Load and go increases, by a fair amount, the likelihood of needing the launch escape system. If Falcon were to fail during fuelling, the Crew would be subject to the risks inherent in the escape system. If the Atlas were to fail during fuelling procedures, there would be no risk because no one is near the rocket.
This balances the risk of anything happening during the short period where crew is entering the loaded, but otherwise static, rocket.
You’re forgetting ground crew safety
You're limiting the "danger" phase to just the fueling phase. There's no reason to do that. The danger exists whenever combustible materials exist, which only starts after fueling begins and continues to exist when the rocket is sitting fueled.
No, I'm not limiting danger at all. Of course there is some danger while the rocket is fueled. It is less than the danger while the rocket is being fueled, however.
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
GTO comsatPre-launch test failureNOTE: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below.
Decronym is a community product of r/SpaceX, implemented by ^request
5 acronyms in this thread; the most compressed thread commented on today has 11 acronyms.
[Thread #12733 for this sub, first seen 7th May 2024, 06:42] [FAQ] [Full list] ^[Contact] [Source code]
For Crew Dragon, if they scrub and thus need to unload fuel, do they do a purge of the LOX with LN2 before letting people egress? A 1% (or even 0.1%) full rocket is still dangerous.
they purge the lox with helium. ln2 would turn to slush because lox is so much colder.
Not sure what you mean, LOX is not much colder than LN2, it is 13K warmer (at atmospheric pressure at least)
SpaceX chills their LOX to below its usual temperature to cram more in the tank.
Thanks ...
I was wondering why they didn't use argon instead. Checking, I'm surprised that argon's boiling point is so close to liquid oxygen's, and its freezing point is only a few degrees colder. So it looks like it would have the same problem as nitrogen.