Expected loss standard procedure = 2*n*2*q*p = 4*n*p = 0.016Expected loss SpaceX procedure = n*q*2*p = 0.008What this shows is that the SpaceX procedure is safer because less people are exposed to risk and that the crew escape system is safer than having the ground and flight crew try and get away using slide wires. As the Space Shuttle did not have an escape system, the standard procedure is the safest way.
Quote from: Negan on 01/17/2018 09:24 pmSad part is SpaceX has already proved at least 38 times in a row they can safely fuel F9 without blowing it up, and that's with some flight-proven 1st stages in the mix.That's 19 times in a row since the last fuelling explosion on 1 September 2016 with AMOS 6.
Sad part is SpaceX has already proved at least 38 times in a row they can safely fuel F9 without blowing it up, and that's with some flight-proven 1st stages in the mix.
Quote from: Steven Pietrobon on 01/18/2018 05:17 amQuote from: Negan on 01/17/2018 09:24 pmSad part is SpaceX has already proved at least 38 times in a row they can safely fuel F9 without blowing it up, and that's with some flight-proven 1st stages in the mix.That's 19 times in a row since the last fuelling explosion on 1 September 2016 with AMOS 6.Negan is counting static fires. Should probably also count test fires at McGregor. So the number of successful fires with the current procedure is probably >50.
Quote from: Steven Pietrobon on 01/18/2018 05:17 amExpected loss standard procedure = 2*n*2*q*p = 4*n*p = 0.016Expected loss SpaceX procedure = n*q*2*p = 0.008What this shows is that the SpaceX procedure is safer because less people are exposed to risk and that the crew escape system is safer than having the ground and flight crew try and get away using slide wires. As the Space Shuttle did not have an escape system, the standard procedure is the safest way.Which suggests (no proof, just suggests) that ASAP is thinking that programme vehicles don't have launch escape systems designed in, IE just like Shuttle. This is simply bizarre, given they they know both capsules do (and DC will) and IIRC didn't they insist on them having such systems to begin with?In aviation, loading passengers happens after the vehicle is fueled. This has (potentially) serious implications for ConOps with any future P2P BFS flights. OTOH getting unstrapped from a capsule and running in a full pressure suit is a PITA. However if you're in the same capsule with a finger poised over the Big Red Switch to fire the LES and watching any vehicle telemetry for anomalies that sounds quite a bit safer than being crew on the pad. My instinct is go to the toilet, suit up and strap in then let the pad crew do their work, while being ready to punch out if anything looks off.
Because the highest danger is during fueling. It's a dynamic process both in terms of the propellants themselves flowing but also the vehicle hasn't reached thermal stasis. The danger that something goes wrong and causes an accident is much higher during this period than that it is during the relatively static period of topping-off/replenishment. So, that added risk has to be weighed against the lower risk of fewer man minutes of exposure to a loaded rocket. Exactly which one turns out to have the true lower risk is dependent on the variables: number of astronauts and ground crew exposed, loading duration, etc.
Quote from: rockets4life97 on 01/18/2018 07:07 amQuote from: Steven Pietrobon on 01/18/2018 05:17 amQuote from: Negan on 01/17/2018 09:24 pmSad part is SpaceX has already proved at least 38 times in a row they can safely fuel F9 without blowing it up, and that's with some flight-proven 1st stages in the mix.That's 19 times in a row since the last fuelling explosion on 1 September 2016 with AMOS 6.Negan is counting static fires. Should probably also count test fires at McGregor. So the number of successful fires with the current procedure is probably >50.That makes some assumptions that aren't necessarily supported though. Firstly, McGregor firings are of each stage individually and not of a combined stack. Seems like this shouldn't really be a factor, but maybe there is some unexpected difference. Secondly, while I have a hard time believing that this would be so, IIRC, we don't actually know that the loading process at McGregor is exactly the same as at the launch pad. Slightly more believable is that environmental factors could be a factor. With the static fires, we absolutely know that it is being done the same as on launch day. So, while you're probably right that there have been more successful firings with the current procedure, I don't think we can yet say so definitively.
That's 19 times in a row since the last fuelling explosion on 1 September 2016 with AMOS 6.
As an aside, whatever risk there is in Astros needing to use the Boeing crew escape system (the slide wire) from the pad must be accounted for. I would assume the estimated level of risk in using the system itself is generally considered to be low. Presumably the window of time where it would be used is also low, as once the Astros are in the craft and buckled in, the LES should take over responsibility rather than using the slide wire.Also worth noting that SpaceX has no equivalent system because of their plans to board unfueled. If at some point those plans change, they will presumably have to implement a crew escape system similar to Boeing's.
Also worth noting that SpaceX has no equivalent system because of their plans to board unfueled. If at some point those plans change, they will presumably have to implement a crew escape system similar to Boeing's.
Quote from: abaddon on 01/18/2018 03:08 pmAlso worth noting that SpaceX has no equivalent system because of their plans to board unfueled. If at some point those plans change, they will presumably have to implement a crew escape system similar to Boeing's.I thought SpaceX is also going to have a slide wire system on 39A?
I wonder what ASAP had to say about fuel transfers to the ISS? And next fuel depots in space. Although a different environment it will become SOP (or has) one day with crew onboard.
Quote from: punder on 01/17/2018 08:09 pmQuote from: Rocket Science on 01/17/2018 07:26 pmWow this thread is like Deja vu all over again from AMOS-6... Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.It's statistical analysis. It's the same reason it's fine for them to store large amounts of fuel and oxidizer on site for months and have people working around them, but why no extraneous personnel can be around when it's transferred from the trucks.
Quote from: Rocket Science on 01/17/2018 07:26 pmWow this thread is like Deja vu all over again from AMOS-6... Sorry if I'm annoying people. I just can't wrap my head around the idea that working around, riding an elevator beside, climbing into etc. an empty shell might be considered more dangerous than doing the same things when the empty shell has been transformed into a very large bomb.
Wow this thread is like Deja vu all over again from AMOS-6...
Nope. Dragon2 is not their end-game. BFR is where they want to be and why waste the money and time getting legs on a Dragon?
So let me understand this. Currently, during even a static fire, they close off the pad, put up road blocks , remove everyone to a distance to 50,000 miles and then do the static fire.What Nasa are proposing is the same process, but then stick their prized Astos and employees (and Spacex) in a bus, drive back to the pad, climb the gantry, out on the crew arm , open the hatch and get the crew seated (and if I remember from the Shuttle days this took forever) all the while standing a couple of metres away from this fully fuelled and loaded , hissing and grumbling rocket.Are they serious? Seems to me it's lack of logic and more "we've always done it this way and therefore there is no other way" thinking.