SpaceX Falcon 9 / Dragon 2 : SpX-DM2 : May 27, 2020 : DISCUSSION

[ajmarco]

There is a very detailed timeline on L2 if you hurry and subscribe

It is not available from SpaceX directly?
Not everyone can afford an L2 subscription.

From spacex for the upcoming DM-2
spacex.com/launches

[eric z]

 L2 is one of the best bargains on line. The photo archives alone are priceless, but the main thing is you get to pontificate and crack jokes in the space policy section; and in all seriousness help support the complexity and costs of running a truly mind-boggling fantastic place where "all space cadets unite".

[edkyle99]

NASA Worm is on the tower-facing side, so it likely won't show up in most launch photos.  Does anyone know which direction the tower-side faces during ascent, after any rolls, etc.?  I wonder if Worm will even appear in any long-range tracking camera views.  Plus, it is on the LOX tank anyway, so will probably be iced-over.

 - Ed Kyle

[AS_501]

Do any space program old timers like me remember the build-up to STS-1?  Just like that now.  Yes, Columbia had ejection seats, but a lot of us were scared of a major, inescapable explosion.  I'll be breathing much easier this time during liftoff and through staging.  Are we there yet, are we there yet?   

[abaddon]

Jim B conveniently stepping out before questions, which is probably a good call as I expect there would have been a lot of distracting questions about Loverro rather than the launch.

[Surfdaddy]

Do any space program old timers like me remember the build-up to STS-1?  Just like that now.  Yes, Columbia had ejection seats, but a lot of us were scared of a major, inescapable explosion.  I'll be breathing much easier this time during liftoff and through staging.  Are we there yet, are we there yet?   

I remember watching the launch. On live TV, with the camera angle, the ignition occurred and a huge cloud of steam obscured the entire shuttle. I held my breath and then a moment later the shuttle stack rose from  behind the huge steam cloud.

Shuttle was much more exciting and IMHO much more dangerous, as the combination had NEVER been flown before, and it had people on it. Relatively speaking, the Falcon 9 and Dragon 2 are pretty well tested.

[tadaniels]

Kirk mentioned SpaceX modified the Dragon to assuage Russian concerns about a possible, though remote, catastrophic failure mode.  Curious minds are interested in details.

As I recall it, they objected to a lack of physical redundancy in the digital control system that was used to control Dragon during the ISS approach and docking phase. There was redundancy in the software control strings, but they all ran on the same flight control computer. The reply infers that SpaceX have added physical redundancy since DM-1.

[Oersted]

Shuttle was much more exciting and IMHO much more dangerous, as the combination had NEVER been flown before, and it had people on it. Relatively speaking, the Falcon 9 and Dragon 2 are pretty well tested.

I remember watching the Shuttle launch with total confizence it would work out just fine. Don't know why I was so confident, but I remember that I just parroted the general view in Denmark at the time. Everybody were sure the Americans would pull it off.

The lost tiles meant that the landing was a bit more exciting. I also remember that it impressed me much more than the lift-off because of the breath-taking and revolutionery visuals. Spacecraft landing on a runway, astronauts getting off by jet stairs. So futuristic. Plopping into the ocean does come across as a bit more old-fashioned...

[abaddon]

Kirk mentioned SpaceX modified the Dragon to assuage Russian concerns about a possible, though remote, catastrophic failure mode.  Curious minds are interested in details.

Wonder if the burst discs had anything to do with this.  Certainly a 'catastrophic' failure mode...

[ugordan]

Kirk mentioned SpaceX modified the Dragon to assuage Russian concerns about a possible, though remote, catastrophic failure mode.  Curious minds are interested in details.

Wonder if the burst discs had anything to do with this.  Certainly a 'catastrophic' failure mode...

Pretty sure it was related to Dragon computer redundancy. Burst discs have nothing to do with it, they're only relevant for launch abort and SuperDracos. Near the station, those SDs would damn well be safed long since.

[ugordan]

I wonder if Worm will even appear in any long-range tracking camera views.

I get where you're coming from, Ed, but a part of me just can't help but think #FirstWorldProblems 

[kessdawg]

NASA Worm is on the tower-facing side, so it likely won't show up in most launch photos.  Does anyone know which direction the tower-side faces during ascent, after any rolls, etc.?  I wonder if Worm will even appear in any long-range tracking camera views.  Plus, it is on the LOX tank anyway, so will probably be iced-over.

 - Ed Kyle

I'm hoping we'll get some Apollo style tower-cam views of the liftoff. Those will show the worm nicely rising off the ground.

[abaddon]

I wonder if Worm will even appear in any long-range tracking camera views.

I get where you're coming from, Ed, but a part of me just can't help but think #FirstWorldProblems 

I think you mean #FirstWormProblems

[Prober]

Ok design work over......now into testing.


Dragon 2 was to have "magnitudes of Safety" greater than the Shuttle.


What are the safety levels for Dragon 2?


missed that info....can someone point me in the direction?

[kdhilliard]

Dragon 2 was to have "magnitudes of Safety" greater than the Shuttle.
What are the safety levels for Dragon 2?
missed that info....can someone point me in the direction?

The Commercial Crew requirement was 1-in-270 Loss Of Crew.  Here is Program Manager Lueders addressing the risk question from Spaceflight Now's Stephen Clark, saying that they have met their 1-in-270 requirement.

[Lars-J]

Dragon 2 was to have "magnitudes of Safety" greater than the Shuttle.

I'd like to see a source for such a statement, magnitudeS means at least 100x safer. I doubt anyone would claim that.

[kdhilliard]

Dragon 2 was to have "magnitudes of Safety" greater than the Shuttle.

I'd like to see a source for such a statement, magnitudeS means at least 100x safer. I doubt anyone would claim that.

Yep.  The 1-in-270 was chosen as being three times better than the 1-in-90 LOC risk estimate for STS missions toward the end of that program.

_{I suppose 3X is two orders of magnitude in base sqrt(3).  Seen any aliens with approximately 0.866 fingers per hand?}

Edited just to note that 1-in-270 is nearly 1.5 orders of magnitude better than the retrospective 1-in-9 estimate for STS-1.  Here's hoping that we won't see such a dire retrospective analysis for Commercial Crew flights, but those unknown unknowns are hard to account for.

[Vettedrmr]

Kirk mentioned SpaceX modified the Dragon to assuage Russian concerns about a possible, though remote, catastrophic failure mode.  Curious minds are interested in details.

As I recall it, they objected to a lack of physical redundancy in the digital control system that was used to control Dragon during the ISS approach and docking phase. There was redundancy in the software control strings, but they all ran on the same flight control computer. The reply infers that SpaceX have added physical redundancy since DM-1.

I believe you have that backwards.  There are multiple redundant channels of hardware, but they all run the same software (just like military and commercial flight control systems).  For DM-1, the Russians wanted SpaceX to run dis-similar software on different hardware platforms (i.e., don't fly for years).

NASA said "fly".

[rdale]

If you like podcasts - today’s release has a flight director explaining the details not only of the mission, but how the separate mission controls will work together.

https://overcast.fm/+Pjd9-HXeE

[tadaniels]

Kirk mentioned SpaceX modified the Dragon to assuage Russian concerns about a possible, though remote, catastrophic failure mode.  Curious minds are interested in details.

As I recall it, they objected to a lack of physical redundancy in the digital control system that was used to control Dragon during the ISS approach and docking phase. There was redundancy in the software control strings, but they all ran on the same flight control computer. The reply infers that SpaceX have added physical redundancy since DM-1.

I believe you have that backwards.  There are multiple redundant channels of hardware, but they all run the same software (just like military and commercial flight control systems).  For DM-1, the Russians wanted SpaceX to run dis-similar software on different hardware platforms (i.e., don't fly for years).

I wasn’t sure myself, so I did some searching and found a quote from Gerstenmaier in the DM-1 FRR that said, “That's the basic concern the Russians brought up, why isn't there a separate system or separate box to go provide this backup capability? We think we have sufficient rationale for that." Whichever The case, as you said, NASA convinced the Russians that the risk was acceptable and DM-1 flew a successful mission. The NASA rep said today that SpaceX made a modification post-DM-1 that eliminated the issue entirely.