SpaceX Falcon 9 / Dragon 2 : SpX-DM2 - EOM/Return: August, 2020 : DISCUSSION

[sdsds]

In today's briefing Stich didn't actually say it but implicitly he seemed to indicate LiOH for CO2 scrubbing was the hard limit factor for undocked operation. Is that generally accepted as true?

[John44]

SpaceX DM 2 - Post Return to Earth Flight Readiness Review Briefing
http://space-multimedia.nl.eu.org/index.php?option=com_content&view=article&id=65

[gemmy0I]

In today's briefing Stich didn't actually say it but implicitly he seemed to indicate LiOH for CO2 scrubbing was the hard limit factor for undocked operation. Is that generally accepted as true?

Is it publicly known whether Dragon's LiOH supply is serviceable/replenishable from within the capsule on-orbit? (Ditto for O2 and water which I'd guess are the next limiting factors.)

If so, that would open the option of restocking Dragon with new supplies sent up on a cargo vehicle in the event Dragon ran out the clock on its supplies and had to return to the ISS due to lack of a feasible landing site. Not an ideal situation by any stretch, as it would throw an expensive monkey wrench into ISS logistics and mission scheduling, but I could see it being preferable if they encountered a perfect storm of bad weather conditions across the whole Florida/Gulf region (very possible during hurricane season, like now) and the only alternative was to go for one of the military-supported emergency splashdown sites elsewhere in the world (e.g. in the Pacific). (I suspect having to resort to a military recovery would mean giving up on things like being able to maintain time/temperature-sensitive science experiments for intact return to NASA.)

Since Dragon has such a copious delta-v budget due to the unused launch abort propellant which remains with the capsule and (IIRC) is usable by the Dracos, as long as life support consumables could be replenished on-orbit, the capsule should be able to gain quite a bit more free flight time. If Dragon consumables could be pre-positioned as "in stock" items on the ISS, having to return to the station wouldn't even have to mean waiting for the next cargo flight, making it a far less logistically impactful choice.

Given that subsequent Dragons are supposed to have better wind margins, this may not be as much of an issue going forward, but the ability to maintain a Dragon on-orbit for long periods of time could be especially valuable in the future as new stations and launch vehicles enter reality. For instance, if Starship is used to launch and return ISS crews, but is deemed too big to safely dock to the ISS, Dragons could be used as on-orbit taxis between ISS and a free-flying Starship. They could also be used to ferry crew between the ISS and commercial successor stations that might overlap with it operationally. Or for visiting lunar/interplanetary vehicles being staged in LEO...etc. For that purpose, it would be nice to not have to rotate Dragons every six months.

[sdsds]

Given that subsequent Dragons are supposed to have better wind margins, this may not be as much of an issue going forward

Yes but for subsequent missions there will be four crewmembers aboard rather than two.

(And personally I'm betting the LiOH scrubbing is via canisters not unlike those used on station and previously shuttle. So resupply as you suggest does seem like a viable option.)

[Jorge]

Apologies if it's been discussed somewhere else, but I haven't seen anything relating to a preference for an ascending (northeast) track versus a descending (southeast) track for re-entry?

Are there any kind of failure modes during re-entry that would make one path the logical choice over the other?

For the space shuttle, ascending was preferred due to lower public entry risk, and (during summer) noctilucent clouds. Don't know if the same considerations apply for Dragon.

[KC7NEC]

it's looking more and more likely they will need to delay. The most recent track by the NHC has this going straight up Florida which will for sure affect both coasts and all landing sites. Even if this ends up not being a tropical storm over Florida on Sunday it's going to be very bad weather over a wide area including the sites. I personally would put a Sat-Sun return at less than 30% at this point.

[sdsds]

Some hashtags you just gotta love: #LandAmerica

https://twitter.com/Explorer_Flight/status/1284327250897375234 et al.

[Zed_Noir]

it's looking more and more likely they will need to delay. The most recent track by the NHC has this going straight up Florida which will for sure affect both coasts and all landing sites. Even if this ends up not being a tropical storm over Florida on Sunday it's going to be very bad weather over a wide area including the sites. I personally would put a Sat-Sun return at less than 30% at this point.

NASA & SpaceX could select the Pensacola or the Panama City landing zone. Which according the current NHC forecast map are not affected by tropical storm Isaias by landing time for DM-2.

[Orbiter]

Not looking too good this morning for August 2nd. Center of Isaias is predicted to be basically directly over the recovery zone.

[Eagandale4114]

Cone has shifted a bit eastwards. Gulf recovery may be possible.

https://www.nhc.noaa.gov/storm_graphics/AT09/refresh/AL092020_5day_cone_with_line_and_wind+png/205640_5day_cone_with_line_and_wind.png

[Comga]

Cone has shifted a bit eastwards. Gulf recovery may be possible.

https://www.nhc.noaa.gov/storm_graphics/AT09/refresh/AL092020_5day_cone_with_line_and_wind+png/205640_5day_cone_with_line_and_wind.png

This is NOT the map to use to see where the storm is predicted to be.
That’s where the storm center is likely to travel.
It does NOT show the extent of the windblown areas. The description says as much.
Use the tropical winds forecast graph and the “Earliest arrival” map.

[sdsds]

NASA still seems upbeat about the possibility of getting them safely downhill this weekend.

https://twitter.com/Commercial_Crew/status/1289021785862819845

[Yazata]

Cone has shifted a bit eastwards. Gulf recovery may be possible.

https://www.nhc.noaa.gov/storm_graphics/AT09/refresh/AL092020_5day_cone_with_line_and_wind+png/205640_5day_cone_with_line_and_wind.png

The thing has strengthened into a hurricane and the evolving predictions appear to have it gradually curving onto a more easterly course. Which is good for Chris G, Julia B and everyone else who lives in eastern FL. There might be some hope that the storm will have cleared out and moved north by splashdown time. Unfortunately, while the NHC tries to predict the arrival of tropical storm force winds, it doesn't predict their cessation. So my guess is that all of the Atlantic DM-2 recovery sites are pretty much out of the question, given the uncertainties. 

Which leaves the Gulf. All of the Gulf sites still look viable to my layman's eye, most obviously Pensacola and Panama City. Tampa/St. Pete. might be riskier. Julia B. tweets that Go Navigator is currently in the Gulf.

https://www.nhc.noaa.gov/storm_graphics/AT09/refresh/AL092020_wind_probs_34_F120+png/115720.png

[Vernon]

Is there anything preventing a splashdown off the coast of Houston if SpaceX/NASA wanted to just chopper the astronauts directly from the recovery ship to Houston? Too many offshore rigs or too much disruption to shipping traffic?

[mattkamper]

We have TFR's for both Pensacola along with Panama City for Sunday issued by the FAA. It looks like these 2 are the options for Splashdown on Sunday.

https://tfr.faa.gov/save_pages/detail_0_7075.html

https://tfr.faa.gov/save_pages/detail_0_7074.html

[sdsds]

Is there anything preventing a splashdown off the coast of Houston if SpaceX/NASA wanted to just chopper the astronauts directly from the recovery ship to Houston? Too many offshore rigs or too much disruption to shipping traffic?

For DM2, count on the vehicle splashing down in one of the previously designated landing zones exactly according to plan, without any improvisation. For future missions, who can say? But note they aren't likely to be refurbishing Dragon spacecraft in Houston!

[CJ]

From the update thread;

Great animated thread by NASA on the undocking & EOM stages (PDF of thread attached)

Thank you for posting this. This tweet from it raised by eyebrows;
"VESTIBULE DEPRESSURIZATION: Valves remove the air from Dragon, taking it near vacuum. "

I suspect they mean that this takes the vestibule, not the Dragon, to near vacuum.

[TorenAltair]

German news reporting the usual bulls*** stuff: "SpaceX-Astronauts stuck on ISS"... "weather denies return"

[Alvian@IDN]

We all know that the DM-2 reentry times will be well within the first window of SN5's hop, so that would be obviously interesting to see if they're going to bother having two livestreams)

[Eer]

Timeline:

LOL - and the time zone of the estimated times will be left to your imagination.  CDT? EDT? PDT? Presumably not GMT (Zulu).