SpaceX Dragon 2 Updates and Discussion - Thread 3

[Alexphysics]

Which brings to mind another question:  For D2 missions with 4+ crew, can any of them sleep in the spacecraft? There are only so many sleep stations in the ISS.

USOS has 4 crew bunks with direct expedation hangovers. With the expeditions running at 3 members till Comerical Crew is operational, they have plenty of bunks. For the short durations test crew missions the guys and gal can bunk in a laboratory or they will schedule it were they will not meet. Currently they are assessing if DM-2 will be a longer mission.

DM-2 is definitely going to be a long duration mission. What's being decided yet is the duration which can be from 6 weeks to maybe up to 3 months. They want DM-2 to come down about a month before the first rotation mission currently eyed for the end of the summer. That's what will determine the duration of DM-2.

[Comga]

This thread is struggling to stay on topic about Dragon 2.
AS-501 asked a relevant question about the ability Dragon 2 to act as additional sleeping quarters.
The duration of DM-2 is only relevant here if Dragon 2 has some sort of time limit as sleeping quarters, like limited capacity in its toilet tank.
(By the way, does Dragon 2 retain “waste fluids and solids” and bring them down or does it have some way to vent at least the water?)
Can we limit this thread to Dragon 2?

[dondar]

This thread is struggling to stay on topic about Dragon 2.
AS-501 asked a relevant question about the ability Dragon 2 to act as additional sleeping quarters.
The duration of DM-2 is only relevant here if Dragon 2 has some sort of time limit as sleeping quarters, like limited capacity in its toilet tank.
(By the way, does Dragon 2 retain “waste fluids and solids” and bring them down or does it have some way to vent at least the water?)
Can we limit this thread to Dragon 2?

the most important limiting factor for any space bubble is CO2 scrubbing capacity. Everything else (humidity control, waste management etc.) is "secondary"

[Comga]

This thread is struggling to stay on topic about Dragon 2.
AS-501 asked a relevant question about the ability Dragon 2 to act as additional sleeping quarters.
The duration of DM-2 is only relevant here if Dragon 2 has some sort of time limit as sleeping quarters, like limited capacity in its toilet tank.
(By the way, does Dragon 2 retain “waste fluids and solids” and bring them down or does it have some way to vent at least the water?)
Can we limit this thread to Dragon 2?

the most important limiting factor for any space bubble is CO2 scrubbing capacity.
Everything else (humidity control, waste management etc.) is "secondary"

And so what do we know about CO2 scrubbing in Dragon 2?
Given that up to four crew will ride in it on two or three day rendezvous flights, it will have some capacity for that.
If it's base on some expendable, and needs to be saved for a fully occupied but somehow delayed reentry, perhaps it cannot be used for extended periods of time, such as sleeping quarters.

So a question about Dragon 2 and DM-1:
When Dragon 1 is berthed wasn't there an ~6" air "hose" that brought air from the ISS into Dragon?
There would be a lot less room for a air hose going through the narrower docking adapter.
My recollection is that this was not the case for Dragon 2 on DM-1.
So there must already have been some ability of that first Dragon 2 to do it's own air handling.
Can anyone point me to where we have discussed this?

[docmordrid]

>
And so what do we know about CO2 scrubbing in Dragon 2?
>

We know the ECLSS was designed for a crew of 7 + margins, and the change to a max crew of 4 is relatively recent to accomodate a seat angle change NASA wanted. It cost 3 seats.

ISTM down-modding an already certified ECLSS isn't SpaceX's style, and why would NASA ask for it?

[gongora]

We know the ECLSS was designed for a crew of 7 + margins

We do?

[Coastal Ron]

We know the ECLSS was designed for a crew of 7 + margins

We do?

Well SpaceX advertises that the Dragon 2 can carry "...up to 7 passengers to and from Earth orbit, and beyond."

Can't speak for the "+ margin" part...

[whitelancer64]

Which brings to mind another question:  For D2 missions with 4+ crew, can any of them sleep in the spacecraft? There are only so many sleep stations in the ISS.

You can strap a sleeping bag to a wall nearly anywhere you want to on the ISS, so long as there's good air circulation in that area. You don't need to use a commercial crew capsule as a sleeping room.

There are 4 sleeping cabins on the USOS side, in the Harmony module. There are 2 more on the Russian side, but as far as I know, when there are three Russian astronauts on the ISS, they typically all stay on the Russian side. Again, they use a sleeping bag strapped to a wall, from what I've heard, that's usually in the Pirs docking module.

For direct handoffs, where the crew of the ISS is temporarily bumped up to 11, I imagine they will use the sleeping bag strapped to the wall method. I know the US laboratory module has been used for sleeping quarters in the past.

[docmordrid]

We know the ECLSS was designed for a crew of 7 + margins

We do?

Well SpaceX advertises that the Dragon 2 can carry "...up to 7 passengers to and from Earth orbit, and beyond."

Can't speak for the "+ margin" part...

Why would anyone not design in margins on a crew ECLSS?

NASA CC selection press kit

https://www.nasa.gov/sites/default/files/atoms/files/commercialcrew_press_kit.pdf

Dragon was designed from the beginning to carry humans, and the upgraded human-rated vehicle will be one of the safest, most reliable spacecraft ever flown. The vehicle holds seats for 7 passengers, and includes an Environmental Control and Life Support System (ECLSS) that provides a comfortable environment for crewmembers.

[dondar]

This thread is struggling to stay on topic about Dragon 2.
AS-501 asked a relevant question about the ability Dragon 2 to act as additional sleeping quarters.
The duration of DM-2 is only relevant here if Dragon 2 has some sort of time limit as sleeping quarters, like limited capacity in its toilet tank.
(By the way, does Dragon 2 retain “waste fluids and solids” and bring them down or does it have some way to vent at least the water?)
Can we limit this thread to Dragon 2?

the most important limiting factor for any space bubble is CO2 scrubbing capacity.
Everything else (humidity control, waste management etc.) is "secondary"

And so what do we know about CO2 scrubbing in Dragon 2?
Given that up to four crew will ride in it on two or three day rendezvous flights, it will have some capacity for that.
If it's base on some expendable, and needs to be saved for a fully occupied but somehow delayed reentry, perhaps it cannot be used for extended periods of time, such as sleeping quarters.

So a question about Dragon 2 and DM-1:
When Dragon 1 is berthed wasn't there an ~6" air "hose" that brought air from the ISS into Dragon?
There would be a lot less room for a air hose going through the narrower docking adapter.
My recollection is that this was not the case for Dragon 2 on DM-1.
So there must already have been some ability of that first Dragon 2 to do it's own air handling.
Can anyone point me to where we have discussed this?

"we" "know" that Crew Dragon can do 5 days of the autonomous flight with crew of 4.(Space Adventures "contract"). One can safely add another 24h to get norminal scrubbing capacity.

[FutureSpaceTourist]

March 31, 2020

NASA, SpaceX Simulate Upcoming Crew Mission with Astronauts

[…]

Image caption:

On Thursday, March 19 and Friday, March 20, SpaceX teams in Firing Room 4 at NASA's Kennedy Space Center in Florida and the company's Mission Control in Hawthorne, California, along with NASA flight controllers in Mission Control Houston, executed a full simulation of launch and docking of the Crew Dragon spacecraft, with NASA astronauts Bob Behnken and Doug Hurley (front) participating in SpaceX's flight simulator.
Credits: SpaceX

https://www.nasa.gov/feature/nasa-spacex-simulate-upcoming-crew-mission-with-astronauts

Funny how I didn’t notice the iPad when I originally posted the above

https://twitter.com/therealjonvh/status/1252560578951946246

I’m not saying @SpaceX is the @Apple of Rocket companies. But...

[tyrred]

March 31, 2020

NASA, SpaceX Simulate Upcoming Crew Mission with Astronauts

[…]

Image caption:

On Thursday, March 19 and Friday, March 20, SpaceX teams in Firing Room 4 at NASA's Kennedy Space Center in Florida and the company's Mission Control in Hawthorne, California, along with NASA flight controllers in Mission Control Houston, executed a full simulation of launch and docking of the Crew Dragon spacecraft, with NASA astronauts Bob Behnken and Doug Hurley (front) participating in SpaceX's flight simulator.
Credits: SpaceX

https://www.nasa.gov/feature/nasa-spacex-simulate-upcoming-crew-mission-with-astronauts

Funny how I didn’t notice the iPad when I originally posted the above

https://twitter.com/therealjonvh/status/1252560578951946246

I’m not saying @SpaceX is the @Apple of Rocket companies. But...

The shadows on the wall were more attractive 

[Silmfeanor]

I'd like to draw some attention to this excellent interview with Hans Königsmann (in german):
https://www.spiegel.de/wissenschaft/weltall/spacex-chefingenieur-zum-stat-des-crew-dragon-wilde-party-kommt-noch-a-998ff592-1071-44d5-9972-ff2b73ec8fb6

Some choice quotes and short translations of main points in relation to Crew Dragon

-on the usage of the touch screens for steering the capsule:

SPIEGEL: Das Cockpit des "Crew Dragon" sieht futuristisch aus. Ging es Ihnen vor allem um die Optik?

Königsmann: Nein, die Steuerung über Touchscreens ist auch sehr praktisch. Ein Flugzeug könnte man wohl nicht so fliegen. Aber eine Kapsel reagiert langsam, wenn sie auch schnell fliegt. Und die Steuerung über den Bildschirm zwingt einen dazu, ebenfalls langsam zu sein. Als ich das im Simulator getestet habe, war ich mit dem Touchscreen besser unterwegs als mit einem Joystick.

Hans was better at steering with the touchscreen than with a joystick in sims.

- on chances of loss of crew:

Königsmann: Es gibt Anforderungen der Nasa zum Design des Transportsystems. Demnach darf das Risiko, die Crew zu verlieren, über die gesamte Mission gerechnet nur bei 1 zu 270 liegen. Wir liegen etwas besser, bei einem rechnerischen Wert von 1 zu 276. Und da ist noch nicht einmal das Rettungssystem berücksichtigt, das die Kapsel bei Startproblemen absprengen und wegtransportieren kann. Berücksichtigt man das, ist das reale Risiko für ein katastrophales Ereignis noch deutlich geringer.

SPIEGEL: Wie hoch liegt es?

Königsmann: Die Zahl haben wir nie im Detail ausgerechnet. Aber sicher bei 1 zu mehreren Tausend. Das sollte passen.

SpaceX has a 1 in 276 chance of loss of crew by NASA's calculations. This is without taking into account the LAS system. Therefore the real number is way lower. SpaceX has never calculated that real number precisely; Hans estimates the number to be certainly at least  1:several thousand.

-mission duration:

Königsmann:  Uns wurde gesagt: Sechs bis sechzehn Wochen könnte es dauern. Ich glaube, es wird eher eine längere Mission.

Uncertain apperantly as of the date of interview for SpaceX; but 6 till 16 weeks, Hans estimates it on the longer end of that range.

Some other choice tidbits regarding solar cells duration ( Hans does not expect them to be a problem in duration) and starship, but i'll post in the relevant threads.

[abaddon]

SpaceX has a 1 in 276 chance of loss of crew by NASA's calculations. This is without taking into account the LAS system. Therefore the real number is way lower. SpaceX has never calculated that real number precisely; Hans estimates the number to be certainly at least  1:several thousand.

Well, that is simply fascinating, and not something I have heard elsewhere.  On the 1 in 276, Kathy Leuders, when asked about the exact number in the last week or so, simply said that the system "met the design criteria in that regard" or something equally vague and did not state a number, which seems odd if it in fact (slightly) exceeds the requirement of 1 in 270.

[NaN]

On the 1 in 276, Kathy Leuders, when asked about the exact number in the last week or so, simply said that the system "met the design criteria in that regard" or something equally vague and did not state a number, which seems odd if it in fact (slightly) exceeds the requirement of 1 in 270.

These numbers come from statistical models which have, IMO, a large range of uncertainty. The two capsules will both meet or exceed the requirement, but would you for example want to field a question from a reporter asking why one capsule was "more dangerous" than another one because it had a slightly different number?
The crew capsules both meet (or will meet, in the case of Starliner) the design criteria and are as safe as they can reasonably be made, not too much point in publicly delving into the details of what is just a model for a sensitive subject.

[kdhilliard]

SpaceX has a 1 in 276 chance of loss of crew by NASA's calculations. This is without taking into account the LAS system. Therefore the real number is way lower. SpaceX has never calculated that real number precisely; Hans estimates the number to be certainly at least  1:several thousand.

That sounds uncomfortably similar to the overly optimistic "certainty" NASA managers had about STS safety prior to 51-L, and not something I expected to hear from a SpaceX engineer heading Mission Assurance.  Even assuming a 100% LAS success rate, over 6/7ths of the 1:276 risks would have to come during ascent to achieve his estimate.

[Vettedrmr]

Even assuming a 100% LAS success rate, over 6/7ths of the 1:276 risks would have to come during ascent to achieve his estimate.

If the LAS was 100% successful, then by definition *all* of the 1:276 risks would come outside of ascent.

[kessdawg]

Even assuming a 100% LAS success rate, over 6/7ths of the 1:276 risks would have to come during ascent to achieve his estimate.

If the LAS was 100% successful, then by definition *all* of the 1:276 risks would come outside of ascent.

You'd still have parachute/recovery risks unless you're counting that as part of the LAS.

[kdhilliard]

Even assuming a 100% LAS success rate, over 6/7ths of the 1:276 risks would have to come during ascent to achieve his estimate.

If the LAS was 100% successful, then by definition *all* of the 1:276 risks would come outside of ascent.

No.  Not all of the 1:276, but all of the 1:2000.

Koenigsmann was saying that the 1:276 wasn't "taking into account the LAS system", and that if you did, that would reduce the odds to lower than 1:2000, thus going from 0.36% to at most 0.05%, implying that the difference of at least 0.31% (or more then 6/7ths of 1:276) was from events for which the LAS could provide a save.

Edit -- Nerd note: Apologies for writing 1:276 and the like where I should have written 1 in 276 or 1/276.

[whitelancer64]

IIRC the LOC risk is a cumulative number, and IIRC way back NASA said the LOC risk during the ascent phase can't be less than 1 in 500. So for ascent it may be true that LOC risk could be 1 in 2000, or better, when considering the use of the LAS would save the crew. Naturally the LAS will have its own LOC risk as well, which would be the limiting factor for that calculation. For it to be "1 in thousands" overall, then the LOC risk during ascent would have to be something like 1 in 5000, or better, with the use of the LAS. I really don't see how that could be the case, but maybe it is.

IIRC the greatest LOC risk - that both CC providers had trouble with - was MMOD risk while on orbit.