Author Topic: SpaceX Dragon 2 Updates and Discussion - Thread 3  (Read 81028 times)

Offline TripleSeven

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #160 on: 08/19/2018 08:41 AM »
When it comes to Dragon 2 and its snazzy large-sized touchscreens -- how are these things able to stand up against the vibrations, shocks and stresses of space launch and re-entry? I'd imagine that such large thin screens (tablets?) would be particularly vulnerable to such forces.

Are these primary control/viewing interfaces backed up by some kind of simpler and more rugged backup control scheme if they fail?

Are these touchscreens the most modern choices available? Or could they one day give way to Augmented Reality (AR) projections on a spacesuit helmet visor?



anything that the crew can survive (and much worse) the screens wont even notice

Online matthewkantar

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #161 on: 08/19/2018 02:55 PM »
The shock a phone experiences falling from a table top to a wood floor is probably worse than anything a screen would experience on a round trip to ISS in a Dragon. Falls like that are routine for smart phones and their screens.

Matthew

Offline gongora

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #162 on: 08/19/2018 03:11 PM »
We really don't need simultaneous discussions in multiple threads of user interfaces the Dragon isn't going to use.

Online kdhilliard

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #163 on: 08/19/2018 03:47 PM »
Back to Helium preloading ...
I don't see why the helium would be at ambient. I would expect it to be supper chilled, possibly below the LOX temperature and "warm up" to the LOX temp as it is being loaded.

Do you not remember the Amos-6 F-9 exploding, destroying the pad, during a static fire? The cause is thought to be  densified LOX, in the weave of the COPV, near its solidification point being frozen by colder Helium inside the COPV.

Matthew
It was a little bit more complex. LOX permeated the carbon fiber overwrap and filled cavities caused by buckles in the liner. Than two things happened: the supercooled helium caused the LOX close to the liner to freeze and the growing pressure inside the helium bottles caused the liner to expand. The frozen oxygen could not escape the same way it got in and instead got pressed against the overwrap. That was either enough to ignite the overwrap or it caused some fibres to rip which triggered the ignition.

By pressurizing the COPVs before they are submerged in LOX, they won't expand when the LOX gets loaded.

Following the AMOS-6 loss, weren't the propellant loading procedures changed (taking longer) to mitigate the issue until a new COPV was fielded?  And about the time of the first Block 5 flight, weren't the propellant loading times shortened, suggesting use of the new COPV design, and surprising everyone when it was revealed that the new COPV wouldn't fly until DM1?

Is it possible that those quicker loading times were a result of implementing the Helium preloading procedure, where the COPVs are precharged to full pressure with ambient temperature Helium, and then topped off (filled the remaining 80% of the way) at constant pressure as the COPVs were chilled during LOX load?

Offline CorvusCorax

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #164 on: 08/19/2018 05:12 PM »
Back to Helium preloading ...
...

Following the AMOS-6 loss, weren't the propellant loading procedures changed (taking longer) to mitigate the issue until a new COPV was fielded?  And about the time of the first Block 5 flight, weren't the propellant loading times shortened, suggesting use of the new COPV design, and surprising everyone when it was revealed that the new COPV wouldn't fly until DM1?

Is it possible that those quicker loading times were a result of implementing the Helium preloading procedure, where the COPVs are precharged to full pressure with ambient temperature Helium, and then topped off (filled the remaining 80% of the way) at constant pressure as the COPVs were chilled during LOX load?

Thinkable, but that would be speculation. A big question is, at which temperature the helium is loaded, and how fast it would potentially heat up. It would not make much sense to load helium at ambient temperature. The shock when adding supercooled oxygen into a tank with pressure vessels that hot would not be good for anything. You'd get instant oxygen vaporisation on the pressure vessels, with bubbles forming and the related microcavitation issues. Then the stresses on the COPV itself, liner shrinking, inside still hot. The raisin supposedly doesn't conduct heat too quickly, but the metal inside does...

To make this safe, the temperature of the COPV after helium loading should be somewhere between 60K and 90K. Below the boiling point of oxygen at least.

Allowing a small amount of liquid oxygen into the oxygen tank could ensure that the temperature in the tank stays below the boiling point of oxygen. Any additional heat from the outside would first cause some of the oxygen to boil off.

At this rate, one could possibly even load helium into the COPV at around 60K. It would not heat up as quickly in a 90K gaseous oxygen environment as it would in a 300K Florida ambient temperature. If Helium is loaded at 90K there'd be a 30K difference when loading the supercooled LOX, but the pressure in the COPV would reduce by approximately 1/3 as it cools down, if not topped off during oxygen loading.

Maybe they load the Helium at 60K, then allow it to heat to somewhere between 60K and 90K - dumping the expanding helium into the oxygen tank to keep the COPV pressure constant, and venting the oxygen tank as needed as well to keep its pressure constant. The cold helium would slow liquid oxygen boiloff rate and maybe slowly condense gaseous oxygen into liquid, so just before propellant loading proper begins, there's only a bit of liquid oxygen but mostly gaseous helium in the tank.

This has the advantage that nothing has to be loaded at all into the vehicle at all during crew boarding. The vehicle would keep itself pressurized thanks to the expanding helium as it heats a bit and vent mostly helium along a bit of GOX.

Then once the crew is strapped in, supercold LOX is fueled, and helium might or might not need to be topped of, depending on how long crew loading took and how hot it got. But since the worst case is 30K - less than 50% helium loss, they might have enough margin to fly without adding any helium after the crew boarded.


Offline Comga

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #165 on: 08/19/2018 07:50 PM »

COPVs, will be loaded with helium and verified to be in a stable configuration prior to astronaut arrival at the launch pad. The astronauts then will board the spacecraft about two hours before launch



This timeline is consistent with the fueling procedures SpaceX uses for its commercial resupply missions and satellite launches.

COPVs being loaded with helium more than 2 hours before launch is new isn't it?

Whether or not it’s new it indicates, albeit not definitely, that the early-load He is at ambient temperature. Otherwise it would not be “quiescent “, as it would warm and vent from the uninsulated COPVs in the ambient temperature and pressure LOX tanks before fueling.

As the super-cooled LOX is loaded, the COPVs near the top will be bathed in cold gaseous oxygen, which will be expelled as the tank fills. This will cool the He, which will need to be added to to maintain the pressure. This added He can be chilled, both by pre-cooling in a heat exchanger and by compression, due to its negative Joule-Thompson coefficient.

It would be great if we someday are told the details of this, but I am not holding my breath. It sounds like the kind of nitty-gritty detail SpaceX has no motivation to release. 
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline FutureSpaceTourist

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #166 on: 08/20/2018 08:25 AM »
Quote
SpaceX gears up for Crew Dragon’s first recovery with a giant inflatable cushion
By Eric Ralph
Posted on August 19, 2018

Paired with observations and comments from sources familiar with the company, all signs seem to indicate that SpaceX is planning to recover their first Crew Dragon spacecraft with a giant inflatable cushion, to be towed a hundred or so miles off the coast of California by one of the company’s Port of LA-stationed recovery vessels.

https://www.teslarati.com/spacex-crew-dragon-sea-recovery-giant-inflatable-cushion/


Online nacnud

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #167 on: 08/20/2018 08:57 AM »
Another fine product from the nonsense factory.  ;D

Offline speedevil

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #168 on: 08/20/2018 09:17 AM »
Another fine product from the nonsense factory.  ;D
It's not quite ridiculous - they presumably have a lot of data on D1 entry profile, that would pretty much work for D2.
Landing on a low profile 'boat' would have some benefits - there may be a bit of additional padding over hitting the ocean, reducing forces a little, and obviously less seawater may be nice.
The issue of what happens on a landing straddling the edge is probably the reason this wouldn't happen, as that case adds risk, never-mind the risk of hitting the towing vessel.

Offline FutureSpaceTourist

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #169 on: 08/20/2018 09:54 AM »
Main issues in my mind are landing accuracy / descent speed and thus time available to get the cushion in the right position. We know SpaceX have made changes to slow the descent rate of fairings so Mr Stephen can try and catch them, I don't know how Dragon2 descent may compare?

Offline ScottMC

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #170 on: 08/20/2018 10:09 AM »
That doesn't look like something that can be towed at high speed (although it might be fun having a ride on the back).  Does that mean they're going to use all that super draco fuel to power the draco thrusters to steer the dragon to the right (drifting) spot?  I wonder how the parachute lines would feel about that.

Online kevinof

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #171 on: 08/20/2018 10:15 AM »
One thing about Space X is that they will try something and see if it works, instead of relying on  some report or paper from 30 years ago dismissing it. It's the "answering questions and questioning answers" approach which is great.

May not work but it will be fun and interesting to watch.

Another fine product from the nonsense factory.  ;D

Online nacnud

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #172 on: 08/20/2018 11:21 AM »
Another fine product from the nonsense factory.  ;D
It's not quite ridiculous...

List of Culture ship names 😉

I think there is nothing wrong with the idea. I must remember to be less obtuse.
« Last Edit: 08/20/2018 01:02 PM by nacnud »

Online kdhilliard

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #173 on: 08/20/2018 01:25 PM »
The speculative nature of this particular Teslarati article is clear from its first sentence.

Aside from the accuracy issues involved in catching a Dragon coming down under unsteered round parachutes while not yet managing to get under a fairing half coming down under a steered ram air parachute, I question the premise of avoiding seawater exposure on DM1.  They argue that refurbishment of an ocean landed capsules takes so long that, were DM1 to land in the water upon its return to Earth in December, they wouldn't have enough time to get it ready for the InFlight Abort test in March which is necessary prior to the April DM2.

I contend that if there is any chance of missing a Dragon 2 returning from an operational mission, then NASA will want to see how well the DM1 capsule performs splashing down following reentry.  Yes, they've done splashdown and recovery tests with capsule mock-ups, but that's not the same as testing the performance of a just reentered production capsule.

Color me skeptical.

Offline envy887

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #174 on: 08/20/2018 01:29 PM »
Is there any scope for Augmented Reality micro-projection onto the Spacesuit helmet visor?

This technology seems to be coming into availability for the consumer market, so why couldn't such a concept be useful for space applications as well?

Augmented Reality micro-projection onto the helmet visor is not going to happen. It's unnecessarily complex, prohibitively expensive, inefficient for what is needed, and a waste of time because the suit is only worn during ascent and descent. During those periods the crew may as well be asleep for all the good that would do because the spacecraft is totally automated - which means that no human intervention is ever required - ever. Every possible contingency that in the past would have required a crewmember to do something is now handled by triple-redundant computer control faster than the ability of a human to even think. By the time any crew member even realized that there was some action needed the avionics package would have already identified the problem, analysed all possible reactions, made the appropriate selection and executed the command. The only thing a human being could do after that would be to screw it up. There is nothing - nothing - that visor displays could add to that. Truth be known the only real detail the crew actually needs to know is that the computer is on and functioning. Other than that, relax and enjoy the ride.

rah rah but no...really no

all that is kind of accurate as long as well the script is followed..when it doesnt...well they had a Dragon that required a lot of human intervention to stop from being space junk.

it will happen again...

This is not true. It would not have been space junk. The CRS-2 Dragon was still able to control its orbit and would have been able to deorbit safely into the intended landing zone on its own if required. That would have been a LOM scenario, but not LOCV.

Online abaddon

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #175 on: 08/20/2018 01:39 PM »
I contend that if there is any chance of missing a Dragon 2 returning from an operational mission, then NASA will want to see how well the DM1 capsule performs splashing down following reentry.  Yes, they've done splashdown and recovery tests with capsule mock-ups, but that's not the same as testing the performance of a just reentered production capsule.

Color me skeptical.
Exactly.  This is DM-1 - the only end-to-end demonstration without crew, before crew will fly.  There's no way NASA will let them try and land on that cushion, nor should they.

Offline OnWithTheShow

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #176 on: 08/20/2018 03:37 PM »
I think it more likely that it is for fairing drop tests.

Offline Johnnyhinbos

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #177 on: 08/20/2018 04:46 PM »
I think it more likely that it is for fairing drop tests.
That is my thought as well. And now I'm going to ask one of those far fetched questions that drive me nuts on this forum - so I apologize to myself...


Any chance they could upend one fairing from the net into the kiddie pool and reset in time to catch the second fairing - or... could they catch the second fairing directly in the kiddie pool?
John Hanzl. Author, action / adventure www.johnhanzl.com

Online kevinof

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #178 on: 08/20/2018 04:48 PM »
Musk did talk about "bouncy castles" for fairings long time ago. Maybe this is it?

I think it more likely that it is for fairing drop tests.

Online nacnud

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #179 on: 08/20/2018 05:09 PM »
I like this physical version of software development, try some stuff to see if it works. If it breaks, iterate and try a bunch of other stuff.

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