Author Topic: SpaceX Dragon 2 Updates and Discussion - Thread 3  (Read 789113 times)

Online yg1968

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #120 on: 08/17/2018 03:36 pm »
I hope there's a safeguard for the cut mains beyond just the "use only after landing" warning next to the button!
They would still have the Super Dracos. Could they be used for a powered landing in an emergency (like originally planned)?
I wouldn't bet on it.

Perhaps, the Super Dracos could be used (in an emergency)  for a land-landing (similar to Soyuz)?

Offline SWGlassPit

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #121 on: 08/17/2018 03:56 pm »
I hope there's a safeguard for the cut mains beyond just the "use only after landing" warning next to the button!
They would still have the Super Dracos. Could they be used for a powered landing in an emergency (like originally planned)?
I wouldn't bet on it.

Perhaps, the Super Dracos could be used (in an emergency)  for a land-landing (similar to Soyuz)?

I highly doubt it.  I don't know what the land landing g-loads would be, but I doubt that the super dracos are necessary to keep them below contingency limits.  Since they're hypergolic thrusters (as opposed to Soyuz's solid motors), firing them so close to the ground would require decontamination and safing of the area before crew could be extracted -- exactly what you don't want to have to deal with in an emergency situation.

Offline russianhalo117

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #122 on: 08/17/2018 04:11 pm »
I hope there's a safeguard for the cut mains beyond just the "use only after landing" warning next to the button!
They would still have the Super Dracos. Could they be used for a powered landing in an emergency (like originally planned)?
I wouldn't bet on it.

Perhaps, the Super Dracos could be used (in an emergency)  for a land-landing (similar to Soyuz)?

I highly doubt it.  I don't know what the land landing g-loads would be, but I doubt that the super dracos are necessary to keep them below contingency limits.  Since they're hypergolic thrusters (as opposed to Soyuz's solid motors), firing them so close to the ground would require decontamination and safing of the area before crew could be extracted -- exactly what you don't want to have to deal with in an emergency situation.
could fire in the event of a chute loss to lessen the vehicle mass.

Offline jpo234

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #123 on: 08/17/2018 04:24 pm »
Perhaps, the Super Dracos could be used (in an emergency)  for a land-landing (similar to Soyuz)?

I highly doubt it.  I don't know what the land landing g-loads would be, but I doubt that the super dracos are necessary to keep them below contingency limits.  Since they're hypergolic thrusters (as opposed to Soyuz's solid motors), firing them so close to the ground would require decontamination and safing of the area before crew could be extracted -- exactly what you don't want to have to deal with in an emergency situation.

I would prefer that over slamming into the ground at terminal velocity.
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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #124 on: 08/17/2018 04:49 pm »
Perhaps, the Super Dracos could be used (in an emergency)  for a land-landing (similar to Soyuz)?

I highly doubt it.  I don't know what the land landing g-loads would be, but I doubt that the super dracos are necessary to keep them below contingency limits.  Since they're hypergolic thrusters (as opposed to Soyuz's solid motors), firing them so close to the ground would require decontamination and safing of the area before crew could be extracted -- exactly what you don't want to have to deal with in an emergency situation.

I would prefer that over slamming into the ground at terminal velocity.

That's quite different from the Soyuz comparison. The counterargument was for landing with nominal parachutes.

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #125 on: 08/17/2018 05:02 pm »
Can anyone confirm or deny that even though there are no plans to use the super dracos for landing that the capability to do so does still exist.
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Offline woods170

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #126 on: 08/17/2018 05:19 pm »
I hope there's a safeguard for the cut mains beyond just the "use only after landing" warning next to the button!
They would still have the Super Dracos. Could they be used for a powered landing in an emergency (like originally planned)?
I wouldn't bet on it.

Perhaps, the Super Dracos could be used (in an emergency)  for a land-landing (similar to Soyuz)?

I highly doubt it.  I don't know what the land landing g-loads would be, but I doubt that the super dracos are necessary to keep them below contingency limits.  Since they're hypergolic thrusters (as opposed to Soyuz's solid motors), firing them so close to the ground would require decontamination and safing of the area before crew could be extracted -- exactly what you don't want to have to deal with in an emergency situation.
could fire in the event of a chute loss to lessen the vehicle mass.
Not necessary. Chute loss, and the repercussions of it on landing velocity, due to vehicle mass, is the very reason why a fourth chute was added.

Offline woods170

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #127 on: 08/17/2018 05:22 pm »
Can anyone confirm or deny that even though there are no plans to use the super dracos for landing that the capability to do so does still exist.
The software for it was in early stages of develpment, with prototype versions of it being active on the Crew Dragon hover tests that were witnessed at McGregor.

I highly doubt that an operational version of it, if only for emergency use, exists in the DM-1 and DM-2 flight software.

A definitive answer to your question can be given by inside SpaceX personnel only, either in public of via the usual leaks.

But consider this: why do you think a fourth chute was added? Why do you think the parachute system for Crew Dragon is going thru an extremely rigorous qualification program, despite the fact that the same basic parachute system (minus one chute) has been successfully used on over a dozen Cargo Dragon missions?


It is to make sure that the parachute sequence will ALWAYS work when commanded to do so. Much the same for Starliner and Orion.
« Last Edit: 08/17/2018 05:27 pm by woods170 »

Offline envy887

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #128 on: 08/17/2018 05:45 pm »
Can anyone confirm or deny that even though there are no plans to use the super dracos for landing that the capability to do so does still exist.
The software for it was in early stages of develpment, with prototype versions of it being active on the Crew Dragon hover tests that were witnessed at McGregor.

I highly doubt that an operational version of it, if only for emergency use, exists in the DM-1 and DM-2 flight software.

A definitive answer to your question can be given by inside SpaceX personnel only, either in public of via the usual leaks.

But consider this: why do you think a fourth chute was added? Why do you think the parachute system for Crew Dragon is going thru an extremely rigorous qualification program, despite the fact that the same basic parachute system (minus one chute) has been successfully used on over a dozen Cargo Dragon missions?


It is to make sure that the parachute sequence will ALWAYS work when commanded to do so. Much the same for Starliner and Orion.

Parachutes are pretty reliable, so it would almost certainly never be used. But the only reason I can think of to not load that software for an emergency is if they are planning to burn or vent the hypergols before popping the chutes. Otherwise it's always better to have the option, and not need it, than to need it and not have it.

Offline Chris Bergin

Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #129 on: 08/17/2018 05:46 pm »
FEATURE ARTICLE: SpaceX readies for installation of LC-39A Crew Access Arm, previews Crew Dragon -

https://www.nasaspaceflight.com/2018/08/spacex-installation-lc-39a-caa-previews-crew-dragon/

- By Chris Gebhardt
- Includes photos and footage from Jack Beyer
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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #130 on: 08/18/2018 02:21 am »
NASA, SpaceX Agree on Plans for Crew Launch Day Operations


Quote
NASA’s Commercial Crew Program and SpaceX are finalizing plans for launch day operations as they prepare for the company’s first flight test with astronauts on board. The teams are working toward a crew test flight to the International Space Station, known as Demo-2, with NASA astronauts Bob Behnken and Doug Hurley in April 2019. 

A key question the program and the company have been assessing is whether the astronauts will climb aboard the Crew Dragon spacecraft before or after SpaceX fuels the Falcon 9 rocket. NASA has made the decision to move forward with SpaceX’s plan to fuel the rocket after the astronauts are in place. While the agreement makes this plan the baseline for operations, it is contingent upon NASA’s final certification of the operation.

“To make this decision, our teams conducted an extensive review of the SpaceX ground operations, launch vehicle design, escape systems and operational history,” said Kathy Lueders, manager of NASA’s Commercial Crew Program. “Safety for our personnel was the driver for this analysis, and the team’s assessment was that this plan presents the least risk.”

Additional verification and demonstration activities, which include five crew loading demonstrations of the Falcon 9 Block 5, will be critical to final certification of this plan. These loading demonstrations will verify the flight crew configuration and crew loading timeline prior to Demo-2. After these conditions have been met, NASA will assess any remaining risk before determining that the system is certified to fly with crew.

If all goes according to plan, on launch day, the Falcon 9 composite overwrap pressure vessels, known as 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, when the launch system is in a quiescent state. After the ground crews depart the launch pad, the launch escape systems will be activated approximately 38 minutes before liftoff, just before fueling begins. SpaceX launch controllers then will begin loading rocket grade kerosene and densified liquid oxygen approximately 35 minutes before launch. The countdown and launch preparations can be stopped automatically up to the last moment before launch. In the unlikely event of an emergency at any point up to and after launch, the launch escape systems will allow the astronauts to evacuate safely.

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

The crew launches of NASA’s Commercial Crew partners SpaceX and Boeing will return the nation’s ability to launch our astronauts from the United States to and from the International Space Station on American spacecraft.


https://www.nasa.gov/feature/nasa-spacex-agree-on-plans-for-crew-launch-day-operations

Offline Nomadd

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #131 on: 08/18/2018 02:35 am »



Parachutes are pretty reliable, so it would almost certainly never be used. But the only reason I can think of to not load that software for an emergency is if they are planning to burn or vent the hypergols before popping the chutes. Otherwise it's always better to have the option, and not need it, than to need it and not have it.
I keep thinking that CRS-7 could have been a great success in a way if there had been a few lines of software to cover a circumstance that nobody thought would happen.
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Offline Comga

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #132 on: 08/18/2018 02:36 am »
NASA, SpaceX Agree on Plans for Crew Launch Day Operations


Quote
NASA’s Commercial Crew Program and SpaceX are finalizing plans for launch day operations as they prepare for the company’s first flight test with astronauts on board. The teams are working toward a crew test flight to the International Space Station, known as Demo-2, with NASA astronauts Bob Behnken and Doug Hurley in April 2019. 

A key question the program and the company have been assessing is whether the astronauts will climb aboard the Crew Dragon spacecraft before or after SpaceX fuels the Falcon 9 rocket. NASA has made the decision to move forward with SpaceX’s plan to fuel the rocket after the astronauts are in place. While the agreement makes this plan the baseline for operations, it is contingent upon NASA’s final certification of the operation.

“To make this decision, our teams conducted an extensive review of the SpaceX ground operations, launch vehicle design, escape systems and operational history,” said Kathy Lueders, manager of NASA’s Commercial Crew Program. “Safety for our personnel was the driver for this analysis, and the team’s assessment was that this plan presents the least risk.

Additional verification and demonstration activities, which include five crew loading demonstrations of the Falcon 9 Block 5, will be critical to final certification of this plan. These loading demonstrations will verify the flight crew configuration and crew loading timeline prior to Demo-2. After these conditions have been met, NASA will assess any remaining risk before determining that the system is certified to fly with crew.

If all goes according to plan, on launch day, the Falcon 9 composite overwrap pressure vessels, known as 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, when the launch system is in a quiescent state. After the ground crews depart the launch pad, the launch escape systems will be activated approximately 38 minutes before liftoff, just before fueling begins. SpaceX launch controllers then will begin loading rocket grade kerosene and densified liquid oxygen approximately 35 minutes before launch. The countdown and launch preparations can be stopped automatically up to the last moment before launch. In the unlikely event of an emergency at any point up to and after launch, the launch escape systems will allow the astronauts to evacuate safely.

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

The crew launches of NASA’s Commercial Crew partners SpaceX and Boeing will return the nation’s ability to launch our astronauts from the United States to and from the International Space Station on American spacecraft.

Emphasis added
I am very relieved to see this approval given.  It says a lot to me about NASA really working to blend the SpaceX method with their long history and appropriately extreme caution. 
There was a fear that this would not happen.

One thing:  This says that the COPVs are loaded with Helium before the LOX is loaded.  That will mean the gas is at ambient temperature, which will drop by more than two thirds as the LOX is loaded. 
I would assume that this initial load would not be enough He for the mission, and that normal procedure has them adding He as the COPVs cool, perhaps keeping the pressure constant. 
Is this what will actually happen?
(That would certainly work to prevent the formation of oxygen crystals and the He supercools, as the composite would be under nearly constant tension. )
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline abacus

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #133 on: 08/18/2018 10:11 am »

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?

Offline marsbase

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #134 on: 08/18/2018 11:04 am »
COPVs being loaded with helium more than 2 hours before launch is new isn't it?
Does that mean helium is being constantly topped off?

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #135 on: 08/18/2018 11:51 am »
NASA, SpaceX Agree on Plans for Crew Launch Day Operations

...

If all goes according to plan, on launch day, the Falcon 9 composite overwrap pressure vessels, known as 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, when the launch system is in a quiescent state. After the ground crews depart the launch pad, the launch escape systems will be activated approximately 38 minutes before liftoff, just before fueling begins. SpaceX launch controllers then will begin loading rocket grade kerosene and densified liquid oxygen approximately 35 minutes before launch. The countdown and launch preparations can be stopped automatically up to the last moment before launch. In the unlikely event of an emergency at any point up to and after launch, the launch escape systems will allow the astronauts to evacuate safely.

...

OK, if helium is loaded PRIOR to LOX, it means helium is at ambient T. Since
p*V = n*R*T
then
n1 * T1 = n2 * T2
where indexes 1 and 2 stand for ambient temperature ("1") and temperature of over-chilled LOX ("2") and "n" - total amount of He (in mols).
Let's take T1 = 300 K (27°C) and T2 = 70 K (-203°C)
then
n1 = 0.23 n2

or, in other words
at ambient T (27°C) you can load COPV to only about 23% of what it can hold (to the same pressure limit) at temperature of over-chilled LOX...

Offline lonestriker

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #136 on: 08/18/2018 12:07 pm »
NASA, SpaceX Agree on Plans for Crew Launch Day Operations

...

If all goes according to plan, on launch day, the Falcon 9 composite overwrap pressure vessels, known as 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, when the launch system is in a quiescent state. After the ground crews depart the launch pad, the launch escape systems will be activated approximately 38 minutes before liftoff, just before fueling begins. SpaceX launch controllers then will begin loading rocket grade kerosene and densified liquid oxygen approximately 35 minutes before launch. The countdown and launch preparations can be stopped automatically up to the last moment before launch. In the unlikely event of an emergency at any point up to and after launch, the launch escape systems will allow the astronauts to evacuate safely.

...

OK, if helium is loaded PRIOR to LOX, it means helium is at ambient T. Since
p*V = n*R*T
then
n1 * T1 = n2 * T2
where indexes 1 and 2 stand for ambient temperature ("1") and temperature of over-chilled LOX ("2") and "n" - total amount of He (in mols).
Let's take T1 = 300 K (27°C) and T2 = 70 K (-203°C)
then
n1 = 0.23 n2

or, in other words
at ambient T (27°C) you can load COPV to only about 23% of what it can hold (to the same pressure limit) at temperature of over-chilled LOX...

Do we know if they've simply added more COPVs instead?  I imagine going the inconel route would have been a similar mass penalty, though not sure of the volume penalty in the LOX tank.

Offline marsbase

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #137 on: 08/18/2018 12:15 pm »
"Quiescent state" means nothing is changing.  The temperature of the helium is not necessarily at 27C.  If it is being topped off constantly, the temperature could be much lower but steady. 

Offline Comga

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #138 on: 08/18/2018 03:47 pm »
"Quiescent state" means nothing is changing. 
The temperature of the helium is not necessarily at 27C. 
If it is being topped off constantly, the temperature could be much lower but steady. 

The statement is that the rocket is “quiescent” when the astronauts board.
That means that no fuel, oxidizer, or pressuant is being loaded at that time.
Without LOX the helium will start out near ambient temperature.

My guess of the He COPVs having only a third of their full load once cooled was shown by smoliarm’s calculations (thanks!) to be optimistic. It is less than a quarter. It is hard to imagine compensateing for this by installing 4 times as many COPVs. It defeats the purpose of installing them in the tank and immersing them in LOX. 

Therefore, by deduction without the benefit of inside knowledge, it seems SpaceX will load the bulk of the He  during fueling, as the LOX cools the COPVs. They might even do this at a rate that maintains constant pressure.

Given the negative Joule-Thompson coefficient  helium will cool as it is compressed, which may have contributed to the AMOS-6 incident. Topping off at constant pressure may eliminate this.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline allfiredup

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #139 on: 08/18/2018 05:08 pm »
How much speed could be shaved off of orbital velocity using the superdracos?

If it was a substantial amount, wouldn't it reduce the loads on the heat shield quite a bit?

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