Commercial Crew - Discussion Thread 1

[TripleSeven]

Everything I have read points to an extremely small issue being blown out of proportion regards the "parachute failure". But I have to give TrippleSeven his due, if there really is a serious issue, I wish NASA would make it public and quickly so this divisive debate can be put to bed.

I think that they will get it sorted out...its a learning process by both Boeing and SpaceX and NASA.  neither company has really built a human spaceflight vehicle as a product and NASA has never really overseen that effort and acted in largemeasure like the FAA does to aviation.

its not a role NASA is very good at...but it might be one of their future roles. 

[rcoppola]

Well...According to Hans during Today's CRS-16 briefing, DM-1 is still on the books for January and he believes they have any supposed "Parachute Issues" well understood and under control (paraphrasing).

[envy887]

adding a 4th parachute?

Crew Dragon is significantly heavier than Cargo Dragon. If using a 3 parachute system and one failed, the water impact speed would be too high. 4th parachute allows one to fail and splashdown speed to remain within tolerance.

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

[speedevil]

adding a 4th parachute?

Crew Dragon is significantly heavier than Cargo Dragon. If using a 3 parachute system and one failed, the water impact speed would be too high. 4th parachute allows one to fail and splashdown speed to remain within tolerance.

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

If there were humans in it.
The issue is as I understand it injurious G levels, not 'dragon falls apart'.

[whitelancer64]

adding a 4th parachute?

Crew Dragon is significantly heavier than Cargo Dragon. If using a 3 parachute system and one failed, the water impact speed would be too high. 4th parachute allows one to fail and splashdown speed to remain within tolerance.

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

Cargo Dragon does.

Crew Dragon is heavier. It needs 4 chutes.

[envy887]

adding a 4th parachute?

Crew Dragon is significantly heavier than Cargo Dragon. If using a 3 parachute system and one failed, the water impact speed would be too high. 4th parachute allows one to fail and splashdown speed to remain within tolerance.

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

Cargo Dragon does.

Crew Dragon is heavier. It needs 4 chutes.

For single fault tolerance, or dual fault tolerance? Do you have a source for this?

[woods170]

adding a 4th parachute?

Crew Dragon is significantly heavier than Cargo Dragon. If using a 3 parachute system and one failed, the water impact speed would be too high. 4th parachute allows one to fail and splashdown speed to remain within tolerance.

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

Cargo Dragon does.

Crew Dragon is heavier. It needs 4 chutes.

For single fault tolerance, or dual fault tolerance? Do you have a source for this?

I'm that source. A fourth chute was added to the Crew Dragon design because propulsive landing went out the window. The road to that decision and its consequences are all explained in these posts:

https://forum.nasaspaceflight.com/index.php?topic=41018.msg1854726#msg1854726
https://forum.nasaspaceflight.com/index.php?topic=45594.msg1854724#msg1854724
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1838743#msg1838743
https://forum.nasaspaceflight.com/index.php?topic=33596.msg1717648#msg1717648

[envy887]

adding a 4th parachute?

Crew Dragon is significantly heavier than Cargo Dragon. If using a 3 parachute system and one failed, the water impact speed would be too high. 4th parachute allows one to fail and splashdown speed to remain within tolerance.

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

Cargo Dragon does.

Crew Dragon is heavier. It needs 4 chutes.

For single fault tolerance, or dual fault tolerance? Do you have a source for this?

I'm that source. A fourth chute was added to the Crew Dragon design because propulsive landing went out the window. The road to that decision and its consequences are all explained in these posts:

https://forum.nasaspaceflight.com/index.php?topic=41018.msg1854726#msg1854726
https://forum.nasaspaceflight.com/index.php?topic=45594.msg1854724#msg1854724
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1838743#msg1838743
https://forum.nasaspaceflight.com/index.php?topic=33596.msg1717648#msg1717648

I've seen those, but they don't answer my question about single or dual fault tolerance.

If Crew Dragon would have had dangerous impact speeds with a single chute failure, that seems like a good reason to add a 4th.

[Tomness]

I've seen those, but they don't answer my question about single or dual fault tolerance.

If Crew Dragon would have had dangerous impact speeds with a single chute failure, that seems like a good reason to add a 4th.

Doesn't this stim from Pad Abort using a modified Dragon 1, the SuperDracos underperformed. The test showed what need improved & 4 chutes give them margin they needed.

[mgeagon]

adding a 4th parachute?

Crew Dragon is significantly heavier than Cargo Dragon. If using a 3 parachute system and one failed, the water impact speed would be too high. 4th parachute allows one to fail and splashdown speed to remain within tolerance.

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

Cargo Dragon does.

Crew Dragon is heavier. It needs 4 chutes.

For single fault tolerance, or dual fault tolerance? Do you have a source for this?

I'm that source. A fourth chute was added to the Crew Dragon design because propulsive landing went out the window. The road to that decision and its consequences are all explained in these posts:

https://forum.nasaspaceflight.com/index.php?topic=41018.msg1854726#msg1854726
https://forum.nasaspaceflight.com/index.php?topic=45594.msg1854724#msg1854724
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1838743#msg1838743
https://forum.nasaspaceflight.com/index.php?topic=33596.msg1717648#msg1717648

I take it from your sources that NASA didn’t trust SpaceX’ knife edge entry, though that was used successfully on every human capsule spaceflight in history? The agency required more redundancy, though Orion is in fact heavier, from much faster re-entry speeds? If so, it appears a single chute failier would not impact the human crew in the slightest and and dual failier might result in a higher than expected but not catastrophic crew injury. Am I intimating correctly?

[woods170]

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

Cargo Dragon does.

Crew Dragon is heavier. It needs 4 chutes.

For single fault tolerance, or dual fault tolerance? Do you have a source for this?

I'm that source. A fourth chute was added to the Crew Dragon design because propulsive landing went out the window. The road to that decision and its consequences are all explained in these posts:

https://forum.nasaspaceflight.com/index.php?topic=41018.msg1854726#msg1854726
https://forum.nasaspaceflight.com/index.php?topic=45594.msg1854724#msg1854724
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1838743#msg1838743
https://forum.nasaspaceflight.com/index.php?topic=33596.msg1717648#msg1717648

I take it from your sources that NASA didn’t trust SpaceX’ knife edge entry, though that was used successfully on every human capsule spaceflight in history? The agency required more redundancy, though Orion is in fact heavier, from much faster re-entry speeds? If so, it appears a single chute failier would not impact the human crew in the slightest and and dual failier might result in a higher than expected but not catastrophic crew injury. Am I intimating correctly?

On a four chute system for Crew Dragon a single chute failure will not impact the human crew in the slightest. A dual chute failure is perfectly survivable with only non life-threatening injuries expected.


So, single fault redundant for no impact to the crew whatsoever.
Dual fault redundant for non-catastrophic damage to the crew.


If three of the four chutes fail, the crew is dead. And so will be the capsule.

[ncb1397]

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

Cargo Dragon does.

Crew Dragon is heavier. It needs 4 chutes.

For single fault tolerance, or dual fault tolerance? Do you have a source for this?

I'm that source. A fourth chute was added to the Crew Dragon design because propulsive landing went out the window. The road to that decision and its consequences are all explained in these posts:

https://forum.nasaspaceflight.com/index.php?topic=41018.msg1854726#msg1854726
https://forum.nasaspaceflight.com/index.php?topic=45594.msg1854724#msg1854724
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1838743#msg1838743
https://forum.nasaspaceflight.com/index.php?topic=33596.msg1717648#msg1717648

I take it from your sources that NASA didn’t trust SpaceX’ knife edge entry, though that was used successfully on every human capsule spaceflight in history? The agency required more redundancy, though Orion is in fact heavier, from much faster re-entry speeds? If so, it appears a single chute failier would not impact the human crew in the slightest and and dual failier might result in a higher than expected but not catastrophic crew injury. Am I intimating correctly?

On a four chute system for Crew Dragon a single chute failure will not impact the human crew in the slightest. A dual chute failure is perfectly survivable with only non life-threatening injuries expected.

Does this take into account 6 months of microgravity? 12 months? 18 months? What kind of injuries are we talking about in each case? Multiple hip fractures? damaged spinal columns? Non-life threatening injuries runs the gambit from paper cuts to lifelong disability.

[woods170]

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

Cargo Dragon does.

Crew Dragon is heavier. It needs 4 chutes.

For single fault tolerance, or dual fault tolerance? Do you have a source for this?

I'm that source. A fourth chute was added to the Crew Dragon design because propulsive landing went out the window. The road to that decision and its consequences are all explained in these posts:

https://forum.nasaspaceflight.com/index.php?topic=41018.msg1854726#msg1854726
https://forum.nasaspaceflight.com/index.php?topic=45594.msg1854724#msg1854724
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1838743#msg1838743
https://forum.nasaspaceflight.com/index.php?topic=33596.msg1717648#msg1717648

I take it from your sources that NASA didn’t trust SpaceX’ knife edge entry, though that was used successfully on every human capsule spaceflight in history? The agency required more redundancy, though Orion is in fact heavier, from much faster re-entry speeds? If so, it appears a single chute failier would not impact the human crew in the slightest and and dual failier might result in a higher than expected but not catastrophic crew injury. Am I intimating correctly?

On a four chute system for Crew Dragon a single chute failure will not impact the human crew in the slightest. A dual chute failure is perfectly survivable with only non life-threatening injuries expected.

Does this take into account 6 months of microgravity? 12 months? 18 months? What kind of injuries are we talking about in each case? Multiple hip fractures? damaged spinal columns? Non-life threatening injuries runs the gambit from paper cuts to lifelong disability.

NASA has a list of injury types it considers to be life-threatening. Damaged spinal column is considered life-threatening. So does damaged organs and severe grades of concussion and damaged arteries. As well as a host of other injuries including severe damage to the lungs.
Non life-threatening runs the gambit from small cuts, bruises, broken bones in extremeties to mild types of concussion, inner-ear damage and damaged eardrums.

Nominal crew duration for Crew Dragon is six months in microgravity under normal ISS exercise regime.

[Roy_H]

adding a 4th parachute?

Crew Dragon is significantly heavier than Cargo Dragon. If using a 3 parachute system and one failed, the water impact speed would be too high. 4th parachute allows one to fail and splashdown speed to remain within tolerance.

Are you saying that Cargo Dragon has no tolerance to a single chute failure? That doesn't sound right to me.

Cargo Dragon does.

Crew Dragon is heavier. It needs 4 chutes.

For single fault tolerance, or dual fault tolerance? Do you have a source for this?

I'm that source. A fourth chute was added to the Crew Dragon design because propulsive landing went out the window. The road to that decision and its consequences are all explained in these posts:

https://forum.nasaspaceflight.com/index.php?topic=41018.msg1854726#msg1854726
https://forum.nasaspaceflight.com/index.php?topic=45594.msg1854724#msg1854724
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1838743#msg1838743
https://forum.nasaspaceflight.com/index.php?topic=33596.msg1717648#msg1717648

Thank you very much for all these links, I had not read any of this before and corrects my mis-conceptions.
One of the reasons given for the 4 chutes vs 3 for cargo Dragon was that the Crew Dragon was considerably heavier, largely due to the full prop load. Since base area is the same, wouldn't the higher mass mean the capsule would penetrate farther into the water, thus reducing g-forces? I guess not enough. And I don't understand the reference to "knofe" entry. Is the capsule tilted to reduce impact?

[woods170]

I'm that source. A fourth chute was added to the Crew Dragon design because propulsive landing went out the window. The road to that decision and its consequences are all explained in these posts:

https://forum.nasaspaceflight.com/index.php?topic=41018.msg1854726#msg1854726
https://forum.nasaspaceflight.com/index.php?topic=45594.msg1854724#msg1854724
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1838743#msg1838743
https://forum.nasaspaceflight.com/index.php?topic=33596.msg1717648#msg1717648

Thank you very much for all these links, I had not read any of this before and corrects my mis-conceptions.
One of the reasons given for the 4 chutes vs 3 for cargo Dragon was that the Crew Dragon was considerably heavier, largely due to the full prop load. Since base area is the same, wouldn't the higher mass mean the capsule would penetrate farther into the water, thus reducing g-forces? I guess not enough. And I don't understand the reference to "knofe" entry. Is the capsule tilted to reduce impact?

Re: "Knife" impact/splash-down.

The Apollo capsule was suspended under its parachutes at such an angle that the "edge" between the primary heatshield and the backshell hit the water first. That particular edge had an angle of substantially less than 90 degrees. As such, going into the water "edge first" the capsule kinda "knifed" into the water, which makes for a more gentle deceleration.

On Crew Dragon the angle between the primary heathshield and the backshell is much closer to 90 degrees, making for a much more "blunt" edge. And although Crew Dragon is also hitting the water "edge first", the bluntness of its edge makes for a much more sudden deceleration. It is therefore necessary to kill off as much vertical velocity as possible prior to hitting the water. That requirement is one of the contributing factors to having four parachutes on Crew Dragon.

[gongora]

Some of the slides from the NAC meeting.  Hopefully NASA will post the entire presentation at some point.

[yg1968]

Commercial crew slides from the NAC meeting are now available:
https://www.nasa.gov/sites/default/files/atoms/files/nac_ccp_status_dec_6_2018_non-sbu.pdf

[docmordrid]

Boeing hasn't begun shock testing on their docking adapter? Really?

[woods170]

Boeing hasn't begun shock testing on their docking adapter? Really?

In the 2012 - 2014 timeframe the NASA Docking System (NDS) adopted the SIMAC design. Which, by the way, is a Boeing design. SIMAC is what is used on Starliner. So, what Boeing is using on Starliner also happens to be the baseline system for NDS.

http://www.spaceref.com/news/viewsr.html?pid=42614
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140009916.pdf
https://boeing.mediaroom.com/2014-8-26-Boeing-Continues-Progress-on-Improved-Space-Station-Docking-System#assets_117

[docmordrid]

Irene Klotz
@Free_Space
 SpaceX Falcon 9 that will launch GPS III is first to include COPV 2s on both first and second stage, the configuration needed for seven Commercial Crew certification flights. Previously two F9s flew with new COPVs on upper stage. published 12/19 http://Awin.aviationweek.com  (paywall)
10:38 AM - Dec 20, 2018

https://twitter.com/Free_Space/status/1075777466323460103