SpaceX test parachute system for Commercial Crew Dragon

[joek]

It doesn't have to be the "FINAL" layout, but it is certainly the current reference location in their design documents. After all, the test is to test the chute deployment in the new configuration.
...

Yes.  From the SpaceX SAA amendment 1, Dragon Parachute Tests (emphasis added):

Full-scale Dragon test unit prepared with all characteristics deemed appropriate by SpaceX (mass, moment of intertia, etc.) as close to those of the flight configuration following an on-pad abort as possible.

[Elmar Moelzer]

I am pretty sure that the test article we saw there is not what Dragon2 will look like. E.g., there is no room for the super dracos, which would also change the center of gravity.

[Lars_J]

I am pretty sure that the test article we saw there is not what Dragon2 will look like. E.g., there is no room for the super dracos, which would also change the center of gravity.

But Dragon 2 and Dragon 1 aren't that different, from what we have seen. Dragon 2 adds SD thrusters, and relocates parachutes/drogues. It might even have legs. Otherwise it will from an external point of view look pretty much the same.

[Rabidpanda]

I am pretty sure that the test article we saw there is not what Dragon2 will look like. E.g., there is no room for the super dracos, which would also change the center of gravity.

Of course the test article doesn't look exactly like Dragon 2. It just needs to have the parachutes in the correct location and have the same center of mass and moment of inertia, which shouldn't be too hard to adjust.

[a_langwich]

I am pretty sure that the test article we saw there is not what Dragon2 will look like. E.g., there is no room for the super dracos, which would also change the center of gravity.

Of course the test article doesn't look exactly like Dragon 2. It just needs to have the parachutes in the correct location and have the same center of mass and moment of inertia, which shouldn't be too hard to adjust.

Right, the standard solution is to use ballast as appropriate, which need not advertise itself for Internet observers.  I don't see any use for outer mold line fidelity.

[Joffan]

I am pretty sure that the test article we saw there is not what Dragon2 will look like. E.g., there is no room for the super dracos, which would also change the center of gravity.

But Dragon 2 and Dragon 1 aren't that different, from what we have seen. Dragon 2 adds SD thrusters, and relocates parachutes/drogues. It might even have legs. Otherwise it will from an external point of view look pretty much the same.

All right, but apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what have the Romans ever done for us?

[joek]

I am pretty sure that the test article we saw there is not what Dragon2 will look like. E.g., there is no room for the super dracos, which would also change the center of gravity.

Undoubtedly crew Dragon will look significantly different than the test article.  However, the test article doesn't need to look like to act like--or at least act like sufficient to prove the new parachute arrangement and be "as close to those of the flight configuration following an on-pad abort as possible".  That means the parachute arrangement for crew Dragon will be as seen with the test article.

I'm sure SpaceX will try for as much commonality between crew and cargo Dragon as possible.  If you think that includes a common parachute configuration, some changes to cargo Dragon would be required.  As others have suggested, that would include at minimum:
1. Fitting a CBM given the placement and intrusion of the crew Dragon drogues.
2. Relocating the grappling fixture and sensor bay (e.g., LIDAR) compartment and hatch given that the crew Dragon mains will occupy that space.

edit: Also, crew Dragon will likely have forward-looking sensors up top (next to the offset docking ring), which would make it that much harder to fit a CBM in a common configuration.

[Roy_H]

I agree with those who say that re-locating the grapple fixture etc. should be possible. But, is it really required? Why can't the cargo Dragon dock like the crew version instead of having to be berthed by the CanadaArm?

[Elmar Moelzer]

There is a small possibility that Dragon2 will not jetison the cover for the docking adapter (or the CBM in case of the cargo version), but that it will open like a clamshell. Would it make sense to put the things currently in the sensor bay into/onto the cover (attached to either side of the cover)?
Anyway, we will see what Dragon2 will look like, hopefully soon. Then we will know.

[Elmar Moelzer]

I agree with those who say that re-locating the grapple fixture etc. should be possible. But, is it really required? Why can't the cargo Dragon dock like the crew version instead of having to be berthed by the CanadaArm?

I think it has to do with the availability of docking ports, but I might be wrong.

[Jcc]

I agree with those who say that re-locating the grapple fixture etc. should be possible. But, is it really required? Why can't the cargo Dragon dock like the crew version instead of having to be berthed by the CanadaArm?

I think it has to do with the availability of docking ports, but I might be wrong.

also the docking ports have a smaller diameter, which makes unloading bulky cargo more difficult, besides, with less confidence in the control of the COTS spacecraft, they would prefer not to have them thrust into the port, but would rather grapple them.

[Prober]

I am pretty sure that the test article we saw there is not what Dragon2 will look like. E.g., there is no room for the super dracos, which would also change the center of gravity.

Agree with you.   Looks like two options are available.   Keeping the pressure hull size the same (given), and enlarging the panels surrounding it, or major compromises in the Dragon 1 design.

[joek]

I agree with those who say that re-locating the grapple fixture etc. should be possible. But, is it really required? Why can't the cargo Dragon dock like the crew version instead of having to be berthed by the CanadaArm?

I think it has to do with the availability of docking ports, but I might be wrong.

Good point.  There are currently only two USOS docking ports planned, and nominally one must be open in case there is a problem with the other.  One will be occupied by a crew vehicle for most of the time.  Beyond that, CBM (berthing) allows larger cargo/containers than NDS (docking) and is also the only way to get ISS standard racks in and out.  Not sure if the latter is still a significant consideration.

[manboy]

I agree with those who say that re-locating the grapple fixture etc. should be possible. But, is it really required? Why can't the cargo Dragon dock like the crew version instead of having to be berthed by the CanadaArm?

It could but it's not going to happen. Two berthing ports are shared between Dragon Cargo, Cygnus and HTV. Two docking ports are reserved for Commercial Crew, although only one will be used at a time (the other is meant as a backup). If Dragon Cargo starts to use a docking mechanism than it would mess up how ISS traffic management is currently planned.

Also docking mechanisms have smaller hatches, so you wouldn't be able to transport certain cargo.

[JBF]

I agree with those who say that re-locating the grapple fixture etc. should be possible. But, is it really required? Why can't the cargo Dragon dock like the crew version instead of having to be berthed by the CanadaArm?

It could but it's not going to happen. Two berthing ports are shared between Dragon Cargo, Cygnus and HTV. Two docking ports are reserved for Commercial Crew, although only one will be used at a time (the other is meant as a backup). If Dragon Cargo starts to use a docking mechanism than it would mess up how ISS traffic management is currently planned.

Also docking mechanisms have smaller hatches, so you wouldn't be able to transport certain cargo.

As the crew will double as life boats they will need to be able to undock quickly and independently. This is not possible with a berthing port.

[mheney]

I agree with those who say that re-locating the grapple fixture etc. should be possible. But, is it really required? Why can't the cargo Dragon dock like the crew version instead of having to be berthed by the CanadaArm?

It could but it's not going to happen. Two berthing ports are shared between Dragon Cargo, Cygnus and HTV. Two docking ports are reserved for Commercial Crew, although only one will be used at a time (the other is meant as a backup). If Dragon Cargo starts to use a docking mechanism than it would mess up how ISS traffic management is currently planned.

Also docking mechanisms have smaller hatches, so you wouldn't be able to transport certain cargo.

I think manboy's question is "is it possible to dock rather than berth using the CBM mechanisms?"  I don't see any reason myself why it makes any difference physically whether the approach and contact is done via arm-and-grapple vs thrusters - but I readily admit that I might be missing something.

[Go4TLI]

I think manboy's question is "is it possible to dock rather than berth using the CBM mechanisms?"  I don't see any reason myself why it makes any difference physically whether the approach and contact is done via arm-and-grapple vs thrusters - but I readily admit that I might be missing something.

No. 

There are many reasons from thruster plume impingement to other areas of the station, tolerances for the CBMs to mate and lock, vibration dampening, etc. 

[manboy]

I agree with those who say that re-locating the grapple fixture etc. should be possible. But, is it really required? Why can't the cargo Dragon dock like the crew version instead of having to be berthed by the CanadaArm?

It could but it's not going to happen. Two berthing ports are shared between Dragon Cargo, Cygnus and HTV. Two docking ports are reserved for Commercial Crew, although only one will be used at a time (the other is meant as a backup). If Dragon Cargo starts to use a docking mechanism than it would mess up how ISS traffic management is currently planned.

Also docking mechanisms have smaller hatches, so you wouldn't be able to transport certain cargo.

I think manboy's question is "is it possible to dock rather than berth using the CBM mechanisms?"

I wasn't asking anything and there really isn't any reason why Dragon would dock with a CBM. The point I was trying to make is that I think it's highly unlikely that the Dragon Cargo will start using NDS.

[Sesquipedalian]

There is a small possibility that Dragon2 will not jetison the cover for the docking adapter (or the CBM in case of the cargo version), but that it will open like a clamshell. Would it make sense to put the things currently in the sensor bay into/onto the cover (attached to either side of the cover)?

That's a very insightful thought, but think of the Dragon berthed to the ISS using this arrangement.  Would there be enough clearance for the arm to grapple the PDGF?

[Joffan]

There is a small possibility that Dragon2 will not jetison the cover for the docking adapter (or the CBM in case of the cargo version), but that it will open like a clamshell. Would it make sense to put the things currently in the sensor bay into/onto the cover (attached to either side of the cover)?

That's a very insightful thought, but think of the Dragon berthed to the ISS using this arrangement.  Would there be enough clearance for the arm to grapple the PDGF?

If we're making up new configurations using the nosecone, it could be hinged at the top and at one side, allowing the split nosecone to lay along one wall of the Dragon capsule. Then if it latched to the side, it could provide an accessible location for the sensor bay equipment, comparable to the current location.

It's a relatively large change though, to a mission-critical piece of kit. Ideally any opening nosecone placement would be flown on a Dragon that has the current sensor bay configuration so that actuation and clearances can be easily tested. Since the closure (or worst-case, jettison) of the nosecone might be a critical task for successful re-entry, NASA would probably be a little anxious about downmass risks.

EDIT... but all this is cargo dragon speculation, off-topic here.