Speculation into what future versions of Dragon will involve

[mlindner]

Dragon X (since we're debating version #'s)

I don't think we're debating version numbers anymore. Anyone that still was hadn't seen the latest interviews.

I doubt that they will want to throw away the superdracos after every launch together with the trunk. It may be that they will integrate the trunk with the main dragon capsule (since it is still quite a waste and they want reusability), but that would be a lot more complex and would mean that the dracos would need to push more mass.

They can't throw away the superdracos.
These are the things that _must_ come down from orbit according to the current requirements:
* Heat Shield
* SuperDracos (for propulsive landing)
* Dracos (for control)
* Capsule (of course)
* Landing Gear/Feet/etc
Optional items:
* Solar panels (I don't think these cost much, they're dirt cheap commercial silicon)

[Lobo]

I must agree with Jim here, there are only two versions of Dragon currently flying (or currently being designed):

Dragon 1 -- the current unmanned cargo transport
Dragon 2 -- the currently planned manned spacecraft

However, I also think that it is likely that Dragon 2 has undergone a thorough redesign in the past year, and no longer resembles the known mock-up.  The hints we have had from Musk indicated that the SuperDracos have been shifted from their previous 90-degree spacing, that the landing gear has been modified from the mock-up, and that it will be much more "cool looking" in appearance.  He gives as a reason for the change, that SpaceX did not really know what they were doing when designing Dragon 1, but they do now.

It will be years before Dragon 2 flies in any case.  SpaceX has the time and resources to do a complete redesign if they feel that it will result in a superior spacecraft.

This sounds like the most plausible explaination given what I've heard.  Once "Dragon 2/Dragonrider" is ready and flying, they'll replace DRagon 1 with it and just build one common spaceship that'll have a crewed and cargo version of it.  By saying "we didn't know what we were doing with DRagon 1", he probably means they thought there'd be enough room in DRagon 1 for the LAS/landing thrusters and landing gear within it's geometery, and have recently been figuring out they can't, and that's lead to a substantial redesign of the Dragon2/Dragon rider and so it'll look much different...or "cooler"...

[Lars_J]

By saying "we didn't know what we were doing with DRagon 1", he probably means they thought there'd be enough room in DRagon 1 for the LAS/landing thrusters and landing gear within it's geometery, and have recently been figuring out they can't, and that's lead to a substantial redesign of the Dragon2/Dragon rider and so it'll look much different...or "cooler"...

My advice: Don't read too much into the "different" or "cooler"... Most likely the Dragon 2 changes appearance-wise will be mostly cosmetic. It should be the same size, same pressure vessel, same heat shield. The fairings for the SD thrusters should be the major difference.

[alienmike]

What I'm trying to figure out is the reason for not placing the solar panels on the Dragon. Is it because of mass, or is it because of volume and configuration? For this we need some type of estimate for the mass of those panels. First, how many cells do they use?

From this photo, http://spacexlaunch.zenfolio.com/p208064181/h29AF8179#h29af8179, it appears the panels are 18x13 cells, but it looks like the first panel is a bit shorter, only 18x9. So there are 6 panels of the full sized panels and 2 shorter panels. From http://en.wikipedia.org/wiki/Solar_cell, it looks as though these are 150mm cells. That would make the panel sizes and area roughly:

18 x 13 -> 2700mm x 1950mm or 270cm x 195cm -> 52650 cm2
18 x 9   -> 2700mm x 1350mm or 270cm x 135cm -> 36450 cm2

And Total Area is about:

52650 cm2 * 6 -> 315,900 cm2
36450 cm2 * 2 ->   72,900 cm2

or 388,800 cm2 Total

From http://www.emcore.com/space-photovoltaics/space-solar-cells/, I get an estimate of 84mg/cm2, which gives 32659200 mg, or about 33 kg. It is hard to estimate how much the supporting hardware weighs, but let's say it is double the mass of the panels. That means we would be in the very rough neighborhood of 100kg.

The total down-mass capability of the Dragon is listed as 3000kg. I really don't think they would move the solar panels to the trunk for anything even close to 100kg of lost down-mass.

From this I conclude that the reason for moving the solar panels to the trunk has nothing to do with mass and everything to do with volume and configuration – the panels don't fit volume wise and would not allow for the proper placement of the thrusters.

If this is correct, it is very unlikely that the panels would be moved to the Dragon. They will need more room for the SuperDracos, not less. The only thing that might change this is a larger faring.

Any thoughts or corrections?

[mlindner]

The current solar arrays don't have the capability to refold. They unfold on simple torsion springs. Adding the capability to refold adds a lot of complexity to the mechanism, not to mention weight (adding motors etc) and is basically a complete redesign

[alienmike]

The current solar arrays don't have the capability to refold. They unfold on simple torsion springs. Adding the capability to refold adds a lot of complexity to the mechanism, not to mention weight (adding motors etc) and is basically a complete redesign

I don't doubt you are correct. But if they wanted to, I'm sure they could redesign and it still would not affect the mass to such a degree that they wouldn't be able do it. My only point is, it is not mass, but volume and configuration that is preventing them from moving the panels to the Dragon.

Unless they REALLY redesign the Dragon - larger faring, this is a no go. That said, a larger faring would make the Dragon V2 look more like a flying saucer and look really cool. Is there any possibility? It would give them the extra volume they need at the base for the SuperDracos, extra fuel and landing legs. The pressure vessel could remain the same.

[mlindner]

The current solar arrays don't have the capability to refold. They unfold on simple torsion springs. Adding the capability to refold adds a lot of complexity to the mechanism, not to mention weight (adding motors etc) and is basically a complete redesign

Come to think of it, do any currently flying, or flown in the past spacecraft (besides ISS) have the ability to refold/retract solar panels?

[Lars_J]

Guys, the trunk has more than just the solar arrays (like radiators), so you cannot get rid of it that easily.

My prediction: Dragon 2 / Crew Dragon / Dragonrider will have a trunk that is virtually identical to the current one - if not completely identical.

[alienmike]

Guys, the trunk has more than just the solar arrays (like radiators), so you cannot get rid of it that easily.

My prediction: Dragon 2 / Crew Dragon / Dragonrider will have a trunk that is virtually identical to the current one - if not completely identical.

Right, so we can eliminate that speculation. Truck is still there, solar arrays have not moved. How about the wider base, or elliptical base? I believe someone already mentioned that the solar arrays protrude out of the truck, so having the Dragon extend out on each side would not change much aerodynamically, right?

[go4mars]

the trunk has more than just the solar arrays (like radiators), so you cannot get rid of it that easily.

There will probably be at least 3 legs.  I would assume exactly 3.  Perhaps these fold down legs would be be multi-purpose:  Including storage for origami solar panels and heat radiators.  Other uses could be as control surfaces (2 wings and a tail rudder for when subsonic), and one of the legs could also be an egress ramp for people or rovers.  One or more of them might act as a structural window-shield during times of applied force like launch and re-entry. 

Still wondering why the engines would be concentrated, apparently to the leeward side.  Maybe for added cross-range?

[meekGee]

Guys, the trunk has more than just the solar arrays (like radiators), so you cannot get rid of it that easily.

My prediction: Dragon 2 / Crew Dragon / Dragonrider will have a trunk that is virtually identical to the current one - if not completely identical.

Right, so we can eliminate that speculation. Truck is still there, solar arrays have not moved. How about the wider base, or elliptical base? I believe someone already mentioned that the solar arrays protrude out of the truck, so having the Dragon extend out on each side would not change much aerodynamically, right?

Wait - Lars_J opinion, while he has some justification for it, is really just as speculative - there's some good justification to support the possibility of a pretty deep re-design which might extend to the trunk.  I think it's pretty open right now, until new evidence shows up.

[douglas100]

Come to think of it, do any currently flying, or flown in the past spacecraft (besides ISS) have the ability to refold/retract solar panels?

X-37

[Lobo]

What I'm trying to figure out is the reason for not placing the solar panels on the Dragon. Is it because of mass, or is it because of volume and configuration? For this we need some type of estimate for the mass of those panels. First, how many cells do they use?

The total down-mass capability of the Dragon is listed as 3000kg. I really don't think they would move the solar panels to the trunk for anything even close to 100kg of lost down-mass.

From this I conclude that the reason for moving the solar panels to the trunk has nothing to do with mass and everything to do with volume and configuration – the panels don't fit volume wise and would not allow for the proper placement of the thrusters.

If this is correct, it is very unlikely that the panels would be moved to the Dragon. They will need more room for the SuperDracos, not less. The only thing that might change this is a larger faring.

Any thoughts or corrections?

This is probably one reason.

Another could be that a failure to deploy solar panels would result in a LOM.  The crew/cargo would probably have to do an emergency reentry within an orbit or two (how long to the batteries last?  A couple hours?)  In order to have them on the capsule, that means you need to have actuating doors in the skin of the capsule instead of just spring loaded pop-off covers.  Something like the grapple fixture that deploys, but more complex than that.  If there’s a snag in the hatches opening, or the arrays deploying, then it’s a LOM.  And it could be even worse if the hatches can’t be closed again, because that removes the TPS for that area in the sidewall, and could kill a crew.   I don’t believe a crewed Dragon will even have the grapple fixture because it will be actively docked, rather than captured and berthed.  So there likely won’t be anything opening or popping out of the capsule sidewalls on a crewed Dragon.
Additionally, instead of a more reliable spring loaded one-time-deploy system like they have now (I believe that’s how it currently works), they’d need some sort of more complex system of motors and guide wires (?) that can retract the arrays, and perhaps deploy them too (although they could be spring deployed, and motor retracted…but they still need a mechanism to retract them.)  Sort of like how the ISS arrays worked when they deployed and then retracted the first array, and I know they had a lot of problems retracting that array, requiring a few spacewalks and some improvised tools to finally get fully retracted.  Even if SpaceX comes up with a much more simple and reliable system for deploying and then retracting the solar panels, all it takes is a problem one time…
I would think the overall millions of dollars any Dragon mission will cost, then a few tens of thousands of dollars (or whatever it is) doesn’t seem like enough savings to warrant the risks to the mission and crews lives, most likely.   

[Dave G]

The current solar arrays don't have the capability to refold.

Are you sure?  If I remember correctly, just before berthing, the pictures show the solar arrays refolded so they wouldn't hit anything by accident.  Then after berthing, they unfolded them again.

[Silmfeanor]

The current solar arrays don't have the capability to refold.

Are you sure?  If I remember correctly, when Dragon got near the ISS, the pictures show the solar arrays refolded so they wouldn't hit anything by accident.  Then after berthing, they unfolded them again.

not true. They where rotated, not folded.

[Dave G]

The current solar arrays don't have the capability to refold.

Are you sure?  If I remember correctly, when Dragon got near the ISS, the pictures show the solar arrays refolded so they wouldn't hit anything by accident.  Then after berthing, they unfolded them again.

not true. They where rotated, not folded.

OK, thanks for the correction.

[Elmar Moelzer]

Here is a quick mockup that I made of what I believe the shape of the Dragon2 will be roughly like. the engines might be a bit further apart, making the bulges slightly wider, but I hope people get the general idea.
With the SuperDraco pods being moved closer together, I think it makes sense to combine them into a single pod on each side. That will IMHO reduce drag compared to multiple pods. If the pods were slightly wider with a larger gap between the two sets of two, there might be just enough room there for a landing leg that folds out sideways. But that space might also be needed for the maneuvering thrusters.

[robert_d]

My prediction is that the super dracos and landing legs will be external and mounted on pivots, attached just above the heatshield. They will be in the rearward position for launch. For reentry they will pivot forward and be partially covered with PICA-X. Once subsonic, they will pivot down again to use the super dracos to slow descent and then extend the legs. Latest SpaceX simulation shows parachutes almost all the way down. If the super dracos could be explosively separated in case of malfunction the current chutes would be able to land the capsule portion safely.

[douglas100]

I think it's unlikely the SuperDracos will pivot out. It's an unnecessary complication. The nozzles are designed to take high temperatures and already get some protection from being in the stagnation zone behind the shock wave produced by the heat shield.

The landing gear will have to deploy, of course.

[Dave G]

For sake of arguement let's say an ellipsled incorporated capsule, trunk and arrays in a single, landable unit. Would you land it on its tail or would you bring her down horizontally? If the latter ISTM all the thrusters would have to be in its "belly." If the former do you extract the crew with a ladder or platform, or do you provide an exit at the tail end?

There's a lot of ways to play with that shape.

Assuming the super-dracos will also be used for LAS, then it seems Dragon will have to land on the heat sheld end.