Red Dragon Discussion Thread (1)

[baldusi]

I've always assumed that Red Dragon would be Dragon derived. My question about the friction welding is because here using a counter thread seems easier. But that would need to stop the drill, put the new segment on top. Have a mechanism to do the counter screwing. And start the drill again.
In a friction welded case, you keep moving the drill, but you stop pushing down. You put the new segment right above, and all you need is a good clutch to keep the upper segment fixed while getting friction to the still turning drill. Like in this video.

With some ingenuity, you could make the part of the drill that pushes down the drill the same that catches and clutches the new segments. Of course I don't know if you could have enough torque. But in the end it might work in a future if anybody in the world finally decides to develop space worthy reactors.

[Jim]

I've always assumed that Red Dragon would be Dragon derived. My question about the friction welding is because here using a counter thread seems easier. But that would need to stop the drill, put the new segment on top. Have a mechanism to do the counter screwing. And start the drill again.
In a friction welded case, you keep moving the drill, but you stop pushing down. You put the new segment right above, and all you need is a good clutch to keep the upper segment fixed while getting friction to the still turning drill. Like in this video.

With some ingenuity, you could make the part of the drill that pushes down the drill the same that catches and clutches the new segments. Of course I don't know if you could have enough torque. But in the end it might work in a future if anybody in the world finally decides to develop space worthy reactors.

retracting the drill would be an issue.

[mmeijeri]

Thanks for that link baldusi, I never understood what friction stir welding looked like!

[krytek]

While it is friction welding, I believe "stir" friction welding looks like this:

[mmeijeri]

Yeah, I looked around for some more videos and it looks as if this is inertial stir welding or something like that. Then again I did see a video showing something that was claimed to be FSW that had a red hot, rotating and glowing implement being pushed against the workpiece as it traversed its circumference.

[go4mars]

Stick an RTG on it.

Even with an ASRG type of RTH you only getting about 110W per generator. It's not enough power. Never mind the shortage of Plutonium  238 isotopes.

That might not be a problem.  Have a few of them hooked up to batteries.  If you are coring through Ice, you wouldn't want to drill any faster than heat conductance allows anyway.  Besides, the States needs to make a bunch more Pu 238.  This could be another reason. 

[Chris-A]

The issue is all the previous landers shed their heatshields and aeroshells.  Dragon can't (or then it isn't a Dragon anymore).  Dragon wouldn't put a large payload on Mars, it is going to put a large amount of Dragon structure on Mars.  The Dragon structure is going to be a limiting factor.

Yes, there is, it is not that simple just to enlarge the hatch.  There are load paths that must be taken into account.  Payload bay doors?  You got to be joking.
Dragon is a pressure vessel.

Jim is right. The pressure vessel is a limiting factor. If the lower section of the pressure vessel is used for a structure to build a flat platform, something needs to replace the sidewalls for reentry and the nose for launch. I almost forgot the parachutes, but modifications for Mars is needed, unless they are not too effective.

[Dave G]

Yeah, I looked around for some more videos and it looks as if this is inertial stir welding or something like that. Then again I did see a video showing something that was claimed to be FSW that had a red hot, rotating and glowing implement being pushed against the workpiece as it traversed its circumference.

Here's another example of stir welding:

[Nathan]

There is no reason that there cannot be a larger hatch on the dragon for this mission. Can have payload bay style doors open out instead, to enable a full volume payload to descend to the surface via deployable ramps. Or no descent to surface but have the payload deployed sideways above the surface (for sampling mission)
Dragon derived is probably  correct. Minimal modification but certainly modified.

Yes, there is, it is not that simple just to enlarge the hatch.  There are load paths that must be taken into account.  Payload bay doors?  You got to be joking.
Dragon is a pressure vessel.

Not joking. I just don't know. the real solution to deploying a payload to the surface is to open the hatch and deploy from there.

Given you are the expert on everything, can you provide an analysis of what would be required in terms of modifications to land a dragon on Mars? Not sure we have nailed the edl problem.

[Jim]

Given you are the expert on everything, can you provide an analysis of what would be required in terms of modifications to land a dragon on Mars? Not sure we have nailed the edl problem.

Don't start with a Dragon.

[Lee Jay]

Yeah, I looked around for some more videos and it looks as if this is inertial stir welding or something like that. Then again I did see a video showing something that was claimed to be FSW that had a red hot, rotating and glowing implement being pushed against the workpiece as it traversed its circumference.

Odd as it may sound, friction stir welding doesn't melt the materials.

[baldusi]

BTW, I proposed friction welding, not friction stir welding. Not the same. The extra border that forms, could be taken out with a lathe tool, which could work for cutting the segments to take out the drill. Obviously I assumed a single long drill, and not multiple hole. I also assumed that the drill's torque would be similar to a lathe's. But given those conditions, it could make for a more reliable mechanism (just one way of turning and two solenoids for the tool), than threading the segments.

[go4mars]

he real solution to deploying a payload to the surface is to open the hatch and deploy from there.

What about spring-loading dragons floor?  When dragon is about to touch down propulsively, have the top open, and just fire the toy out the top with rapid-inflate balloon cushions (like pathfinder had).   

[Jim]

The Dragon shape is optimized for astronauts and bulk cargo.  It is a pressure vessel.  It is not a good platform to deploy rovers or instrument from. 

[Prober]

Yeah, I looked around for some more videos and it looks as if this is inertial stir welding or something like that. Then again I did see a video showing something that was claimed to be FSW that had a red hot, rotating and glowing implement being pushed against the workpiece as it traversed its circumference.

Here's another example of stir welding:

isn't photoshop wonderful?

[Jason1701]

What's photoshopped?

[manboy]

What's photoshopped?

The SpaceX logo?

[Dave G]

What's photoshopped?

The SpaceX logo?

The picture came right off the SpaceX web site.
http://www.spacex.com/updates_archive.php?page=0205-0505

"Our barrel sections are constructed from rolled aluminum sheet with stringers stir welded in for stiffness. This method yields substantial cost savings over the conventional launch vehicle approach of using machined isogrid. With isogrid and its variants, you start with a plate of aluminum that can be as thick as two inches and then machine away up to 90% of the material, leaving behind sheet with integral stiffeners. This is obviously very inefficient use of material and requires thousands of hours of machining time. "

[ugordan]

isn't photoshop wonderful?

You're hilarious.

[mmeijeri]

That doesn't look very rigid, can anyone explains how this works?