Author Topic: Speculation about Dragon 3 (Read 18579 times)

cuddihy · « **on:** 01/27/2014 01:08 pm »

I know, "What? We haven't even seen Dragon 2 yet!"

But I think it's a fair topic given folks are speculating about a fully reusable Mars Colonial Transport.

Dragon 2 is the next version of the Dragon vessel being used to fulfill NASA CRS contracts, and possibly also crewed Dragon flights. The consensus seems to be that it is recognizeably the same--possibly even the same pressure hull--as Dragon 1, and shares many less-than desirable features with Dragon 1, such as an expendable trunk.

My proposal for Dragon 3 speculation would be to suggest what improvements the next generation of crew transport would offer. Perhaps this is also a milestone on the road to MCT.

I suggest we limit it to being able to be lofted by FH to bound the problem. Some suggestions:

1. Increase in size to max diameter of 5 meters (in line with fairing diameter).
2. Elimination of solar arrays by replacement with methane-LOX fuel cells.
3. Inclusion of reusable "trunk" within form of returning capsule.

Others?

docmordrid · « **Reply #1 on:** 01/27/2014 01:12 pm »

1) go larger, the same diameter as the "7+ meter" FX core. Then you may be able to fit a respectable trunk & doors behind the heat shield.

pospa · « **Reply #2 on:** 01/27/2014 01:46 pm »

MCT should allow us think BIG ... why not to consider directly Mars Base MB-10 ?
http://www.marspapers.org/papers/Doule_2008.pdf
http://spacearchitect.org/pubs/AIAA-2012-3557.pdf

docmordrid · « **Reply #3 on:** 01/27/2014 02:00 pm »

Intetesting. Can't wait to see the comments.

Rabidpanda · « **Reply #4 on:** 01/27/2014 03:52 pm »

Before we can speculate on what a hypothetical Dragon 3 might look like we need to know what it's purpose would be. Is it used for crew transport to LEO? How many crew? Will it transport cargo as well? Will it go to destinations beyond LEO? Who exactly is going to be purchasing Dragon 3 flights?.

Rifleman · « **Reply #5 on:** 01/27/2014 06:55 pm »

I would imagine Dragon 3 would be Red Dragon, but honestly, its probably not much more than some pretty animations on SpaceX promotional videos, and sketches on napkins in Elon's desk at this point.

Chris Bergin · « **Reply #6 on:** 01/28/2014 12:50 pm »

Right so this thread is back and trimmed. Don't get sarcastic about this thread. It's not Dragon 2 and it's not Red Dragon.

Ben the Space Brit · « **Reply #7 on:** 01/28/2014 01:08 pm »

A Dragon-? My call is that the diameter would be the same 5.2m as the Falcon 9 fairing and would be designed for full re-usability.

However, I would also expect Dragon-3 to be only an Earth-to-orbit vehicle. The Mars orbiter and lander would be totally different machines, although the lander might have some software commonality and I'd expect them all to use Dracos for RCS purposes.

Dragon 3 might not be a ballistic capsule.

R7 · « **Reply #8 on:** 01/28/2014 02:38 pm »

Quote from: cuddihy on 01/27/2014 01:08 pm

2. Elimination of solar arrays by replacement with methane-LOX fuel cells.

Connected to this, elimination of NTO/MMH for more eco-friendly / less hazardous to handle option?
GOX/GCH4 RCS? LOX/LCH4 SuperDracos? Ethane/NOX? HAN?

Quote from: Chris Bergin on 01/28/2014 12:50 pm

Don't get sarcastic about this thread.

It was difficult!

darkenfast · « **Reply #9 on:** 01/28/2014 04:14 pm »

Question for the aerospace-knowledgeable types: what are the problems in scaling up a shape like that of Dragon (or Soyuz or Apollo, for that matter)? Do you gain anything in structural weight versus volume, or do other considerations such as heatshield mass and design make scaling a dead-end? Is there any rule-of-thumb for when you are better off abandoning a shape and trying something completely different?

Mongo62 · « **Reply #10 on:** 01/28/2014 04:48 pm »

Quote from: darkenfast on 01/28/2014 04:14 pm

Question for the aerospace-knowledgeable types: what are the problems in scaling up a shape like that of Dragon (or Soyuz or Apollo, for that matter)? Do you gain anything in structural weight versus volume, or do other considerations such as heatshield mass and design make scaling a dead-end? Is there any rule-of-thumb for when you are better off abandoning a shape and trying something completely different?

Certainly not aerospace-knowledgeable, but common sense says that as the mass increases, the square-cube law dictates that the capsule's diameter must increase more quickly than the height, if you want the terminal velocity to remain the same. So a significantly larger Dragon might look more like the MSL entry shape:

Lars_J · « **Reply #11 on:** 01/28/2014 05:04 pm »

Quote from: darkenfast on 01/28/2014 04:14 pm

Question for the aerospace-knowledgeable types: what are the problems in scaling up a shape like that of Dragon (or Soyuz or Apollo, for that matter)? Do you gain anything in structural weight versus volume, or do other considerations such as heatshield mass and design make scaling a dead-end? Is there any rule-of-thumb for when you are better off abandoning a shape and trying something completely different?

According to some, this is part of the problem with Orion's mass budget. They thought that scaling up the Apollo shape would be easy and simple, but it is proving more difficult than expected. It is much heavier than originally planned, and will have to go on a diet to avoid overloading the parachutes.

Nomadd · « **Reply #12 on:** 01/28/2014 05:07 pm »

Quote from: Mongo62 on 01/28/2014 04:48 pm

Quote from: darkenfast on 01/28/2014 04:14 pm
Question for the aerospace-knowledgeable types: what are the problems in scaling up a shape like that of Dragon (or Soyuz or Apollo, for that matter)? Do you gain anything in structural weight versus volume, or do other considerations such as heatshield mass and design make scaling a dead-end? Is there any rule-of-thumb for when you are better off abandoning a shape and trying something completely different?

Certainly not aerospace-knowledgeable, but common sense says that as the mass increases, the square-cube law dictates that the capsule's diameter must increase more quickly than the height, if you want the terminal velocity to remain the same. So a significantly larger Dragon might look more like the MSL entry shape:

Only if density stays the same. Mass doesn't equal size. Larger capsules could be mostly for more room and could have a smaller or equal mass/surface area ratio.

SpacexULA · « **Reply #13 on:** 01/28/2014 06:48 pm »

Quote from: Ben the Space Brit on 01/28/2014 01:08 pm

A Dragon-? My call is that the diameter would be the same 5.2m as the Falcon 9 fairing and would be designed for full re-usability.
However, I would also expect Dragon-3 to be only an Earth-to-orbit vehicle. The Mars orbiter and lander would be totally different machines, although the lander might have some software commonality and I'd expect them all to use Dracos for RCS purposes.
Dragon 3 might not be a ballistic capsule.

I agree.

IMHO Dragon 3 will see 2 variants: a dedicated 5.2 Meter LEO only capsule for cargo return and crew transport, and an inflatable heat shield variant for Mars entry.

llanitedave · « **Reply #14 on:** 01/28/2014 08:14 pm »

Why would it be 5.2m? If we're talking about a larger, more advanced crew module, we're probably talking about something beyond the FH generation, which Dragon 2 will cover just fine. Might as well go for the 7-9 meter MCT version and carry a crowd of passengers.

jtrame · « **Reply #15 on:** 01/29/2014 12:02 am »

Quote from: Lars_J on 01/28/2014 05:04 pm

Quote from: darkenfast on 01/28/2014 04:14 pm
Question for the aerospace-knowledgeable types: what are the problems in scaling up a shape like that of Dragon (or Soyuz or Apollo, for that matter)? Do you gain anything in structural weight versus volume, or do other considerations such as heatshield mass and design make scaling a dead-end? Is there any rule-of-thumb for when you are better off abandoning a shape and trying something completely different?

According to some, this is part of the problem with Orion's mass budget. They thought that scaling up the Apollo shape would be easy and simple, but it is proving more difficult than expected. It is much heavier than originally planned, and will have to go on a diet to avoid overloading the parachutes.

Which is why developing propulsive landing makes sense. Much more scalable. If successful, I think it will be the defining feature of the Dragon family.

cuddihy · « **Reply #16 on:** 01/29/2014 02:37 am »

Quote from: llanitedave on 01/28/2014 08:14 pm

Why would it be 5.2m? If we're talking about a larger, more advanced crew module, we're probably talking about something beyond the FH generation, which Dragon 2 will cover just fine. Might as well go for the 7-9 meter MCT version and carry a crowd of passengers.

Well, if Dragon 2 is the same as Dragonrider, it seems to be on a near-term schedule, as in testing this year and next year, possibly in-service by 2015 or 16.

So if the next step after that is MCT, you've just jumped from something in early production for next year to something that's barely in the beginning phases of design that may not appear for 10 years or more. SpaceX hasn't even built & tested a TPA yet for Raptor that we're aware of, much less actually announced a 7-9 meter launcher.

That's why I suggested limiting the problem set to what could you accomplish on a near term like FH.

All that said...is there a reason you couldn't launch a 7m capsule on FH?

I'm trying to figure out if you can fit a useful "trunk"/SM in a reusable 5.2m form.

go4mars · « **Reply #17 on:** 01/29/2014 06:12 am »

Quote from: cuddihy on 01/29/2014 02:37 am

is there a reason you couldn't launch a 7m capsule on FH?

No.

go4mars · « **Reply #18 on:** 01/29/2014 06:16 am »

Quote from: llanitedave on 01/28/2014 08:14 pm

Why would it be 5.2m? ... Might as well go for the 7-9 meter MCT version and carry a crowd of passengers.

I agree with you.

Perhaps some people think 5.2m is road transportable, while 5.3 isn't?

Also, I remember someone (not me) fretting pretty hard about egress issues if too many people are in a capsule.

Ben the Space Brit · « **Reply #19 on:** 01/29/2014 08:48 am »

Quote from: go4mars on 01/29/2014 06:16 am

Also, I remember someone (not me) fretting pretty hard about egress issues if too many people are in a capsule.

It's no worse than a modern super-jumbo airliner, which has maybe a dozen egress points at most for over 600 passengers. If there is a really bad incident, you're going to lose a lot of people and aerospace seems to have come to terms with that long ago.