SpaceX: General Falcon and Dragon discussion (Thread 2)

[Nate_Trost]

Are Dragon CRS flights going to be mass limited or volume limited? I suppose that answer could depend on whether or not it's a Block 1 or Block 2 Falcon 9.

[robertross]

Are Dragon CRS flights going to be mass limited or volume limited? I suppose that answer could depend on whether or not it's a Block 1 or Block 2 Falcon 9.

That's essentially a question I was about to ask.
If NASA is paying for a certain mass and/or volume to the ISS, if SpaceX could improve the launch vehicle performance to gain margin, they 'should' be able to use that towards anything they want (experiments, crew development activities, ect).

It would therefore depend on the contract, and if that margin is possible to obtain. There might be a way to buy back mass/volume from the NASA contract (if so wrirtte), but if anything NASA would want more if they could get it.

[Comga]

If I were Elon I would find every way possible to test as much of the manned equipment as possible on the cargo flights. Anything I could do to move deployment of crew capability to the left. He has a real opportunity here and I'll bet dimes to dollars he is all over it.

I hope he succeeds - big time.

In effect he is already doing that.  There is recovery system including parachutes, on the COTS-1 Dragon, and indications are that they will be included on the CRS flights.  These address a secondary goal of downmass, and recovery will ostensibly allow post-flight evaluation of the hardware, but they do detract from the up-mass load. 

But as Nomadd said, not only would carrying an LAS on a cargo flight be a hit to up-mass, you couldn't very well test it.  Among a host of reasons, wouldn't the LAS leave behind the trunk and its unpressurized cargo?

However, a recovered capsule could be great for a ground test of the LAS.  Why build a boilerplate model when you have a flight version, albeit a bit scorched?

[alexw]

I suppose it would also work to have a LAS aboard cargo missions for no other reasons than to save the cargo. If your launch is a success, then great. If not, then you get the opportunity to test the LAS, plus the added benefit of being able to relaunch the same cargo.

    Perhaps the only unmanned rocket in the world where LOM != LOC. A pity that little of the cargo is anticipated to be high-value. Not quite like saving some of those errant Titans. Although, some of the science experiments might possibly be difficult to replace.
       -Alex

[Ben the Space Brit]

FWIW, I have speculated that the LAS/Ground Landing equipment might be in a seperate pod in between the Dragon and the trunk.  You fit it to  the Dragon for a crewed flight, whilst a cargo flight just had the Dragon CM directly attached to the trunk.

[Comga]

FWIW, I have speculated that the LAS/Ground Landing equipment might be in a seperate pod in between the Dragon and the trunk.  You fit it to  the Dragon for a crewed flight, whilst a cargo flight just had the Dragon CM directly attached to the trunk.

How would that work with the "Ground Landing equipment" below the heat shield? 

And on what basis do you speculate that the LAS goes above the trunk, rather than inside it?

[docmordrid]

SpaceX has already said the dual-purpose LAS/landing motors will be in the equipment bays above the heat shield and share fuel with the fhrusters. No separate pod ubder the heat shield as with CST-100.  Basically, if you need them as an LAS you don't need them as landing motors & vice versa.

[sitharus]

Basically, if you need them as an LAS you don't need them as landing motors & vice versa.

Surely if you fire your LAS you still need to land?

[pathfinder_01]

Basically, if you need them as an LAS you don't need them as landing motors & vice versa.

Surely if you fire your LAS you still need to land?

The LAS would be used to cushion a land landing if not used but the capsule would land in the ocean if used.

[ChefPat]

Isn't the Pusher LES also going to be the OMS & Deorbit Engine? If that is the case won't there be a net decrease in weight if all these things are combined instead of being separate systems?
Since cargo return will require a deorbit burn won't the LAS be useful even on ISS cargo ships?

[pathfinder_01]

Isn't the Pusher LES also going to be the OMS & Deorbit Engine? If that is the case won't there be a net decrease in weight if all these things are combined instead of being separate systems?
Since cargo return will require a deorbit burn won't the LAS be useful even on ISS cargo ships?

It would be useful on a cargo ship. It would allow a land landing, which is probably cheaper than plucking the thing out the sea. It would probably increase the mass of the dragon capsule a bit.

[Lars_J]

A land landing will be problematic from a regulatory standpoint. At least until they have demonstrated the reliability of the system.

It won't happen for the ISS cargo flights.

[Sparky]

I suppose it would also work to have a LAS aboard cargo missions for no other reasons than to save the cargo. If your launch is a success, then great. If not, then you get the opportunity to test the LAS, plus the added benefit of being able to relaunch the same cargo.

    Perhaps the only unmanned rocket in the world where LOM != LOC. A pity that little of the cargo is anticipated to be high-value. Not quite like saving some of those errant Titans. Although, some of the science experiments might possibly be difficult to replace.
       -Alex

True, but I imagine saving a reusable Dragon would be worthwhile.

[butters]

SpaceX has already said the dual-purpose LAS/landing motors will be in the equipment bays above the heat shield and share fuel with the fhrusters. No separate pod ubder the heat shield as with CST-100.  Basically, if you need them as an LAS you don't need them as landing motors & vice versa.

Really?  Where did they say that?  Isn't the aft equipment deck already filled with propellant tanks, dracos, main chutes, etc?

My pet theory was that the abort nozzles would be housed in the forward equipment ring around the LIDS tunnel, with feed lines running inside the side walls to the propellant tanks in the aft. 

The volume reclaimed by exchanging the CBM tunnel of the cargo version for the smaller LIDS tunnel on the crew version would make room for the abort nozzles in the forward ring.  The forward-mounted nozzles would also provide more ground clearance when used for landing propulsion.

Musk mentioned some sort of landing gear for dry landing, which would presumably require more space in the aft ring, since it would be awkward to deploy landing legs/bags/whatever from the forward end of the capsule.

Sure they aren't putting the abort nozzles around the LIDS docking tunnel, with LAS and dry landing only for the crewed version of Dragon?

[Ben the Space Brit]

It surprises me that I, a layman, should have to tell all you guys the obvious answer.  The pod isn't below the TPS.  The TPS is not fitted to the base of the capsule but is fitted to the base of the pod instead.

Like butters, I have to say that I can't see how the system docmordrid tells us about can possibly work.  Putting the motors into the service equipment bay on the Dragon itself would, IMHO, be difficult.  I doubt that there is much spare room left in there with the parachutes and Draco RCS already there, unless you want to go without one or two Draco quads.  Naturally, I assume that SpaceX knows more about the vehicle than I do.  However, in these early days of Crewed Dragon development, I wonder how well-thought-through the idea is.

[MP99]

I suppose it would also work to have a LAS aboard cargo missions for no other reasons than to save the cargo. If your launch is a success, then great. If not, then you get the opportunity to test the LAS, plus the added benefit of being able to relaunch the same cargo.

    Perhaps the only unmanned rocket in the world where LOM != LOC. A pity that little of the cargo is anticipated to be high-value. Not quite like saving some of those errant Titans. Although, some of the science experiments might possibly be difficult to replace.
       -Alex

True, but I imagine saving a reusable Dragon would be worthwhile.

1) I would expect that the LAS would subject the Dragon to very high G's.

2) If so, how many valuable cargo elements would be qualified to survive those sort of loads, then be re-flown on a subsequent flight? "Tang, t-shirts and toilet paper" would be fine, but the value here doesn't justify recovering the capsule & re-flying. (ISTM they could be safely re-flown, but that wouldn't recover huge value).

3) A LAS abort will also subject the Dragon's structure to high G's. Would such a capsule be re-used?

cheers, Martin

[Comga]

It surprises me that I, a layman, should have to tell all you guys the obvious answer.  The pod isn't below the TPS.  The TPS is not fitted to the base of the capsule but is fitted to the base of the pod instead.

Even as "a layman" you should know a rhetorical question when you read it.

The heatshield cannot be moved, "fitted to the base of the pod".  That changes everything significant about the capsule for reentry.  If SpaceX is going to include land landing rockets, they have to fit within the OML.

[Comga]

My pet theory was that the abort nozzles would be housed in the forward equipment ring around the LIDS tunnel, with feed lines running inside the side walls to the propellant tanks in the aft. 
...
Sure they aren't putting the abort nozzles around the LIDS docking tunnel, with LAS and dry landing only for the crewed version of Dragon?

That wouldn't be a "pusher LAS" now, would it? 

[Ben the Space Brit]

It surprises me that I, a layman, should have to tell all you guys the obvious answer.  The pod isn't below the TPS.  The TPS is not fitted to the base of the capsule but is fitted to the base of the pod instead.

Even as "a layman" you should know a rhetorical question when you read it.

The heatshield cannot be moved, "fitted to the base of the pod".  That changes everything significant about the capsule for reentry.  If SpaceX is going to include land landing rockets, they have to fit within the OML.

Agreed that it would require significant re-engineering and possibly a re-balancing of the main spacecraft.  However, that is equally the case in conversion of the Cargo Dragon to the Crewed Dragon according to the current official plans.  You are adding new engines and landing gear (either legs or airbags) to the lower service equipment bay.  That will probably require moving a lot of stuff around, especially when you recall that Crewed Dragon will also need space to fit in its LSS too.

My idea has the advantage of maintaining the current OML of the main vehicle and does not require re-arranging the internal plumbing of the lower service bay to fit in new engines and air bags (or landing gear).  All you need is what is essentially an extension to the base of the capsule.  Literally Cargo and Crewed variants would remain essentially identical on the line right up to the point where the TPS is attached.

Look, the point is whether my idea is viable or not really isn't relevant.  My concern is that SpaceX has invalidated the biggest advantage of the Dragon system with this plan - the high degree of commonality between cargo and crew versions.  I'm worried that the two models will be so different that they will end up needing seperate lines with the consequential increase in costs.

[docmordrid]

Isn't the Pusher LES also going to be the OMS & Deorbit Engine?

Both cargo and crew Dragons will deorbit and perform orbital maneuvers with the Draco clusters.  That's what they're for.

The LES engines are different and optional parts for crew escape and land landings only, and will not be installed on cargo Dragons - unless, presumably, there is a reason to return cargo on land. 

Military DragonLab missions to Edwards AFB, perhaps?