SpaceX Falcon 9 v1.1 - Dragon - CRS-5/SpX-5 -Jan. 10, 2015 - DISCUSSION

[macpacheco]

Good thing NASA is buying the ride, not the rocket, huh? If something adds just a miniscule amount of risk to a flight, NASA doesn't necessarily have much say.

Besides, it can indirectly add to the flight reliability in the future by allowing a much higher flight rate. That would more than make up for the infinitesimal increase on risk on this flight.

I wouldn't be surprised if NASA gets something in exchange for agreeing to adding the fins. They got data for Mars landings on the last flight. Might be something like that.

True but in those cases NASA contributed with monitoring assets to get the data. It wasn't about NASA objecting to SpaceX doing a minor change to F9R in exchange for that data. NASA might not be convinced SpaceX will succeed in reusability, but they sure would love half off F9R launch prices.

[Antares]

Good thing NASA is buying the ride, not the rocket, huh? If something adds just a miniscule amount of risk to a flight, NASA doesn't necessarily have much say.

So I wonder who had the legs removed from the last CRS launch?

[Antares]

To deploy prematurely on ascent the fins would have to open against the aerodynamic force of the slipstream. So I think you're right: there is little chance that the fins themslves would cause LOM.

You're assuming a steady slipstream, which is never the case during ascent.  Q is constantly changing, and transonic is quite chaotic albeit brief.  Then there are winds that are unpredictable.  I somewhat agree that properly designed panels shouldn't cause LOM, but NASA would be right to check the work.

[sublimemarsupial]

Good thing NASA is buying the ride, not the rocket, huh? If something adds just a miniscule amount of risk to a flight, NASA doesn't necessarily have much say.

So I wonder who had the legs removed from the last CRS launch?

SpaceX did. The core that flew for last CRS flight was originally intended for an expendable GTO flight, and as such did not have the internal landing leg bulkhead, so it could not have had legs. Meanwhile, Asiasat 6 had a first stage with the landing leg bulkhead but no legs as the mission didn't have the performance margin for them. The cores were shifted due to manifest issues, NASA played no part in it.

[mme]

...

These are huge stretches but the probability is not zero, and I expect there are others. So while I think the risk is very low and worth it, NASA just possibly might not agree. We have no indication of such, that I know of.

I'm sure NASA knew that this mission would have grid fins long before we did, just like they knew about the legs way before we did.  And I seriously doubt SpaceX would fly with them if NASA had a problem with them.

SpaceX has no interest in losing a rocket and their is no way that deployment isn't locked out in the software until several conditions are met.  And you can bet that the interstage has been through a ton of simulations. Remember, SpaceX is the company people were accusing of "abort fever" not too long ago.

[cambrianera]

@sublimemarsupial,
Very interesting, can you expand on landing leg bulkhead details?
Please answer (if you can/want  ) in the landing legs general discussion thread.

[douglas100]

To deploy prematurely on ascent the fins would have to open against the aerodynamic force of the slipstream. So I think you're right: there is little chance that the fins themslves would cause LOM.

You're assuming a steady slipstream, which is never the case during ascent.  Q is constantly changing, and transonic is quite chaotic albeit brief.  Then there are winds that are unpredictable.  I somewhat agree that properly designed panels shouldn't cause LOM, but NASA would be right to check the work.

Thanks for the insight.

[mvpel]

True but in those cases NASA contributed with monitoring assets to get the data. It wasn't about NASA objecting to SpaceX doing a minor change to F9R in exchange for that data. NASA might not be convinced SpaceX will succeed in reusability, but they sure would love half off F9R launch prices.

I suspect that NASA has at least as high a percentage of SpaceX amazing people and fangrls - with SpaceX wallpaper on their computers and cubicle walls and SpaceX model rockets under the tree - as we do here at NSF and that they are, top to bottom, just as excited to see them succeed as any other space nerds, and not only that they're in the enviable position of being able to help them do so.

[Dudely]

Heck, NASA probably helped them model the grid fins!

[Prober]

For reusable missions, I think adding grid fins will more than make up for their weight and increase payload margin, because they add very little drag going up, but appreciable drag coming down, resulting in less fuel needed for the landing burn. Not that I calculated the numbers or anything, but just notionally, it seems likely.

see this is where things are going wrong.  CRS-5 is a contracted ISS supply mission, and that should be the total focus.  Max payload right now should be the focus with the Orbital losses.   Everyone seems to be excited with good reason, about the landing legs etc., but let's not forget the mission is supplies to the ISS, not reusability.

The focus should be extra payload to the ISS not extra fuel available to land the launcher

[rpapo]

The focus should be extra payload to the ISS not extra fuel available to land the launcher

That's all well and good, but Dragon, much more so than Cygnus, is volume limited, not weight limited.

[mvpel]

Heck, NASA probably helped them model the grid fins!

Ames does have a big HPC facility...
http://www.nas.nasa.gov

[guckyfan]

The focus should be extra payload to the ISS not extra fuel available to land the launcher

You think they should design and build a new larger Dragon until mid December?

[oiorionsbelt]

see this is where things are going wrong.  CRS-5 is a contracted ISS supply mission, and that should be the total focus.  Max payload right now should be the focus with the Orbital losses.   Everyone seems to be excited with good reason, about the landing legs etc., but let's not forget the mission is supplies to the ISS, not reusability.

The focus should be extra payload to the ISS not extra fuel available to land the launcher

This kind of thinking is why things have been stagnant for so long in launch technology.

[douglas100]

The focus should be extra payload to the ISS not extra fuel available to land the launcher

NASA are the customer. They know what the ISS requirements are and what the F9 and Dragon can carry. They know where the "focus" should be. They appeared to have signed off on SpaceX attempting this experiment. Which would mean that there is no conflict between the proposed payload mass and prop margin for landing.

[douglas100]

see this is where things are going wrong.  CRS-5 is a contracted ISS supply mission, and that should be the total focus.  Max payload right now should be the focus with the Orbital losses.   Everyone seems to be excited with good reason, about the landing legs etc., but let's not forget the mission is supplies to the ISS, not reusability.

The focus should be extra payload to the ISS not extra fuel available to land the launcher

This kind of thinking is why things have been stagnant for so long in launch technology.

That is beside the point. If NASA needed the extra margin on this flight (and I don't think they do) then then SpaceX would do whatever was necessary to carry out the mission, even if it meant removing the legs and using the prop assigned for landing. That would have a negligible affect on the long term viability of re-usability.

[yg1968]

Good thing NASA is buying the ride, not the rocket, huh? If something adds just a miniscule amount of risk to a flight, NASA doesn't necessarily have much say.

So I wonder who had the legs removed from the last CRS launch?

Because of core swaps, SpaceX said that they didn't have time to add the legs for CRS-4. They didn't want to delay the mission for that.

[Robotbeat]

Can we stop with the concern-trolling, already? It's boring.

[kevinof]

May be a silly question here but I assume Dragon is volume limited because of it's shape, and the shape is required because it has to return back and is aero dynamically stable due to this shape. Cygnus doesn't return so there are no compromises in terms of the shape and volume.

Am I correct in my thinking?

The focus should be extra payload to the ISS not extra fuel available to land the launcher

That's all well and good, but Dragon, much more so than Cygnus, is volume limited, not weight limited.

[rpapo]

May be a silly question here but I assume Dragon is volume limited because of it's shape, and the shape is required because it has to return back and is aero dynamically stable due to this shape. Cygnus doesn't return so there are no compromises in terms of the shape and volume.

Am I correct in my thinking?

The focus should be extra payload to the ISS not extra fuel available to land the launcher

That's all well and good, but Dragon, much more so than Cygnus, is volume limited, not weight limited.

Generally, but the constraints on Dragon's volume and size aren't due just to the requirement/feature that it can return from orbit intact, but are also due to how it is intended to eventually carry people as well.

Of course, it is quite possible that if SpaceX had had the Falcon 9 1.1 from the start, they just might have designed Dragon somewhat bigger.  Or maybe not: the base of Dragon fits the diameter of Falcon, and Falcon's diameter is what American highways can tolerate.