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

[Hauerg]

You must have missed his "and eventually to the stars" part.   

[deruch]

https://twitter.com/elonmusk/status/536262624653365248

Base is 300 ft by 100 ft, with wings that extend width to 170 ft.  Will allow refuel & rocket flyback  in future.

Amazing! Where will he stop?

Three thoughts:
1) Does this end the discussion of whether the Falcon first stage will be shipped back vertically or horizontally.  Neither — it's going to fly back.

2) If the barge cost less to build than one Falcon first stage it pays for itself when it recovers its first launch.

3) I had wondered if Spacex would try to successfully recover a first stage before flying the in-flight abort test.  Why waste a perfectly good rocket. (I realize the aerodynamic forces on the top of the second stage at MaxQ might make recovery impossible.)

Welcome to the site!

1) As you've posted this in the discussion for this specific mission- CRS-5/SPX-5 - and not in one of the general threads that are discussing what will happen going forward, I will tell you that you're wrong.  The tweet being quoted is about "future" operations [I've adjusted what was bolded to highlight this fact].  Not this upcoming flight.  For CRS-5, if SpaceX is successful in landing the first stage on the barge, they will have to bring it back either horizontally or vertically.  If for no other reason than that Range Safety won't let them land there yet.

2)  Your math works only once they are able to actually use a recovered stage.  Just having one doesn't save them any money.  But I don't agree with the premise either.  IMO, SpaceX won't refly the first booster that is recovered.  I expect them to take apart and study at least one and maybe more of them before actual reflights happen.  Plus all of the knowledge gained in that process has a value.  What's learned may help them make cheaper or more durable rockets moving forward.  So the stage can help pay for the barge even before reflight occurs.

3)  See above for one reason they're unlikely to use the booster from this flight if it's successfully recovered.  I'm not prepared to speculate on whether they use one from one of the upcoming flights until I see how repeatable the recovery is.

[GreenShrike]

@elonmusk

Grid fins are stowed on ascent and then deploy on reentry for "x-wing" style control. Each fin moves independently for pitch/yaw/roll.

I wonder if he needs permission from George Lucas (or Disney) to use the term X-Wing. More awesomeness in any case.

If he's selling a starship called an "X-Wing", sure. Here's it's purely descriptive, and could be easily argued that it's merely a functional description of the fin configuration and not a Star Wars reference at all.

Of course that argument would be unavailable if the MCC-X team should happen to call "Lock S-foils into attack position." right before deploying the fins... ;-)

[llanitedave]

If he starts bragging about doing " the Kessel Run in less than twelve parsecs," then all bets are off.

[Ben the Space Brit]

If he starts bragging about doing " the Kessel Run in less than twelve parsecs," then all bets are off.

Well, Mr Musk is very proud of being a pop culture nerd so it is possible that he'll drop in the occasional Trek or Wars reference...

[yg1968]

@elonmusk Good luck. We had supersonic control inversion issues with actuated fins, went back to little thrusters that worked at all speeds.

@ID_AA_Carmack No choice. Entry velocity too high for a precision landing with N2 thrusters alone. Must have aero surfaces for pitch trim.

@elonmusk I don't disagree, but I'm concerned. Maybe offset CG or static trim tab for a touch of body lift, then roll it?

https://twitter.com/ID_AA_Carmack/status/536277962803650562

Another reply by Musk:

@ID_AA_Carmack That works for Dragon, but hard to do for something long like Falcon

https://twitter.com/elonmusk/status/536354292396228608

[Chris Bergin]

Remember, we have a "barge" thread. Use that thread please.
http://forum.nasaspaceflight.com/index.php?topic=36140.0

CRS-5 is the mission to the ISS, the absolutely priority of this mission.

[mvpel]

We saw how effective the grid fins worked at low altitude and velocity with F9R Dev1 and now we know they are intended to be used during hypersonic reentry.  I am still wondering if (1) the issue of transonic "choking" has been address with this fin design and (2) if not, will the fins be stowed during this transonic period and then redeployed for landing or (3) will the issue of "choking" simply not influence the vehicle's attitude and control enough to worry about?

When grid fins are choked out their drag increases markedly, which is beneficial to a returning booster, and so they may not stow them but rather leave them extended to help slow down. You'd expect they'd simply use the N2 for any adjustments needed during the period when the control authority of the fins was compromised during the transonic flight regime.

[Prober]

The flight grid fins look like the ones on this test we did, but larger:

the fins are far superior to the gas

how much a hit to payload?

[deruch]

the fins are far superior to the gas

how much a hit to payload?

Though interesting for knowledge's sake, the payload hit is irrelevant to any LEO mission SpaceX has flown so far, including all CRS missions.  There's plenty of margin.  Probably a better discussion topic in the General Falcon thread.

[Prober]

the fins are far superior to the gas

how much a hit to payload?

Though interesting for knowledge's sake, the payload hit is irrelevant to any LEO mission SpaceX has flown so far, including all CRS missions.  There's plenty of margin.  Probably a better discussion topic in the General Falcon thread.

margin is not the question.   Sure NASA wouldn't allow any expensive experiments to launch.

The question relates to maximum payload utilization.    Frankly after the Orbital event to see this:

"It is loaded with more than 3,700 pounds of scientific experiments, technology demonstrations and supplies, including critical materials to support 256 science and research investigations that will take place on the space station during ISS Expeditions 42 and 43."

 "CRS-3 is carrying 2,215 kilograms (4,883 lb) of cargo – with an additional 81 kilograms (179 lb) of packaging."   http://www.nasaspaceflight.com/2014/10/orbitals-antares-loft-fourth-cygnus-iss/

[Dudely]

the fins are far superior to the gas

how much a hit to payload?

Though interesting for knowledge's sake, the payload hit is irrelevant to any LEO mission SpaceX has flown so far, including all CRS missions.  There's plenty of margin.  Probably a better discussion topic in the General Falcon thread.

margin is not the question.   Sure NASA wouldn't allow any expensive experiments to launch.

The question relates to maximum payload utilization.    Frankly after the Orbital event to see this:

"It is loaded with more than 3,700 pounds of scientific experiments, technology demonstrations and supplies, including critical materials to support 256 science and research investigations that will take place on the space station during ISS Expeditions 42 and 43."

 "CRS-3 is carrying 2,215 kilograms (4,883 lb) of cargo – with an additional 81 kilograms (179 lb) of packaging."   http://www.nasaspaceflight.com/2014/10/orbitals-antares-loft-fourth-cygnus-iss/

You asked about a hit to the payload. Margin is certainly the question you asked.

The dragon does not have a lot of room inside it for the various experiments and supplies. So, usually when it is full up with stuff they still have some extra weight left. 4,900 pounds is probably about half of the maximum payload they can take to the ISS (I can't remember the fuel requirements per kg, so I could be off).

And adding the fins isn't dangerous because they won't use them until after they separate from the second stage.

[Lar]

And adding the fins isn't dangerous because they won't use them until after they separate from the second stage.

There are scenarios (hopefully highly unlikely) in which the fins cause LOM,
- premature (partial) deployment causing aerodynamic instability and loss of vehicle on ascent (what if one fin deployed and there was a loss of control due to an unrelated bit of bad luck)
- fin shearing off while undeployed and impacting something causing an engine RUD

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.

[OnWithTheShow]

Not really any greater of a chance than adding the legs.

[Dudely]

And adding the fins isn't dangerous because they won't use them until after they separate from the second stage.

There are scenarios (hopefully highly unlikely) in which the fins cause LOM,
- premature (partial) deployment causing aerodynamic instability and loss of vehicle on ascent (what if one fin deployed and there was a loss of control due to an unrelated bit of bad luck)
- fin shearing off while undeployed and impacting something causing an engine RUD

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 actually thought of a premature deployment causing LOM when I wrote that. But I decided to stand by the phrase "isn't dangerous" because of the low likelihood of it happening. But yes, there are lots of things that could go wrong, it's just fairly easy to mitigate the risks of something lik this.

[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.

[Jcc]

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.

[Lar]

I totally agree that the chance of grid fins causing LOM is very very slight. But it would always be non zero for just about anything you could name.

[Robotbeat]

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.

[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.

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.