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

[Kabloona]

Does the Falcon 9 use fuel as hydraulic fluid? (Like the Saturn V did). I.e., running out of fluid actually means running out of gas?

See discussion here:

http://forum.nasaspaceflight.com/index.php?topic=35853.msg1313564#msg1313564

F9 does use RP-1 fuel for TVC actuators, but probably not for the grid fins.

[Lee Jay]

Hydraulic fluid doesn't get used up unless there's a leak.  I'm guessing what they lost was hydraulic pressure which was probably generated from an accumulator style system and what happened is that all the fluid had been pushed out of the accumulators, through the system, and into a collection reservoir.

[Kabloona]

Hydraulic fluid doesn't get used up unless there's a leak.

Or unless they decided to used an open system in which the hydraulic fluid is simply dumped downstream of the actuator, which makes for a simpler system and eliminates the mass of a collection tank and associated plumbing.

[Raj2014]

oh ok. then that must have happened at pretty high speed I guess.

He said the loss of grid fin control authority happened "right before landing." And remember, when the grid fins lock up, they're suddenly providing unbalanced pitch/yaw forces, because it's probable they were at non-zero angles when they locked up. So now the grid fins are destabilizing, instead of stabilizing, and that can be a  problem even at low speed, even if the engine is firing.

The grid fins have holes in them, would that reduce instability? Also would they open the grid fins when it was at a centre height, when it was safe and needed?

[meekGee]

So if they "Already" have 50% more fluid planned, that means they are and/or continue to be ridiculously fast at iterative design or more likely in this case, already knew through modeling they'd need more margin. Or both.

It goes back to the fact that these are flight rockets, and there's a production pipeline.  They learned stuff about grid fins even 4 months ago, and realized that they need a larger reservoir, but this specific rocket was already at some point down the pipeline and only the next rocket got the mods.  ("got", also in past tense, since it's already at McGregor by now)

Compare this with a more sane cycle where you fly, learn, design mods, and then build the next article - which can be a year's cycle at least.

Otherwise:

At 7:42 in that video, you can see a deployed grid fin on the monitor at upper left. At 11:10, I believe you can see what looks like the landing burn video reflected off the control room's back window, also at upper-left.

What was the T+time then?

[cscott]

Does the Falcon 9 use fuel as hydraulic fluid? (Like the Saturn V did). I.e., running out of fluid actually means running out of gas?

See discussion here:

http://forum.nasaspaceflight.com/index.php?topic=35853.msg1313564#msg1313564

F9 does use RP-1 fuel for TVC actuators, but probably not for the grid fins.

Thanks for the cite, Kabloona.

Remember, from bottom to top the core is: nozzle, chamber, turbopump (where high pressure RP1 can be found), RP1 tank, LOX tank, interstage (with grid fins).

So pushing the nozzle around with high pressure RP1 makes a lot of sense.  Trying to plumb high pressure RP1 all the way through the RP1 and LOX tanks up to the interstage... not so much.

There are also cold gas RCS thrusters in the interstage, with their associated high pressure nitrogen tanks,  and a pneumatic pusher system for stage separation.  It stands to reason that the complete grid fin system, however it is powered, is also contained in the interstage.

The wildcard is that I don't actually know exactly where the COPV helium tanks are located.   It's not impossible that they are involved in the grid fin system -- the legs are deployed using high pressure helium, for example.  But again, the legs are on the "other side" of the core...

[Raj2014]

Has it been confirmed when SpaceX will do another attempt at landing on the autonomous spaceport drone ship?

[savuporo]

If he is talking about hydraulic actuation loss pre landing, that would be TVC actuation, not grid fins as grid fins would not be providing a lot of control authority pre landing. It's the TVC+throttle that does the final approach and landing, not the fins.

Final approach and landing - yes.
The grid fins have no effect for the last of the trajectory.
However - it's reasonable to say that they're going to have some effect even at 1/2 freefall velocity, which is some 15s before landing.

My comment above was pretty uninformed coffee-deprived one - i just went back and looked at the F9R cows flight and saw ( and remembered ) fins flapping around all the way through flight and touchdown, so they obviously use all the control authority they can get from them.

[NovaSilisko]

My comment above was pretty uninformed coffee-deprived one - i just went back and looked at the F9R cows flight and saw ( and remembered ) fins flapping around all the way through flight and touchdown, so they obviously use all the control authority they can get from them.

The grid fins on this flight are much larger than F9R-Dev's as well, so there's even more authority to be gained from them now.

[vanoord]

If the actuators for the grid fins ran out of the hydraulic fluid, the fins would have been fixed in their final position?

Assuming that, the descending stage would suffer from aerodynamics it wasn't programmed to deal with and couldn't deal with by using the fins. That's going to result in a loss of control - and a few metres variance will be enough to cause a sufficiently difficult landing sufficient to destroy the stage.

I'm (obviously) not familiar with the grid fin actuators, but I suspect they would be fitted with non-return valves to prevent them feeding back into the system. In that case, failure of the supply would lock them in place, unless gas has got into the system - in which case it would be rather more unpredictable.

[StuffOfInterest]

Considering how accurate the targeting was, regardless of how the actual landing went, I wonder how many more barge missions will be required before the powers that be at the Cape are comfortable with them doing a land landing?  If this attempt had been on land, about the worse that would have come out of it is the need to patch a few holes in the concrete pad.

[InvalidAttitude]

Elon Musk @elonmusk
Upcoming flight already has 50% more hydraulic fluid, so should have plenty of margin for landing attempt next month.

How much plus weight it means?

[OxCartMark]

(The rest of the telemetry data was captured by the ASDS -- it began receiving telemetry at T+1:45 or so.  It will take some time for that to be downlinked to SpaceX mission control; depending on their satellite connection Hans indicated "a day or two".)

Hopefully said data recording device isn't on the list of items that SpaceX's purchasing department would presumably be working to find replacements for this fine Saturday afternoon.  Or maybe hopefully its recorded on Go Quest.

[JamesH]

Considering how accurate the targeting was, regardless of how the actual landing went, I wonder how many more barge missions will be required before the powers that be at the Cape are comfortable with them doing a land landing?  If this attempt had been on land, about the worse that would have come out of it is the need to patch a few holes in the concrete pad.

Quite a few - the accuracy today may have been pure luck.

[JamesH]

(The rest of the telemetry data was captured by the ASDS -- it began receiving telemetry at T+1:45 or so.  It will take some time for that to be downlinked to SpaceX mission control; depending on their satellite connection Hans indicated "a day or two".)

Hopefully said data recording device isn't on the list of items that SpaceX's purchasing department would presumably be working to find replacements for this fine Saturday afternoon.  Or maybe hopefully its recorded on Go Quest.

I'd expect the recorders to be buried inside a lot of steel plate down in the hull somewhere. In fact I'd have two or three systems in different parts of the barge. And inside a fireproof container.

[cscott]

Considering how accurate the targeting was, regardless of how the actual landing went, I wonder how many more barge missions will be required before the powers that be at the Cape are comfortable with them doing a land landing?  If this attempt had been on land, about the worse that would have come out of it is the need to patch a few holes in the concrete pad.

My guess (above in this thread) was that the reservoirs were oversized on the next flight because they want to test deploying the legs earlier and using the grid fins for active stability control.  But perhaps I got it slightly wrong, and there are other different tweaks to the reusability kit they want to try out.  If that's the basic plan, there might be a longish sequence of ASDS landings as they incrementally expand their flight envelope.  They might defer dealing with all the paperwork at the Cape until they've finished their "test flight" series, however long that is, and are ready to move into production mode.

On the other hand, if it turns out that barge motion contributed to the hard landing and there's no easy/reliable fix, perhaps we'll see an accelerated move on-shore.

[NovaSilisko]

Must also remember that the stage has no roll authority from the engine as there's only one burning during the landing burn. Only thrusters, the grid fins, and the resistance to rotation of the wide legs. I can imagine the fins getting stuck into a roll position, spinning up the stage, and causing the legs to shear off sideways on impact, or even causing a bit of fuel starvation like happened in the CASSIOPE return.

[cscott]

(The rest of the telemetry data was captured by the ASDS -- it began receiving telemetry at T+1:45 or so.  It will take some time for that to be downlinked to SpaceX mission control; depending on their satellite connection Hans indicated "a day or two".)

Hopefully said data recording device isn't on the list of items that SpaceX's purchasing department would presumably be working to find replacements for this fine Saturday afternoon.  Or maybe hopefully its recorded on Go Quest.

I think it's actually on Go Quest -- didn't someone identify a largish dish antenna on Go Quest, up-thread?  I was using ASDS loosely to refer to the flotilla.

[avollhar]

Given the complexity of today's attempt I am seriously impressed that they managed to hit the barge ... And go public with their first post mortem analysis in less than 12h. Elon is absolutely right to be proud of his crew! All fingers crossed for attempt #2 with DSCOVR!

[rcoppola]

Considering how accurate the targeting was, regardless of how the actual landing went, I wonder how many more barge missions will be required before the powers that be at the Cape are comfortable with them doing a land landing?  If this attempt had been on land, about the worse that would have come out of it is the need to patch a few holes in the concrete pad.

Impossible to predict exactly how many but certainly they'll want a couple in a row from different mission profiles to land successfully on the ASDS. Besides, they don't have LC-13 at CC ready to receive a returned core yet. So they couldn't even if they wanted to and I don't recall the construction timeframe, if any has been been stated.

2015 may turn out to be the year of the ASDS exclusively unless they can pull it off later this year at VAFB first.