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

[Hauerg]

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

Lon twittered "next month".

[inventodoc]

The landing could have failed in at least three ways.

1. Grid fins froze in a non neutral position, putting the stage out of control at the last moment.
2. Lack of grid fins movement resulted in excess need for gimballing and nitrogen thrusters. Perhaps resulting in rocket being at an angle while attempting to maintain course, resulting in landing on 1-2 legs first, buckling structure.
3. Reduced control authority resulted in hitting ground equipment.
Add your own.... we will probably know in a couple days....

[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?

It was 7 minutes in.  It's interesting to watch the body language of the two controllers watching the video.  They're practically yawning.  They've seen re-entry videos before (though without the fins of course).

So fins deploy in vacuum, cool.

[samoo]

There's an image of F9's 1st stage deceleration burn on Reddit http://www.reddit.com/r/spacex/comments/2rybgo/stage_1_deceleration_burn_viewed_from_causeway/

[Lee Jay]

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.

And will get you the opportunity to explain yourself to the EPA.

[Avron]

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.

And will get you the opportunity to explain yourself to the EPA.

hydraulic fluid in this case could be beet juice  or prune juice to really get things going

[Mader Levap]

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?

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

While I think they will want more barge landings, it is quite inprobable it was "pure luck".

[somepitch]

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.

And will get you the opportunity to explain yourself to the EPA.

There are vegetable-based hydraulic oils available

[Avron]

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?

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

While I think they will want more barge landings, it is quite inprobable it was "pure luck".

odds for pure luck would be astronomical ..  them spx avionics folks did a top notch job..

[JamesH]

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.

And will get you the opportunity to explain yourself to the EPA.

As I commented above, some military jets have total loss hydraulic systems (see pictures of Panavia Tornado and all the crud that ends up on the tailplane), airliners dump all sorts of crap in to the air whilst flying along. Are the EPA really going to be that bothered?

[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.

And will get you the opportunity to explain yourself to the EPA.

??  open system hydraulics have been used on numerous aerospace vehicles (see Conestoga LV, for example).

[OxCartMark]

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.

One factor that pushes contrary to earlier than necessary leg deployment is that in the GH videos we've seen some smoke or vapor coming off the legs during descent due I assume to descending into 'warmer' air and IR heating.  Those were steel legs (possibly coated with paint or something ablative that generates the smokey trail).  For the carbon / epoxy (presumed) legs on the real thing you'd want to minimize heat exposure, especially if the goal was to re-use them many times without a recoating process.

Counter arguments to what I'm saying here is that a real (non-grasshopper) landing may expose them to less heat due to a) more airflow due to higher descent speed and b) less time that the legs are out there (relative to GH) even if the legs deploy earlier than they have in past ocean landings.

[JamesH]

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?

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

While I think they will want more barge landings, it is quite inprobable it was "pure luck".

odds for pure luck would be astronomical ..  them spx avionics folks did a top notch job..

I do agree that it is in all likelihood a top notch bit of engineering and computer skill that meant they hit the barge first time.

But pure luck is still a possibility, albeit a small one. And hence they will need to do it a number of times before they get to land anywhere near inhabited land.

[rcoppola]

Concerning telemetry, recorders, etc.:

Mission Control stated, "Landing platform has received acquisition of signal." This was stated before MECO or 2nd Stage Sep. I heard that as meaning the first stage has locked onto the position of the ASDS as it's return target.

Now, I know the core return is autonomous but does it use the ASDS as its' target as opposed to each, the core and the ASDS having the same GPS coordinates pre-programed and they each autonomously stay, arrive at the same location?

Or is the ASDS given its' hold coordinates, the core is pre-programmed with the same but can and does lock its' return path to the ASDS and can then account for any motion, height variations autonomously?

I also got the sense that it doesn't mean the ASDS stores the telemetry, ie. recorders, but rather Go Quest would be the safer option.

[OSE]

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.

Nice catch.

Mattthew

Any of our video editing experts think they can subtract the mean from that video at 11:10 to get a better look at the reflection?

[Norm38]

Well I'm encouraged that they've already identified a fault and will have it corrected for the next flight.  Using every 1st stage they can as free experiments is really paying off for them.  It's a shame they lost F9R Dev1 though, they might have found this issue sooner.  But no harm done and they keep learning.

[meekGee]

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.

There's telemetry.  They can show exactly how in control they were.

[Grandpa to Two]

I found video on YouTube that says he caught the first burn by the first stage. It's apparently edited down for lots of black screen looking for the burn after MECO.

[Kabloona]

Concerning telemetry, recorders, etc.:

Mission Control stated, "Landing platform has received acquisition of signal." This was stated before MECO or 2nd Stage Sep. I heard that as meaning the first stage has locked onto the position of the ASDS as it's return target.

It sounds to me just like MC said: the barge (or GO Quest?) locked onto a signal from the rocket, probably a telemetry stream.

This has been discussed to death elsewhere, but I doubt the stage is receiving anything from the barge. It's guiding itself to pre-programmed GPS coordinates and expecting the barge to be there, then landing with whatever radar system they tested on GH in order to judge vertical distance from the deck. IMHO.

[Avron]

Concerning telemetry, recorders, etc.:

Mission Control stated, "Landing platform has received acquisition of signal." This was stated before MECO or 2nd Stage Sep. I heard that as meaning the first stage has locked onto the position of the ASDS as it's return target.

It sounds to me just like MC said: the barge (or GO Quest?) locked onto a signal from the rocket, probably a telemetry stream.

This has been discussed to death elsewhere, but I doubt the stage is receiving anything from the barge. It's guiding itself to pre-programmed GPS coordinates and expecting the barge to be there, then landing with whatever radar system they tested on GH. IMHO.

I am speculating that they may have a localizer on the Barge that the vehicle locks on for final landing adjustments