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

[Proponent]

1) At some point I heard: "Nose cone pyros triggered" --> I thought there were no pyros used... Anyone can help understand what these are about?

As said by Jim, nose cap jettison.
Pyros are used also for Dragon-Trunk separation and for solar panels fairings jettison.

As said by Jim, nose cap jettison.
Pyros are used also for Dragon-Trunk separation and for solar panels fairings jettison.

So it's just the payload fairing (not used on this flight, of course) that has no pyros?

I do recall SpaceX crowing about the lack of pyros somewhere.  Would this have been in the payload fairing (obviously not flown on this flight)?  Are there any other functions performed normally performed by pyros where SpaceX does without?

[abaddon]

I do recall SpaceX crowing about the lack of pyros somewhere.  Would this have been in the payload fairing (obviously not flown on this flight)?  Are there any other functions performed normally performed by pyros where SpaceX does without?

Stage sep, fairing sep.

[malu5531]

3) What about the piece of something that floated of at solar deployment... Is this normal? Is this allowed?

My impression was that it was some ice.

[Jarnis]

2) I briefly saw a screenshot of seemingly the inside of the LOX tank of S1!? --> So there must be video of at least that camera up to landing/exploding.... Likely never to be published publicly, but would be awesome to at least have something on L2?

2.  it was stage two

He's probably thinking of the one on the left:

That appears to be a view from inside the interstage towards the departing second stage.

[Jim]

So it's just the payload fairing (not used on this flight, of course) that has no pyros?

I do recall SpaceX crowing about the lack of pyros somewhere.  Would this have been in the payload fairing (obviously not flown on this flight)?  Are there any other functions performed normally performed by pyros where SpaceX does without?

Payload separation (not Dragon) is done by pyros.

[cambrianera]

1) At some point I heard: "Nose cone pyros triggered" --> I thought there were no pyros used... Anyone can help understand what these are about?

As said by Jim, nose cap jettison.
Pyros are used also for Dragon-Trunk separation and for solar panels fairings jettison.

As said by Jim, nose cap jettison.
Pyros are used also for Dragon-Trunk separation and for solar panels fairings jettison.

So it's just the payload fairing (not used on this flight, of course) that has no pyros?

I do recall SpaceX crowing about the lack of pyros somewhere.  Would this have been in the payload fairing (obviously not flown on this flight)?  Are there any other functions performed normally performed by pyros where SpaceX does without?

They use pneumatics cylinders for staging and payload fairing.
There should be pyros also for emergency removal of grapple door on Dragon.

As usual, SpaceX is one step beyond in doing things, and two step beyond in crowing about what they do.

[ugordan]

That appears to be a view from inside the interstage towards the departing second stage.

It is not. There is visible liquid sloshing from the separation kick shortly after that.

[speedevil]

Considering the "pieces" statement and Elon's penchant for understatement, I expect it was quite hard. If not hard enough to punch right through the deck plating.

Assuming for the moment it's coming down vertically, and neglecting the legs.

The deck is 20mm thick steel, and is rated for 20 tons per square meter.
The rocket weighs about 20 tons, and has an area of around 10m^2.
The engine bells are almost ideally designed as crumple zones.

Neglecting _much_ stuff, and assuming that the decks failure limit for prompt loading is 60 tons/m^2.

This is 600 tons - conveniently about the launch thrust of the F9.

Assuming for the moment, the engines crumple with that amount of force consistently over 1m, it's decellerating at 30G.

This means that at ~25m/s - the stage can come to a stop on the deck with crumpled engines. (and then fall over and the tanks burst on the sharp steel containers and things), and do 'not much' damage.

This is a really substantial velocity - it's a quarter of the pre-landing-burn velocity, equivalent to falling from about 30m up.

It doesn't take much below this to get to the utterly normal specified loads of the barge.

The question of if the stage has enough integrity to puncture the deck - even at unbraked speed is an interesting one.
It will certainly take it way out of spec - and buckle bits of it - but the stage may well 'shatter' well before the puncture limit.

[cscott]

During ascend at around 1:45 into the flight, the launch radio said "Landing platform received aquisition signal" or something along that lines. What does that mean? Do they have a data link between the rocket and the ASDS? If so, what data are they transmitting?

This is referring to the telemetry information.  In the prelaunch presser Hans was very clear about this: the first stage comes down "over the horizon" from the Cape (and from other tracking resources) and so the descent telemetry needs to be acquired by a receiver close to the landing site.  Remember that on the CRS-3 landing SpaceX had to fly Elon Musk's personal jet over toward the landing site with a pie-plate antenna in the window to capture the telemetry stream.  At T+8:26 you can hear them confirm that they lose telemetry with the first stage as it descends above the horizon.

The ASDS now captures that telemetry stream, and Elon referred to this in his "will piece it together' tweet.

It is still rather controversial whether there is additional data exchanged between ASDS and the core, but again Hans was pretty clear in the presser that the stage is complete autonomous -- it is not being "controlled" from the ground -- and that the barge sits very still in one spot and the ASDS hits that spot. (That leaves a little opening for DGPS-style position sync, and there is probably an FTS on board that can be controlled.)

[guckyfan]

Can we safely assume there was a landing burn? The assumption is that without one the stage would miss the barge.

[Remes]

We know that the landing stage has on-board radar altimeter.

Which, I assume, will be useless once the engine fires and the plume comes between the rocket and the alitmeter. So after the final engine firing the rocket will descent open loop. Startup of the engine might not have a very high repeatability, leading to a lot of uncertainty.

But regarding the radar altimeter: as an engine nozzle more or less reflects downward (similar to a corner reflector) it might have a very good signal (with nothing else around to disturb). Using the doppler effect it might also give a very good estimate on the velocity.

[SoulWager]

I wonder if a microphone could be used as an altimeter, picking up the noise reflected by the landing surface.

[Raj2014]

I just found this on www.spaceflightnow.com Apparently they were planning to do another test on 29th January but it has not been confirmed and SpaceX officials said they were determined to conduct more recovery experiments on future missions. I hope they will do another test as soon as possible.

[cscott]

We know that the landing stage has on-board radar altimeter.

Which, I assume, will be useless once the engine fires and the plume comes between the rocket and the alitmeter. So after the final engine firing the rocket will descent open loop. Startup of the engine might not have a very high repeatability, leading to a lot of uncertainty.

This has already been tested on Grasshopper.  The radar altimeters on the legs work fine.

[hrissan]

Can we safely assume there was a landing burn? The assumption is that without one the stage would miss the barge.

Hitting ASDS @ 150 m/s with 20 tons stage would likely cause more damage than just replacing some on-deck equipment, though it may be argued the stage is "soft", SpaceX would probably try to avoid testing this scenario.

If the landing burn does not start, probably the grid fins will steer the rocket away from the ship, I do not know if fins have enough control authority to divert 200 meters sideways from 1500 meters altitude, if not, than hitting ship dead center might be better than hitting the side.

I follow the thread closely, and most posters think that there was rather small altitude/velocity mistake at landing, either too short burn due to low fuel or need to compensating for unexpected wing gust, or may be hardware itself worked flawless, but the software was targeting wrong altitude due to erroneous radar readings (detecting altitude of container top or ocean surface as a target) or software error.

IMHO if the stage landed perfectly, but crashed due to problem with leg, Elon would use different words, something like "landing is perfect, though toppled afterwards" or sometihng like this.

[cscott]

Oh, and WRT video: I'm fairly certain that SpaceX actually has quite a lot of video of the stage coming back: both on-board video telemetry captured by the ASDS, as well as cameras of various sorts on the ASDS itself.  Hans indicated in the prelaunch presser that the satellite internet connection on the ASDS was spotty and very slow, and so telemetry and ASDS video would likely take "a few days" to publish.  So Elon probably didn't have any of that immediately in hand.  The stage hard-landed on the ASDS, which might have further complicated or delayed recovery of some of that data.

I take his tweet to mean that the video he had on hand *immediately in real-time* was poor quality due to darkness/fog/etc.  Probably low-resolution, too, due to the spotty internet.  Once they collect the non-real-time telemetry info and process it, I bet they'll have much better video -- including video of the interior of the first stage O2 tank, as a previous poster noted.

Not sure they'll publish it, though.  They tend to keep crash video close to their vest.  Perhaps if there's some nice shot of the stage descending pre-crash Elon might tweet it out.

[ugordan]

Since the propellant tank photo has a distinctly yellow tinge, versus the distinctly blue tinge we've clearly seen in the previous LOX tank interior photos, it is possible that the tank view we are seeing here is the stage 2 RP-1 tank? 

It's nearly empty and there's no LOX feedline running along the center so, no, it's not possible. Also, 2nd stage feed was already showing the view on the right. Only one camera feed per stage at any one moment.

[CardBoardBoxProcessor]

Cannot be the RP-1 tank as there is no central LOX feed line.

[JamesH]

I wouldn't trust the colours - I suspect an automatic white balance 'problem'. It's actually quite difficult to do auto WB in those sorts of situations. Would be better to manually set it based on the interior of the tank. Interesting that they must have lights in the tank though, as well as the camera.

[Jakusb]

Since the propellant tank photo has a distinctly yellow tinge, versus the distinctly blue tinge we've clearly seen in the previous LOX tank interior photos, it is possible that the tank view we are seeing here is the stage 2 RP-1 tank? 

It's nearly empty and there's no LOX feedline running along the center so, no, it's not possible. Also, 2nd stage feed was already showing the view on the right. Only one camera feed per stage at any one moment.

So this seems to strengthen my first assumption of it being the first stage LOX tank....

@Jim: any counter facts to the opposite? Or might this be one of the few times you were wrong? ;p