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

[Antares]

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?

Precise location of the barge.  If I'm trying to land, I'd like to know where the airport is; especially if it's an autonomous mobile platform.

[Antares]

We saw quite a lot of the S2 LOX tank after Dragon sep.  I wonder if they were doing some S2 reuse experiments as well?

For me, it is more likely that they want to have data for better estimations of fuel left. In space, gauging fuel level is surprisingly hard problem.

Not unusual for a new vehicle to collect temperature data for longer missions after the primary mission is over.  Depending on how much is left, there could be restart demos.

[SoulWager]

Lets go through the possible causes of a hard landing:

Run out of fuel before altitude reached 0.
More fuel than expected decreased the acceleration.
targeted altitude was below the surface of the barge at impact (waves?)
targeted altitude was above the surface of the barge, causing a fall after v=0 and engine cutoff.
control software didn't get a reliable altitude input.
engine failure or slow ignition.
one or more legs failed to fully deploy.

And possible consequences of the hard landing:

Legs compress beyond design limits and break, allowing the rocket to tip over
Legs don't break, but the bounce tips the rocket over.
Engines bottom out into the deck.
Tank walls buckle.
Tank walls rupture then buckle.

Anyone see a possibility I missed?

[NovaSilisko]

One possibility: It hit the barge, but missed the pad, and came down on the support equipment.

[JamesH]

Legs failed to deploy.
Orientation of stage at burn time 'non-optimal' - wind sheer etc
Landing partly of side of barge.

[Pete]

Ok, so for this mission we have:

Primary mission: Dragon launch. check
Stage 1 retroburn, reentry. check
Stage 1 targeting. Actually hit the barge, check. Much better than the previous +- 10 km targeting.

So it manages all except the final landing perfectly.
Either landed sufficiently off-center so as to fall off,
or it landed with too high residual velocity.
Vertical or horizontal speed could have been off, but seeing as horizontal aim was spot-on +- 50 feet
I'm thinking it simply landed right on target, but either 10 feet up in the air or 10 feet below the deckline

Landing ballistically with a TWR >> 1 and only one chance to shut down engines, and (comparitively) slow throttle response time must be a very, very interesting control problem for the engineers.

[mmeijeri]

Do you mean thermal infrared? Because I 'm not sure that ordinary infrared would have helped much, it's still as dark, it will still see some fog and the stage would still be much brighter than anything else.

I found this link with video, which mentions short wave infrared.

I think the end result would be much the same, especially if what Elon was talking about was video shot from the ships ~10 miles away.

Ah. Maybe in the future they'll have camera's on the barge itself. And maybe a couple of quadrotors!

[Mader Levap]

Ah. Maybe in the future they'll have camera's on the barge itself. And maybe a couple of quadrotors!

I think they DO have cameras on barge. I don't think these would see much except blurred flame in last moments, though.

[Pete]

Lets go through the possible causes of a hard landing:

We know it ended up right at the barge, so reentry profile, braking burn, etc.. have to be just about perfect.
We know that there is damage to support equipment, but vessel is basically intact. So whatever collision/impact happened, happened *very gently* (as such things go). No 300km/h impact to deck due to early engine cutoff, etc.

>Run out of fuel before altitude reached 0.
If it did, it was only *right* before the end.

>More fuel than expected decreased the acceleration.
No chance. The systems would know the fuel remaining down to the last kg, as a resultant from the previous burn. Significant deviation of fuel mass would have skewed the braking burn's effect.

>targeted altitude was below the surface of the barge at impact (waves?)
>targeted altitude was above the surface of the barge, causing a fall after v=0 and engine cutoff.
Both of these is possible, but unlikely. We know that the landing stage has on-board radar altimeter.

>control software didn't get a reliable altitude input.
Requires a malf in the software, or hardware of the altimeter.

>engine failure or slow ignition.
even 1/2 second delay would result in a high-speed impact, more damage.

>one or more legs failed to fully deploy.
Very possible.
Or, leg deployed and failed to lock
Or, leg deployed correctly, but 1 or more leg trying to stand on open air off side of deck.
Or, leg deployed fine but failed under landing shock
Or, leg deployed fine, but 1 or more leg trying to balance on obstacle on deck (such as the damaged support equipment)
Or, lands perfectly, but residual horizontal motion is too much for RCS to compensate, and it gently tips over, rips through some support equipment, and slides off the deck.

[eriblo]

Do you mean thermal infrared? Because I 'm not sure that ordinary infrared would have helped much, it's still as dark, it will still see some fog and the stage would still be much brighter than anything else.

I found this link with video, which mentions short wave infrared.

That was actually better than I thought, so forget that part unless "foggy" was more pea soup than ocean haze It would still be awfully dark though.

I think the end result would be much the same, especially if what Elon was talking about was video shot from the ships ~10 miles away.

Ah. Maybe in the future they'll have camera's on the barge itself. And maybe a couple of quadrotors!

They most likely have, they knew the state of the barge almost immediately. And i think they have even confirmed UAVs, but flying them on a dark and foggy night from 10 miles away might be a bit gutsy. Especially on the first landing attempt...

[jak Kennedy]

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?

Differential GPS?

I would imagine they use RTK-GPS.  Maybe put a base station on the ASDS. A high accuracy position of the ASDS isn't necessary just a high accuracy between it and the Falcon 9.

Edit: RTK - Real Time Kinematic

[malu5531]

>More fuel than expected decreased the acceleration.
No chance. The systems would know the fuel remaining down to the last kg, as a resultant from the previous burn. Significant deviation of fuel mass would have skewed the braking burn's effect.

How about unexpected vehicle mass when performing T/W>>1 landing burn, due to ice and soot build up during free fall, moments before landing burn? With the control system unable to compensate in time (slow throttle response).

[Jakusb]

I just watched the replay and got a couple of questions.. Awesome launch btw 
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?
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?
3) What about the piece of something that floated of at solar deployment... Is this normal? Is this allowed?

But again, awesome launch! really thrilled to hear so clear updates on S1 too. And the camera shot of S1&S2 LOX tanks was amazing..

Congrats SpaceX!

[Ben the Space Brit]

To me, the most likely caues of the recovery failure were:

1) Centre engine did not fire (hardware);
2) Centre engine fired too late and the core was going too fast on contact (probably need to double-check the altimeter radar and maybe tweak the software).

However, this is positive in one important way. What is that? It hit the barge. That means that the guidance/navigation part of the descent is pretty much in-the-bag. All that needs to troubleshoot is the actual landing sequence.

So, yeah, Elon was right to say that there were more positives than negatives.

[edit]
I doubt that there was a big 'boom' either. There would have been very little propellent left in the tanks so it would have been more a case of high-velocity flying debris when the vehicle broke-up on contact.

[Jim]

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

1. they are used to jettison the nose cap
2.  it was stage two
3.  it happens

[toruonu]

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

Are you sure. I'd have to re-watch the launch, but I do remember too that I saw the LOX tank going weightless and relatively empty and then MECO happened at the same time. That's why I too assumed it was S1 tank as I'd have expected S2 tank to be quite full at the time still. But I'm writing from memory of a live event so probably should go and re-watch the coverage once it's up on youtube or what not.

[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.

[Jakusb]

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

Are you sure. I'd have to re-watch the launch, but I do remember too that I saw the LOX tank going weightless and relatively empty and then MECO happened at the same time. That's why I too assumed it was S1 tank as I'd have expected S2 tank to be quite full at the time still. But I'm writing from memory of a live event so probably should go and re-watch the coverage once it's up on youtube or what not.

See attached. Looks really different from S2 images and went weightless at startup of S2!

[laszlo]

US Naval aviators are basically the best in the world (not jingoism, just a result of the amazing amount of resources put into training and equipping them), yet even they are pushing their limits when it comes to a low-visibility night carrier landing. And that's with a 1000 foot target equipped with the best active landing aids available. So is it any wonder that Falcon, which has only "trained" on land makes a hard landing on its first try? I'm betting that it was the wave action messing up the closing rate calculation, BTW.

On the other hand, Elon is now the proud owner of the first commercial IRBM anti-shipping bombardment system.

Alternatively, he could settle his patent dispute with Bezos by licensing his system as the Amazon maritime package delivery drone.

Cigar next time.

[ugordan]

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: