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

[SoulWager]

It was doing in much faster than Grasshopper, *and* had to time the engine startup just right. Grasshopper or F9R-Dev1 never turned off its engine. The Grasshopper experience helps a lot, but this is a lot harder.

Are they that low on fuel margin that engine ignition has to be timed exactly?  I thought they'd be able to ignite, go to full thrust, slow down, and then throttle the engine down to handle the precision needed for touchdown.
But if they waited too long and were still slowing down at full thrust....

Even at minimum throttle their TWR is over 1. It's not a question of running out of fuel or getting the timing precise enough, it's a question of guessing how much the landing altitude will change based on the waves.

[OSE]

I wonder if maybe it was off by a large enough amount that it had to do a significant sideways divert, and ran out of fuel in the final seconds.

This sounds very plausible to me.

[ericspittle]

I, for one, am at least happy that Elon was so forthcoming with information about the landing. Given the statements at the presser last week I was concerned we wouldn't find out right away.

The fact that they hit the barge is a major success, and I am looking forward to the next launch (DISCOVR?) landing successfully on the barge.

I just hope the barge is ready in time.  Lots of specialized equipment on that barge that if damaged could take time to replace.  But as has been said here already, this is a great, great achievement.  To paraphrase Edison, they didn't fail.. just found another way that didn't work.

I've followed the ASDS thread fairly closely and most of what is on that barge has been identified; all of it is commercial equipment that (and I'm wish-casting here) should be able to be replaced fairly quickly.

I actually think that what they find out when they get the pieces home will be what determines whether they try for a landing on the next launch or not. Elon/Space X certainly isn't concerned about the money for rushing barge parts in to fix any damage, but if they think there was some error in the code that is supposed to land the first stage successfully they won't make another attempt until they think they've fixed the problem.

I'm hoping that the great folks here and on Reddit that have found several places to observe the barge coming and going may be able to shed some light on what the damage looks like and that may give us a better idea of what type of failure we're looking at. Given Elon's statements that the first stage was broken into pieces but came very close to landing I'm hoping that the problem was that a badly timed wave happened at the same time as the rocket was supposed to be touching down and it kind of just fell over.

[enkarha]

Even at minimum throttle their TWR is over 1. It's not a question of running out of fuel or getting the timing precise enough, it's a question of guessing how much the landing altitude will change based on the waves.

To paraphrase, maybe a little too much slam in that hoverslam.

[speedevil]

I actually think that what they find out when they get the pieces home will be what determines whether they try for a landing on the next launch or not. Elon/Space X certainly isn't concerned about the money for rushing barge parts in to fix any damage, but if they think there was some error in the code that is supposed to land the first stage successfully they won't make another attempt until they think they've fixed the problem. r.

Telementry is IMO more likely to give a prompt answer.
The fact it's on the deck in bits is inarguable, nor is the speed it hit.
Telemetry can tell you why.

Wind of 30mph would lead to the stage needing to be canted about 15 degrees.
Fighting a crosswind on landing is - I think - new.

[neoforce]

I'm hoping that the great folks here and on Reddit that have found several places to observe the barge coming and going may be able to shed some light on what the damage looks like and that may give us a better idea of what type of failure we're looking at. Given Elon's statements that the first stage was broken into pieces but came very close to landing I'm hoping that the problem was that a badly timed wave happened at the same time as the rocket was supposed to be touching down and it kind of just fell over.

Unless the barge has enough damage to head back to the original ship builder for refit?  then we don't get those great views of the return back to port to see the damage ourselves.

But yeah, I'll be optimistic for now!  Here is hoping for a quick refit.  Getting to the barge was a great step.

[meekGee]

I like the fuel hypothesis.

Since we know that nominal landings work well (from GH) then either there was a mundane failure (unlikely IMO) or the failure has to do with the inbound phase.

If the inbound phase put them just beyond the edge of the envelope, the final landing maneuver might have run out of fuel even a few feet high, resulting in a hard landing.

The deceleration on landing is such that if you stop thrusting before the end of the maneuver, you're still coming down pretty fast.

[the_other_Doug]

So -- the forum went down 40 minutes after launch?  Maybe a lot of people got their EST and CST, etc., confused and thought they were piling in to follow the launch and were running an hour late?

Or did everyone decide the launches are mundane and only wanted to check on the barge landing?

[neoforce]

So -- the forum went down 40 minutes after launch?  Maybe a lot of people got their EST and CST, etc., confused and thought they were piling in to follow the launch and were running an hour late?

Or did everyone decide the launches are mundane and only wanted to check on the barge landing?

Didn't Chris say once that the site gets hammered after the video feeds end?  People need to go somewhere to discuss it and NSF is the place to be!

[the_other_Doug]

So -- the forum went down 40 minutes after launch?  Maybe a lot of people got their EST and CST, etc., confused and thought they were piling in to follow the launch and were running an hour late?

Or did everyone decide the launches are mundane and only wanted to check on the barge landing?

Didn't Chris say once that the site gets hammered after the video feeds end?  People need to go somewhere to discuss it and NSF is the place to be!

That must be it, since the forum was working just fine until about T+40 min. and then got real sluggish, then crapped out altogether for about 10 minutes.

[meekGee]

What a difference between "picking up pieces" of F1 (how many years ago?) and "picking up pieces" today...

Too bad about the landing, but getting to "hit hard" on the first try is good enough to go to sleep happy.

It's been a very long time since something's gotten me this wired...

[dgates]

Are they that low on fuel margin that engine ignition has to be timed exactly?  I thought they'd be able to ignite, go to full thrust, slow down, and then throttle the engine down to handle the precision needed for touchdown.
But if they waited too long and were still slowing down at full thrust....

The engine has significantly more thrust than the weight of the stage - they cannot hover.

Huh?  If the vehicle has more thrust than weight, then it follows that it WOULD be able to hover.  Just not for very long, because the available fuel, I'd imagine, is quite low.

[Chris Bergin]

Yeah, it's weird, but a lot of people watch the live webcast and don't post. Then after it all happens they pile on the site to talk about it.

Just hit a bottleneck. Cleared after five mins.

[NovaSilisko]

Huh?  If the vehicle has more thrust than weight, then it follows that it WOULD be able to hover.  Just not for very long, because the available fuel, I'd imagine, is quite low.

Its minimum thrust level gives it a thrust-to-weight ratio of greater than 1. It needs exactly 1 to be able to hover.

[ericspittle]

I actually think that what they find out when they get the pieces home will be what determines whether they try for a landing on the next launch or not. Elon/Space X certainly isn't concerned about the money for rushing barge parts in to fix any damage, but if they think there was some error in the code that is supposed to land the first stage successfully they won't make another attempt until they think they've fixed the problem. r.

Telementry is IMO more likely to give a prompt answer.
The fact it's on the deck in bits is inarguable, nor is the speed it hit.
Telemetry can tell you why.

Wind of 30mph would lead to the stage needing to be canted about 15 degrees.
Fighting a crosswind on landing is - I think - new.

You're absolutely right, I just kind of considered the data gathered to be part of the pieces coming home

I suppose the physical damage won't tell them much that the telemetry doesn't, but so long as it returns to it's normal dock the physical damage might give us a teaser that Space X may not release to us right away. Now more than ever I wish that I was back to work so I could afford an L2 subscription.

[cscott]

Huh?  If the vehicle has more thrust than weight, then it follows that it WOULD be able to hover.  Just not for very long, because the available fuel, I'd imagine, is quite low.

The *minimum* thrust is still greater than the weight.  So once the stage hovers, it can only go up after that point --- until the engines are cut (or run out of fuel) and then it's gravity who's in charge.

And no, the stage can't toggle on and off rapidly.

There is a minimum thrust limit because the rocket combustion is unstable at low fuel pressures.

[Tonioroffo]

I'm curious how 'hard' the landing was.  However let's not forget this is another mission going well.  And the video from within the tank was beautiful!!

[mlindner]

I'm curious how 'hard' the landing was.  However let's not forget this is another mission going well.  And the video from within the tank was beautiful!!

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.

[ericspittle]

I'm curious how 'hard' the landing was.  However let's not forget this is another mission going well.  And the video from within the tank was beautiful!!

That was a really cool view. I woke my son up for the launch and he thought it was really cool to see what the inside of the tank in minimal gravity looks like.

[SoulWager]

I wonder if we'll get to see video from the onboard camera.