SpaceX Falcon 9 v1.1 - SpX-6/CRS-6 DRAGON - Discussion Thread

[SwissCheese]

I wonder if optical feedback wouldn´t work better than radar then? Maybe guiding lasers on the barge? Or just cameras on the rocket calculating the geometry of the SpaceX logo (and other visual clues) to give an accurate mesurement of distance and angle...

The problem with optical or laser systems is that they do not work in the final seconds when you have a lot of smoke/vapor/dust. That's also a problem for example for helicopters landing in the desert or on snow, and I know that they were testing landing radars for German army helicopters for example.

Radars are fine ! (I work on synthetic aperture radar data so maybe I am not totally neutral... )

[CraigLieb]

Seems like the leg closest to the camera would have hit the deck first at that angle, but may be fish-eye distortion.

[aceshigh]

I was writing something related to first stage landing technical hurdles that SpaceX has already retired, but clearly something is missing.

What technical hurdles are left to solve?

They've done soft touchdowns in water. Soft touchdowns on the barge are the final missing piece. They used landing radar in tests of the F9R Dev vehicle at McGregor, and presumably are using landing radar on the flight vehicles. The landing radar may be having difficulty discriminating between sea level height and barge deck height. (Speculation)

I wonder if optical feedback wouldn´t work better than radar then? Maybe guiding lasers on the barge? Or just cameras on the rocket calculating the geometry of the SpaceX logo (and other visual clues) to give an accurate mesurement of distance and angle...

Actually an issue with the radar would make sense. The landing pad (if i remember rightly) is not a solid surface but rather a grating. The radar rather than get a strong signal from it would get a weaker signal. A Ladar might have the same issue.

seems to be you are considering lasers FROM the rocket TO the barge, in which case the grating surface might be a problem.

I was talking about lasers ON THE barge, locking on the rocket as it approached. Am I making sense?

I wonder if optical feedback wouldn´t work better than radar then? Maybe guiding lasers on the barge? Or just cameras on the rocket calculating the geometry of the SpaceX logo (and other visual clues) to give an accurate mesurement of distance and angle...

The problem with optical or laser systems is that they do not work in the final seconds when you have a lot of smoke/vapor/dust. That's also a problem for example for helicopters landing in the desert or on snow, and I know that they were testing landing radars for German army helicopters for example.

Radars are fine ! (I work on synthetic aperture radar data so maybe I am not totally neutral... )

what if the lasers locked on the top of the rocket? Lasers mounted on the 4 corners of the barge... the farthest away possible from the bullseyes and thus less blocked by smoke, locking on the top part of the rocket?

[oiorionsbelt]

I wonder if any of it is still on the barge or did the whole thing " tip over post landing" and into the ocean.

[meekGee]

So does this mean the grid fins aren't effective enough?  The only reason I can think of for it to have too much lateral velocity is if it was thrusting laterally to get to the barge and didn't have enough height to do it and then null that velocity.  Which sounds a lot like the previous attempt...

It means the terminal approach required too large of a final correction.

There can be several reasons why that happened.  Lack of authority to perform the correct maneuver.  Wrong maneuver due to bad positioning data.  Last-minute external influence.  etc.

Hopefully Musk will clue us in.

[LouScheffer]

So does this mean the grid fins aren't effective enough?  The only reason I can think of for it to have too much lateral velocity is if it was thrusting laterally to get to the barge and didn't have enough height to do it and then null that velocity.  Which sounds a lot like the previous attempt...

This seems odd to me as well.  The job of the grid fins should be to deliver the rocket to just above the ship, with small enough residuals in velocity and displacement such that these can both be nulled by engine vectoring during the deceleration burn.  It looks like they were close enough to null the displacement, but not also the velocity.  I can't imagine this is an algorithm failure (surely they simulated nulling out both horizontal displacement and velocity) so I agree the fins were not as effective as they thought.

Maybe they are not big enough, hence not enough control authority, perhaps since engine-first aerodynamics in the lower atmosphere are yuckier than expected?  Maybe they ran out of fluid again - extra margins not enough? Maybe one or more fins failed to deploy?  It will be interesting to find out....

[RonM]

Seems like the leg closest to the camera would have hit the deck first at that angle, but may be fish-eye distortion.

It looks to me like it slid off the edge of the barge. Got to keep all three legs on the barge or over it goes.

[Lars-J]

Seems like the leg closest to the camera would have hit the deck first at that angle, but may be fish-eye distortion.

Yeah... There are no straight lines in this extreme wide angle view. You can't determine that. We don't even know for sure that the two frames are from the same camera. (they likely have a camera in every corner)

[sanman]

Maybe they need some sub-sonic control surfaces to supplement the hypersonic grid-fins?

[Lars-J]

Maybe they need some sub-sonic control surfaces to supplement the hypersonic grid-fins?

Grid fins work well both at hypersonic and subsonic speeds. That's why they are used. But there is a limit to how much they can do, given their size. And if the stage had a significant sideways motion, the fins can't stop that by themselves. It has to be done together by the landing burn *and* fins.

[Jcc]

Check out @SpaceX's Tweet: https://twitter.com/SpaceX/status/588082616890449920?s=09

Exhaust plume impinging on the white circle but stage seems to lean toward the center of the target, like it is trying to maneuver to the X, but too late. Wonder the direction it was coming from, if it overshot.
Also wpndering if we will be able to call a bingo winner.

[Lars-J]

Check out @SpaceX's Tweet: https://twitter.com/SpaceX/status/588082616890449920?s=09

Exhaust plume impinging on the white circle but stage seems to lean toward the center of the target, like it is trying to maneuver to the X, but too late. Wonder the direction it was coming from, if it overshot.
Also wpndering if we will be able to call a bingo winner.

If the two released frames are from the same camera (likely), then it was coming in from the left... drifting to the right, then tipping over.

[Mapperuo]

Check out @SpaceX's Tweet: https://twitter.com/SpaceX/status/588082616890449920?s=09

Exhaust plume impinging on the white circle but stage seems to lean toward the center of the target, like it is trying to maneuver to the X, but too late. Wonder the direction it was coming from, if it overshot.
Also wpndering if we will be able to call a bingo winner.

Remember its a fisheye camera, it may look to be leaning but its possibly dead vertical.

[AJA]

Seems like the leg closest to the camera would have hit the deck first at that angle, but may be fish-eye distortion.

Yeah... There are no straight lines in this extreme wide angle view. You can't determine that. We don't even know for sure that the two frames are from the same camera. (they likely have a camera in every corner)

This. I don't imagine the cameras are mobile. So if it was the same camera, we should be seeing the barge surface, and the flagpole on the right as well. I think they're both views of the same instant, but from different cameras. The direction of the sun (illumination source) reaffirms that guess too.

[mme]

Check out @SpaceX's Tweet: https://twitter.com/SpaceX/status/588082616890449920?s=09

Exhaust plume impinging on the white circle but stage seems to lean toward the center of the target, like it is trying to maneuver to the X, but too late. Wonder the direction it was coming from, if it overshot.
Also wpndering if we will be able to call a bingo winner.

I think there is way too much distortion in that image to determine the angle of the rocket.  But the next photo has it on the right, so it's moving left to right in the photo.

[drjrkuhn]

A couple of pictures up there already:

https://twitter.com/elonmusk/status/588082574183903232

The deck camera is stationary based on the position of the valve in the bottom-right. The lateral motion of the Falcon is quite apparent if you flip back and forth between the two images on twitter.

[Lars-J]

Seems like the leg closest to the camera would have hit the deck first at that angle, but may be fish-eye distortion.

Yeah... There are no straight lines in this extreme wide angle view. You can't determine that. We don't even know for sure that the two frames are from the same camera. (they likely have a camera in every corner)

This. I don't imagine the cameras are mobile. So if it was the same camera, we should be seeing the barge surface, and the flagpole on the right as well. I think they're both views of the same instant, but from different cameras. The direction of the sun (illumination source) reaffirms that guess too.

They cannot be from the same instant, judging by the size and placement, and smoke. Looking at details around the edge of the frame, they are likely from the same camera.

[Rocket Science]

They still got it to "grasshopper-mode" close so pretty dam impressive...

[Fr4nK]

So it looks like a bigger barge would have solve the problem?

[jaufgang]

I was writing something related to first stage landing technical hurdles that SpaceX has already retired, but clearly something is missing.

What technical hurdles are left to solve?

They've never done a landing on a solid surface from high altitude free-fall at terminal velocity.  All grasshopper and F9R-Dev tests had the engine firing continuously and a slow controlled descent.   A F9R-Dev test involving engine cutoff and a separate last moment landing burn has never been attempted, let alone succeeded.