Author Topic: SpaceX Falcon 9 v1.1 - SpX-6/CRS-6 DRAGON - Discussion Thread (Read 488704 times)

Earendil · « **Reply #260 on:** 04/14/2015 08:50 pm »

I always assumed hitting the tiny drone (compared to the ocean) from space will be the hard part..
It appears vertical velocity is way harder.. especially when they cannot hover..

'There are mere seconds for reaction and no one can know if the drone will be +10 or _10 feet in the next couple of seconds.. Maybe the engine cannot react so quickly.. is this a dead end? (for ship landing at least)

aceshigh · « **Reply #261 on:** 04/14/2015 08:51 pm »

Quote from: Kaputnik on 04/14/2015 08:46 pm

Quote from: aceshigh on 04/14/2015 08:43 pm
Quote from: meekGee on 04/14/2015 08:16 pm
Just remember people, this is all about ISS supply, not about recovery.

Who am I kidding.

I guess there would be more people cheering here if the Dragon had "punched" the ISS and the 1st stage had docked perfectly with the barge.

I think you are on your own with that one.

it was just a clear exaggeration to show how much people wanted to see a successful first stage perfect landing.

Kabloona · « **Reply #262 on:** 04/14/2015 08:54 pm »

Quote from: Elmar Moelzer on 04/14/2015 08:50 pm

I think the problem could have been that the drone ship suddenly moved up in some way...

Drone Ship ‏@TheDroneShip 22m22 minutes ago
Sorry guys... I sneezed.

Unlikely, since wave height was around 3 feet, which is practically zero for a barge that size.

VulcanCafe · « **Reply #263 on:** 04/14/2015 08:54 pm »

Elon twitter
Looks like Falcon landed fine, but excess lateral velocity caused it to tip over post landing

aceshigh · « **Reply #264 on:** 04/14/2015 08:55 pm »

Quote from: Kabloona on 04/14/2015 08:52 pm

Quote from: VulcanCafe on 04/14/2015 08:46 pm
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...

aceshigh · « **Reply #265 on:** 04/14/2015 08:57 pm »

Quote from: VulcanCafe on 04/14/2015 08:54 pm

Elon twitter
Looks like Falcon landed fine, but excess lateral velocity caused it to tip over post landing

that was my first impression from the reaction of people on the control room... celebration (it landed) followed by hands on their heads (it tipped over).

but it seems the wording used on twitters later, like saying the 1st Stage had "punched" the barge, made it seem like it had "impacted" the barge at considerable speed.

thinking it now, it wouldn´t make sense for people at the control room to even celebrate for half a second if the rocket had crashed hard on the barge... it´s not like they would celebrate before touch down nor seeing an impact at 100, 200 km/h.

the twitter wording threw us off.

I wonder if this horizontal speed problem is a bigger problem than vertical speed problem.

litton4 · « **Reply #266 on:** 04/14/2015 09:00 pm »

A couple of pictures up there already:

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

Lars-J · « **Reply #267 on:** 04/14/2015 09:00 pm »

Quote from: litton4 on 04/14/2015 09:00 pm

A couple of pictures up there already:

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

Rocket Science · « **Reply #268 on:** 04/14/2015 09:02 pm »

Who knows, maybe my "snare" idea might have saved it...

abaddon · « **Reply #269 on:** 04/14/2015 09:03 pm »

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...

Lars-J · « **Reply #270 on:** 04/14/2015 09:04 pm »

Quote from: abaddon on 04/14/2015 09:03 pm

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...

They have the video, so they should be able to tell if the stage was drifting horizontally during landing, or if something else (wave motion or wind) caused it to tip.

Rocket Science · « **Reply #271 on:** 04/14/2015 09:05 pm »

Quote from: abaddon on 04/14/2015 09:03 pm

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...

They wouldn’t provide much control authority at low speed...

aceshigh · « **Reply #272 on:** 04/14/2015 09:05 pm »

@ElonMusk

"All we have right now is low frame rate video (basically pictures). Normal video will be posted when ship returns to port in a few days."

Lars-J · « **Reply #273 on:** 04/14/2015 09:07 pm »

Quote from: aceshigh on 04/14/2015 09:05 pm

@ElonMusk

"All we have right now is low frame rate video (basically pictures). Normal video will be posted when ship returns to port in a few days."

So this tells use that the barge does not have the bandwidth to broadcast full live video at the moment. (something they will probably fix in the future)

mrhuggy · « **Reply #274 on:** 04/14/2015 09:08 pm »

Quote from: aceshigh on 04/14/2015 08:55 pm

Quote from: Kabloona on 04/14/2015 08:52 pm
Quote from: VulcanCafe on 04/14/2015 08:46 pm
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.

abaddon · « **Reply #275 on:** 04/14/2015 09:09 pm »

Quote from: Rocket Science on 04/14/2015 09:05 pm

They wouldn’t provide much control authority at low speed...

Right, but as long as the first stage is close to the barge in the X and Y, the engine has control authority to spare. It's only if the rocket is somewhat far away that the engine wouldn't have time to get the rocket over and null horizontal velocity from getting there before running out of Z.

Of course, this is complete speculation. Hopefully we get more information soon!

Kaputnik · « **Reply #276 on:** 04/14/2015 09:09 pm »

Quote from: mrhuggy on 04/14/2015 09:08 pm

Quote from: aceshigh on 04/14/2015 08:55 pm
Quote from: Kabloona on 04/14/2015 08:52 pm
Quote from: VulcanCafe on 04/14/2015 08:46 pm
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.

No, the grid idea was merely speculation whilst we waited for better information. The deck is now known to be just steel plate.

Sohl · « **Reply #277 on:** 04/14/2015 09:09 pm »

Quote from: mrhuggy on 04/14/2015 09:08 pm

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.

Don't think it is a grating, and if the radar has the right wavelength, they should get plenty of signal anyway.

Lars-J · « **Reply #278 on:** 04/14/2015 09:09 pm »

Cool things in the launch broadcast:

- The nose cone was very visible dropping past the upper stage rocket cam
- A nice new graphic showing the planned stage 1 and stage 2 trajectories (see image)
- Wonderful to see the solar arrays deploy from the upper stage (and the RCS thrusters are now keeping it very stable, no tumbling)

John Alan · « **Reply #279 on:** 04/14/2015 09:12 pm »

It look like it landed on the edge of the deck then fell overboard... $:-\$
Three paws on and one off... momentum then rolled it off... pivoting on the engines...
That's my guess looking at the above two pics posted...

Better video should clear this up...

Oh... and I lost in the bingo pool... I think...