Falcon 9 / Dragon CRS-6 ISS resupply


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FloatingFatMan

So it landed OK?

 

Looks like the bottom swings out just as it makes contact with the landing platform, tipping it over.  Hard to tell though, at the video cuts off at that point.

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Steven P.

Yeah that's what I saw too, hope they were successful!

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DocM

It didn't land intact. A sluggish throttle valve caused the terminal guidance to slew it left/right on final approach, then one leg touched down and it tipped over. Now that they know the problem they'll fix it and try again with CRS-7, current set for June 22. The launches before then are going to higher geostationary orbits, which means no fuel for landings

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DocM

Hearing a leg may have failed due to the off nominal impact.

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SALSN

Wow, that top cold gas thruster is trying at the end, but too much weight.
I can't remember if this has been mentioned, but Is all the manoeuvring done by cold gas thrusters, or can the middle Merlin Engine pivot as well?

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DocM

All 9 Merlins gimbal but only the center one is used for landings. The problem here was a throttle lag from static friction (stiction) in the propellant valve. This valve controls both the RP-1 and LOX.

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Unobscured Vision

That's good news.  (Y)

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anthdci

Looks so close! I thought the barge was huge, but it looks tiny in comparison to the 1st stage. It is no wonder the stage is lost if it falls over.

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Beittil

Well, the landing deck is roughly 52 m

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DocM

Think in terms of landing a 14 story building on the 50 yard line of a football field. The scale boggles. Now imagine landing the BFR core, which will make F9 look like a toothpick.

Aviation Week article....

SpaceX Checks Throttle Valve After Flawed Falcon 9 Recovery Attempt

COLORADO SPRINGS SpaceX is thought to be focusing on static friction in an engine throttle valve as the prime suspect for the loss of the Falcon 9 first stage during the third attempt at recovering the booster.

The Falcon 9 was seconds away from what would have been the first successful landing of a used booster stage on SpaceXs Autonomous Spaceport Drone Ship (ASDS) when the vehicle toppled over and was destroyed. The landing attempt occurred following the launch on April 14 of SpaceXs sixth cargo resupply mission to the International Space Station from Space Launch Complex 40 at Cape Canaveral Air Force Station, Florida.

Video of the stage descending to the landing ship showed the vehicle approaching quickly but decelerating. However, closer to the platform the Falcon 9 showed an excessive horizontal velocity component that prompted the single engine used for landing to gimbal to correct the flight path angle. Exhaust from the Merlin engine could be seen raising clouds of water from around the platform as the stage maneuvered close to the edge of the landing zone. The control system then commanded vectoring of the engine nozzle to an angle that effectively over-compensated for the previous flight path angle correction. By this time the vehicle was too low to make further corrections and landed at too great a tilt and speed to safely land.

SpaceX founder and chief technology officer Elon Musk tweeted that excess lateral velocity caused it [the booster] to tip over post landing. In a later tweet that was subsequently withdrawn, Musk then indicated that the issue was stiction in the biprop throttle valve, resulting in control system phase lag. In this statement, Musk was referring to stiction or static friction in the valve controlling the throttling of the engine. The friction appears to have momentarily slowed the response of the engine, causing the control system to command more of an extreme reaction from the propulsion system than was required. As a result, the control system entered a form of hysteresis, a condition in which the control response lags behind changes in the effect causing it.

Despite the failure of the latest attempt, SpaceX will be encouraged by the landing accuracy of the Falcon 9 and the bigger-picture success of its guidance, navigation and control (GNC) system in bringing the booster back to the drone ship. The GNC also worked as designed during the prior landing attempt in January, which ended in the destruction of the vehicle following a hard touchdown on the edge of the platform.

>

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DocM

View from the ASDS JRtI. Looks like 2 legs failed, but otherwise it was in great shape.

https://vid.me/i6o5

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DocM

YouTube of above

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DocM

Dragon is at the grapple capture point.

The ISS approach has been textbook - almost as if it were on rails.

30f4ada6127c63dd304656e59ba683c4.jpg

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Beittil

Excuse me... there is some debris in your face :D

index.php?action=dlattach;topic=36326.0;

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DocM

Italian astronaut Samantha Cristoforetti grappled the Dragon in Kathryn Janeway style, also referring to their new zerp-G espresso machine.

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FloatingFatMan

OK, she is now officially the coolest astronaut EVER!

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Unobscured Vision

... and she's cute on top of being smart and cool. That's a fantastic mix. :yes:  (Y)

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DocM

Elon tweeted a new image of the big rocket that tried so hard to land. Easy to see why a leg or two let go.

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