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The attempted landings on the drone ship all failed, while the landing on land was successful. As far as I'm aware, all major changes to the rocket were made to allow it to land on land, so I assume the two rockets are very similar.

Are there any significant differences between landing on the drone ship vs landing on land? Is landing on the drone ship somehow harder? Would the successful landing on land indicate increased chance of landing successfully on the drone ship?

Is it know if SpaceX will attempt another drone ship landing?

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  • $\begingroup$ the drone ship might have stability issues during stormy weather. considering falcon-9's 220 ft (68 meters) height it might cause tipping similar to last drone ship landing attempt. (Although it was not issue with the drone ship) $\endgroup$ – dvdmn Dec 22 '15 at 15:59
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    $\begingroup$ I think had this one attempted to land on a drone ship it would have succeeded this time. They were expecting to fail a few times while they learned how to do it - one of the failures was primarily down to running out of hydraulic fluid! I fully expect to see many successful landings on both drone ships and land from here on out, the target being chosen based on the payload profile. $\endgroup$ – James Thorpe Dec 22 '15 at 16:04
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Generally the information available indicates that there is no difference between the landing on a barge or on land in terms of the rocket itself.

The Falcon 9 1.1 Full Thrust (SpaceX continues to deny this is a 1.2 version, the theory behind that is that a change of 1.1 to 1.2 might imply a need to recertify a new version. It seems to assume people are stupid, which may be a correct assumption on this subject.) has all the modifications for landing period.

As they attempted the Grasshopper/F9DevR1 programs, they added and modified hardware to get better and better at landing. Then they tested it on a several flights, where the ASDS was not there, due to weather or other reasons.

They attempted two landings, and ran into two different hardware issues (Lack of hydraulic fluid for the grid fins first attempt, slow reacting valve second attempt) that were resolved in later builds.

This was just the next test in a long line of tests, and it succeeded.

Landing on the ASDS has complexities beyond that of LZ-1. The ASDS is a bit smaller, but if you look at the targeting in the second ASDS attempt, they got to the barge no problem. If you look at the video of the OG2 landing attempt, they hit the X marks the spot pretty much spot on. (I really want to know HOW close, and divide that by 160K to get a percentage of accuracy!)

There is a concern with the ASDS moving while a landing is under attempt. It has been noted that the ASDS is big enough, that a wave would have to be very wide in order to significantly make the ASDS tilt. Generally the arm chair critics do not consider this aspect to be a real issue.

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  • $\begingroup$ I don't think the size of the ASDS is a problem since they were pretty much spot on the during the first two attempts. The rocket is not that much different, so why did they switch to landing on land vs landing on the ASDS? To do the land landing they had to change the second stage, load more fuel, etc, etc. Wouldn't it been simpler to just fix what was wrong with the valve and attempt another ASDS landing? The only thing I can think off is that the ship might be rocking from the waves, but I can't convince myself that it would have been enough of a reason to switch the landing site. $\endgroup$ – ventsyv Dec 22 '15 at 16:27
  • $\begingroup$ @ventsyv Personally I think the main reason they did a land landing now was because of the way Blue Origin overstated their achievement (which was still cool) a month ago. $\endgroup$ – James Thorpe Dec 22 '15 at 16:33
  • $\begingroup$ @JamesThorpe I figured they thought the ASDS landing was close enough and if the valve would've worked, the landing would have succeeded, therefore they was no value in repeating that test and instead they moved to the next thing. To me that sounds very risky, so I was wondering if I'm missing something. $\endgroup$ – ventsyv Dec 22 '15 at 17:05
  • $\begingroup$ @ventsyv No that's also probably close to the truth - in reality they've been making huge steps with every test and probably had a very large amount of data showing that the next attempt would result in success. Combined with the upgraded rocket it meant a land landing was easily feasible on this mission profile, so why not go for it. I'm sure we've not seen pictures of so many people on previous attempts on the web streams before either, which leads me all the more to conclude it's very much been done for publicity :) $\endgroup$ – James Thorpe Dec 22 '15 at 17:06
  • $\begingroup$ The "Full Thrust" modifications needed for return-to-launch-site had been in the works for a while, and the delay after CRS-7 gave them time to complete them. I expect that if the next customer in line had a heavy payload they would have done a (successful) barge landing on a F9-1.1 instead. $\endgroup$ – Russell Borogove Dec 22 '15 at 17:41
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Landing on a barge is more difficult for 2 reasons:

  1. the size of the target is much smaller.
  2. the barge moves in 3 dimensions. Especially the pitching motion (up/down) gave them trouble:

The magic to a smooth landing is to make it so that you reach EXACTLY zero altitude at precisely the same moment when your forward motion puts you at the beginning of the runway, at the same instant that your lateral adjustment, with wind, puts you in the middle of the runway, while at the same instant you have ceased lateral motion against the wind and brought the yaw exactly parallel to the runway, at the same time roll goes to zero, while maintaining proper flare (pitch). In other words, the craft is moving in six dimensions* and you try to hit just the right mark in all six dimensions at precisely the same time. It's awfully tough to hit zero AGL at exactly the right time when the ground is moving up towards you, then down away from you. Too difficult for me to try in real life. SpaceX has had much trouble with this. They had the rocket perfectly vertical, and they were able to reach 0 AGL, but they couldn't do both at the same time - touch down while the vehicle was vertical. It's much easier to do that if zero AGL remains constant, rather than having the ocean move the barge up and down.

Having been on board a 30,000 ton ferry crossing the English Channel: wave motion is definitely a concern even in those ships which weigh approx. 15 times as much as the ASDS barge.

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