SpaceX News

[DeltaV]

Looking at the high res video from a distant viewpoint, looking at the direction of the flame from the engine, the flame is still tilted for faster rotation until shortly after the rocket passes vertical. Then it snaps over to the other side.

That's due to the unwanted "phase lag".

[ladajo]

As for what happens after landing I understand they are going to rush onto the platform and weld the legs down before moving the barge. And as far as stability goes there are many dampers that can make it steady as a rock. cruise ships use wings under the water and there is also the cone that can be deployed on barges to reduce pitching. And if you really wanted to get high tech you could mount one of those sway stabilizers they use in skyscrapers to stop sway from winds and earthquakes.
http://en.wikipedia.org/wiki/Tuned_mass_damper
http://gizmodo.com/5019046/how-a-730-to ... earthquake#

Active fin control (wings) only works when you are moving. And the bigger the thing, the faster you need to go for it to work.

As for the "cones", this may be a better answer. I have seen this done with other platforms with a degree of success.

Another means to help stabilize as well as improve transit times and station keeping would be to implement a SWATH design for the barge.

At the end of the day, I would probably not be thrilled to be a "Run Out Welder" on the barge. Still a big ass boom waiting to happen...

[Maui]

Would it be impractical to put magnets in the legs' feet? I'll guess at the answer:

Added complication and risk to the launch and leg operation, added weight, and not a very large increase in stability in return?

[krenshala]

Would it be impractical to put magnets in the legs' feet? I'll guess at the answer:

Added complication and risk to the launch and leg operation, added weight, and not a very large increase in stability in return?

If you were going to go that route, it would be much simpler to put an electromagnet (or a group of them) just under the deck of the barge and make sure to include ferromagnetic metal in the feet of the landing legs. Probably still not a great solution, but better than trying to add magnets to the rocket itself.

[ladajo]

I like the deck magnet idea, you could cover a large area, and the barge would only improve in stability. I don't think that the added weight would do anything but keep CG lower for the rocket/barge construct. And barges tend to have large amounts of reserve buoyancy.

You could even turn them on by zone, or have them auto trigger by field dynamics sensors once the feet touch down.
With the magnets placed under the deck in an array, and on at low power during the landing cycle, once the feet contact and disrupt the power feed (easily detectable) for the magnets the feet land over, then you could trigger full power feed selectively for those magnets.
The rocket would thus be more held in place until another locking mechanism can be brought into play.
You could even turn off the magnet set for the foot your team is securing or welding selectively. Thus they could address each landing foot individually in a much safer manner.

I am intrigued with this idea, someone should tell Musk...

Anyone ready to argue over IP rights...

[kunkmiester]

Is there steel in the legs?

[paperburn1]

Magnets on the legs would most likely be subject to high temperatures , this would rapidly reduce the holding power of any rare earth magnets.

[ladajo]

More supporting arguments to mount steel pads to the bottom of the feet (if not there already), and not put magnets on the booster feet, but in an under-deck array on the barge. I truly imagine at this point that there is a lot of unused volume inside that barge right now.

[KitemanSA]

If you just need to stabilize the barge, two simple options. Put an extensible, large area cruciform (or box-kite) keel under the barge and it will slow the roll rate of the barge thru large moment arm drag. Or, place what amounts to an inverse quad-copter off the corners of the barge and vary the thrust too counter the roll.

A SWATH probably wouldn't work due to the fairly large change in load and also due to the possibility that the load will be added quite off center. Swaths don't handle that well.

[ladajo]

Good point on the off center issue for SWATH.

The "boxkite" could also be 'deployable', once on station by having it pivot or lower into place. Thus reducing transit drag and port requirements.

The cones also work fairly well and have been used in other stable platform applications. Simple physics in action is always cool.

[paperburn1]

The after action photo
http://www.businessinsider.com/spacex-p ... ded-2015-4

[TDPerk]

A SWATH probably wouldn't work due to the fairly large change in load and also due to the possibility that the load will be added quite off center. Swaths don't handle that well.

I understand they handle it well if you can have large volumes which are pressurized by dumpvalves to accept or expel seawater under the influence of pressurized air, for example to create differing water column heights in the corner columns.

[ladajo]

An interesting control problem that would require a fairly receptive dynamic range feedback mechanism. Also, it would need to have some large flowrate capability to ingest and expel water from the volumes.

[TDPerk]

If I recall you use seawater because you have a lot of it. But the flow isn't between vessel and the sea, but between chambers in the vessel. The final control elements are the air valves, with the ability to shut off flow between vessels when not active.

[KitemanSA]

Seems to be a much more difficult temporary solution than a long arm drag mechanism. Probably even more expensive than a quad-copter stabilizer, either of which would work with their current barge.