I was surprised by something in the re-entry profile. They use what they call "lift" from tilting the rocket body against the air stream to control horizontal motion. I call it "falling with style". So they can go back uprange some distance without an additional fuel expenditure.

All of their communication so far has been that they can get back to the pad with the F9 or the two outer stages of the F9 Heavy. The center stage of F9 Heavy would probably need the barge.

That would be hot for an aircraft, but it was the planned vertical speed profile for the rocket. The grid fins need speed to work and they are the main control surfaces. The cold gas thrusters don't have infinite gas behind them and the engine burns are very short.

They planned the fast approach. Consider that the main control surfaces are the grid fins. They don't work at slow speeds. It's all about landing with the minimum use of weight (thus fuel).

I must confess that most of my programs have bugs the first time I write them. I don't start over from zero when that happens.

The Wright Flier didn't get to San Francisco, but it started the path that led there. Actually touching down on the planned point, at the planned vertical velocity, is pretty good. They'll fix the rest.

The required longer burn to make up for a shut down engine does use extra fuel. It also changes the orbital injection point.

Speed and distance are the big problems. Rockets can do both. Things that are tied to ships or the ground have trouble keeping up with the rocket.

The first stage is most of the rocket by weight. The second stage has one engine, while the first has 9. And as you can see from a photo, the second stage is much smaller.

What makes it recoverable is that it doesn't take much fuel to bring an empty first stage back down. It's really light when empty. They only use one engine out of the 9, for very short burns, to do that.

It's lighter to not reuse the hydraulic fluid.

It's an open loop system with pressurized gas pushing the fluid out and then it's dumped in the air. Pumps and whatever powers them have weight.

Remember that big fuel-required multiplier in getting any weight at all to 78 miles height and suborbital speed.

We could start with our already phallic looking rocket and then have it come down into something that looks like the world's largest inflatable sex toy. Elon Musk might have trouble living that one down. :-)

Yes, there have been many proposals to somehow catch the rocket.

Where I used to live they had trucks dump salt on the road!

The Kerbal Space Center?

Not until the next time we cut the NASA budget to pay for a subsidy of some incredibly rich industry. Like oil. We need more oil drilling subsidies, don't we? Or intellectual property. That's just another word for innovation, isn't it?

In those tests, both Grasshopper and R9 were coming down much more slowly. But it appeared they could come down slowly. Pretty close to hover.

The tweet from Musk this morning used the word "sticktion", meaning static friction. And said it was the cause of a phase delay. And then the tweet got deleted.

Oh, they're Canadian. That explains everything!

(Ducks and runs for cover)

:-)

But we've seen Grasshopper and Falcon R9 position properly on land. Nobody's told us what the maximum wind was in those tests.

Musk alluded to a process control issue this morning and then deleted the tweet. It will take time to find out what the deal is.

Merlin 1D can throttle to 70% and the old 1C could go to 60%. Perhaps there's room for deeper throttling. I would expect that they'd try that before adding a new system and its weight.