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Comment by mikeyouse | Hacker News Reader

I think you're reading more into his comment than he intended. The first tweet,

    Last known state for rocket boost stage is 360 m/s,
    Mach 1.1, 8.5 km altitude and roll rate close to zero
    (v important!)

Was a very upbeat message in the context of their previous attempts.

This rocket was only doing 360 m/s, but importantly, wasn't rolling at all -- Their last 'test' failed when the rocket started rolling at a very high rate of speed and they lost engine power.

Musk was then asked:

    if anything could go better, what would it be?

To which he replied:

    Rocket boost stage reaching 0 m/s in one piece :)
    Will know soon. Odds not high.

The first line is just a joke that the test would go better if the rocket got to the surface in 1 piece. I think his 'odds not high' statement is just to dampen excitement a bit, since they went into this with a ~40% chance of success for the landing stage.

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I believe the 0 m/s refers to the boost stage's speed after a successful landing.

Since this is over the ocean, I interpreted this to mean reaching a state of stable hover.

It does, but the hover is at sea level... ;-)

Agreed, it appears I was unnecessarily pessimistic. Seems like SpaceX has pulled it off [1]:

"Data upload from tracking plane shows landing in Atlantic was good! Several boats enroute through heavy seas."

Congrats to the SpaceX team if this is the case. I've been glued to my laptop since the launch. I can finally say we've made a significant breakthrough in aerospace during my lifetime.

The last time a breakthrough of this magnitude occurred was during the Apollo program.

1. https://twitter.com/elonmusk/status/457307742495993856

UPDATE: Further confirmation.

"Flight computers continued transmitting for 8 seconds after reaching the water. Stopped when booster went horizontal."

It appears that we've witnessed history today ladies and gentlemen.

Woooooooo!

I was probably unnecessarily optimistic, but I'm so glad they are making this much progress so quickly!

Wow, I had no idea this was such a breakthrough. I'm not in the industry and I barely know anything about this, but can you explain what it is about recovering the booster that is such a huge breakthrough? Haven't we had recoverable space equipment for ages (e.g. space shuttle?) Forgive what is surely an ignorant question.

The F9R would be the first sub-orbital booster to return to Earth and land vertically under its own engine thrust.

SpaceX suggested that the boosters account for upwards of 75% if the rocket's cost so reuse is a huge economic benefit. SpaceX estimated that it could reduce a launch from $60m to under $10m.

The space shuttle did have recoverable boosters but the refurbishing process offered much less cost savings.

I believe no other rockets provide for booster recovery.

http://en.wikipedia.org/wiki/SpaceX_reusable_launch_system_d...

The Space Shuttle was only partially recoverable. There were three main parts to the system.

1. The shuttle itself - this needed extensive maintenance work done to it after each flight.

2. The big orange fuel tank - this couldn't be reused

3. The solid rocket boosters on either side - these had to be completely rebuilt after they splashed down in the ocean (it is easier to splash them down in the ocean than the Falcon 9 first stage, as they separate at a lover altitude).

Overall this didn't save much on costs, with the average cost of a flight (inclusive of development costs) being about US$1.5 billion.

"The shuttle itself - this needed extensive maintenance work done to it after each flight."

Including complete rebuilds for the three Space Shuttle Main Engines (SSMEs), they were I gather somewhat needlessly too high performance/sports car types of devices.

In general, the Space Shuttle design was twisted by various unnecessary requirements (e.g. while the Air Force didn't want it, it could originally do a single polar orbit mission, which required extreme heat shield technology to land back at the same location while the earth turned underneath it. This was later mitigated by replacing a lot of those tiles with a ... glass fiber mat???), and to minimize development costs. Solid fuel booster you can't turn off were formerly considered to be unacceptably dangerous for manned missions, but they were the cheapest to develop.

Operating costs? Well, NASA post-Apollo makes the most sense if you view it as a public works project.... Low launch rates, especially post-Challenger after more people realized what an abomination it was, plus a huge fixed work force made it very expensive to operate.

The key engineering problem that they solved is related to fuel and weight. They need more fuel for the landing, but more fuel adds more weight, which requires more fuel for lift off.

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