Comment by alexggordon | Hacker News Reader

Comment by alexggordon | Hacker News Reader

This is an absolutely huge test. Musk's entire vision for SpaceX[0] involves cheap, reusable spaceflight, simply because there’s no other way to colonize a different planet without it. According to Musk, abandoning “disposable” rocket technology would result in a 100 fold reduction of the cost of rocket launches[1]. While it might not be that significant, I fully believe than NASA could utilize the minute budget it has much better without throwing away millions of dollars of technology every launch.

Based on that, landing this rocket perfectly is the proof Musk needs to show the world he can launch that rocket again in 10 hours, essentially turning rocket launches into a daily—not monthly—occurrence.

Musk’s vision aside, it would be so cool to land a fucking rocking on floating object in the middle of the ocean. It’s basically a reverse missile maneuver. They’re not ramming the object, they’re just gently touching down, but with all the more accuracy.

[0] http://www.space.com/25636-spacex-reusable-rocket-test-elon-... [1] http://shitelonsays.com/transcript/npc-luncheon-with-elon-mu... (paragraph 13)

For efficient re-usability, you need at least three things. The first is reliable launches that don't have lots of delays. The second is reliable recovery. The third is efficient readying for another launch.

That last one is trickier than people think. It was the main thing that stopped shuttles from launching faster, for instance. It took months of work to verify that all the systems were as reliable as they were before launch. It will be interesting to see how SpaceX handles that.

The shuttle is in no way comparable with the SpaceX solution. The shuttle was notoriously slow for turn around because it was a massively complicated machine that had to be man-rated. A Falcon 9 first stage is a much simpler machine. On top of that, the shuttle had to go through re-entry, with all of the G forces, and thermal shock associated with that. The Falcon 9 first stage has neither of these problems.

Exactly. SpaceX has completely designed this rocket around easy readiness tests. That's why the rocket was switched from a parachute landing, to a VTOL device[0].

They basically want this to be a smart rocket. Something that can just launch payloads into and out of orbit, and come home like a good dog after a long day of work.

[0] http://en.wikipedia.org/wiki/Falcon_9#Reusability

Well, either they tear apart and inspect the engine in between launches or they don't. If they don't, their turnaround will be way faster, but there is a greater chance of failure, and if there is a failure, a much lower chance of figuring out the reasons.

The engines are fired up, shut down and then re-lit again for many dozens of cycles during testing. Plus it's re-started 3 times during landing manoeuvers on top of the launch burn, so it's definitely capable of re-use without being stripped and cleaned. How many times I don't know, but like I said they run the engines though a lot of cycles during testing so they should have a good handle on that.

> so it's definitely capable of re-use without being stripped and cleaned. How many times I don't know

I'm confident SpaceX themselves would have tested multiple engines to failure with many, many re-light, shutdown, re-light cycles so they have a good understanding of what's going to happen when they try to re-use one of these things.

There is no way they'd be going to all this trouble to design a rocket that can come back, all the trouble of giving it someplace to land if they were not already confident the engine can be used at least a few times.

OTOH, there's still huge cost savings even if you need to take apart and reinspect the engines. Building space components is not cheap.

The Falcon 9 still has to deal with heat cycles, vibration, and soot/chemicals byproducts from the engines. The heat cycles and vibration lead to work hardening and cracking or softening of components. Soot can and will get into everything and destroy bearings and connectors.

Even the spray from the ocean combined with the heat from the latent heat in the craft can lead to accelerated corrosion.

They're shooting for a final touchdown speed of 2m/s which seems fairly slow but that's still a lot of mass to stop very quickly. The ocean helps soften touchdown for sure.

It would not surprise me if the turn around procedure was to r&r the entire bottom third of the craft and (possibly) the fuel tanks. The removed components could get inspected and rebuilt and flown again.

It won't be anywhere near the scale of the shuttle turn around but it won't be as simple as hosing it off and fueling it up.

SpaceX has of course considered all of these things and it will be an amazing thing for space travel if they pull it off.

> Even the spray from the ocean

The ultimate goal is to land at least most of the cores on land, not the barge, in part to avoid this.

One thing that concerns me about reusing it is how do you account for unknown components failing or wearing down in quality after repeated use? Does SpaceX have the metallurgy capacity or experience to deal with cases that no one has ever encountered (reusing a rocket multiple times)?

I'm worried that one small tear or some mold or rust will increase the risk.

I always wonder why they don't launch a rocket from a plane at around 60,000 feet, wouldn't that cheapen the cost rather than launching it form ground zero?

Launching at 60k feet doesn't buy you many advantages except there's less atmospheric drag up there - it's about the speed, not so much the altitude. But you'd gain the problem of hauling a ~500 ton rocket up to 60k feet, and you'd anyway have to launch that plane from ground zero.

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