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Space X CR6 First stage landing

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Re: Space X CR6 First stage landing

#51

Post by rdoherty »

hurin wrote: post #48

Question: Why don't they land into the water instead of a hard surface? (Wouldn't this give them more leeway in terms of impulse?) Edit: i.e. landing on a net stretched (under the lake/ocean-surface) by 3 or 4 ships - reel the net it in to raise stage out of the water, I'm pretty sure seawater is not significantly corrosive from 2-3 hours of exposure.

They have landed it in the water once as a proof of concept. Seawater is very corrosive and would require cleaning & inspection of nearly all the components.

Landing on a dry surface means they can eventually reuse rockets soon after landing (a few days I believe).

Re: Space X CR6 First stage landing

#52

Post by elif »

hurin wrote: post #48

Question: Why don't they land into the water instead of a hard surface? (Wouldn't this give them more leeway in terms of impulse?) Edit: i.e. landing on a net stretched (under the lake/ocean-surface) by 3 or 4 ships - reel the net it in to raise stage out of the water, I'm pretty sure seawater is not significantly corrosive from 2-3 hours of exposure.

same reason they don't land planes in water. it would damage the plane, and then you'd have to get it out of the water somehow.

Re: Space X CR6 First stage landing

#53

Post by ansible »

magic5227 wrote: post #29

I almost think it would be easier to let it do what this video shows, and build a giant metal net to just prevent it from sinking. Or is that harder than landing on a small platform?

The goal is not to recover the stage per-se, but to land successfully.

If they get a the 1st stage down on the drone ship, with all four legs touching, the main engine shut off, and it stays upright for even a few seconds, there will be much celebration. They would, of course, want to then actually examine the rocket afterwards, but that is a bonus.

Re: Space X CR6 First stage landing

#55

Post by olex »

hurin wrote: post #48

Question: Why don't they land into the water instead of a hard surface? (Wouldn't this give them more leeway in terms of impulse?) Edit: i.e. landing on a net stretched (under the lake/ocean-surface) by 3 or 4 ships - reel the net it in to raise stage out of the water, I'm pretty sure seawater is not significantly corrosive from 2-3 hours of exposure.

Currently they land on an autonomous ship (huge flat barge with stationkeeping engines and autonomous control). Reason is, they haven't yet proven that their approach and landing are accurate enough to get permission to try a landing on land. If the rocket misses the ship, it goes for a swim and damages nothing except itself. It it goes out of control during approach over land, there's much more damage it can do to all kinds of things.

Also, there's no land downrange from the launch site, and returning the stage to land at the launch site costs a lot of extra fuel. It is possible and actually planned to do so later (SpaceX is constructing a landing pad for this purpose at the Cape at this time), but for now they are trying to get the ship landings down properly.

Re: Space X CR6 First stage landing

#58

Post by ZoFreX »

hurin wrote: post #48

Question: Why don't they land into the water instead of a hard surface? (Wouldn't this give them more leeway in terms of impulse?) Edit: i.e. landing on a net stretched (under the lake/ocean-surface) by 3 or 4 ships - reel the net it in to raise stage out of the water, I'm pretty sure seawater is not significantly corrosive from 2-3 hours of exposure.

The eventual goal is to land it on land, they're only doing water landings right now due to the high chance of failure. In the future, the first stage will land back at the rocket pad, which massively reduces the logistics for re-using it.

There's a cool mock-up video of what that might look like: https://www.youtube.com/watch?v=4Ca6x4QbpoM

Re: Space X CR6 First stage landing

#59

Post by melling »

CHY872 wrote: post #35
melling wrote: post #27

Earlier quoted context omitted.

Complete destruction is obviously expensive. Finding a way to prevent an explosion if it falls over after landing seems worthwhile. If it hovered for 5 seconds at .5 meters, for example, could it burn off enough extra fuel?

Their eventual goal is for every rocket to land and not have problems. Providing enough fuel for five seconds of hovering is a waste of valuable fuel (see how they're already so low that they run out in the process). Also, falling over almost certainly also leads to a writeoff, as otherwise they'd just fly the rocket into a big pit of fire retardant foam blocks. I'd imagine that the lateral stresses involved in a cra…

Of course, their plan is to not have problems. That's everyone's plan. It's planning for when things don't go right that makes the difference.

Re: Space X CR6 First stage landing

#60

Post by hurin »

ZoFreX wrote: post #58
hurin wrote: post #48

Question: Why don't they land into the water instead of a hard surface? (Wouldn't this give them more leeway in terms of impulse?) Edit: i.e. landing on a net stretched (under the lake/ocean-surface) by 3 or 4 ships - reel the net it in to raise stage out of the water, I'm pretty sure seawater is not significantly corrosive from 2-3 hours of exposure.

The eventual goal is to land it on land, they're only doing water landings right now due to the high chance of failure. In the future, the first stage will land back at the rocket pad, which massively reduces the logistics for re-using it. There's a cool mock-up video of what that might look like: https://www.youtube.com/watch?v=4Ca6x4QbpoM

So you're saying the real cost-savings don't kick in until you're landing it back on the pad, hence salvage from sea is only important as far as perfecting the technology?
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