Space Things

[Irace86.2.0]

Originally Posted by Ultramaroon

Here's a pretty good summary.

https://courses.cs.vt.edu/cs2104/Spr...calingLaws.pdf

For clarification, I wasn't just pulling this out of my ass or something. Parachutes have been used since the 1970's to recover boosters for the US Space Shuttle program. Hundreds rocket boosters weighing around 100 tons have been recovered. My post of the China rocket booster was just to show that they are still in use, and the boosters seem to be strong enough for a parachute to guide them to the hard ground and have them pitched on the side of a ledge. I was proposing parachutes and a series of nets to make recovery easier and cheaper than fishing them out of the ocean. I don't think it is outlandish or hubris to consider something like that. The parachutes used below could theoretically hold almost 300 tons, so we are getting close to a 500 ton booster for SpaceX. The rocket boosters hit the water vertically, which could be the orientation of how it hits a netting system too. I'd imagine hitting a netting system at 50mph might be easier than hitting water, as far as loads on the booster's structure. I suppose the booster could hit a body of water too, but if it could hit a huge net first then recovery might be easier. It would be a big project to make, but if it reduced the cost over time then it might be worth it.

Each of the 136 ft (41 m) diameter, 20° conical ribbon parachutes have a design load of approximately 195,000 lb (88 metric tons/97 US tons) and each weighs approximately 2,180 lb (990 kg). Source

[Spuds]

The ocean is a pretty big net though. Parachutes like that are neither accurate nor precise.

[Dadhawk]

Originally Posted by Spuds

The ocean is a pretty big net though. Parachutes like that are neither accurate nor precise.

Are those stages buoyant enough to float?

Personally, I think SpaceX has the right idea, and have proved it's a viable solution with direct fueled landings.

[Ultramaroon]

The SRBs do float. Once the fuel is gone, they're just empty cans. I don't know how, or if water is kept from entering the big hole at the bottom.

Did I read that correctly? Each of those parachutes weighs a ton? Never mind trying to steer the thing into a small target, it's literally a massive waste to lift anything that isn't actually payload. Every extra part that isn't actually rocket goes to the wrong side of the scaling issue.

Also, Elon wants to land on Mars and come home. Regardless of how one feels about that project, I feel safe in assuming that plays into his current decisions.

[Dadhawk]

Originally Posted by Ultramaroon

The SRBs do float. Once the fuel is gone, they're just empty cans. I don't know how, or if water is kept from entering the big hole at the bottom.

Did I read that correctly? Each of those parachutes weighs a ton? Never mind trying to steer the thing into a small target, it's literally a massive waste to lift anything that isn't actually payload. Every extra part that isn't actually rocket goes to the wrong side of the scaling issue.

Thanks for the SRB info. Yea I suppose they would float before water ingress sinks them anyway.

I saw that too on the chutes and was surprised at the total weight. Still lighter I would imagine than enough fuel for the SpaceX landing which subjects the same weight penalty.

[Ultramaroon]

Originally Posted by Dadhawk

Still lighter I would imagine than enough fuel for the SpaceX landing which subjects the same weight penalty.

Ah! Good point. Thanks.

[Irace86.2.0]

Originally Posted by Spuds

The ocean is a pretty big net though. Parachutes like that are neither accurate nor precise.

I would imagine side thrusters and the winglets could correct for wind, but that is just me guessing wind would have a low impact against the inertia and momentum of 500 tons.

[Ultramaroon]

Originally Posted by Irace86.2.0

I would imagine side thrusters and the winglets could correct for wind, but that is just me guessing wind would have a low impact against the inertia and momentum of 500 tons.

Think about the chutes themselves, flying kites, even umbrella in a slight breeze should bring some perspective.

[Dadhawk]

Originally Posted by Ultramaroon

Ah! Good point. Thanks.

It's one of those diminishing return things... How much fuel do you need to fly the fuel that flies the fuel that flies the fuel for landing.....

[Ultramaroon]

Originally Posted by Dadhawk

It's one of those diminishing return things... How much fuel do you need to fly the fuel that flies the fuel that flies the fuel for landing.....

Oh, yeah! I smacked my forehead as soon as you mentioned it. Good stuff.

[x808drifter]

Cost/time of water landing and recovery w/ parachute then prep for relaunch vs Land and reuse.

Figure the parachute way is initially cheaper but removing all the equipment and personnel for is must save a bunch.

Wonder where the break even point is.
Hope it's less than 20-50 launches before landing it starts to become cheaper. (for Falcon-9)

[Dadhawk]

The other factor is that sometimes you need every ounce of fuel to get to lift the payload. Even SpaceX has plans to recover some rockets and "sacrifice" others for the good of the mission.

Also, if I recall correctly, SpaceX doesn't recover the center booster of the Falcon Heavy, only the two outside ones.

there is a similar plan for Starship where sometimes they'll recover the first stage and sometimes they won't.

[gen3v8]

Originally Posted by Dadhawk

The other factor is that sometimes you need every ounce of fuel to get to lift the payload. Even SpaceX has plans to recover some rockets and "sacrifice" others for the good of the mission.

Like Apollo 11. Enough fuel to break earth orbit, fly to the moon,power land, take off again and break lunar orbit for the return. All in, fuel hungry, 70`s tech.

[Irace86.2.0]

Originally Posted by Ultramaroon

Think about the chutes themselves, flying kites, even umbrella in a slight breeze should bring some perspective.

Well, it could be about this, where scaling changes the relationship. Maybe lateral winds acting on an object of a large mass with significant total momentum would have a hard time pushing it significantly off course like trying to veer the Titanic away from an iceberg.

When I went skydiving, we landed on a ten by twenty foam mat from 30k feet. There are GPS guided parachute systems already in use for dropping supplies and Humvees (Source 1, Source 2), so I have to imagine that with the grid fins, side thrusters, GPS systems, and with the sheer mass of the object, that landing in a reasonable zone would be achievable.

The reentry puts the booster fairly vertical, so it would be a matter of devising a way of catching a massive object.