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Could someone explain to me why they attempt this? Wouldn't inflating a set of floating devices when it goes down the ocean an easier way of retrieving it? Or s
by bantunes 11y ago
Could someone explain to me why they attempt this? Wouldn't inflating a set of floating devices when it goes down the ocean an easier way of retrieving it? Or something other than this REALLY HARD TO PULL OFF maneuver? Genuinely interested.
- dchesterton 11y agoThey want to use this tech to eventually land rockets on other planets so the rocket needs to be able to land upright. Short term it might be easier to land on inflatables but they're looking at the bigger picture.
- jsumrall 11y agoNo, its just not possible to maintain the integrity of the rocket if you're going to somehow lay it down on an inflatable. How could an inflatable withstand the temperature of the firing engines?
- el_zorro 11y agoThe utility here is not really landing on other planets, but instead the order of magnitude decrease in launch costs if they don't have to build a new first stage for every launch.
- dchesterton 11y agoThis could theoretically be achieved by either means. The question was specifically why a vertical landing is favoured over a cushioned inflatable landing. Musk has stated in the past that they're looking to eventually use this tech to create rockets which can be used on Mars, hence why parachutes and inflatables are out of the question.
- ansible 11y agoParachutes also have the problem that you can't as easily control the landing point.
- Grue3 11y agoYeah, I don't understand why they won't keep landing them on the ground like everyone else does. It's not like there's not enough space on Earth.
- el_zorro 11y agoIt has to do with the payload mass. If it's too massive, it won't have enough fuel to return to the launch site, so they do a landing at sea.
- brianwawok 11y agoSo if you launch out of Cali going west and separate stage 2 300 miles out.... What is under you to land on?
- alkonaut 11y agoI assume the parent poster meant that the launch should take place from somewhere on earth where there is earth 2300 miles out. It's likely not convenient to do so, at least not for all launch directions.
- lmm 11y agoIt would be convenient enough but the FAA isn't too happy with the idea of a 12-story missile full of explosive fuel and oxidiser flying over populated areas.
- alkonaut 11y agoYes, part of the inconvenience of course is that it's unlikely to be anywhere near the continental US.
- lmm 11y agoIf you just needed to find two bits of ground with room for rocket pads and one 2300 miles east of the other it really wouldn't be that hard to have both in the continental US. It's the fact that the whole flight path has to be safe that makes it virtually impossible.
- jsumrall 11y agoHow do you expect it to be able to land on an inflatable raft? The point of landing the rocket is to reuse it, which is not possible if it falls over or gets wet. Landing in the ocean is only done for certain types of missions, where its not possible to carry enough fuel to turn the first stand around a fly it all the way back to the launch site. Instead, they can carry just enough fuel to land wherever they are finished boosting the 2nd stage, to put it simply.
- JoeAltmaier 11y agoYou don't want to carry heavy landing-maneuver gear to space and back. Thus the skeletal landing struts that were not-quite-strong-enough for rough seas. Further, the ocean platform it was landing on was built to sustain heavy seas and stay relatively flat. Recovering a rocket bobbing in the waves could be much harder than this. Also a challenge: quenching a very hot engine in cold ocean water. No, this platform-landing is probably one of the simplest, safest ways to recover/reuse a stage.
- Already__Taken 11y agoKeeping it out of the sea water is a key part of reusability.
- ohyes 11y agoThey want to be able to relatively quickly send it back into space. If they have to pull it out of the ocean and dry it out/fix it, I assume this makes their turnaround time less than ideal. Think what you do with a 747, it lands, a technician checks it out, it gets refueled, it takes off again. We'd be able to build things in space so much faster with that sort of round-trip lifting capability. I assume there are also implications for exploring other planets. This is my guess as someone who has not studied the issue closely.
- el_zorro 11y agoThe corrosion from the salt water would completely ruin the engines, obviating any benefits from returning the first stage.
- alkonaut 11y agoRockets have always been able to land in the ocean more or less intact (i.e. without disintegrating). However, if the rocket is dipped in salt water, the restoration would be enormously expensive, so it needs to stay dry to be re-used. Of course, you could just try to land it vertically on the water on some cushion and have more cushions deploy to make it tip over horizontally and float (all the time staying above the surface of the ocean). Such a solution isn't as compatible with recovery on dry land. If you want to do e.g. space tourism missions and land on dry land, the vertical landing seems better.
- zardo 11y agoRockets have always been able to land in the ocean more or less intact (i.e. without disintegrating). No they haven't. SpaceX started doing that in 2013 before the barge landings. I don't think anyone had ever even tried to land(sea?) a liquid fuel booster before that. You may be thinking of the STS solid boosters, but solid boosters are really a different game. They can be built sturdy enough to hit the ocean at 60mph, but they couldn't possibly be simply refueled and reflown.
- ruffmuff 11y agoTwo main reasons I can think of: 1) Sea water is extremely corrosive. If your booster takes a dunk in the drink, it's going to be very hard to refurbish for another launch. Lots of components (electronics, valves, etc) would need to be replaced and the structural integrity of the tanks themselves may be compromised by rust. 2) Flotation devices attached to the booster = extra payload. It would be the canvas/dinghys AND compressed gas canisters for inflating them. This is arguably (a lot?) more weight than just landing struts + fins. Any extra payload on a rocket represents a massive cost and means less stuff you can haul for paying customers.
- martindevans 11y agoIn addition to that the vehicle is extremely weak when lying on its side. I should think there's a good chance the tanks could be damaged by waves bending the vehicle.
- Gravityloss 11y agoCorrect. Also the terminal velocity even with a parachute can be high, and if you hit a rising wave, even more. Actually parachuting and fishing the stage from the sea was their first idea, but they never recovered a single stage that way, and moved to active controlled recovery, which is much much much better in my opinion.
- refurb 11y agoFlotation devices attached to the booster = extra payload Yes, but how much extra fuel does the rocket have to carry to land? That's a ton of extra payload as well.
- ramidarigaz 11y agoEstimates I've heard say 15% loss of payload mass for a barge landing, 30% for land.
- refurb 11y agoWhat do you mean by "loss of payload mass"? If the rocket lands on a barge it has to reduce it's payload by 15%? Any ideas why it's higher on land? Seems like it wouldn't differ that much.
- agumonkey 11y agoOr even a different kind of barge. A floating 'jar' rather than a flat surface, the thing could tip and not fall all the way.
- startupfounder 11y agoSalt water isn't good for rockets. Once you solve this really hard problem of landing a rocket on a barge on a dynamic ocean you have a real competitive advantage.
- valhalla 11y agoIs that the reason they've been using the barges for landing? I'd always assumed they were just being extra cautious since it could endanger civilians or crew if the reusable stage was supposed to land on solid earth. I'd imagine that the barge landings introduce a lot of uncertainty and complicating factors that are impossible to completely nullify. High waves and (comparatively) strong open-ocean winds seem (to me at least) to make consistently successful lands much harder.
- estel 11y agoThere was definitely a safety issue that lead to earlier landings taking place on a barge, but it also requires a lot less fuel to land somewhere downrange (which is always over the ocean) rather than boost all the way back to the launch site.
- AaronM 11y agoSome flights wouldn't have enough fuel to make it back to the launch site. That's the reason I've seen. There is also a large amount of water, so that increases the places you can land.
- benjaminl 11y agoThe key thing to remember about rockets is that they are incredibly fragile. The rocket is about 15 stories tall and is designed for force to only be applied at the end either via the rocket engines or the landing gear. Any type of lateral forces will irreversibly damage the rocket. As an illustration, extreme care is taken when the rocket needs to be transported on its side. Some rockets, not the Falcon 9, can't even be transported on their side without being pressurized. So pretty much anything other than a perfect soft touch landing would leave the rocket unable to fly again. Anything touching the 3/16" thick skin of the Falcon 9, would cause the very least extensive refurbishment at the least, but more likely irreversibly damage the frame of the 15 stories tall 1st stage. So this rules out every alternative that has been suggested in this thread.
- Dylan16807 11y agoWhile that's true, the metal tube is not the part that's expensive to build.
- sbierwagen 11y agoYou'd be surprised: https://en.wikipedia.org/wiki/Isogrid https://en.wikipedia.org/wiki/Isogrid
- tavert 11y agoSpaceX mostly uses friction stir welding to avoid the costs of isogrid