I suspect that the momentum involved would be more than a net could handle to not damage the rocket.
I’m guessing equatorial launches for geostationary satellites .
I believe that someone up thread posted that they may take off from Vandenburg, but are not allowed to land there.
The barge is for landing, not launching. They have no plans to launch from a barge.
lazybratsche has the correct answer above. They will use the barge:
- when they don’t have permission to land back at the launch site (as with the most recent landing)
- for Falcon 9 missions that are too heavy, and there is not enough fuel for a boostback to the launch site
- for landing the center core of Falcon Heavy missions, since it stages much later than the boosters
I was thinking of Sea Launch. Which does serve as an equatorial platform for geostationary satellites.
Sea Launch seems like a better idea than it is. Unfortunately, the operational overhead of doing things in the middle of the ocean overwhelms the marginal performance benefit you get from being at the equator.
Maybe it would be a different story if they were able to automate more. But for some reason they need a command ship the size of a mid-sized cruise liner.
Shame that it failed, I do find it enthralling to see them getting closer and closer to a repeatable and reliable system.
One thing that occurred to me. As the rocket enters the final few metres to settle on the legs, could not three or four retaining arms “flip up” from the deck and provide some element of lateral support and stabilisation in case of a slightly uneven landing or leg failure?
I love how so many people watch the landing and really want a way to just grab the rocket to keep it from tipping over!
The problem is that rockets have to be as light as possible, so they are built to be just strong enough to handle forces along a nice straight line from the engines to the payload. The outer walls of the rocket are also the outer walls of the tanks and are just a few mm thick. Structurally they’re a lot like a soda can*: hard to crush from top to bottom, but extremely easy to crush from the side. The tanks are also pressurized, so a small dent will quickly become a larger torn hole spewing kerosene or oxygen. I can’t imagine that any of the proposed schemes to grab the top of the rocket will ever work. There are a some very strong mounting lugs on the bottom near the engines, but trying to grab those on a rocket that could land anywhere within a few meters of center seems like a ridiculous engineering challenge.
Edited to add: here’s a picture that shows the segments that will become the entirety of the tank and rocket structure. They’re reinforced with stringers on the inside, but it shows how thin the outer skin is.
*I’ve heard that the walls of the Falcon 9 are a lot thinner than a soda can scaled up to the same diameter, though I can’t find a good cite this morning…
I see what you are saying. Any support system coming in from the side is going to place a large amount of force on that thin skin if the rocket is substantially off-vertical. And if it isn’t off-vertical then the support isn’t needed (assuming that the legs can be modified to reduce the risk of failure.)
The other thing that I hadn’t quite appreciated is the speed of the landing and variability in touch-down position. That presents a substantial challenge in getting an accurate, non-damaging support structure into place quick enough. Overall, improvements to the legs is likely to be the easier engineering challenge.
It is all still way cool though.
For a restraining system to be worthwhile, it is not necessary that if used it leave the rocket undamaged. It would be worth it if the money it saved by preventing explosions was greater than the cost of the system and the cost of damage done by the restraint.
It’s close. A soda can is 66 mm in diameter and uses 0.1 mm thick aluminum, for a 660x ratio. A Falcon 9 is 3660 mm across and has skin in the ballpark of 6 mm (this is my estimate from visiting the factory), for a 610x ratio.
A Falcon 9 first stage stores 389,000 liters of propellant with a dry mass of 23,100 kg, while a soda can stores 0.355 liters in 0.149 kg. That’s 0.059 kg/l for the F9 and 0.042 kg/l for the can. So even with all the engines and other components included, it’s barely more.
The second stage does even better, with 0.043 kg/l, which almost matches the can.
I thought this animation from Reddit was a funny one. But the guy didn’t really think through the physics. The sliders moving along the length travel 45 meters in about 0.5 s. Since they have to accelerate and decelerate, that means they need to go from 0 to 22.5 m in 0.25 seconds, which is 720 m/s[sup]2[/sup] of acceleration, which is 73 gees. Kind of a lot.
I think most of the ideas for grabbing the stage suffer from the same kind of problem. The scale here is huge–the stage is the height of a 10 story building. Legs are really just the best way. They’ll fix the problems eventually. Aircraft landing gear also fails occasionally, but we don’t invent crazy schemes for grabbing aircraft from the ground (well, mostly). It generally just works.
I think the fail is not letting them land on solid ground in the first place. I mean WTH? What possible reason can they have for using such a setup?
We have a ridiculous amount of desert land out west that could be utilized for this.
The Russians and Chinese are all too happy to allow rocket overflights of populated areas. The US is not. Eastern-bound flights go from Cape Canaveral and polar flights from Vandenberg. In both cases, the rocket is over the ocean after launch. SpaceX’s new launch facility in Boca Chica, Texas will also launch over the ocean (threading the needle between Florida and various islands along the way).
They will have a landing pad at Vandenberg eventually, but they just haven’t gotten permission yet. I don’t know why, but this stuff takes time.
At any rate, they will need the barge in the future, so they may as well keep practicing. They have done very well in targeting the barge with high precision; they just haven’t quite stuck the landing yet. It seems there aren’t many variables remaining.
They may launch from Vandenberg, but are not allowed to land there.
I believe that you have to use fuel to return, and a barge landing is less costly. Things at sea do tend to behave in such a way as to make a fellow seasick, it must be much more difficult to land on a barge that solid, level, unmoving land.
And the mentioned above overflying populated areas. A hot air balloon landed in Mama Plant’s neighborhood, but a booster would have been a different matter. :dubious:
Well I was thinking in terms of the deserts out West for both launch and recovery. Yes, no? I have no idea how far the rocket arcs over before it returns. I just hate to see a perfectly good rocket destroyed for no good reason. unless the ocean barge is super stable then this is an event destined to repeat itself.
I don’t know how much fuel they would need to land in the desert, or how much it would cost to retrieve a booster from there. Where they put the satellite in orbit determines how they return, and I am completely ignorant of orbital mechanics.
Meh, it’s been done.
For one thing, The US as a whole is pretty averse to sending rockets over even slightly populated areas. With disposable rockets all the lower stages and payload fairings would come crashing back to earth somewhere tens or hundreds of miles downrange. Even if SpaceX can reliably land their first stage, there’s still a substantial risk of the rocket exploding and raining debris across a wide area downrange. And some of the debris can be pretty nasty: propellants that are mildly toxic (wash it off your skin before you get a nasty rash), other propellants that are very toxic (if you can smell it you might survive with hospitalization), and the occasional radioactive power supply.
In contrast, the Chinese government doesn’t give much a fuck where their rocket debris lands. Usually that’s just “haha an engine fell through the roof of a shack!” but it’s also lead to the deadliest ever rocket accident. I doubt that would go over well with the US NIMBY crowd.
Secondly, rocket launches have to head in many directions depending on the orbit the payload needs to reach. Many go east-ish and are best launched from the lowest possible latitude, others go north-ish or south-ish or just about any direction. The optimal downrange landing spot would also vary based on the payload. All this means that you couldn’t just use one or two pads for all landings.
Neither of those objections are absolute. Maybe decades from now, if rockets can launch and land as reliably as airplanes, there could be a launch pad somewhere like West Texas and a few dozen landing pads covering the optimal landing areas for most launches.
Getting back to crazy ideas to make barge landings more reliable, a semi-submersible platform could be converted into a much larger and more stable landing pad. (Not unlike Sea Launch’s platform, except much simpler and cheaper since all that’s needed is a flat surface, and maybe a crane and storage hangar.)
Nice links to the Chinese launch sites.
I thoroughly get the point about launching over civilian areas even if they’re remote. But I’m talking about land out west where NOBODY lives. They’ll be finding crashed planes out there until the end of time.
As for sea landings I think it would be much cheaper to focus on locking down the rocket than stabilizing the platform. In an era of robotic systems I would think it easier to seek out and latch on to the rocket then to try to control the pitch of the sea.