4 ms·

While that sounds great, i wonder what the advantage to that is over using parachutes and making a water landing like the Shuttle Solid Rocket Boosters did.

InclinedPlane 14y ago
This question always comes up. It's about turnaround time and precision. Parachutes are messy. They use pyrotechnics to deploy, they have to be packed very carefully and precisely, etc. They also don't lend themselves to precision landings well. They're fine for landing in an enormous landing zone in the ocean or in some unpopulated, featureless desert, but otherwise they're not so good for targeted landings. Now, compare this to propulsive landings. You "waste" a lot more fuel and cut into the payload of your vehicle but on the other hand you get to streamline the turnaround process to just a matter of refueling and inspection, which you would do regardless of the landing mode. More so, by landing the vehicle in a designated spot you dramatically lower the cost and time necessary to put the vehicle back into service. You don't have to drive out to the desert and retrieve the vehicle (which could take a day at least) you just pick the thing up with a crane and you move it a few hundred meters to the hangar / processing facility.
- ericcumbee 14y ago
  thats what i figured. Although to me it seems like a lot of moving parts, and big hit to fuel and payload. I wonder if development focused on optimizing it as a one use booster and driving down the cost of each booster might be more efficient in the long run.
  - InclinedPlane 14y ago
    That's a very worthwhile point but there are a few major reasons why it's a more problematic strategy. First, reliability. When you engineer a vehicle as large and as complex as an orbital launcher which only operates once in its entire lifetime you typically need to over-engineer a lot of key parts of the thing in order to ensure a high level of overall reliability. This runs counter to the sorts of optimizations necessary to bring production costs down by orders of magnitude. More so, when a full up test inevitably results in the destruction of the vehicle (because it is expendable) and tests cost as much as a launch (tens of millions of dollars) it makes it very, very difficult to evolve the design of the vehicle extensively. That leads to a catch-22, you have to run a lot of launches to make the vehicle design significantly cheaper to manufacture. Buuuut, now you've vastly increased the development cost of the vehicle so you've erased all of the cost gains you've made. But, if you design for reusability then you can actually increase reliability because the cost of the vehicle is amortized over multiple flights, so you can have a more expensive vehicle. Also, while a lot of aerospace components (like fuel tanks, electronics, etc.) can be mass produced with the right design, this is a lot more difficult with rocket engines which have a very high number of precision machined parts made out of special alloys. This makes the engines the long-pole in the costs of a rocket, and it's very difficult to reduce those costs. Right now SpaceX is already the world's largest manufacturer of high-power rocket engines, so if there was a way to cut costs on them they would already be on top of them. Now, back to reusability. Another thing that you get from reusability is that testing can be much cheaper, since you can make incremental changes to a vehicle design and then re-test it. With reusability you have the best of all 3 worlds. You have reliability, you have low per-flight costs, and you have an enhanced ability to prove out potential vehicle redesigns economically. Now, if the size of the launch market were much larger and reusability were more difficult then the equation could change, because it might be easier to recoup expensive cost-saving efforts over a shorter period of time.
reneherse 14y ago
It's basically a savings in recovery and turnaround time & expense. Sea recovery is logistically costly and difficult, plus the vehicle must be completely rebuilt and refurbished once it's back in the hanger. A saltwater bath and the stresses of a water touchdown are not easy on equipment. While a controlled, retrorocket touchdown is obviously s huge engineering challenge and greatly complexifies the vehicle and increases its launch weight, the possible cost savings apparently make it a desirable goal. Also, I believe SpaceX hopes to perfect the technology as part of their strategy to be make their tickets to Mars "round trip" :)
toomuchtodo 14y ago
Turn around time. You can turn around a self-landing ignition stage much faster than something you have to turn around after a water landing.
tsotha 14y ago
At least for the first decade or two (maybe still - I don't know) the shuttle SRBs were only recovered for political reasons - the system was supposed to be reusable and they didn't want to be accused of building an expensive disposable rocket. By the time the boosters were recovered disassembled, had every inch checked for damage (visible and xray), and rebuilt, the cost was more than if they'd just left off the parachutes and built a new pair for every launch. In theory if you landed the first stage of a liquid fueled rocket back near the launch site you could just gas it up and launch again, since the stresses are so much lower. I doubt that's what will happen, though - they'll give it a pretty thorough (and expensive) going over the way NASA did with the SSME. There are two ways this could make sense from a cost perspective. One is after a confidence-building period they just do quick inspections and live with a slightly higher failure rate on subsequent launches. This would mean the second and subsequent missions are unmanned only, and it would have to bring the cost down so much that satellite makers could afford the risk. The second is they just do relatively quick and cheap inspections and the increased failure rate is so small it's balanced out by the decrease in failures due to manufacturing error. This is really the holy grail of the rocket business, since it means you start to operate on the same economics the airlines do, where fuel is the cost driver. In rocket launches fuel typically comes to about 2% of the cost. Putting a kg into LEO takes about the same amount of energy as flying it from LA to Sydney on a 747. The reason sending that kg to Sydney is so much cheaper is they turn the plane around and fly somewhere else instead of throwing it away.

InclinedPlane 14y ago

This question always comes up. It's about turnaround time and precision. Parachutes are messy. They use pyrotechnics to deploy, they have to be packed very carefully and precisely, etc. They also don't lend themselves to precision landings well. They're fine for landing in an enormous landing zone in the ocean or in some unpopulated, featureless desert, but otherwise they're not so good for targeted landings. Now, compare this to propulsive landings. You "waste" a lot more fuel and cut into the payload of your vehicle but on the other hand you get to streamline the turnaround process to just a matter of refueling and inspection, which you would do regardless of the landing mode. More so, by landing the vehicle in a designated spot you dramatically lower the cost and time necessary to put the vehicle back into service. You don't have to drive out to the desert and retrieve the vehicle (which could take a day at least) you just pick the thing up with a crane and you move it a few hundred meters to the hangar / processing facility.

ericcumbee 14y ago
thats what i figured. Although to me it seems like a lot of moving parts, and big hit to fuel and payload. I wonder if development focused on optimizing it as a one use booster and driving down the cost of each booster might be more efficient in the long run.
- InclinedPlane 14y ago
  That's a very worthwhile point but there are a few major reasons why it's a more problematic strategy. First, reliability. When you engineer a vehicle as large and as complex as an orbital launcher which only operates once in its entire lifetime you typically need to over-engineer a lot of key parts of the thing in order to ensure a high level of overall reliability. This runs counter to the sorts of optimizations necessary to bring production costs down by orders of magnitude. More so, when a full up test inevitably results in the destruction of the vehicle (because it is expendable) and tests cost as much as a launch (tens of millions of dollars) it makes it very, very difficult to evolve the design of the vehicle extensively. That leads to a catch-22, you have to run a lot of launches to make the vehicle design significantly cheaper to manufacture. Buuuut, now you've vastly increased the development cost of the vehicle so you've erased all of the cost gains you've made. But, if you design for reusability then you can actually increase reliability because the cost of the vehicle is amortized over multiple flights, so you can have a more expensive vehicle. Also, while a lot of aerospace components (like fuel tanks, electronics, etc.) can be mass produced with the right design, this is a lot more difficult with rocket engines which have a very high number of precision machined parts made out of special alloys. This makes the engines the long-pole in the costs of a rocket, and it's very difficult to reduce those costs. Right now SpaceX is already the world's largest manufacturer of high-power rocket engines, so if there was a way to cut costs on them they would already be on top of them. Now, back to reusability. Another thing that you get from reusability is that testing can be much cheaper, since you can make incremental changes to a vehicle design and then re-test it. With reusability you have the best of all 3 worlds. You have reliability, you have low per-flight costs, and you have an enhanced ability to prove out potential vehicle redesigns economically. Now, if the size of the launch market were much larger and reusability were more difficult then the equation could change, because it might be easier to recoup expensive cost-saving efforts over a shorter period of time.

reneherse 14y ago

It's basically a savings in recovery and turnaround time & expense. Sea recovery is logistically costly and difficult, plus the vehicle must be completely rebuilt and refurbished once it's back in the hanger. A saltwater bath and the stresses of a water touchdown are not easy on equipment. While a controlled, retrorocket touchdown is obviously s huge engineering challenge and greatly complexifies the vehicle and increases its launch weight, the possible cost savings apparently make it a desirable goal. Also, I believe SpaceX hopes to perfect the technology as part of their strategy to be make their tickets to Mars "round trip" :)

toomuchtodo 14y ago

Turn around time. You can turn around a self-landing ignition stage much faster than something you have to turn around after a water landing.

tsotha 14y ago

At least for the first decade or two (maybe still - I don't know) the shuttle SRBs were only recovered for political reasons - the system was supposed to be reusable and they didn't want to be accused of building an expensive disposable rocket. By the time the boosters were recovered disassembled, had every inch checked for damage (visible and xray), and rebuilt, the cost was more than if they'd just left off the parachutes and built a new pair for every launch. In theory if you landed the first stage of a liquid fueled rocket back near the launch site you could just gas it up and launch again, since the stresses are so much lower. I doubt that's what will happen, though - they'll give it a pretty thorough (and expensive) going over the way NASA did with the SSME. There are two ways this could make sense from a cost perspective. One is after a confidence-building period they just do quick inspections and live with a slightly higher failure rate on subsequent launches. This would mean the second and subsequent missions are unmanned only, and it would have to bring the cost down so much that satellite makers could afford the risk. The second is they just do relatively quick and cheap inspections and the increased failure rate is so small it's balanced out by the decrease in failures due to manufacturing error. This is really the holy grail of the rocket business, since it means you start to operate on the same economics the airlines do, where fuel is the cost driver. In rocket launches fuel typically comes to about 2% of the cost. Putting a kg into LEO takes about the same amount of energy as flying it from LA to Sydney on a 747. The reason sending that kg to Sydney is so much cheaper is they turn the plane around and fly somewhere else instead of throwing it away.