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Can someone explain to me the value of landing a tall, cylindrical rocket vertically like this? It just seems like such an odd thing to do.

by smegel 12y ago

DuskStar 12y ago
Rockets are extremely weak in any direction other than straight up/down. The reinforcement to allow a Falcon 9 core to even lay on its side unpressurised would probably weigh more than the entire set of recovery hardware (legs, grid fins, extra rcs fuel, etc) to land vertically.
- marktangotango 12y ago
  Falcon 9 stages are stored on their sides unpressurized, see any of the numerous roll out videos, and factory images. There are launchers that require pressurization for handling (atlas 5?) but falcon is not one. Musk has mentioned this as a cost reduction and simplification withyou respect to encumbent providers, don't have a link unfortunately.
  - outworlder 12y ago
    Yeah. But storing and gently moving are one thing. Flying and landing horizontally would require much more structural reinforcement.
    - XorNot 12y ago
      Bingo it's all about dynamic pressure: to be reusable the hull of the rocket has to land intact and not having undergone plastic deformation of any kind, so it's as close to "factory condition" as possible.
dshankar 12y ago
The point is reusability. Reusable rockets will dramatically lower the cost of rocket launches. (On the other hand, if you're questioning why rockets are tall & cylindrical, it's because that's the best design for rockets: https://www.quora.com/Spacecraft/Why-are-rockets-tall-and-slender https://www.quora.com/Spacecraft/Why-are-rockets-tall-and-sl...)
- smegel 12y ago
  So just to be clear, these rockets are going into space, then somehow coming all the way back down and landing? It seems fantastical that such a rocket could have a controlled descent from space and then land vertically (considering how the shuttle does it for example). How will it control decent speed? Will they carry enough fuel to control the entire descent and land?
lmm 12y ago
The engine is at the bottom pointing down, so the only way to do a powered soft landing is vertically. Other posts talk about why they're using the engine rather than e.g. parachutes.
tinco 12y ago
Landing it horizontally would require the rocket to be able to coast horizontally, meaning it would have to have wings. I can imagine wings would make the whole thing more complex but even if they nailed that, imagine what it would have to do on the descent. You basically have two choices, either fall straight down and try to control spin, or coast down, trying to control horizontal and vertical speed like an aeroplane. I have the suspicion that when dropping from space it's very hard to get into coasting mode since the air is so thin. However it is, a rocket that simply falls down instead of coasting like an aeroplane is so much less structurally complex, the only real challenge is controlling its landing which modern computers and their rocket engine make feasible.
InclinedPlane 12y ago
Aerodynamically it wants to be aligned along the vertical axis. Similar thing for thrust forces. So at a minimum you want to decelerate all the way down from terminal velocity with the vertical direction aligned to the direction of travel. And that only leaves a narrow window of time after which you could bother concerning yourself with reorienting. And, of course, reusing the main engines saves on complexity a great deal.
andygates 12y ago
The heavy stuff is all at the engine-end, so absent any lift, that's the orientation you get. Shuttle SRB's hung from parachutes in the nose, but a chute landing is still pretty fast. The hot motors were dunked in salt water at speed... generally worse all round. Solid rockets are one-shot deals that can't be relit. The Russians have been working on a booster that deploys a wing and glides back home, with a little nose-mounted engine to drive it. But that's been in development hell for over a decade.
- seanflyon 12y ago
  http://en.wikipedia.org/wiki/Baikal_(rocket_booster) http://en.wikipedia.org/wiki/Baikal_(rocket_booster)
jccooper 12y ago
It re-uses existing systems (gimballing engines, computers) to effect the recovery. They do add some stuff (legs, RCS, and now fins) but those have nothing like the mass and aero penalties from wings. It also minimizes development cost, since it's a modification of the existing expendable stage and can be tested during revenue flights, rather than development of a whole new vehicle. Hovering a rocket, btw, is not that hard these days. Look up the Lunar Lander Challenge and/or Masten, Armadillo, Unreasonable Rocket, Morpheus, Mighty Eagle. Big and tall rockets are also easier to hover, given their large moment arm. Think balancing a broom on your hand vs a pencil. (Not that an F9-1 can hover--it's too powerful and too light--but it's a similar operation to do a controlled slowdown.)

Can someone explain to me the value of landing a tall, cylindrical rocket vertically like this? It just seems like such an odd thing to do.

by smegel 12y ago

Can someone explain to me the value of landing a tall, cylindrical rocket vertically like this? It just seems like such an odd thing to do.

DuskStar 12y ago

Rockets are extremely weak in any direction other than straight up/down. The reinforcement to allow a Falcon 9 core to even lay on its side unpressurised would probably weigh more than the entire set of recovery hardware (legs, grid fins, extra rcs fuel, etc) to land vertically.

marktangotango 12y ago
Falcon 9 stages are stored on their sides unpressurized, see any of the numerous roll out videos, and factory images. There are launchers that require pressurization for handling (atlas 5?) but falcon is not one. Musk has mentioned this as a cost reduction and simplification withyou respect to encumbent providers, don't have a link unfortunately.
- outworlder 12y ago
  Yeah. But storing and gently moving are one thing. Flying and landing horizontally would require much more structural reinforcement.
  - XorNot 12y ago
    Bingo it's all about dynamic pressure: to be reusable the hull of the rocket has to land intact and not having undergone plastic deformation of any kind, so it's as close to "factory condition" as possible.

dshankar 12y ago

The point is reusability. Reusable rockets will dramatically lower the cost of rocket launches. (On the other hand, if you're questioning why rockets are tall & cylindrical, it's because that's the best design for rockets: https://www.quora.com/Spacecraft/Why-are-rockets-tall-and-slender https://www.quora.com/Spacecraft/Why-are-rockets-tall-and-sl...)

smegel 12y ago
So just to be clear, these rockets are going into space, then somehow coming all the way back down and landing? It seems fantastical that such a rocket could have a controlled descent from space and then land vertically (considering how the shuttle does it for example). How will it control decent speed? Will they carry enough fuel to control the entire descent and land?

lmm 12y ago

The engine is at the bottom pointing down, so the only way to do a powered soft landing is vertically. Other posts talk about why they're using the engine rather than e.g. parachutes.

tinco 12y ago

Landing it horizontally would require the rocket to be able to coast horizontally, meaning it would have to have wings. I can imagine wings would make the whole thing more complex but even if they nailed that, imagine what it would have to do on the descent. You basically have two choices, either fall straight down and try to control spin, or coast down, trying to control horizontal and vertical speed like an aeroplane. I have the suspicion that when dropping from space it's very hard to get into coasting mode since the air is so thin. However it is, a rocket that simply falls down instead of coasting like an aeroplane is so much less structurally complex, the only real challenge is controlling its landing which modern computers and their rocket engine make feasible.

InclinedPlane 12y ago

Aerodynamically it wants to be aligned along the vertical axis. Similar thing for thrust forces. So at a minimum you want to decelerate all the way down from terminal velocity with the vertical direction aligned to the direction of travel. And that only leaves a narrow window of time after which you could bother concerning yourself with reorienting. And, of course, reusing the main engines saves on complexity a great deal.

andygates 12y ago

The heavy stuff is all at the engine-end, so absent any lift, that's the orientation you get. Shuttle SRB's hung from parachutes in the nose, but a chute landing is still pretty fast. The hot motors were dunked in salt water at speed... generally worse all round. Solid rockets are one-shot deals that can't be relit. The Russians have been working on a booster that deploys a wing and glides back home, with a little nose-mounted engine to drive it. But that's been in development hell for over a decade.

seanflyon 12y ago
http://en.wikipedia.org/wiki/Baikal_(rocket_booster) http://en.wikipedia.org/wiki/Baikal_(rocket_booster)

jccooper 12y ago

It re-uses existing systems (gimballing engines, computers) to effect the recovery. They do add some stuff (legs, RCS, and now fins) but those have nothing like the mass and aero penalties from wings. It also minimizes development cost, since it's a modification of the existing expendable stage and can be tested during revenue flights, rather than development of a whole new vehicle. Hovering a rocket, btw, is not that hard these days. Look up the Lunar Lander Challenge and/or Masten, Armadillo, Unreasonable Rocket, Morpheus, Mighty Eagle. Big and tall rockets are also easier to hover, given their large moment arm. Think balancing a broom on your hand vs a pencil. (Not that an F9-1 can hover--it's too powerful and too light--but it's a similar operation to do a controlled slowdown.)