8 ms·

Am i missing something, is the need to land vertically a requirement of a fragile fuselage? Seems wasteful to carry extra anything (in this case rocket propella

Am i missing something, is the need to land vertically a requirement of a fragile fuselage? Seems wasteful to carry extra anything (in this case rocket propellant) to space, just to avoid having to re-right the rocket when you get it back on earth for a subsequent launch. Is extra fuel payload < landing gear or parachutes?

Davesjoshin 10y ago
I'm guessing they want a single solution like vector thrusting because it can be used on planets with and without atmospheres.
ehnto 10y ago
It is partly because they are trying to develop a system which can be used regardless of atmospheric conditions, so reusable in another sense. Parachutes don't do so well on the moon, for example. But also because a parachute landing actually does a lot more damage than you might expect, and sea water is the last thing you want in your million dollar rocket engine.
jonknee 10y ago
IIRC it's the most stable position because it's a big empty tube with some really heavy rocket engines at the base. It's also precise so they can land on a tiny barge in the ocean.
mikeash 10y ago
Parachutes aren't massless. The parachutes you'd need to land a rocket like this are actually comparable in mass to the extra fuel and landing legs needed for the vertical landing approach. You also can't land on a ship with parachutes. You don't have enough control. You can still land at sea, but then you have to actually land in the water, which means getting seawater on all your rocket hardware. That causes lots of problems when you want to use that hardware again. SpaceX did experiment with this approach. Here's a picture of the second Falcon 9's interstage with parachutes packed inside: http://i.imgur.com/PGXIqKX.jpg http://i.imgur.com/PGXIqKX.jpg But it turned out not to work so well. NASA had some success with this approach on the Shuttle SRBs. It's easier with solid fuel rockets, because they're less efficient and built tougher. Even then, the cost of recovery and refurbishment ended up roughly breaking even compared to just building new ones each time. As far as "wasteful" goes, that depends on what you're looking at. Saving fuel for the landing subtracts from payload capacity, which is wasteful in theory... but in practice, many payloads are smaller than the maximum anyway. If you suffer a 30% payload penalty, but you're launching a satellite which is 40% smaller than your maximum, then who cares? The only waste is some extra fuel, which is super cheap. The full fuel load for a Falcon 9 launch is something like $200,000, compare to the total mission price of around $60 million.
- sevenless 10y ago
  If the problem is simply the seawater, you could use a large plastic liner to create a pool of fresh water floating in the sea, and land in that.
  - mikeash 10y ago
    Given the lack of fine guidance control that parachutes imply, your "large" plastic liner would have to be miles in diameter.
    - deleted 10y ago
      [deleted]
    - deleted 10y ago
      [deleted]
  - rtkwe 10y ago
    That's a lot of complexity to add compared to the current landing which boils down at it's simplest to an inverted pendulum balancing problem, hard but the dynamics are pretty well understood. First parachute landings aren't super accurate without a lot of engineering and controls and would rely on calm or no winds down range wherever you're landing to have any chance of hitting the 'pool'. Second that pool would want to float and to my knowledge no one's made anything like that, so they'd have to invent and build then deploy a huge piece of engineering for every single launch.
  - CydeWeys 10y ago
    This pool of freshwater would need to be many kilometers in diameter to give a high chance of hitting it with an unpowered parachute descent (thanks to unpredictability of the winds). At this point you are talking about doing something that is much, much more expensive than the current approach of a powered landing. How are you going to get so much freshwater out into the sea, anyway? That's way more water than could be carried in the largest cargo ship that exists.
    - 10y ago
arijun 10y ago
I believe they did try or at least look into parachutes initially, but gave it up as not feasible. With the powered landing, you already have the engines there, it's just a matter of leaving a bit more fuel. It's not a lot of fuel because you've already dropped a bunch of mass (the whole second stage and a bunch of fuel), and air is helping instead of hindering. There's also the fact that, unlike parachutes, you can use a powered landing on Mars and the Moon.
usrusr 10y ago
Lack of wings. (That's obviously for the landing gear part of the question) But fragile fuselage is certainly spot on. Parachute-landings still have quite some impact velocity. Strengthening an object the size of a Falcon 9 first stage to survive that impact would require a much stronger and thus prohibitively heavy structure, even if the parachute itself was free. The nice thing about powered upright landing is that all the forces involved are pretty much the same as during launch so that there is little (if any) additional strengthening required. Note also how the ULA plans for the use of parachutes to recover first stage engine blocks require the parachute to be caught in-flight by a helicopter to avoid any uncontrolled ground contact.
- gozur88 10y ago
  Even if you were sure the engines would survive impact, you wouldn't want your expensive, complex rocket engine to take a dunk in salt water.
- lutorm 10y ago
  This is a good point. Remember that the early "sea landing" experiments ended with the stage breaking up just from falling over into the water.
danielweber 10y ago
Armadillo lost several craft to parachutes. When you add them to a system, you also have to worry about them deploying at the wrong time.
InclinedPlane 10y ago
If it's such a good idea, why don't all airlines use it for airplane landings?
- lmm 10y ago
  Airliners don't land on their tails either. If that's your model then Adeline is the correct approach.
  - InclinedPlane 10y ago
    I think you missed the observation there. Airliners could certainly land with parachutes. They could even glide in for unpowered landings. And doing so would save a lot of fuel in either case. But that fuel savings would come at the cost of adding huge operational complexities, and risks. Powered landings are more precise, more predictable, and more reliable. They reduce operational complexities, even if they are costly, and for that reason they are more than worth the fuel costs. An airplane could carry more weight a farther distance if it glided into landing unpowered, but effectively all landings would become emergency situations, and it's just not worth the small benefit of increasing payload. The same is true in orbital rocketry as well. Parachutes may seem like a good idea, but they increase recovery complexity and costs, they increase the likelihood of damage to the rocket, they reduce predictability, and so on. Powered landings are the most dependable way of ensuring the stage can be returned and of doing so within an operational profile that can be streamlined and optimized until its very reliable and efficient, just like landing a plane. The fact that it comes at some cost of payload capacity is comparatively inconsequential, as it substantially increases the likelihood of recovering the tens of millions of dollars worth of launch vehicle hardware (which over its lifetime will service launches worth hundreds of millions of dollars).
    - lmm 10y ago
      I just don't think you can generalize like that. A "powered" landing for an aeroplane is very different from what SpaceX is doing, e.g. an aeroplane can and often does abort and go around, whereas the rocket has no such capability.
grecy 10y ago
Keep in mind everything SpaceX are doing is with the goal of getting to Mars. They don't want to use cranes, or parachutes or helicopters or complex landing structures, because none of those things will work on Mars in such a way the rocket just needs to be refueled and can fly again.
paulsutter 10y ago
Elon intends to land rockets on Mars and return them to Earth. Mars is light on facilities for refurbishing rockets.

Davesjoshin 10y ago

I'm guessing they want a single solution like vector thrusting because it can be used on planets with and without atmospheres.

ehnto 10y ago

It is partly because they are trying to develop a system which can be used regardless of atmospheric conditions, so reusable in another sense. Parachutes don't do so well on the moon, for example. But also because a parachute landing actually does a lot more damage than you might expect, and sea water is the last thing you want in your million dollar rocket engine.

jonknee 10y ago

IIRC it's the most stable position because it's a big empty tube with some really heavy rocket engines at the base. It's also precise so they can land on a tiny barge in the ocean.

mikeash 10y ago

Parachutes aren't massless. The parachutes you'd need to land a rocket like this are actually comparable in mass to the extra fuel and landing legs needed for the vertical landing approach. You also can't land on a ship with parachutes. You don't have enough control. You can still land at sea, but then you have to actually land in the water, which means getting seawater on all your rocket hardware. That causes lots of problems when you want to use that hardware again. SpaceX did experiment with this approach. Here's a picture of the second Falcon 9's interstage with parachutes packed inside: http://i.imgur.com/PGXIqKX.jpg http://i.imgur.com/PGXIqKX.jpg But it turned out not to work so well. NASA had some success with this approach on the Shuttle SRBs. It's easier with solid fuel rockets, because they're less efficient and built tougher. Even then, the cost of recovery and refurbishment ended up roughly breaking even compared to just building new ones each time. As far as "wasteful" goes, that depends on what you're looking at. Saving fuel for the landing subtracts from payload capacity, which is wasteful in theory... but in practice, many payloads are smaller than the maximum anyway. If you suffer a 30% payload penalty, but you're launching a satellite which is 40% smaller than your maximum, then who cares? The only waste is some extra fuel, which is super cheap. The full fuel load for a Falcon 9 launch is something like $200,000, compare to the total mission price of around $60 million.

sevenless 10y ago
If the problem is simply the seawater, you could use a large plastic liner to create a pool of fresh water floating in the sea, and land in that.
- mikeash 10y ago
  Given the lack of fine guidance control that parachutes imply, your "large" plastic liner would have to be miles in diameter.
  - deleted 10y ago
    [deleted]
  - deleted 10y ago
    [deleted]
- rtkwe 10y ago
  That's a lot of complexity to add compared to the current landing which boils down at it's simplest to an inverted pendulum balancing problem, hard but the dynamics are pretty well understood. First parachute landings aren't super accurate without a lot of engineering and controls and would rely on calm or no winds down range wherever you're landing to have any chance of hitting the 'pool'. Second that pool would want to float and to my knowledge no one's made anything like that, so they'd have to invent and build then deploy a huge piece of engineering for every single launch.
- CydeWeys 10y ago
  This pool of freshwater would need to be many kilometers in diameter to give a high chance of hitting it with an unpowered parachute descent (thanks to unpredictability of the winds). At this point you are talking about doing something that is much, much more expensive than the current approach of a powered landing. How are you going to get so much freshwater out into the sea, anyway? That's way more water than could be carried in the largest cargo ship that exists.
  - 10y ago

arijun 10y ago

I believe they did try or at least look into parachutes initially, but gave it up as not feasible. With the powered landing, you already have the engines there, it's just a matter of leaving a bit more fuel. It's not a lot of fuel because you've already dropped a bunch of mass (the whole second stage and a bunch of fuel), and air is helping instead of hindering. There's also the fact that, unlike parachutes, you can use a powered landing on Mars and the Moon.

usrusr 10y ago

Lack of wings. (That's obviously for the landing gear part of the question) But fragile fuselage is certainly spot on. Parachute-landings still have quite some impact velocity. Strengthening an object the size of a Falcon 9 first stage to survive that impact would require a much stronger and thus prohibitively heavy structure, even if the parachute itself was free. The nice thing about powered upright landing is that all the forces involved are pretty much the same as during launch so that there is little (if any) additional strengthening required. Note also how the ULA plans for the use of parachutes to recover first stage engine blocks require the parachute to be caught in-flight by a helicopter to avoid any uncontrolled ground contact.

gozur88 10y ago
Even if you were sure the engines would survive impact, you wouldn't want your expensive, complex rocket engine to take a dunk in salt water.
lutorm 10y ago
This is a good point. Remember that the early "sea landing" experiments ended with the stage breaking up just from falling over into the water.

danielweber 10y ago

Armadillo lost several craft to parachutes. When you add them to a system, you also have to worry about them deploying at the wrong time.

InclinedPlane 10y ago

If it's such a good idea, why don't all airlines use it for airplane landings?

lmm 10y ago
Airliners don't land on their tails either. If that's your model then Adeline is the correct approach.
- InclinedPlane 10y ago
  I think you missed the observation there. Airliners could certainly land with parachutes. They could even glide in for unpowered landings. And doing so would save a lot of fuel in either case. But that fuel savings would come at the cost of adding huge operational complexities, and risks. Powered landings are more precise, more predictable, and more reliable. They reduce operational complexities, even if they are costly, and for that reason they are more than worth the fuel costs. An airplane could carry more weight a farther distance if it glided into landing unpowered, but effectively all landings would become emergency situations, and it's just not worth the small benefit of increasing payload. The same is true in orbital rocketry as well. Parachutes may seem like a good idea, but they increase recovery complexity and costs, they increase the likelihood of damage to the rocket, they reduce predictability, and so on. Powered landings are the most dependable way of ensuring the stage can be returned and of doing so within an operational profile that can be streamlined and optimized until its very reliable and efficient, just like landing a plane. The fact that it comes at some cost of payload capacity is comparatively inconsequential, as it substantially increases the likelihood of recovering the tens of millions of dollars worth of launch vehicle hardware (which over its lifetime will service launches worth hundreds of millions of dollars).
  - lmm 10y ago
    I just don't think you can generalize like that. A "powered" landing for an aeroplane is very different from what SpaceX is doing, e.g. an aeroplane can and often does abort and go around, whereas the rocket has no such capability.

grecy 10y ago

Keep in mind everything SpaceX are doing is with the goal of getting to Mars. They don't want to use cranes, or parachutes or helicopters or complex landing structures, because none of those things will work on Mars in such a way the rocket just needs to be refueled and can fly again.

paulsutter 10y ago

Elon intends to land rockets on Mars and return them to Earth. Mars is light on facilities for refurbishing rockets.