5 ms·

SpaceX is a cutting edge pioneer of the modern space race. Their Falcon 9 rocket represented more than 50% of all US rocket launches in 2017. When they announc

SpaceX is a cutting edge pioneer of the modern space race. Their Falcon 9 rocket represented more than 50% of all US rocket launches in 2017. When they announced their vertical landing program, critics across the industry laughed at them. Only a couple years later, their landings are so routine they don't even warrant press anymore.

sschueller 8y ago
Vertical landing is a parlor trick that isn't that hard and has been done before (McDonnell Douglas DC-X). It is a huge waste of fuel. You loose half of the payload capacity in order to land these things. In the long run it is not economically sustainable.
- Jonnax 8y ago
  So how else do you propose to have a reusable rocket? Smashing it into the ground or sea doesn't quite work.
  - sschueller 8y ago
    Add parachutes and dump them in the sea.
    - olex 8y ago
      That actually adds more mass than the extra fuel required for propulsive landing. And significant refurbishment of engines is needed after they've contacted salt water.
      - dexen 8y ago
        We were using parachutes for the Space Shuttle SRBs, but there are certain important distinctions - the SRBs were, to a first approximation, "big dumb pipes", and had much less of a problem with saltwater damage due to water landing needed to cushion the impact. There were 3 parachutes, for a total of 3x 990kg [1] for the SRB's empty mass of 91'000kg. While Falcon Heavy's first stage is lighter (25'600 kg empty, each [2]), you would need disproportionately larger parachute size to achieve soft landing on the ground as opposed to SRB's water landing, to avoid salt water damage. And to possibly handle passenger flights. Off of the top of my head, with parachute landing you add mass because both: - the large parachutes are quite heavy themselves as above (add some overhead for covers and support installation; I can't find any numbers) - needs increased structural integrity to handle the tug during deployment and the much faster touch-down on landing; with propulsive landing you can essentially touchdown at 0/0/0 vertical/horizontal/angular velocities, as soon as you nail down the math of flight characteristics and engine control - possibly some sort of reaction control, to achieve proper deployment attitude - probably a smaller drogue chute(s) to handle supersonic flight, with all the complexity it adds Moreover, using chutes: - completely prevents RTL flights - complicates abort modes; you'd need to dump fuel and oxidizer quick (without mixing and igniting, good luck) to be able to rely on the chutes alone. However I guess the overriding concern for Musk was quick turn-around. With a parachute landing you have less control over the touchdown point [3]; the logistics of recovery, refurbishment and relaunch become much more involved, possibly spanning an ocean [4]. And with longer turn-around you need more flight hardware, and more ground support, to handle given amount of orbital or surface-to-surface traffic. Call it reducing the capex by going for somewhat costlier option that ensures much higher flight hardware utilization. Lastly, using parachutes would create an image of low reliability; it's not something we would consider as to be routinely performed by commercial passenger flights. You don't want to ship passengers to "somewhere near your destination"; you want to deliver them to the airport, right next to the jet bridge (call it rocket bridge?) and promptly usher them to the passenger terminal. Yes, yes, the routine BFR passenger travel is coming. [1] https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster#Descent_and_recovery https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Boo... [2] http://www.spaceflight101.net/falcon-9-v11.html http://www.spaceflight101.net/falcon-9-v11.html [3] Gemini-style Rogalo wing would help, if it could be scaled. See https://i.pinimg.com/564x/b0/84/87/b08487e18f16402e4867981ffe5e5bf1.jpg https://i.pinimg.com/564x/b0/84/87/b08487e18f16402e4867981ff... and https://vintagespace.files.wordpress.com/2011/12/rogallo-wing-model.jpg https://vintagespace.files.wordpress.com/2011/12/rogallo-win... Not as preposterous as it may seem, given that Buran's side-boosters were to glide to landing on deployable wings; see http://www.buran.ru/images/jpg/gk175-5.jpg http://www.buran.ru/images/jpg/gk175-5.jpg [4] you could bulk up the 1st stage enough to let it coast suborbitally all the way around globe to RTL, but that's another matter - and again uses up valuable fuel, and you run up against the rocket equation pretty quickly.
    - C14L 8y ago
      1. No sea on Mars. 2. Turnover of 24 hours would become impossible. 3. Structural stress so 10 re-flights would become unlikely.
    - adrianN 8y ago
      Parachutes don't work very well on Mars. Salt water kills delicate machines. Parachutes need very sturdy (and heavy) rockets.
    - gliptic 8y ago
      If you knew history, you'd know this has been tried before. The shuttle boosters did this; they barely saved any money after refurbishing. SpaceX tried it too, but had significant problems even re-entering without the rocket ripping apart, not even getting to the problems of recovering and refurbishing salt-water damaged hardware. This kind of attitude might have made more sense before SpaceX had demonstrated it was possible. After showing how the technology can be further refined for full and rapid reuse, and landing on Mars, it just reads as ignorant or intentionally misleading.
- adrianN 8y ago
  If only Space X had asked the experts on the Internet before pouring so much money into building reusable rockets...
- sjwright 8y ago
  Yes, what the DC-X did was a parlor trick. Vertical landing a post-orbit rocket onto a floating barge is not a parlor trick. The DC-X never did that. And vertical landing for real commercial orbital flights—then reusing those rockets for more real commercial orbital flights—is orders of magnitude more impressive again.
- sjwright 8y ago
  It might be "a huge waste of fuel" but the alternative is a huge waste of rocket. And the rocket is far more valuable than the fuel.
- wongarsu 8y ago
  Fuel cost is less than half a percent of launch cost. Wasting fuel isn't really a problem. If you want to land you need a bigger rocket for the same payload. But with how expensive rockets are, building them bigger and reusing them seems cheaper than letting them burn up. (And after a splashdown in saltwater refurbishment is way too expensive, so parachutes don't work well for reusability)

sschueller 8y ago

Vertical landing is a parlor trick that isn't that hard and has been done before (McDonnell Douglas DC-X). It is a huge waste of fuel. You loose half of the payload capacity in order to land these things. In the long run it is not economically sustainable.

Jonnax 8y ago
So how else do you propose to have a reusable rocket? Smashing it into the ground or sea doesn't quite work.
- sschueller 8y ago
  Add parachutes and dump them in the sea.
  - olex 8y ago
    That actually adds more mass than the extra fuel required for propulsive landing. And significant refurbishment of engines is needed after they've contacted salt water.
    - dexen 8y ago
      We were using parachutes for the Space Shuttle SRBs, but there are certain important distinctions - the SRBs were, to a first approximation, "big dumb pipes", and had much less of a problem with saltwater damage due to water landing needed to cushion the impact. There were 3 parachutes, for a total of 3x 990kg [1] for the SRB's empty mass of 91'000kg. While Falcon Heavy's first stage is lighter (25'600 kg empty, each [2]), you would need disproportionately larger parachute size to achieve soft landing on the ground as opposed to SRB's water landing, to avoid salt water damage. And to possibly handle passenger flights. Off of the top of my head, with parachute landing you add mass because both: - the large parachutes are quite heavy themselves as above (add some overhead for covers and support installation; I can't find any numbers) - needs increased structural integrity to handle the tug during deployment and the much faster touch-down on landing; with propulsive landing you can essentially touchdown at 0/0/0 vertical/horizontal/angular velocities, as soon as you nail down the math of flight characteristics and engine control - possibly some sort of reaction control, to achieve proper deployment attitude - probably a smaller drogue chute(s) to handle supersonic flight, with all the complexity it adds Moreover, using chutes: - completely prevents RTL flights - complicates abort modes; you'd need to dump fuel and oxidizer quick (without mixing and igniting, good luck) to be able to rely on the chutes alone. However I guess the overriding concern for Musk was quick turn-around. With a parachute landing you have less control over the touchdown point [3]; the logistics of recovery, refurbishment and relaunch become much more involved, possibly spanning an ocean [4]. And with longer turn-around you need more flight hardware, and more ground support, to handle given amount of orbital or surface-to-surface traffic. Call it reducing the capex by going for somewhat costlier option that ensures much higher flight hardware utilization. Lastly, using parachutes would create an image of low reliability; it's not something we would consider as to be routinely performed by commercial passenger flights. You don't want to ship passengers to "somewhere near your destination"; you want to deliver them to the airport, right next to the jet bridge (call it rocket bridge?) and promptly usher them to the passenger terminal. Yes, yes, the routine BFR passenger travel is coming. [1] https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster#Descent_and_recovery https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Boo... [2] http://www.spaceflight101.net/falcon-9-v11.html http://www.spaceflight101.net/falcon-9-v11.html [3] Gemini-style Rogalo wing would help, if it could be scaled. See https://i.pinimg.com/564x/b0/84/87/b08487e18f16402e4867981ffe5e5bf1.jpg https://i.pinimg.com/564x/b0/84/87/b08487e18f16402e4867981ff... and https://vintagespace.files.wordpress.com/2011/12/rogallo-wing-model.jpg https://vintagespace.files.wordpress.com/2011/12/rogallo-win... Not as preposterous as it may seem, given that Buran's side-boosters were to glide to landing on deployable wings; see http://www.buran.ru/images/jpg/gk175-5.jpg http://www.buran.ru/images/jpg/gk175-5.jpg [4] you could bulk up the 1st stage enough to let it coast suborbitally all the way around globe to RTL, but that's another matter - and again uses up valuable fuel, and you run up against the rocket equation pretty quickly.
  - C14L 8y ago
    1. No sea on Mars. 2. Turnover of 24 hours would become impossible. 3. Structural stress so 10 re-flights would become unlikely.
  - adrianN 8y ago
    Parachutes don't work very well on Mars. Salt water kills delicate machines. Parachutes need very sturdy (and heavy) rockets.
  - gliptic 8y ago
    If you knew history, you'd know this has been tried before. The shuttle boosters did this; they barely saved any money after refurbishing. SpaceX tried it too, but had significant problems even re-entering without the rocket ripping apart, not even getting to the problems of recovering and refurbishing salt-water damaged hardware. This kind of attitude might have made more sense before SpaceX had demonstrated it was possible. After showing how the technology can be further refined for full and rapid reuse, and landing on Mars, it just reads as ignorant or intentionally misleading.
adrianN 8y ago
If only Space X had asked the experts on the Internet before pouring so much money into building reusable rockets...
sjwright 8y ago
Yes, what the DC-X did was a parlor trick. Vertical landing a post-orbit rocket onto a floating barge is not a parlor trick. The DC-X never did that. And vertical landing for real commercial orbital flights—then reusing those rockets for more real commercial orbital flights—is orders of magnitude more impressive again.
sjwright 8y ago
It might be "a huge waste of fuel" but the alternative is a huge waste of rocket. And the rocket is far more valuable than the fuel.
wongarsu 8y ago
Fuel cost is less than half a percent of launch cost. Wasting fuel isn't really a problem. If you want to land you need a bigger rocket for the same payload. But with how expensive rockets are, building them bigger and reusing them seems cheaper than letting them burn up. (And after a splashdown in saltwater refurbishment is way too expensive, so parachutes don't work well for reusability)