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Why SpaceX Is Using Rocket Powered Landing

Discussion in 'SpaceX' started by Skotty, Apr 28, 2014.

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  1. Skotty

    Skotty 2014 Model S P85

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    Anytime I see a thread of comments about SpaceX's landing attempts, there is often talk from one or more people about landing efficiency and suggesting or questioning that using parachutes or wings would be better than exclusively using a rocket powered landing. However, I think there is a reason why SpaceX is favoring rocket powered landing, but I don't ever see anyone suggest it. So I'm suggesting it here to see what others think. To understand why SpaceX is favoring rocket powered landing, other than it being feasible and just being cool, I believe has to do with the bigger picture that most people don't seem to consider.

    I think part of the answer has to do with logistics. A glider would require a rather complex rocket design in order to carry wings and finish with either a powered vertical landing or rolling landing gear. And parachutes might hurt rapid reusability due to needing to repack the parachutes.

    But more than that. Think beyond Earth. How adaptable would glider or parachute designs be to other planetoids with different atmospheres and different gravity? I think it would be a big problem. And they wouldn't work at all in places with no atmosphere like our Moon. Now think about the powered rocket landing technology that SpaceX is using. This could work almost anywhere, possibly with only minor design changes for the more extreme environments. I think, in this context, suddenly powered rocket landing makes a lot more sense.

    This could also be a contributing reason as to why SpaceX has not had much interest in the rocket designs that attempt to use our own atmosphere to assist the boost stage to where it doesn't have to carry as much fuel (sorry, can't remember what those are called at the moment).

    And finally...well...it's just so darn cool. :cool:
     
  2. Larry Chanin

    Larry Chanin Model S Perf Sig 1055

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    Personally I think the answer is pretty simple. The economics and reusability of a booster section would be greatly impacted if it lands in water.

    So it needs to return to land and ideally it needs to return to its launch site. Parachutes don't provide enough of a soft landing nor can they precisely return the space craft to the launch site.

    Larry
     
  3. ecarfan

    ecarfan Well-Known Member

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    Larry I agree but Skotty has a good point: once SpaceX has mastered soft landings using the booster's onboard rockets on Earth (which they appear to be very close to achieving), they will also be able to do it on Mars. And in the future rocket fuel can be manufactured on Mars.

    It's all part of Elon's master plan...
     
  4. GlennAlanBerry

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    I think Elon is mainly trying to reduce lift costs (from Earth), so that it will become more affordable and feasible to have a permanent and growing space capability and presence. That will eventually make things like mining asteroids, going back to a permanent presence on the Moon and going to Mars, permanently, possible.
     
  5. Reykjavik

    Reykjavik Member

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    Just because the stage can land on earth doesn't mean it can land on Mars or the Moon. Having too much thrust can be a problem, if you can't get a thrust to weight ratio of 1, you have to time your burn perfectly. If you can throttle between less than and more than 1, you can land as long as you have enough fuel. But Even on one engine, the falcon 9 first stage is going to have high TWR when mostly empty, especially in low gravity.

    I think it is really more about simplicity of the vehicle and logistics. using the same propulsion and control system means less cost and less that can go wrong.
     
  6. ElSupreme

    ElSupreme Model S 03182

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    He has mentioned reasons in places here and there. Here is a list that I can remember:

    Powered landing is very soft, minimizing potential for damage.
    Powered landing is accurate and precise, minimizing time to recover/rebuild/refuel/relaunch.
    Powered landing allows for powered deceleration, allowing recovery at reentry speeds potentially.
    Parachute landings are actually fairly violent.
    Parachutes are time consuming to turn over properly and safely.

    Versus wings and wheels I think it adds much more complexity and weight to launch it isn't worth it cost wise. He also mentions that much of the shuttle wasn't reusable.

    EDIT: And as Reykjavik points out. Adding such detailed control to what is basically the flight/launch systems makes both more robust, and precise.
     
  7. VolkerP

    VolkerP EU Model S P-37

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    Reusing all the flight systems (fuel tanks + rocket boosters) for a landing minimizes the overhead of soft landing capability: more fuel, restartable and throttleable boosters and landing legs. Plus on a mission where soft landing is not desired, you can do away with the landing legs and use the full fuel capacity for lifting more payload to orbit.

    Whereas a parachute or wings/landing gear system would introduce more overhead and call for totally different design of the vehicle in the reusable/expendable variants.
     
  8. Larry Chanin

    Larry Chanin Model S Perf Sig 1055

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    The simple point that I am making is that first and foremost the decision to go with powered landings is governed by the economics of reusability here on Earth now, not future considerations else where. If it can be used later else where fine, but that is not the governing consideration for powered landings now.

    Larry
     
  9. Doug_G

    Doug_G Lead Moderator

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    I think the most obvious things are precision landings, simplicity, and minimal extra weight.

    Parachutes can't get you to a designated location and land you safely without damage.

    This is simpler because the same engines and control systems are used for both ascent and descent.

    The only substantial things you have to add is extra fuel and landing legs. If you added wings you'd have a lot more weight and complexity - control surfaces on the wings, additional control systems, wheeled landing gear, brakes, etc.
     
  10. jeff_adams

    jeff_adams Member

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    When Elon was 12 he wrote the video game Blastar. His rockets didn't land with sissy parachutes, they landed with their engine.....

    A case of life imitating art.

    j/k.....I never saw his game played
     
  11. mknox

    mknox Well-Known Member

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    I wonder about the "rapid turnaround" capability, especially when crewed flights begin. The Space Shuttle had to practically be re-built after each flight. Forget the SRBs, I'm talking about removal and overhaul of the 3 main engines. Are SpaecX's 9 main engines that more robust and reliable that you can just refuel and go?
     
  12. jeff_adams

    jeff_adams Member

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    They seem to do quite a few test fires. I'm guessing they don't rebuild the engines after that, but the test fires may only last seconds instead of minutes
     
  13. nwdiver

    nwdiver Active Member

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  14. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    You also want a powered landing because if something goes wrong, you have more control over how wrong.
     
  15. EarlyAdopter

    EarlyAdopter Active Member

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    Yes, according to Elon. "In principal we should be able to refly it the same day." in response to a question starting at 12:50 Reuters Insider
     
  16. Mario Kadastik

    Mario Kadastik Active Member

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    I was really surprised that they expect a turnaround time of less than a day. That's huge. But we've already seen it. Even for aborted launches that had a 1h launch window they were able to do multiple attempts and I found the most interesting one to be when they aborted on the SRS flight T+00:00:01 after engine firing and reset to T-00:13:00 and were going for a second attempt. Most launch vehicles firstly cannot abort post-ignition, but I'd assume even if they could they'd not be able to re-launch in minutes. They decided to scrub it in the end as they wanted more data on the slow pressure buildup and ended up changing a valve, but mentioned they could have gone for a launch.
     
  17. mknox

    mknox Well-Known Member

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    I think that would be fantastic, but I'll believe it when I see it. That was the early promise for the Space Shuttle too. I realize they're not the same thing, but even traditional rocket stages are subject to some pretty extreme stuff, and I'm not sure I'd want to get in to a Dragon capsule atop rocket stages that were being turned around "the same day". Not a lot of time for a thorough inspection.
     
  18. Skotty

    Skotty 2014 Model S P85

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    If they're not, I think you'll see some additional engine design changes.
     
  19. dsm363

    dsm363 Roadster + Sig Model S

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    Every time I launch that link I see the article for two seconds then a McDonalds ad pops up and I can't get around it. Is there a direct link you YouTube videos?
     
  20. dsm363

    dsm363 Roadster + Sig Model S

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    Aren't they talking about turnaround in order of a few weeks? There still would be time to inspect things.
     

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