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Science Forum

  1. 09 Apr '16 07:36 / 1 edit
    SpaceX has finally successfully landed a first stage rocket on a drone ship.
    They had previously landed on land, but that is not an option for some launches. Drone ships are harder because of the waves but cheaper fuel wise and in some cases necessary.

    https://www.youtube.com/watch?v=sYmQQn_ZSys

    As soon as they are confident enough to start reflying the first stages, spaceflight will drop in cost significantly.

    Full launch here:
    https://www.youtube.com/watch?v=7pUAydjne5M
  2. 09 Apr '16 13:13
    I watched it live last night, The reaction from the guys at SpaceX was fantastic, that was
    some really hard engineering magic they pulled off.


    Now they need to start reusing the boosters and reliably landing them.

    Making the impossible routine, which has always been the hard part about space.
  3. 09 Apr '16 13:34
    Originally posted by googlefudge
    Now they need to start reusing the boosters and reliably landing them.

    Making the impossible routine, which has always been the hard part about space.
    I believe this is the fifth attempt at landing on the sea platform. Their only attempt at landing on land was successful. So that's already two out of seven. Even that success rate would, if they reuse the rockets, make a significant impact on space-flight costs. Obviously we actually expect that they will get something like a 90% or better success rate before long. The thing is that even with a 50% failure rate, it would be better than the current 100% discard rate that everyone has used up until now.
    I believe the first stage is worth about three quarters of the price tag of a launch. A 50% failure rate (or relaunch rate depending on how you choose to see it) would bring the cost of launches down by about 12%. Push that up to one failure in three and you get a 50% reduction in launch costs.
  4. Standard member sonhouse
    Fast and Curious
    12 Apr '16 19:04
    Originally posted by twhitehead
    I believe this is the fifth attempt at landing on the sea platform. Their only attempt at landing on land was successful. So that's already two out of seven. Even that success rate would, if they reuse the rockets, make a significant impact on space-flight costs. Obviously we actually expect that they will get something like a 90% or better success rate b ...[text shortened]... by about 12%. Push that up to one failure in three and you get a 50% reduction in launch costs.
    What about the lower payload of such a system?
  5. 12 Apr '16 19:21
    Originally posted by sonhouse
    What about the lower payload of such a system?
    Most of SpaceX's recent launches have used the system without an issue ie they have met the payload requirements whilst still managing to return the first stage booster. If you need higher payloads, use a bigger rocket. I believe Falcon Heavy will have three boosters, which can all theoretically be returned.

    For the launch in question, it would actually have been possible to return the rocket to land, but there was a higher margin of success at sea so they choose to do that.

    For divisible cargo, it is possible to have multiple missions, and if they can achieve over 60% success rate it is cheaper to launch two missions and return the first stage booster than to have a single heavy lift mission and loose the booster. More missions also divides the risk, so it has other advantages.

    This particular mission for example had cargo destined for the ISS, but was also delivering some Cube Sats for Planet Labs.

    SpaceX says that if tests go well, the first stage from this mission will be reused. That's potentially a massive saving for SpaceX or their customer or both. One potential customer is prepared to use it but wants a 50% reduction in price! Keep in mind that SpaceX is already by far the cheapest launch provider out there.


    https://en.wikipedia.org/wiki/SpaceX_reusable_launch_system_development_program#First_landing_on_drone_ship
  6. Standard member sonhouse
    Fast and Curious
    12 Apr '16 19:42
    Originally posted by twhitehead
    Most of SpaceX's recent launches have used the system without an issue ie they have met the payload requirements whilst still managing to return the first stage booster. If you need higher payloads, use a bigger rocket. I believe Falcon Heavy will have three boosters, which can all theoretically be returned.

    For the launch in question, it would actuall ...[text shortened]... wikipedia.org/wiki/SpaceX_reusable_launch_system_development_program#First_landing_on_drone_ship
    Why can't they just use a high end parachute?
  7. 12 Apr '16 20:33
    Originally posted by sonhouse
    Why can't they just use a high end parachute?
    Because dropping a spacecraft into the sea causes damage and corrosion that takes
    a long time to repair even after the expensive recovery operation. A lesson learned from
    the Space Shuttles SR Boosters. [Also, even without fuel the first stage is a ~40m tall
    multi-tonne beast that is very hard to successfully parachute down, and the parachute and
    reinforcing required doesn't weigh a whole lot less than the fuel. And unlike the fuel it
    can't be used in a pinch to help recover from a failure to try to complete the primary mission.]

    Landing on land, or the drone ship, means far less work and expense to do a rapid turnaround.

    I would also note that SpaceX's Falcon Heavy is slated to be able to lift more payload to
    orbit than any other vehicle aside from the Saturn V [~50 metric tonnes]... And while NASA's proposed
    Space Launch System [SLS] is slated to be able to beat both [~70 metric tonnes], it will do so at
    vastly greater cost and at most 2 launches per year. Assuming it doesn't get cancelled and doesn't slip
    even farther behind schedule.

    And looking farther ahead... SpaceX is looking to build for it's next craft, a launch system
    capable of lifting 100+ people and putting them [and associated life support and/or cargo]
    not just into LEO but into Mars transfer orbit. [and use the same reusability system as the falcon]
    And at their current rate of progress, it's entirely possible that SpaceX will have the prototype
    built before NASA gets the SLS human rated.
  8. Standard member sonhouse
    Fast and Curious
    12 Apr '16 20:44 / 3 edits
    Originally posted by googlefudge
    Because dropping a spacecraft into the sea causes damage and corrosion that takes
    a long time to repair even after the expensive recovery operation. A lesson learned from
    the Space Shuttles SR Boosters. [Also, even without fuel the first stage is a ~40m tall
    multi-tonne beast that is very hard to successfully parachute down, and the parachute and ...[text shortened]... irely possible that SpaceX will have the prototype
    built before NASA gets the SLS human rated.
    That is really impressive, no doubt about it. That then begs the question, why didn't NASA do this 30 years ago?

    One thing I noticed on that booster return, the legs were really small extensions of the overall height of the booster. I think I would have made them stick out a bit more to make it more stable landing.

    I also thought the barge was not the most stable craft for such a landing, the height of the booster was way higher than the barge, just seemed a bit scary to get that thing to land safely. Any kind of high wind condition could have knocked it over.

    They still have some engineering to do I think.
  9. 12 Apr '16 20:49
    Originally posted by sonhouse
    That is really impressive, no doubt about it. That then begs the question, why didn't NASA do this 30 years ago?

    One thing I noticed on that booster return, the legs were really small extensions of the overall height of the booster. I think I would have made them stick out a bit more.
    Then they would weigh more... They stick out just enough to work.

    NASA is a bureaucratic basket-case with no clear mission and every shifting budgets.

    Without reforming your government, I am not convinced NASA is ever going to be at the
    forefront of anything over much any-more.

    Which is tragic.
  10. 12 Apr '16 20:54
    Originally posted by sonhouse
    I also thought the barge was not the most stable craft for such a landing, the height of the booster was way higher than the barge, just seemed a bit scary to get that thing to land safely. Any kind of high wind condition could have knocked it over.

    They still have some engineering to do I think.
    The barge landing area is apparently the size of [an American] football field.

    And given that if the stage falls-over it undergoes an "unplanned rapid exothermic disassembly event"
    it's not a particular worry about it falling off, it makes no difference.

    However, my thought about the barge is that they would do better to have the landing pad
    elevated up on bladed pillars from a submerged primary buoyancy float so that waves pass
    through between significantly reducing the motion of the landing pad. [a bit like an oil rig, but
    streamlined for rapid movement]

    I also note that weather conditions at the landing site are taken into account when deciding to
    launch.
  11. 12 Apr '16 21:49
    Originally posted by googlefudge
    And while NASA's proposed Space Launch System [SLS] is slated to be able to beat both [~70 metric tonnes], it will do so at vastly greater cost and at most 2 launches per year. Assuming it doesn't get cancelled and doesn't slip
    even farther behind schedule.
    https://en.wikipedia.org/wiki/Space_Launch_System
    During the joint Senate-NASA presentation in September 2011, it was stated that the SLS program has a projected development cost of $18 billion through 2017,


    Given that SpaceX launches are in the region of US$ 60m per launch and likely to go down, it would seem sensible to cancel the NASA program and pay SpaceX to do it all. The Falcon heavy may cost more per launch, but lets say it costs $500m. That still allows for over 36 launches with just the US$18 billion that NASA has lying around for the next two years. Keep in mind that the $18 billion budgeted does not include the actual rockets to be used as they are to be expendable.

    Even if SpaceX didn't develop a heavier lift version, one could presumably use multiple launches to get what you need into space?
  12. 12 Apr '16 21:53
    Originally posted by sonhouse
    They still have some engineering to do I think.
    It worked. You may not like how it looked, but you honestly can't say they got it wrong. When they have more failures, then start criticizing the leg length or the barge size.
    Note that a larger barge is not significantly more stable, and in all previous tests they have not missed the barge. I believe previous problems have included leg failure, but longer legs doesn't fix that.
  13. 12 Apr '16 22:01
    Originally posted by googlefudge
    Without reforming your government, I am not convinced NASA is ever going to be at the
    forefront of anything over much any-more.

    Which is tragic.
    I think they are still leaders in missions beyond earth. They have failed to keep up in the launch area, but spaceX has proved that the private sector can do that so they should let the private sector do that and stick to satellite / rover / telescope / spacecraft design.

    The James Webb telescope is at least in part a NASA project.
  14. Standard member sonhouse
    Fast and Curious
    12 Apr '16 22:01
    Originally posted by twhitehead
    It worked. You may not like how it looked, but you honestly can't say they got it wrong. When they have more failures, then start criticizing the leg length or the barge size.
    Note that a larger barge is not significantly more stable, and in all previous tests they have not missed the barge. I believe previous problems have included leg failure, but longer legs doesn't fix that.
    One thing I would fix would be to have a stable platform somewhat like the guns on the new tanks, you see the video's where the tank is up and down hilly ground but the gun stays aimed at the same place.

    They could do that for the barge with a platform that would be adjustable in real time to counter wave action. Does anyone know how much Musk spent getting to this point? I bet a lot less than NASA. I think though, he was awarded a huge contract.
  15. 13 Apr '16 06:45 / 2 edits
    Originally posted by sonhouse
    One thing I would fix would be to have a stable platform somewhat like the guns on the new tanks, you see the video's where the tank is up and down hilly ground but the gun stays aimed at the same place.
    That would be an expensive exercise which, as has been proven, would be unnecessary. You would need hydrolic actuators moving a football sized platform. You are trying to solve an engineering problem that you haven't proven actually exists. Yes the ship clearly moves a lot due to the waves, but is it really a problem needing solving? To what extent does it really affect the landing?
    If there really is a problem, then I would try and create a mechanism that grabs the legs and holds them to the deck once it is landed. That would probably be easier and cheaper than trying to stabilise the whole platform.

    They could do that for the barge with a platform that would be adjustable in real time to counter wave action. Does anyone know how much Musk spent getting to this point? I bet a lot less than NASA. I think though, he was awarded a huge contract.
    Wikipedia says the cost so far is unknown. Whatever the cost was, it will pay off very quickly. NASA hasn't got to this point, so there is no comparison to be made.
    It is possible the launch pricing covers all the costs, or it is possible SpaceX has invested a little in their future.
    In terms of rocket technology, SpaceX has beaten all the competition by a long long way in terms of price / performance.
    Their biggest challenge now is keeping up with demand. They are ramping up launches and will soon be launching every few weeks and within a year or two will be launching weekly. They may also build their own space port.

    Unless serious competition comes along, the re-usability of the first stage will allow them to undercut their competitors by such a large margin that nobody will want to use anyone else. Currently there is a lot of politics and corruption involved in choosing a launch provider, but when the price difference is big enough that becomes harder and harder to get away with.