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Thread: SpaceX

  1. #1471
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    Quote Originally Posted by Nicolas View Post
    That's also how I understood it. They just went to the limit.

    Thought exercise I'm doing:
    -imagine launching 3 identical rockets next to each other in the perfect world. They'd launch in perfect sync.
    --> if you'd interconnect these 3 identical rockets, no forces would be passed from either rocket to the other ones; it would feel for each of the rockets as if it was flying by itself.
    -Now let's go to a FH, D4H, SST design. Here you have enormous forces generated by the side rockets/boosters on the main core. Following the reasoning above, is the sole reason for that the fact that the central core has the extra mass of the upper stages and payload slowing it down? So effectively on FH the side cores are pulling up the central core which wants to go slower because of its extra weight.
    -So that also means that, the larger the weight difference between boosters and central core, the larger the forces excerted by the side cores on the central core (assuming identical thrust for all three cores).

    Any errors in this reasoning or is my degree actually worth something?
    The difference I see between that and the actual launch was that the side rockets ran through their fuel faster than the central core. In some of the CNN footage the flame spout coming out of the central rocket was noticeably shorter than that coming out of the sides which were at full throttle, at least for a time early in the launch (that didn't seem as visible in the SpaceX feed). That's why the central core still had about 30 seconds of fuel left after the side rockets jettisoned.

  2. #1472
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    If the cores are rigidly attached to each other, as they are, wouldn't it be the same physics problem as a single rocket with multiple engines?

  3. #1473
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    @Darrell the thrust being generated by every single engine still needs to be sent/spread through the entire stack to make everything go up at once. Because in essence, it's only the engine itself that, really, really, desperately wants to go upwards and it will only take other parts of the vehicle with it on its way up if that part is connected to the engine and that connection can deal with the forces due to the acceleration.

    @crescent a difference in thrust between the cores would make the forces on their interconnections even larger than just the weight difference. All in all, I can believe it comes to a point where "way hard" is the correct way to describe the (re)design effort to make it all work.
    Last edited by Nicolas; 2018-Feb-07 at 10:53 PM.

  4. #1474
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    Quote Originally Posted by Nicolas View Post
    All in all, I can believe it comes to a point where "way hard" is the correct way to describe the (re)design effort to make it all work.
    I believe that Musk said that the redesign of the core was a much bigger task than he had originally thought.
    He also said (or at least I read) that the boosters are essentially F9 cores with cones on the top.

    So, for whatever reason, the biggest difficulty is with the central core.
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  5. #1475
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    Quote Originally Posted by schlaugh View Post
    Any comment yet why the third burn put the Tesla into a deeper orbit than originally announced?
    As far as I'm aware, they never gave any details on the target orbit apart from it being one that could be used to reach Mars. The Heavy has considerably more performance than is needed for a minimal-energy Hohmann transfer with such a light payload, and they had no reason to target any specific orbit or encounter velocity when Mars isn't even going to be there to encounter, so they might as well burn all the propellant to demonstrate what the vehicle can do.

  6. #1476
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    SpaceX

    Quote Originally Posted by cjameshuff View Post
    As far as I'm aware, they never gave any details on the target orbit apart from it being one that could be used to reach Mars. The Heavy has considerably more performance than is needed for a minimal-energy Hohmann transfer with such a light payload, and they had no reason to target any specific orbit or encounter velocity when Mars isn't even going to be there to encounter, so they might as well burn all the propellant to demonstrate what the vehicle can do.
    Yes that was my assumption. It was a first-time, full up, integrated test of the whole stack.

    I am having an argument with a numb....other person...on another forum who asserts that the new orbit is a screw up and Musk should not be allowed to play with nice things like rockets. I think the guy may work for ULA. :banghead:


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  7. #1477
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    Any idea of how long before they lose contact with Starman. It's interesting to watch the live feed as Earth slowly recedes in the distance.

  8. #1478
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    Just imagine what any future space travelers, Human or Alien, will think if they ever stumble across Starman and his ride while exploring the solar system.

  9. #1479
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    Quote Originally Posted by Superluminal View Post
    Any idea of how long before they lose contact with Starman. It's interesting to watch the live feed as Earth slowly recedes in the distance.
    Some time ago: https://www.instagram.com/p/Be6VZEzgAEk/

    IIRC, they had an estimated 12 hours of battery life, and of course no suitable transmitter on the second stage for interplanetary communication.

  10. #1480
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    Quote Originally Posted by Nicolas View Post
    That's also how I understood it. They just went to the limit.

    Thought exercise I'm doing:
    -imagine launching 3 identical rockets next to each other in the perfect world. They'd launch in perfect sync.
    --> if you'd interconnect these 3 identical rockets, no forces would be passed from either rocket to the other ones; it would feel for each of the rockets as if it was flying by itself.
    -Now let's go to a FH, D4H, SST design. Here you have enormous forces generated by the side rockets/boosters on the main core. Following the reasoning above, is the sole reason for that the fact that the central core has the extra mass of the upper stages and payload slowing it down? So effectively on FH the side cores are pulling up the central core which wants to go slower because of its extra weight.
    -So that also means that, the larger the weight difference between boosters and central core, the larger the forces excerted by the side cores on the central core (assuming identical thrust for all three cores).

    Any errors in this reasoning or is my degree actually worth something?
    Yes; the central core also throttles back further during launch so it can burn after the boosters separate. This increases the dV by improving the effective mass fraction.

  11. #1481
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    Quote Originally Posted by schlaugh View Post
    Any comment yet why the third burn put the Tesla into a deeper orbit than originally announced?


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    That might be part of the spacial orbital maneuver put for the US air force.

    https://www.cnbc.com/2018/02/08/elon...s-claimed.html

    "After launch, the Tesla cruised through space for a good six hours — a trip that was also live-streamed by SpaceX. This "coast" phase was meant to show off a special orbital maneuver for the US Air Force, before the rocket completed one final engine burn in space and put the car on its final orbit. It looks like that burn might have happened somewhere over Southern California, as some people in the area started reporting sightings of the rocket igniting in the night sky after 9:30PM ET on Tuesday."

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  12. #1482
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    I wonder what kind of testing or analysis the Tesla went through prior to launch.

    Imagine the embarrassment if the seat or dashboard foam popped open in the vacuum. The car would have looked like a 1973 Ford I once owned.



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  13. #1483
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    They may have placed it in a vacuum chamber to be sure nothing went horribly wrong. Other than that, not much. It's also a standard car, so none of the materials have been tested to survive a vacuum/radiation environment for a long time. It may look terrible after a few years. Or not.

  14. #1484
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    A source unknown to me claims the central core ran out of fuel and that's why only one engine started, resulting in a 400km/h crash 100m next to the ship.

  15. #1485
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    Quote Originally Posted by Nicolas View Post
    A source unknown to me claims the central core ran out of fuel and that's why only one engine started, resulting in a 400km/h crash 100m next to the ship.
    I heard someplace (sorry, couldn't find a reference) that it wasn't that it ran out of fuel, but that it ran out of TEA-TEB. TEA-TEB is used to relight the engines
    Reference about TEA-TEB
    Both the Saturn V and the Falcon 9 use TEA-TEB to ignite their kerosene-fueled engines. TEA-TEB is pyrophoric, igniting spontaneously on contact with air. This poses handling issues; it must be stored in nitrogen.

    It's also an expendable resource which puts limits on the number of times an engine can be started in flight; the Falcon 9 only loads TEA-TEB for restarts on those engines that will be restarted on a given mission, reasonably enough, but this makes it susceptible to engine failures in the reentry and landing burns that could otherwise be recovered from by using different engines.
    That is why they only got one engine to restart, not three.
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  16. #1486
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    Quote Originally Posted by Nicolas View Post
    A source unknown to me claims the central core ran out of fuel and that's why only one engine started, resulting in a 400km/h crash 100m next to the ship.
    There's no mystery here. Musk said in the press conference that it ran out of TEA/TEB ignition fluid, and the two outboard engines failed to light. It did not run out of fuel.

  17. #1487
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    Quote Originally Posted by Nicolas View Post
    They may have placed it in a vacuum chamber to be sure nothing went horribly wrong. Other than that, not much. It's also a standard car, so none of the materials have been tested to survive a vacuum/radiation environment for a long time. It may look terrible after a few years. Or not.
    Musk said they didn't do any testing on the materials, and it was showing some signs of deterioration shortly after launch...what appeared to be blistering/flaking paint, warping parts, fogging windows, etc.

    They weren't launching his car to preserve it for future generations. From what I know of Musk, he probably wanted to see what would happen to his actual car if it got put in space, not launch a car-shaped object that was made to stay pretty in such conditions.

  18. #1488
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    I thought they lost contact with Starman. I just checked the live feed, looks as if he's still going. But, the Earth looks very different today, for there is he sitting in his Tesla, for above the world, planet Earth is blue, and there's nothing he can do. 'Cause he's just a dummy.

  19. #1489
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    Quote Originally Posted by cjameshuff View Post
    There's no mystery here. Musk said in the press conference that it ran out of TEA/TEB ignition fluid, and the two outboard engines failed to light. It did not run out of fuel.
    And that is why I don't like stories that don't mention a source. Thanks for the concrete information.

    (popular media stated the car is already beyond Mars yesterday, so counting on them to get to know something is the last thing to do...)

  20. #1490
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    SpaceX's success is an inspiration to Chinese scientists.

    http://www.chinadaily.com.cn/a/20180...dcc13b65f.html

    "The successful test flight of the US Falcon Heavy, now the world's most powerful carrier rocket, has provided experience to China's space sector as the nation strives to design its own super-heavy rocket, according to industry insiders.

    The 23-story jumbo rocket, carrying a Tesla Roadster electric sports car as a mock payload, blasted off at 3:45 pm on Wednesday at Kennedy Space Center in Cape Canaveral, Florida.

    The gigantic launch vehicle, propelled by 27 engines, was developed and built by Space Exploration Technologies Corp, popularly known as SpaceX, and has been regarded as a new milestone of the US space endeavor as well as a remarkable victory for technology tycoon Elon Musk, the head of SpaceX and Tesla.

    Many scientists, researchers and engineers working for China's space programs expressed congratulations for the success, calling it exciting news for the space industry, not only in the United States but around the world"

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  21. #1491
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    Quote Originally Posted by Nicolas View Post
    And that is why I don't like stories that don't mention a source. Thanks for the concrete information.

    (popular media stated the car is already beyond Mars yesterday, so counting on them to get to know something is the last thing to do...)
    The core did however impact the water at about mach 0.4.

    The scale is a bit deceptive, and I wonder how many people really grok how aggressive those landing maneuvers are:
    https://www.youtube.com/watch?v=Z_kfM-BmVzQ

    For each of the two boosters that came back to land, you heard 3 sonic booms from the exhaust, bottom of the rocket, and top of the rocket, and could see a bit of a bow shock in the exhaust. They were still supersonic for the initial part of the landing burn, and for that gentle descent to the ground after the 3-engine flare that seemed to almost bring them to a halt, they were still decelerating under about 3 times too much thrust to hover.

  22. #1492
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    Quote Originally Posted by cjameshuff View Post
    https://www.youtube.com/watch?v=Z_kfM-BmVzQ

    For each of the two boosters that came back to land, you heard 3 sonic booms from the exhaust, bottom of the rocket, and top of the rocket, and could see a bit of a bow shock in the exhaust. They were still supersonic for the initial part of the landing burn, and for that gentle descent to the ground after the 3-engine flare that seemed to almost bring them to a halt, they were still decelerating under about 3 times too much thrust to hover.
    Thanks, that is an awesome video. Coming in like meteors indeed. Wow.

    Quote Originally Posted by cjameshuff View Post
    The scale is a bit deceptive, and I wonder how many people really grok how aggressive those landing maneuvers are:
    I do now!

    ETA: I thought in the launch video they said the reentry burn made it sub-sonic, but they actually said (around 28:00) the burn decelerated from way faster than speed of sound to just faster than the speed of sound.
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  23. #1493
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    The future looks bright for SpaceX to get US Air Force certification a few years down the road. They already have a US test load to fly in the middle of the year.

    http://spacenews.com/military-certif...-falcon-heavy/

    The inaugural launch on Tuesday of the world’s most powerful rocket sets the stage for SpaceX’s Falcon Heavy to begin the qualification process to compete for lucrative U.S. government contracts.

    The U.S. Air Force has already booked the massive rocket for a June launch of a test payload. But the Falcon Heavy may have to nail many more missions before it passes the threshold to be certified by the U.S. Air Force.

    Certification could take as many as 14 or as few as two flights, a spokesperson for the Air Force Space and Missile Systems Command, in Los Angeles, told SpaceNews. For new rockets like the Falcon Heavy, there are many variables at play, such as the confidence the government has in the design and its record flying commercial payloads into orbit.

    The process is articulated in detail in the United States Air Force Launch Services New Entrant Certification Guide that was published in 2011. The Air Force calls it a “risk-based approach” with four certification options based on the maturity of the launch system. These options require as many as 14 flights, or as few as two. With fewer flights there would be more in-depth technical evaluations.

  24. #1494
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    Keep up with the adventures of Starman here. http://www.whereisroadster.com/

  25. #1495
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    Quote Originally Posted by slang View Post
    ETA: I thought in the launch video they said the reentry burn made it sub-sonic, but they actually said (around 28:00) the burn decelerated from way faster than speed of sound to just faster than the speed of sound.
    They were also below terminal velocity at the end of the reentry burn, and accelerated for a bit due to gravity until drag started slowing them down again. You can see this in the other landings where they show velocity and altitude of the landing first stage.

  26. #1496
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    My drone won't sleep alone

    spaceflightnow.com

    SpaceX will deploy a new rocket landing platform off Florida’s Space Coast to enter a rotation with another drone ship stationed at Cape Canaveral, company founder Elon Musk said Monday.

    The third drone ship in the company’s fleet of ocean-going rocket recovery vessels is under construction, Musk said. He wrote on Twitter that it will be named “A Shortfall Of Gravitas.”

    The name of the new landing platform is a nod to “Experiencing A Significant Gravitas Shortfall,” a starship featured in the “Culture” science fiction novel series by the late Scottish author Iain M. Banks.

    SpaceX’s two other drone ships are also named for sentient, planet-sized ships in Banks’ novels: “Just Read the Instructions” currently based at the Port of Los Angeles for launches out of Vandenberg Air Force Base, California, and “Of Course I Still Love You” positioned at Port Canaveral for SpaceX missions from Florida.

    Musk wrote that “A Shortfall of Gravitas” will be stationed in Florida to support high flight rates of SpaceX’s Falcon 9 rocket, and allow for dual ocean landings of the two side boosters carried on the Falcon Heavy rocket.
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  27. #1497
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    SpaceX is also continuing progress on recovering the payload fairing.

    SpaceX recovery boat spotted with huge claw-like “fairing grabber”

    A snippet from the article,

    While CEO Elon Musk has previously hinted at a sort of inflatable cushion (“bouncy castle” in his words) as the solution for keeping the fairings out of the ocean after landing, the mechanism spotted aboard would appear to be a small departure, likely instead making use of a net to catch the fairing.

  28. #1498
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    I’d like to see a description of how they plan to catch a fairing. The net area doesn’t look that big, and I’m not sure I’d want to be driving the boat while trying to snag a fairing.


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  29. #1499
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    Yeah. My first thought when I saw that article and the pictures was, is that boat armored? A point brought up in the article is how are they going to catch both pieces with that thing? Contrive the returns to be at different times somehow? With an interval large enough to remove the 1st one from the capture device? Catch both at the same time? That seems . . . , crunchy. Or is this just a proof of concept and they only intend to catch 1 of them with this particular gizmo?

  30. #1500
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    I assume the fairings will be descending by parachute, relatively slowly, but still...
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