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Thread: SpaceX

  1. #1651
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    Quote Originally Posted by Glom View Post
    The airlines seem to consider engine count to be important. But then aeroengine reliability is ridiculous these days.
    Airlines would probably still favor a larger number of identical engines over a set of large and small engines, each needed for a particular phase of flight. They'd certainly favor it over a craft with only large engines that was incapable of a controlled landing.

  2. #1652
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    Also, 2019 airliners are acting in a different economic reality than even SpaceX rockets. Airliners need to be extremely reliable, which is also true for rockets. Airliners also need to fly as economical as possible, because of the killing competition. When 2 large engines weigh/consume less than 4 smaller ones, they'd opt for two any time. Well, there are always exceptions where apparently 4 smaller engines were considered better, such as the BA 146. I don't think SpaceX is looking at the very last dollar in launch costs just yet; as long as they are significantly cheaper than the competition and get sufficient thrust and landing capability by using a heap of identical "small" engines, it's a viable solution.

    And indeed, imagine trying to do a controlled landing with a single herculean engine the size of an F1. I'm not saying it's generally impossible, but we're not there yet.
    Last edited by Nicolas; 2019-Feb-10 at 10:04 AM.

  3. #1653
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    Quote Originally Posted by cjameshuff View Post
    Airlines would probably still favor a larger number of identical engines over a set of large and small engines, each needed for a particular phase of flight. They'd certainly favor it over a craft with only large engines that was incapable of a controlled landing.
    Quote Originally Posted by Nicolas View Post
    Also, 2019 airliners are acting in a different economic reality than even SpaceX rockets. Airliners need to be extremely reliable, which is also true for rockets. Airliners also need to fly as economical as possible, because of the killing competition. When 2 large engines weigh/consume less than 4 smaller ones, they'd opt for two any time. Well, there are always exceptions where apparently 4 smaller engines were considered better, such as the BA 146. I don't think SpaceX is looking at the very last dollar in launch costs just yet; as long as they are significantly cheaper than the competition and get sufficient thrust and landing capability by using a heap of identical "small" engines, it's a viable solution.

    And indeed, imagine trying to do a controlled landing with a single herculean engine the size of an F1. I'm not saying it's generally impossible, but we're not there yet.
    It's all twin-engines for airliners these days. The BA146 is long gone, as is the A340, which actually used to advertise that it was safer by having four. Only the A380 and 747 remain, and are getting very few sales.

    Rocket economics, of course, are going to be different.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  4. #1654
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    I haven't really followed up on the BA146 (and I'm not going to google it now to pretend infinite wisdom) so it might indeed very well be long out of construction/sale. I still see them flying around a lot though (or is it another very similar design); but with the lifespan of aircraft that's not surprising.

    Interesting to note how natural (ok, economical) evolution has sent the entire industry to two-engined aircraft. And as reliable as they might be, I find it comforting to know there is a bit of backup hanging under the wings in contrast to a single engined plane.

    I'm curious on what design the rocket industry will settle somewhere down the road.
    Last edited by Nicolas; 2019-Feb-10 at 05:35 PM.

  5. #1655
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    The 146 was last produced in 2001. Its big advantage was noise. It was the only jet allowed in some airports.
    Rockets, of course, are pretty noisy!
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  6. #1656
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    Ah that explains why I saw them where I saw them.

    Regarding rocket engines, would many small (ahem) ones be less loud than a few huge ones? I understand that even at 32 small engines, a BFR launch would be insanely loud by any standard. But perhaps slightly less so than with, say, 8 huge engines? Not that I'm concerned with waking up the neighbours, but huge rockets tend to get so loud they literally scream themselves to pieces if you don't apply the right measures to steer away/dampen the sound waves.
    Last edited by Nicolas; 2019-Feb-10 at 07:25 PM.

  7. #1657
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    Another Raptor TweetStorm...

    Elon Musk ✔ @elonmusk
    Raptor reached 268.9 bar today, exceeding prior record held by the awesome Russian RD-180. Great work by @SpaceX engine/test team! pic.twitter.com/yPrvO0JhyY
    |
    John Kraus @johnkrausphotos
    Replying to @elonmusk @SpaceX
    What was the duration of the test fire?
    |
    Elon Musk ✔ @elonmusk
    About 11 secs
    |
    Eric Ralph @13ericralph31
    Replying to @elonmusk @SpaceX
    Wow Can you say how many tests have been performed thus far? I doubt it can speak much to the long-term longevity of Raptor, but I feel like 3-5+ static fires in the first 7 freaking days of integrated hot-fires is a damn good sign.
    |
    Elon Musk ✔ @elonmusk
    I think 6 where we lit main chamber & several with only preburners
    |
    Elon Musk ✔ @elonmusk
    Yes, aiming for 380 sec Isp with vac nozzle. Maybe 382 if we get lucky.
    |
    Anthony Iemole @SpaceXFan97
    Replying to @elonmusk and 2 others
    I know you said Raptor would eventually reach 300 bar, but will you stop there or go furthur? 300 is already impressive but is it capable of more?
    |
    Elon Musk ✔ @elonmusk
    Much above 300 bar main chamber pressure means extreme oxygen preburner pressure of 700 to 800+ bar. Definitely pushing the limit of known physics.
    |
    Elon Musk ✓ @elonmusk
    Propellant was not deep cryo. CH4 & O2 were just barely below liquid temp at 1 bar. In theory, Raptor should do ~300 bar at deep cryo, provided everything holds together, which is far from certain. However, only 250 bar is needed for nominal operation of Starship/Super Heavy.
    |
    Elon Musk ✓ @elonmusk
    This will sound implausible, but I think theres a path to build Starship / Super Heavy for less than Falcon 9
    |
    @SpaceXFan97
    Wow! I assume the switch to Stainless Steel is a big factor in this?
    |
    Elon Musk ✓ @elonmusk
    Yes
    Last edited by docmordrid; 2019-Feb-11 at 03:32 AM.

  8. #1658
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    Randomness as a human @epoxy101
    Replying to @elonmusk and 3 others
    will it be cheaper than F9 for kg to LEO for instance?
    |
    Elon Musk ✔ @elonmusk
    At least 10X cheaper

  9. #1659
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    Cheap construction method + reusable load of identical high performance engines will bring down costs a lot, but these kind of statements (and, for the time being, results) make you wonder why others are dragging along so much. (don't answer that one!).

    I'm curious if he's considering using a BFR for his 4000+ satellite constellation, but it might come a bit too late for that. Still, even at 200 sats per launch it would require 20 F9 launches. Then again, you'd likely need multiple launches for the different orbits of the constellation anyway.
    Last edited by Nicolas; 2019-Feb-11 at 08:04 AM.

  10. #1660
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    Assuming the $80M/seat to Russia is correct, does anyone have what SpaceX is going to charge to shuttle astronauts to the ISS?

  11. #1661
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    Quote Originally Posted by Nicolas View Post
    >
    I'm curious if he's considering using a BFR for his 4000+ satellite constellation, but it might come a bit too late for that.
    Musk said version 1 of StarLink goes uphill on Falcon, version 2 on Starship. I'm assuming v1 is the 4,425 satellite LEO constellation and v2 is the 7,000+ satellite VLEO constellation.

    Quote Originally Posted by bknight View Post
    Assuming the $80M/seat to Russia is correct, does anyone have what SpaceX is going to charge to shuttle astronauts to the ISS?
    The Commercial Crew development contracts were,

    Boeing: $4.2 billion
    SpaceX: $2.6 billion

    Seat cost: $58 million

    The above is based on a standard mission with 4 occupied seats. Both Crew Dragon and Starliner can carry a crew of 7, so a crew of 5+ lowers the per-seat cost. Also, $58m is an average, so it's clear whose missions will cost less.

    Another wrinkle: Commercial Crew missions will also carry Russian cosmonauts. Likewise, Soyuz will continue to carry US astronauts. The difference is that it'll be a no-charge ride-sharing arrangement.

    Another wrinkle comes when Russia flies its Federation (Federatsiya) spacecraft in the early 2020's. Crew: 4-6.

    Still wondering if Starship will pay ISS a visit. Hell, it's virtually a space station itself.
    Last edited by docmordrid; 2019-Feb-12 at 08:12 AM.

  12. #1662
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    In true Chuck Norris mode, it would be the ISS that docks to Starship. Not the other way around.

  13. #1663
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    SpaceX has spun off SpaceX Services Inc. to run the StarLink system.

    DoD and SpaceX testing the two MicroSat test satellites for military aircraft comms, the FCC papers being filed last summer.

    Dozens of early (v1) satellites will launch on Falcon 9 & Falcon Heavy, later (v2) satellites will bulk launch on Starship.

    Alan Boyle ✔ @b0yle (GeekWire)
    .@SpaceX's Hans Koenigsmann says first set of #Starlink satellites (beyond last year's prototypes) will launch this year, but isn't able to say anything more than that. #CST201
    4:53 PM - Feb 12, 2019

    https://twitter.com/b0yle/status/1095440746566610945

  14. #1664
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    Everyday Astronaut @Erdayastronaut
    Replying to @elonmusk and 4 others
    Will there still be these header tanks inside starship?

    BFS headers.jpg
    |
    Elon Musk ✔ @elonmusk
    Yeah, but simpler. Needed for landing burn or engines will suck in a bubble.
    2:10 AM - Feb 13, 2019

    https://twitter.com/elonmusk/status/1095580873624190977

  15. #1665
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    Can anyone explain the "suck in a bubble" part? It seems to me that all liquid in the tanks would be nicely down low as the craft is decelerating from a fall. Or would there simply be so little fuel left that it wouldn't have enough "water depth" in the full diameter main tanks?

  16. #1666
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    Quote Originally Posted by Nicolas View Post
    Can anyone explain the "suck in a bubble" part? It seems to me that all liquid in the tanks would be nicely down low as the craft is decelerating from a fall. Or would there simply be so little fuel left that it wouldn't have enough "water depth" in the full diameter main tanks?
    t would seem like during the "free fall" portion of reentry the fuel would have neutral gravity and may not necessarily settle low in the tank. Not reading the whole post it would seem like some form of pressurization would be used to ensure the fuel is at the bottom.

  17. #1667
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    I would expect to have a bladder system in free fall to avoid cavities, but then the details get complex, you nee ribs or something to stop folds getting in the way.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
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  18. #1668
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    Without header tanks, before the rotation to vertical completes the free-fall, sloshing etc. would cause the propellant tank intakes to be uncovered and they'd suck in ullage gases. The engines stall and the landing doesn't end well.

    With full header tanks, the intakes are covered through rotation to vertical, and from there gravity and deceleration keep them that way. The ship lands and everyone smiles.

  19. #1669
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    I saw some COPV tanks, but that's just for the star hopper right?

    "This will sound implausible, but I think there's a path to build Starship / Super Heavy for less than Falcon 9"

    And there is the raison d'etre for heavy lift in a nutshell. Sometimes, a smaller LV actually costs you more. Truax lamented the fact that an upper stage cost as much if not more than a first stage:
    Aerospace America (The Future of Earth To Orbit Propulsion, Jan. 1999, p.34)

  20. #1670
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    Quote Originally Posted by docmordrid View Post
    Without header tanks, before the rotation to vertical completes the free-fall, sloshing etc. would cause the propellant tank intakes to be uncovered and they'd suck in ullage gases. The engines stall and the landing doesn't end well.

    With full header tanks, the intakes are covered through rotation to vertical, and from there gravity and deceleration keep them that way. The ship lands and everyone smiles.
    Uum could you provide a link to cut-a-away drawing. I'm not sure what you are talking about.

  21. #1671
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    Quote Originally Posted by bknight View Post
    Uum could you provide a link to cut-a-away drawing. I'm not sure what you are talking about.
    Ahhh, sorry about that.

    This image isn't the current config, Musk saying they've changed, but they are tanks within the methane tank which contain landing and thruster propellants. The outer tanks are vented during the trip, creating a giant Dewar to help prevent evaporation.

    BFS_4-1280.jpg
    Last edited by docmordrid; 2019-Feb-15 at 10:11 PM.

  22. #1672
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    dup
    Last edited by docmordrid; 2019-Feb-15 at 10:10 PM.

  23. #1673
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    Quote Originally Posted by publiusr View Post
    I saw some COPV tanks, but that's just for the star hopper right?
    Pressurizing the tanks once at least one engine is running only needs some lines taking high pressure gaseous O2 and CH4 from the preburners, but a full autogenous pressurization system is going to need a way to pressurize tanks full of subcooled propellant before any engines can start up. Some tanks of pressurized gas can stand in for such a system on an early test platform like the Hopper.

    Also, they are now using cold gas thrusters, which are going to need something higher than tank head pressure. They could generate this by boiling some propellant, but will likely need some reservoirs for pressurized gas. At minimum, they'll need to be able to produce some thrust to settle the propellants so they can pump them to a boiler. Again, for Hopper a few tanks of compressed gas are a fine substitute.

  24. #1674
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    Quote Originally Posted by docmordrid View Post
    Ahhh, sorry about that.

    This image isn't the current config, Musk saying they've changed, but they are tanks within the methane tank which contain landing and thruster propellants. The outer tanks are vented during the trip, creating a giant Dewar to help prevent evaporation.

    BFS_4-1280.jpg
    Thanks for the drawing. I understand now.

  25. #1675
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    Confirmed: the Super Heavy booster and Starship will be built in Brownsville, TX

    https://www.linkedin.com/jobs/view/1120859043/

    Tank Fabricator/Welder

    Company Name: SpaceX*

    Company Location: Brownsville, TX, US

    Posted Date: Posted 2 days ago*

    Number of applicants: Be among the first 25 applicants

    Apply: Apply to Tank Fabricator/Welder on company website

    SpaceX was founded under the belief that a future where humanity is out exploring the stars is fundamentally more exciting than one where we are not. Today SpaceX is actively developing the technologies to make this possible, with the ultimate goal of enabling human life on Mars.

    TANK FABRICATOR/WELDER*

    Tank fabricators will work to build the primary airframe of the Starship and Super Heavy vehicles at the SpaceX South Texas build site. The tank fabricator will work with an elite team of other fabricators and technicians to rapidly build the tank (cylindrical structure), tank bulkheads, and other large associated structures for the flight article design of both vehicles.
    >

  26. #1676
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    https://www.recruit.net/job/supervis...A52544507D7B8C

    SUPERVISOR, TANK FABRICATION

    The Tank Fabrication Supervisor is responsible for leading a team of fabricators, welders, and technicians building the Primary and Secondary structures for the Starship and Super Heavy vehicles. The Tank Fabrication Supervisor is the most influential person on-site to drive progress on an hour-by-hour and day-by-day basis. The Supervisor of the team will take technical direction from the Engineering team and turn it into reality by building, retaining, and managing their team effectively; distributing labor resources, prioritizing certain aspects of the build, and setting headcount requirements where necessary. The Supervisor is also a key enabler to a productive, fun, and hard-working culture. For this role specifically, it is highly important that the Supervisor is an inspiring leader, often-times working side by side with their build team.

  27. #1677
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    (My first thought on seeing the job title was the other kind of tank and I thought “Huh, SpaceX is branching out...”)
    The greatest journey of all time, for all to see
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  28. #1678
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    The "other kind" was called that during WWI to mislead the Germans into thinking they were just water carriers.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  29. #1679
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    SpaceX ✔ @SpaceX
    Static fire test of Falcon 9 complete targeting February 21 launch of Nusantara Satu from Pad 40 in Florida.
    8:03 PM - Feb 18, 2019

    Secondary payloads

    S5: Space Situational Awareness mission, a 60kg micro-sat from the US Air Force Research Laboratory. It's stated purpose is detecting and locating near-GEO objects to update the GEO catalog, but it could also keep track of those Russian birds maneuvering around commercial and soverign GEO satellites.

    SpeceIL's Beresheet (Genesis, "in a beginning") lunar lander (an Israeli non-profit).
    Target: Mare Serenitatis

    http://www.technology.spaceil.com
    Last edited by docmordrid; Yesterday at 02:59 AM.

  30. #1680
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    DM-1: Crew Dragon un-crewed test flight to ISS

    Jeff Foust @jeff_foust
    [NASA Deputy Administrator] Morhard says SpaceX Demo-1 uncrewed test flight still scheduled for March 2. Starliner uncrewed test flight some time in the spring. #CST2019
    5:14 PM - Feb 13, 2019
    Last edited by docmordrid; Today at 07:52 AM.

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