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sevenperforce

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Everything posted by sevenperforce

  1. Wow, that makes a LOT of sense. The more pitch authority they can get, the more aggressive body lift they can get, which means less propellant consumption on the boostback burn. And having them out to the sides keeps them out of the booster’s wake. Super smart.
  2. Yep! Those icicles on the outside of the RL-10 are just incredible. Of course, the RL-10 uses an expander cycle so it has to suck every last Kelvin it can out of that engine bell in order to function. And while the RS-25 doesn’t need the heat to operate since it uses a staged-combustion preburner, it is also using liquid hydrogen, which has a much greater heat capacity than liquid methane. Even so, the heat capacity of subcooled liquid methane should be plenty to keep the Raptors chilled.
  3. That would actually be illegal, believe it or not. You cannot use work product gained from the interview process without paying for it. It’s unlikely that someone would do an “on the spot” challenge like this using actual work, but it does come up, more often in the context of more significant projects. You might be asked to prepare a brief or a report or code block as part of the selection process for the job. If that ever happens, do it, but if you DON’T get the job then you should absolutely send them an invoice for your time. Billed at your contractor rate (which should be 70-80% higher than your hourly rate). The only time this happened to me was when I was interviewing for an engineer position and I had not done any engineering work since graduating. The team lead handed me a dry erase marker and asked me if I could draw the diagrams and write out the equations for a simple electromagnet. I thought that was an acceptable ask because they were just making sure I had retained enough technical knowledge to be useful. Which I had.
  4. I stated it very poorly, so I fully understand why @mikegarrison was taken aback. When the engines are firing, they are regeneratively cooled, so they aren’t hot. If kerosene-regenerative cooling can handle nine Merlin engines, methane-regenerative cooling can definitely handle the full array under Superheavy. My point with respect to the outer ring was separate (and, again, poorly-phrased). The only time the engines are not regeneratively cooled is during the retropropulsive burn, when the outer engines are just sitting there and the inner engine(s) are roaring. There is more physical distance between Superheavy’s outer ring and its core cluster than there is between Falcon 9’s outer ring and its core engine, so the heat flux from the core exhaust plume to the outer ring of Raptors will be lower than from the core Merlin to the outer ring of Merlins. Thus the larger the outer ring of engines, the less heat those outer engines receive from the overall thermal environment. But, again, very poorly phrased. Mea culpa.
  5. The nozzles are cooled by the liquid methane which has a MUCH better heat capacity than kerosene AND comes in at a much lower temperature. So if Falcon 9 can handle nine Merlin engines in close proximity, Superheavy can DEFINITELY handle 20 engines in close proximity. The more engines you have in the ring, the less radiative heating there is from one engine to the next.
  6. SN20 aft flap install. This is happening SO fast. Do we think this is the flap root cover? EDIT: For those watching the livestream, BN4 is starting to inch her way out of the High Bay.
  7. I think the straight seams that run circumferentially are fine. It would be longitudinal seams that would cause trouble. During the worst of re-entry, Starship will be flying in with a high angle of attack in order to achieve a lifting-body entry, and thus the plasma flow path will be at a sharp angle to any circumferential seams.
  8. That's my thought. @RealKerbal3x Interesting that they already freely have circumferential straight seams. Also, I think we have a candidate for those catching arms: Look how absolutely massive those hinges are.
  9. Of note: Just below the tip, the taper is so aggressive that they are only doing three tile layers between each latitudinal straight seam. Probably large-medium-small. There are no studs above that line so the odds of a large single-piece (or perhaps 2-3 piece) glued-on nosecone seem high.
  10. Now THAT is the most Kerbal thing I have ever seen. How many times have I wrapped an ungodly number of Vector engines around the base of a monster rocket.....
  11. Fascinating that they installed the Raptors underneath the mobile mount. I was wondering how they were going to do the transport but that makes sense. Note also that they are now using the catch points for the hoist lift. Just a single I-beam across the top, secured to the catch points. And here's what looks like one of SN20's aft fins being carted past the base of BN4:
  12. Wait, are they installing the engines before they transport the booster?? I thought engine installation was going to keep happening on the pad!
  13. I'm assuming they will just use hexes cut to fit. That's what we see on the flaps.
  14. Looks absolutely amazing. I now think I know how they are tiling the nosecone, too. It's absolutely ingenious and I can't believe I didn't think of it. (well, actually I kind of DID think of it, nearly...it was my first render a few months ago) I went through and pixel-counted the average width of each tile in each row. What I found is that they step up very very gradually. The way the math works out, it appears they are using just two extra tile widths in addition to the regular hexes. They are narrower, but they don't taper. EDIT: Here's an earlier wide-angle shot of the flap being lowered into place.
  15. Yes, it's a really good look. The tiles go past the halfway point in certain areas to protect from plasma streaming around the elonerons. I don't think there is any suggestion of doing a kick-flip with Superheavy. Superheavy's engine cluster is much much bigger and heavier than Starship's and so it will be VERY tail-heavy; there's no way they could get it to fall horizontally. Starship needed the LOX header tank in the nosecone just to get the right balance, after all. I would more-expect to see them replace Superheavy's grid fins with conventional fins/canards like the ones on New Shepard and New Glenn. They could be fixed to vertical during ascent and then rotate to act like airbrakes on descent: The canards/fins could turn in unison for guidance during initial re-entry and then turn opposite to each other to act as airbrakes and really slow down the booster.
  16. Finally some really good detail on the SN20 nosecone heat shield. It looks like we have tiles that become progressively narrower (but do not taper) with each row, moving up, until you hit a seam and start over. It's particularly visible at the top seam, between the very thin/narrow tiles and the much wider tiles above. Also note curious square tiles on the flap fairing with hex tiles between them, custom-cut to fit.
  17. As the dad of the kid on the spectrum, I am inclined to think it has a lot to do with Elon being on the spectrum as well.
  18. The catch/lift point is just barely under the grid fins: It’s the thing that looks like a bathtub faucet. These could be just for a fit check, but how can you be sure these cannot rotate? The rotating actuator could be inside and thus concealed.
  19. Communication is hard. How we choose to communicate surrounding issues of public health and public safety has major consequences. How much is too much to share? How much is not enough? Would we rather use strong communication to get highly effective compliance from a small subset of the population or moderate our language and get less effective compliance, but from more people? What are the short-term goals? What are the long-term goals? It is all extremely difficult.
  20. One advantage is that if the arms were to miss the catch/lift points, they would likely still snag on the grid fins. Would probably still cause serious damage but would at least prevent RUD and pad FUBAR.
  21. My intuition is that the drag will be higher in this configuration BUT the weight will be lower and so the overall penalty will be negligible, if anything. They are pretty thick folded, but in the folded config the airflow would end up going around them pretty smoothly. There’s going to be a lot more overall shock drag from the large extension.
  22. It looks absolutely accursed. But, as I once pointed out: if duct taping fresh hot chicken sandwiches to the fairing would improve aerodynamics, rocket engineers would make a Chick Fil A run before every launch.
  23. I blew up that photo and the pattern is very curious. It looks like there are spacers between some of the tiles? But the straight seam solution was clearly the straightforward one. My understanding is that the central ring of engines on the N-1 did not have particularly good gimbal range and so the grid fins were intended for roll control. I don’t think they worked very well, though. In contrast, the four large fixed fins on the Saturn V were only there to provide passive aerodynamic stability in an abort scenario. IIRC the vehicle had more passive stability than expected and so if crewed flights had continued much longer they would have axed the fins. The only reason that the Skylab launch had the fins was because it was the booster intended for Apollo 18. Fit test makes perfect sense. They do a lot of those.
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