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sevenperforce

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Posts posted by sevenperforce

  1. 4 hours ago, kurja said:

    That name rang a bell for me... but I suppose you're not also a scottish chemist

    Nope, not me. However, my dad and I have the same name, and he is a fairly accomplished chemist, which makes things even more confusing.

    1 hour ago, JoeSchmuckatelli said:

    ...are not often raised in the weird world of American Christian Fundamentalism. 

    Yes, fortunately.

    I’ve become somewhat of a black sheep….

  2. 52 minutes ago, AtomicTech said:

    No way, I don't believe it!

    I couldn’t believe it either, haha! They just kept asking me to come back for repeat interviews over and over and then suddenly they were flying me out to SF for the premiere!

    It’s worth a watch if you want to see something super interesting.

  3. On 6/4/2021 at 2:44 PM, SpaceFace545 said:
    On 6/4/2021 at 2:17 PM, tater said:

    I kinda like it. Course I liked the tiny wing and scissor-wing  shuttle concepts.

    Same, not sure how or if it could reenter but it reminds me of the StarTram space plane.

    https://imgur.com/a/AspxR3B

    Maybe it wasn't meant to re-enter, but was intended to use aerodynamic passes to change inclination like the X-37B.

  4. 1 hour ago, adsii1970 said:
    1 hour ago, sevenperforce said:

    Minor quibble: by the time of Apollo 11, NASA knew for sure that the moon dust wasn't a foot thick. The unmanned Surveyor landings gave them enough data to establish that the dust was compacted.

    There was still a fear of what was under the dust - was it all solid rock or a mixture that could support the weight of a lander:
    https://www.icr.org/article/moon-dust-solar-system/

    ICR is known to be a particularly unreliable source.

    (The reason I happen to be knowledgeable on the moon dust issue is that I used to work with that and related groups, back in my anti-science days, and this was a common bone of contention.) 

  5. 1 hour ago, adsii1970 said:

    This is why the Apollo lander was designed as it was. At the time, NACA/NASA believed the surface of the Moon was covered in roughly a foot of lunar dust. They believed the wide, concave landing pads at the end of the legs, the wide span of the legs, and the low center of gravity. In the end, they learned from the Apollo 11 mission the dust wasn't as thick as they expected it to be.

    Minor quibble: by the time of Apollo 11, NASA knew for sure that the moon dust wasn't a foot thick. The unmanned Surveyor landings gave them enough data to establish that the dust was compacted.

    The larger concern for the landings were the possibility of coming in with a non-negligible horizontal velocity component and the associated tipover. 

  6. 48 minutes ago, wumpus said:

    It was a bit of a miracle that none of the Mercury astronauts weren't killed.  I've heard they had to get someone else to press the button to "light this candle" for Alan Sheppard as the original guy thought it would kill him.  I think the engineers on the job gave him a 50/50 chance of living.  They may have been pessimistic after the satellite flights (while Sheppard simply looked at the Mercury test flights), but they still seem a deathtrap.  And don't ask about the rigid thinking that launched  Vladimir Komarov on a rocket that clearly wasn't ready.

    There was also a huge amount of re-work after NASA killed the first three astronauts (presumably they thought being ahead of their goal was a good thing, but they cut way too many corners to get there).  But don't forget they lost two Gemini astronauts jaunting around in T-38s.   Micheal Collins seemed to think they were more dangerous (to astronauts) than space (presumably because of crazy test pilot antics).

    The ejection seat on the Vostok was absolutely not strong enough to get Gargarin high enough for his chute to open in the case of a pad abort, so they strung a net around the launch site to catch him if they had to abort on the pad.

    And as we all know, "trapped in a net next to an actively failing launch" is just a wonderful place to be.

    As for Gemini, I know there's some degree of disagreement over whether the ejection seats would have actually burned the pilots alive or not....

  7. 16 minutes ago, magnemoe said:

    Obvious problem is that the success rate get high, its get as boring as falcon 9 first stage landings. This is obviously an good thing for everything but the number of views 

    Maybe they can use their excess payload to drop a secondary experimental re-entry vehicle to keep things SPICY.

  8. 45 minutes ago, cubinator said:

     

    47 minutes ago, AtomicTech said:

    Why can't they just keep the flaps as is!

    Because they've found a way to make the flaps better at their job, namely flipping the ship.

    Keep in mind this is only a fan render; we don’t know whether this is actually what they will look like. We know that they will be slightly smaller and further back but I’m not sure about placement otherwise. 

  9. 1 hour ago, Meecrob said:

    Which begs the question of why did so many smart people decide to have such a stupid process? I mean I get the US was embarrassed in the late 50's with all their launch failures, and don't want a repeat of those "dark days" of failure after failure, but the fact that nobody took a step back and asked "How did they get so successful so quickly in those early days?" boggles my mind. The answer is they failed!

    I would argue that they didn’t get successful quickly in the early days. The USSR did, but the USSR concealed its failures. We didn’t get successful by embracing fast failure; we got successful by gratadim ferociter — albeit much more ferociter than Blue.

    We used a lot of competition to push innovation, which meant we had everything already in place once it was time for Apollo. But that culture of competition engendered a notion that distribution of responsibility enhances safety, which drove costs through the roof. And once the money dried up, so did the innovation.

  10. On 10/3/2021 at 3:12 PM, tater said:

    He'll go to space at some point, his goal is not to put himself in space, it's to make humans a multiplanetary species. Ideally before the end of the century.

    Commercial launch probably tops out at $3-$4B/yr.

    If they can capture ~3% of internet would be more like $1T/yr. Revenue stream for SS and Mars.

    Best case F9 marginal cost (reused) not counting overhead, etc ~$15M for 15t.

    Marginal cost for SS could be <$1M/launch.

    A lot to learn on the Moon, and "frickin cool." Analogous to Antarctica science labs.

    LSS does 8-10 times as much as NT lander for half the price.

    "Suborbital is a step in the direction . . . of orbit. So . . . it's still good to do something in space."

    So few words. So much shade.

    6 minutes ago, tater said:

     

     

    So a payload delay, not an engine delay?

    Hmmmmm.

  11. On 10/2/2021 at 12:33 PM, Beccab said:

    Info on that from our usual reddit insider:

    - Unlike falcon 9 which pressurizes with Helium in COPVs, superheavy is autogenous (i.e. engines produce the gas maintaining tank pressure)

    - Maintaining ullage pressure will be a problem with such a large tank. With a header tank, less gas is needed to maintain pressure flow for landing

    - While B4 does not have that there should be sufficient gas volume tap-off produced by the engines to maintain ullage pressure, but it reduces engine performance.

    I also suspect that having the header tanks place off center will assist Superheavy in performing a more aggressive glide maneuver on its way back, which further reduces propellant consumption during the boostback burn. Falcon 9 depends exclusively on its grid fins to provide the pitch authority for the body lift glide maneuver, but having Superheavy’s center of mass offset that means it will naturally get some body lift even in the passively stable configuration, like a capsule.

    In addition, superheavy will be using its main tank ullage gas for RCS, which is another reason to keep the header tank separate. 

  12. 16 hours ago, mikegarrison said:

    I will add, though, that this whole response has the tone of some white guy saying "I never see racism or sexism around here".

    Well no %$#& you don't, because it's not aimed at you, dude.

    Yep, that’s exactly the impression I got.

    A better response would have been to say something more like, “Here’s what we’ve done to remedy issues as they were brought to us” rather than “We have all these structures in place so there can’t possibly be any issues.” Indignance smells of indifference; humility would have gone a lot further.

    16 hours ago, JoeSchmuckatelli said:
    16 hours ago, tater said:

    I absolutely think he's a big part of the problem with BO (not the harassment claims, I have zero information aside from that article), but what's he supposed to do, say nothing?

    If they had slightly changed it to 'we are looking into our leadership practices' rather than 'we as a whole have been maligned' I think it would stink less.

    Fair as well. The “entire team” line was gratuitous when anyone reading the article could see that the criticism was leveled at the leadership culture, not the workers as a whole. 

  13. On 9/22/2021 at 12:26 PM, KSK said:

    Either that or they’ll seek leave to amend their pleadings way after any applicable deadline and then complain that the court is being arbitrary, capricious, and abusing their discretion by not letting them do it.

    Not actual lawyer so the above faux legal terminology might be complete guff but hopefully you get the idea.

    No, you're absolutely right.

    This lawsuit is complete nonsense. Like the whole Kraken.

  14. 6 hours ago, Lisias said:

    Because people are speculating on using SS to bring things down. And I'm argumenting that the descent cargo capability is way less than the ascent. ;) 

    [T]he heavier the vehicle are, harder is for the fins to do their job timely (if at all, too much weight, too higher terminal velocity, way harder for the fins' actuators to work!!).

    You see, I'm  not disputing the technical viability of the vehicle to land. I'm disputing how much cargo it can bring down from space.

    Let’s do the maths, then. Aspirational dry mass of Starship is 85 tonnes. We know the header tanks hold 30 tonnes of propellant. Thus, a notional 100-tonne return payload would increase its total entry mass by a factor of 87%. This means terminal velocity goes up by 87% and the stagnation forces on the flaps go up by 250% during free-fall.

    However, because speed has gone up, the control authority of the flaps also goes up. So the flaps will be able to handle the control as long as they are structurally able to handle the stagnation forces. And since the vehicle nominally experiences much more than the one gee of free fall during intermediate entry, that’s no problem.

    As far as the kick-flip is concerned, having additional mass towards the nose actually makes it easier, because the Raptors have a larger moment arm around the center of mass. Starship will need more prop reserves to land, but that’s fine.

    Starship probably can’t take 100 tonnes to LEO and bring it all back in one go, but no one is expecting that.

     

  15. 1 hour ago, CatastrophicFailure said:

    Er... Vostok/Voshkod? Pure spheres...

    Whoops, yes. I meant the Soyuz family. Modern Soyuz is still derived from Vostok and Voshkod.

    1 hour ago, CatastrophicFailure said:

    Not quite a rock, they've already demonstrated pure aerodynamic control during terminal descent: close enough to the pad for the engines to get it the rest of the way. F9 also has a 1:1 LD ratio as just a cylinder with fins. 

    I will note that the F9 booster achieves its 1:1 L/D ratio only in the lower atmosphere. Can’t do that during hypersonic reentry.

    1 hour ago, SpaceFace545 said:

    Here me out: but what if you swapped out starship's fins for wings. Lets not kid ourselves, this thing is never going past earth's SOI. It's a tin can when empty and wings would allow it to glide down, a much safer and reliable approach.

    Try standing on an overturned soda can.

    Also, a better glide ratio brings back the problems of the Shuttle orbiter’s AoA.

  16. Just now, Lisias said:

    But such L/D on subsonic speeds will not hold, and the thing would fall as a rock.

    Well, yes. "Fall as a rock" is a feature, not a bug.

    Just now, Lisias said:

    The SS needs to do a flip and land standing on her feet - what means that the total weight at landing must not exceed the available thrust (and maneuverability) from two engines - otherwise you would need yet more fuel on landing, what implied on less payload on descent (and on ascent too!).

    It can land on three engines if it needs to. Not a problem. If you need to reserve more propellant on ascent to give yourself more propellant reserves on landing, you do so. No big deal.

  17. 6 hours ago, Lisias said:

    The Space Shuttle managed to get way less heat and stress (proportionally) than a hypothetical Mercury style capsule of the same size because it could control how fast it would sink in the atmosphere by using lift and then staying a bit longer 'up there' where the air friction is sensible less.

    Time is the key. You don't want to dissipate all that speed at once (ask the few Cosmonauts that had to do a ballistic reentry). But the heavier you are, more drag you will need to prevent that. But there's a limit on the size of the fins you can attach to SS. 

    The only pure ballistic re-entry vehicles (i.e., no lift) that humans have ridden are the Soyuz capsules. And even in a Soyuz, ballistic entry is only a contingency.

    The Apollo capsule had an L/D ratio of 0.38 at hypersonic speeds, increasing to about 0.68 just below Mach 2. This was somewhat better than the Mercury capsule.

    In contrast, the Shuttle had a higher L/D ratio during hypersonic flight, but not dramatically higher. The STS orbiter could get an L/D ratio of about 1.5 during the peak-heating, hypersonic phase, increasing to 4.5 at subsonic speeds.  This was actually lower that what the orbiter could have attained; wind tunnel testing showed that the orbiter could have achieved an L/D ratio of up to 1.9 in hypersonic flight at the proper AoA (in this case, ~17.5°). However, the orbiter's heat shield couldn't handle entering at that angle; it had to hold an AoA of ~40° during peak heating to avoid burning off the nose and windows. 

    But Starship is not the Shuttle orbiter. It has fewer design constraints since it doesn't have to be able to land horizontally, which means its heat shield can be designed for whatever AoA will provide peak L/D. A flat plate can achieve an L/D ratio of 2.2 at 17.5° or even higher at more shallow AoA (up to 3.5 at 10°).  And an ogive cylinder can achieve an L/D ratio of up to 0.85 at hypersonic speeds.

    Thus, between its flaps and its body lift, it's very possible that Starship can get a hypersonic L/D ratio just as high or higher than the Shuttle orbiter. And since Starship will be much fluffier than the Shuttle, it should have even less loading. Starship's entry profile will be designed to have the highest possible AoA during the initial entry before the air gets thick so that you can slow down as much as possible, then nose farther forward to increase lift to prevent extreme gees, then tilt the nose back again for the terminal descent.

  18. 15 minutes ago, kerbiloid said:

    Nothing common in shape with the Shuttle orbiter, as it was described not once before.

    The Buran and STS orbiters had a triangular cross section with flat control surfaces. Triangular-cross-section capsules work. The Buran and STS orbiters worked.

    Starship has a circular cross section with flat control surfaces.  Circular-cross-section capsules work. Starship will work.

     

  19. 1 hour ago, zolotiyeruki said:

    What I'm imagining is airflow running from tail-to-nose and trying to get under the scales.

    The angles of entry would make the scaled tiles problematic. The direction of airflow goes in one way on ascent, another way during peak hearing, another way on terminal descent, and yet another way during the landing burn. The shear forces from the airflow are nonlinear with respect to air density and air speed. I can’t imagine there would be a scale tile orientation that would work for all of those. 

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