sevenperforce

What happened?

The vents are off again.

Is this official? As much as it feels like you really, really want an engine in the middle, putting them in a ring farther apart like this gives much better roll authority.

Is there any public data on the effectiveness of Sputnik V? Did they do double-blind placebo-controlled studies?

One thing to note is that the scale on the left-hand side of the graph I posted is a log scale, not a linear scale. So the second dose increases the number of antibodies by a factor of ten.

Some interesting data. Cropped and re-annotated from this study. This study took seven antibody count measurements from 15 individuals who received the two-dose Moderna vaccine over the first 17 weeks. There's a large immunological spike from the initial dose to the two-week mark, while the growth in the second two-week period is lower (or, in some cases, dropped). However, the second dose then pushes the antibody count up significantly higher and it remains higher consistently thereafter. I get my second dose Friday.

Pad closeouts in process per NSF.

NSF says launch expected between 12 and 6 central.

It looked like there was a LOT of vibration on fairing sep. It also looked like the "eye of sauron" entry burn started at a higher altitude and lasted longer than it usually does. (checks other missions) Oh, wow, yes. There's no Stage 1 telemetry to get altitude, but you can still measure the duration of the burn. In the Transporter-1 mission, the first stage entry burn went from T+7:49 to T+8:19, a total of 30 seconds. In contrast, the 1/20/21 Starlink mission had an entry burn that went from T+6:24 to T+6:44, just 20 seconds. The 1/7/21 Turksat 5A mission had an entry burn that went from T+6:21 to T+6:44, just 23 seconds. Definitely much longer than expected. It looks like it's higher-altitude because the initial startup plume is transparent, suggesting significant expansion. That might just be the result of different atmospheric effects, but I doubt it. In the Transporter-1 mission MECO took place at 81.6 km while it took place at 64.1 km for the last Starlink mission and 63.7 km for the Turksat 5A mission. This must have been a significantly more lofted trajectory. I suppose the (unfueled) Sherpa FX third stage is rather heavy?

I believe the droneship landing burns are still 1-3-1 while the RTLS landing burns are single-engine all the way down. And as @Elthy said, Starlink is volume-constrained, not mass-constrained, so a three-engine hoverslam simply isn't necessary. We might see a three-engine hoverslam if they really needed it for a more massive payload. One possibility would be a really large MEO or LEO payload, with a lofted trajectory where they needed all the TWR they could get.

Yes, I am positive they did a WDR. And presumably they will need to do at least one WDR with the full stack. So if they need to retest, that's 4 of 9.

This is a surprisingly tricky question, actually. The best way I know to handle it would be to take into account the hypothetical gravitational lensing effects of the sun. The sun's radius is 232,000 times its Schwarzschild radius, and we have been able to make weak gravitational lensing observations during solar eclipses. So I'm going to make the baseline assumption that visible gravitational lensing is negligible at the edge of a disc 232,000 times the Schwarzschild radius of an object. Since the Schwarzschild radius of the moon is 0.1 mm, that means the "lensing disc" of the moon would be about 23 meters, which is of course far too small to see any distortion with the naked eye. Then again, one of the proposals for a space telescope would be to place a satellite at 542 AU, where gravitationally-lensed rays converge. Applying the same linear approach to the lunar black hole, the ideal place to put a space telescope would be about 2,681 km away. The effect diminishes with distance. The lunar-black-hole gravitational lensing visible from the surface of the earth would be comparable to viewing the sun from about 1.2 light-years away, which I believe would be too far for any meaningful lensing effects.

What have I been saying all along? From the research:

This sort of AI/machine learning algorithm seems like a recipe for disaster. Not sure how you'd work around it, though. Suppose, for example, that the machine learns to recognize behavior from certain classes of vehicles (perhaps certain luxury brands) which, as a result, makes it change its behavior around those brands. This allows it to successfully reduce its overall accident rate. However, its change in behavior in turn makes accidents with OTHER vehicles more violent. What's the trade-off? Do you end up with a self-driving algorithm that effectively discriminates against poor people? What about prioritization? Is the AI's objective to reduce total property damage? Total injuries? Total number of people injured? Prioritize the safety of the occupant(s)? Suppose I'm driving a large SUV and a dump truck suddenly stops directly in front of me, and I have the opportunity to swerve either to the right or to the left. If I'm paying attention and I see that there is a motorcycle ahead to my left and a sedan ahead to my right, then I'm probably going to swerve right, hoping in either case to avoid the accident entirely but knowing that the occupants of the sedan are going to be much less injured by a collision than the guy on the motorcycle. Or maybe if the sedan is much closer to me than the motorcycle then I will swerve left, knowing that the motorcyclist is more vulnerable but deciding that I'm less likely to hit him at all. Whatever decision I make, I'm going to be forgiven because it's assumed I will make the best snap decision I have with the information at my disposal. But when you introduce an AI with access to VASTLY more information, VASTLY more processing power, and (almost) infinitely faster reaction time, things change. How many factors is the AI going to use? What if the AI determines that there are 4 occupants in the sedan and calculates that the totality of minor injuries to them would be greater than the totality of serious injuries to the motorcyclist? What if the AI decides, "This vehicle is extremely safe and so I will not swerve at all, committing to an accident with the dump truck because I know my own driver will only suffer minor injuries"? What if the AI decides, "That is a particularly expensive motorcycle and so the motorcyclist is probably wearing expensive motorcycle armor, so he's probably going to be okay"? Any statistically-collected data reflects our very racist and classist society which means any machine learning algorithm that uses that data is going to end up being...well, racist.

In the past week, more Americans have died of COVID-19 than died of the flu during the ENTIRE 2019-2020 flu season.

Edge cases are always going to be the problem. There will be accidents in AI cars. The important thing, however, is that the accident happens because it was a set of unavoidable conditions, not because of a software error. They need to be able to analyze it afterward and say something like, "The other vehicle spun out so abruptly and so unpredictable that there was no combination of control input which would have prevented the collision, but the AI's reaction time was able to reduce the collision impact by 20% well before a human driver would have been able to react." The edge cases are the thing that will cause a problem because we don't know what we don't know. What does AI do if a crowd of protesters enters a city street? You don't want it to sort through a bunch of options and end up with something that results in a sudden burst of acceleration, for example. What does AI do if it thinks it detects a pedestrian on an interstate highway, where sudden braking could cause a multi-vehicle collision? What you want to avoid is a post-accident press conference where the software engineer says, "Well, rain splatter on the sensors caused the computer to determine there was a 55% likelihood that the cyclist had suddenly swerved into our lane, when in fact the cyclist had not changed her direction of travel. This is why the vehicle swerved and ran straight into a crowded dining patio at 35 mph."

It looks like there was a guidance problem right after restart. Maybe a stuck/stalled fin? Or a gimbal during restart that kicked the booster over. Either way the engine gimbaled very hard to correct and then very nearly tipped over while trying to zero out lateral velocity. After it zeroed lateral velocity it hung there for a pretty long moment in hover before finally dropping to the pad, well off of the center. This does show the advantage of the deep throttle. If a F9 booster came down with that much lateral velocity, it would have no way to make it work. Then again its grid fins cannot stall. Superheavy and Starship will both have the significant advantage of gas-gas thrusters to help, and they can also hover.

Elon has said that the challenge is not to get AI to be as good as a human driver, but to get AI to be SO MUCH BETTER than a human driver that you KNOW it's safer to get in the car with an AI. The tricky thing is that humans are not all the same. Human reaction time, human distraction level, human ability to solve edge cases and react to new situations, human memory -- these all lie on bell curves, and combine to form one big bell curve. We heuristically assume that people we're getting in the car with are average drivers. But to have the same level of confidence with AI, the software needs to be way, way, way out on the upper side of the bell curve. The AI needs to be better than 99.99% of human drivers.

Go for launch in under two minutes. Was it just me or did that hold-down last longer after ignition than usual? Maybe I'm just used to Falcon 9. excrementsttt something went WRONG on that final approach. Shocking it landed safely.

Obligatory:

Came here to post this. Very cool! This sort of rapid restart practice is essential.

Arrestor cables are a good place to start but there's a degrees-of-freedom problem. For a carrier tailhook system, gravity and friction with the deck damp any motion perpendicular to the direction of travel. But with a vertical "midair" catch with motion in the z-axis, you can have motion in the x and y axes that remains undamped. If the wires provide vertical damping in the same way as the arrestor cable on a carrier, then Superheavy is going to be hanging from rather long cable loops. Any slight timing difference in which cable catches first is going to result in a tremendous torque/rotation, which is amplified by the length of the cables. I have a mental image of Superheavy being caught by the wires and then swinging back and forth like a 22-story explosive pendulum until the lower end smashes into one of the towers and kablooey. Superheavy still has to have the heaviest loads during boost when the tanks are under compression, so it has to be strong enough to support itself from the base for that reason. Helium remains a gas at much higher densities and pressures than nitrogen, which allows it to be stored in a much smaller space and makes the tanks much less heavy.

I'm not ascribing any mythical abilities to steel, nor would I. My point is that aircraft tailhooks are made out of welded steel, too. If you are designing the grid fins to take a wire catch point load, steel is a perfectly fine material to work with. They could design for that -- whatever the impact of tower blowback would be, you just aim slightly in the opposite direction.

A few pages back I did the math and just two hot-gas thrusters will be able to handle gusts of up to 50 mph. Plus, Superheavy is HUGE so even without thrusters firing, even a tremendous wind gust would only produce a tiny amount of acceleration on the booster (f = ma, so when m is very big, a is very small).

That was my first thought as well. Magnetic linear generators in the pistons. Easy peasy, metal squeezy.