sevenperforce

Ascending node can be mostly handwaved on the assumption that all orbits would be roughly circular, but yeah, inclination has gotta hurt. The stations end up being connected with a thin little tube running unreasonably long distances between each one. The station is then rotated around the long axis to produce artificial gravity. The buckling moment on that little tube would be immense....also there's no reason for it to be, like, hundreds of meters long between each "station".

I KNEW IT! The worst of it is, there could so easily have been science involved in the show. It just would have taken someone who knows a handful of basic things: I don't think they had that capability. In the first season, anyway. They can go down to the ground easily enough but they don't appear to have any return rockets. Oh, there was no mention of asteroid mining on the show. I was just saying that stitching together multiple space stations isn't too far-fetched if you imagine that perhaps asteroid manufacturing capabilities would be operating a century from now. Nah, they have a couple of large dropships. The capsule was more of a hackjob. Hmmmm....I have to wonder whether men or women did that particular study.

Oh, I certainly wasn't saying I've learned it all, either. I meant that the one-semester class is what I needed to get my feet wet.

You'd have to select the mating population beforehand. The point is that if you wanted to preserve the genetic variation currently present in 7 billion people, you'd need individuals with completely different genomes in regions of intraspecies variation. Theoretically, the variation present in 7 billion people could fit into just 23 people, if you selected from the right regions and ethnicities. But 2,000 people selected at random from the world would have less than 1% of the genetic variation of the overall population.

I learned C++ in a single semester college CS course required for my physics degree. Learned more from teaching the other students in the class than I did from the prof.

Not enough time for evolution to work.

Maybe their ability to retrieve near-earth asteroids got tanked shortly after the nuclear holocaust and so they had to make do with what was already in LEO. Oh, yeah, definitely.

The teen drama aspect is a bit ridiculous. Also, apparently everyone on the space station had children which EXACTLY resemble SoCal natives. Everyone has the exact same "b-movie-model" bone structure and appearance. Would be so easy to make shows like this accurate. Only finished with season 1 so far. I saw one "floating", as they call it when they toss someone out of the airlock, and I also think they commit the "pressure is weight" fallacy. As soon as they blow the airlock, the person starts floating off into the void. If the station was spinning, then either their "floor" would drop away and they would fall like a rock, or the airflow would pull them off what would essentially be a cliff and they would drop out of sight. Oh, and orbital mechanics fail...midway through the first season, they sacrifice 300 people to help conserve air. Originally they were just going to murder 300 people and make it look like an accident, but then the protagonist's mom tells everyone the plot, and so like 400 people just volunteer to die. Anyway, they suffocate them all in a small chamber, then open it up and toss them all out of the airlock. The bodies are visible from the ground, re-entering as a cloud of shooting stars just minutes later. How did they get the dV to re-enter??!! Also, if you have the kind of manufacturing capabilities to stitch together space stations in orbit, surely you could rig up an electrolysis system to get more oxygen flowing. Maybe they just call it hydrazine, but it's actually mixed with some sort of metastable fluorine compound. Though I doubt even that would make it pinkish-purple. That ridiculous mushroom cloud could be realistic if Raven was actually rigging up a fuel-air bomb, with the gunpowder used for dispersal of the hydrazine followed by spontaneous ignition once the fuel/air mixture reached the LEL. Something like that. Four atoms?!

It was so stupid, because there was literally nothing requiring that line. The dude could have said "40 mph" or "30 mph" or "50 mph" just as easily. I wasn't going to come right out and say it........

Partner and I started watching The CW's The 100 on Netflix a couple of weeks ago. Now finished with the first season, and.......oye. The concept is nifty enough. The only (presumed) survivors of a global nuclear holocaust are those able to relocate from Earth to a handful of space stations in LEO. As the mushroom clouds dissipate, the space stations come together, dock, and form one giant super-station within which humanity is preserved. There are roughly 2,000 inhabitants of "The Ark" at the start of the series: Because resources are so tight on board, all crimes are punished by execution via airlocking. Juveniles, on the other hand, are permitted to live, but on reduced rations. The titular "100" are a hundred such delinquents sent on a dropship a century afterward to see if Earth is inhabitable, since the station is running out of consumables. And from this, the show is born. I do think this show had a science consultant. However, either the science consultant was a biologist, or was drunk the entire time, because the attempts at rocket science are entertaining and yet so, so wrong. First, the good. The concept of space stations assembling into a ginormous "ark of humanity" isn't that much of a stretch. Assuming this is set in a few hundred years in the future, it's not inconceivable that we could have substantial zero-gee manufacturing industry operating in orbit with thousands of tonnes of raw material (sourced from captured LEO asteroids, probably), so building an Ark in orbit isn't entirely out of the question. 2,000 people isn't nearly enough to reconstitute the human race, but that's not really a question addressed within the series; they're just trying to survive. So that's not an issue either. Artificial gravity is generated by rotation of the Ark, which is reasonable enough. Atmospheric re-entry is depicted as being "hot". So hey, at least they got that right. And then the not. Artificial gravity by rotation? Sure, great. The ship rotates noticeably. However, despite numerous shots on the ship looking out of windows, none show any actual rotation from inside, even though it would be readily apparent. Virtually every corridor on the ship has curvature, but it's all 90 degrees off from where it should be (i.e., you're walking around corners, rather than the floor sloping "up" behind and in front of you). Even when the ship breaks apart and stops rotating (see below), artificial gravity persists. A "Soviet-era" capsule (which looks nothing like any actual capsule) is hijacked to get down to Earth. Descent ends up being prone, not supine, and while the thrusters used to initiate descent are accurately labeled "retrorockets", they have a thrust of about 3 gees, fire radially, and produce an IMMEDIATE entry into the atmosphere, with fire instantly starting to erupt around the heat shield, which is pointed directly toward the ground rather than prograde. At one point, they need to signal the space station that they are alive and well, so they build rockets to use as flares. The rockets are built from the thrusters on board the capsule/pod, each one boasting two nozzles and measuring about 3 feet long: They are explicitly stated to be fueled by hydrazine. And of course this is what they look like when they are fired up rails: Somehow there were, like, 40 of these rocket pod things on a single capsule. Yet they travel under power for hundreds of miles and produce bright pink light the entire way, easily visible from the space station. Any rocket with nozzles of that size, or capable of making it out of the atmosphere, or fueled by hydrazine at all, would kill everyone anywhere close to that distance from the ignition site. Oh, and hydrazine in the show is a viscous, reddish liquid which is toxic enough to cause immediate wooziness to anyone who comes close to it, yet is not toxic enough to have any long-term ill effects. It's as sensitive as nitroglycerine and detonates readily if heated, with an energy density that makes C4 look like baking soda. The original dropship lands in what is clearly the Pacific Northwest, which means the Ark needs to have a pretty substantial inclination. And yet they see it pass overhead literally every few hours, and everything dropped from the Ark automatically is visible (and, if it survives entry, lands within a few miles of their location at most). Finally, in the first season finale, they concoct a hairbrained scheme to "ride the Ark" down to the ground: "We'll use one set of thrusters, the ones that keep us spinning so we stay in orbit, to send us down toward the atmosphere. When we hit the air, the station will break apart into its original component stations. Some of those...and there's no way to predict which ones...will EXPLODE. The ones that survive can then use the other set of thrusters on the other side to slow down. We will hit the ground at around 70 mph." SMH.

Which is why both diatomic nitrogen and diatomic oxygen float in an atmosphere of carbon dioxide and sulfuric acid. Each carbon dioxide molecule masses 44 amu. Diatomic nitrogen molecules mass 28 amu. Diatomic oxygen molecules mass 32 amu. No matter where you are in the Venusian atmosphere, a balloon or bladder filled with oxygen will float, because oxygen is lighter than carbon dioxide. Microbial colonies grow and thrive in Earth's clouds.

Let's see here. The Star48B (with or without vectoring) masses 126 kg dry and 2137 kg wet, with an Isp of 286s. The probe, with fuel, masses 685 kg. So the Star delivered 3.495 km/s. A Venusian Hohmann costs about 3.5 km/s out of LEO, while a Mercurian costs 5.5 km/s. So we know the DIVH pushed a payload of 2.8 tonnes at least 2 km/s beyond LEO. The reusable FH, sandbagged, delivered the Roadster and an indeterminate amount of ballast to at least 3.6 km/s beyond LEO. Back of the envelope says that the Block 4 FH could have done it with center-core expenditure, though I don't know whether they'd be able to manage RTLS for the side boosters. Block 5 FH could likely have done it with RTLS on the side boosters but would still need to expend the center core. Innnnnnnnnnnteresting. Elon said a week or so ago that we were able to get more BFR news.

I don't see that there would be any significant difference in the engineering challenge of designing a 100-kN-class expander nozzle and a 300-kN-class expander nozzle. Certainly wouldn't be worth redesigning the entire combustion chamber.

We'd need to know the dV imparted to the vehicle out of LEO before the Star motor fired.

It doesn't matter, because it's an issue of composition. Pure oxygen (or even ordinary dry Earth air) is less dense than Venus's carbon-dioxide atmosphere at any altitude, and so it will be more buoyant regardless of where it floats. The biggest challenge would be bioengineering an algae capable of metabolizing hydrogen disulfide in place of water; there are trace amounts of water vapor in the Venusian atmosphere, but it's not enough.

Finally. This was a no-brainer. Unrelated: would a Falcon Heavy have been able to deliver Parker Solar Probe with the same performance as the DIVH last night? My guess is that it would have had to expend at least its core.

Presumably the heat shield will outlive both. I wonder what will happen first: sun-induced sputtering that significantly changes the orbit of the derelict vehicle, or an accidental close encounter with Venus that sends it out of its intended orbit?

C or C++.

Well, that's the million-dollar question. Or the 38-million-dollar question, in this case. The RL-10 is an expander-cycle engine, which means that it uses the high thermal coefficient of its liquid-hydrogen fuel, in an expansion chamber, to drive a turbopump. It's more efficient than a full-flow staged-combustion engine and wastes no propellant at all. The current BE-3 is a "combustion tapoff" engine, which vents a small amount of hydrogen-rich steam from the combustion chamber to run the turbopump. It's about as efficient as a gas-generator cycle but has a better TWR. If the BE-3U is being converted to expander cycle, then we could conceivably see an engine every bit as efficient as the RL-10, for a fraction of the price. The geometric limit to a full-flow expander-cycle engine is about 270% the thrust of an RL-10. However, it's possible to run only a portion of the hydrogen through the nozzle (about 72%, in this case), use that on the same expansion loop originally used by tap-off to run the same turbopump, and let the remaining 28% run straight from the tanks into the chamber. Don't know if it would have enough power to run, but it's a possibility. It may be that such a "bypass-expander-cycle" engine relies on a larger engine bell and thus would not work for the atmospheric variant.

About as thick as the buoyancy of O2 in dry air. Venus's dry air is a helluvalot denser than our dry air.

...people who read trinary, people who don't, and people who mistake trinary for binary.

Skycrane FTW.

Wait, they are making the BE-3U an expander cycle? This changes a LOT.

Kestrel, Merlin, Falcon, Raptor. Thinking bigger? Eagle Heron Penguin Ostrich Pelican Vulture Buzzard Pelagornis sandersi Argentavis magnificens Teratornis merriami Kelenken guillermoi Brontornis burmeisteri Titanis walleri Arambourgiania philadelphiae

I've seen "Big flipping Booster" for the long end and "Big flipping Spaceship* for the short end, with "Big flipping Rocket" for the whole stack. We may see something like "Heart of Gold, a BFR-class spaceship, left for a cislunar flyby today." Or it may be, "BA1031, the first Heron booster to launch a manned interplanetary mission, was retired today after its sixty-second flight."