sevenperforce

Also, younger people getting it: https://www.cnn.com/2020/03/25/health/georgia-coronavirus-girl-improving/index.html?utm_source=twCNN&utm_content=2020-03-25T16%3A30%3A07&utm_medium=social&utm_term=link 12 years old. No health conditions, no travel history.

Eh, I think it's a little more than that. I'm almost 31. I'm not in the best shape of my life but I'm reasonably healthy and a nonsmoker. Six months ago, there was no reasonably conceivable scenario in which I would end up choking to death on blood and cellular fluid leaking out of my lungs, absent some acute injury like a car crash. Today, the odds of that happening are no longer negligible. That's rather scary. It is a mistake to conflate risk of death with risk of hospitalization (and I'm going to fight @tater on this one). This disease has a low kill rate for people under 65 without pre-existing conditions, but hospitals can still run out of ventilators due to volume even if all patients were under 65 because it leads to pneumonia so readily. There is also no guarantee of immunity. And home quarantine as you've described only works if there are no contacts between those quarantined and the rest of us. There are lot of people under 65 without pre-existing conditions who live with people over 65 or with people who have pre-existing conditions. If we did a full shutdown we would eventually starve the virus out. You could still get reintroduction by asymptomatic carriers like Rand Paul, but only if asymptomatic carriers never actually beat it, which seems unlikely.

I understand the first U.S. death under age 18 (with no pre-existing conditions) happened yesterday. Related: https://fox40.com/news/covid-19-not-at-all-like-flu-say-doctors-treating-patients/ It's basically a form of pneumonia that makes you bleed out through your lungs.

Right -- you may still need to do a pulsejet approach (though perhaps not), but you can scale down the pulse amplitude to where you don't need any pusher-plate at all and can use a conventional engine bell with a converging-diverging nozzle, etc. Much more efficient. For the purposes of your fiction, exactly how much delta-v does your vehicle want? Are these monsters going to go from orbit to the surface and back to orbit? Are they planet-hopping? Will they need to make multiple VTOL SSTO cycles on a single propellant tank? All of these are questions that impact optimization. Here you've got it right. When you're talking about pure rockets and liquid fuel tanks, the square-cube law promises increasingly better and better results the larger your vehicle becomes; there's no upper limit. On the other hand, air is a low-density propellant and so a larger ship will fare poorly if it tries to get off the ground using air alone as reaction mass. That's why a tiny drone can easily get off the ground with tiny propellers running at high speeds but a helicopter needs a huge, huge rotor to do the same thing: you're going up against the wrong side of the square-cube law. Once in flight, collecting air via ramscoop is essentially "free" in terms of dry mass (intakes don't really weigh much), though not in terms of induced drag. On the ground, however, you need huge rotors and heavy compressors to accomplish the same goal. Accordingly it is better to jump-start liftoff using auxiliary propellant injection until you get up to ram-collection speed. The propellant you use for liftoff is spent mass, as opposed to heavy rotors and compressors you'd have to drag with you to orbit. Your landing mode becomes another issue, though. If your ship is intended to drop out of orbit, land, and then return to orbit without refueling, you're gonna need a really robust landing system. You might want to consider a rolling landing and rolling liftoff, because you can save the weight of that extra propellant you'd need to inject for takeoff by using a runway to get up to ram-collection speed.

Good news:

If nuclear-thermal air turborocket engines were good as boosters, they would be good as main-stage engines.

If you have antimatter confinement, there is no need for a pusher plate design at all. Pusher plates are very inefficient with respect to the use of the available energy; it's just that nuclear bombs have SO MUCH energy that it beats chemical propellants: A nuclear pusher plate design is the functional equivalent of ripping the pistons out of your car's engine and detonating them one at a time to push yourself down the road. The only reason it works is because the energies involved are so immense, or we would never consider it. We have to use a pusher plate because we have no way to contain a prompt-supercritical nuclear fission reaction, so we toss it out the back, let it blow up (wasting most of the energy) and ride the shockwave. If you have antimatter confinement, on the other hand, you don't need to waste all that energy because you can make the explosion as small as you want. A NTTR has increased thrust once over Mach 0.8 or so, but it has poor liftoff performance. Liftoff is where you really need thrust; an SSTO needs to get off the ground as quickly as possible. The solution is not to add energy in the form of antimatter, but to add more propellant. Au contraire -- the larger your vehicle, the easier it is to make it an SSTO. The square-cube law means that the bigger your ship, the better. And yes, every rocket is mostly hollow. Hollow is the essential nature of propellant tanks. Not at all. An antimatter-based turbo-ramrocket could lift anything. Heck, you could lift a destroyer-sized vehicle with SRBs, if you wanted to. Just add more engines. More thrust means more propellant, which makes the engines less likely to melt.

An NTTR aerospike is actually three engines all on its own. Sure, you need a lot of thrust to launch a heavy craft, but conceptually there's no difference between launching a 20-tonne payload, a 200-tonne payload, and a 10,000-tonne payload. The type of engine does not really speak to thrust; you can have a very thrusty pure-rocket engine or a very unthrusty antimatter rocket. To a first order, there's no real limitation on the size of a rocket engine. Practically speaking you run into combustion instability with chambers exceeding 22 cubic meters, but that's just an engineering problem. What you need for an SSTO is not a lot of thrust per se, but a high liftoff thrust-to-weight ratio as well as a high specific impulse. A NTTR has a higher specific impulse than a pure-rocket NTR but a lower thrust-to-weight ratio at takeoff.

One thing to keep in mind is that the envelope of usefulness for each of your engines' modes is pretty narrow. You wouldn't build an ATV with wheels for roads, deployable floats for amphibious use, deployable treads for rough terrain, and a jet-assisted autogyro rotor for jumping ravines; at some point you should just stick to a plain old helicopter. In the same way, having an Orion pusher plate PLUS pure rockets PLUS ramjets PLUS turboramrockets is probably less efficient than just sticking with one or two primary engine modes. A gas-core antimatter rocket (where a small amount of antimatter is injected into a stream of propellant) has specific impulse comparable to a nuke pusher plate approach, albeit without the massive thrust capabilities. Start there.

Probably not much. The dV requirement is the dV cost of an orbital plane change times the percentage of orbital velocity at which the dogleg takes place.

I wrote about the impact of pseudoscience on this public health crisis: https://medium.com/@davidstarlingm/creating-coronavirus-f0cfbc3429f3?source=friends_link&sk=2573760bc32147cc4c42d18f26a537b3 Yes, Italy is case in point. During the 2018-2019 flu season, there were 490,600 hospitalizations for the flu in the United States. 34,200 died and 456,400 recovered. In Italy right now, they have closed 7,000 cases, of which 3,000 died and 4,000 recovered. Those are not good numbers, no matter how you try to work it. The total number of cases reported in Italy right now is 35,713. Some of those will die. But even if none of them die, that's still an 8 percent death rate. The death rate after hospitalization with the flu in 2018-2019 was 6.9 percent; the death rate for people who received some sort of medical attention was 0.2%. So we can say that even if no one else in Italy dies (and right now the death rate is climbing exponentially), COVID-19 is at least between 115% and 4,000% as fatal as the flu. These numbers are especially not good when the spread of the virus is so easy and people pass it asymptomatically.

Source? I saw 50% there. Which is still amazingly high. And also horrifying since literally everyone I know could have it and be passing it to everyone else and not know until someone is susceptible. Some research indicating that blood type is an indicator, with O being nearly bulletproof and A being more susceptible. Would make sense given the receptor binding mode of the virus. Also, what do you think of these numbers?

I seriously doubt they had definite plans for B1048.6 as of this morning. Each life leader gets extensive reinspection before it's assigned to any upcoming mission.

There was a ton of roll following termination of entry burn shutdown, much more than typical. Grid fins working overtime. If the engine that shutdown ended up fragging, then it's possible that produced an aerodynamic asymmetry on re-entry that messed with stability.

Shaping the charge doesn't make the blast not-spherical, it just makes one side of the spherical blast wave denser than the other so that you increase the total impulse delivered to the plate. Reality is exciting! You can stay in reality and still do a LOT of cool stuff.

New York now considering the same Shelter In Place ordered in San Francisco. <snip>

The plate needs to be a circle because the explosion is spherical.

CDC rec (rolling on 15 days) now no more than 10-person gatherings.

Enough skiers rent their skis that it would remain a major spread vector. Plus indoor facilities like restrooms....

I would be worried about getting to the ski resort (is she taking any public transit) and contact at the lodge. Then again if she owns her own equipment and drove herself to the location then good for her.

Best article I've seen so far: https://medium.com/@tomaspueyo/coronavirus-act-today-or-people-will-die-f4d3d9cd99ca

I got the flu shot, and I never get fevers. Hence the concern. Thanks for taking social distancing seriously.

Now presenting with a very mild cough and a mild fever. I ride the DC metro twice a day so I am about as likely to catch it as anyone without direct confirmed contact. Masking and self-isolating but not much of a consolation when I've been snuggling my newborn twins all weekend.

I am sure with sufficient power and gas density of the field bubble it is possible. May not be easu, but one can do s lot with magnets, air, and plasma. Magnetic flux drops off with the cube of distance, so the square-cube law really punishes this kind of approach. With the high-efficiency nuclear engines you're discussing, any appreciably-sized ship will soon need more mass associated with the magnetic entry shield than it would take to simply uses retropropulsion all the way down.

Ionized field shield doesn't do enough for entry. You can use it for aerocapture into a lower orbit though.