sevenperforce

T-42 minutes.

The very first rocket which put an American satellite into space, Juno 1, used an MGM-29 Sergeant as its upper stage. Actually, it used 15 MGM-29 Sergeants, with 11 on the second stage, 3 on the third stage, and 1 on the fourth stage. The MGM-29 had been launched many times on its own and was equipped to carry a payload of up to 431 kg, while Explorer 1 only massed 14 kg.

Simply delightful that our main view is of Raptor number 42......

Ah, good point. I forgot about that. Hahahaha!!

I can see it. Oh Darn it

Good question. I suspect it is not but I am not sure. Saturn V was flown all-up from the beginning, rather than using dummy upper stages, but I'm not sure about Saturn I. [does some quick research] The first four Saturn I test flights used dummy upper stages and made it up to an apogee of 167 km. The S-I first stage had an empty mass of 45 tonnes and a gross mass of 433 tonnes, but was flown with a dummy payload massing in the neighborhood of 86 tonnes, for a total launch mass of 519 tonnes. Technically, three Raptors at full thrust could lift up to 673 tonnes off the ground, but since they will probably want to have a higher TWR at launch, it will probably have a lower propellant load. At a TWR of 1.5 it would have a gross liftoff mass of 449 tonnes which would make it lighter than the S-I test launches. At a TWR of around 1.25 it would have a gross liftoff mass of 538 tonnes which would make it heavier than the S-I test launches.

Krypton Hall Effect thrusters can push up to 2700 seconds at a discharge potential of 600 volts. I don't know the voltage potential for Starlink but the specific impulse is definitely going to be somewhere between 1400 and 2700 seconds at any rate. v1.0 is listed at 260 kg, so to get 3600 m/s it would need to carry between 33 and 60 kg of krypton. I don't know if that's realistic or not. You need about 2300 m/s to get from a Mars transfer orbit into low Martian orbit.

Off topic, but does anyone know how many kg of krypton the Starlink satellites carry? I'm wondering whether they have enough dV to do an orbital injection at Mars.

Judging by the flu season we've just had in the Southern Hemisphere (or rather, haven't had), I'd be inclined to think that flu is a lot less infectious than COVID. I could be wrong but I think @K^2 was saying that SARS-CoV-2 doesn't mutate into new strains as rapidly as Alphainfluenzavirus, not that it was less infectious than Alphainfluenzavirus. Yeah, if the vaccine targets the receptor binding domain (RBD) on the SARS-CoV-2 spike protein, then it should cover mutant varieties fairly well. The reason SARS-CoV-2 is so infectious is that its spike protein has a REALLY effective RBD. If it mutates enough to avoid being within the coverage of the vaccine, it should no longer be particularly infectious.

Neat to see three engines on the ascent element with engine-out capability. It's the same arrangement as Starship. Presumably they can gimbal through the center of mass. Shame there's no airlock. Those two BE-7s look spectactular.

And the side Draco thrusters are still in place. They're just covered in protective tape for right now. It's only the SuperDracos that are removed. It will have the same forward adapter, though. Less high-gee firing time, I suppose? Firing the engines with the upper stage attached doesn't stress the booster as much because there's less gee-loading. Once the upper stage is gone, the boostback burn is a stressor. Eliminating that means less loading on the upper stage.

As usual, antibody tests have a higher false positive rate than PCR tests because they can trip on other coronaviruses........particularly NL63.........which also binds to ACES2............ Yet another paper showing what Fauci said in January: asymptomatic people are not significant drivers of respiratory disease outbreaks. Sick people should self-isolate, everyone else should go about their business as usual. Ugh. No. I hate arguing with you on this but I just can't let it stand, because you're not accurately representing the study. The baseline secondary infection rate for this study was 3.7%. The secondary infection rate (95% CI) for each class of patients was: Asymptomatic: 0%-1% Mild: 1.8%-4.8% Moderate: 4.4%-6.8% Severe: 0.6%-6.0% Critical: 4.6%-16.3% But there are two critical limitations. First, there were 391 index cases whose contacts were traced. However, 168 of these lacked information on clinical symptoms, and so we don't know how many of them were asymptomatic: it could have been none of them, or half of them, or all of them. Those 223 index cases which did have information on clinical symptoms were linked to 2,610 close contacts, resulting in 121 secondary infections from 68 of those index cases. Only one of those 68 index cases was asymptomatic. The number of asymptomatic index cases going into the study was ALWAYS going to be low because asymptomatic cases are simply less likely to be detected, so the data just isn't large enough to draw meaningful conclusions about asymptomatic transmission. However, the second problem is much bigger. That's the problem. Over and over, analysis of actual patients have shown that in all but the most severe cases, the peak-positive presence of the virus (and thus the highest opportunity for secondary infection) occurs before the onset of symptoms. "Sick people should self-isolate" doesn't work. If you do not currently have symptoms, you simply do not know whether you are uninfected, infected and asymptomatic, or infected and presymptomatic. Additionally, for persons with seasonal allergies, mild symptoms will be missed during the period of highest infectiousness. I'm on Zyrtec year-round for my allergies...should I have been self-isolating the entire year? Fauci was right in January: before COVID-19, asymptomatic transmission had never been a major driver of a pandemic. SARS-CoV-2 is one of the first viruses which has significant contagiousness for an extended period of time prior to symptom onset. This study was able to conclude that patients whose cases were ULTIMATELY more severe generally were more likely to have infected close contacts. This makes sense, because they were the ones who had the highest viral load prior to symptom onset. It does not say that people who are presymptomatic are not a major driver of secondary infection.

R.I.P.

In the movie, the explanation was that a "rogue comet" had knocked the "Texas-sized" asteroid out of the asteroid belt. We can do the math for a gravity assist as an elastic collision. Dawn needed 7.8 km/s to get to Vesta, which was a spiral trajectory (lower efficiency) but also used a Mars gravity assist, so 7.8 km/s is probably about right for the injection or departure dV from the asteroid belt to an Earth-crossing trajectory. Your "Texas-sized asteroid" is whirling between Mars and Jupiter at around 17 km/s. Texas is 660-760 miles across, meaning our "asteroid" is somewhere between the size of Charon and Iapetus. Let's say Charon to be conservative, so we're looking at a mass of 1.6e21 kg. How large does our "rogue comet" need to be? The maximum gravity assist occurs with a deflection angle of 180 degrees, meaning that the rogue comet would need to be retrograde with a periapsis at around 2.7 AU. Presumably if this was an interstellar comet they would have said that, so let's place its apoapsis at the farthest reaches of the Oort cloud, 200,000 AU away. That means its retrograde velocity at periapsis is -25.6 km/s. To rob our "Texas-sized asteroid" of the largest possible velocity, the comet will need to reverse its velocity plus get a boost from the (new) velocity of the asteroid, a difference of 60.4 km/s. If the change in momentum of the asteroid is 7.8 km/s and the change in momentum of the comet is 60.4 km/s, then by conservation of momentum the mass of the comet is 2.1e20 kg, about twice the size of Enceladus. At least you wouldn't have to worry about a future Giant Enceladus encounter, since this gravity assist would eject it from the solar system. (Realistically, this would only be possible if both the "Texas-sized asteroid" and "rogue comet" were point masses. The gravity assist would be less efficient because they would be separated by their surfaces, meaning the "rogue comet" would likely need to be much, much larger.)

I think Elon really wants to avoid heat-shield seams if at all possible, but that may end up being the only solution.

We need antiflint, antisteel, and antitinder so that we can create some antisparks and start a merry blaze by combusting antiwood and antioxygen. That'll show'em!

Yeah, that would be unnecessarily complicated for sure. The 2016 ITS would have used a PICA-X heat carbon fiber heat shield, which is much more robust (but not nearly as reusable). The glass tiles on Starship are tougher than the ones on the Shuttle, but if you recall the Shuttle tiles could be crushed with your fingertips. The only way to do it without a seam in the tiles, I think, would be to use fairly large nacelles that enclose legs telescoping out at an angle. Like my example above but with a heat shield cowling that maintains its angle and doesn't move -- the legs would need to protrude out under it. The only problem there is that you're lifting the vehicle higher off the ground, which raises the center of gravity and obviates some of the advantages of that wide stance. Yeah. Fortunately the legs here are largely decoupled from the rest of the design so they can iterate a bit but they are running out of room.

One thing you have to avoid is the ground contact point being heat-shielded. The tiles on Starship are far, far too fragile to have any ground contact. The legs on Falcon 9 deal with much less entry heat and so they can be exposed to the airstream, but whatever actually touches the ground for Starship cannot be shielded. The good thing about the current legs is that the angle is fairly low, so the force is transferred pretty directly to the skirt. There's a little torque at the hinge, but not a lot. If the current rotating legs curved out more, the torque on the base of the skirt would be too high. Falcon 9 style legs are awesome because the telescoping piston transfers the force up higher at a more narrow angle, which avoids extreme torque at the hinge. And it works well because the legs themselves act as a heat shield for the piston. But trying to fit a telescoping piston under an orbital-class heat shield is NOT an easy task.

That's clearly why he preferred the tripod design earlier on -- those three legs had a ridiculously wide stance. You could have landed anywhere. But building the flaps to actuate along the medial axis while ALSO taking a transverse load at touchdown would have been way, way harder. I'm sure the flaps are much lighter and stronger with lighter actuators since they don't have to take any transverse load. The current leg design uses a fold-out-and-telescope design so that there is no need for shielding. In contrast, the lunar starship legs (as depicted) drop straight down. I wonder if it would be possible to telescope through the skirt:

Yeah, I agree. The short hops without the nose cone made sense for the sake of getting the leggy touchdown correct, but once they go higher, they're going to want to test the belly flop.

No. Yes. Physics. This is why it would not work. [snip]

I was always amused at the scene in Armageddon where a nuclear device roughly the size of three backyard-grill propane tanks, detonated just 0.039% of the way below the surface, somehow packs enough energy to split an entire dwarf planet into two pieces and launch them away from each other rapidly enough to pass on both sides of Earth. Forget Project Orion. We need whatever kind of nuke they were using.

Hot-gas thrusters?

The 1968 influenza epidemic killed an estimated one million people worldwide in just over a year and a half, or about 50,000 per month. COVID-19 has killed 1.4 million people in under a year...and those are only the confirmed deaths. Using the same estimation framework used for the 1968 flu, that's 170,667 deaths per month. And yes, there are more people alive today, but the seasonal flu is also much less deadly today because we have much better therapeutics than we had half a century ago. The average flu season between 1967 and 1976 killed about 35 people per 100,000 in the U.S.; the 1968 influenza pandemic killed 50 people per 100,000. That's only a 42% increase. In comparison, the average flu season between 2010 and 2018 killed less than 12 people per 100,000 in the United States. Current projections have the death toll for COVID-19 reaching 150 people per 100,000 in the United States by February. That's a 1164% increase. It's not even close. And you're correct -- there weren't many mitigation measures taken in 1968. But travel was simply not the same in the 60s and 70s. For example, the number of airline passenger tickets in 1970 represented 8.4% of the world population; today, the number of airline passenger tickets represents 47% of the world population. So mitigation strategies just weren't comparable. Calculating those numbers based on IFR is pointless because COVID-19 is far, far more transmissible than influenza. You have to look at the actual number of per capita deaths within each cohort. During the 2018-2019 influenza season, the number of deaths per 100k in the U.S. was 1.8 for the 18-49 cohort, 9.0 for the 50-64 cohort, and 48.7 for the 65+ cohort. I looked up the current COVID-associated deaths by age bracket. Adjusting those numbers by the February projections, the number of COVID-19 deaths per 100k in the U.S. will be 60 for the 18-49 cohort, 178 for the 50-64 cohort, and 466 for the 65+ cohort. Even if you subtract the number of deaths which would have happened due to flu anyway, that's a 3,000% increase in deaths per capita for the 18-49 cohort, an 1,870% increase in deaths per capita for the 50-64 cohort, and an 860% increase in deaths for the 65+ cohort. I agree, comparative studies of mitigation strategies are very challenging because we do not know the base rates, susceptibility, pre-existing resistance rates, or really anything else. The population density of New York City is more than thirty times the population density of Florida's densest and most populous counties. That alone more than explains the difference. Then you factor in things like average income, access to healthcare, and so on. But yes, any mitigation until vaccine should have been sustainable. I agree. I'll take these one at a time. "Tell people facts, and let them make their own decisions." Bad idea. People are dumb and they are immune to facts. Public health officials, not Facebook misinformation threads, should be leading the response to a pandemic. "Provide support for people actually at risk..." The risk is hundreds to thousands of times greater for ALL age groups. "The only impact on employers should probably have been to actually allow sick people to stay home." Federally-funded incentive programs would be great, yeah. "You could even close mass gatherings." Agreed. But we really haven't done that consistently, which has resulted in repeated superspreader events. "Telling my wife's Pilates instructor she can't teach 1 on 1 classes is insane..." See, here's the problem. Public health officials have to make recommendations that can be broadly implemented and enforced. I'm sure that the risks of 1-on-1 Pilates lessons are minor, but you have to come up with broad categories. At the end of the day, maybe the category boundaries could have been better-chosen. I'm sure they also could have been worse-chosen. Agreed.

Evidently it was placed by an anonymous artist between 2015 and 2016.