sevenperforce

Strength would seem to be the biggest problem here. Towers large enough to hold all this actuated machinery, which in turn must be robust enough to catch and hold Superheavy, are going to be quite heavy themselves. Trying to put THAT on tracks seems like it would be really tough. That being said, this is my favorite design so far: Presumably one of the arms could rotate less and one of the arms could rotate more if it was coming in off-center. The only things I'm concerned about here are the bending moment on the tower attachment point and the inability to catch it if it's a little further from the tower.

The design I proposed can actually handle a considerable amount of displacement by adjusting the swing angle and the platform height. For example: This will handle off-center displacement in any single axis, and the semicircles are wide enough that the grid fins should be able to "catch" in the corresponding arms. They're also wide enough to handle a little bit of off-center rotation. The grid fins are welded steel and should be able to handle a wire snag. There's a point load at the booster attachment point anyway.

If Elon persists in this hairbrained scheme to catch Superheavy by its grid fins, I have an idea how it could be done. I like the idea of snagging Superheavy's grid fins on wires, but having the wires strung bare between towers doesn't make much sense and doesn't give much control. You aren't able to control different axes of freedom because attempting to "shock absorb" in the vertical axis will allow the booster to swing in the opposite direction. What you want is a system that controls the tilt of the booster and the vertical displacement of the booster separately. Here's what I'm thinking: The "catch" wires for the grid fins are taut across the semicircle arms, so as soon as contact is made (even if it's just one wire) it immediately tugs on the entire arm. Each arm, in turn, rotates on a single axis, held by a crane-like wire set. Finally, each entire arm platform rests on shock absorbers which can only actuate up and down. As the booster descends, the arms lay flat to stay out of the way of the rocket plume. Then, at the correct time, they are rapidly lifted into place to snag the grid fins. (Alternately, they could be folded up and lowered into place to snag the grid fins.) They are more or less locked in place by their crane wires and the entire platform provides vertical shock damping. Finally, once the engines have cut off and the booster has come to rest, the platforms are lowered gently and the arms provide fine control to guide the booster onto the launch clamps.

Does that mean they've 'fixed' something on 15 prior to stacking that was already integral to the earlier iterations? Something they don't want to waste time, energy or money tearing down those to fix it? I suspect that 12-14 are going to be partial prototype tests, like SN7.

Check out the tiling arrangement on this SN15 section.

We have liftoff

If I had a dime for every time I accidentally put my payload decouplers as stage zero and staged them off on the pad before firing my engines...well, I'd have like, a dollar.

I'm sure that if I had done as much research into Sputnik V as I've done into the Pfizer and Moderna vaccines, I'd be a little less skeptical. But it's interesting that I was as hesitant as I was, just now. If I instinctively recoil, that helps to explain why so many laypeople do too.

See, I would be wary of a vaccine like that. And I'm me. So maybe I can understand.

I’ve also been told via friends in France that the population there tends to be more organic-eating, veganism-promoting, and so forth. Most of the current antivax sentiment in the US is right-wing but there could be some more left-wing sentiment in France. That’s a good point. It’s why I intentionally publicized my own vaccine. I want people to think, “Wow, I want that to happen to me!”

I just had an interview with the largest French news organization and she told me that half of the people in France are refusing the vaccine. Ridiculous. More interviews: https://www.insideedition.com/man-goes-to-dc-grocery-store-to-run-errand-leaves-having-gotten-surprise-covid-19-vaccination-64125

For Moderna it's two injections four weeks apart; for Pfizer it's two injections three weeks apart. The particular antibodies that bind to SARS-CoV-2 spike proteins are produced very rapidly by the body and, for reasons we don't quite fully understand, tend to be short-lived. Giving a second dose causes those antibodies to be produced again and leads to them becoming fixed in the immune system.

Guess who got the vaccine? Me! It was also on the news. https://www.nbcwashington.com/news/local/friends-get-lucky-randomly-receive-covid-19-vaccine-before-doses-expire/2527704/

If they do actually end up doing this I would expect the "catch" mechanism to also be the stabilizing member during Starship loading, similar to the function of the clasper arms on the F9 transporter-erector: The arms would hold onto the extended grid fins while the Starship is mated and loaded. At T-1 min, they would fold away and the grid fins would fold down for launch. At landing, the arms would remain open as Superheavy initially approached, then come together quickly to catch the grid fins. Once caught, they would lower the booster on the launch clamps and remain attached for stability until the next launch. I am about 95% confident that Elon specifically said the booster would have aft and forward hot-gas thrusters for fine translation control back when he was talking about landing on the launch clamps.

I doubt it. Superheavy is basically a bigger Saturn V. You would need extremely strong winds to have any significant effect. Plus, it will have hot-gas thrusters at both the top and bottom (rather than only the top like the Falcon 9 first stage) for fine translation. Actually I can calculate that, come to think of it. Let's say that worse-case scenario you only have two of the ten-tonne RCS thrusters firing continuously, one at the top and one at the bottom. That's 20 tonnes of thrust or 196 kN. What kind of wind can that compensate for? The drag equation says that Fd = Cd*ρ*v2*A/2. So we set Fd = 196 kN and solve for v to find the maximum windspeed that two hot-gas thrusters can compensate for. Solving for v, we get v = sqrt(2*F/(Cd*ρ*A)). The drag coefficient of a cylinder perpendicular to an airflow is approximately 1. Superheavy will have a cross-sectional area of 9 m * 72 m = 648 m2. The density of dry air at sea level is 1.225 kg/m3. Plug and chug and you get v = 22.2 m/s or about 50 mph for us Americans. So unless Superheavy is planning on landing during a severe thunderstorm then it should be just fine.

The “catch by the grid fins” idea reminds me of the structural loading design of the Soyuz family of rockets. The four side boosters are suspended from the four payload arms and the sustainer stage hangs off of them while also supporting the upper stage in compression. This works really, really well because it mimics how the loads are distributed in flight: the side boosters are lighter, so the sustainer “hangs” from them in flight while continuing to support the upper stage in compression. Elon’s idea isn’t too far from this. The grid fins are supporting a dramatic amount of weight during entry (remember that the booster will have a significant amount of propellant prior to landing) and have to be fixed to the booster with enough strength to provide significant torque and pitch control. I am pretty sure that the booster decelerates by more than one gee during the extremes of re-entry. So they should be more than capable of supporting the weight of an otherwise-empty booster. The combination of hot-gas thrusters and the ability to hover should make that touchdown quite gentle. What would be REALLY cool would be if the grid fins also provided the primary support during launch. But that might be asking too much. The booster is vastly heavier at launch, and unlike the Soyuz, it is supported in flight entirely from the 28-engine thrust puck.

It didn't cross the Karman line, though. Didn't get anywhere close. Blue Origin has test-fired a bigger engine. SpaceX has flown a bigger engine.

This was a meta-analysis of 54 studies with almost 78,000 participants. Out of the studies analyzed, only 3 studies looked at presymptomatic tarnsmission, and those included a total of less than 24 presymptomatic patients. That's why the reported confidence interval for asymptomatic and presymptomatic cases is so large. When the upper limit of your 95% confidence interval (4.9%) is 700% of your average (0.7%), you know you don't have enough data to draw a good conclusion. Besides, what exactly is the point of this? Are you trying to say that isolation/quarantine is effective? Isn't effective? No, it just needs to be coordinated. There was no federal coordination. I'm not sure why you think this demonstrates good data for the US. Look at the area under the curve. While most of Europe rapidly brought the daily per capita death rates way, way down after the initial peak, the United States kept merrily plugging along, averaging well over a thousand deaths per day, all summer long. In a normal year, there are around 7,800 deaths in the United States every day...from ALL causes. "Don't worry, this pandemic isn't serious. It will only increase the average daily death rate by about 13% during the summer. It will get twice as bad in the winter, though...hope that's okay." As of yesterday, COVID-19 has killed one out of every thousand Americans. Think about that. In the United States, it is half of that: 39-42%. Why mention "some countries" when you know that's not the number for the United States? More importantly, this nonsense about how people "were going to die soon anyway" has got to stop. Nursing homes may be considered a sort of hospice; the average stay is 1-2 years before death (not 1 year as you claimed). But that number includes nursing homes and assisted-living facilities. The average length of stay in assisted living is 2.5-3 years before moving to a skilled-care nursing home. And even within skilled-care nursing homes, the length-of-stay distribution has a VERY long tail: About half of the people who are moved into a skilled-care nursing facility are dead in six months. But once you go past that point, the distribution becomes very flat. That means that at any given point, the majority of the people actually in a skilled nursing facility have been there for quite some time and will continue to be there for quite some time. The total average duration of long-term care received by elderly patients who ultimately die in institutions is 4-5 years. "Don't worry. Between a third and a half of the people who will die from this disease probably would have been dead in half a decade anyway." That's not a good argument. The lockdowns in the United States were nothing like what China did. There were no doors welded shut, no blockaded roads, no mandated shopping schedules, no household food ration deliveries, no door-to-door screening. There's no comparison whatsoever. Which is why nipping this thing in the bud back in July would have been nice. Average annual mortality in the United States is 867.8 deaths per 100,000 citizens. By February (one year from when all this started), COVID-19 will have killed 150/100k. Only a 17% increase in mortality. Tiny. For the 15% of COVID-19 patients whose illness becomes severe, it is FAR worse than the flu. And while we can argue over CFR vs IFR, the fact remains that 10% of patients who DON'T die end up with complications that last for months or are permanent. This is not a tiny percentage.

Lockdown? If you want to take my freedom, you need to demonstrate efficacy FIRST. Guess what, I might vote for it—but I get to vote. This should be passed by legislatures, NOT by executive fiat. Not any executive, anywhere. You did vote for it. I mean, I assume you vote, right? And you vote for elected representatives. And in 2003, those elected representatives passed House Bill 231, codified as N.M.S.A. § 12-10A-5, authorizing the governor of New Mexico to declare a state of public health emergency upon consultation with the secretary of health. This law provides plenary power to the governor to authorize specific public health officials to enforce necessary orders, rules, and procedures. The powers granted to the executive branch by the legislature during a public health emergency include rationing of health care supplies, government control of health care facilities, isolation orders, quarantine orders, compulsory vaccinations, and even specifically isolation orders without prior written ex parte court authorization (§ 12-10A-9). It also provides a way for isolated individuals to request a hearing to contest the necessity of the orders in court. We don't live in a pure democracy. We live in a representative democracy. We voted for them; they voted for this. This is the law. You might not like it, but that's the way it is. We've discussed this claim before and it's simply not true. SARS-CoV-2 was not in worldwide community spread in mid-2019. RNA sequencing can trace exactly how the spread happened. We know who the first carrier to enter the United States was, and we know that the majority of cases in the United States actually came through NYC via European travel. This is known. I'm not saying it would be easy. It's quite challenging, and obviously there are essential workers who would have to continue showing up. If the federal response had been better and all states had instituted the kinds of lockdown standards practiced by the District of Columbia, plus broad economic relief, then we would have had this thing under control by June. Unfortunately, locking down one jurisdiction but not the one next door is like having a peeing section in the pool. I already addressed this here. The 1968 epidemic resulted in 42% more deaths per capita than an average flu season in the United States. By February, the COVID-19 pandemic will have resulted in 1164% more deaths per capita than an average flu season in the United States. They aren't comparable. And neither are mitigation strategies; the world was much less mobile in 1958. I would trust competent state and federal executives to consult with public health officials and use legislated powers. I am not a public health official. Thought experiment: an international terrorist group begins releasing clouds of sarin gas at random in specific, predictable areas. The terrorist network is large enough that initial efforts by DHS to stop the attacks are unsuccessful. How long would it take the government to order people to stay away from the specific, predictable areas where the gas is being released?

How would I pay [mental health professionals] though? With the money I don't have?? I'm sorry, man. That sucks. I'm not a mental health professional and I wouldn't attempt to give any sort of medical advice, but I truly feel for your plight. I certainly wasn't trying to yell at you. If you'd like to reach out privately, I'd be happy to learn a little bit more about your situation and see if I can find a source of no-cost counseling or therapy that you'd have access to. I happen to be rather good at that. I've really benefited tremendously from therapy. We have highly effective vaccines against the flu, but the flu mutates rapidly enough to limit their long-term effectiveness. SARS-CoV-2 does not mutate as rapidly as the flu, and its specific mechanism of cell entry (which is what makes it so virulent) involves proteins that are susceptible to a highly targeted vaccine. We were able to do it quickly for two reasons: first, our understanding of protein-folding has gone through the roof in the last few years, and second, we skipped some of the intermediate steps that often drag this stuff out. For example, we began building factories to produce the vaccine immediately instead of waiting until it had been proven in trials. Ordinarily a corporation would wait until a vaccine went through all its trials before investing money in production. But here, speed was more important than ROI. Yes, mRNA vaccines are new technology. One of the reasons we were able to develop an mRNA vaccine for SARS-CoV-2 so rapidly is that we've been studying mRNA vaccines for the flu already. Moderna's Phase 1 clinical trials for an mRNA flu vaccine concluded in May 2019, with fairly good results. It's a little more challenging because the influenza vaccine's spike proteins bind to sialic acid, which is an extremely simple molecule. The external shape of the influenza spike protein can mutate a lot while still being able to bind to the sialic acid on the outside of host cells. In contrast, the spike proteins of SARS-CoV-2 bind to the hACES2 receptor, which is MUCH more complicated and thus requires a very specific spike protein shape, which in turn is more easily targeted. Moderna and Pfizer both had a leg up in developing an mRNA vaccines for SARS-CoV-2 because they had already been studying the structure of the MERS-CoV spike protein. MERS-CoV binds to the DPP4 receptor, not the hACES2 receptor, but it is externally similar to the SARS-CoV-2 spike protein. Protein-folding is a very challenging problem but it's made easier when you can compare the output of two very similar codes...just like how you can more easily solve a cipher if you are able to intercept multiple messages. This comic was back in 2014, after the 11th bi-annual CASP competition. We first began using artificial intelligence to predict protein-fold structure in 2016 and by 2018 artificial intelligence was winning handedly. This really is the cutting edge. The mRNA vaccine works by instructing muscle cells to produce copies of the SARS-CoV-2 spike protein, which trains the immune system to recognize and attack the spike protein and thus fight off a real infection. We were actually able to produce this mRNA sequence almost instantly, just by copying and pasting from the SARS-CoV-2 genome. However, the spike protein will become "floppy" and lose its structure if not attached to the virus. The trick was to write mRNA code that would fold a "backbone" inside the spike protein to keep it stiff without changing its external shape. And that's what scientists did, in a matter of weeks. Strongly disagree. The past year has been a disaster but it could have been averted if governments had actually done their job. Complete lockdown. Pay everyone to stay at home for six weeks. Then reopen slowly, continuing to pay people. The "it just affects old people" argument is BS. It doesn't just affect old people. It causes long-term disability damage to LOTS of people. A huge percentage of the population has at least SOME pre-existing condition. Yes, it kills off really old people really fast, but that's not the point.

MMH (which is obviously hypothetical) has a high energy density and specific energy because it is monatomic. You cannot extract energy from it without recombination, and that recombination will release hydrogen gas. So even without the heating problem, you will need a place to put hydrogen gas. Hydrogen fuel cells are extremely well-understood and robust technology, and they convert hydrogen gas (plus atmospheric oxygen) into electricity with minimal waste heat. The only reason they're not in more common use is because hydrogen gas is ridiculously hard to store in any meaningful density. A gallon of gasoline contains more hydrogen than a gallon of liquid hydrogen, let alone a gallon of compressed hydrogen gas at any pressure. Metastable metallic hydrogen, on the other hand, would have a density ten times greater than liquid hydrogen. So if you could design a form of metastable hydrogen which somehow recycles recombination energy to maintain its stability, it would be great for a hydrogen fuel cell. "Give me a second, I need to let my phone breathe." When we are talking about energy densities on the order of metastable metallic hydrogen, thrust to weight ratio in space is NOT an issue. At all. TWR in space is rarely an issue anyway. Rule of thumb for science fiction: In the atmosphere you need high TWR; in space you need high specific impulse. Besides, if you're using a battery as an energy source for your propellant in space, then you can simply dump the waste heat into the propellant as it exits. No radiator fins needed, and it amps up your specific impulse too!

The simplest thing would be to have a single mechanism provide deployment, shock absorption, and self-leveling all in one. That's basically what notional landing leg in current SpaceX renders shows: Pneumatic or hydraulic pistons to deploy, shock-absorb, and auto-level. This just doesn't provide QUITE as much footprint as Elon, would like, though. Using this same design and simply angling it through the skirt would do the trick: Yeah, they could. No atmosphere and no heat shield. At the same time I'm sure they would prefer to use the Moon landings as a testbed for the Mars legs, so if it's possible to make them the same design, they should. Yeah, I agree. Deploying entirely from inside is probably too long a pole. Nah, I take criticism. No offense taken. But I do think there's value in separating the dynamic and static loads, if possible. One element is simple and robust and designed for the static load; the other provides the fine control and actuation needed for shock absorption and auto-leveling. With twelve legs instead of six, you could have multiple deployment failures and still stick the landing, assuming the descent was otherwise smooth. Or you could have a very nasty rough landing and damage 3-4 legs and still come out standing.

After some reflection, I don't actually think Starship needs a dramatically wider stance. Elon has said he wants a wider stance, yes, but there are diminishing returns. Starship is not going to be able to successfully land if it is coming in at an angle greater than what a single engine and the landing thrusters can compensate for. The current legs are actually quite useful because they correct off-axis loading when Starship comes in at a tilt: Obviously the tilt shown is exaggerated, but you can see that as long as the angle of descent is less than the angle of the legs, they act correctively. A little wider footprint would be nice, but auto-leveling is going to be more important. In my opinion. Yeah, I'm thinking the slots in the skirt would need to be reinforced to the skirt and also allow it to transmit force directly to the tank underside...probably using the same mounting approach as the vacuum Raptors. They're my designs, so yes, you're right. I have no experience designing landing gear. That said, the current legs look EXTREMELY fragile. One advantage of having multi-element legs like this last design is that it provides redundancy. Ordinarily they work together, but if one fails to deploy then the other can compensate...perhaps with some damage, but it's better than a failed landing. I'm assuming the heat shield will wrap around the leg fairings as shown: The elements don't have to extend through the shield; all the extension is through the base.

More notional landing leg designs from ongoing discussions over at NSF... Pneumatic pistons that run through the skirt, with embedded fold-out feet. The existing landing feet deploy from inside the skirt and brace against the fold-out feet to provide redundancy crush cores. The pistons provide the shock-absorbing and auto-leveling elements at touchdown. You can retract and replace individual landing feet crush cores (if necessary) while the vehicle remains standing. Good grief. "I am become ubercrane, the lifter of worlds." There's something so cool about seeing the heat shield "growing" on the side of Starship like moss.

That crane is such an absolute monster