sevenperforce

Cool shot. Evidently they're laying electrical lines, etc. Reminds me a little of the Saturn IB milkstool. It was high enough up that IIRC it didn't need any water deluge at all to avoid damaging sound reflection off the ground, although it did use a flame diverter. Of course, the Saturn IB was about 9% the thrust of Superheavy. Hard to imagine how Superheavy will be able to NOT get ripped apart by sound waves without a deluge.

Best response I have heard so far: “It was his first time. No one is going to hold it against him for only lasting five minutes. Everyone has performance anxiety. Some breathing exercises, a little extra oxygen, and then maybe next time he can keep it up long enough to actually hit the big O.”

Thank you for the inspiration....

The lack of in-space imagery and in-capsule imagery was disappointing.

Now imagine 10 times this much fire and fury in the same space.

I haven't had a chance to look very closely at the orbital parameters, but as far as mounting an extremely high-dV mission is concerned, I think the best we can reasonably do is build something like Dawn (but with bipropellant hypergolics and probably 6-8 krypton thrusters rather than 3 xenon thrusters), mount it on top of a Centaur SEC, and then launch that entire stack to LEO on a Starship. Retank the Starship from a waiting tanker and burn nearly to depletion on the intended trajectory, then release the Centaur, which executes the next burn, then release the rendezvous spacecraft. The Starship would turn around and retroburn in order to reach a high-elliptical Earth orbit so it can return. If we assume a 3-tonne spacecraft (a little over twice the size of Dawn) with similar total dV (around 11 km/s), then a fully-tanked Centaur SEC is going to be able to give it 7 km/s. That whole assembly is going to be about 26 tonnes. A full-fueled Starship in LEO can send a 26-tonne payload out with about 10.5 km/s with 30 tonnes of reserve propellant for landing, although the need to retroburn will likely lower that to around 8-9 km/s. If we use one of Elon's described stripped-down expendable Starships, it would be able to push 13 km/s. So this approach can get us between 26 and 31 km/s worth of dV. Is that enough for a rendezvous?

Nah, you only need to find the static friction in order to figure out how much total impulse you need at the beginning. The rocket motor burn would be very short; it doesn't last for the entire duration.

Ah, yes, you’re right. Rolling friction will be nearly constant so you can multiply the force of rolling friction by 100 meters to get the kinetic energy that will be lost to friction, then use the mass of the skateboard and rider to solve for the necessary starting velocity. All so you can light yourself on fire and probably blow limbs off. Best-case scenario you’d get flung off the skateboard at high speed by a steering failure and end up with road rash. It’s a great idea as long as you aren’t riding it, though. Duct tape a potato and a GoPro to the skateboard and have fun with it. Take a video and post it on YouTube and call it the world’s fastest rocket-propelled potato. Instant sensation. One of the things that makes homemade rockets with PVC casings very dangerous is that PVC turns into shrapnel if it bursts. Ordinary amateur rocket motors have cardboard casings that will rupture much less harmfully if you have an overpressure event. If you experiment at all with PVC casings, make sure you use an endcap and nozzle made out of packed clay or something that similarly will fail before the PVC does.

I'm not touching the main subject of this thread, but this is pendulum rocket fallacy. A pusher rocket is no less stable than a puller. The pendulum fallacy relies on that if the rocket is free to rotate, then it doesn't matter where the exhaust is as long as it is inline with the center of mass. Once you add wheels (which provide a fulcrum for the exhaust to torque around), you are in a different case and rocket placement matters. In reality it will be almost impossible to get a homemade rocket's thrust vector lined up properly with the skateboard's center of mass, let alone the shifting center of mass of a whole person sitting on top. A "puller" arrangement (with a sufficiently long dowel) would be more stable if you could hold onto the dowel, because it would allow you to essentially gimbal the engine thrust. But the shifting center of mass would actually be useful in the sense that a pilot with sufficiently good reaction time would be able to steer by shifting their weight to the left or to the right and thus changing the center of mass relative to the thrust vector. I would not want to be the pilot attempting to steer a skateboard by shifting my body mass while screaming as a homemade rocket motor is continuously (we hope) exploding under me. Even this non-endorsement seems insufficiently discouraging of the very bad idea that this proposal represents. It's a little more complicated than that. The rocket motor's burn isn't going to last long enough to do a constant-speed arrangement. You would need to determine what starting speed is required to get a 100-meter roll-to-a-stop and then figure out how much thrust is required to get you up to that speed within the burn time of the motor. Have I mentioned that this is an exceptionally bad idea?

It's estimated that Earth's core would take 91 billion years to cool to the "hard rock" stage.

This is a very bad idea. Please do not do this idea. That being said, if you do this very bad idea, it is to your advantage to know a little bit about what you’re doing and how to go about it. Do not use two rockets; it will be impossible to light them simultaneously and they will burn at different rates. Use one. The safest way to do this would be to mount the rocket motor on a pair of wheels fixed to a very long dowel, which in turn would be mounted to the front of your skateboard. You would be facing into the exhaust, of course, but if the dowel is long enough it should be fine. That way you can just let the rocket motor tow you and you could release the dowel to abort. Experiment with a motor in advance (perhaps using sheets of paper hung at intervals behind the rocket exhaust) to figure out a safe distance. If you insist on mounting a rocket motor to the skateboard itself, then please protect yourself by mounting a metal plate of some kind to the underside of your skateboard and putting the motor under that. You can rig a crude torsion system to determine the thrust level of your rocket motor. Attach a wooden broom handle firmly to a stable structure like a tree, attach a test motor to it, and video the test-fire to identify how much the thrust causes the broom handle to bend before springing back. Then you can attach weights to the same point on the broom handle and figure out the thrust level from that. Again, this is a very bad idea and you should not do it.

The galactic habitable zone is considered to begin at around 7 kpc, which is actually quite close to the Galactic Center. Radiation wouldn't preclude life until you went significantly closer.

The moon absolutely does contribute to heating in the Earth's mantle (physics says that frictional heating has to go somewhere), but it is comparatively negligible when you put it next to the degree of tidal heating that the moons of Saturn and Jupiter experience. One reason that it's not a 1-to-1 comparison is that the mechanism for tides is different with the gas-giant moons than it is for Earth. Lunar tides on Earth are caused primarily by Earth's rotation with respect to the moon's gravity. As the Earth rotates, the tidal bulge remains pointed toward the moon, so from Earth's perspective the bulge is traveling around the Earth. In contrast, our moon (as well as all the large moons of Jupiter and Saturn) are tidally locked, so their bulge doesn't rotate from the perspective of the surface. Instead, the bulge gets larger and smaller between periapsis and apoapsis, and that squeezing-and-stretching cycle is what causes frictional heating. A tidally-locked moon in a perfectly-circular orbit would have a tidal bulge but it would never change and so it wouldn't have any tidal heating. The power output of Earth's core and mantle from radioactive decay is approximately 44 trillion watts. The total power output of all ocean tides is about 3 trillion watts, and only a fraction of that is dissipated as heat. The oceans experience much more significant lunar tides than the Earth's mantle, but of course Earth's mantle is a lot more "there" and so I'm not sure whether internal lunar tides would have greater power than ocean lunar tides.

The biggest safety concern, I think, is black zones for ballistic-trajectory aborts. That's why they had to put two engines on the Centaur for Starliner; the usual lofted trajectory used by Atlas V would result in too violent a re-entry if they had to abort near or after the end of the core burn.

It also had no zero-zero launch abort system. If he had ejected on the pad, he wouldn't have gotten high enough to open his parachute. So they put a net around the launch pad...which would have trapped him next to an exploding rocket.

Oh, yep, you are absolutely right. For some reason I had it in my head that all comets had to have a perihelion closer than Mercury to experience coma cycles but that's definitely untrue, lol. The shortest-period comets, like Encke, don't even cross Jupiter's orbit. And PANSTARRS doesn't cross the orbit of ANY planet. Maybe it's better to just designate comets as a subset of asteroids and say that a comet is an asteroid with an orbit eccentric enough to undergo periodic outgassing near perihelion?

The safety concerns (for crew, etc.) apply primarily to reusable vehicles, yes. But 1.5 is still a bad idea even for expendables because you are taking so much dry mass to orbit. Look at Long March 5 and its whole out-of-control stage debacle. 2.5 stages is much more efficient. Atlas V, almost all Semyorka-derived rockets, the Delta IV Medium family...it's just an all-around good design.

Yeah I think we assume that you'd have a larger inner moon and a smaller outer -- probably in part because of KSP -- but moon formation doesn't necessarily operate like that at all. The Galilean moons go small-smallest-biggest-big in order from inside to outside. My intuition is that having a larger outer moon will help force a resonance but I don't know that for sure. I think you would have much higher amplitudes because the tides are similar in overall size. Oh yeah, you're absolutely correct. I had that twisted. Jupiter has such absolutely massive gravity that its tides are strong enough to keep Io's mantle molten and to keep the subsurface ocean of Europa from freezing. Saturn doesn't have as much gravity as Jupiter, of course, but it is enough to drive cryovolcanoes on Enceladus. But the amount of internal heating produced on Earth by our moon is comparatively negligible. The volcanoes on Earth and Venus are driven by internal heat from radioactive decay, since both Earth and Venus are massive enough to have accumulated quite a lot of radioactive material during solar system formation. Mars once had volcanoes, but it wasn't as massive and so what internal heat it used to have from radioactivity has long since cooled. You don't have to 'cause they would eject each other.

I feel the same way. I’m not a fan of the 501, but the rest look super cool, especially 521 and above. They just have a really powerful look to them.

Yep, absolutely. They never failed at the job they were supposed to do. As much as I love the idea of a 1.5-stage-to-orbit vehicle, it’s just a fundamentally bad idea outside of KSP.

That lesson plan also said the heat from re-entry comes from friction and claimed foam strikes happen on orbit, so take it with a grain of salt. Not everyone who works at NASA knows everything about the Shuttle.

Another really cool look.... Look closely at the three tiles going from the top of the flap root forward. One of the tiles is clearly a transition tile from the thicker tiles at that flap root to the thinner “standard” tiles along the overall flap body. Also, those super-thick curved tiles DON’T have the cloth underlayment, but the “standard” tiles do. It really looks like they used computer modeling to say “here is where we need special tiles, and here is how they are shaped, and here is how they fit into the ordinary tiles we use everywhere else.”

I liked this post. But here’s the thing. The sky is falling. The science is clear and unavoidable: the worst-case scenario IS happening if we don’t change things. The uncertainty is how quickly the sky is falling. Thankfully, the sky is not falling as quickly as we had initially feared. But it’s still falling. It will continue to fall. It will not stop falling unless we take drastic action. We have one side saying “the sky is falling” and the other side saying “the sky is falling slower than some estimates, therefore it probably isn’t falling at all, so don’t do anything.” WRT the OP: Agreed. Most of the people here discuss in good faith. And people who do not discuss in good faith are quickly shot down by actual scientists. Like @mikegarrison. And @Rakaydos. And me.

This is incredible to see. Curved tiles galore. Each of the tiles cut to size to fit. Some very special “ring cap” tiles at the top. The tile nearest the ring cap is cut to size. It’s hard to tell for sure but it looks like the other tiles are getting larger as you go down the root...but maybe that’s just perspective. It seems that they are going Full Shuttle. Well, not quite full Shuttle; they still have pure hex tiles on most of the vehicle. But they clearly have no qualms about using aggressively custom tiles wherever they need them.

The fact that they are only installing three Raptors on BN3 for the static fire told me that they were almost definitely doing 3-10-20.