sevenperforce

A change in diamagnetic properties won’t help with a railgun; the limiting factor for a plasma armature railgun is the compressive strength of the slug material. If you’re going to do a coilgun, on the other hand, the magnetic field impulse is applied across the entire slug and so compressive strength is not an issue. There the issue is Ohm-induced heating due to eddy currents in the slug.

Or they could arrive at a dead planet, with nothing but an obelisk to explain. https://www.smbc-comics.com/comic/2013-11-22

My Fermi Estimation (which I did before posting the compressive strength of tungsten) gave a barrel length of 800 km, so you pass sanity check. That’s why I posted the compressive strength; I was busy and didn’t want to do all the math to come up with the real number.

Oh, absolutely. And that’s part of the vision. The problem with maneuvering in a fabric suit, fundamentally, is the ballooning effect. If the joints are full of air, they puff up, and you can’t bend them without compressing the air inside your suit. To keep them from puffing up, you can make the fabric very stiff (as with the existing ISS EVA suits), but that makes them harder to bend too. But if you have an evolved IVA suit with basic EVA functionality, that’s not too bulky, you have a lot of options. You can attach a hard shell “knee pad” that wraps around the fabric of the joint to keep it from puffing, and also has either a magnetic pad or a grapple attached. You could even have the grapple actuated by the ankle. It would take some work to figure out how to move around but it would become natural pretty quickly.

Oh, entirely the former. “That’s dumb! IVA suits are totally different from EVA suits. There’s no way an IVA suit could be the base layer of an EVA suit!” Surely there is some way that your legs could be useful during a space walk, right? Otherwise they are just sort of dangling there with no purpose.

In practice, a deployable plasma armature railgun projectile would look a lot like a conventional firearm cartridge. The projectile itself would likely be a depleted uranium slug with a ceramic jacket, not unlike the rounds fired from the GAU Avenger on the A-10 Warthog (although those have a metal jacket on the DU core). Behind the projectile, you’d have the material designed to vaporize and form into the plasma armature…some sort of metal, possibly with an initiator explosive in it to trigger the vaporization. To answer @Spacescifi’s question: no, a “cold plasma” absolutely won’t work. What you are basically doing, in a plasma armature railgun, is creating a ball of artificial lightning and accelerating that ball of lightning at ludicrous speeds, using it to push your non-conductive projectile. The challenge is figuring out how to keep the electricity flow from going anywhere other than through the plasma armature. You’d probably need to pull a vacuum in the barrel and then backfill the barrel with a nonconductive gas as the round is fired. Most of the limitations here are going to center around the engineering of the plasma armature. The only hard physics limit here is going to be dictated by the length of your gun barrel, the diameter of your bore, and the compressive strength of your projectile. Since your ball of lightning is pushing the projectile from behind, not unlike in a conventional firearm, there is a limit to how much acceleration you can subject your projectile to before it crumbles. The compressive strength of tungsten is 142,000 psi, so depending on the size of the bore, you can calculate the maximum gees you can pull without cracking the tungsten; with max gees you can calculate how long of a barrel you need to hit any desired velocity.

With respect to the EVA suits, it seems like they are heading down the same path I suggested several years ago (and for which I was roundly mocked over at the NSF forums). Build IVA suits, then use those lessons learned to upgrade the IVA suits into something which can provide a very basic level of EVA functionality, without limiting or impairing their IVA role. Then, the combo IVA/EVA suit can be evolved to accept optional add-ons for specific, expanded tasks. One suit per person, but lots of specialized modules for different activities. For longer or more complex spacewalks, the upgrade module would be a self-contained life support backpack so you didn’t need the tether, and perhaps also magnetic boots/knee pads or grapples to make navigating microgravity less challenging. For lunar surface EVA, overshoes and perhaps mechanical joints around the knees and hips to help avoid suit-ballooning and to help assist with balance.

Seems like a safe assumption.

Whatever happened to “the first two flight engines are in acceptance testing and are almost ready to be shipped to ULA”?

from http://blog.beretta.com/everything-you-need-to-know-about-shotgunning-with-buckshot Which is 3,5 grams. Still a big boom, but changes the rate of fire quite a bit. Ooooh I see now. I was accidentally using the total load weight of 1.11 ounces (484 grains or 32.5 grams) rather than the weight of the individual pellets. There are 9 pellets of 00 buckshot in a standard load, so I’m off by a factor of 9. Fortunately, the equation for relativistic kinetic energy is linear with respect to rest mass, so I just have to divide all my numbers by 9. So if you want to fire one pellet per second, you don’t need half the total power consumption of the United States; you only need 4.5% of the total power consumption of the United States, or approximately the same as the total continuous power consumption of the state of New York. Totally doable. And the relativistic kinetic energy of the explosion on impact will be only 4 times the blast yield of the largest non-nuclear bomb in the US arsenal. Yes, but the accelerations required to dodge a projectile moving above solar escape velocity (which itself is a tiny fraction of low relativistic velocities) are so wildly high that dodging is simply not an option. So actually this is NOT a problem with a plasma armature rail gun. A plasma armature can accelerate at arbitrarily high speeds and can push a non-conductive projectile at the same speeds. The accelerations are high enough that you don’t have enough time for the projectile to heat up. I should look into this. Nope. Categorically nope. Haven’t you ever heard of absolute zero? Yes, that is your solution. The speeds you’re proposing are completely overkill.

Le sigh. I'm going to regret this. A single pellet of 00 buck shot has a mass of 31.5 grams. At a speed of 30 seconds per light-second, or c/30, the relativistic kinetic energy of that pellet is 1.57e12 Joules or about 376 tonnes TNT equivalent. That's 34 times the ordnance yield of the largest non-nuclear bomb in the US arsenal, and a little less than the yield of the W54 nuclear warhead, the smallest nuclear warhead ever deployed by the United States. Well, you need a gun that can deliver 1.57e12 Joules of energy to the projectile, plus thermal losses. That's going to be rather challenging. An ordinary gun with ordinary propellant can't push a projectile faster than the speed of sound in the gas. A light gas gun can get up to 8.5 km/s but there's a hard limit. A railgun works up to a few km/s, but railguns require physical contact between the projectile and the rails and so heat becomes an overwhelming problem if you want to go much faster than that. So if you want to go faster, you need an electromagnetic coilgun. The energy requirements themselves are not THAT overwhelming. If you want to fire one pellet per second, then you need a powerplant which is rated at 1.57e12 Watts. That's only about half the average total power consumption (factoring in gas, electric, etc.) of the entire United States. Surely that will be easy enough to duplicate. Well, for once, your constant concerns about heat and cooling issues have FINALLY proven correct. Because yes, heat is a VERY big problem. Although it's not the "electromagnetic launch energies" so much as it is the process by which electromagnetic acceleration happens. In a coilgun, you use a magnetic field to induce an opposing magnetic field in a conductive projectile, and the two magnetic fields then interact, which pulls the projectile forward. But induced magnetic fields result in the production of electrical current in the projectile, and electrical current flowing through a metal results in heat (since even very highly conductive materials have SOME resistance). So some percentage of the energy being used by the coilgun is going to be lost to heating the projectile, not as a result of abstract "launch energies" but as a fundamental consequence of the acceleration mechanism. So there's a fundamental limit to how much velocity your projectile can be given before it melts. Once it melts, the magnetic fields will rip it apart and it won't be able to accelerate further. Well, no -- if you do that, you can't make it interact magnetically. But supercooling the projectile to begin with won't help much. Even if you start at 0 K, it will still absorb heat energy as a consequence of the acceleration process, so you will still "max out" your speed at the melting point of your metal. You should not ignore relativistic effects at 0.03c; you underestimated kinetic energy by a factor of 3.

Isn’t there a company known for shipping things on short notice?

Super reasonable. If they could only find engines.

Someone did a side-by-side of the old IVA gloves with the new gloves: Looks like plate armor gauntlets:

The difference between the orbital velocity in a 310x310 km orbit and the perigee velocity in a 310x1500 km orbit is only 252 m/s. That translates to a slightly higher re-entry speed, yes, but I don't believe the heat shield on Crew Dragon will care overmuch about that small of a difference. As @NFUN said, it's harder to control where you land if you are doing a deorbit burn from an elliptical orbit. I am Iron Man. That's precisely what it looks like. Also precisely what I've been begggggging for, for...like three years now.

I reckon it's because Atlas isn't available and Vulcan isn't accredited. Well, Vulcan isn't available either, because it doesn't have any engines yet. I don't know the maximum capabilities of Ariane 5, but it has sent up to 11.2 tonnes to GTO and up to 20.3 tonnes to LEO at an ISS orbit. That's 3.5 tonnes more than what an Atlas V 551 can send to the ISS and 2.2 tonnes more than what an Atlas V 551 can send to GTO. According to NASA, the JWST required an effective apogee of approximately 1.06e6 km, which (according to the vis-a-vis equation) requires a perigee velocity of 10,970 m/s. Whether you're starting at 167 or 200 km, it doesn't make much of a difference; you need about 3.19 km/s leftover in LEO. The Roman Space Telescope's launch mass is 4.17 tonnes. For reference, the SEC and F9US have the following dV at full prop load with a 4.17-tonne payload: SEC: 6,377 m/s F9US: 8,972 m/s A typical 27-degree GTO is about 2.27 km/s out of LEO, 920 m/s shy of what JWST or Roman needs. An Atlas V 421 can send 6,890 kg to GTO; in that configuration, it stages with 5.24 km/s, of which 2.97 km/s is used to reach LEO and the remainder is the 2.27 km/s used to reach GTO. With 4,170 kg on board, the remainder is 3.41 km/s, more than enough to get Roman where it needs to go. (And yes, I did the math for the Atlas V 411; it's not enough.) With three-core recovery, Falcon Heavy can send up to 8 metric tonnes to GTO. In that configuration, it stages with 7.89 km/s, of which 5.62 km/s is used to reach LEO and the remainder is the 2.27 km/s used to reach GTO. With 4,170 kg on board, the remainder is 3.35 km/s, which is not quite as much as the Atlas V 421 but still enough to send Roman packing to its destination. Or it could fly on a single-stick expendable Falcon 9 Block 5 with ease. Flying expendable, Falcon 9 beats three-core-recovery Falcon Heavy for payload to GTO. Note that this illustrates some of the distinctions between high-energy and low-energy orbits. For LEO (e.g., the ISS), a reusable Falcon 9 easily outperforms the Atlas V 421. But for high-energy orbits it's not even slightly competitive.

It's not as heavy as JWST. What kind of a launch does it need? Just an escape orbit (C3=0)?

See, I just don't know how they can possibly expect to catch Starship. The booster is straightforward enough, but the ship?? There's just no way the ship can hover motionless to the point that this kind of precision is actually realizable. Future Starships could have fold-out catch arms in that position, I suppose, but the forces would be tremendous. The crew won't need to be doing a lot of the exertion and fine detail work that usually goes into ISS EVAs, so they don't need that much mobility. The big challenge of wearing an unmodified IVA suit is not the life support -- their umbilicals can take care of that -- it's the "spread eagle" problem. With high pressure inside and no pressure outside, the fabric expands and balloons outward, forcing all the joints to open up and occupy the maximum amount of space. This forces you into a spread eagle/snow angel position; if you want to bend your joints, you have to force the air in the suit into a smaller space, which means almost every movement is like compressing a bike pump. The atmosphere in Crew Dragon is ordinary sea level air, not pure oxygen, and I don't believe it was designed with the capability to switch it out and do a prebreathing sequence to use low-pressure oxygen. Although I suppose it's a fairly simple fix. Everything in there should be pure-oxygen-fireproof anyway. I wonder if it would be possible to equip the IVA suits with some sort of an active-venting smart valve, so that if you attempted to compress a joint, it would automatically relieve the pressure into a reservoir, and then fill it back up once you expanded that joint back out. Another option: not all movements cause compression. Joint rotation, for example, does not. The main movements which cause compression are adduction and flexion, with abduction and extension doing the opposite. The ISS EVA suits use carefully-designed constant-volume fabric joints to allow abduction and extension without a change in the volume: The trouble is that unless you have the very low pressure pure-oxygen mix that the ISS EVA suits use, the high internal pressure is going to cause those outside gores to "pop" out even during extension, which doesn't get you anywhere. My favorite solution would be to enclose any adduction/flexion joints in an external hard shell which prevents the excess fabric from ballooning outward unless the joint is closed. Basically you would take the existing IVA suit and add what look like elbow pads, knee pads, etc. which use a combination of compression and a hard external shell to constrain the movement of the joint to a constant-volume approximation.

Not only is it kerballed, it's a significantly older version of what I ended up doing. Here's the most recent version of the lander: 4378 funds, 1779 kg, not including kerbal. This can bring a kerbal from Eve sea level to low Eve orbit with about half of a jetpack remaining. This implies further room for both mass and cost reduction but I don't want to do that. I actually abandoned the "lowest cost to Eve" mission in order to do a "lowest mass to Eve" mission. Turns out, a low cost Eve ascent vehicle tends to also be quite low mass. I got the total mass at launch down to 7.5 tons, which I believe is a record (that is, for missions that don't abuse aerodynamic bugs). Holy mackerel. That's truly exquisite.

An Atlas V 401 can only put around 9.8 tonnes in LEO, but you can add up to five solid boosters. It takes two solid boosters to push the 13-tonne Starliner to an ISS orbit, but that's the limit. More boosters mean a higher staging velocity, though. The Atlas V 531 can put 15.6 tonnes into LEO just like we saw with the max-capacity Starlink launches, so the Atlas V 531 is probably comparable to Falcon 9 Block 5 at max reusable capability. Supposedly, the Atlas V 552 (a possible configuration, though not one that has ever flown) can put 20.5 tonnes into LEO, which is close to the capability of an expendable Falcon 9 Block 5. However, that's to a different reference orbit than the others provided by ULA. The math here is actually easier than the math for Falcon 9 since the masses and propellant loads of the single-engine and dual-engine Centaur (SEC and DEC) are well-described. Moreover, ULA helpfully specifies its reference orbits. The Atlas V 521 can send 12,510 kg to the ISS, while the Atlas N22 sends the 13-tonne Starliner to the ISS. The only difference between the two (treating drag considerations as de minimis) is the engine count, which helps with gravity drag losses. Centaur carries 20.83 tonnes of propellant and has a dry mass of 2.25 tonnes (SEC) or 2.46 tonnes (DEC). The RL10C-1 has 449.7 seconds of specific impulse, so the SEC with a 12.5-tonne payload develops 3,883 m/s of dV, while the DEC with a 13-tonne payload develops 3,763 m/s of dV. Since they are going to the same orbit, this helpfully tells us that the gravity drag savings for a payload of this mass are approximately 120 m/s by doubling the thrust (actually a little more because the staging velocity is a little lower with the DEC+Starliner, but again, de minimis). ULA says that the Atlas V 551 can put 18,850 kg into a 200x200 km circular orbit; the 521 configuration only puts 13.5 tonnes into the same orbit. I'll treat the 200 km orbit as the minimum because even in a DEC configuration, the T/W ratio of Centaur is poor compared to F9US. Headed to this orbit, the SEC develops 3,029 m/s of dV while pushing 18.85 tonnes and 3,716 m/s of dV while pushing 13.5 tonnes. Since everything else is equal, we know that adding those three extra solid boosters results in a staging velocity that is 687 m/s higher. This gives us what we need to evaluate the performance of a hypothetical Atlas V N52 (Starliner on top, 5 boosters, 2 RL10s) to that minimal 200x200 km staging orbit. On N22, a 13-tonne payload gets 3,763 m/s of dV, so it would reach a 200x200 km orbit with 47 m/s to spare (3,763 - 3,716) plus the extra 120 m/s it gets from lower gravity drag. Adding three solids would add another 687 m/s, so Atlas V N52 + Starliner reaches a 200x200 km parking orbit with 854 m/s left in the tank. The vis-a-vis equation tells us that adding 854 m/s of velocity onto a 6,583x6,583 km circular orbit raises the apogee to 10,548 km, or an altitude of over 4,000 km. That's not nearly as high as an expendable Falcon 9 could send Crew Dragon, but it is much higher than a reusable Falcon 9 can do and it is deep into the inner Van Allen belt. One reason to choose a polar orbit for high-altitude Crew Dragon launches is that the apogee can always be at a very high latitude, ensuring that there is no passage through the Van Allen belts. On a related note, I was curious to know what kind of on-orbit dV Starliner has. According to this page, Starliner's abort motors burn 700 pounds of propellant per second, and the Nov 2019 pad abort test showed a six second burn, so I will assume 4,200 pounds or 1,906 kg of useable propellant. Boeing says that the main OMS engines come from Aerojet Rocketdyne and produce 1,500 pounds of thrust each, so they are probably a larger variant of the 900 lbf R-40B bipropellant OMS engine, which has a vacuum specific impulse of 293 seconds with hypergolics. So I estimate that Starliner has about 457 m/s of dV on orbit. That's a bit more than Crew Dragon's 346 m/s (its Draco thrusters give it 300 seconds of vacuum specific impulse but it only carries 1,388 kg of propellant). I may be overestimating Starliner's onboard propellant, though; the abort engines may not fire at full thrust through the entire abort.

My suspicion is that while the current suits are bespoke, they’re not THAT bespoke. Like, you get someone’s measurements and then the computer tells you the sizes of the pieces to cut out and then it’s all standard from there. I want to see them solve the ballooning problem in an inventive way.

Well yes, we all are in solar orbit, but we aren’t in Earth orbit. Solar orbit is our primary orbit. The ISS is in an Earth orbit first and solar orbit second. A satellite at the Earth-moon L2 is in Earth orbit first and solar orbit second, but with the moon dominating its orbit of Earth. The moon itself is in solar orbit, not earth orbit, but Earth dominates its orbit. Which means the Apollo astronauts in low lunar orbit were in lunar orbit first, then in solar orbit, but with a solar orbit dominated by Earth. On the other hand, if you were in a low orbit of Titan, you’d be in a Titan orbit first, then a Saturn orbit second, then a solar orbit third.

Depends on how you define orbit. We are all orbiting the sun, which in turn is orbiting Sagittarius A*, and so we are also orbiting Sagittarius A*. But one useful way of distinguishing whether you are orbiting a primary or a secondary is to look at the path described by your orbit. The path taken by a spacecraft orbiting the moon in low lunar orbit goes convex-away from Earth and concave-back towards Earth, so we can say with a fair degree of certainty that the spacecraft is orbiting the moon, which in turn is orbiting the earth. But an object at the Earth-Moon L2, or in a 1:1 resonant orbit with the moon, is always following a concave path with respect to Earth, so we say it is in an Earth orbit even if its orbit is dominated by the moon. Of course this also suggests that because the moon’s path around the sun is always concave, it is orbiting the sun directly in an orbit dominated by Earth.

I am all in support of realism. What is not realistic (and is also rather annoying) is when individuals make emphatic, easily-rebuttable claims suggesting that they know a particular system will not work. It would be like me saying that I know SLS will never actually launch, because it is supposed to send people to the moon and no crewed moon rocket used solid rocket boosters, but SLS has solid rocket boosters. And then adding that the only solid rocket boosters of this size were recoverable, but the SLS rocket boosters are not recoverable, and therefore they will not burn properly. And then adding that because SLS Block 1 cannot send a useful crewed payload to NRHO, SLS Block 1B won’t be able to, either. (Note, that last criticism is different from claiming that the EUS is vaporware, which it is. I can criticize EUS for being vaporware without claiming that EUS cannot do the thing it is being designed to do. Clearly it is possible to design EUS to do the thing EUS is designed to do.) There are many legitimate criticisms of the yet-unretired risks associated with SLS, just like there are many legitimate criticisms of the yet-unretired risks associated with Starship+SuperHeavy. But claiming that these risks/issues are per se unsolvable (particularly by allusion or analogy to utterly unrelated issues or grassgrab math) is silly.

Crew Dragon launches have had specified launch masses of 12.1-13 tonnes when launching to the ISS and a launch mass of 12.5 tonnes on the Inspiration4 launch to a 585 km circular orbit. In each of those cases, booster recovery was downrange on a droneship. We know that the largest payload SpaceX has launched to date was in each of the launches in the 550 km shell of Starlink satellites, with a 15.6-tonne payload mass, but we don't know exactly what orbit those are being released into (release altitude was 230 km in the one I saw but I don't know the apogee and perigee). More usefully, however, we know that Falcon 9 lifted a 14.5 tonne payload to a 435x425 km orbit at 53.2° inclination in the BlackSky rideshare Starlink mission on December 2, 2021. In that particular mission, SECO-1 took place at 167 km and the stage coasted up to an apogee of 447 km. A few minutes later, it executed a small 71 m/s burn, probably with a slight radial component. Unfortunately, we can't simply take the altitude numbers at face value, because they are reporting altitude ASL and Earth is an oblate spheroid, not a sphere. The animation shows SECO-1 taking place at around 42 degrees north, where the distance to the center of the Earth is approximately 6,368 km, for an estimated perigee of 6,535 km. The animation also shows apogee at approximately 51 degrees south, where the distance to the center of the Earth is approximately 6,366 km, for an estimated apogee of 6,813 km. Plugging all this into the vis-a-vis equation gives a perigee velocity of 7.89 km/s, 80 m/s greater than a circular orbit at 167 km altitude. MECO for the December 2 mission took place at a telemetry speed of 7,962 km/hr and altitude of 64.7 km. This is probably close to the peak of what the Falcon 9 first stage can do and still be recovered; the 15.6-tonne Starlink launch from November 13 had MECO at 7,864 km/hr and 66.6 km so that's about what you'd expect if they were both going all-out. Applying simple arithmetic tells us that the Falcon 9 upper stage, then, has at least 80 + 71 = 151 m/s of dV margin when lofting a 14.5-tonne payload to a 167x167 km orbit. Estimating the Falcon 9 upper stage mass at 4.5 tonnes and the total usable propellant at 111.5 tonnes, the total dV in the upper stage with the 14.5 tonne mission is 6,576 m/s. A little more math tells us that if we replace the 14.5 tonne payload from the BlackSky mission with a 12.5-tonne Crew Dragon payload and assuming no appreciable difference at MECO, the total dV in the stage would be 6,903 m/s, giving it 327 m/s more. Accounting for the Hohmann transfer the BlackStar mission did from an effectively 167x167 km orbit, that means the Falcon 9 has 478 m/s of dV margin with Crew Dragon at a 167 km parking orbit. This is when we pull the vis-a-vis equation out again, which tells us helpfully that adding 478 m/s to a 167 km parking orbit will raise your apogee distance to 8,423 km, or an altitude (taking the average Earth radius of 6,368 km) of 2,055 km, approximately 50% higher than the apogee of Gemini 11. So Falcon 9 Block 5, with recovery, can easily take Crew Dragon much higher than Gemini 11. And that's not even accounting for all the dV onboard Crew Dragon. It could do a series of burns to raise its perigee, then raise its apogee even higher, then deorbit. With the booster expended, Falcon 9 can put 22.8 tonnes into LEO. With that large of a payload, the upper stage only develops 5,550 dV, meaning that expending the first stage provides roughly 1,353 m/s more than in a downrange recovery situation. If you add an extra 1,353 m/s to that same parking orbit as before, on top of the 478 m/s we were already accounting for, the apogee is 20,919 km, more than halfway to geostationary orbit and well past the Van Allen belts. Falcon Heavy could send a Crew Dragon nearly to GTO with three-core recovery and it could send Crew Dragon around the moon if the core was expended and the boosters were recovered downrange.