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sevenperforce

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  1. Can you add propellers if they are powered by the Juno's alternator? Like a turboprop?
  2. With 28.44 tonnes of spaceplane on a horizontal takeoff and some aggressively optimized staging, plus a Munar gravity assist, I was able to land Jeb on Minmus in a proper command pod with 858 m/s of dV remaining. Returning him to Kerbin was of course trivial. Rethinking whether it would be possible to reach Minmus with a command chair and an ISRU unit. I didn't optimize aero entirely.
  3. Very nice work. I figured horizontal launch with optimal staging would yield something like this.
  4. The Constellation architecture itself, for which Orion was designed, was not optimal. The propellant you use for your lunar orbit insertion burn requires tanks; carrying those tanks down into the gravity well requires more propellant than merely leaving them in LLO (going from LLO to the lunar surface costs 1.87 km/s while going from LLO to Earth entry interface costs just 0.9 km/s). Constellation used the lander to perform the LOI burn because (a) it used more efficient cryogenics, and (b) giving Orion enough props to perform LOI for the entire stack would have made it too heavy to launch on Ares I. A more optimal approach, with a Constellation architecture, would have been cryogenic drop tanks on the lander to supply props for LOI. Then you get hydrolox efficiency for your LOI burn but you don't have to carry those oversized empty tanks through 1.87 km/s down to the lunar surface.
  5. NRHO is best described as the lunar equivalent of a sun-synchronous orbit (since precession keeps it oriented perpendicular to Earth, like the precession of a sun-synch orbit keeps it oriented perpendicular to Sol), but elliptical. It does have the advantage of permitting very low-cost phase changes, which makes it useful as a gateway back to Earth entry interface or to deep space -- except that if you were already in a polar LLO, you could achieve the same utility by using an optimal three-burn maneuver: apoapsis raise burn, phase change burn at apoapsis, and Oberth ejection burn. Plus the Oberth savings from staging deep space missions from NRHO are not nearly as much as the Oberth savings from simply burning direct out of LEO. NRHO is supposed to be super duper great for access to the lunar poles, but it really isn't. If your command module is in a polar orbit and your lander is at one of the poles, you can literally launch into a matched-phase trajectory at any time and get a fast transit to your command module. In contrast, fast transits to NRHO are only possible once every few days, and the added dV requirement on your ascent vehicle far outweighs the meager additional station-keeping that a command module would need if it just loitered in a polar LLO.
  6. Shoulder pad, clearly. But seriously WTH? There's nothing currently on Starship that is this shape and needs to be covered up. I know they have discussed adding lift/catch points that pop out, but that would require an opening of some kind. Is this thing hinged on the top somehow? Because that could actually work.
  7. I believe those are understood to be dirty bombs, i.e., conventional-explosive radiological dispersal devices. Here's another image of the W48 (or, a scale model of it) to demonstrate size: NATO has virtually no use for tactical nuclear weapons today. However, during the Cold War, the sheer volume of ground forces that the Soviet-led Warsaw Pact could have thrown at western Europe would have overrun NATO's defenses, even though NATO equipment and training was generally far superior. Accordingly, NATO was prepared to use low-yield tactical nuclear weapons against Pact ground forces to blunt any invasion, both as a battlefield deterrent and through area denial. Ground troops can't march through a radioactive wasteland. Why make tactical nuclear weapons with lower yield than conventional-explosive weapons? Well, weapons like the Davy Crockett weren't designed for their yield at all, but for their radioactive capabilities. A Cold-War era tank has sufficient armor to survive virtually all conventional high-explosive munitions; you need to hit them precisely with a shaped-charge explosive or kinetic penetrator to actually destroy them. A nuclear fireball from a W54 doesn't have significantly more energy than a conventional high-explosive munition, but it DOES produce a massive burst of neutrons that would fry the troops inside a tank, even though the tank itself would survive. Today, the United States only has around 230 remaining weapons in the tactical class, around 4% of its total stockpile. And even those are only considered tactical because they are dial-a-yield and thus can be deployed tactically OR strategically depending on the situation.
  8. The smallest size you can make a fission weapon, in terms of radius, is constrained by nuclear physics to around 6 inches, the size of the physics package on the W48. That's because you need to be able to form more than just a critical mass; you need a prompt-supercritical mass, or the weapon will fizzle. A solid sphere of plutonium-239 can be exactly critical at a little under 4 inches in diameter, but you can make it prompt-supercritical using high explosives with a heavy tamper to compress it to a significantly higher density. That's how the Gadget (Trinity) and Fat Man (Nagasaki) functioned: However, the requisite arrangement of high explosive lenses made the overall physics packages in those bombs around 5 feet in diameter: One of the reasons these were so big is that we had very little plutonium available when these bombs were being built. To build a smaller bomb, you actually need more plutonium, kept subcritical by being in a non-spherical shape. You can then use two-point linear implosion to reshape the subcritical ovoid fissile pit into a prompt-supercritical sphere with less compression (and, IIRC, no tamper at all): This design is considered to be less efficient because it uses more fissile material, but it allows extremely small diameters. The smallest known weapon is the W48 at 6.1 inches in diameter (that's 155 mm), as shown below in the center: It should be theoretically possible to get a diameter as low as 4-5 inches by using even more plutonium in a very thin oval shape, but the physics to ensure precise linear implosion becomes extremely difficult and the likelihood of a fizzle goes up. A "suitcase nuke" is quite realizable, while a "briefcase nuke" is probably on the edge of what's possible. If there was a denser fissile fuel then it would be possible to make it smaller, but the only known fissile nuclides are uranium-233, uranium-235, and plutonium-239. Plutonium is slightly denser than uranium.
  9. Opens this thread . Hmm, I'm sure I can figure out a way to beat that time . Reads everything from @camacju . Reads everything from @OJT . Okay, yeah, never mind.
  10. Question. I know there are 16 booster separation motors that fire to pull the boosters away from the core, but are there any core separation motors to pull the core away from ICPS? Or does ICPS use propulsive hydrogen venting to separate itself? ICPS doesn't fire its RL10-B2 at all until the coast to apogee.
  11. Well, Starliner has twelve monopropellant RCS engines on the capsule which are separate from the twenty OMS engines, twenty-eight RCS engines, and four abort engines on the service module. The abort engines and OMS engines are definitely plumbed to the same bipropellant tanks; I'm assuming the service module RCS engines are also plumbed to the same bipropellant tanks but I suppose there is a chance they could be monopropellant. The RCS engines on the capsule don't fire until re-entry. Orion is the same way -- twelve monopropellant thrusters on the capsule for re-entry only; all orbital maneuvering and attitude is handled by the service module. Crew Dragon of course has a fully-integrated bipropellant OMS/RCS for the entire vehicle, plumbed to the same propellant reserves used for the abort engines. Using abort propellant for OMS is a very good idea on paper; the only thing you "lose" in a nominal mission is the weight of the abort engines themselves. But obviously it does add complexity. Presumably the Orion/Starliner approach is technically safer because there are no bipropellants inside the capsule itself, only in the service modules. Although I suspect that if the Starliner's service module bipropellant tanks did the same RUD that happened to Crew Dragon in April 2019, the Starliner capsule itself wouldn't have faired any better.
  12. Terrible here on the east coast.
  13. I must confess I did not realize that Centaur placed Starliner in a properly suborbital trajectory.
  14. The temperature of the balloon will not have any impact. The entry angle will, though; I'll give you that.
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