Propulsion

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May 11, 2021
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Um, not really. Dark Matter was actually invented as a mathematical tool to cover up the mass that is not being detected across galaxies. For example, if the 95% of the Milky Way was not made up of Dark Matter, the spiral arms of the galaxy would have ripped apart and the galaxy wouldn't even exist. That is why there came a need to account for the extra undetected amount of matter. And please, not MOND again. :)
I think we are basically in agreement. Dark matter is an invention to paper over huge discrepancies between theory and observation.
 
Jun 1, 2020
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I think we are basically in agreement. Dark matter is an invention to paper over huge discrepancies between theory and observation.
What are the discrepancies? DM is, interestingly, the label used similarly as Newton used the term “gravity” for his remarkable universal equations. He admitted that he could not offer any explanation for what gravity might be.
 
May 11, 2021
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What are the discrepancies? DM is, interestingly, the label used similarly as Newton used the term “gravity” for his remarkable universal equations. He admitted that he could not offer any explanation for what gravity might be.
The discrepancies between the measured speed of rotation of galaxies v the theoretical speeds based on gravitational calculations with observed mass of stars
 
Jun 1, 2020
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The discrepancies between the measured speed of rotation of galaxies v the theoretical speeds based on gravitational calculations with observed mass of stars
The revised models aren’t just paperworks, but they include tons of observations that support the theoretical claims for DM. The Bullet Cluster study is strong evidence, but the historical data also helps bring a confluence favoring the DM model.

But the point made that we don’t have direct evidence is an important one. Nevertheless, indirect evidence can be as powerful. Black holes, for instance, offer no direct evidence, but the indirect evidence supporting BHs is not in dispute.
 
May 14, 2021
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First, launching from the Moon, the Apollo did the gravity turn pretty much as soon as they cleared terrain and the vessel gymbals could turn the vessel. Accelerating horizontally will certainly add orbital velocity quickly. But, that's because there is no air on the Moon and they could do that. Fortunately for us the Earth has air, but unfortunately for the rocket, the Earth has air. The rocket's engine is quite inefficient in the atmosphere as it interferes with the reaction thrust as the engine has to overcome air pressure, works most efficiently in vacuum. In addition, as the rocket speeds up it is subject to aerodynamic stresses from the atmosphere, so, it wants to get above the atmosphere as quickly as possible. The Space Shuttle used about 95% throttle until it passed 'MaxQ' then it throttled up to 105% because of aero stresses on the ship and its wings, tanks, etc. Trig it out, the atmosphere thins out only a few miles or kilometers up but there would be hundreds of miles of thick atmosphere if the ship tried to go horizontal too soon. So, they go pretty much straight up then do the gravity turn after passing most of the atmosphere. A 'flying saucer' would be very dynamically inefficient, too much drag. That's why I fly on a long skinny airplane (or is it aeroplane, Cat?:)) rather than a saucer when I go to Disney. Borg cubes work well in space, but, atmosphere - not so much.
Go straight up rather fast, but, not too fast, then turn and go faster.

The fuel that gets the best ISP for reaction engines is hydrogen, but it can be difficult to handle and store, it finds itself leaking in places where no other fuel would leak. Liquid hydrogen and LOX can be dangerous to handle on the launchpad and during launch (ask the folks on Challenger). Kerosene is much more stable and easier to handle. Many launches use kerosene for the first stage, then LH and LOX on stages in space. But, the Apollo used hypergolic propellant for the lander and lunar ascent module because when you mix the materials together it burns, guaranteed, without an ignition system, they wanted to guarantee the system worked to get the guys back home.
Nuclear power is not a reaction system in itself, it uses the heat created by the reactor to heat xenon or hydrogen to make it go fast out the nozzle thereby accelerating the vessel. But, at this point, it's a low thrust engine, it can burn for months, but not much acceleration. Over time it'll get you there faster if you're going far, but, not for a launch system. Also, the problem of contamination of the environment in case of a breech or crash.

Anitparticles have been created here and there in labs, but certainly not enough to use in launching systems. Anyone have a bucket of antimatter JPL can use for research, let 'em know. Antimatter would not have any more mass than its equivalent of normal mass, so, it wouldn't necessarily create any more thrust. It would have to be created, then stored. We don't have any good containers to hold it. A 'magnetic bottle' would have to be absolutely foolproof without fail, or whatever it's in and everything else within spittin' distance would be completely annihilated. Sorry, I'm not applying for that job anytime soon.

We don't even know what Dark Matter is let alone how to use it for anything. We can't take a bucket of it to use for thrust either. So, we're still back to SRBs, kerosene, hydrogen, LOX, and hypergolics until we invent something better, which won't be anytime soon. And it's still best to go straight up, then turn with long skinny ships.
 
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