Quote from: Robotbeat on 01/14/2021 11:33 pmQuote from: ncb1397 on 01/14/2021 10:01 pmQuote from: Robotbeat on 01/14/2021 06:39 pmTo reduce acceleration from 10,000 gees down to 10 gees would require an arm 1000 times as long, so a pressure vessel with a billion times the volume (shape stays the same as it's already pretty optimal). At best, pressure vessel mass scales with volume. This will be worse as it's "negative" relative pressure. A billion times the material. Steel prices alone will kill the concept because we're still talking just a Mach 6 assist.If you were to theoretically build a vacuum chamber 1000x bigger, why would you still limit yourself to mach 6? You could increase your speed by 5x and still reduce your g-forces to 40x(10000g -> 250g). And you could largely eliminate your rocket system. At 250 g, humans wouldn't be launchable (live at least), but certain small insects could be. Anyways, there are tons of variables (g-forces, arm radius, exit speed, payload mass). Not every value you can plug into them or calculate would make sense practically, that doesn't mean there isn't a trade space where it might. The (10 g, 50,000 meter long arm, mach 6, 100 kg) solution probably isn't in the "makes sense category". Neither is a 100 km tall Big falcon rocket.Well probably because you'd effectively vaporize whatever it is you're launching (so like half your mass would be ablative shielding). Losses are very nonlinear with speed, so you would need a launch speed much higher than orbital velocity. And, you know, have a pressure vessel weighing approximately a trillion tons (give or take). And still not be able to launch humans without turning them to jelly.EDIT: Also, there aren't materials strong enough to build a centrifuge arm that spins that fast. Or, rather, there are, but it'd require a payload-to-arm mass of worse than one to a million in order to enable your 10.26km/s launch speed. Since electric motors are at best ~99% efficient and needs to spin up the whole arm, that means you've basically invented the most inefficient launch method ever (chemical rockets being like 1000 times as energy efficient).EDIT: Math is from this paper, using materials with 4GPa/(g/cc) specific strength (which has some small amount of factor of safety). https://www.researchgate.net/publication/245438136_Design_of_Tether_Sling_for_Human_Transportation_System_Between_Earth_and_Mars (equations 7-9)It still doesn't explain why you would limit yourself to mach 6. 6 km/s reduces the tether mass (for Zylon) from 4.5 million times the payload mass to under 500 or a factor of ~10,000. If the chemical rocket is 1,000x more energy efficient, then you would have closed your gap. But theoretically, you could have material strong enough for the 10 km/s case (using numbers for boron nitride nanotubes that is lab demonstrated but not commercially available gives a mass for the tether of under 200x)....
Quote from: ncb1397 on 01/14/2021 10:01 pmQuote from: Robotbeat on 01/14/2021 06:39 pmTo reduce acceleration from 10,000 gees down to 10 gees would require an arm 1000 times as long, so a pressure vessel with a billion times the volume (shape stays the same as it's already pretty optimal). At best, pressure vessel mass scales with volume. This will be worse as it's "negative" relative pressure. A billion times the material. Steel prices alone will kill the concept because we're still talking just a Mach 6 assist.If you were to theoretically build a vacuum chamber 1000x bigger, why would you still limit yourself to mach 6? You could increase your speed by 5x and still reduce your g-forces to 40x(10000g -> 250g). And you could largely eliminate your rocket system. At 250 g, humans wouldn't be launchable (live at least), but certain small insects could be. Anyways, there are tons of variables (g-forces, arm radius, exit speed, payload mass). Not every value you can plug into them or calculate would make sense practically, that doesn't mean there isn't a trade space where it might. The (10 g, 50,000 meter long arm, mach 6, 100 kg) solution probably isn't in the "makes sense category". Neither is a 100 km tall Big falcon rocket.Well probably because you'd effectively vaporize whatever it is you're launching (so like half your mass would be ablative shielding). Losses are very nonlinear with speed, so you would need a launch speed much higher than orbital velocity. And, you know, have a pressure vessel weighing approximately a trillion tons (give or take). And still not be able to launch humans without turning them to jelly.EDIT: Also, there aren't materials strong enough to build a centrifuge arm that spins that fast. Or, rather, there are, but it'd require a payload-to-arm mass of worse than one to a million in order to enable your 10.26km/s launch speed. Since electric motors are at best ~99% efficient and needs to spin up the whole arm, that means you've basically invented the most inefficient launch method ever (chemical rockets being like 1000 times as energy efficient).EDIT: Math is from this paper, using materials with 4GPa/(g/cc) specific strength (which has some small amount of factor of safety). https://www.researchgate.net/publication/245438136_Design_of_Tether_Sling_for_Human_Transportation_System_Between_Earth_and_Mars (equations 7-9)
Quote from: Robotbeat on 01/14/2021 06:39 pmTo reduce acceleration from 10,000 gees down to 10 gees would require an arm 1000 times as long, so a pressure vessel with a billion times the volume (shape stays the same as it's already pretty optimal). At best, pressure vessel mass scales with volume. This will be worse as it's "negative" relative pressure. A billion times the material. Steel prices alone will kill the concept because we're still talking just a Mach 6 assist.If you were to theoretically build a vacuum chamber 1000x bigger, why would you still limit yourself to mach 6? You could increase your speed by 5x and still reduce your g-forces to 40x(10000g -> 250g). And you could largely eliminate your rocket system. At 250 g, humans wouldn't be launchable (live at least), but certain small insects could be. Anyways, there are tons of variables (g-forces, arm radius, exit speed, payload mass). Not every value you can plug into them or calculate would make sense practically, that doesn't mean there isn't a trade space where it might. The (10 g, 50,000 meter long arm, mach 6, 100 kg) solution probably isn't in the "makes sense category". Neither is a 100 km tall Big falcon rocket.
To reduce acceleration from 10,000 gees down to 10 gees would require an arm 1000 times as long, so a pressure vessel with a billion times the volume (shape stays the same as it's already pretty optimal). At best, pressure vessel mass scales with volume. This will be worse as it's "negative" relative pressure. A billion times the material. Steel prices alone will kill the concept because we're still talking just a Mach 6 assist.
My main thing is the accelerations involved mean your rocket stages have to be built very heavy and therefore will have crappy mass fractions and much of your advantage is eaten in aero losses which are already high for small vehicles. So you get maybe a 1km/s advantage but you can only launch tiny payloads that can withstand high gees and the stages have to be really sturdy and so have a high dry mass and will be significantly more expensive to make plus expendable.It’s actually possible to do it. “Viable” in the sense that it may not even be the craziest rocket system anyone has ever built (Sprint missiles or something like it gotta take that prize). But outside of MAYBE munitions tests, I don’t see how it’s competitive.I mean, maybe if you’re launching up to a Rotovator or something and so don’t need a rocket (other than maneuvering thrusters)? But without a rotovator, you already need an 8km/s rocket, and I doubt a 9.3km/s rocket built to withstand 10gees max (and only getting Mach 1 at about 0.3 atmospheres of pressure) will be more expensive than an 8km/s rocket able to withstand 20,000 gees and Mach 5 at sea level.
Quote from: Robotbeat on 01/11/2021 09:58 pmMy main thing is the accelerations involved mean your rocket stages have to be built very heavy and therefore will have crappy mass fractions and much of your advantage is eaten in aero losses which are already high for small vehicles. So you get maybe a 1km/s advantage but you can only launch tiny payloads that can withstand high gees and the stages have to be really sturdy and so have a high dry mass and will be significantly more expensive to make plus expendable.It’s actually possible to do it. “Viable” in the sense that it may not even be the craziest rocket system anyone has ever built (Sprint missiles or something like it gotta take that prize). But outside of MAYBE munitions tests, I don’t see how it’s competitive.I mean, maybe if you’re launching up to a Rotovator or something and so don’t need a rocket (other than maneuvering thrusters)? But without a rotovator, you already need an 8km/s rocket, and I doubt a 9.3km/s rocket built to withstand 10gees max (and only getting Mach 1 at about 0.3 atmospheres of pressure) will be more expensive than an 8km/s rocket able to withstand 20,000 gees and Mach 5 at sea level.Would it be considered trolling to say that having seen their technical solution (at least where it was 2yrs ago), you and some of the others are still making assumptions about the design that are incorrect...It would be nice if they'd post more details so I could do more than trolling, because a lot of these issues are ones they actually have clever, and completely obvious in hindsight solutions to...~Jon
Stealthy alternative rocket builder SpinLaunch conducted the successful first test flight of its one-third scale suborbital accelerator at Spaceport America in New Mexico last month.
SpinLaunch CEO Jonathan Yaney: “This is about building a company and a space launch system that is going to enter into the commercial markets with a very high cadence and launch at the lowest cost in the industry."
SpinLaunch plans to conduct ~30 suborbital test flights over the next six to eight months, with the company now finalizing the design and launch site location for its planned orbital accelerator.
I was just talking about them last week during an NSS workshop on space settlement. Glad to see they're making real progress. I'm still somewhat skeptical that their approach will win the day vs RLVs for terrestrial launch, but I'd love to see this tried on the Moon.~Jon
Quote from: jongoff on 11/09/2021 10:07 pmI was just talking about them last week during an NSS workshop on space settlement. Glad to see they're making real progress. I'm still somewhat skeptical that their approach will win the day vs RLVs for terrestrial launch, but I'd love to see this tried on the Moon.~Jonsling launch could work in Earth orbit, too. Could put a sling launcher on a commercial LEO space station or something so cubesats launched from the station could go beyond LEO. Could also be used for sending stuff back to Earth without as much of a heatshield. Or for sending to different inclinations.
Not necessarily. Can absorb the angular momentum change with flywheels and alternate the direction you launch at so it cancels out. Also, in LEO, you can use the magnetic field to dump angular momentum into.
Quote from: Robotbeat on 11/09/2021 11:16 pmNot necessarily. Can absorb the angular momentum change with flywheels and alternate the direction you launch at so it cancels out. Also, in LEO, you can use the magnetic field to dump angular momentum into.Have you done any math on how big of a flywheel array you'd need to deal with something of that scale? It's a ginormous flywheel itself...
I was just talking about them last week during an NSS workshop on space settlement. Glad to see they're making real progress. I'm still somewhat skeptical that their approach will win the day vs RLVs for terrestrial launch, but I'd love to see this tried on the Moon.And yeah, that video is pretty amazing.~Jon
Quote from: jongoff on 11/10/2021 01:42 amQuote from: Robotbeat on 11/09/2021 11:16 pmNot necessarily. Can absorb the angular momentum change with flywheels and alternate the direction you launch at so it cancels out. Also, in LEO, you can use the magnetic field to dump angular momentum into.Have you done any math on how big of a flywheel array you'd need to deal with something of that scale? It's a ginormous flywheel itself...Well, it's no bigger than the launcher itself. That's only a factor of 2...
Too large to attach here, but their website has a much higher quality copy of the twitter video. If you go through the drone shot frame-by-frame, it does appear that the projectile is tumbling after exit, and the high-speed shot also shows it starting to lean over.
