Quote from: ringsider on 06/16/2018 06:02 pmQuote from: Bananas_on_Mars on 06/16/2018 04:53 pmOr 10km at 20g. But i'm sure they have some special tricks up their sleeve. You don't get that kind of investment for crazy ideas, and they already have a lot of hardware in that only picture i have seen.I'm definitely looking forward to seeing more of their tech.That picture:is a rendering.Mea maxima culpa...It's a very good render...
Quote from: Bananas_on_Mars on 06/16/2018 04:53 pmOr 10km at 20g. But i'm sure they have some special tricks up their sleeve. You don't get that kind of investment for crazy ideas, and they already have a lot of hardware in that only picture i have seen.I'm definitely looking forward to seeing more of their tech.That picture:is a rendering.
Or 10km at 20g. But i'm sure they have some special tricks up their sleeve. You don't get that kind of investment for crazy ideas, and they already have a lot of hardware in that only picture i have seen.I'm definitely looking forward to seeing more of their tech.
The centrifugal acceleration can be kept relatively low if the centrifuge has a large diameter.
Quote from: jongoff on 06/17/2018 03:28 amI have to be careful about what I say, since the details were shared confidentially, but yes they know that they have to deal with centrifugal forces, yes, they've done a significant amount of analysis and testing, and no, it's not an insurmountable problem. Artillery shells regularly see 2-3x the acceleration this vehicle would see, and many modern shells have electronics and mechanisms. It is totally possible to harden structures for those kind of loads, especially when they're well known in advance.There is (theoretically) a way to side step the centripetal acceleration problem.Implement the accelerator ring as an N-sided polygon of linear accelerators. At the corners the the vehicle is moving in a straight line, only subject to gravity. It can then be reorientated with relatively low stress ready for entry into the next segment. It also means that the exit could be at several different directions to the Equator, rather than a single fixed direction. The attraction is the acceleration can be relatively sedate. 10g's could get you to orbital velocity (at ground level) within 90 secs. The problems would be formidable. Heavy duty power electronics, fast acting control systems and some fairly large scale tunneling (or at least trench cutting, followed by covering over). You'd want an exit ramp to put it on a fairly steep climbing trajectory and some fast acting foil shutters to retain vacuum. Then there's the LV. It'll need some serious TPS. OTOH liquid fuel is not as difficult as you might think. The Germans in WWII developed an artillery shell with a a 300Km+ range using the spin to inject liquid fuel into a circular duct (essentially a ramjet wrapped round an artillery shell). However this used the phenomenally dangerous Carbon Disulphide as the fuel. I'd guess they'd want something more benign today. Gerald Bull (who I like to think of as "The last of the long range gunmen" ) reckoned solid propellant charges were adequate for circularizing to orbit, probably fired by a time delay or some kind of burnout trigger. Using rotation to pressurize propellant was also the plan of Rotary Rocket. The question with these concepts is not "Can it be done?" It is "Will commercial customers be prepared to swallow the costs inherent in making their payloads more rugged to survive this launch method than others" ?GPS guided artillery shells are in use and are effective but the electronics package was designed to do that as part of the customers requirements. What happens when the launch price is very low but the payload has to be re-engineered from the ground up use the launch method?
I have to be careful about what I say, since the details were shared confidentially, but yes they know that they have to deal with centrifugal forces, yes, they've done a significant amount of analysis and testing, and no, it's not an insurmountable problem. Artillery shells regularly see 2-3x the acceleration this vehicle would see, and many modern shells have electronics and mechanisms. It is totally possible to harden structures for those kind of loads, especially when they're well known in advance.
Quote from: intrepidpursuit on 06/16/2018 05:23 amIs there some piece we are missing here that would make this thing possible? Have they addressed the seemingly insurmountable issues of the centripetal forces at launch and the drag through the low atmosphere?I have to be careful about what I say, since the details were shared confidentially, but yes they know that they have to deal with centrifugal forces, yes, they've done a significant amount of analysis and testing, and no, it's not an insurmountable problem. Artillery shells regularly see 2-3x the acceleration this vehicle would see, and many modern shells have electronics and mechanisms. It is totally possible to harden structures for those kind of loads, especially when they're well known in advance.As for drag going through the atmosphere, once again, yes they will slow down, but the square-cube law means that its easier to get a high ballistic coefficient (which means you decelerate less from drag) with a large vehicle than a small round. That doesn't mean that their system is bound to obsolete all existing rockets, just that they've put more thought and effort into this than you can easily tell from the existing public articles.~Jon
Is there some piece we are missing here that would make this thing possible? Have they addressed the seemingly insurmountable issues of the centripetal forces at launch and the drag through the low atmosphere?
@John Smith 19How does that solve the centripetal acceleration problem? Unless I misunderstand you, you pack all the turning acceleration into a jerk at each corner instead of having it distributed around the whole curve. That seems much worse.
Quote from: uranium on 06/17/2018 02:17 pm@John Smith 19How does that solve the centripetal acceleration problem? Unless I misunderstand you, you pack all the turning acceleration into a jerk at each corner instead of having it distributed around the whole curve. That seems much worse.It would depend on the size of the circle and the number of segments. It also depends on the size of the joint between those segments. I'm picturing a turning couple as one end of the vehicle turns out and the other end turns in to align with the next segment. With 4 segments (a square) they change in angle is 90 degs, but at 8 it's 45. At high number it's a small angular change. At 360 it's 1 deg per segment and the turning forces rise with as the payload is accelerated.
Their main stumbling block to gaining funding (beyond all the normal issues of funding space startups) is that the launcher is not compatible with current payloads. You either need to convince satellite manufacturers to design and assembly kilogee-tolerant satellites just for your launcher, or find something else to launch.
Quote from: edzieba on 06/18/2018 11:30 amTheir main stumbling block to gaining funding (beyond all the normal issues of funding space startups) is that the launcher is not compatible with current payloads. You either need to convince satellite manufacturers to design and assembly kilogee-tolerant satellites just for your launcher, or find something else to launch.I wonder if the plan is to build up the velocity very gently, using a very long acceleration time on a long track, such that the payload experiences "normal" G loads? If you accelerate at 10-15G for a long time you can get to a large velocity without damaging anything...Vf = Vi + atIf you set Vf large, say 60,000 kph (orbital velocity being about half that), Vi =0, a = 20G i.e., 200 m/s2, what t do you need to get to that Vf? Answer = 1111 seconds i.e. 14 minutes.
Quote from: ringsider on 06/18/2018 11:57 amQuote from: edzieba on 06/18/2018 11:30 amTheir main stumbling block to gaining funding (beyond all the normal issues of funding space startups) is that the launcher is not compatible with current payloads. You either need to convince satellite manufacturers to design and assembly kilogee-tolerant satellites just for your launcher, or find something else to launch.I wonder if the plan is to build up the velocity very gently, using a very long acceleration time on a long track, such that the payload experiences "normal" G loads? If you accelerate at 10-15G for a long time you can get to a large velocity without damaging anything...Vf = Vi + atIf you set Vf large, say 60,000 kph (orbital velocity being about half that), Vi =0, a = 20G i.e., 200 m/s2, what t do you need to get to that Vf? Answer = 1111 seconds i.e. 14 minutes.I think you miscalculated, i'm getting about 83 seconds. Even with that, i'm getting a linear track that's almost 700 kilometres long for your 60000 kph.For LEO orbital velocity, at 20g linear acceleration, that's a track 155 km long.
Centrifugal launchers/rotary mass drivers aren't exactly a new idea. No real technical barriers to construction of both the accelerator and the projectile (as mentioned before, SMT electronics have crazy high acceleration tolerance even without any potting), and plenty of designs for the accelerator from basic bar-centrifuges with detaching counterweights and opposing decel-sumps, to rim-linear-motor designs with trapdoors or 'over the lip' detachment, to spiral accelerator tracks, etc. Their main stumbling block to gaining funding (beyond all the normal issues of funding space startups) is that the launcher is not compatible with current payloads. You either need to convince satellite manufacturers to design and assembly kilogee-tolerant satellites just for your launcher, or find something else to launch. If ULA make good on their offer to pay $3k/kg for water in LEO that's about the only market I can think of that this launcher would serve, beyond a handful of cubesats potted in epoxy. That of course means launch prices need to be below $3k/kg.
The application I'm most interested in though would be using this same technology for propellantless launch from the lunar surface. That's an area where these systems could totally shine. But that's a bit far off, so I'm keeping my fingers crossed that they'll be successful enough to stay in business and put this technology "on the shelf".
You would have to assume to attract those investors that the concept is simple and easily proven, and doesn't need the entire satellite customer base to change they way they work to handle extreme loads.