Space guns are a great technology, but the problem is the market. Space guns would not be able to launch sensitive systems. They would only be able to launch things that can withstand the G forces. Only things like fuel, water, oxygen, some foods, radiation electronics, and etc could be launched this way. The only things that a space gun would be able to service are space stations and fuel depots.
I have now come to believe that high flightrate RLVs would beat both gun launch and even a space elevator in cost to orbit, at least for Earth.
Quote from: DarkenedOne on 04/11/2017 07:59 pmSpace guns are a great technology, but the problem is the market. Space guns would not be able to launch sensitive systems. They would only be able to launch things that can withstand the G forces. Only things like fuel, water, oxygen, some foods, radiation electronics, and etc could be launched this way. The only things that a space gun would be able to service are space stations and fuel depots. If you think that's all they're good for... then if you do happen to build one, (a) please don't tell your military about it and (b) please don't aim it in the direction of North Korea! (..or the Middle East, Russia or anywhere else on Earth, pretty much)
Quote from: Robotbeat on 04/12/2017 12:23 pmI have now come to believe that high flightrate RLVs would beat both gun launch and even a space elevator in cost to orbit, at least for Earth.Very well might. Although it's hard to say, as we don't yet have examples of either (although we're certainly closer to the former).IMHO my favorite non-rocket launch system is the launch loop, which I don't feel gets enough attention versus older, more showy things like space elevators (which require unobtanium).
A "space gun" could launch with less acceleration, but it would need to be a lot longer.
Quote from: Rei on 04/13/2017 10:15 amQuote from: Robotbeat on 04/12/2017 12:23 pmI have now come to believe that high flightrate RLVs would beat both gun launch and even a space elevator in cost to orbit, at least for Earth.Very well might. Although it's hard to say, as we don't yet have examples of either (although we're certainly closer to the former).IMHO my favorite non-rocket launch system is the launch loop, which I don't feel gets enough attention versus older, more showy things like space elevators (which require unobtanium).Space elevator doesn't require unobtainium, it's just that with current materials (which require an AREA taper ratio of on the order of a million, so a diameter ratio of 1000), the space elevator would be a meter in diameter in the middle but for only a small payload (100kg), so would never pay for its own mass because a space elevator is really slow.And actually the taper ratio improves a lot as you increase specific strength, so it's possible we'll reduce the taper ratio to 10,000, but even then, the really long travel time kills you.
Rockets FTW.
ITS is supposed to get the cost of propellant in LEO down to just $9/kg. Nine. Dollars.
And ITS isn't the end-all, be-all, either. It's possible to improve efficiency by increasing chamber pressure, modifying mixture ratio so you run either oxygen-rich or stoichiometric, improving mass fraction, using hydrogen on the upper stage to better match the Isp to the flight speed, perhaps using a lower speed launch rail to accelerate the first little bit where it's not possible to lower the Isp far enough to match the flight speed, launch from high altitude, etc.
Quote from: Rei on 04/13/2017 10:15 amQuote from: Robotbeat on 04/12/2017 12:23 pmI have now come to believe that high flightrate RLVs would beat both gun launch and even a space elevator in cost to orbit, at least for Earth.Very well might. Although it's hard to say, as we don't yet have examples of either (although we're certainly closer to the former).IMHO my favorite non-rocket launch system is the launch loop, which I don't feel gets enough attention versus older, more showy things like space elevators (which require unobtanium).Space elevator doesn't require unobtainium, it's just that with current materials (which require an AREA taper ratio of on the order of a million, so a diameter ratio of 1000), the space elevator would be a meter in diameter in the middle but for only a small payload (100kg), so would never pay for its own mass because a space elevator is really slow.And actually the taper ratio improves a lot as you increase specific strength, so it's possible we'll reduce the taper ratio to 10,000, but even then, the really long travel time kills you.Rockets FTW. People underestimate how efficient rockets are. ITS, for example, would be about 10% efficient at converting chemical energy of methane into potential and kinetic energy of reusable payload in orbit (15% if we're talking expendable). Considering it runs on methane, which is the cheapest source of energy on Earth right now at 1¢/kWh, you could beat the energy cost of a laser-powered space elevator or any sort of electrically powered launch method that has to pay 10¢/kWh for electricity. (Of course there are costs to properly condition that chemical energy so it is cryogenic, etc, but that's true for converting electricity into laser/rail gun power, too.)ITS is supposed to get the cost of propellant in LEO down to just $9/kg. Nine. Dollars.And ITS isn't the end-all, be-all, either. It's possible to improve efficiency by increasing chamber pressure, modifying mixture ratio so you run either oxygen-rich or stoichiometric, improving mass fraction, using hydrogen on the upper stage to better match the Isp to the flight speed, perhaps using a lower speed launch rail to accelerate the first little bit where it's not possible to lower the Isp far enough to match the flight speed, launch from high altitude, etc.But for a first shot at a truly large, full, rapidly reusable RLV, ITS (and possibly whatever Bezos has planned for New Armstrong) would already demolish the $50/kg benchmark that these alt-launch concepts are struggling to meet.
Quote from: Hanelyp on 04/12/2017 04:04 amA "space gun" could launch with less acceleration, but it would need to be a lot longer.Yes that is always true, but you have to remain within a reason length. In order to accelerate a mass up to 5 km per second with max G force of 50g you would need a barrel 25 km long.
Quote from: DarkenedOne on 04/13/2017 04:14 pmQuote from: Hanelyp on 04/12/2017 04:04 amA "space gun" could launch with less acceleration, but it would need to be a lot longer.Yes that is always true, but you have to remain within a reason length. In order to accelerate a mass up to 5 km per second with max G force of 50g you would need a barrel 25 km long. There is an possible workaround to this that can be exploited in some cases. It might be hard to apply to direct launch from earth but could be used in other cases.Rather than a huge rail gun used only momentarily, you could have a much smaller rail gun that fires a stream of momentum carrying elements. Then you would need a similar rail on your vehicle to catch this stream and send it back to the first rail gun in a loop. It would sort of be equivalent to having a temporary magnetic rail that stretches over say a million kilometers.If you do not attempt to recover these elements then the catcher on the vehicle can be lighter than the launcher. In the extreme case with smaller elements this becomes a variation on beamed powered propulsion.https://en.wikipedia.org/wiki/Beam-powered_propulsion#Direct_impulse