You are not logged in.
Rheinmetall's 120mm L55 tank cannon fires a 10kg dart / projectile with 13.5MJ / 3.75kWh of muzzle energy, near 1,650m/s. A figure of 200kg of steel per kWh of steel flywheel energy storage is accepted as doable, so 3.75kWh per 10kg of projectile weight implies 750kg of flywheel weight. To launch 1,000kg projectiles, that implies a flywheel mass of 75t (375kWh). A 1,500m^2 solar array could provide the power, at 250W/m^2. I'm sure we'd need more energy and flywheel storage than that since flywheels have about 90% round-trip efficiency, but multiple Starships could deliver the required tonnage of machinery. We'd probably need 4 to 5 landings to deliver the equipment.
A solar array would work. The problem is that the gun would be inactive for 50% of the time and for the other 50%, its recharge time would follow a sine function between dawn and sunset. If we had a 24/7 power source, the same gun could deliver 3x more material to orbit across a lunar day. Storing sufficient solar power to run the mass driver across a 28 day-night cycle, would be extremely difficult. Solar thermal power is the only technology that might theoretically do it. But you must then store a lot of heat in a lot of rock. That means a lot of heat transfer pipework and a lot of mass. This why a nuclear power source makes such a big difference to the economics of the operation. Every MW of nuclear power is worth at 10x its equivelent solar capacity, when you factor in storage losses and additional weight.
The gun itself needs to kept in an insulated tube, allowing it to operate within a very narrow temperature range across the diurnal cycle. The lunar surface at the equator, has an ~250K temperature range. Whatever the calibre of the cannon happens to be at noon, it will be different at night unless it is kept under controlled thermal conditions. Ideally, we want people to be able to access it for maintenance without being exposed to solar heat, radiation and micrometeors. So keeping the gun under a tube covered with about 1m of regolith, takes care of thermal cycling and provides protection for maintenance. That is easier if the gun is smaller, but pushing dirt over a tube isn't technically difficult. If the gun is a few hundred metres long, we could still do that easily enough. One the differences to naval technology, is that we do not require such a compact device. If we can build a gun that is 10x heavier but has 100x the operational life, then we come out ahead.
In terms of preserving the barrel, if we are dealing with a system that has physical contact rather than maglev, then it makes sense importing some kind of teflon sleeve or sabot for projectles.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
Offline
Several years ago the US navy funded research into electromagnetic gun. The call it a rail gun, but the WW2 definition is quite different. Their goal was muzzle velocity of 100,000 feet/second. They refused to say why, but I suspect they wanted to hit satellites in GSO. They failed; the shockwave inside the barrel caused the gun to explode. Or other problems. They did achieve 10,000 feet/second.
Offline
Calliban,
If we had space-rated multi-MW nuclear reactors ready to deploy, then we'd use them, but we don't have any. That's a developmental technology item required for Mars exploration and colonization, though. That's why I proposed using solar power. I'm well aware of its numerous deficiencies. I'm proposing that we launch in cycles when power is available, that if we have KiloPower reactors, we use those in conjunction with mining vehicles and smelters, and that we start with a small prototype to prove the overall feasibility of the concept. A 10kg cannon ball to orbit, captured in LLO, is a good start. That can be done with a small solar array. We will be using another solar array in orbit to re-melt the captured projectiles, producing sheet / plate, bar stock, fasteners, and for EBW or electrical spot welding. This is a demonstrator mission with a lot of moving parts, but we need to prove all the basic concepts to learn about what the problems will be.
Offline
Article on Earth - Mars cyclers posted in Next Big Future.
https://www.nextbigfuture.com/2023/05/g … rneys.html
Cosmic ray shielding does appear to skew the economics of interplanetary transits in favour of cyclers. If we need 5 tonnes of shielding for each square metre of hull, then it pays to put it on a cycler orbit and avoid the enormous propellant cost of having to shift orbits. However, as ships scale up, surface area - volume ratio goes down and shielding becomes progressively less burdensome. Also, cyclers would tend to dictate infrequent and very long journeys between the planets, as you won't neccesarily be leaving the cycler on the same orbit that you alight. So you might be stuck on it for a few years. Also, return on capital investment is a function of passengers carried from Earth to Mars and vice versa per unit time. Long journey times detract from this. So I would expect cyclers to have advantages early in Mars colonisation efforts. But as ships scale up, they will eventually lose their economic edge.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
Offline
For Calliban re #29
Thanks for this addition to the collection of posts about cyclers!
After reflecting on your vision for a few minutes, it occurred to me to ask if there is a need for crew in the vessel while it is on unproductive parts of it's orbit?
If a large cycler is useful for a passage between two locations, then it might well pay for it's mothballed status for the portions of the orbit that are not productive.
(th)
Offline
Lunar Science and Exploration Highlights: Recent Updates
Offline
a Shipyard is a great idea but what risks would evolve
'Space Debris' might become an issue
Ouch. Canadarm2 Took a Direct Hit From a Micrometeorite
https://www.universetoday.com/164960/ou … meteorite/
Offline