Would it be a good idea to use a railgun to propel a person into combat in a low/zero grav environment, à la human cannonballs in a circus? If a person was strapped into some sort of temporary frame, and launched out of a sizable railgun, would they survive the G-force shock unscathed? Could it be used to launch soldiers with jetpacks or other forms of Futurey stuff safely (relatively) into battle?
Yes, just put them in a housing for comfort, protection, and aerodynamics, and accelerate them slowly so as to not feel much physical discomfort.
Wait a second...
A Maglev train is basically a railgun for safely shooting people around.
Ok, now for realsies. Could you safely launch and land a human with a railgun for a mile? @Tezra is correct that so long as you accelerate and decelerate them over a long enough distance the felt G-Force is manageable no matter the velocity you need.
Unfortunately humans aren't very aerodynamic. @Tezra estimated 126 m/s but the terminal velocity for a human in free fall in atmosphere is about 53 m/s. This causes problems during launch, the human is now being pressed at 5Gs against an increasingly hard wall of air. Once launched, drag will cause them to rapidly decelerate and potentially not reach the 1 mile.
An aerodynamic shell would help. This would make the human more aerodynamic, increasing velocity and range, and protect them against being buffeted to death by wind.
Because of this deceleration in transit, they'll approach the catching ramp at a lower speed. Lower speed means less length is needed to safely decelerate, so the "catch" platform needs to be much smaller.
But this is extremely dangerous. If the calculations are off, if there's a flaw in the shell, if there unaccounted for wind shifts or turbulence, they'll miss the catch platform. Splat. It's much simpler and safer to use a parachute. They're well understood and provide the person with a modicum of control over their landing.
You would need to launch the person at 126m/s (math). So to not murder them with G-Force (about 5 gs (49 m/s2)), you need to accelerate them over the course of about 2.5 seconds and need a launch/catch pad about 162m long (Distance = accel*time^2, where time = velocity/accel).
NOTE: (This is HYPER-dangerous, and good luck finding a test pilot, let alone riders. Also, the energy of the rail-gun has to be calibrated to the weight of the passengers, or else they die. I have ignored wind resistance, because else they would die from landing in the wrong place)
Lets assume for a moment that the idea is remotely plausible.
You still need a fairly massive installation (a mass driver with a large enough diameter to house a full equipped soldier, an elevating and traversing mechanism and a fairly large power generation system. Transport vehicles will be needed as well, leaving a fairly large footprint on the ground
And of course, there will be a platoon or more of soldiers standing around waiting to be shot out of the cannon. Overall, there will be a lucrative target waiting to be "serviced" by artillery, mortars, fast air or even ground troops (a mile is 1600m, a distance which can be covered in a short time on foot). In fact, many machine-guns have effective ranges of over 2000m when mounted on tripods, so your entire device and all the soldiers waiting to be launched will be under attack in a matter of moments.
Now there is a place where this might make more sense, and that is in space, where there is no aerodynamic drag to slow the troops down, and large power plants would be common on spacecraft. A spacecraft might be able to disgorge a large number of Space Marines in the manner of Starship Troopers. They can use on board rocket belts or packs to manoeuvre in space and land on an airless moon or asteroid. The large barrel of the mass driver can also launch large calibre rounds, missiles or countermeasures as well.
"Have Sting" railgun concept. Space Shuttle included for scale. Illustration by Scott Lowther
And since the spacecraft is both powered and armoured, and capable of using its weaponry to suppress enemy defences and manoeuvring to bring the Space Marines to the proper place, this is probably the most reasonable place to use this system.
In high school physics, you learn that v=at and d=½at². (velocity, acceleration, time, distance respectively) so let's assume a= 20g is the maximum tolerable acceleration for a man, and that a reasonable muzzle velocity is 1000 m/s. This gives you 8.7 sec. of 20g acceleration. Calculating d, we find that a distance of 5.6 kilometers would be required to APPLY that acceleration. The amount of energy required would be enormous, since the 20g assumes the guy is laying perpendicular to the direction of motion, hence the 'shell' he is encased in would be 2+ meters in diameter. In other words, this isn't practical.
There are transportation uses for a railgun, two of which are outlined here. I suppose you could theoretically use a railgun to shoot a train down to the next station, or instead of an F-35 you could launch a glider to some nearby destination. But those both sound expensive and impractical to me.
The physics have been pretty well covered and the answer is yes, with a pod of some sort including a catch or parachute mechanism and slow enough acceleration and deceleration this could technically be done.
Now the question becomes in what scenario would this be worthwhile...and believe it or not, one exists. (well at least one) First, you have to ditch the one mile range, at one mile you are way to close to your enemy for it to not be destroyed...standard artillery can shoot farther than that. So if you put this on the range of 10+ miles you may have something useful.
In conventional warfare this would be a suicide mission without any likelihood of it also being helpful to the cause.
Now, if you have this scenario it could be useful.
- You lack air superiority
- Your ground to air defenses have kept the enemy air craft at bay
- You need to insert special ops troops into the enemy's territory
- You are already actively at war
Stay with me here...
So you create a pod that is both transport for a human (or maybe two) AND a guided missile...or more like a mortar I suppose.
You launch your spec ops guys toward their destination over enemy lines, along with a full artillery bombardment to mask that you are launching people.
At some point along the travel arc the pod ejects your troops and they descend via parachute
The pod continues on and blows something up (well itself AND something else). This way the pod will hopefully not be identifiable so the enemy won't know you have snuck people behind enemy lines.
Your ops guys go do what ever it is they need to do and are aided by the fact that the enemy is distracted by some sort of explosion that can either have been a diversion or an attempt to soften the target they are after.