Talk:Space gun

2008
the section criticism of the space gun seem counter intuitive, rockets used now to deliver satellites have already been converted long range ballistic missiles, is the worry that the new technology is easier to achieve for smaller countries? —Preceding unsigned comment added by 24.4.205.21 (talk) 06:08, 21 February 2008 (UTC)

I am currently working on a gun assisted launch project with Columbiad Launch Services http://www.columbiad.ca/

Earthism
The article is currently written from an Earth perspective. Is it necessarily true, for an example, that space guns are ruled out for propelling sensitive instruments, or humans, if the space gun is sitting on an asteroid? I suppose the easiest fix is for a knowledgeable editor to add "from Earth" or the like to each such statement? Comet Tuttle (talk) 18:29, 2 July 2010 (UTC)
 * You have it basically correct. It also assumes that the barrel is fairly short. Hypothetically, if the barrel were several hundred miles long, passengers could be launched at a safe acceleration. — Preceding unsigned comment added by 24.223.130.32 (talk) 21:47, 14 May 2016 (UTC)

Question
Couldn't you flood the cabin with water? I think it would dissipate most of the G force. —Preceding unsigned comment added by 24.18.34.114 (talk) 02:14, 13 November 2010 (UTC)

You're talking about this line of research (popularized by the movie The Abyss) I presume https://www.esa.int/gsp/ACT/projects/liquid_ventilation/

You can't dissipate G forces, but it does provide enough support to the lungs and internal tissues to increase maxinim G forces from 24 G to 100 G, a ~4x improvement Habanero-tan (talk) 00:30, 21 November 2021 (UTC)

Answer
That would do nothing to change the fact that you need to accelerate an object from essentially being at rest to having escape velocity. How would a cabin filled with water counteract that? Simply put: the problem is the cabin pushing against its occupants in order to accelerate them, which would be quite lethal. Filling the cabin with water would change that to the cabin pushing against the water, which in turn needs to push against the occupants (or, more likely, the occupants would "sink" to the bottom of the cabin and you're back where you started anyway). If there is no pushing on the travelers, they stay put. — Preceding unsigned comment added by 130.37.38.197 (talk) 13:05, 16 November 2011 (UTC)

It actually would help. Buoyancy reduces the effect of acceleration in the same way as it opposes the force of gravity. In physics there's an equivalence between gravity and acceleration, so it may help to think about what would happen to a diver under a pulse of very high gravity. For best results you would have to match the density of the water to that of the body (e.g. by adding salt), and keep the bodies in shallow water to minimize the peak water pressure. There are some limits: variations in density would lead to some internal forces, but the main problem would be the lungs and other pockets of air. Under very high acceleration any air would need to be replaced by liquid. 78.86.112.217 (talk) 14:50, 3 March 2015 (UTC)

Rail/coil gun problems
The idea of using a railgun/coilgun technique to build a space gun keeps emerging (see http://simulationsllc.com/pdfs/resources/electromagnetic%20launcher%20propulsion/Launch%20to%20Space%20with%20and%20Electromagnetic%20Railgun.pdf, and https://www.quora.com/SpaceX-company-Why-dont-we-use-a-system-similar-to-a-railgun-to-accelerate-space-ships-to-escape-velocity

What hasn't been discussed in this article though is whether the railgun wouldn't damage the electrical components of satellites (that would be fired with it, if build). I think the (electromagnetic) damage would be huge, making this unusable. Something like the V-3 gun however might work I think. KVDP (talk) 10:58, 27 June 2016 (UTC)

Circular Tracks Don't Work
I removed where the article said: ″Theoretically, a space gun with a circular (ring shaped) track could utilize much lower accelerations because its effective track length is infinite (with the object going around the ring numerous times), though the centripetal acceleration could be enormous as the payload neared escape velocity, depending on the track size." I'm pretty sure this is not at all correct. The acceleration that is supposedly lower is technically the magnitude of the acceleration vector of the object. The average acceleration vector when an object changes velocity is its change in velocity vector divided by the time of this change, the magnitude of the acceleration may become larger than this if the acceleration is not constant. Moving an object half way around a circular track requires transitioning from a velocity vector completely in one direction at the object's speed, to a velocity vector completely in the other direction at the object's speed, which would have, per the previous sentence, at least the acceleration from zero to twice the speed in the time required for the object to move half way around the track. This acceleration is the constant acceleration of a straight track from zero to twice the speed over that time. If T is the period around the circular track and s is the object speed around the track, the straight track acceleration equivalent to the velocity change from one side of the circular track to the other would have a change in speed of 2s and a time of T/2, so the acceleration would be 2s / (T/2) = 4s/T, the straight track length is ½ * acceleration * time^2 = ½ (4s/T) * (T/2)^2 = ½ s*T, where the total circular track length is s*T, so a straight track of half the length gets twice the final speed with the same or less acceleration. It's actually quite a bit less acceleration on the straight track versus the circular because of added acceleration in the transverse direction to follow the semi-circular path. It is true that "the centripetal acceleration could be enormous as the payload neared escape velocity", but in fact the magnitude of the acceleration of an object on a circular track will always be significantly larger than a constant acceleration on a straight track with the same length and terminal speed. For an exact comparison of the two accelerations, if L is the circumference of a circular track, the centripetal acceleration is speed^2 / radius = 2 pi s^2/L. For an equivalent length straight track, final speed = sqrt(2 * acceleration * L), so the acceleration is ½ s^2/L. Therefore a straight track of the same length with the same final speed as a circular track has 4 pi times less acceleration as the centripetal acceleration of the circular track.

My above explanation is OR. However, I am not proposing putting this explanation into the article text. The statement I removed from the article text appears to also be OR, it is not sourced, and I think it is incorrect for the above reason. If anyone has a source for the statement I removed, please do add it back with the source, and I will be glad to invest my 5¢ in your launch system. Spintwo (talk) 07:23, 1 January 2020 (UTC)

Move discussion in progress
There is a move discussion in progress on Talk:Space gun (disambiguation) which affects this page. Please participate on that page and not in this talk page section. Thank you. —RMCD bot 17:34, 28 November 2020 (UTC)