Rocket Launching using a mortar mechanism

Why the mortar wants launch method for a rocket is advantageous compared to a rail gun or other electromagnetic means of launch.

I wrote a previous post on this subject which can be found here:

http://rethinking-tomorrow.blogspot.com/2018/03/method-to-launch-large-rockets-using.html

On Wednesday, September 12, 2018, 1:17:14 PM EDT, Keith Klipstein wrote:

As I began reading your blog on Rocket to Mars I couldn’t help but thinking a Long Rail Gun might be simpler..

The capital required for an electromagnetic launch would be vastly greater than what would be needed for a mortar launch tube to be drilled into the Earth with a tunnel boring machine. TBMs have previously been used to create ICBM tunnels. Muzzle velocity ExitingThe end of the tunnel Depends strongly on the average acceleration Of the projectile as it travels down the Launch tube. and also the Length of the launch tube. the capital required for a mortar launch Tube That is 10 m in diameter Could be less than $100 million if it was created in the right kind of soft rock. I believe An electromagnetic Launcher that is 5 km long and capable of Launching large rockets Would cost at least $10 billion.

The total acceleration time inside the Launch tube is typically less than 15 seconds. Both Elon musk and I have imagined total rocket masses that are around the mass of the Saturn five rocket (300,000 kg). The total power needed for accelerating 300,000 kg at 10 times normal gravity is quite high. It is not expensive to get that much power out of exploding gas mixtures, but it is exceedingly expensive to achieve that kind of acceleration using electromagnetic means. This is best illustrated by an example; in order to accelerate a 300,000 kilogram rocketship at 110 m/(s squared) Through a 5 km launch tube would take 9.53 seconds, and would require an average power level of 17.3 GW. It is obvious this would be quite an inexpensive electromagnetic rig.

The vast difference in cost of these methods is due to how the force is applied to the rocket. In one case it is gas pressure from behind, using the well understood method by which a bullet is pushed through the barrel of a gun. Indeed in various drafts of my work on this I have called the launch tube a barrel; However I have decided to uniformly use the term Launch tube Henceforth.

In an electromagnetic launch, there is a need for lots of wiring and capacitors and inductors… you get the idea. The electronic hardware alone costs far more than it will cost to build the launch tube according to my idea.

The fuel for a mortar launch could be as simple as natural gas and air. This mixture in particular is easy to control Because the propagation velocity of the combustion front is very modest.One can control the propagation of the flame By use of initiators along the wall of the tube. The potential for pollution would be minimal Compared to conventional rocket launches. For non-living payload launches, One could use much more powerful combustible gas mixtures, including hydrogen/oxygen mixtures for the launch. Because of the high speed of sound In hydrogen,It is feasible to get to muzzle velocities that are way beyond what would be possible with Methane/air, all the way up to orbital velocity.  

With a single Mortar It would be relatively easy to launch different objects using quite different accelerations, And both by varying the mass that is being launched as well as the combustible mixture that that is creating the launch force. For nonliving satellites one could accelerate at several hundred g's (~2000 meters per second squared). Note that the maximum acceleration contemplated for the mortar launch idea is much less than for a typical gun in which the acceleration can be on the order of 4000 or more g's (40,000 m/s per second or more). For humans one would have to keep the maximum acceleration much lower, but I'm pretty sure it's okay to go to a maximum acceleration of even 20 g's provided that people are laying down flat, and are attached to a breathing apparatus so that if a black out occurs, that will be medically okay. After all, the high acceleration will only last 10 seconds at most. Increasing acceleration makes a big difference And in terms of launch velocity; What is the maximum acceleration? The length of the tube matters less, so In my calculations I have adopted a standard 5 km tube.

In case anyone has read to this point in my comments, Let me say again that I am trying to reach Elon musk about this idea.