Space flight - part I

I've always wanted to travel through space. I don't mean as an astronaut launched into orbit and then back down. All of our spacecraft today are basically projectiles with seats. There is some motion control, but it's mostly for alignment. The shuttle isn't going to explore any planets, much less stars. I want to build a spacecraft that is fully capable of sustaining life. I have quite a few ideas on the subject, but I'll only write about one today since I ended up writing much more than I expected. I should note that these are all ideas and "back of the envelope" calculations. I do not claim to be an expert or that everything will be right. Nonetheless these ideas will be important before a large spacecraft can ever be built.

Acceleration and Inertia are difficult problems for large space ships. Inertia is basically an objects resistance to change it's momentum. Newton's first law states this as "A body at rest remains at rest and a body in linear motion remains in motion with constant velocity until and unless an external force is applied to it." (Wikipedia) So A large ship at rest will stay that way until we apply a force. The force will be equal to the mass multiplied by the acceleration. This acceleration will come from some type of propulsion system.

Well this seems simple enough. The larger the ship the larger the force needed to move it. This is true, but a large ship built out of metals we have today will not act a rigid body. Therefore the part or parts of the ship with the engines will accelerate faster than the other parts due to the inertia. It's like pushing on jello. You are adding a force to one part and it's moving, but the rest of it moves less and less the farther you get from the point of contact. This will lead to bending and eventually failure in metals and cracking and crumbling in concrete and ceramics.

Engine placement is also important to inertial effects. From an engineering point of view it's relatively easy to put a big engine or a few at the back of a ship. There is just one area for propulsion and no one has to worry about emissions. This will affect the ship like a building on the earth. Since the back of the ship will accelerate faster than the front of the ship there will be pressure generated. This pressure is like the pressure the base of a building feels under the weight of the building on top of it. If a building gets too heavy it will collapse because the base will melt. So if we accelerate too fast or have a ship that is too large it will also melt when we turn the engines on. We can get around that by placing many engines all over the ship, but if the ship is large enough the same problem will occur in the center.

The ship can also be accelerated slowly, but this applies to departure and arrival. Gravity on earth acts at 9.8 meters per second squared on the surface, so a sky scraper sized space ship can accelerate about 10 m/s which is actually really fast if it can be sustained. It would take this ship only 87 days to reach a velocity of one fourth the speed of light. That is 75,000,000 meters per second. At this speed relativistic effects begin to be important, so this is probably an unrealistic speed. Also while particle density is extremely low at these speeds there might be some type of friction. I can't find any data on the density of intergalactic space. That's outside my area of space physics. We might not know yet. Qualifiers aside it would take 16 years to reach the nearest star, Proxima Centauri, at one fourth the speed of light. That's not very long at all. Unfortunately it would take 100,000 years to reach the nearest galaxy, Canis Major Dwarf. The closes galaxy would take three times that long and it just gets worse from there.

So we have some compromises to make. The size of the ship determines the maximum acceleration and friction, and possibly other things I haven't thought of will limit the velocity. I'm not an expert on relativity so I'm not sure how important these effects would be on humans in a spacecraft. All I can think of is that it wouldn't effect anyone since they'd all be in the same reference frame. Relativistic speeds could make navigation more challenging though.

Well, I could talk about this forever. Since I'm starting to get off topic and I have to stop somewhere I'll stop here.