Space Travel Part Five : Miscellaneous Travel
There are a few other means of travel but all have limitations.
Magnetic Monopolar Transit
This would involve creating or finding (they may be rare natural occurrences) a magnetic monopole and attaching it to a vehicle. This monopole would thus be accelerated towards any north or south pole of a magnetic field, depending on its polarity, and so could simply cruise along magnetic lines of force with no need of power. It could engage and disengage with any field by shielding the monopole core and maneuvering itself by other means (such as low power ion thrusters). However this could not exceed light speed, and may not be able to operate in atmospheres unless it had a secondary means of propulsion, it is thus limited to interplanetary shuttling.
It has been proposed that rotating certain magnetoelectric material in the quantum vacuum field can induce fields that push the material forward without applying any energy or external force. This is one of the various means of creating such a free energy drive that ignores the conservation of momentum principle. However it in may in fact be impossible. Even if possible it produces such slight momentum that only very small or light objects could be propelled by it a low to medium speeds.
A manned vehicle need not carry a crew but could generate one on arrival, either as a sentient clone or some biological robot, or even a parasitic host seeking virus. However this is really just a crew issue and the craft still has to arrive by one of the earlier means. It could however be a nano scale craft and so very light and fast. Alternatively some spore or virus could be projected via a microwormhole or similar means.
The previous examples have all dealt with one particular technological means of transport but a hybrid drive would use several means for different situations. The current limitation on this is the size and space requirements for the different drives, as well as power requirements, but nano-technology will allow for miniaturization of drives and power units making this possible.