User:Mcherrin/sandbox

=Interstellar Transfers=

Summary
Interstellar transfer is the orbit path between two solar systems. The orbit path depends on the amount of energy the transfer vehicle can generate. The travel time for these transfers is dependent upon the path chosen between the two solar systems. The distance between solar systems is typically hundreds of thousands of AU, and is normally expressed in light years.

Objective
The goal of interstellar travel would be to find a planet, which is probably acceptable for human life. In order to get to this planet, a transfer vehicle would need to leave our current solar system and enter the space between solar systems known as interstellar medium. Once the vehicle has reached the target solar system, the transfer vehicle will enter the gravitational influence of the main body. This is known as using the method of patched conics.

Cosmic rays
The transfer vehicle would first leave the safety of the Earth’s magnetic field. Cosmic rays would bombard the vehicle for the entire time of flight. The transfer vehicle will also need to navigate through the rest of the planets’ gravitational fields. Upon entry of the target solar system, the transfer vehicle will be bombarded with a new level of cosmic rays output by the main body. The worst case would be if the cosmic rays were significantly higher than that of our solar system. Cosmic ray shielding and the ability to withstand/avoid large asteroids is a must for interstellar transfers.

Escape velocity from solar systems
The first task for interstellar travel is to determine the change In spacecraft velocity for leaving the solar system. The required velocity for escaping the gravitational influence of a mass is given by the following equation derived from the two body dynamics problem. V_esc=√((2*μ_SS)/R) Note: These values were found using the radius of Earth's orbit.

These values represent the minimum change in velocity to exit the sphere of influence. For a transfer between two solar systems, the escape velocity would need to be much greater than these values in order to lower the time of flight. For space travel between multiple solar systems, the transfer vehicle will need to be captured by the target solar system and refuel for its next mission. The transfer vehicle will enter the solar system and will need to avoid orbiting objects around the main body. These orbiting bodies include asteroids and planet. The transfer vehicle will need

Transfer types
There are many types of orbital transfers possible between solar systems. The most energy efficient transfer between solar systems would be a Hohmann transfer (provide link). The travel time would be on the order of millions of years. With travel time being of particular interest, the fastest method would be using an engine provide thrust for the entire trip. The ship would accelerate for half of the trip and then decelerate the other half of the trip. The transfer would resemble a straight line between the solar systems, or a highly eccentric hyperbolic orbit relative to the center of the galaxy. The following table provides an estimate of travel times for a hohmann transfer and two hyperbolic orbits. These values were found using the approximate distance from our solar system to the center of the galaxy and the approximate mass of the main body of the galaxy. The hohmann transfer values also assume the two galaxies are in the perfect spot in the orbit to perform this maneuver. Time=1/2*(2π/μ*a^(3/2)) Note: These values were found using the radius of the Sun's, Vega's and Tau Ceti's orbit about the Milky Way Center, ,.

When entering the target solar system, the transfer vehicle will need to slow down to enter a parking orbit around the target planet or to enter the planet’s atmosphere and land. This means the transfer vehicle will need an additional amount of velocity change on top of the already expended amount during the interstellar transfer.

Interstellar Travel Using Constant Acceleration
In order to reach the local solar systems within a human life span, the velocity of the space craft will have to approach the speed of light. For a human to survive this, a constant acceleration less than 3Gs is required for comfortable travel. To achieve this constant acceleration, the spacecraft engines will need to be producing a thrust force that is slightly decreasing over time.