I think I said this in the last thread about interstellar spacecraft, but rockets are probably the wrong paradigm for interstellar travel. People are right to point out that the amount of energy and mass ratios needed are huge. However, if instead you leave your reaction mass behind, and use reaction mass from where you arrive, then this is much less of an issue.
The classic example of a system which does something like this is the Bussard ramjet. Another would be beamed power or beamed propulsion, ala the Moties from Niven's The Mote in Gods Eye or Leik Myrabo's work. My personal favorite idea is using electromagnetic interactions to accelerate using the Sun itself as the reaction mass, and then doing the same process in reverse at the arrival star to generate power at the other end. The power could be put in using a beamed system or other system where the infrastructure would stay in this star system. But the energy could then be used at the other end to either power needs for exploration or colonization, or to re-accelerate the ship for another trip to another star.
To go travel to another close star in tens of years, you will need to have around 10% of your mass energy in kinetic energy (a Lorentz factor of around 1.1). So, as a first approximation, if energy alone were the issue and a reaction mass the size of a sun were used, an amount of energy equal to the US energy consumption in 2008 could accelerate about 30 tons to 10% of c (see http://en.wikipedia.org/wiki/Orders_of_magnitude_%28energy%2...). This is big, but not out of the range of human capabilities. And if the energy were recyclable many times, then this amount of energy would be essentially the largest investment in the creation of a true reusable starship.
This is interesting, because it gives us a good minimum cost for such a starship. If we assume a typical cost of energy of 10 cents per kWh, and a 60 ton vehicle (around the size of a Space Shuttle orbiter) going 10% of c, this gives us $750 billion for the cost of energy alone. This is about six times the inflation adjusted cost of the Apollo program.
The classic example of a system which does something like this is the Bussard ramjet. Another would be beamed power or beamed propulsion, ala the Moties from Niven's The Mote in Gods Eye or Leik Myrabo's work. My personal favorite idea is using electromagnetic interactions to accelerate using the Sun itself as the reaction mass, and then doing the same process in reverse at the arrival star to generate power at the other end. The power could be put in using a beamed system or other system where the infrastructure would stay in this star system. But the energy could then be used at the other end to either power needs for exploration or colonization, or to re-accelerate the ship for another trip to another star.
To go travel to another close star in tens of years, you will need to have around 10% of your mass energy in kinetic energy (a Lorentz factor of around 1.1). So, as a first approximation, if energy alone were the issue and a reaction mass the size of a sun were used, an amount of energy equal to the US energy consumption in 2008 could accelerate about 30 tons to 10% of c (see http://en.wikipedia.org/wiki/Orders_of_magnitude_%28energy%2...). This is big, but not out of the range of human capabilities. And if the energy were recyclable many times, then this amount of energy would be essentially the largest investment in the creation of a true reusable starship.
This is interesting, because it gives us a good minimum cost for such a starship. If we assume a typical cost of energy of 10 cents per kWh, and a 60 ton vehicle (around the size of a Space Shuttle orbiter) going 10% of c, this gives us $750 billion for the cost of energy alone. This is about six times the inflation adjusted cost of the Apollo program.