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903 km/s is .003c, which would get you to Alpha Centauri in about 1500 years.

I looked at magnetic sails as a form of propulsion... unfortunately they are limited by the velocity of the solar wind which is less than .01c.  They might be useful for slowing down near the destination star system though.

I looked at electric propulsion, and the power requirements are way beyond any conceivable fission power plant.  Using multiple stages helps some, making so that a super advanced fission plant might be able to power the ship.  This would require a huge ship though, and even with many stages it is well beyond current technology.  Fusion or antimatter power might help some, though it seems quite possible that electric propulsion will never be practical for interstellar travel.

Well, if interstellar travel were easy, aliens would already have colonized Earth 

Nuclear electric has some advantages, and would probably be better than solar for a mars mission.  The problem with nuclear is that it has to be done on a large scale to be efficient.  In the 100s of kW range, the specific mass of the reactors (mass/power) decreases roughly by the square root of the amount of power.  This means that a 400 kW reactor might only be twice the mass of a 100 kW reactor.  In the several mW range that would likely be used for an NEP Mars mission, nuclear would have a specific mass at least as good as solar at Earth orbit and superior at Mars orbit.

I am not really sure about the whole nuclear safe orbit thing. Is it really necessary?  I don’t know of any reason why nuclear power at ISS orbit would be especially dangerous.

The main problem with the plans for the solar sail interstellar probe is that it requires a solar sail about an order of magnitude thinner than is currently available.  It is unlikely that the required aerial densities can be achieved in the near future, so such a vehicle is probably at least several decades away.

However, there are many interesting scientific questions that could be answered by such mission, so I thinking about whether or not a mission with similar objectives could be launched using current or near term technology.  The main alternative to solar sails is nuclear ion propulsion, so I decided to do some calculation on the performance of an NEP probe.

Assuming an isp of 10,000 and 50% propellant mass, the NEP probe would match the solar sail probe's maximum velocity of 14 au/year.  An isp of 10,000 is a little above that used in any current thruster but there are not any technical problems preventing higher isp values- shorter ranged missions use lower isp values because high isp comes at the expense of thrust.  Since efficiency increases with isp for ion engines, the overall engine efficiency should be over 85%.  If the reactor and thruster have a 10 kg/kW specific mass and are 25% of the vehicle's mass, the total burn time would be about 3.5 years.  This is about the lifetime of current ion engine thrusters.  10 kg/kW is achievable for current or near future high power nuclear power plants.  Nuclear power is not nearly as efficient on small scales though, so this would have to be a fairly large probe.  The remaining 25% should be sufficient for fuel tanks, structural mass, and a formidable array of scientific instruments.

Note that none of these numbers have been optimized.  Better performance could probably be achieved with a larger % of the mass being used for power instead of fuel and with an even higher isp.  If the thrusters and power plant can operate for longer than 3.5 years, the isp can be raised still further with a longer burn time. 

While the NEP version of the probe would be somewhat larger and more expensive than the projected solar sail version, the propulsive technology needed to make it work is available now.  With sufficient funding, it should be possible to launch the probe within 10 years.

Even without the increases in power plant efficiency, a mission to mars could increase thrust by decreasing isp.  The reduced isp engine would take substantially less than 2.5 years to get out of earth’s gravity well and it would still be much more efficient than chemical power.

Most of the recent progress in ion engines has gone toward solving this problem.  The current HiPEP engines have increased thruster lifetime by a factor of 5-8 since the ds1 ion engine.

[=http://en.wikipedia.org/wiki/Internet_troll]Internet troll

Well, my last statement probably oversimplifies the case.  However, you certainly cannot assume a particle's volume is directly proportional to its mass in quantum physics.

Actually ion engines get more efficient as power and isp increase because a greater portion of the energy is used on the efficient acceleration of ions and less on the inefficient ionization.  The ds1 ion engine had an isp of 3300 and about 60% efficiency while the new hipep engine has an isp of above 6000 and at least 80% efficiency.  The reason why ion engines have lower isp values is to increase thrust.  If power and efficiency are constant, then thrust and isp are inversely proportional to each other.

There is a lot of research that can be done on the ISS, such as finding ways to counter the negitive effects of 0g or investigating methods of 0g manufacturing.  If we do not complete the ISS, in 10 or 15 years we will have to build ISS 2 to do the research that ISS was supposed to do.

I think that the 20,000 lbs of supplies does not include the earth return vehicle or its fuel.  With the ERV, fuel, and supplies for the return trip there is 130,000 lbs.

  Terrorism also fails if the terrorists are ignored.  We must try to avoid making rash decisions under the guise of fighting terrorism.  We can harm ourselves more through poorly thought out over reactions to terrorism than the terrorists could ever harm us by themselves.

Friction and temperature are not concepts that are applicable on the sub-atomic scale.  The photon has no rest mass.  However it is traveling at the speed of light.  Due to relativity, an object's apparent mass is equal to its rest mass times (1-v^2/c^2)^(-1/2).  Since photons travel at the speed of light, in this case (1-v^2/c^2)^(-1/2)=infinity.  0*infinity is undefined, but in practice the apparent mass of a photon can be found using E=mc^2.

On March 2, the ESA launched [http://en.wikipedia.org/wiki/Rosetta_space_probe]Rosetta space probe.  Its itinerary looks very impressive with 3 Earth fly-bys, 2 asteroid fly-bys, a Mars fly-by, and ending with a landing on a comet.