## Why Mars Is Not the Limit For Human Space Flight 256

"Mars is not just the next or most accessible human destination, it is the ultimate one," writes Louis Friedman, executive director emeritus of The Planetary Society. He says the concept of manned spaceflight is progressing so slowly, and robotic developments so swiftly, that Mars will be the first and last planet humans set foot on. "By the time human spaceflight technology is theoretically capable of journeys beyond Mars, humans in modern space systems will be virtual explorers interacting with the environments of distant worlds, but without the baggage of physical transportation or presence." Mark Whittington disagrees, saying Friedman is demonstrating Clarke's First Law, and that the history of human exploration is rife with periods of stagnation interrupted by technological achievement that led to swift progress.

## Re:Where are the FTL comms coming from? (Score:5, Informative)

Just to be pedantic, by definition, as soon as you have FTL transportation, you have FTL communication. Depending on the nature of the FTL transportation, it may be the "van loaded up with tapes" level of high-latency FTL communication, but it's still faster than light....

## Re:Not what he meant by virtual: (Score:5, Informative)

I disagree. It is certain that if a bunch of molecules were arranged the same as yours are, including the electrical charges, there would be a person who is you. (Naturally the original you would still feel that your consciousness had

notdeparted him, but it would also exist equally in the new body.) So, unlike speed-of-light travel, there is no theoretical barrier to teleportation.## Re:Sadly, no, we are not advancing (Score:4, Informative)

Good news! NASA already has a high-speed relay in orbit around Mars - the Mars Reconnaissance Orbiter [wikipedia.org]. Speeds of up to 6Mbit/s from the orbiter back to Earth (it went past a hundred terabits total [nasa.gov] a few years ago), and up to 2Mbit/s as a relay for surface probes such as, erm, Curiosity.

NASA's Mars Odyssey and ESA's Mars Express orbiters can also act as data relays. Bandwidth is still a definite problem for Curiosity and the like, but it's already sent back some pretty impressive imagery [nivnac.co.uk] that's somewhat above Viking-level...

If you want more data, get some geostationary (areostationary?) communications satellites around Mars - currently surface probes are limited to relaying data when a probe is visible in the sky - and invest in the Deep Space Network [wikipedia.org] back on Earth.

## Re:Dead wrong (Score:5, Informative)

On a trip to Alpha Centauri, to take advantage of relativity, you'd pretty well need 1 G of acceleration. At 1 G for a year you'd be close to light speed and not even 25% there. A few more months ship time and it would be time to slow down. Perhaps 3 years ship time and 7 years Earth time. (Numbers pulled out of my ass but fairly close).

Any less acceleration and you're not going to get much of an advantage from relativity. Any faster acceleration would be uncomfortable but even with inertia dampers so you can accelerate to 99+% of light speed instantly, it'll still mean less then 5 years passing on the Earth.

That 1G acceleration helps much more on longer trips, 30 light years only takes perhaps a year more ship time and still only 33 years pass on Earth.

There was a chart around that I can't find right now that showed trip times, if you just accelerate all the way it was something like 30 years to Andromeda and only 70 years ship time to the edge of the Universe. Of course by the time you got there the edge would be 27 Billion light years further away.

One big problem is how do you protect your ship? At 90% C, hitting a grain of sand would be deadly and at 99.99999999% of C, light itself gets pretty energetic, little well a molecule.

## Re:Dead wrong (Score:4, Informative)

I think I'm still misunderstanding you. If the reference frame is Earth and you are not considering time dilation or the elapsed time from the POV of the space traveler then the total elapsed time would just depend on the average speed of the ship and the amount of time he spent "puttering around".

Or perhaps you want to consider time dilation. I've always like the Lorentz time dilation equation: T = To / sqrt(1 - (v^2/c^2)) where T is the elapsed time for a fixed reference frame observer on Earth, To is the elapsed time for the moving clock or person, and v is the constant or (roughly) average velocity of the ship (or the clock that is in motion wrt the fixed reference frame).

Assume that you have a ship that quickly accelerates to 0.93c (so that the acceleration time is negligible) with an average velocity of 0.9c. It would take a photon 40.6 years to make a round trip to Gliese 581. The ship is traveling 10% slower and will take 10% longer for a trip time of 44.66 years. That is how much time will have elapsed for clocks on Earth. That's T. So what is the elapsed time To for the traveler? You could use this time dilation calculator [gsu.edu] or just plug and chug.

So T = 44.66 years and v=0.9(299,792,458 m/s). The radical becomes 0.43589. So 44.66 = To / 0.43589 or To = 44.66 * 0.43589 = 19.466 years or around 19 years and 6 months.

At a more realistic average speed for current abilities with a nuclear pulse propulsion system of .05c the trip would take 20 times longer than a photon or 812 years from earth clocks. So T = 812 years and v=(.05)(299,792,458 m/s). The radical becomes 0.99875. So 812 = To / 0.99875. To = 812(.99875) = 810.984 years. Just one year less time will have elapsed for the astronaut's ship in that case.