Solar Sails in a Globular Cluster

Whenever a sci fi writer sits down to write a space opera, he/she must decide what mode of space travel to use. Can our ships travel faster than light? If not, how do we deal with the vast distances that must be traveled?

Star Wars introduced the idea of setting a story “a long time ago in a galaxy far away…”. Why not place the story in a globular cluster, a dense spherical collection of stars that orbits the galactic core? Stars could conceivably be on the order of 0.01 light years apart in this setting, much closer than the stars in our neighborhood.

I had hoped that the densely packed stars would provide enough energy to let the sail accelerate for the whole journey between suns. Unfortunately, my calculations show there just is not enough light in the regions between stars to really matter. A beautiful idea killed by an ugly fact!

However, a set of satelites equipped with mirrors and/or lasers could be placed at each star supplying the necessary force for acceleration or deceleration. If I did my calculations correctly, one could build a ship with a mass of 50 metric tons (just for reference, the Starship Enterprise was 190,000 metric tons), solar sails with an area of 100 km^2 (the sail mass would be another 10 metric tons if we suppose advanced materials with .1 g/m^2), and an energy flux about 140 mega watt / m^2 (that’s about 100,000 times larger than the flux of light from the sun to the earth).

The journey would start with an 8 grav acceleration. That might be a little rough, but perhaps the people who live in this globular cluster are hardy specimens. They should eventually reach a terminal speed of 1% the speed of light. This would allow transit between nearest stars on the order of one year (!), but the trip would be fraught with peril. What if the other end does not start firing its laser on time or on target? You might not be able to stop. If you want to play it safe, you send a signal to your destination and wait for a response. (Of course, I am not even mentioning the possibility of running into something at speed)

If you wanted to fight an interstellar war, attacking a system you did not control might be very difficult. You might have to make do with a drive-by shooting. You’d have to be careful, the enemy would be likely to dump small rocks along your approach path, so you might have to settle for a distant trajectory. Could you still make your targets then? Certainly not that hard if you are accustomed to shooting womp rats from a rickety desert speeder.

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