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I’ve looked in to the mathematics of Einstein’s General Relativity theory regarding the possibility of some form of wormhole, star gate, or warp drive using space contraction. I’ve concluded that while Einsteinian General Relativity does allow space contraction using magnetic fields, the space-time fabric is very stiff. The energy required for useful space contraction may only be available to Kardashev Type II or possibly even Kardashev Type III civilizations. Since humanity has yet to reach Kardashev Type I, this approach may be beyond our reach for some time to come. In fact, to reach the point where “warp drive” becomes possible it may be necessary to first travel to other stars.

Using Special Relativity

If we must travel to other stars before we can access the energy for a “warp drive”, how can we travel to other stars? We can travel to other stars using some form of impulse drive. What is “impulse drive”? “Impulse” refers to change in momentum, so an “impulse drive” is a propulsion system that operates through momentum transfer. Rockets are good examples of impulse drives.

Within impulse drives, there are options. Low power options such as conventional chemical rockets might work, but the journeys will be extremely slow. High power impulse drives would be much more interesting. Running at a sustained exhaust power of 3 gigawatts per kilogram, a vessel could sustain a physiologically-comfortable 1 g acceleration. At this acceleration, the vessel would approach relativistic speeds in about a year. Allowing for the same rate of deceleration at journey’s end, stars could be reached in about two years more than their distance measured in light-years. Since the nearest stars are several to tens of light-years away, journeys to these stars would last for several years or a few decades as measured by observers on Earth. Allowing for Special Relativity’s time-dilation effects, travelers would experience shorter journey durations of less than an decade for nearby starts.

High Power Impulse Drive

How would such high powers reach a starship? A good option might be to gather energy near the Sun and then beam it out to the ship. These beams might be radio-frequency beams to get better conversion efficiencies since lasers lose efficiency as the frequency rises and the wavelength shrinks. Use of radio-frequency beams might also enable the use of non-laser technology. For example, the beam transmitters could be high-power radar transmitters.

What about absorption of the beamed energy by the ship? The power required for 1 g acceleration is immense and might vaporize anything that tried to absorb the energy. While this might be excellent for clearing a path, it would be hard on the ship. However, there is an option other than absorption: almost all of the energy could be reflected. Reflection gives better momentum transfer than absorption, so reflection could significantly reduce the immense power requirements. One type of reflection might be particularly useful: total internal reflection. This type of reflection is used in fiber optic cables and in an ideal case involves zero absorption. With zero energy absorption a ship might be able to survive 1 g acceleration without being vaporized by the power source. Of course, a very small controlled amount of the beamed power might be absorbed to power ship onboard systems.

Slowing Down

Beamed power makes acceleration easy. Deceleration is the greater problem. With momentum coming from behind, how do you lose momentum without a medium to push against? One possible solution might be use of forward retroreflectors. Such reflectors ahead of a ship could reverse the beamed power momentum. There are challenges with this approach: this ship will have to stop reflecting the beamed power from its back, and more seriously the reflectors will tend to accelerate away from the ship. The ship may need to carry multiple retroreflectors and launch new ones as the old ones become less effective. On the other hand retroflectors running ahead of the ship might help sweep out debris from the ship path.

Robotic Probes

To prove out propulsion techniques, to evaluate collision risks, to scout ahead, and possibly to preposition infrastructure, wisdom suggests sending robotic vehicles ahead of manned missions. Possible missions include accelerated telescope probes. Such probes could use an effect called aberration of starlight to increase the apparent angular size and separation of astronomical targets near the direction of travel.

Would you like to share your thoughts on how to travel to nearby stars? Please leave a comment in the “Leave a Reply” section below.

I recently noticed that three of the five star systems listed in the Habitable Exoplanets Catalog with known potentially habitable exoplanets are listed as “Gliese” systems. Why “Gliese”? “Gliese” refers to a catalog of nearby stars (within 25 parsecs or about 82 light-years of the Sun). So these planets are all relatively close. Checking further, HD 85512 also has the identifier Gliese 370, so four of the five star systems with known potentially habitable exoplanets are listed in the Gliese catalog and are therefore relatively nearby. Continue reading →

In an analysis released a few days ago, the Planetary Habitability Lab indicates that a new potentially habitable exoplanet has been discovered. This confirmed exoplanet, Gliese 163c, orbits a dim low-mass red dwarf star almost 50 light-years from Earth. Initial estimates of its surface temperate are a roasting but potentially viable 332 K (140 °F/60 °C).  This is hot but not much above record high surface temperatures on Earth — and the hottest places on Earth may not have weather observing stations.  Also, this is an average, so there may be cooler places on this planet.  For instance, mountaintops might merely be warm due to cooling of air with height.  Also, since this planet orbits a red dwarf one side of the planet probably faces the star all of the time.  Locations near the permanent day-night line might be comfortably warm, although such locations may be windy due to dayside-to-nightside heat transfer winds.  Finally Earth’s deep oceans get cold with depth due to physical properties of water, and any deep oceans on Gliese 163c should exhibit a similar ocean temperature profile. Continue reading →