The Interstellar Index is about interstellar travel, that is – Spaceships that travel to other stars. But what does it really take to send a spacecraft through the void of space to those distance sea of Suns? For simplicity, we can consider the speed requirements for a linear distance profile to an effective Alpha Centauri distance of 4.3 light years (LY) or 272,000 Astronomical Unites (AU), where a 1light year = 9.46×1016 m = 63,240 AU and an astronomical unit AU is the distance between the Earth and the Sun, where 1 AU = 1.496×1011 m. For this simple analysis we can ignore the fact that Alpha Centauri is out of the ecliptic plane. We can also ignore the obvious acceleration requirements. The table below shows typical journey times to reach this distance for given constant velocities. The data clearly shows that to reach the nearest star in a time frame of order a century or less, a vehicle must travel at a cruise velocity of >10,000 km/s, which equates to >3% of light speed. It is worth noting that for mission durations of approximately 50 years the spacecraft must reach approximately 1/10th of light speed and for mission durations of around a century or so the spacecraft must reach approximately 1/100th of light speed. For much faster missions of order a decade or so, the vehicle must reach a speed of order 1/3rd of light speed.
To put these speed requirements into perspective, we can compare this to the fastest spacecraft that we have so far sent out into deep space. This is the Pioneer and Voyager spacecraft. Pioneer 10 was launched in March 1972 and is currently travelling at around 13 km/s or 2.6 AU/year. Pioneer 11 was launched in April 1973 and is currently travelling at 12 km/s or around 2.4 AU/year. Voyager 1 was launched in August 1977 and Voyager 2 in September 1977 and both are travelling at around 17 km/s or 3.6 AU/year. In January 2006 NASA also launched the New Horizons mission, which will visit Pluto and move on to the Kuiper belt. It is currently travelling at around 18 km/s or 3.8 AU/year. To reach Alpha Centauri we must cross a vast distance of 272,000 AU. At current speeds, most of these spacecraft would reach their nearest line of sight star in many tens of thousands of years. For any technology moving at these speeds presents such a jump from our current capabilities that star travel looks to be prohibitive in the near-term. However, future blog articles will show that in fact the situation is not so difficult as presented here.
***TSL***