Appreciating the challenges of interstellar travel

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

17 November 2024 

A reader sked me to calculate how long it would take to travel to the nearest start to the sun. The answer is that it depends on how fast one is moving. The nearest star is Proxima Centauri and it is over 40 trillion km away. It is so far that a beam of light travelling at 300,000km/s (over one billion km/h) takes more than four years to get there. Yes; if it went out today, its disappearance would only become apparent to us in the year 2029!

Now, the highest speed ever reached by a man-made object is 176km/s or 633,600km/h recorded by the Parker Solar Probe which studies the sun. At this speed, the spacecraft would take over 63 million hours, or about 2.6 million days, or about 7,200 years. Obviously, no human being can live that long.

The alternative is to make a spacecraft that can travel a lot faster, say, 1,000 times the current record. That is, at least 176,000km/s (over 600 million km per hour!). At that speed (which is more than half the speed of light), the spacecraft would take about 7 years to get there. Now that is not a long time to wait; it is within the lifetime of a human being.

It is also not unusual. Humans have sent our spacecrafts on such long journeys. The longest being the Voyagers (I and II) which have been flying non-stop for the last 47 years (since 1977). They are currently 25 billion km and 20 billion km away, respectively. Voyager-I is moving at 17km/s and, if it was heading towards Proxima Centauri (which it isn’t), it would take over 70 thousand years to get there!

To get an interstellar spacecraft to reach speeds of hundreds of millions of kilometres per hour would require a huge amount of fuel. In addition, the craft would need to be accelerated carefully if it is carrying humans. Our bodies cannot survive greater than 5 times Earth’s gravity.

Perhaps the best acceleration should be that equal to earth’s gravity – adding 36km/h every second. At this rate, it would take about 200 days or seven months of continuous acceleration and then the engines can be turned off. In that time, the craft would travel about 1.55 trillion km. This is very far beyond the current distance of the Voyager spacecrafts but still less than 4 percent of the journey to Proxima Centauri.