Half a lifetime to leave the solar system

After more than 41 years of flying, the twin Voyager spacecraft have finally reached interstellar space. It is a journey that has taken 90 per cent of my professional career and more than half my lifetime. And it's a powerful demonstration of how long it takes to travel across the solar system, and how far away the stars are on human scales of time and distance.

In 1977, when my hair was considerably darker and longer than it is today, I attended the launch of Voyager 2. Then I followed its journey over the following 12 years, visiting mission control as it flew by all four of the giant planets: Jupiter, Saturn, Uranus and Neptune. Unfortunately, Pluto was not in the right position for Voyager to pay a visit, but the New Horizons probe, which itself took nine years to make the journey, passed the dwarf planet in 2015. I also attended that flyby, to complete my vicarious exploration of the solar system.

Since passing the planets, the Voyager probes have been on what is called the interstellar mission to reach out beyond the heliosphere, the region dominated by the sun and its powerful solar wind, and enter the space between the stars. Now more than 16 billion kilometres from Earth, they have finally crossed that boundary and are reporting back on the conditions of interstellar space.

During all this time it wasn't just my own hair that changed length and colour. I watched my journalistic colleagues and the mission scientists all grow old and grey. Some even died during this journey out of our solar system. When it comes to deep space travel using current technology, a human lifetime is barely enough.  

It now takes about 20 hours for a radio signal to reach Voyager 1. In astronomical terms, that is almost one light day. At its current speed, it will take roughly 15,000 years to cover one light year and will take about 40,000 years before the Voyagers come close to another star. On a galactic scale, these probes are moving at a snail's pace.

That means until we find faster ways of getting around, humans will be restricted to the inner space relatively close to the Earth. Even a trip to Mars would take six or seven months one way, which will require a dedicated and hardy crew. I expect few people would be willing to endure the multi-year journeys it would take to reach the outer planets and beyond.

A number of proposals have been put forward to deal with the fact that space is really, really, unimaginably, mind-bogglingly big, and our spaceships are woefully slow.

One of the most time inefficient methods is called the Generation Starship, an idea that has been around since the 1920s and often portrayed in science fiction.

A Generation Starship doesn't travel much faster than our current spaceships, but the idea is to make the journey more comfortable using a Noah's Ark approach. The ship would be a huge self-sufficient space colony housing hundreds, or even thousands of people, animals, plants, farms and factories. It would set off on a centuries-long journey to a nearby star.

Along the way, the original crew would die off. Their children would take over running the ship, then the grandchildren, until many, many generations later, they reach their destination. One can only imagine the social issues that would arise with a large group of people living in a tin can for their entire lives.  In fact, it's a complex problem that serious ethicists have engaged with. 

Alternative propulsion methods like the plasma drive offer some hope for crossing the great gulfs between stars at higher speeds. This kind of engine does not put out as much power as a chemical rocket in the short term, but can run continuously for years, constantly accelerating, ultimately reaching much higher velocities. But this technology has not made it out of the laboratory setting. The same is true for other exotic propulsion systems like nuclear rockets and laser powered light sails.

Even if a new propulsion system is developed that can accelerate spaceships up to speeds approaching that of light, there are new problems that arise. One is that dust particles drifting through space would impact with the energy of grenades at those speeds. Shields up!

Then there are the relativistic problems posed by Albert Einstein, such as time dilation where your time slows down relative to your friends back home, so they age much faster than you do and may not even be there by the time you get back.

Unless the fictional warp drive is developed, which allows imaginary starships to zip through space at super-luminal speeds, humans may not be the best subjects for exploring deep space. Let the robots, who don't mind spending years travelling, do the exploration, while we remain on Earth gathering data from their instruments and peering into our telescopes to reach out  to the stars.

Humans have the remarkable ability to abstract, so once we have discovered new worlds with our remote senses, we can travel anywhere in the universe in our imagination rather that spending more than a lifetime trying to get there ourselves.