Solve Global Warming and make Interstellar Travel possible at once
We could not only save our planet but also make possible to reach Proxima Centaury by the end of our century. And it might cost less than the International Space Station.
About a year ago, I wrote an article on using a large fleet of solar sail spacecraft to compensate for the released CO2. It seems to be far the cheapest option to save our planet of the effect of Global Warming. However, that is not the only benefit. We could use them for interstellar travel.
Power of Sun
The fleet of solar sails probes to combat Global Warming will need to cover 1.2 million sq. km. That represents the power of about 10 TW ~ 120.000.000 Newton force provided by solar radiation (assuming F slightly higher than 9.08 μN/m2 at 1AU — the distance between Sun and Earth). That is enough force to accelerate full-scale Interstellar Spacecraft with weight up to 10.000.000 kg by 120 m/s2 = 12 g (12 times the acceleration we do experience on Earth). The Spacecraft could have a solar sail of a few sq. kilometers and a lot of apparatus.
The fleet of solar sail probes protecting Earth from the effects of Global Warming is parked close to the L1 point between Earth and Sun. It would need to form a convex shape to reflect the beam of light into a single point. All that solar radiation will aim into the sail of our Interstellar Spacecraft. Even with an average 50% efficiency (depending on the angle of the probe), we would have an abundant of power to accelerate Spacecraft.
How fast we can go to spread life?
If we would achieve 20% of the speed of light (0.2 c ~ 60.000.000 m/s) the Spacecraft will reach Proxima Centauri solar systems in less than 22 years in Earth time (4.244 light years). The time passed on Spacecraft time will be almost the same. At that speed, the time dilatation is about 1%.
If humans should be on board, we will need to accelerate approximately for 6.000.000 seconds with 1g. That sounds like a lot, but every hour has 3600 seconds, so it represents just a bit less than 70 days. However, Spacecraft would make 180,000,000,000 km within these 70 days. That is 1200 AU (1 AU = the distance between Sun and Earth). Too far out of our Solar system to reflected even carefully pointed laser beam to a giant solar sail.
So we would need to accelerate much much faster.
Let’s assume that a medically seduced crew with special equipment could survive 50 g acceleration. Spacecraft will need 34 hours to achieve 0.2c (20% speed of light) and traveled of 24 AU. That is still too far away to be propelled to such speed. We will need to aim to solar sail 6 AU to speed-up to 0.1c. However, the time to travel to Proxima Centaury will be almost 50 years.
What about a robotic mission with 500 g of acceleration? It would take just 3.4 hours and 2.4AU to achieve 0.2 c and 0.6 AU if we would like to achieve just 0.1 c. Our Interstellar Spacecraft will stay quite close to the fleet of solar sails and in a directly focused beam of the reflected solar radiation. This acceleration is also survival for plant seeds or animal embryos/stem cells. So life could be eventually spread.
To prolong the acceleration phase, we could equip the solar probes with cheap short-wavelength lasers. These will be powered by solar panels. Every 100W of laser beams per probe would mean 12GW of total power. These could be also very useful for Spacecraft direction steering. As it will need to be pointed very accurately as course correction during the flight will be practically impossible.
Top speed flyby
What if we could build much smaller and robust Interstellar Spacecraft with higher acceleration. For example, Breakthrough Starshot design expects 10.000 g acceleration with a spacecraft of a few meters in diameter.
With that acceleration, the travel distance to achieve 0.2 c is just 0.12 AU. The Spacecraft will accelerate for 10 minutes. To get to 0.5c (50% speed of light) we would need to keep the beam focus into 0.75 AU distance. That seems possible even that the size of the spacecraft is much smaller. More and more probes from the fleet of solar sails could be gradually involved to compensate the part of the beam which would miss the Spacecraft. It would shorten the time to travel to just less than 9 years for an observer on Earth! We will learn more about Proxima and Alpha Centaury solar systems just in 15 years after launch. That’s about the duration we do explore distant objects in our solar system nowadays.
Unfortunately at speed of 0.5c would a small Spacecraft rush through the solar system without any option to even slow down. Even the solar radiation of all three starts of Alpha Centaury would not be enough to slow the Spacecraft down. It will spend just a few hours within the explored solar system. However, It could take photos, make distance measurements and observations. Practically any collision with more than a few atoms would destroy the Spacecraft.
Could we find a way to slow it down?
The kinetic energy at 0.2c is enormous. Each kilogram is like the most powerful nuclear bomb. Nevertheless, a larger Mother Spacecraft equipped with a strong power source could deploy a smaller and lighter Baby Spacecraft and slow it down by laser as it is closing to the Proxima Centaury.
The laser beam could be even bounced back multiple times between the solar sails of both Spacecraft reducing the power need by a factor of 10x. We will still need a powerful laser beam (~GW) to slow down Baby Spacecraft with the weight of a few kgs. All slow-down has to happen within a few hours before the distance between these two ships is too high. That leaves us again with a deceleration of a couple of hundred g. So the seeds of life could survive. Ideally, multiple spacecraft babies will be deployed as passing around the star.
The maneuver could be used for the correction of the interstellar navigation error, which wouldl cumulate over the years. So Baby Spacecrafts get closer to its target locations and Mother Spacecraft bounces towards its next star to explore.
As a result, Baby Spacecrafts would slow down and start orbiting and exploring the solar systems for years. They could study all planets, its moons and measure stars of Alpha and Proxima Centaury in detail. They will use its sail to navigate around and could leverage the Mother Spacecraft to boost-up its communication signal towards Earth.
How much it would cost?
We would not need to worry about the cost of the solar fleet orbiting our Sun. These probes will be built anyway to protect Earth from the impact of Global Warming. As part of that endeavor, we would already master the technology of solar sailing.
There is no need to build extremely expensive Earth-based lasers as suggested by Breakthrough Starshot design. Hence only a small incremental cost would be required to launch the Interstaller Spacecrafts.
The smallest version designed for interstellar flyby would leverage most of the components from the solar probes. We could send thousands to each of the nearest stars for a few billion USD in total.
To build the pair of Spacecrafts Mother and Baby, we would need to master the nuclear fusion reactor first to power. Otherwise, there would not be enough power for the laser. Baby Spacecraft could leverage some ion drive eventually a positron anti-matter drive to navigate itself. These highly efficient engine converting energy/radiation into momentum to power a spaceship. Both technologies are being developed and would be available by the time, we have mapped the nearest start with flyby interstellar explorers.
Proxima Centauri b is an exoplanet orbiting in the habitable zone of the red dwarf star Proxima Centauri. We could park our Spacecrafts there and explore the planet. Perhaps we could find or seed a new life there by the end of 21. century. Let’s save our Earth and expand to Universe!