Reducing insolation could also be accomplished with space-based mirrors or other structures. One proposal here involves the placement of roughly 16 trillion small disks at a stable position 1.5 million km above the Earth. Each disk would have a diameter of 60 cm and would weigh just one gram. They would not be true mirrors, but would scatter enough sunlight to reduce the insolation by 2%, which be sufficient to cool the planet by 2°C. Getting these disks into place and then keeping them there would be a challenge, and it is estimated that it would take 10 years to put them into place using a special type of gun that could transport up to 10 million of them at a time. The total cost could be 5 trillion dollars every 50 years (the lifetime of the disks). This sounds a bit like science fiction, but it has been developed by a group of prominent astronomers and physicists, so we should assume it is viable, but nevertheless very costly and not something we could easily control. As with all of the insolation reduction schemes, this would do nothing to deal with the problem of ocean acidification.