Rank #1: Caravans in Space
These are not dreamers - although they all have an ambitious dream - but well qualified experts. Several work at Nasa, others have day jobs at universities and research institutes.
Richard hears of proposals to build giant space stations and worldships - vessels packed with the best of humanity. These caravans in space might be lifeboats to escape an approaching asteroid or perhaps the first step to colonising the galaxy.
With contributions from Technical Adviser to Nasa's Advanced Concepts Office Les Johnson, Director of the Space Engineering Centre at the University of Arizona John Lewis, architect Rachel Armstrong and anthropologist Cameron Smith.
This programme first aired in November 2016.
Rank #2: Space Flight
Rank #3: How Do We Rule The Universe?
Rank #4: How to Survive in Space: Deep Space
Rank #5: Enceladus: Is There Life On Saturn's Moon?
Rank #6: 'I Nearly Drowned in Space'
Rank #7: How to Survive in Space: Into Orbit
Rank #8: Sounds of Space 1: The Solar System
Rank #9: Space 1977
Launched in 1977, the twin spacecrafts have explored the giant planets and their strange moons, investigated the boundary of the Solar System and changed how we see our place in the Universe. The probes even carry a message for aliens in the form of a golden record.
Retired NASA astronaut Ron Garan meets many of the original team still working on the mission, nursing the twin spacecraft through their final years.
Photo: The Voyager 2 spacecraft passes by Saturn in 1981 Credit: NASA