Ellie Goulding

'I Know You Care' is about my dad. And I haven't seen him for a long, long time. And my parents divorced when I was really young. And I guess I just wanted a - it was my way of saying that I wasn't bitter or angry anymore. I was just sad and just felt like something was missing.

Supplying fuel for a Mars expedition from the lunar surface is often suggested, but it's hard to make it pay off - Moon bases are expensive, and just buying more rockets to launch fuel from Earth is relatively cheap.