Landing on Mars: 'We can't just assume it will work again'
Putting a robot safely on the surface of Mars is always an immense challenge, however many times you've done it in the past. Allen Chen played a key role in the landing of Nasa's Curiosity mars rover in 2012. Now, he's back to lead the effort to put the Perseverance robot on the Red Planet. He spoke with our science correspondent Jonathan Amos.