Go to Navigation (front of the ship) and select Earth. Scroll around to the golden coloured tab labelled Gift From The Lotus
and start a game. You will have to defend the cargo from 20 waves of enemies. These enemies can be tough, so make sure you have a good group of players. After the 20th wave, the mission will complete and you will earn this challenge.
** You do not actually need to play through all 20 waves in order to complete this challenge. I joined a mission during wave 12 and still unlocked the challenge after the 20th wave.
You will also earn the Ride the Wave achievement if you haven't already done so.
The Ride the Wave achievement in Warframe worth 44 pointsComplete 20 waves of Defense and successfully extract