2001 – 
Chris A. Hadfield becomes the first Canadian to walk in space. (Endeavour STS-100 mission to ISS, launched April 19) Today’s Wake-Up Song was “Take It From Day to Day” by Canadian Stan Rogers –played for Hadfield in honor of the space walk.
Hadfield and Parazynski connected cables that will feed the initial electrical power, computer commands and video between the station and the new robot arm, which is also known as Canadarm2. They installed and deployed an ultra high frequency communications antenna that will enable the station to conduct future space walk communications and that will improve future shuttle-station communications. Then, they released launch bolts that held the Canadarm2 secure during its trip to orbit, unfolded the arm and prepared it for control from inside the station.
Canadarm2 is a “bigger, better, smarter version” of the space shuttle’s robotic arm, per NASA’s description on its website. Capable of handling large payloads and assisting with docking the orbiter, the Space Station Remote Manipulator System, or SSRMS (as Canadarm2 is formally titled) can be attached to ports spread throughout the space station’s exterior surfaces.
1983 – Landing of Soyuz T-8 a crewed mission to the Salyut 7 Soviet space station. Shortly into the mission, the spacecraft failed to dock with the space station. Launched April 21
Crew: Serebrov, Strekalov, Titov, Vladimir.
1971 – Soyuz 10 launched to dock with the first space station Salyut 1. Mission duration however was only 1 day 23 hours and 46 minutes. The docking was not successful and the crew, Vladimir Shatalov, Aleksei Yeliseyev, and Nikolai Rukavishnikov, returned to Earth. Post-flight analysis indicated that the cosmonauts had no instrument to provide the angle and range rate data necessary for a successful manual docking when the automatic docking failed.
1970 – The first Earth Day is celebrated.
Every year – April 21-22 The usual peak of the Lyrids Meteor Shower: Associated Comet C/1861 G1 (Thatcher): Meteors per Hour 15
Birthdays
1976 – Yelena Olegovna Serova is a Russian politician and former cosmonaut. Her selection group was RKKE-14 group in October 2006. On 25 September 2014, she traveled aboard Soyuz TMA-14M spacecraft to serve as a flight engineer for Expedition 41/42 and spent 167 days in space.
1891 – Sir Harold Jeffrey was an astrogeophysicist and the first to hypothesize the Earth’s liquid core; Jeffreys also made contributions to our understanding of tidal friction, nutation, general planetary structure, and the origin of the solar system.