The US Army parachute team Golden Knights perform during the opening ceremony of the 50th anniversary of the Apollo 11 moon landing at Space Center Houston in Texas, the United States, July 20, 2019. (Photo: Xinhua)

People visit the mission control room during the 50th anniversary of the Apollo 11 moon landing at Space Center Houston in Texas, the United States, July 20, 2019. (Photo: Xinhua)

Visitors look at the gravity simulator during the 50th anniversary of the Apollo 11 moon landing at Space Center Houston in Texas, the United States, July 20, 2019. (Photo: Xinhua)

Visitors select souvenirs during the 50th anniversary of the Apollo 11 moon landing at Space Center Houston in Texas, the United States, July 20, 2019. (Photo: Xinhua)

An image of a Saturn V rocket, which was used during the Apollo 11 moon landing mission, is projected on the Washington Monument in Washington D.C., the United States, July 20, 2019. The projection show is to celebrate the 50th anniversary of the Apollo 11 moon landing. (Photo: Xinhua)

An image of a Saturn V rocket, which was used during the Apollo 11 moon landing mission, is projected on the Washington Monument in Washington D.C., the United States, July 20, 2019. The projection show is to celebrate the 50th anniversary of the Apollo 11 moon landing. (Photo: Xinhua)

An image of Neil Armstrong's footprint on the Moon is projected on the Washington Monument in Washington D.C., the United States, July 20, 2019. The projection show is to celebrate the 50th anniversary of the Apollo 11 moon landing. (Photo: Xinhua)

An image of a Saturn V rocket, which was used during the Apollo 11 moon landing mission, is projected on the Washington Monument in Washington D.C., the United States, July 20, 2019. The projection show is to celebrate the 50th anniversary of the Apollo 11 moon landing. (Photo: Xinhua)