Editor 's note : Buzz Aldrin , whose new book is `` Magnificent Desolation , '' was one of the two American astronauts who were the first people to set foot on the moon . Buzz Aldrin walks on the moon in a photo taken by Neil Armstrong , his colleague on the 1969 mission . ( CNN ) -- Four decades have passed since the summer of 1969 , when Neil Armstrong , Mike Collins and I flew America 's first lunar landing mission . The passage of time has not faded either the memory of that summer or the importance of what we achieved , for our mission was about more than just exploring the moon . On July 20 , 1969 , Neil and I were peering out the window of our lunar lander , the Eagle , as it descended toward the lunar surface . The ship 's computer was steering us toward a field of boulders the size of cars . That same computer -- with less power than today 's pocket calculators -- was signaling that it was overworked and dangerously overloaded . Our single tank of fuel was nearly empty as we approached the surface , invisible to us , cloaked in a cloud of swirling dust . Neil took manual control and flew us toward a smoother terrain . Then , as the shadow of our landing gear appeared etched onto the surface in the gloom , a light on our console flashed that contact had been made . `` Houston , Tranquility Base Here , '' Neil radioed to the listening world back home . `` The Eagle has landed ! '' For more than two hours , we explored the moon 's dusty surface . We could easily tell that the planet we had landed on was very different from our home . The horizon visibly curved away in the distance , a sign of the moon 's much smaller landscape . When my boot struck moon dust , the soils flew away in a straight line , a sign of the lighter gravity load , one-sixth that of Earth . When I looked around the stark landscape , it was a magnificent desolation . An uninviting world greeted us in eerie silence , hostile to our presence and to all visitors from Earth . The following day , we rocketed up off the surface , rejoined Mike Collins orbiting alone in our command ship , the Columbia , and headed home to a hero 's welcome . That welcome took us all around the world in parades , banquets and greetings from millions . I was astonished that so many had followed every facet of our flight from start to finish , almost as if they were part of the adventure . That spirit , of a world come together in celebration of a peaceful scientific achievement , was perhaps our greatest legacy . More than just exploring a hostile new world , Apollo 11 was about bold vision and great risk , about the obstacles a great nation could overcome with dedication , courage and teamwork . It was about choosing a goal that exceeded our grasp -- and then reaching across history to make it happen . For me , the most difficult part of the mission was n't what happened during the flight but what happened after we came home . Without a new mission to train for , I felt lost and without a purpose . My personal life was marked by deep depression and bouts of drinking . Nothing I did seemed to have meaning or motivation for me . I left the Air Force , the space program , and was adrift . But then , as I began to recover my bearings , something wonderful happened . I met a woman , Lois Driggs Cannon , who helped me to climb out of my depression and see a role for me in space -- but this time while on Earth . I came to dedicate my life to opening space to the average person and crafting designs for new spaceships that could take us far from home . But since Apollo ended , such travels were only in our collective memory . For these past decades , our country has achieved great things in space . It has built a reusable spacecraft and flown it more than 100 times . It has orbited great observatories that have unlocked the secrets of the universe . Most impressively , it has helped construct an orbiting laboratory that offers the prospect of long-term research into the effects of space flight , research that can not just improve the health and safety of our astronauts but also of people on Earth . But what America has n't done is inspire the world -- and itself -- with a bold vision for our future in space . We have remained , since our Apollo days , locked in Earth orbit . But five years ago , NASA was tasked with returning to the moon by 2020 , rerunning the moon race that we won 40 years ago . Not surprisingly , this new race has failed to ignite the imagination of young Americans -- or their leaders . What we truly need is not more Cold War-style competition but a destination in space that offers great rewards for the risks to achieve it . I believe that destination must be homesteading Mars , the first human colony on another world . By refocusing our space program on Mars for America 's future , we can restore the sense of wonder and adventure in space exploration that we knew in the summer of 1969 . We won the moon race ; now it 's time for us to live and work on Mars , first on its moons and then on its surface . Exploring and colonizing Mars can bring us new scientific understanding of climate change , of how planet-wide processes can make a warm and wet world into a barren landscape . By exploring and understanding Mars , we may gain key insights into the past and future of our own world . Just as Mars -- a desert planet -- gives us insights into global climate change on Earth , the promise awaits for bringing back to life portions of the Red Planet through the application of Earth Science to its similar chemistry , possibly reawakening its life-bearing potential . Four decades ago , I was privileged to have been part of a great mission of exploration and discovery . But America 's future in space has only just started . It is time for us to continue the journey . The opinions expressed in this commentary are solely those of Buzz Aldrin .
Buzz Aldrin : Our mission to the moon was shared by the world as an adventure . He says he became depressed after the mission was over . Aldrin says he took on a new mission : to open space to the average person . He says a mission to colonize Mars would restore adventure of space travel .