I took Neil Armstrong's death personally. I was surprised to find myself so upset, honestly, since I knew so little about him: I had never seen him speak, never read his biography, and the Moon landings happened long before I was born. But, as I'm sure he would have understood, my grief wasn't really just about him. His death represented, to me, the end of an era, and the slow passing from living memory one of the most profound achievements of the human race.
Also, Neil Armstrong reminded me of my grandfather, Captain Willard "Sam" Houston, who saved his life once.

Credit: NASA
I should perhaps provide some background. I'm a theoretical astrophysicist. I grew up in California and my career has carried me steadily east since then--I went to grad school at Princeton and I'm now a postdoc at Cambridge University. Soon, I'll be moving on to Melbourne, Australia, to take up a research fellowship there. I got into astrophysics because I love figuring things out, and because I've always been fascinated by the quest to understand the cosmos. But I also remember a moment, when I was a small child, that fundamentally changed my view of the world and my place in it. It was the first time I saw a photograph of the Earth from space. It was the first time I understood, beyond just hearing the words, that I lived on a *planet*. That my home was just one of many rocks, careening through space, and that there were real places, *out* *there*, where people could go. I can't say for sure, but the picture was probably this one, taken by the astronauts of Apollo 17, on their way to the Moon. The last time human beings would go there.
This is a photograph that couldn't have been taken by a satellite or from low-Earth orbit. It couldn't be taken today. The perspective of Earth from afar is one that we have lost. And one of the very few human beings to have personally experienced that perspective has now been lost to us, too.
When I was growing up, knowing I wanted to be a scientist, my grandfather was the person I most idolized. Like Armstrong, he had a quiet dignity and a fundamentally scientific outlook. He was also talked about in similar terms--as a man of great integrity, humility, and responsibility. Granddad had been a meteorologist in the Navy during World War II, and as part of his training he took courses at the California Institute of Technology--a place that seemed to me, as a teenager, to be a paradise of scientific discovery and rampant, celebrated geekiness. Granddad used to tell me stories of how his fellow Navy men tried to challenge the Caltech undergrads at poker and lost their shirts every time. He'd tell me about the pranks and traditions and feats of cleverness that abounded at Caltech in the 1940s. When I eventually attended Caltech as an undergrad, it was with the intention of making my grandfather proud, and with the additional thrill of sharing a special kinship with him.
After the war, my grandfather travelled all over the world with the Navy, so he had a lot of stories. But there was only one that I made him tell again and again: the one in which he worked with NASA and saved the mission, and the crew, of Apollo 11.
As a meteorologist, my grandfather's job for Apollo 11 was to check for weather problems around the capsule's splashdown site at the conclusion of the return trip. When the time came, he consulted all the data NASA had available and it looked okay. But he wanted to be sure. His previous assignment, in the Navy, had given him access to data from secret spy satellites, a product of the Cold War, and a project no one at NASA had clearance to know about. With just 72 hours to splashdown, he went to a nearby read-out station.
As soon as my grandfather arrived, Air Force Major Hank Brandli dragged him into his office and told him he'd seen "screaming eagle" thunderclouds forming in the satellite images. Brandli knew about NASA's intended splashdown site, but was forbidden to let on that the satellites existed, much less share any information with other agencies. And now my grandfather was in the same position. The capsule had to be rerouted or Armstrong, Aldrin and Collins would die, but no one could be told the reason for the change.
It was then up to my grandfather, alone, to convince NASA that there was a storm building at the splashdown site, without providing any proof or corroborating data. The satellite program's existence had to be kept secret, even from other government agencies. He had to rely only on his reputation as a trusted Navy man and a respected scientist. Thankfully, my grandfather's commanding officer agreed to take him at his word, and alerted Mission Control to reroute the capsule to a safe location and move the recovery team. But at the same time, the military also commanded a plane to fly out to the original site, just to check that the storm was really there. My grandfather was warned: he'd better be right. The new coordinates were sent, the capsule came down without incident, and the reconnaissance plane flew into weather so rough that the capsule's parachutes would certainly have been ripped to shreds. The astronauts were safe and so was my grandfather's career. He would even be awarded the Navy Commendation Medal when the program was declassified in the 1990s.
The more I learn about the Apollo program, the more I appreciate how much of it was a seat-of-the-pants effort, built on untested technology, driven by human ingenuity and tinged with more than a little hubris. As Apollo astronaut Jim Lovell said, "We just decided to go." The Moon landings weren't miraculous, or fated. They weren't convenient. They were incredibly dangerous and by no means guaranteed to end in success. But we did it. We went there. And I say "we" because that journey, perhaps more than any other in history, was a journey of humanity as a whole. Our *species* advanced. From that momentous day in 1969, we were no longer confined to the Earth; we could venture out, *in* *person*, and walk upon other worlds.
Don't get me wrong; I'm a big believer in robotic space exploration. As a scientist, I understand that it can, and does, offer us incredible insights into the formation of the Solar System, the history of life on Earth, and the environmental conditions of other planets and moons. I understand that robotic exploration is cheaper and safer than human spaceflight, and I understand that there are places robots can explore that no human being could ever survive.
But the Apollo program wasn't about science. It wasn't about doing anything cheaply or safely. It wasn't about what we would learn by bringing samples back from the Moon, or even about all the technological advances that came out of it. It was, fundamentally, about wonder. It was about expanding our horizons as a species and setting foot on a new world. It was about reaching out into the cosmos, being viscerally connected to it, and bringing that experience back to share with all who have looked up to the stars with a sense of awe and anticipation. It was about the recognition that we are all part of one human race, all living together on a tiny blue marble in the great black void. It was about heroes, like Neil Armstrong. And like my grandfather, too.
My grandfather passed away in January at the age of 88. Before he died, I visited him in the hospital to say goodbye, and to tell him I've applied to NASA's astronaut program. I haven't heard yet whether I'll be selected, though about a month ago I found out that I've made the first cut. I still want to make him proud.
Whether or not I ever go into space myself, I hope that we, as a nation and as a species, don't give up on human space exploration beyond low-Earth orbit. The Moon is so close. Mars is just next-door. Orbiters and rovers will continue to bring us tremendously valuable images and information, but I hope we remember the value of actually going there--the way it can change our perspective and make us, fundamentally, greater.
Neil Armstrong knew what it felt like to walk on another world. That experience will soon pass out of living memory entirely. But the footprints on the Moon will remain. And I hope others will follow them, soon, and walk farther.
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Katie Mack is a postdoctoral researcher at Cambridge University.