This Scientist Spent Decades Cataloging 57,424 Man-Made Objects in Space

The General Catalog of Artificial Space Objects is the most complete catalog of satellites, spacecraft, debris, space organizations, and launches, ever compiled. Its creator, astronomer Jonathan McDowell, put it online for anyone to use, for free.
This Scientist Spent Decades Cataloging 57,424 Man-Made Objects in Space
Image: NASA

A scientist and space history hobbyist has published the General Catalog of Artificial Space Objects (GCAT), an open-source database containing the most complete catalog of man-made objects in space such as satellites, spacecraft, and debris, as well as space organizations and launches. 

The catalog is a culmination of decades of work, and some data, like end-of-life dates for satellites, have never been published before or hosted in one place.


Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, released GCAT on Sunday. McDowell has written a newsletter that chronicles launches and missions since 1989, but the inklings for GCAT arose in his youth, when he was captivated by the Apollo program, the first to successfully land people on the Moon.

“It was hard for me growing up in England to get details about space because the media there weren't as interested in it as the U.S. media, so in a slightly obsessive way I started making a list of rocket launches,” McDowell said. “Many kids did at that time, but I just took it a little further and tagged on with it for 40 years. Now I have the best list.”

GCAT includes previously unpublished information that underpins McDowell’s newsletter, as well as the results of years of archival research that McDowell has undertaken. For example,  McDowell started tracking end-of-life data for satellites in order to answer a seemingly simple question: How many working satellites are currently in space? (The answer is around 2,000, plus or minus 10 percent, he said.) Other variables he tracked include the mass of artificial space objects and rocket launch times down to the minute.

“My audience is the historian 1,000 years from now”

McDowell said that he hopes other researchers and space aficionados use the database, which is open source and published under a Creative Commons license, to answer fundamental questions about space programs. Each satellite in the database is categorized as commercial, military, or civilian; one could, for instance, look at the proportion of commercial satellites over time and stratify by variables like mass, altitude, or country of origin.


The database contains text and .tsv files stratified by several major categories, as well as documentation describing the conventions and data collection methods used. McDowell said that he worries that the comprehensive database will be overkill for most users, and he is starting to think about ways to make a simplified version for less experienced folks.

"I want 15-year-old me to have access to this," he said.

Creating and maintaining the most comprehensive space object database was no easy task—McDowell said he had to learn Russian to translate information about ongoing and historical launches. National and commercial space agencies make mistakes in their press releases, like confusing standard time and daylight saving time, he added. Archival research is a big part of the job, and it’s taken McDowell to space agencies around the world.

Once, a newsletter reader who worked at CNES — the French government space agency — invited McDowell to the Toulouse Space Centre.

“They wanted to show me the pretty control center and everything, but then I managed to push down to, ‘Oh, yeah, we do have a list of our old rockets. It's in microfiche in the basement somewhere,’ and so I left with a Xerox of that in my hands,” he said.

The decision to publish the database under a Creative Commons CC-BY license, in which it can be used and shared freely with citation, was an easy one for McDowell. He explained that publishing GCAT online preserves it.

“There’s no point if it dies with me,” he said, adding that “the thought of COVID and imminent death” motivated him to publish the database, which has been on his bucket list for several years.

Making the database easily accessible also lets others notice errors, which McDowell can then fix. Already, he has received feedback about the database and updated it since its release. McDowell said that he’s started work on the next phase of the project, which is delineating the life history of each satellite in the database. He also has another project in the works, a catalog of deep space that includes objects beyond Earth’s orbit.

Ultimately, McDowell hopes that GCAT can be a long-lasting resource on the Space Age, which he believes we’ve only just started.

“I'm imagining that 1,000 years from now there will be more people living off Earth than on, and that they will look back to this moment in history as critically important,” he said. “My audience is the historian 1,000 years from now.”