It sounds like something straight out of a Hollywood science fiction blockbuster, but back in 2012, a major feasibility study sponsored by the Keck Institute for Space Studies (KISS) mapped out exactly how we could robotically capture a near-Earth asteroid and drag it back to orbit around our Moon.
I have been reading through this proposal recently, and the sheer audacity of the engineering is absolutely fascinating. But beyond the spectacle, this outlines a highly practical mission. Here is how we could actually pull off an "Asteroid Capture and Return" mission, and why turning a space rock into a local lunar satellite might just be the smartest next step for human space exploration.
The Target: A 500-Ton Space Rock
We naturally assume asteroid mining involves snagging a massive, planet-killing leviathan. But the ideal target for this particular capture mission is actually a C-type (carbonaceous) asteroid roughly seven meters in diameter. Despite being roughly the size of a large truck or bus, a rock this dense weighs an astonishing 500,000 kilograms, or 500 metric tons.
These C-type asteroids are perfect targets because they are essentially flying treasure chests packed densely with water, organic molecules, and precious metals. Even better from a planetary defense standpoint, they are physically weak enough that if anything went critically wrong with the towing mission, the rock would safely and harmlessly burn up in Earth's atmosphere upon reentry.
The Plan: A Giant Space Bag
So, how exactly do you move half a million kilograms of rock across the solar system?
The mission would launch atop a single heavy-lift vehicle, like an Atlas V 551-class rocket. Once in open space, the robotic capture spacecraft unspools a highly efficient, 40-kW solar electric propulsion (SEP) system. Unlike chemical rockets that burn out in minutes, SEP uses solar energy to continuously accelerate ions, allowing the craft to gracefully cruise out into deep space to intercept the asteroid over a period of a couple of years.
Once the spacecraft successfully arrives, it spends about ninety days precisely matching the asteroid's unique orbit and chaotic tumbling spin. Then, in a moment of pure science fiction made real, it deploys a massive 10-meter by 15-meter inflatable bag to literally swallow the tumbling rock whole.
High-strength mechanical drawstrings automatically cinch the immense bag securely closed. Once the target is bagged, the spacecraft rigorously fires its thrusters to completely halt the asteroid from spinning, stabilizes the entire rig, and then slowly and methodically tows the whole package back toward Earth to place it into a stable, high lunar orbit.
Plan B: The "Space Snow Blower"
There is always a major catch in orbital mechanics. In this case, finding a free-flying, pristine seven-meter rock with the absolute perfect Earth-return orbit is surprisingly difficult. Because of this unpredictable variable, the engineering study included a brilliant fallback strategy called the "Pick Up a Rock" approach.
Instead of trying to chase down a tiny, solitary asteroid, the spacecraft could fly to a much larger, easier-to-find asteroid (something over one hundred meters across) and simply pluck a reasonably sized, seven-meter boulder right off its surface.
If they cannot find the perfect boulder resting on the surface, the spacecraft could deploy anchoring tethers and use a robotic "snow blower" tool. This mechanism would actively suck up hundreds of tons of loose dirt, pebbles, and gravel (known as regolith) directly into the giant capture bag until it hit the 500-ton capacity, effectively building an artificial asteroid to bring home.
Why Are We Doing This?
You might reasonably be wondering why we would spend an estimated $2.6 billion on the first operational mission to bring a random space rock back to the Moon. As it turns out, the economic and scientific benefits are massive:
Mining for Water and Resources: A 500-ton carbonaceous asteroid can hold up to 100 tons of raw water. Once in lunar orbit, we could extract that water and split it into hydrogen and oxygen to create vast amounts of rocket fuel in space. Alternatively, we could use that dense water as bulk shielding to protect deep-space astronauts from deadly galactic cosmic rays on long voyages.
The Ultimate Astronaut Training Ground: By permanently parking an asteroid right next door in cislunar space, human crews could visit it and study it in a matter of weeks instead of the many perilous months it ordinarily takes to reach deep space. It would functionally serve as the perfect local stepping stone, allowing us to test our specialized mining tools and deep-space habitats before we commit to sending humans to Mars.
Massive Cost Savings: Delivering 500 tons of material to a lunar orbit utilizing this robotic, solar-powered tugboat is roughly eight times cheaper than launching that exact same weight from Earth's gravity well using traditional chemical rockets. For subsequent capture missions, utilizing the established technology, the cost savings could rapidly jump to a staggering factor of twenty.
Ultimately, capturing and moving a 500-ton rock into lunar orbit is entirely about humanity learning how to successfully live off the land in space. It is exactly the kind of bold, visionary engineering mission that provides us with a completely new technological capability, and it could single-handedly jump-start an entire space-based industrial economy.