Fermi Explorer Mission Aims to Test Interstellar Travel Filters in Fermi Paradox

There are, by various estimates, several trillion planets within the Local Group of galaxies, which includes our own Milky Way. Many of these are within the habitable zone of their stars. So if life finds a way, where are the alien civilizations?

This is the crux of what is known as the Fermi paradox, which posits that if life is fairly common in the Universe, humans should have collected credible evidence for the existence of extraterrestrial civilizations by now. People who think about this paradox believe there may be some “filter” that limits or entirely prevents an advanced civilization from sending out probes or even life-bearing spacecraft to nearby stars.

Philip Johnston is someone who thinks a lot about the Fermi paradox. A mathematician and physicist from the United Kingdom, Johnston has gained some notoriety lately in the space community as one of the biggest proponents of orbital data centers. He co-founded Starcloud in 2024 to develop such data centers, and the company is presently valued at $2.3 billion.

Johnston is in the midst of scaling up Starcloud, working through technical issues, and raising hundreds of millions of dollars. So he’s pretty busy. But Johnston also wants to send a mission to the nearest star to our Sun and investigate the Fermi paradox.

Meet the Fermi Explorer

On Tuesday, Johnston and a handful of other entrepreneurs announced the “Fermi Explorer” mission. In concept, it is simple. They seek to raise $15 million to build a small spacecraft, carrying a 1 kg payload, and launch it to Alpha Centauri such that it reaches that system in fewer than 80,000 years. Why? In conversations about the Fermi paradox, Johnston realized such a mission would knock two “filters” off the list: Species won’t want to send spacecraft beyond their home star, or species will find that interstellar transit is too difficult.

The goal was not to run to NASA to try to get it to fund a $1 billion mission or seek to develop a new propulsion technology like the Breakthrough Starshot mission proposed a decade ago. Rather, the Fermi Explorer team wants to use existing technology to do something cheap and fast and launch by 2029.

“So we were like, ‘Fuck it, let’s send a spacecraft for the cheapest amount possible, a bog-standard minimum viable mission to Alpha Centauri,’” he told Ars.

The main stumbling block involves getting the probe—essentially a large tank of Xenon gas and some solar panels for solar-electric propulsion, and a few small scientific payloads—moving fast enough. Solar-electric propulsion is super efficient, but once a spacecraft is beyond Jupiter, the solar energy flux is low enough that it might as well be zero for a spacecraft the size of the Fermi Explorer. Johnston and a small team spoke with many people, including trajectory experts at NASA’s Jet Propulsion Laboratory, to find a solution.

Nothing worked until Johnston linked up with Alex Wissner-Gross, a physicist who founded Physical Superintelligence, an AI technology company. They fed the mission parameters into the AI, and it returned an 18-page technical feasibility assessment that offered a novel mission profile. It involves hanging around our Sun for more than a decade before charging out to Alpha Centauri.

Essentially, after launching into low-Earth orbit on a rideshare mission, the spacecraft would fly retrograde arcs to decrease its distance from the Sun at perihelion from 1 astronomical unit (Earth-Sun distance) to 0.42 astronomical units. At these close approaches to the Sun, taking advantage of the higher solar flux as well as the Oberth effect, the spacecraft would operate its propulsion system to increase its velocity with “perihelion pump” maneuvers.

It would achieve an escape trajectory after about 12 years, at a velocity of about 25 km/s, or about 55,000 miles per hour. At this speed, the Fermi Explorer could reach Alpha Centauri within about 77,000 years, flying on a ballistic coast.

Striking off two of the Fermi filters

The team would only have contact with the spacecraft for about 18 months, Johnston said. With retroreflectors on the vehicle, he expected ground-based telescopes to be able to track it until it reached Jupiter. After that, if all the maneuvering goes as planned, it will be gone—long gone. Only to turn up in the Alpha Centauri system a very long time from now.

If this all seems a little whimsical, well, maybe it is. But Johnston said the point is to get humanity thinking about our place in the Universe. If the Fermi Explorer mission can knock down a couple of the filters that might explain the Fermi paradox, that only leaves a few options for why our galaxy appears not to be littered with alien civilizations. One is that civilizations are exceptionally rare. If it is the case, then humans maybe should take our responsibility as stewards of the galaxy a little more seriously.

Another option is that superintelligence does not last long. Perhaps, then, governments on Earth ought not to be building swarms of killer drones? Maybe we should be careful about LLM agents running amok? “We could really be facing the great filter,” Johnston said. So let us go forward with eyes wide open.