Part 2 of 2 Parts (Please read Part 1 first)
There are other ways to create antimatter. That's where Ryan Weed focused his work. Weed's design involves positrons, the antimatter version of an electron.
NASA has also proposed designs for antimatter propulsion that use magnets to separate antimatter particles from particles of regular matter as part of the process. Weed said that positrons “are several thousand times lighter than antiprotons and don't pack quite as much punch when annihilating.” Their advantage is that they occur naturally and don't need a giant accelerator and billions of dollars to create.
Weed's antimatter propulsion system is designed to use krypton-79 which is an isotope of the element krypton that naturally emits positrons.
The Weed engine system would first gather high-energy positrons from krypton-79 and then direct them toward a layer of regular matter. This would produce annihilation energy. That energy would then produce a powerful fusion reaction to generate thrust for the spacecraft.
While positrons may be less expensive to obtain than more powerful forms of antimatter, they are difficult to harness. They are highly energetic and need to be slowed down, or “moderated.” Building a prototype engine to test in space is still too expensive, Weed said.
This is the case for all antimatter propulsion designs. During decades of research, scientists have proposed dozens of antimatter engine concepts, none of which have come to fruition.
In 1953, Austrian physicist Eugen Sänger proposed a “photon rocket” design that would run on positron annihilation energy. Since the '80s, there has been talk of thermal antimatter engines. These would use antimatter to heat liquid, gas, or plasma to provide thrust.
“It's not sci-fi, but we aren't going to see it flying until there is a significant 'mission-pull,'” Weed said about his engine design.
Paul M. Sutter is an astrophysicist and host of “Ask a Spaceman” podcast. To construct Weed's antimatter engine at the scale of a starship, he said, “the devil's in the engineering details. We're talking about a device that harnesses truly enormous amounts of energy, requiring exquisite balance and control..
In general, that enormous amount of energy is another obstacle preventing us from revolutionizing space travel. Steve Howe is a physicist who worked on antimatter concepts with NASA in the '90s. He said that during testing, “if something goes wrong, these are big explosions. So we need an ability to test high energy density systems somewhere that don't threaten the biosphere, but still allow us to develop them. He thinks the moon would make a good testing base. “And if something goes wrong, you melted a piece of the moon, and not Earth.”
Antimatter tends to bring out the imagination in everyone who works with it. Sutter said, “But, we need crazy but plausible ideas to make it further into space, so it's worth looking into.
Weed echoes the Sutter’s sentiment, saying that “until there is a compelling reason to get to the Kuiper Belt, the Solar Gravitational Lens, or Alpha Centauri really quickly or perhaps trying to return large asteroids for mining, progress will continue to be slow in this area.”