Two years after the Starshot Breakthrough Initiative was launched with the aim of sending an object towards our nearest stellar neighbour, we're still left staring at the heavens dreaming of the possibility.
A team of materials scientists has taken a more sober look at the current state of technology and listed what we need to discover before we can build something that's actually up to the task.
Unfortunately, this is still looking like the realm of distant science fiction.
Taking the glass-half-full approach, researchers at the California Institute of Technology are optimistic that sending an object into the Alpha Centauri star system within a human lifetime is theoretically possible, at least given the right materials.
Starshot is one of three projects making up the Breakthrough Initiative, a program founded in 2015 by Russian billionaire Yuri Milner and his wife, Julia, "to explore the Universe, seek scientific evidence of life beyond Earth, and encourage public debate from a planetary perspective."
From a practical position we shouldn't hold our breath on this particular part of the project picking up steam any time soon.
Not only do those materials need to be invented, the whole process behind its acceleration needs to overcome some serious obstacles.
At a distance of just over 4 light years, the three stars making up Alpha Centauri are just over the galactic back fence. If we ever want to gaze upon a different sun, these babies would be the first stepping stones.
It's not exactly a boring place either. It isn't just harbouring dead rock planets, but a potential second home.
The Starshot initiative aims to not only send a small probe into the star system, it intends to cover those light years of distance in decades rather than centuries.
That's around 41 trillion kilometres, or 26 trillion miles, of interstellar highway we're talking about. And it's expected to get there before retirement age of today's younger astronomers.
To put it in perspective, Voyager 1 was launched over 40 years ago and even though it's the farthest human-created object from Earth, it's still a mere 20 billion kilometres away.
Chemical boosters and slingshot physics won't cut it this time, not to hit the astonishing 20 percent light speed required to pull it all off. Our best chance at reaching a sizeable fraction of the speed of light is to actually use light's own velocity.
Pelting a material with photons should impart enough inertia to nudge it slowly up to that all important speed.
But since acceleration needs to take into account mass as well as force that material has to be ridiculously low-weight, not to mention reflective enough to bounce those photons.
Japan's 2010 IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun) mission provides a proof of concept, reaching speeds of 400 metres (just over 1300 feet) per second.
Now we just need a sail that can ramp up a tiny box up to reach speeds of around 60,000 kilometres (just over 37,000 miles) per second. Piece of cake.
Doing the math, the researchers decided that graphene could come close to making a sail of at least 10 square metres (about 107 square feet) while staying under one gram (0.04 ounces) in weight.
Perfect. Except… it isn't reflective enough, and making it shiny with a metal coating would just add too much weight.
But let's now imagine we do have the perfect material. We'll still need to craft it into a shape that would catch that photonic breeze without veering off course over such a mind-numbing distance.
The researchers suggest a sphere or some other convex geometry might offer enough stability, but anything around 10 square metres of surface would risk having tiny but concerning bumps.
The problem of getting this perfectly shaped sail up to speed would demand bombarding them with photons from a battery of lasers. After a while, those lasers would be difficult to focus, especially if we were restricted to shooting them through the atmosphere from Earth's surface.
Using wavelengths in the infra-red part of the spectrum could help. But then we arrive at the question of how to shed excess heat to prevent a catastrophic meltdown.
Now if we solve all of this, our amazing light-sailing nanoprobe could suddenly be brought to a crashing halt if it happened to bump into a dust particle or two. Meaning we'd need the right material to deal with that as well.
Do we manage to solve that one? Great. Then we need to have a system in place to put on the brakes as it arrives. Luckily, some researchers are all over this problem.
Layer upon layer, it's a series of stunningly difficult problems.
But don't let this put a downer on your dreams of an interstellar postal service. No doubt there were similar teams of party-pooper materials scientists pouring cold water on ideas about early missions to Mars and Venus.
This is one case we're desperate to hear of amazing solutions that prove the doubters wrong.
This research was published in Nature.