A trip to the stars? Should be possible, says a researcher from TU Delft

Next stop Mars. After just 28 hours of traveling you can take pictures of the craters of the red planet. If you have time on your hands, you might also consider visiting Jupiter, the largest planet in our solar system, named after the Roman god Jupiter, the king of the gods. Don’t miss out on the ice-covered liquid ocean of Europa, Jupiter’s moon.

This may sound like a paragraph from Douglas Adams’ book The Hitchhikers Guide to the Galaxy, but a weekend trip like this which with current technology would take many years, may actually not be that far-fetched. Well, for miniaturised spacecraft anyway. These are tiny spacecraft carrying microchips. But who knows what may come next. Sending objects through space at near warp speed is the promise of a technology which Richard Norte (Department of Precision and Microsystems Engineering) is working on.

100 million kilometres an hour
Norte was first inspired by an international initiative called Breakthrough Starshot. Its aim is to send spacecraft to neighbouring solar systems using so called light sails. The idea is to use ground-based light beamers to push ultra-light nanocraft – miniature space probes in the form of microchips with integrated cameras, sensors and communication systems attached to light sails – to speeds of up to 100 million kilometres an hour. This is about one fifth the speed of light.

Such sails could allow us to send satellites that reach the closest star outside our solar system – Proxima Centauri, 4.25 light years away – in just 20 years as opposed to 10,000 years. What’s more, the technique would transform trips to planets in our own solar system into little more than strolls around the park. Mars could be reached in 28 hours (it now takes more than four months), and Jupiter would take 8 days (instead of five years).

High-energy laser beams
The idea is not entirely new. Solar sails are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors. A number of spaceflight missions to test solar propulsion and navigation have been proposed since the 1980s. The first spacecraft to use the technology was IKAROS, launched in 2010. A useful analogy to solar sailing may be a sailing boat: the light exerting a force on the mirrors is akin to wind blowing the sail. To boost things, high-energy laser beams could be used as an alternative light source to exert much greater force than would be possible using sunlight.

Extremely powerful lasers that could do the job, do not exist yet. More challenging even, would be to make sails that are ultrathin and highly reflective. Norte experimented with wafer technology, mostly used to make thin slices of semiconductors such as crystalline silicon that is used for the fabrication of integrated circuits and, in photovoltaics, to manufacture solar cells. The specific techniques he worked on while pursuing his PhD at Caltech prior to coming to TU Delft, also seems promising to make extremely lightweight and highly reflective sails.

So promising indeed, that the European Union wants him to continue on this track and awarded him a European Research Council (ERC) Starting Grant of EUR 2.1 million to continue his work with a research team at TU Delft. His project is called EARS (Extreme-Aspect-Ratio nanoSystems).

 ‘This sort of challenge requires a new type of nanotechnology’

“The sails must be ‘macro-scale’ in the length and width – say four by four metres – but have ‘nano-scale’ thickness, around one-thousandth of the thickness of a human hair,” says Norte. “This extreme-aspect-ratio nanotechnology is fundamentally different from any conventional nanotechnology developed over the last half century. This sort of challenge requires a new type of nanotechnology.”

We probably have to wait many years before seeing the first objects being shot into space with sails and high energy beams. “It is a long-term project,” says Norte euphemistically.

In the much shorter term however, lightweight sail materials of a couple of square centimetres and lasers could be used for “unprecedented light-matter interactions” Norte believes. Namely to levitate objects of one milligram.

This idea is not completely new either. Optical tweezers are scientific instruments that use a highly focused laser beam to hold and move microscopic and sub-microscopic objects like atoms, nanoparticles and droplets in a manner similar to tweezers. The development of optical tweezing by Arthur Ashkin in the 1980s was lauded with the 2018 Nobel Prize in Physics.

“But what we are after”, says Norte, “is the optical control of massive objects (objects of one milligram): 100,000 times more massive than anything levitated with coherent light to date. This will also offer new opportunities to study gravity.”