Access to other stars with our current technologies remain out of reach. The fastest probes, such as traveling 1, will never cross the interstellar border at speeds allowing useful scientific return. It is precisely this dead end that a new concept of propulsion developed by David Kipping, astrophysicist at Columbia University, and Kathryn Lampo,. Journal of the British Interplanetary Society, offers a system called Tars (Torqued Accelerator Using from the Sun), capable of accelerating tiny probes without engine or fuel, simply by exploiting sunlight.
By combining mechanical rotation, ultralight materials and controlled orbit, Tars aims to make interstellar exploration accessible without disproportionate infrastructure. This project is part of a wider effort aimed at finding realistic alternatives to conventional propulsions, in a context of stagnation of long -range missions.
A spatial sling born from the sun
The idea at the origin of Tars (Torqued Accelerator Radiation from the Sun) is based on a simple physical principle. We use the energy of the sun to create speed. Unlike conventional solar sails directly pushed by photons in a straight line, Tars accumulates solar energy in the form of rotation. The system imagined by David Kipping and Kathryn Lampo consists of two ultrafine surfaces, placed in opposition. One reflects the light and the other absorbs it. This imbalance generates a couple that gradually runs the whole around an axis.
Over time, this rotation is gaining speed. When a critical threshold is reached, a microsonde – the size of a smartphone – is released at high speed, projected into space. The analogy with a sling is then obvious. The longer the system turns, the greater the energy, the faster the probe.
Tars only works thanks to solar light, without engine, fuel or on -board propulsion. This represents a major asset in terms of mass and cost. According to the calculations of the authors, a simple version of the device – 7 meters wide, 63 meters long, and 2.8 microns thick – would be enough to launch a payload of a few grams at more than 40 km/s. This figure exceeds the minimum speed to escape the gravitational field of the sun.
It is this technical and energetic sobriety that distinguishes tars from existing concepts. Here, innovation does not reside in futuristic technology. It lies in the ingenious reinterpretation of already known physical laws and materials available on the market.
Accessible and reproducible technology
One of the most striking aspects of Tars is its structural simplicity. Where other interstellar projects are betting on giant lasers, nuclear reactors or structures of several tonnes, tars comes down to a light, passive, and potentially reusable structure. The heart of the system is based on ultralight materials (carbon nanotubes leaves, already available commercially). These leaves, extremely resistant to their mass, support the tension stresses generated by rotation.
The study shows that a tars of only 1.6 kilogram can operate independently once placed in orbit. The energy necessary for its operation, coming only from the sun, thus avoids problems linked to the supply, cooling or mechanical wear. No propellants, no fuel, and very few mobile parts. This minimalism makes it possible to envisage a low -cost manufacturing, adapted to university programs or to small space agencies.
In terms of design, Kipping evokes the possibility of removing the central cable connecting the two sails, by promoting a continuous ribbon structure. This version would allow better stability and simplification of the deployment. In space, the system must simply be deployed – which remains one of the main technical challenges. Then he can start accumulating solar energy to the desired speed.
Interestingly, several private companies have already expressed their interest in testing a miniature of tars prototype. They even offer a free launch provided that the team provides a cubesat ready to fly. For Kipping, this type of initiative can become a powerful educational tool. Students would actively participate in the construction of a real interstellar mission.
A stationary orbit to accumulate energy
To operate sustainably, the system must remain in a stable position compared to the sun, at an optimal distance to capture maximum energy. However, a traditional solar sail tends to drift over time, repelled by the pressure of the photons. To counter this effect, David Kipping imagined a very special orbital positioning. It is located halfway between a conventional heliocentric orbit and a quasi-stationary device.
This type of orbit, which Kipping had already theorized before, allows a structure to be maintained at a constant distance from the sun, without getting away or getting closer, despite the push exerted by light. This is made possible by finely balancing solar gravity and radiation pressure. Unlike the classic satellites which follow the laws of Kepler, an object according to this orbit evolves more slowly than expected at this distance. This allows Tars to keep a stable position for months or years, a key parameter for energy accumulation.
This positioning also guarantees maximum and constant solar exposure. It avoids the variations in light that would slow down the speed rise process. Without this stability, the return of Tars would collapse, making any attempt to launch ineffective. It is therefore a dynamic, finely calculated balance. A slight lateral boost is enough to keep tars in orbit, halfway between the fall towards the sun and the ejection out of the system.
A door to the future of spatial exploration
Tars does not promise rapid trips to Alpha from Centaure, but it changes the rules of the game. By reaching speeds of around 40 to 1000 km/s, this system makes missions to targets today inaccessible with conventional means. A speed of 1000 km/s, or 0.3 % of the speed of light, would allow for example to reach the gravitational household of the sun (at 600 astronomical units) in less than three years. At this distance, a well -placed telescope could use the effect of gravitational sun lens to observe exoplanets with unprecedented precision.
Another application mentioned by Kipping: send swarms of microsondes to the Kuiper belt, interstellar comets or even objects like 'Oumamua, too fast to be intercepted today. Thanks to their low cost, these missions could be multiplied, compensating for the risks of failure by the number.
Tars also opens up new perspectives for planetary protection. By placing several orbit devices around Mars, it would be possible, according to Kipping, questioned by Space.com, to create an artificial magnetic field around the red planet, protecting the future settlers from solar radiation.
Finally, the authors plan to further strengthen performance by providing tars with electromagnetic properties. This via charges opposed to the ends, thus creating a field capable of radiating additional energy. This theoretical track could make it possible to reach the highest speeds, but it remains speculative for the moment. More than a simple means of transport, Tars could become a multifunction tool for space exploration, sustainable, scalable. And within the reach of many scientific teams.
Source: David Kipping, Kathryn Lampo. “” “Torqued Accelerator Using Radiation from the Sun (tars) for interstellar payloads”. Arxiv, 2025
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