What is the top speed for a space probe now and in the future?

Currently Helios 2 is “the fastest spacecraft ever built—the Helios 2 probe, launched in 1976 to monitor the sun—attained a top speed of 157,000 miles an hour. At that rate, a spacecraft headed to Proxima Centauri, the nearest star, would take more than 17,000 years to make the 24-trillion-mile journey, a temporal span equal to the one that separates us from Cro-Magnon cave painters.” from National Geograhic’s web article.

Future “sky is the limit” maybe approaching the speed of light.

Due to the primitive nature of our space probes the Galactic Vehicle Licensing Authority has mandated a top speed of 50,000 kilometres per second for any vehicle originating on Earth and with an Earth registration.

There is no limit, basically. Constant thrust will result in faster and faster speed.

well technically the limit is the speed of light.

Isn’t it theoretically possible to utilize the planets, moons and the sun itself to accelerate the velocity of an object to a considerable fraction of the speed of light? It might require dozens or even hundreds of years to build the momentum then point the thing toward another solar system.

@stanleybmanly yep it is possible, Apollo 13 used the Moon’s gravity to “slingshot” itself back towards Earth. Not to the fraction of the speed of light you asked, but it is one example showing that it possible.

@stanleybmanly

Yeah, it’s theoretically possible. In space there’s nothing acting upon an object to slow it down.

Current probes rely on the timing of planetary alignment to allow for multiple gravitational assist manoeuvres. The Voyager and Cassini probes used this to great effect.

With current technology, but far more funding than is currently available, we could construct a solar sail that is projected to reach 0.1c, or 10% of the speed of light. This would essentially be like a sail on a yacht, that uses light rather than wind. Light has momentum, even though it doesn’t have mass, so absorbing its energy would accelerate the sail.

Theoretically, the speed of light is the limit. There has been some exciting research in the field of propulsion recently that has given reason to think we may get close. But the techniques are barely at the experimental stage, and would still take many years to accelerate from an Earth orbit to anywhere near the speed of light.

The big problem with current propulsion systems is Newton’s Third Law of Motion. In order to accelerate the large mass of a rocket, we need to eject the smaller mass of burnt fuel at great speed. So we are limited by the mass of the fuel we can load onto the rocket, and the speed at which it can be ejected. If interstellar travel is to become a reality, we need a propulsion system that doesn’t eject matter, such as the solar sail.

Relativistic mass increase will limit us to light speed (unless someone finds a workaround):
http://www.phy.olemiss.edu/HEP/QuarkNet/mass.html

The equations have been found to work pretty well in particle accelerators, so should be applicable to space probes.