A beam implies a stream of something travelling from a source to a target. Whether it’s a stream of photons or some other particle, it will tend to push the target rather than pull it.
On Earth, you can use a vacuum cleaner to pull something towards you, but what you’re really doing is removing some of the air molecules on the near side of the object, so that the molecules remaining on the far side will push it.
This doesn’t really count as a beam though, and it wouldn’t work in space anyway because, in a vacuum, there are no molecules to remove.
But there are ways to pull things in space that don’t use beams. A ‘gravity tractor’ is a proposed design for a spacecraft that hovers or orbits close to an asteroid and uses mutual gravitational attraction to draw the asteroid off its course.
Ordinarily, the much larger mass of the asteroid would pull the spacecraft into the asteroid, but a gravity tractor counters this by using efficient ion thrusters that always keep it ahead of the asteroid as it gently tugs it forward.
Gravity is convenient because it’s a ubiquitous force between any objects with mass, but it’s also extremely weak.
Hence, the European Space Agency (ESA) has looked into the feasibility of using electrostatic attraction instead, which is a much stronger force, but because it comes in both positive and negative flavours, the charges on an object usually cancel out to almost nothing.
The ESA study considered charging up a suitable asteroid in various ways and one of them was to spray it with electrons.
Provided you also keep the spacecraft charged to about 20,000 volts this would work and you could consider that stream of charging electrons as a sort of tractor beam.
But it would still be much slower than the tractor beams in science fiction.
This article is an answer to the question (asked by Alexandra Rowland, via email) 'How close are we to having tractor beams, like in Star Trek?'
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