[eslaught]

One thing I've always wondered is what fraction of c is actually realistically achievable with current technologies? (Maybe with scenarios for manned/unmanned spacecraft.)

Like are we at 0.1% or 0.01% or more orders of magnitude off?

[btilly]

If you enjoy such questions, I highly recommend https://www.amazon.com/Indistinguishable-Magic-Robert-L-Forw....

The best speed for interstellar travel with technologies that current theory says should be within our reach can be achieved with a vehicle with a light sail pushed by a giant laser, that is powered by solar power. There is even a way to brake it when it reaches the target star. I forget what the predicted velocity was though.

This technology is basically the same as one that the Moties developed in the story, The Mote in God's Eye.

[DiggyJohnson]

Slow down by pulling on the fishing line tied to the back of it, carefully.

[Scarblac]

According to the first Google hit, https://scitechdaily.com/nasas-parker-solar-probe-the-fastes... , the fastest we've made so far went 430k mph (falling towards the sun), or about 0.064% of c. Good guess.

[anon_cow1111]

We have a number! Around 0.1c maximum and unsurprisingly it involves using nuclear bombs to push yourself.

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...