How far can a piece of spacecraft go, where the signal still reaches planet Earth?

Right now, we don't know the distance of which the spacecraft can go but at the moment, we can go to Jupiter, but the signal takes a long time to reach back to planet Earth.

• Welcome to space! Can you edit your question to make it explicitly clear what you are asking? For example, are you asking about a specific spacecraft? Or about the furthest a signal could theoretically be received from a given spacecraft? As it stands your question is likely to be closed as unclear. – Organic Marble Sep 17 '19 at 1:30
• Yes, Dan's "infinity" answer is correct but unlikely to satisfy you. Please narrow down your question. – Camille Goudeseune Sep 17 '19 at 6:12

We have already sent spacecraft much farther than Jupiter. The spacecraft that is farthest away is Voyager 1. It is almost 30 times as far away as Jupiter, and it is still sending signals back. They think the signals will become too faint to detect in about six more years.

But that is not the farthest possible. As another answer said, there really is no clear upper limit. We could probably engineer a craft that could send detectable signals from light years away, especially if we build larger antennas here to pick up the faint signals. The harder part is getting the probe that far away. At currently achievable speeds, it would take a spacecraft thousands of years to reach a light year away.

Theoretically, a radio signal has an infinite range. It's just electromagnetic radiation. We can detect fast radio bursts from galaxies billions of light years from us.

Practically speaking, omnidirectional radio waves diminish in strength proportionally to the square of the distance. To improve on this, you need to use highly directionally beaming using either dish antennas or laser communication. For example, deep space probes typically have high gain dish antennas, and we talk to them through the Deep Space Network, which uses 70 meter dishes. Using that we can still communicate with Voyager, which has only a 23 watt transmitter.

At some point, even a highly directional signal of reasonable power will drop through the background noise floor and we'll no longer be able to hear it. How far that is depends on many things such as the dish size, transmit power, frequency, modulation type, acceptable error rate, etc.

I think it's fair to say that for reasonable probe sizes and power, the limit of radio communications is probably not too far outside our solar system, galactically speaking. Even from the nearest star you would need laser communications or extremely high power. The fast radio burst we detected from 3 billion light years was a few milliseconds long, and the input energy that created it was about what our sun puts out in total over about 80 years.

However, that burst DID get here from 3 billion light years away, and it's a radio signal.

With more details about your spacecraft a more accurate answer could be given, but without that maybe these more general answers will help.