spacecraft

The Doppler shift is tracked, as it tells them how fast (in radial terms) the spacecraft is going.

And since the point of the mission is to escape the sun, what matters is the spacecraft's energy state with respect to the sun, not to Jupiter.

Launches are not cheap, and you have to account for every bit of spacecraft weight which leads to design tradeoffs.

There's also a rather more mundane possibility: it could be residue from some sort of cleaning process done when the spacecraft was still on Earth.

We haven't been able to observe them for the same reasons our telescopes can't see the New Horizons spacecraft out by Pluto, just too small.

Launch: Finding the right rocket is important; it influences spacecraft design.

Is the earth visible in an optical telescope from the spacecraft?

A spacecraft on a mission to Pluto might require a software change or a course correction, but its hardware is not changed once it launches.

At the same time, space travel technology will also have been advanced, allowing for self-sustaining spacecraft that offer protection against the harsh environment of outer space.

The spacecraft's speed with respect to Jupiter doesn't change.

Why do people use sunscreen and shield spacecraft?

Like any spacecraft design they had to choose between high bandwidth (more power == larger RTG == more weight) or large storage (more memory modules == more weight).

The transmitter on earth could track on the "star" of the laser from the spacecraft.

And for anyone who didn't see it, to call this mode "optional" is putting it extremely mildly: to get enough power to run both amplifiers at once, they have to shut down the spacecraft's guidance system (!) and keep it pointed at Earth by using the thrusters to spin it up like a top.

Spacecraft technology always seems outdated because of the lead times required: on something like New Horizons, it's between 15 and 20 years from component design to being used for its primary mission.