It irritates me to hear the word "Astronaut" used as a synonym for what we used to call "spacemen" before gender sensitive folk overthrew the customary rule that "man" could be any member of the species "Homo sapiens".
OK, then, let's call them Space Travellers, or even Space Engineers.
But an astronaut is a traveller to the stars, and in my moderately well informed opinion, it's not gonna happen.
Well, hardly ever.
|Planet||Period in years|
The time it takes a planet to orbit the Sun is a measure of the time it will take a spacecraft to complete such a circuit, unless you have fuel and thrust enough to defy the Sun's gravitational field.
Can any top notch scientist afford to spend even twelve years of his or her life travelling in a spacecraft to and from Jupiter, with no apparatus or information other than what can be sent by radio waves?
Robot exploration is far more efficient, and much safer!
If you know enough about celestial mechanics, you might amuse yourself by computing just how much fuel, cleverness, and good fortune the crew of a spacecraft might need to get to Neptune and back in a working lifetime of 60 years.
I'm pretty sure you cannot do it without some serious nuclear power devices. In short, if NASA were serious about human exploration of the planets, they'd take the funds for "astronaut" studies, and invest them in nuclear power research.
If actual star travel does happen, we're more likely to find a way for the space travellers to live for millennia than for them to exceed the speed of light. So if they do get there, the folk back home when they launched won't hear about it anyway.
There are sequences of living DNA in your body that are identical copies of DNA from the time of your common ancestry with the mouse, and others trace back to your common ancestry with the yeast cell. Given that your body copies quite a lot of itself as part of the process of being alive, some of your DNA is vastly older than Methuselah!
By contrast, the tiny particles in the world's fastest accelerator each have gazillions of times the energy of the atoms in a lightning flash, or the electrons bombarding the biggest CRT television you ever owned, or the cosmic ray particles hitting the atmosphere. They still don't exceed the speed of light.
One of the old science fiction designs is the hydrogen fusion powered ramjet. You project some sort of conical electromagnetic collector ahead of the spaceship, to pick up and funnel interstellar hydrogen into the engines, and by fusion energy you eject a stream of ions out behind the ship, a kind of jet propulsion. You might get to a decent fraction of the speed of light out of that.
In principle, it looks brilliant, but I doubt that it is even theoretically possible.
The Sun's core is extremely hot and dense, but the hydrogen fusion reaction that supplies us with sunlight is so slow that a bumblebee burns far more energy in a minute than a bumblebee-sized volume of the Sun's core produces in that time!