Space Aging
geroscience.com
geroscience.com
Bringing from Earth a few tons of nuclear-powered jet engine to use water as propellant would take building such an engine first. We're not even close.
Chemical engines are lightweight and well-understood. Lifting kilotons of chemical fuel is not feasible, though. So we need to build an orbital chemical / cryo facility to produce at least something as simple as liquid hydrogen and liquid oxygen, again by the kiloton.
This is on top of building an orbital shipyard to construct the actual spaceship, with all that heavy shielding around it, and the skeleton to carry it, the fuel, and the habitable compartment. It's going to be a spectacular feat of space-borne metallurgy, mechanical processing, including precise machining, quite some chemistry to support that all and produce necessary plastic parts, saying nothing about the power plant to feed this all.
Here we assume that we have an asteroid that has enough metals, carbon, and water neatly parked on Earth orbit. How do we achieve that, and how many decades would it take to bring it here, is not even considered.
This all would be great to have! But getting straight to Mars seems simple in comparison.
That's not true. NASA built and tested designs for a nuclear engine in the 80s, human rated even, and the results were spectacular.
True, but small scale solar thermal propulsion systems have been built and require minimal mass. Isp is a largely function of collector area (mylar film is lightweight) and reaction mass. If the water is cracked and the hydrogen used for propulsion, an Isp of 1000 is achievable, far surpassing chemical rockets.
Far more likely, if less romantic to some, is going to be a future of robotic exploration and mining. Once that’s well underway, sending humans on long journeys becomes far more feasible.
Anti-aging drugs?
Gravity is more pervasive. It affects everything in biology and why shouldn't it? It's been a constant in the background that every direction evolution took transitively depends on.