Quantum “unconditionally” secured communications make human-crewed combat aircraft obsolete. The most expensive DOD program in history- the F-35- is a boondoggle and the ultimate expression of “pork.” The most incredibly expensive waste of taxpayer dollars is not this single weapon system though, it is the replacement of legacy systems now underway to the tune of around 2 trillion dollars (adjusted for inflation over the next decade or so).
New ICBM’s, new missile submarines, new stealth bombers, proliferation and weaponization of weapon systems in Earth orbit , new anti-ballistic weapon systems (that will not work due to simple physics) etc. etc.
The best path is to move the nuclear arsenals of the superpowers to human-crewed spaceships months away in deep space. This would also serve to protect the Earth from impact threats and also help along Space Solar Power (using lunar factories) as the solution to the climate change crisis. All part of a Green New Space Deal.
Close to 100,000 of these pieces of space junk are on the way up over the next ten years. It is a disaster unfolding. And it never should have been allowed. At some point, when bad things start happening, many people actually involved and hoping to cash in are going to display their faux shock and outrage that “others” enabled such a profoundly bad idea.
The only solar sail technology that has any practical use is Medusa. It could be argued it is not actually a solar sail but it can utilize fusion energy for space propulsion using a sail.
The Solem Medusa concept is the “soft” precursor to much larger and more efficient “hard” systems using alloy discs. During the decades required to build a lunar industrial infrastructure capable of manufacturing massive pulse propulsion discs (https://newatlas.com/energy/rio-tinto-heliogen-concentrating-solar/) the “spinnaker” of the Medusa concept, though less efficient, could carry the first human missions to the outer solar system.
That first mission could likely to be to Ceres. Mars, like LEO, is a complete dead end.