There are thousands of discarded stages llittering the seabed, when you have sweet sweet uncle sugar money you can throw away stuff for profits.
The Falcon second stage is one of humans most impressive engineering feats. It has by far the best mass ratio of any rocket stage ever made even the Saturn V earth departure stage doesn’t touch it. It’s 3.2 meters wide and 3,500kg empty but holds 100,000+Kg of fuel/O2 and 22,000+ Kg of payload when fully expended. Even reusable it yeets 18,500Kg to LEO.
These guys have some impressive tech. Certainly less than 4,000Kg worth of ballute or encapsulated ballom drag device could safely bring down a F9 stage 2 again it’s only 3.2 meters wide and under 4 tonnes they plan to land 9 tonnes on Mars with much lower atmospheric density...4 tonnes is baby weight in a dense atmo like terra. The idea is you increase drag so much so high you slow down where the air is thin and heating is spread out and low enough you don’t need heat shield mass once slowed to low hypersonic speeds then you dig deeper where stage mass and existing thermal blankets needed for the ride up already have the rating to take the drag heat. The drag device then slows you all the way through transonic and to terminal velocity in double digit km per hour. Pop a GPS flown parafoil and guide your way to either a soft landing on skids, a net or inflatable bag landing or go old skool and midair help capture it again it’s only 4 tonnes a medium lift helo can grab that. Skidding on Teflon coated skis is your least mass choice that doesn’t need ground or aerial infrastructure a parafoil is going to give you a 20 mph or less forward velocity and single meter per second decent rates perfect for a White Sands lake bed landing zone of for SpaceX West Texas or the Gulf of America coastal sand strands. SpaceX could probably kerbal it together in a few months if they had the will to do so. 4,000kg off 18,500 is still a respectable 14,500 to orbit and now you have the cheapest space system humans have come up with. No more yeeting $6 million second stages to Davy Jones in the Pacific.
https://www.gaerospace.com/aerodecelerators/dual-use-lifting-ballute/
https://www.gaerospace.com/aerodecelerators/enveloping-aerodynamic-decelerator-ead-technology/
Design Heatproof parachutes..................