ttocsmi wrote:
The side boosters flip around and navigate themselves back to the Cape. The center booster does the same thing, a few hundred miles offshore. Even the payload fairings have their own avionics to assist with recovery.
It would be cool to interview the engineers and launch managers involved with the space program in the late 1960s. I'd love to hear their thoughts today. Was the idea floated at the time to recover the first stage and/or crew capsule on land? What prevented that from happening? Materials science? Computing resources? Control algorithms? One of those occasions where the math works out but the engineers say, "how do we do THAT?" All of the above?
Yes, the idea has been floated since the beginning of rockets. Just think back to old pictures of pictures of flash gordon type rockets landing on their tail. Everybody knew that throwing away the rocket after each flight was sub-optimal.
Recovering capsules on land? That is how the Russians have always done it. The Gemini capsule was designed to also allow landing on land, they even designed a neat parachute design to allow lots of control. Which is important, because landing on land is tricky with normal parachutes. Normal parachutes don't have much control at all, so you need a very large empty area for landings (which Russia clearly has). Because you don't want you booster landing on house. So the Gemini design had lots of control to only require a small area to be empty. But the Gemini design was ditched to reduce risk and they just continued landing on water. So with a booster they gave lots of thought to recovering over water, since there is lots of empty water. You also generally launch over water, so you don't need to figure out how to get these boosters back to land. You could fire the engines, but that requires flying with more fuel to do, which means you must launch less weight into orbit. Or deploy some wings, with also weigh something, so less payload again. So recovery over water is good, but salt water is bad for pretty much everything, so actually landing in the water is bad. Now there were some ideas to parachute the rockets down and then snag them with a plane or helicopter before they actually hit the water, eliminating the salt water problem, but adding lots more. ULA is actually planning on this for their next gen and have some good arguments over a propulsive landing.
Why wasn't it done before? Because it is difficult. Control systems are difficult, not just controlling the rocket, but controlling the engine to get it to fire up fast and be able to throttle it so well. The other thing was all the techniques in order to do this with the minimum amount of fuel. If you have lots of fuel, this landing is not that difficult, but if you require lots of fuel means you have to take all the fuel up to high altitudes and high speeds, which requires even more fuel at the start or a lighter payload. It is a vicious circle that every pound of fuel required for landing takes 10 pounds of fuel at the launch. That is partly why propulsive landings were dismissed before, it was thought that parachutes were lighter than the fuel it would take to land. But people developed clever techniques in order to reduce the fuel needed. The final factor was the risk reduction performed by others and by spacex's hopper. You don't want to design a giant rocket and plan on propulsive landing. It took lots of companies developing this technology with each building on the lasts and proving that each step was possible. By the time spacex came around, lots of it was proven, so the risk was greatly reduced.