In recent history, SpaceX has demonstrated mastery of first stage reusability with the launch and landing of their first stage Falcon 9 again. What of the second stage? ULA, Blue Origin, and SpaceX all have planned, designed, and are building rockets that make innovative use of the second or upper stage.
The New Glenn rocket, by Blue Origin, is to be a very large reusable first stage. The second stage is a throw away, just like the traditional second stages. The innovation comes where they stack two second stages on top of one another. This effectively makes a bigger overall rocket without extra development costs of designing a bigger second stage. Sounds interesting, but nothing spectacular.
The Vulcan rocket, by ULA, will have the ACES upper stage. ACES will be more than just an upper stage, it will be a space tug capable of taking payloads to the lunar surface. It will also be able to refuel other ACES. It will have a fuel cell to produce its own electricity and take payloads on long duration missions. Reminds me of a five year mission I heard somewhere...hmm. I doubt that it's fuel cell will last that long without ref
ueling, but overall it sound pretty cool for commercial science missions.
|Credit NASA: Saturn V second stage|
The Interplanetary Spaceship, by SpaceX, seemingly doesn't have an upper stage. It's upper stage has been incorporated into the body of the spaceship. Yep, it's that thing in the back with 40 raptor engines. What SpaceX has done in designing this ship, is that they have created a ship straight out of classic science fiction. The second stage has become fully reusable. It does everything. It launches. It refuels. It lands. What more could you ask for from an upper stage? In my mind, this design takes the lot. It's far out there. It makes you think why we weren't designing spaceships like this in the first place. But that's a whole other discussion. In the interim, SpaceX may try to reuse land and reuse an upper stage on its Falcon Heavy. If successful, it would mean another technical and economic victory, over launch prices, for the company.
Rockets are changing, hopefully for the better. Which application of the upper stage will become standard? Only time will tell.