Obviously this is not possible right now since 2nd stage is not reusable, so the question is: how hard would it be to develop some addons to 2nd stage to make it reusable just for reliability testing purposes? The difference from a production reusable 2nd stage is that the testing version is not required to put a payload to orbit, and depending on the test requirements, it itself may not need to reach orbit. The main requirement would be: a. it can be reused cheaply; b. it mirrors production 2nd stage design and flight profile as closely as possible.
Given the recent mishap and the discussion on CRS-7 thread, I was thinking a fully reusable system could really help right now, since you can fly test flights cheaply to verify possible root causes, and later confirm the fix actually works. It could also be used to test future upgrades without endangering customer's payload, and its test flights can be used to build up customer confidence.
...Musk has stated upper stage reusability is off the table till the vehicle after the FH. That will be Methane so any development work here is known to be a dead end.
The technology and operational experience of developing a recoverable second stage would be beneficial and have real financial benefits.As we've seen with the first stage recovery efforts it's not a slam dunk. Lots to figure out with hardware, software and operations. Developing these abilities with an existing, revenue generating vehicle would be cheap development and is what SpaceX is currently doing with the booster.Other tangible benefits is that they would be able to better design a MethLOx upper stage. It can be designed from the very start to be re-useable with the lessons learned reducing those development costs and all that experience .
Obviously this is not possible right now since 2nd stage is not reusable,
so the question is: how hard would it be to develop some addons to 2nd stage to make it reusable just for reliability testing purposes?
The difference from a production reusable 2nd stage is that the testing version is not required to put a payload to orbit, and depending on the test requirements, it itself may not need to reach orbit. The main requirement would be: a. it can be reused cheaply; b. it mirrors production 2nd stage design and flight profile as closely as possible.
What if the Second Stage only needs to fly itself on a suborbital trajectory from the ground and back, as a qualification measure?Suppose you replace the payload with a big set of legs (legs which attach to the top of the stage) and some SuperDracos. The second stage itself is an article intended for orbital flight. In Texas or New Mexico, the stage is fitted to this recovery package, launched off the ground as Grasshopper was, boosted into a sub-orbital trajectory and subjected to the same acceleration profile you'd get in flight, and then landed. The stage is then de-mated from the recovery package, and trucked to a launch site with a "Flight-Tested" stamp. This would weed out defective stages in a fully-reusable manner, and doesn't seem that it should be more expensive than Grasshopper tests (the components are the same--fixed landing gear and a single Merlin engine). I'm just a student, but does this suggestion have merit?