My "favorite" Space Shuttle abort mode is the Return to Launch Site (RTLS) abort[0] because of the complex energy management procedure necessary to pull it off.

As I understand it the energy management of an RTLS is tenuous because, ultimately, the orbiter is an unpowered glider (with a glide ratio similar to a brick). The limits of stress on the orbiter's airframe are a factor, too.

The orbiter's mass, energy (altitude), and downrange position all have to be in a reasonably tight envelope to make the landing without coming up short or overshooting (there's only so much energy you can bleed off doing S turns).

John Young[1] described an RTLS abort working thru "continuous miracles, interspersed with acts of God".

Somebody made a fun (if you like this kind of stuff) simulation of an RTLS abort[2] in Kerbal Space Program.

[0]: https://en.wikipedia.org/wiki/Space_Shuttle_abort_modes#Retu...

[1]: https://en.wikipedia.org/wiki/John_Young_(astronaut)

[2]: https://www.youtube.com/watch?v=Vx94b9nHTHg

NASA proposed STS-1 be an RTLS. John Young wasn't too happy at the idea and compared it to playing Russian roulette.