Several mission ideas crossed my mind:
"Garbage Man"
A quicksave is provided for the mission. There are five objects to be recovered. One in High Earth Orbit, one in LEO, one in Low Moon Orbit, one in elliptical Earth orbit, and one in between Earth and Mars Orbit. All must be recovered without breaking anything. Five launches allowed.
"Near-Realistic Reentry"
Do a Mars, Phobos, Deimos return mission, but the reentry temperature on Mars and Earth must not exceed 2000⁰C. (To be honest, I don't know how high the temperature of heat shield could be. Quick Googling found the numbers around 1500-2700ºC)
A mission that involves a spacecraft / a body that's retrograde to the orbit of planets.
I somewhat think that Reusability and Shuttle challenge can be combined with several Teams challenge. Could be a fully reusable Mars Mission, shuttle delivered space station building, etc.
Heck, maybe make a Deja Vu Club? Redo the Moon Mission, Mars Mission, Space Station, and Galilean Mission in Deja Vu fashion as the requirement. Definitely time consuming and excruciating

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