Because the limb of the Earth is always within about 30deg of regions within the CVZ, the brightness of scattered earthshine may be elevated for long periods during CVZ observations.Because Hubble orbits in the upper atmosphere, its orbit changes over time in a way that is not accurately predictable.. 
These were projects that were both ÌwádìíTífícally important and would ṣàyẹ̀wò significant telescope time, which would be explicitly dedicated to each project.. 