Any size of object will reflect enough light to reach the ground. The question is how much light do you want?
As a tangible near-baseline example, a Starlink satellite is visible from the ground.
They are about 2.4 m by 1.4 m in base area. (Source)
So at least an area of ~3.3 m^2 is sufficient to illuminate the ground.
Discovery 1, launched Feb 28, 1959. The orbit wasn't quite high enough, it crashed a few days later, but it was the first, with an inclination of 90 degrees.
Launch date 28 February 1959, 21:49:16 GMT
Rocket Thor DM-18 Agena-A (Thor 163 - Agena 1022)
Launch site Vandenberg, LC 75-3-4
Reference system Polar orbit
I think the best bet for answering this question will be a community wiki, in which we post what we know for several different L1/L2 orbiters. I'll start.
L1 - the fastest I know:
LISA Pathfinder was launched on the 3rd of December 2015 and reached L1 orbit on the 22nd of January 2016. So that's 50 days.
L1 - other:
SOHO (Solar and Heliospheric ...
Over what areas of the earth would you expect them to orbit?
Short answer: Over all areas except for the poles.
Seen from Earth, a satellite that isn't in a geosynchronous orbit will always move around the earth - so it'll cover every degree of longitude. Latitude is a bit different, the highest latitude a satellite will reach (i.e. the ...
A colleague of mine from years ago, Jan King, told me that he was a consultant for Iridium in their early planning stages and that their original plan was to place the spacecraft in a precisely 90 deg inclined orbit. This has some special properties in terms of orbit perturbations because it means that most of the biggest gravity irregularities like earth's ...
MSR is one of LeoLab's radar stations (LeoLabs being the people who tweeted about the potential collision, a company whose busines is monitoring satellites). It lives in Midland, Texas, and as such is called the Midland Space Radar. I'm not sure what the contours show, but they're presumably related to the region that the radar can observe.
How? Simple, because they launched into those orbits.
Why? Well, first, let me explain what their orbits actually are.
IRAS (13777) and GGSE-4 (2828) are both in high-inclination orbits, 70° and 99°, respectively. The latter is slightly retrograde, as is common for sun-synchronous orbits. However, to fully understand in what plane they are orbiting, we ...