This is a preliminary assessment from data available at the NASA JPL NEO search statistics site to examine just how many Near Earth Asteroids (NEAs) the proposed B612 Foundation Sentinel Telescope will find.
The B612 Foundation states the Sentinel Telescope will "track 90 percent of Earth-orbit-crossing asteroids with impact energy greater than 100 Megatons" [assuming equivalent to a lower limit of a 140 meter Apollo asteroid]. They also state that "Sentinel will discover and track half a million Near Earth Asteroids" (source: B612 Foundation press release material).
Using current statistics [April 2012] here are how estimates as to many NEAs we have found so far (from Lindley Johnson presentation in June 2012):
Between 0-30 m: Found ~1150 or 0.01% of a total est. pop. of 11.5M
Between 30-100m: Found ~1950 or 0.4% of a total est. pop. of ~500k
Between 100-300m: Found 2100 or 10% of a total est. pop. of 21,000
Between 300-1000m: Found 2400 or 50% of a total est. pop. of 4,800
Greater than 1000m: Found 850 or 94% of a total est. pop. of 904
The current statistics indicate that we have found only 5,350 of an estimated population of 26,704 NEAs (about 20%) greater than 100m, thus there are about 21,354 NEAs greater than 100m undiscovered, and only 1.42% of objects greater than 30m in diameter (out of more than 500k objects).
If B612 Foundation were to find 90% of objects greater than 100m, then this would be about 21-24k NEAs. If B612 Foundation were to find 90% of objects greater than 30m, then this would be about 460k NEAs.
Thus over 5.5 years (the stated lifetime of the observatory), the Sentinel telescope would find 354 NEAs greater than 100m per month and 7,011 NEAs greater than 30m per month.
Note: on average we have been finding about 93 NEOs (not NEAs) per month over the last 6 months (this includes all sizes). Thus the Sentinel telescope will be at least 4 to 75 times more effective in finding new NEAs than current approaches (depending upon its specific capability). This would mean that within 5-6 years, the NASA goal of 90% of objects greater than 140 m would be achieved.
Note: the total number of NEAs are estimated and may be slightly off.