We determine the absolute magnitude ( H ) distribution ( or size-frequency distribution , SFD ; N ( H ) \propto 10 ^ { \alpha H } where \alpha is the slope of the distribution ) for near-Earth objects ( NEO ) with 13 < H < 30 and Asteroid Retrieval Mission ( ARM ) targets with 27 < H < 31 that were detected by the 1 ^ { st } telescope of the Panoramic Survey Telescope and Rapid Response System ( Pan-STARRS1 ; e.g . ) .
The NEO and ARM target detection efficiencies were calculated using the NEO orbit distribution .
The debiased Pan-STARRS1 NEO absolute magnitude distribution is more complex than a single slope power law - it shows two transitions - at H \sim 16 from steep to shallow slope , and in the 21 < H < 23 interval from a shallow to steep slope , which is consistent with other recent works ( e.g . ) .
We fit \alpha = 0.48 \pm 0.02 for NEOs with 13 < H < 16 , \alpha = 0.33 \pm 0.01 for NEOs with 16 < H < 22 , and \alpha = 0.62 \pm 0.03 for the smaller objects with H > 22 .
There is also another change in slope from steep to shallow around H=27 .
The three ARM target candidates detected by Pan-STARRS1 in one year of surveying have a corrected SFD with slope \alpha = 0.40 ^ { +0.33 } _ { -0.45 } .

We also show that the window for follow up observations of small ( H \gtrsim 22 ) NEOs with the NASA IRTF telescope and Arecibo and Goldstone radars are extremely short - on order of days , and procedures for fast response must be implemented in order to measure physical characteristics of small Earth-approaching objects .
CFHT ’ s MegaCam and Pan-STARRS1 have longer observing windows and are capable of following-up more NEOs due to their deeper limiting magnitudes and wider fields of view .