How much mercury would actually filter down? Ion engines are extremely high isp (1000-8000 seconds). Literature suggests that 3000s was demonstrated back in the 70s. This implies an exhaust velocity of ~30km/s, while Earth escape velocity is 11km/s (depending on altitude)
It appears that PEER assumes that the ACE engine would be used against the direction of travel (retrograde), but almost all station keeping burns are prograde, in order to keep the satellite up against ionospheric or exospheric drag. And they assume a lower isp than has previously been demonstrated with mercury fueled engines.
It appears that PEER assumes that the ACE engine would be used against the direction of travel (retrograde), but almost all station keeping burns are prograde, in order to keep the satellite up against ionospheric or exospheric drag. And they assume a lower isp than has previously been demonstrated with mercury fueled engines.