A high-level summary of NEOfixer’s workflow is this: for each object, for each follow-up station, for each time in the ephemeris, calculate a unique priority score.
NEOfixer fetches astrometry of all cataloged NEOs from the Minor Planet Center (MPC) database, plus astrometry of NEO and comet candidates from the NEO Confirmation Page (NEOCP) and Potential Comet Confirmation Page (PCCP). These are the fundamental data products that feed NEOfixer. Supplemental information comes from the JPL Center for NEO Studies (Scout and Sentry impact probability, NHATS, Yarkovsky candidates), NEODyS (impact probability), and MPC (multiple designation assignments, historical NEOCP outcomes). NEOfixer also incorporates feedback from follow-up stations regarding their intent to observe particular NEOs, and the outcome of those observations.
Astrometry is separated into objects, and orbits are determined by Project Pluto’s open-source orbit-fitting code Find_Orb. Note that the orbits, ephemerides, and uncertainties determined by NEOfixer all come from Find_Orb, and are independent from other orbit computers such as MPC or JPL.
For each orbit, a geocentric ephemeris is generated (MPC code 500), running forward a few weeks into the future. NEOfixer then checks to see which sites can potentially observe each object at some point during the look-ahead period. The object is then scored according the criteria outlined above (Importance, Confidence, Benefit, Urgency, Cost), and is inserted into that site’s list of potential targets. When all the objects have been scored, the list is sorted by priority and presented as a large table. The amount of work that NEOfixer needs to do to pre-calculate all this information scales with the number of objects (cataloged NEOs and NEOCP objects), the number of participating sites, and the length and resolution of the look-ahead ephemeris (e.g. 3 weeks of ephemerides, every 15 minutes).
NEOfixer maintains a rapid refresh cadence, so when new astrometry is published by the MPC, or information about an object is updated from an external source, NEOfixer detects the change, reprocesses the orbit and ephemeris, re-calculates the score for each site, and publishes the new information. Objects are updated typically within a few minutes of new information becoming available.