As part of the Galactic Bulge Time Domain Survey (GBTDS), Roman will conduct the first ever dedicated gravitational microlensing survey from space. In order to maximize the number of microlensing events Roman will detect, the survey fields will be placed in the highly-crowded stellar region towards the galactic bulge.

There have been several proposed designs for the GBTDS observing strategy, a recap of these designs can be found in the following works:

  1. Spergel et al. 2015
  2. Penny et al. 2019
  3. GBTDS Definition Committee Report

Pre-launch Observing Strategy (as of 2025)

The nominal GBTDS observing strategy will use the wide-field instrument (WFI) to image a total of seven fields (six ‘bulge’ + one ‘GC’) for six 70-day seasons. Each exposure will be 72 seconds, and the imaging cadence for all fields (including the GC) will be 14.6 minutes.  
 

Additionally, at the beginning and end of each season, Roman will obtain several exposures of each field in all of the available passbands (0.62 - 2.13 microns). This will enable very precise classification and stellar properties to be extracted for all sources in each field. Finally, as there will be a significant gap in time between season three and four of the GBTDS, there are Roman visits scheduled at lower cadence to perform ‘gap filling’ during this time (one image every five days).

Caption: This animation shows one 'nominal' design of the GBTDS.
Credit: R. Wilson (NASA GSFC).