  The TESS exoplanet-hunting mission detected the rising and decaying optical
afterglow of GRB 191016A, a long Gamma-Ray Burst (GRB) detected by Swift-BAT
but without prompt XRT or UVOT follow-up due to proximity to the moon. The
afterglow has a late peak at least 1000 seconds after the BAT trigger, with a
brightest-detected TESS datapoint at 2589.7 s post-trigger. The burst was not
detected by Fermi-LAT, but was detected by Fermi-GBM without triggering,
possibly due to the gradual nature of rising light curve. Using ground-based
photometry, we estimate a photometric redshift of $z_\mathrm{phot} =
3.29\pm{0.40}$. Combined with the high-energy emission and optical peak time
derived from TESS, estimates of the bulk Lorentz factor $\Gamma_\mathrm{BL}$
range from $90-133$. The burst is relatively bright, with a peak optical
magnitude in ground-based follow-up of $R=15.1$ mag. Using published
distributions of GRB afterglows and considering the TESS sensitivity and
sampling, we estimate that TESS is likely to detect $\sim1$ GRB afterglow per
year above its magnitude limit.
