CNO cycle at the base of a hydrogen layer. The hydrogen layer, in turn, is replenished by the continuous accretion of gas supplied by a hydrogen-rich brown dwarf companion star, which resides in a 2.01 hour orbit around the pulsar [@Chakrabarty1998; @Bildsten2001].

The X-ray bursts of [SAX J1808]{}have also reliably shown photospheric radius expansion (PRE; see, e.g., @Galloway2008, for a review). Such PRE may drive the ejection of burning ashes, whose presence could cause discrete spectral features in the burst emission [@Weinberg2006; @Yu2018]. Measuring such spectral lines gives a window into the thermonuclear burning reactions, and can potentially be used to constrain the neutron star compactness. Additionally, a large fraction of the burst emission is expected to be intercepted and reprocessed by the accretion disk [@Ballantyne2005; @Degenaar2018; @Fragile2018], providing an opportunity to characterize the state of the accretion disk through the spectrum of the reflected burst emission.

Launched in June 2017, the *Neutron Star Interior Composition Explorer* ([*NICER*]{}; @Gendreau2017) combines good spectral resolution with superb time-resolution and high throughput in the ${0.2-12}$[[keV]{}]{}energy band. These properties make [*NICER*]{}an ideal instrument to study the evolution of PRE in Type I X-ray bursts [see, e.g., @Keek2018b; @Keek2018a; @Jaisawal2019], and search for discrete spectral 