  Cosmic-ray accelerators capable of reaching ultra-high energies are expected
to also produce very-high energy neutrinos via hadronic interactions within the
source or its surrounding environment. Many of the candidate astrophysical
source classes are either transient in nature or exhibit flaring activity.
Using the Earth as a neutrino converter, suborbital and space-based optical
Cherenkov detectors, such as POEMMA and EUSO-SPB2, will be able to detect
upward-moving extensive air showers induced by decaying tau-leptons generated
from cosmic tau neutrinos with energies $\sim 10$ PeV and above. Both EUSO-SPB2
and POEMMA will be able to quickly repoint, enabling rapid response to
astrophysical transient events. We calculate the transient sensitivity and sky
coverage for both EUSO-SPB2 and POEMMA, accounting for constraints imposed by
the Sun and the Moon on the observation time. We also calculate both detectors'
neutrino horizons for a variety of modeled astrophysical neutrino fluences. We
find that both EUSO-SPB2 and POEMMA will achieve transient sensitivities at the
level of modeled neutrino fluences for nearby sources. We conclude with a
discussion of the prospects of each mission detecting at least one transient
event for various modeled astrophysical neutrino sources.
