  The origin of the highest energy cosmic rays is still unknown. At present,
the major uncertainties are located at energies above $\sim 10^{19.5}$ eV, the
expected beginning of the GZK suppression. This is mainly due to the low
statistics available, a problem that will be addressed in unprecedented way by
the upcoming orbital detectors like JEM-EUSO. The detection of very high energy
photons is of great relevance for the understanding of the origin of this
extreme energy cosmic rays (EECR), due to the astrophysical information
content. However, their discrimination is an experimental challenge for current
and future cosmic ray detectors. In this work we study the statistical
separation between hadron and photon showers from space observations at
energies where both, the Landau-Pomeranchuk-Migdal (LPM) effect and
magnetospheric interactions are important for the development of the cascades.
We base our analysis on the $X_{max}$ parameter, which is already a well known
composition discrimination parameter for ground based fluorescence
observatories. Our analysis applies to orbiting detectors in general.
Nevertheless, we exemplify the practical utilization of our technique by
estimating a general upper limit to the photon fraction in the integral flux,
attainable by an ideal orbital detector with characteristics similar to
JEM-EUSO. In the process we describe the resultant asymmetry in the
photon-hadron discrimination efficiency in galactic coordinates.
