Low-temperature photoluminescence and selective pair luminescence has been used to identify shallow acceptor levels in undoped GaAs epilayers grown by molecular beam epitaxy and metallorganic molecular beam epitaxy (triethylgallium/As-4) in the ultra-vacuum of space generated in the wake of the free flying Wake Shield Facility satellite (Space Shuttle Colombia mission STS 80). The low-temperature photoluminescence spectra are typical of high-purity GaAs. The near-band-edge excitonic luminescence are found to be dominated by donor bound excitons. Carbon C-As appears as the main residual acceptor impurity and excited state spectroscopy clearly identifies the presence of zinc residual acceptor (Zn-Ga). Finally, the absence of a Be impurity, introduced in large quantities to the growth environment prior to the MOMBE growth, suggest a minimized memory effect on the free flyer.