The LHCb experiment has the unique possibility, among the LHC experiments,
to be operated in fixed target mode, using its internal gas target SMOG.
The energy scale achievable at the LHC and the excellent detector capabilities
for vertexing, tracking and particle identification allow a wealth of measurements
of great interest for cosmic ray physics. We present the first measurement of
antiproton production in proton-helium collisions at $\sqrt{s_{NN}} = 110$ GeV, which
allows to improve the accuracy of the prediction for secondary antiproton production in
cosmic rays. Prospects for other measurements achievable in the fixed target program
are also discussed.