  We explicitly compute the (NS) sector conventional type-I superstring
tree-level amplitudes at five points after compactifying to 4-D, express the
QFT building block in the helicity basis, and give several attempts towards
arbitrary $n$ points. More specifically, we consider the interaction of one
first excited level and otherwise massless states of conventional type-I
superstrings, where the four-dimensional states can, for instance, be realized
via D$3$ branes. We construct the amplitude by using the Berends-Giele
currents. From the recursion of Berends-Giele currents, we can generate the
higher point amplitude. We also apply the BCFW recursion with massive external
legs shifted and get the amplitude for arbitrary $n$ points.
