  Jets, clusters of collimated particles produced in high energy proton-proton
($pp$) collisions, are an excellent tool to study the internal structure of the
proton. According to perturbative QCD (pQCD) calculations, for center-of-mass
energies of $\sqrt{s} = $ 200 and 510 GeV at RHIC, jet production in the mid
pseudorapidity, $|\eta| <$ 1, is dominated by quark-gluon and gluon-gluon
scattering processes. These jets are sensitive to gluons in the proton with
momentum fraction 0.01 $<x<$ 0.5. The STAR experiment has measured a series of
jet double-spin asymmetries within the pseudorapidity region of $-1 < \eta <
2$, in longitudinally polarized $pp$ collisions, to constrain the gluon
helicity distribution function in the proton. Similarly, jet cross section
measurements from unpolarized $pp$ collisions are effective in constraining the
unpolarized gluon distribution in the proton. In this proceeding, we will
present the analysis techniques and the preliminary results of inclusive jet
cross section measurements in $pp$ collisions at $\sqrt{s} =$ 200 and 510 GeV.
