  This paper studies the drag-tracking guidance design problem of uncertain
entry vehicles. With employing a Nussbaum type function to deal with input
saturation constraint, an output feedback guidance law (bank angle magnitude)
with a high-gain observer is constructed that makes the drag-tracking error
converge near zero in the presence of uncertainties. It is also worthy to claim
that, in contrast to the existing results whose envelope of uncertainty merely
depends on the drag error, the considered uncertainty is allowed to be not
bigger than a function of drag error and integral term of drag error, which
inevitably occurs in practice. The Monte Carlo simulation is done to illustrate
the advantage of the developed method.
