Distributed spacecraft flying in formation can overcome the
resolution limitations of monolithic, Earth-sensing systems.
However, formation spacecraft must now expend fuel to counteract
disturbances and the gravity gradients between spacecraft. We
consider three different formation architectures and determine the
delta-v required to maintain relative positions at accuracies
ranging from 0.1 to 10 m (1 sigma). The three architectures
considered are: (i) Leader/Follower, in which individual
spacecraft controllers track with respect to a passive, leader
spacecraft, (ii) Center of Formation, in which individual
spacecraft controllers track with respect to the geometric center
of the formation, and (iii) Iterated Virtual Structure, in which
a formation template is fit each timestep and individual
spacecraft controllers track with respect to the fitted template.
We show that in the presence of relative and inertial sensor noise
and disturbances (e.g., Earth oblateness and aerodynamic drag) relative positions can be maintained to the 10 m level for 4