A paper describes algorithms for guidance and control (G&C) of a spacecraft maneuvering near a planet, moon, asteroid, comet, or other small astronomical body. The algorithms were developed following a model-predictive-control approach along with a convexification of the governing dynamical equations, control constraints, and trajectory and state constraints

Acikmese, Ahmet

Carson, John M., III

NASA Technical Reports Server

NASA Tech Briefs, June 2007 31
Books & Reports
Smart Data Node in the Sky
A document discusses the physical
and engineering principles affecting
the design of the Smart Data Node in
the Sky (SDNITS) — a proposed Earth-
orbiting satellite for relaying scientific
data from other Earth-orbiting satellites
to one or more ground station(s). The
basic concept of the SDNITS is similar to
that of NASA’s Tracking Data Relay
Satellite System (TDRSS). However, the
SDNITS would satisfy the needs of the
next generation of Earth-observing satel-
lite missions, including, notably, the
need to relay data at much higher rates
— of the order of 10 Gb/s versus ≤400
Mb/s for the TDRSS. 
The document characterizes the prob-
lem of designing the telecommunica-
tion architecture of the SDNITS as con-
sisting of two main parts: (1) finding the
most advantageous orbit for the SDNITS
to gather data from the scientific satel-
lites and relay the data to the ground,
taking account of such factors as visibil-
ity and range; and (2) choosing a
telecommunication architecture appro-
priate for the intended relay function.
The design of the SDNITS would incor-
porate technological advances — espe-
cially in the field of high-rate data trans-
mission — that have occurred during
the three decades since the TDRSS was
designed.
This work was done by Faiza Lansing and
Anil Kantak of Caltech for NASA’s Jet Propulsion
Laboratory. Further information is contained
in a TSP (see page 1).
NPO-30904
Pseudo-Waypoint Guidance
for Proximity Spacecraft
Maneuvers
A paper describes algorithms for guid-
ance and control (G&C) of a spacecraft
maneuvering near a planet, moon, aster-
oid, comet, or other small astronomical
body. The algorithms were developed
following a model-predictive-control ap-
proach along with a convexification of
the governing dynamical equations, con-
trol constraints, and trajectory and state
constraints. The open-loop guidance
problem is solved in advance or in real
time by use of the pseudo-waypoint gen-
eration (PWG) method, which is a blend
of classical waypoint and state-of-the-
art, real-time trajectory-generation meth-
ods. The PWG method includes satisfac-
tion of required thruster silent times
during maneuvers. Feedback control is
implemented to track PWG trajectories
in a manner that guarantees the resolv-
ability of the open-loop-control problem,
enabling updating of G&C in a provably
robust, model-predictive manner. Thruster
firing times and models of the gravita-
tional field of the body are incorporated
into discretized versions of the dynamical
equations that are solved as part of an op-
timal-control problem to minimize con-
sumption of fuel or energy. The optimal-
control problem is cast as a linear matrix
inequality (specifically a second-order
cone program), then solved through semi-
definite-programming techniques in a
computationally efficient manner that
guarantees convergence and satisfaction
of constraints.
This work was done by Ahmet Açikmeşe and
John M. Carson III of Caltech for NASA’s Jet
Propulsion Laboratory. Further information is
contained in a TSP (see page 1).
The software used in this innovation is
available for commercial licensing. Please con-
tact Karina Edmonds of the California Institute
of Technology at (626) 395-2322. Refer to
NPO-42753.
Update on Controlling Herds
of Cooperative Robots
A document presents further informa-
tion on the subject matter of “Controlling
Herds of Cooperative Robots” (NPO-
40723), NASA Tech Briefs, Vol. 30, No. 4
(April 2006), page 81. To recapitulate: A
methodology for controlling a herd of co-
operative and autonomous mobile robots
exploring the surface of a remote planet
or moon (specifically, Titan or Titan-like)
is undergoing development.  The pro-
posed configuration of mobile robots
consists of a blimp and a herd of surface
sondes. The blimp is the leader of the
herd, and it commands the other robots
to move to locations on the surface or
below the surface to conduct science oper-
ations. Once a target is chosen, the sondes
cooperatively aim sensors at the target to
maximize scientific return. This hierarchi-
cal and cooperative behavior is necessary
in the face of such unpredictable factors
as terrain obstacles and uncertainties in
the model of the environment. 
This document describes the coopera-
tion architecture and the estimation al-
gorithm.  Dynamical and kinematical
models of the blimp and surface sondes
are derived, and a robust guidance and
control algorithm, based on a potential-
field mathematical model, is developed.
This guidance-and-control algorithm
can compute actuator forces needed for
moving the surface sondes across the
terrain while avoiding hazards and colli-
sions with each other and at the same
time remaining within communication
range with the blimp.
The document describes the results of
the computational simulations of a one-
blimp, three-surface-sonde herd in vari-
ous operational scenarios, including
sensitivity studies as a function of distrib-
uted communication and processing de-
lays between the sondes and the blimp.
From results of the simulations, it is con-
cluded that the methodology is feasible,
even if there are significant uncertain-
ties in the dynamical models.
This work was done by Marco Quadrelli and
Johnny Chang of Caltech for NASA’s Jet Propul-
sion Laboratory. Further information is con-
tained in a TSP (see page 1).
The software used in this innovation is
available for commercial licensing. Please con-
tact Karina Edmonds of the California Insti-
tute of Technology at (626) 395-2322. Refer
to NPO-35031.
Simulation and Testing of
Maneuvering of a Planetary
Rover
A report discusses the development
of a computational model of a Mars Ex-
plorer Rover maneuvering across ter-
rain under varying conditions. The
model is used to increase understand-
ing of the rover dynamics. Increased
understanding is helpful in planning
further tests and in extending the oper-
ational range of the rover to terrain
conditions that would otherwise have
to be avoided in a conservative ap-
proach. The model is implemented
within MSC.ADAMS®, a commercial
suite of computer programs for simu-
lating a variety of automotive and aero-
nautical mechanical systems. Following
its initial formulation, the model has
been successively refined in an iterative
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Pseudo-Waypoint Guidance for Proximity Spacecraft Maneuvers

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