POLITECNICO

Space field research activities
at the aerospace department
of Politecnico di Milano
Moon Exploration
Since a new interest for lunar exploration and exploitation
is risen up in recent years severa1 topics are
under study to better design a mission to the Moon.
Three are the main areas of interest:
WSB Transfer Trajectories. Weak Stability
Boundaries (WSB) are a new and inhiguing altemative
to classica1 Hohmann transfers. Proposed for the
Cst time by Belbmno, this kind of transfer trajectory
exploits regions of transition between stable and
unstable manifolds, providing a meaningful saving of
propellant An efficient procedure to design an optimal
transfer by WSB is under development along with a
stability analysis of the designed trajectory.
Orbit Maintenance. The non-uniform gravity field of
the Moon yields strong periurbiig effects on low perilune
orbits leadig to a hard landing ahr few revolutions.
A siudy of long and medium term effects aimed
Io identify periodic stable solutions and stabilising
minimum Dv manoeuvres has been camed out.
* Optimal Landing. Minimum mass homing trajectory
to a desired target from a given coasting orbit is ofprimary
for the actual reaiisation of the mission. Optiial
control law and optimal initial conditions have been
denved to perform the desii landing trajectory keeping
into account orbita1 and attitude dynamics and
constraints.
Figure I: Periodic solutions
Figure 2: Optirnal thrust program
Figure 3: w o link planar manipulator
Microsafeiiites Design: PalaMede
Program PalaMede aims to put in a sun-synchronous
polar orbit a micmsatellite entirely designed by students
inside the Department of Aerospace Engineering
of the Politecnico di Milano. PalaMede is an educati&
nal program and is intended Io be an important chance
for students to apply in practise what they have learned
in theory.
Furthermore PalaMede is designed to be a basic
platform to test new concepts for future small and
cheap satellites. In pariicularly No basic ideas are leadig
the entire project: first of al1 the subsystems are
made by standard components not design for space and
second PalaMede will be a muhipurpose bus fora wide
range of payloads. Two cameras repwmt present payload:
one CCD colour camera, which shaU take pictures
of the Earth, and an infrared wnera, which shaU
take picture of the outer space.
The prehmmy design of al1 the suhystems is complete,
at present, and part of the power system and
HDCS is going to be built and tested.
Fiexible Manipdators
Space robots will play an increasing important role in
space missions of the Intemational Space Station era.
Space robot arms are very light and slender: then the
flexibility, causiig long period elastic vibration during
maneuvering, is a critica1 issue to dea1 with. The foilowing
arguments are being studied :
* Path Optimiition. Different kind of optimization are
beiig investigated, e.g. time and energy consumption
minimintion.
Flexibility Control. Both standard optimal control
system, as LQR, and modern method, as Neural
Networks, are applied to contml links and joints flexibili@.
* Interaction between manipulator dynamics and base
strutture.
Experimental tests are earried out on a two rotational
degrees-of-freedom planar manipulator with highly
flexible links, which has been purposely designed and
set up in our laboratories.
Active Control of hrge Fìexible Struciures
Space struciures must be characterized by a very higb
efficiency, measured by the launch costs and the possibili@
of being assembled directly on orbit.
This calls for the adoption of modular tniss shuctures
in al1 the cases where more functional elements must
be wnnected but kept at a certaii relative distance.