SAGE: AN ITALIAN PROJECT OF SATELLITE ACCELEROMETRY
F. Sanso’ (1) , A. Albertella 0) , G. Bianco (2) , A. Della Torre (3) , M. Fermi (4) ,
V. lafolla (5) , A. Lenti (6) , F. Migliaccio 0 A. Milani 00 , A. Rossi (8)
(1) DIIAR Politecnico di Milano -Italy (2) ASI - Centro di Geodesia Spaziale di Matera - Italy
(3) Carlo Gavazzi Space S.p.A. - Milano Italy (4) Telespazio S.p.A. - Roma - Italy (5) IFSI/CNR- Roma - Italy
(6) Laben S.p.A. - Vimodrone - Italy (7) Dip. Matematica - Università di Pisa - Italy (8) CNUCE/CNR - Pisa - Italy
KEY WORDS: Gravity field determination, Satellite accelerometry.
ABSTRACT:
SAGE is a project for a satellite accelerometric mission aimed at determining with high precision the low-medium
coefficients of the earth gravity field and their time variations.
In the international panorama, SAGE would be a prosecution of CHAMP, both in time (in case of approval, SAGE launch
date would be within the year 2001) and in space (SAGE would fly polar, filling in the polar gaps).
SAGE has gone through a Phase A study commissioned by the Italian Space Agency (ASI), which lasted from
December 1997 to October 1998.
1. THE PROJECT OF THE MISSION SAGE
AND ITS RELATION TO THE OTHER
GRAVITY FIELD MISSIONS
SAGE is a fully Italian project aiming at determining the
gravity field of the Earth by exploiting the concept of
high-low satellite-to-satellite tracking (SST). This
means that the satellite orbit is determined by GPS,
while the non-gravitational perturbations are determined
by a three-axes accelerometer which, integrated back
two times, gives the “virtual” orbit followed under
gravitational effects only.
The outline of the mission
requirements are as follows:
SAGE and the general
Launch date
Lifetime
Altitude
Inclination
Nominal eccentricity
Bus
Payload
Italian Spring Accelerometer (ISA)
GPS receiver Lagrange
Laser Retroreflector Array (by GFZ Potsdam)
2001
5 years (minimum)
between 450 and 350 km
87° (possibly polar)
e = 0
MITA (C. Gavazzi Space)
Several Italian research institutions and industries
participated to the SAGE Phase A study. Namely, the
following research centers were involved:
• ASI/CGS Matera, for telemetry and GPS analysis;
• IFSI/CNR Roma, for the development of the ISA
accelerometer;
• Politecnico di Milano - IGeS, for the study of the
spacewise reduction strategy of the data;
• Università di Padova, for the GPS data analysis;
• Università di Pisa - CNUCE, for the sudy of the
timewise reduction strategy of the data and the
orbital analysis;
• Università di Trento, for complementary studies on
the spacewise reduction startegy.
The industrial partners were:
• Carlo Gavazzi Space S.p.A., developing the study
of the MITA bus and of the navigation and data
communication segment;
• Laben S.p.A., involved in the accelerometer
engineering and in the development of the
Lagrange GPS receiver;
• Telespazio S.p.A., for the GPS data analysis, data
downloading and telemetry.
Right Solar
Panel
Braces
Fig. 1 SAGE structure and internal accommodation,
showing the position of the ISA accelerometer next to
the centre of mass of the spacecraft.
It is interesting to remark that SAGE would be logically
and temporarily interwoven with CHAMP, as the two
missions are based on the same scientific principle.
Specifically, SAGE would aim at:
• improving the CHAMP goals aiming at the useful
determination of coefficients up to degree 70;
• extending in time the CHAMP mission allowing for
a high-low SST sampling of the gravity field at an
altitude of 400 km with an overall time span of 7 to
8 years, which could give more reliable information
on time variations of the field;
• cross-checking the two missions one with respect
to the other, because they will fly together more or
