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The potential risk of spacecraft colliding with space debris
increases steadily. About 4000 launches in 42 years have produced
more than 25 000 observable space objects, which are larger than
10 cm in diameter. About 8700 of these are still in orbit (Ref.
ESOC, ESA). The number of smaller particles is much higher. Space
debris fluxes of millimetre or smaller sizes are basically unknown
for orbits above 600 km. Knowledge on impacting fluxes, their
seasonal variations and their long term evolution is required for
a reliable spacecraft risk assessment and the design of protective
shielding.
A snapshot of observable objects
The velocities of spaceborn objects are usually
very high and even a small particle can seriously damage spacecraft.
The velocity of micrometeoroids (natural debris) can vary between
10 km/s and 70 km/s, average is around 20 km/s. Micrometeoroids are
originating from the Solar System, from comets and asteroids. Besides
constituting a hazard for spacecraft they serve also the science.
They can give us more information from the origin of the Earth
and the Solar System.
In orbit the impacting velocity of space debris (man
made debris) depends on the direction of the impact. The average is
about 10 km/s.
Larger and faster particles can penetrate the
protecting shields of the spacecraft and damage its instruments.
Smaller particles, even if not causing a catastrophic failure, can
degrade the performance of sensitive instruments and detectors.
Impact crater on solar cell of EURECA spacecraft.
The bright lines are spaced by 1.25 mm
DEBIE - DEBris In orbit Evaluator
Objects larger than couple of centimetres can be tracked with
radar or with optical telescopes. Particles smaller than two
centimetres in diameter can only be investigated by analysing
retrieved spacecraft, with passive detectors, or by in-situ
monitors. Retrieving space hardware from orbits higher than 600 km
is not possible, so active monitors are required to measure impacting
fluxes. In-situ space debris monitoring instruments will give
valuable information for more accurate debris models.
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Patria Finavitec has developed and manufactured DEBIE instrument,
which is used to determine the parameters of space debris and
micrometeoroids in-situ by their impacts with a detecting surface. The
main goal has been to develop an economic and low resource instrument,
which is easy to integrate to any spacecraft and still provides good
data in real time for space debris modelling. The other main goal has
been to develop a standard space debris-monitoring instrument, which
will produce comparable data from different orbits and spacecraft.
This instrument can measure particles, which are smaller than 1 mm.
DEBIE Sensor Unit
The DEBIE instrument is based on a prototype sensor
unit, which was developed at the University of Kent at Canterbury,
England. The idea is to combine several different detectors. Patria
Finavitec has designed the electronics and been the prime contractor
in developing an industrial version of the instrument. Subcontractors
include Metorex International (mechanical design and manufacturing of
the Sensor Unit) and Space Systems Finland (flight software). The
University of Kent has provided scientific support.
Construction and Principle
DEBIE instrument consists of a Data Processing Unit and up to four
Sensor Units. The Sensor Units can be placed on different sides of
the spacecraft to detect particle hits from different directions. The
data from each particle hit is classified and logged for further
telemetry transmission to the ground station via the spacecraft's on
board data handling.
First flight model of DEBIE instrument: Data Processing Unit and two Sensor Units
Each Sensor Unit implements three plasma detectors and
two piezoelectric detectors. The detecting area of the Sensor Unit is
10 x 10 cm. Two of the plasma detectors are placed in front of a thin
aluminium foil. They measure the plasma (one channel measures electrons
and the other one ions) generated by the particle impacts on the foil.
The piezoelectric transducers are coupled mechanically to the foil and
measure the momentum of the impact. The plasma detector (electrons)
behind the foil detects those particles, which have enough energy to
penetrate through the foil. The particle velocity and mass can be
calculated from the measurement data with the aid of predefined
calibration data. Particles of a 10-15 g or larger mass
(depending on the impacting velocity) can be detected by the instrument.
The first flight of the DEBIE instrument will be in year
2001 on-board PROBA satellite. A second flight model, which is under
construction, will be placed on the International Space Station.
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