Israel's miniature space satellites.

Venus - The next eye in the sky
Posted Friday, Mar. 10, 2006 on IsraCast.com

By the end of the decade a revolutionary new micro-satellite will orbit
around
the world at an altitude of 700km sending precise information on
agriculture and
marine changes in unprecedented precision and detail. The
Israeli-French project
will allow farmers to better treat their crops, fisherman to locate
large
quantities of fish in mid-sea and will also vastly increase the ability
of the
scientific community to study and monitor the flora and fauna in many
areas
around the globe. Equipped with an advanced plasma engine, VENUS will
be able to
operate for at least 4-5 years in its planed orbit.

The roots of the VENUS project date back to 1994 when the Israeli Space
Agency
(ISA) and the French CNES established space cooperation. In 1997, the
two
agencies envisioned working together on micro-satellites. It took
another six
years but in December 2003, the objectives of the VENUS (or Vegetation
and
Environment Monitoring New Micro-Satellite) mission were defined and
the project
was officially underway. VENUS's primary mission has been defined as a
multi-spectral observation satellite for the European Global Monitoring
for
Environment and Security program (GMES). CNES officially stated four of
the main
goals of the VENUS mission:

* Enable significant advances in understanding and modeling of
continental
land surfaces, by combining space-based and in situ observations with
vegetation
and soil models.
* Promote research procedures of monitoring water quality in the
coastal
plain and inland water bodies.
* Help to improve how terrestrial surfaces are represented in
meteorology,
climate, and carbon models.
* Demonstrate the value of this kind of observation for sustainable
land
management, decision support, and environmental monitoring.

In an interview with Dr. Zvi Kaplan, the director of the Israeli space
agency,
IsraCast was told that the VENUS satellite, using its super-spectral
camera,
will enable farmers to view their fields with high resolution (5.3m)
and using
the data received from the analysis of the camera's various spectral
bands to
decide how much nitrogen, water and fertilizer every part of their
field
requires. This could lead, in the future, to a fuller implementation of
the idea
of Precision Agriculture in which farmers use data from GPS satellites
as well
as from observation satellites in order to improve their crops. Since
the VENUS
satellite will orbit the earth in a 500-700km polar orbit (which will
permit the
vehicle to receive continuous sunlight and hence power during its
entire
mission) passing over every point around the globe every 48 hours, it
can become
an ideal tool for monitoring changes in vegetation for farmers and
scientist
alike.

VENUS in the sky with ions

Two other aspects of the satellite which are also worth mentioning are
the
engine and the over all size and weight of the system. After being
denied access
to advance space technologies for many years, Israel developed its own
unique
space infrastructure. Joining only a handful of other countries that
possess the
ability to build, launch and maintain their own satellites, Israel has
become a
leader in building sophisticated small, lightweight satellites. These
micro
satellites can achieve today what some multimillion dollar satellites
could only
dream of a few years back and with a fraction of the cost. One
important aspect
of this revolution is the propulsion system, a field in which the
Israeli RAFAEL
Armament Development Authority has grown to become a world leader.
Although
people might think that satellites do not need a propulsion system
orbiting the
earth at a constant altitude, the reality is very different. Low Earth
Orbit
(LEO) satellites (like the VENUS) are exposed to some extreme "weather
effects"
in space. The biggest space weather effect to LEO satellites is the
atmosphere
of Earth itself, and the way it inflates during solar storm events.
This causes
high-drag conditions that lower the satellite orbit by tens of miles at
a time.
To prevent premature orbital degradation as well as to be able to
perform other
planned and unplanned trajectory changes, satellites are equipped with
a special
propulsion system. The most common satellite propulsion system is
chemical
propulsion which uses rocket fuel such as Hydrazine. One of the
problems with
using chemical propulsion in lightweight satellites is the need to
allocate a
large portion of the satellite mass for the propellant. To overcome
this problem
engineers have been working for the last several decades on electric
propulsion
system that will use beams of ions for propulsion. Along the years,
several
types of electric thrusters have been developed, one such type is the
Hall
Effect thruster. Hall thrusters were studied independently in the US
and the
Soviet Union since the 1950's but until recently were not used
extensively in
the West. The Hall Effect thruster works by accelerating a propellant
(such as
xenon gas) in a magnetic field. Hall Effect thrusters use the Hall
Effect
(basically a potential difference) to trap electrons and then use them
to ionize
the propellant, accelerating the ions to produce thrust, and (unlike
other types
of ion engines) neutralize the ions in the plume. Hall Effect engines
are
considered to be highly efficient, and while standard chemical rocket
engines
thrust their propellant at speeds of around 1700m/s, Hall Effect
engines can
thrust almost ten times as fast reaching fuel efficiency of 60%, much
higher
than any chemical engine. Using its high efficient Hall Effect
thrusters, VENUS
will be able to perform its task without carrying a large amount of
fuel and
will continue to operate for at least 4-5 years in its planned orbit.

Special thanks to Tal Inbar, senior research fellow at the Fisher
Institute for
Air and Space Strategic Studies, who assisted creating this article

Iddo Genuth - IsraCast

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