Hi My Friends: A VUELO DE UN QUINDE EL BLOG., ESA’s GOCE satellite is not only mapping Earth’s gravity with unrivalled
precision, but is also revealing new insight into air density and wind
in space. This additional information is expected to improve the design
and operation of future Earth observation missions.
Download:
MOV (Size: 571 kb)
The need for GOCE (Gravity Field and Steady-State Ocean Circulation
Explorer) to fly in a low orbit means it has to be equipped with a
system to compensate for the atmospheric drag it will experience at this
exceptionally low altitude. The animation shows a close-up of the
ion-propulsion assembly, which keeps the satellite in a smooth
trajectory – free from all effects except the gravity field itself. Two
winglets provide additional aerodynamic stability.
Credits: ESA/AOES Medialab
Most satellites orbit Earth higher than 400 km. Lower than that and atmospheric drag causes them to slow down quickly and reenter the atmosphere prematurely.
This posed a problem for the designers of the GOCE mission. They needed
to fly the satellite much closer to Earth, at around 270 km, so that the
gradiometer instrument could measure tiny variations in the gravity
field with high precision.
The solution was to equip the satellite with an electric ion engine.
This novel system continuously generates tiny thrusts to compensate for
the drag GOCE experiences as it orbits through the remnants of
Air density from ESA’s GOCE gravity mission (right) compared to model
predictions. The GOCE data show more detail and precision in
fluctuations in the density of the air at 270 km above Earth than the
NRLMSISE-00 model.
Credits: TU Delft
The design has proven to work extremely well and this extraordinary
satellite has been making measurements for more than three years.
What was considered a complication at the design stage of the mission
has now become an opportunity for further scientific investigation.
A team led by Delft University of Technology in the Netherlands is
combining GOCE accelerometer measurements with data on the activation of
the ion thrusters.
The aim of the study, which is being carried out within ESA’s Earth
Observation Support to Science Element, has little to do with mapping
the gravity field. Instead, the data are used to learn more about air
densities and wind speeds that the satellite encounters along its
orbital path.
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HI-RES PNG (Size: 189 kb) Crosswinds in space from ESA’s GOCE gravity mission (right) compared to model predictions. The GOCE data show more detail and precision in fluctuations of the winds than the HWM07 model.
Credits: TU Delft
The first results of this investigation show fine details of space
weather at this altitude, confirming the usefulness of the GOCE
instruments for this additional application.
The information has many practical uses relating to estimating how long a
satellite will function in space, establishing propellant budgets,
optimising mission orbits, planning reentry operations and avoiding
collisions with space debris.
The density and wind data will soon be ready for further analysis by experts in upper atmospheric and space physics.
The GOCE density measurements are lower than those predicted by models.
This is in line with the results of other recent investigations, which
suggest that the upper atmosphere has been cooling and contracting over
the last decades.
Download:
HI-RES JPEG (Size: 6044 kb) | ESA's GOCE mission has delivered the most accurate model of the
'geoid' ever produced, which will be used to further our understanding
of how Earth works.
The colours in the image represent deviations in height (–100 m to +100
m) from an ideal geoid. The blue colours represent low values and the
reds/yellows represent high values.
A precise model of Earth's geoid is crucial for deriving accurate measurements of ocean circulation, sea-level change and terrestrial ice dynamics. The geoid is also used as a reference surface from which to map the topographical features on the planet. In addition, a better understanding of variations in the gravity field will lead to a deeper understanding of Earth's interior, such as the physics and dynamics associated with volcanic activity and earthquakes. Credits: ESA/HPF/DLR
There was an additional drop in temperature and density around the time GOCE was launched.
The causes of these drops are only partly understood. However, GOCE has
benefited from the current environment, using far less propellant than
predicted.
These measurements will continue to be used to improve our knowledge of the gravity field as well as the upper atmosphere.
ESA | . | ||
| Guillermo Gonzalo Sánchez Achutegui | |||
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