ESA Earth observation satellite (2002?2012)
Envisat
("
Environmental Satellite
") is a large
Earth-observing satellite
which has been inactive since 2012. It is still in orbit and considered space debris. Operated by the
European Space Agency
(ESA), it was the world's largest civilian Earth observation satellite.
[2]
It was launched on 1 March 2002 aboard an
Ariane 5
from the
Guyana Space Centre
in
Kourou
,
French Guiana
, into a
Sun synchronous
polar orbit
at an altitude of 790 ± 10 km. It
orbits
the
Earth
in about 101 minutes, with a repeat cycle of 35 days. After losing contact with the satellite on 8 April 2012, ESA formally announced the end of Envisat's mission on 9 May 2012.
[3]
Envisat cost 2.3 billion Euro (including 300 million Euro for 5 years of operations) to develop and launch.
[4]
The mission has been replaced by the
Sentinel
series of satellites. The first of these,
Sentinel 1
, has taken over the radar duties of Envisat since its launch in 2014.
Mission
[
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]
Envisat was launched as an
Earth observation satellite
. Its objective was to support the continuity of
European Remote-Sensing Satellite
missions, providing additional observations to improve environmental studies.
To accomplish the global and regional objectives of the mission, numerous scientific disciplines used the data acquired from the sensors on the satellite to study
atmospheric chemistry
,
ozone depletion
,
biological oceanography
, ocean temperature and colour,
wind waves
,
hydrology
(
humidity
,
floods
), agriculture and
arboriculture
, natural hazards,
digital elevation modelling
(using
interferometry
), monitoring of maritime traffic,
atmospheric dispersion modelling
(pollution),
cartography
and
snow
and
ice
.
Specifications
[
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]
- Dimensions
26 m (85 ft) × 10 m (33 ft) × 5 m (16 ft) in orbit with the solar array deployed.
[5]
- Mass
8,211 kg (18,102 lb), including 319 kg (703 lb) of fuel and a 2,118 kg (4,669 lb) instrument payload.
[6]
- Power
Solar array
with a total load of 3560
W
.
Instruments
[
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]
Instruments carried by Envisat.
Envisat carries an array of nine Earth-observation instruments that gathered information about the Earth (land,
water
,
ice
, and
atmosphere
) using a variety of measurement principles. A tenth instrument, DORIS, provided
guidance and control
. Several of the instruments were advanced versions of instruments that were flown on the earlier
ERS-1
and
ERS 2
missions and other satellites.
MWR (
Microwave
Radiometer) was designed for measuring
water vapour
in the
atmosphere
.
AATSR
[
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]
AATSR (Advanced Along Track Scanning
Radiometer
) can measure the
sea
surface temperature in the
visible
and
infrared spectra
. It is the successor of ATSR1 and ATSR2, payloads of
ERS 1
and
ERS 2
. AATSR can measure Earth's surface temperature to a precision of 0.3 K (0.54 °F), for
climate research
. Among the secondary objectives of AATSR is the observation of environmental parameters such as water content, biomass, and vegetal health and growth.
MIPAS
[
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]
MIPAS (Michelson
Interferometer
for Passive
Atmospheric Sounding
) is a
Fourier transforming
infrared spectrometer which provides pressure and temperature profiles, and profiles of trace gases nitrogen dioxide (
NO
2
), nitrous oxide (
N
2
O
), methane (
CH
4
), nitric acid (
HNO
3
), ozone (
O
3
), and water (
H
2
O
) in the
stratosphere
. The instrument functions with high spectral resolution in an extended spectral band, which allows coverage across the Earth in all seasons and at equal quality night and day. MIPAS has a vertical resolution of 3 to 5 km (2 to 3 mi) depending on altitude (the larger at the level of the upper stratosphere).
MERIS
[
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]
MERIS (MEdium Resolution Imaging
Spectrometer
) measures the reflectance of the Earth (surface and atmosphere) in the solar spectral range (390 to 1040
nm
) and transmits 15 spectral bands back to the
ground segment
. MERIS was built at the
Cannes Mandelieu Space Center
.
SCIAMACHY
[
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]
SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) compares light coming from the sun to light reflected by the Earth, which provides information on the atmosphere through which the Earth-reflected light has passed.
SCIAMACHY is an image spectrometer with the principal objective of mapping the concentration of trace gases and aerosols in the troposphere and stratosphere. Rays of sunlight that are reflected transmitted, backscattered and reflected by the atmosphere are captured at a high spectral resolution (0.2 to 0.5 nm) for wavelengths between 240 and 1700 nm, and in certain spectra between 2,000 and 2,400 nm. Its high spectral resolution over a wide range of wavelengths can detect many trace gases even in tiny concentrations. The wavelengths captured also allow effective detection of aerosols and clouds.
SCIAMACHY uses 3 different targeting modes: to the nadir (against the sun), to the limbus (through the atmospheric corona), and during solar or lunar eclipses. SCIAMACHY was built by Netherlands and Germany at
TNO
/TPD,
SRON
and
Airbus Defence and Space
Netherlands.
[7]
RA-2
[
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]
RA-2 (
Radar
Altimeter
2) is a dual-
frequency
Nadir
pointing Radar operating in the
K
u
band
and
S bands
, it is used to define
ocean
topography
, map/monitor
sea ice
and measure land heights.
Mean sea level measurements from Envisat are continuously graphed at the Centre National d'Etudes Spatiales web site, on the Aviso page.
ASAR
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]
ASAR (Advanced Synthetic Aperture Radar) operates in the
C band
in a wide variety of modes. It can detect changes in surface heights with sub-
millimeter
precision. It served as a data link for
ERS 1
and
ERS 2
, providing numerous functions such as observations of different
polarities of light
or combining different polarities, angles of incidence and spatial resolutions.
Mode
|
Id
|
Polarisation
|
Incidence
|
Resolution
|
Swath
|
Alternating polarisation
|
AP
|
HH/VV, HH/HV, VV/VH
|
15?45°
|
30?150 m
|
58?110 km
|
Image
|
IM
|
HH, VV
|
15?45°
|
30?150 m
|
58?110 km
|
Wave
|
WV
|
HH, VV
|
|
0
400 m
|
5 km × 5 km
|
Suivi global (ScanSAR)
|
GM
|
HH, VV
|
|
1000 m
|
405 km
|
Wide Swath (ScanSAR)
|
WS
|
HH, VV
|
|
0
150 m
|
405 km
|
These different types of raw data can be given several levels of treatment (suffixed to the ID of the acquisition mode: IMP, APS, and so on):
- RAW (raw data, or "Level 0"), which contains all the information necessary to create images.
- S (complex data, "Single Look Complex"), images in complex numeric form, the real and imaginary parts of the output of the compression algorithm
- P (precision image), amplified image with constant pixel width (12.5 m for IMP)
- M (medium precision image), amplified radiometry image with a resolution greater than P
- G (geocoded image), amplified image to which simple geographical transforms have been applied to show relief.
Data capture in WV mode is unusual in that they constitute a series of 5 km × 5 km spaced at 100 km.
DORIS
[
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]
DORIS (
Doppler
Orbitography and Radiopositioning Integrated by Satellite) determines the satellite's orbit to within 10 cm (4 in).
GOMOS
[
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]
GOMOS (Global
Ozone
Monitoring by Occultation of
Stars
) looks at stars as they descend through the Earth's atmosphere and change colour, allowing measurement of
gases
such as ozone (
O
3
), including their vertical distribution.
GOMOS uses the principle of
occultation
. Its sensors detect light from a star traversing the Earth's atmosphere and measures the depletion of that light by trace gases nitrogen dioxide (
NO
2
), nitrogen trioxide, (
NO
3
),
OClO
), ozone (
O
3
) and aerosols present between about 20 to 80 km (12 to 50 mi) altitude. It has a resolution of 3 km (1.9 mi).
Loss of contact
[
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]
ESA
announced on 12 April 2012 that they lost contact with Envisat on Sunday, 8 April 2012, after 10 years of service, exceeding the initially planned life span by 5 years. The spacecraft was still in a stable orbit, but attempts to contact it were unsuccessful.
[8]
[9]
Ground-based radar and the French
Pleiades
Earth probe were used to image the silent Envisat and look for damage.
[10]
ESA formally announced the end of Envisat's mission on 9 May 2012.
[3]
Envisat was launched in 2002 and it operated five years beyond its planned mission lifetime, delivering over a
petabyte
of data.
[3]
ESA was expecting to turn off the spacecraft in 2014.
[11]
Space safety
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]
Space debris
populations seen from outside
geosynchronous orbit
(GEO). Note the two primary debris fields, the ring of objects in GEO, and the cloud of objects in
low Earth orbit
(LEO).
Envisat poses a hazard because of the risk of collisions with
space debris
. Given its orbit and its area-to-mass ratio, it will take about 150 years for the satellite to be gradually pulled into the Earth's atmosphere.
[12]
Envisat is currently orbiting in an environment where two catalogued space debris objects can be expected to pass within about 200 m (660 ft) of it every year, which would likely trigger the need for a manoeuvre to avoid a possible collision.
[13]
A collision between a satellite the size of Envisat and an object as small as 10 kg could produce a very large cloud of debris, initiating a self-sustaining chain-reaction of collisions and fragmentation with production of new debris, a phenomenon known as the
Kessler Syndrome
.
[13]
Envisat was a candidate for a mission to remove it from orbit, called
e.Deorbit
. The spacecraft sent to bring down Envisat would itself need to have a mass of approximately 1.6 tonnes.
[14]
See also
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]
References
[
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External links
[
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Science
| Solar physics
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Planetary science
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Astronomy and
cosmology
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Earth observation
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ISS
spaceflight
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Telecommunications
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Technology
demonstrators
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Cancelled
and proposed
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Failed
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Future missions in
italics
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January
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February
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March
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April
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May
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June
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July
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August
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September
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October
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November
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December
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- TDRS-10
- Hot Bird 7
,
Stentor
,
MFD-A
,
MFD-B
- ADEOS II
,
Kanta Kun
,
FedSat
,
μ-LabSat 1
(
RITE 1
,
RITE 2
)
- NSS-6
- TrailBlazer-2001 STA
,
Saudisat 1C
,
LatinSat A
,
LatinSat B
,
UniSat 2
,
Rubin 2
- Kosmos 2393
- Kosmos 2394
,
Kosmos 2395
,
Kosmos 2396
- Shenzhou 4
- Nimiq 2
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Launches are separated by dots ( ? ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ).
Crewed flights
are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
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