<s>
European	B-Algorithm
Remote	I-Algorithm
Sensing	I-Algorithm
satellite	I-Algorithm
(	O
ERS	O
)	O
was	O
the	O
European	O
Space	O
Agency	O
's	O
first	O
Earth-observing	O
satellite	B-Application
programme	O
using	O
a	O
polar	O
orbit	O
.	O
</s>
<s>
It	O
consisted	O
of	O
2	O
satellites	B-Application
,	O
ERS-1	B-Algorithm
and	O
ERS-2	O
.	O
</s>
<s>
ERS-1	B-Algorithm
launched	O
17	O
July	O
1991	O
from	O
Guiana	O
Space	O
Centre	O
aboard	O
an	O
Ariane	O
4	O
rocket	O
.	O
</s>
<s>
The	O
satellite	B-Application
was	O
put	O
into	O
a	O
Sun-synchronous	O
polar	O
orbit	O
at	O
an	O
altitude	O
of	O
782785km	O
.	O
</s>
<s>
ERS-1	B-Algorithm
failed	O
on	O
10	O
March	O
2000	O
after	O
nine	O
years	O
in	O
orbit	O
.	O
</s>
<s>
ERS-1	B-Algorithm
carried	O
an	O
array	O
of	O
Earth-observation	O
instruments	O
that	O
gathered	O
information	O
about	O
the	O
Earth	O
(	O
land	O
,	O
water	O
,	O
ice	O
,	O
and	O
atmosphere	O
)	O
using	O
a	O
variety	O
of	O
measurement	O
principles	O
.	O
</s>
<s>
RA	O
(	O
Radar	B-Application
Altimeter	O
)	O
is	O
a	O
single	O
frequency	O
nadir-pointing	O
radar	B-Application
altimeter	O
operating	O
in	O
the	O
Ku	B-Algorithm
band	I-Algorithm
.	O
</s>
<s>
SAR	O
(	O
synthetic-aperture	B-Application
radar	I-Application
)	O
operating	O
in	O
C	O
band	O
can	O
detect	O
changes	O
in	O
surface	O
heights	O
with	O
sub-millimeter	O
precision	O
.	O
</s>
<s>
To	O
accurately	O
determine	O
its	O
orbit	O
,	O
the	O
satellite	B-Application
included	O
the	O
PRARE	O
(	O
Precision	O
Range	O
and	O
Range-Rate	O
Equipment	O
)	O
and	O
a	O
laser	O
retroreflector	O
.	O
</s>
<s>
The	O
retroreflector	O
was	O
used	O
for	O
calibrating	O
the	O
Radar	B-Application
Altimeter	O
to	O
within	O
10cm	O
.	O
</s>
<s>
ERS-1	B-Algorithm
had	O
various	O
mission	O
phases	O
using	O
3-day	O
and	O
35-day	O
repeat	O
cycles	O
.	O
</s>
<s>
During	O
the	O
geodetic	O
mission	O
,	O
ERS-1	B-Algorithm
was	O
put	O
in	O
two	O
long	O
repeat	O
cycles	O
of	O
168	O
days	O
,	O
which	O
is	O
equivalent	O
to	O
a	O
single	O
336-day	O
cycle	O
.	O
</s>
<s>
The	O
geodetic	O
mission	O
allowed	O
for	O
accurate	O
mapping	O
of	O
the	O
Earth	O
's	O
bathymetry	O
and	O
geoid	O
over	O
the	O
seas	O
using	O
the	O
Radar	B-Application
Altimeter	O
.	O
</s>
<s>
On	O
10	O
March	O
2000	O
,	O
ERS-1	B-Algorithm
'	O
s	O
attitude	O
control	O
system	O
failed	O
due	O
to	O
a	O
gyroscope	B-Application
malfunction	O
and	O
its	O
mission	O
was	O
officially	O
declared	O
finished	O
.	O
</s>
<s>
Largely	O
identical	O
to	O
ERS-1	B-Algorithm
,	O
it	O
added	O
additional	O
instruments	O
and	O
included	O
improvements	O
to	O
existing	O
instruments	O
including	O
:	O
</s>
<s>
GOME	O
(	O
Global	O
Ozone	O
Monitoring	O
Experiment	O
)	O
is	O
a	O
nadir	O
scanning	O
ultraviolet	B-Application
and	O
visible	O
spectrometer	O
.	O
</s>
<s>
When	O
ERS-2	O
was	O
launched	O
,	O
ERS-1	B-Algorithm
shared	O
the	O
same	O
orbital	O
plane	O
.	O
</s>
<s>
This	O
allowed	O
a	O
tandem	B-Application
mission	O
,	O
with	O
ERS-2	O
passing	O
the	O
same	O
point	O
on	O
the	O
ground	O
1	O
day	O
later	O
than	O
ERS-1	B-Algorithm
.	O
</s>
<s>
ERS-2	O
has	O
been	O
operating	O
without	O
gyroscopes	B-Application
since	O
February	O
2001	O
,	O
resulting	O
in	O
some	O
degradation	O
of	O
the	O
data	O
provided	O
by	O
the	O
instruments	O
.	O
</s>
<s>
Since	O
the	O
tape	O
drive	O
failure	O
additional	O
ground	O
stations	O
have	O
been	O
brought	O
online	O
to	O
increase	O
the	O
data	O
gathering	O
abilities	O
of	O
the	O
satellite	B-Application
.	O
</s>
<s>
The	O
Wind	O
Scatterometer	O
and	O
GOME	O
were	O
the	O
only	O
instruments	O
of	O
their	O
kind	O
until	O
the	O
launches	O
of	O
MetOp-A	O
and	O
Envisat	B-Algorithm
,	O
respectively	O
.	O
</s>
<s>
The	O
successor	O
to	O
ERS-2	O
was	O
the	O
Envisat	B-Algorithm
satellite	B-Application
,	O
launched	O
1	O
March	O
2002	O
.	O
</s>
<s>
Envisat	B-Algorithm
contained	O
improved	O
versions	O
of	O
many	O
of	O
the	O
instruments	O
onboard	O
ERS-2	O
.	O
</s>
<s>
At	O
13:16:38	O
the	O
batteries	O
were	O
switched	O
off	O
and	O
the	O
satellite	B-Application
decommissioned	O
.	O
</s>
