<s>
CryoSat	B-Algorithm
is	O
an	O
ESA	O
programme	O
to	O
monitor	O
variations	O
in	O
the	O
extent	O
and	O
thickness	O
of	O
polar	O
ice	O
through	O
use	O
of	O
a	O
satellite	B-Application
in	O
low	O
Earth	O
orbit	O
.	O
</s>
<s>
The	O
CryoSat-1	B-Algorithm
spacecraft	O
was	O
lost	O
in	O
a	O
launch	O
failure	O
in	O
2005	O
,	O
however	O
the	O
programme	O
was	O
resumed	O
with	O
the	O
successful	O
launch	O
of	O
a	O
replacement	O
,	O
CryoSat-2	B-Algorithm
,	O
launched	O
on	O
8	O
April	O
2010	O
.	O
</s>
<s>
CryoSat	B-Algorithm
is	O
operated	O
from	O
the	O
European	O
Space	O
Operations	O
Centre	O
(	O
ESOC	O
)	O
in	O
Darmstadt	O
,	O
Germany	O
.	O
</s>
<s>
CryoSat	B-Algorithm
's	O
primary	O
instrument	O
is	O
SIRAL	O
(	O
SAR	B-Application
/	O
Interferometric	O
Radar	O
Altimeter	O
)	O
.	O
</s>
<s>
SIRAL	O
operates	O
in	O
one	O
of	O
three	O
modes	O
,	O
depending	O
on	O
where	O
(	O
above	O
the	O
Earth	O
's	O
surface	O
)	O
CryoSat	B-Algorithm
was	O
flying	O
.	O
</s>
<s>
Over	O
the	O
oceans	O
and	O
ice	O
sheet	O
interiors	O
,	O
CryoSat	B-Algorithm
operates	O
like	O
a	O
traditional	O
radar	O
altimeter	O
.	O
</s>
<s>
Over	O
sea	O
ice	O
,	O
coherently	O
transmitted	O
echoes	O
are	O
combined	O
(	O
synthetic	B-Application
aperture	I-Application
processing	O
)	O
to	O
reduce	O
the	O
surface	O
footprint	O
so	O
that	O
CryoSat	B-Algorithm
could	O
map	O
smaller	O
ice	O
floes	O
.	O
</s>
<s>
CryoSat	B-Algorithm
's	O
most	O
advanced	O
mode	O
is	O
used	O
around	O
the	O
ice	O
sheet	O
margins	O
and	O
over	O
mountain	O
glaciers	O
.	O
</s>
<s>
Here	O
,	O
the	O
altimeter	O
performs	O
synthetic	B-Application
aperture	I-Application
processing	O
and	O
uses	O
a	O
second	O
antenna	O
as	O
an	O
interferometer	O
to	O
determine	O
the	O
across-track	O
angle	O
to	O
the	O
earliest	O
radar	O
return	O
.	O
</s>
<s>
The	O
original	O
CryoSat	B-Algorithm
was	O
proposed	O
in	O
1998	O
by	O
Duncan	O
Wingham	O
of	O
University	O
College	O
London	O
.	O
</s>
<s>
The	O
satellite	B-Application
's	O
planned	O
three-year	O
mission	O
was	O
to	O
survey	O
natural	O
and	O
human	O
driven	O
changes	O
in	O
the	O
cryosphere	O
on	O
Earth	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
ESA	O
Earth	O
Sciences	O
satellite	B-Application
selected	O
through	O
open	O
,	O
scientific	O
competition	O
.	O
</s>
<s>
The	O
existing	O
satellite	B-Application
is	O
therefore	O
,	O
formally	O
speaking	O
,	O
CryoSat-2	B-Algorithm
,	O
but	O
the	O
mission	O
is	O
still	O
known	O
simply	O
as	O
CryoSat	B-Algorithm
.	O
</s>
<s>
Although	O
largely	O
the	O
same	O
as	O
the	O
original	O
satellite	B-Application
a	O
number	O
of	O
key	O
improvements	O
were	O
included	O
in	O
CryoSat-2	B-Algorithm
.	O
</s>
<s>
Some	O
of	O
these	O
were	O
caused	O
by	O
obsolescence	O
in	O
the	O
original	O
design	O
,	O
some	O
improved	O
reliability	O
and	O
others	O
made	O
the	O
satellite	B-Application
easier	O
to	O
operate	O
.	O
</s>
<s>
The	O
CryoSat	B-Algorithm
2	I-Algorithm
launched	O
on	O
April	O
8	O
,	O
2010	O
at	O
13:57	O
UTC	O
.	O
</s>
<s>
For	O
positioning	O
purposes	O
,	O
CryoSat	B-Algorithm
included	O
a	O
DORIS	O
receiver	O
,	O
a	O
laser	O
retroreflector	O
and	O
three	O
star	O
trackers	O
.	O
</s>
<s>
The	O
ERS-1	B-Algorithm
and	O
ERS-2	B-Algorithm
satellites	B-Application
were	O
precursors	O
that	O
tested	O
the	O
techniques	O
used	O
by	O
CryoSat	B-Algorithm
.	O
</s>
<s>
CryoSat-1	B-Algorithm
was	O
launched	O
from	O
the	O
Plesetsk	O
Cosmodrome	O
in	O
Russia	O
on	O
October	O
8	O
,	O
2005	O
,	O
using	O
a	O
Rockot	O
launcher	O
.	O
</s>
<s>
According	O
to	O
Mr.	O
Yuri	O
Bakhvalov	O
,	O
First	O
Deputy	O
Director	O
General	O
of	O
the	O
Khrunichev	O
Space	O
Centre	O
,	O
when	O
the	O
automatic	O
command	O
to	O
switch	O
off	O
the	O
second	O
stage	O
engine	O
did	O
not	O
take	O
effect	O
,	O
the	O
second	O
stage	O
continued	O
to	O
operate	O
until	O
it	O
ran	O
out	O
of	O
fuel	O
and	O
as	O
a	O
consequence	O
the	O
planned	O
separation	O
of	O
the	O
third	O
(	O
Breeze-KM	O
)	O
stage	O
of	O
the	O
rocket	O
which	O
carried	O
the	O
CryoSat	B-Algorithm
satellite	B-Application
did	O
not	O
take	O
place	O
,	O
and	O
would	O
thus	O
have	O
remained	O
attached	O
to	O
the	O
second	O
stage	O
.	O
</s>
<s>
The	O
upper	O
rocket	O
stages	O
,	O
together	O
with	O
the	O
satellite	B-Application
,	O
probably	O
crashed	O
in	O
the	O
Lincoln	O
Sea	O
.	O
</s>
<s>
After	O
the	O
launch	O
failure	O
of	O
CryoSat	B-Algorithm
,	O
ESA	O
immediately	O
started	O
to	O
plan	O
a	O
replacement	O
CryoSat	B-Algorithm
mission	O
.	O
</s>
<s>
Due	O
to	O
the	O
importance	O
of	O
the	O
scientific	O
goals	O
of	O
this	O
satellite	B-Application
,	O
there	O
was	O
enormous	O
support	O
for	O
this	O
,	O
and	O
the	O
initial	O
phases	O
for	O
CryoSat-2	B-Algorithm
were	O
approved	O
when	O
ESA	O
's	O
Earth	O
Observation	O
Programme	O
Board	O
agreed	O
to	O
build	O
a	O
copy	O
of	O
the	O
spacecraft	O
on	O
February	O
23	O
,	O
2006	O
.	O
</s>
