ICESat (Ice, Cloud, and land Elevation Satellite) was a
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
satellite mission for measuring
ice sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
mass balance
In physics, a mass balance, also called a material balance, is an application of conservation of mass to the analysis of physical systems. By accounting for material entering and leaving a system, mass flows can be identified which might have ...
,
cloud
In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles, suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...
and
aerosol
An aerosol is a suspension (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be generated from natural or Human impact on the environment, human causes. The term ''aerosol'' co ...
heights, as well as land
topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sci ...
and
vegetation
Vegetation is an assemblage of plants and the ground cover they provide. It is a general term, without specific reference to particular Taxon, taxa, life forms, structure, Spatial ecology, spatial extent, or any other specific Botany, botanic ...
characteristics. It operated as part of NASA's
Earth Observing System
The Earth Observing System (EOS) is a program of NASA comprising a series of artificial satellite missions and scientific instruments in Earth orbit designed for long-term global observations of the land surface, biosphere, earth's atmosphere, at ...
(EOS). ICESat was launched 13 January 2003 on a
Delta II
Delta II was an expendable launch system, originally designed and built by McDonnell Douglas, and sometimes known as the Thorad Delta 1. Delta II was part of the Delta rocket family, derived directly from the Delta 3000, and entered service in ...
launch vehicle
A launch vehicle is typically a rocket-powered vehicle designed to carry a payload (a crewed spacecraft or satellites) from Earth's surface or lower atmosphere to outer space. The most common form is the ballistic missile-shaped multistage ...
from
Vandenberg Air Force Base
Vandenberg may refer to:
* Vandenberg (surname), including a list of people with the name
* USNS ''General Hoyt S. Vandenberg'' (T-AGM-10), transport ship in the United States Navy, sank as an artificial reef in Key West, Florida
* Vandenberg S ...
in
California
California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
into a near-circular, near-polar orbit with an altitude of approximately . It operated for seven years before being retired in February 2010, after its scientific payload shut down and scientists were unable to restart it.
The ICESat mission was designed to provide elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for
stratospheric clouds common over polar areas. It provides topography and vegetation data around the globe, in addition to the polar-specific coverage over the
Greenland
Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...
and
Antarctic ice sheet
The Antarctic ice sheet is a continental glacier covering 98% of the Antarctic continent, with an area of and an average thickness of over . It is the largest of Earth's two current ice sheets, containing of ice, which is equivalent to 61% of ...
s. The satellite was found useful in assessing important forest characteristics, including
tree density.
Satellite instruments
The sole instrument on ICESat was the Geoscience Laser Altimeter System (GLAS), a space-based
lidar
Lidar (, also LIDAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranging, ranges by targeting an object or a surface with a laser and measuring the time for the reflected li ...
. GLAS combined a precision surface lidar with a sensitive dual-wavelength cloud and aerosol lidar. The GLAS lasers emit infrared and visible laser pulses at 1064- and 532-nm wavelengths. As ICESat orbited, GLAS produced a series of approximately diameter laser spots that were separated by nearly along the spacecraft's
ground track
A satellite ground track or satellite ground trace is the path on the surface of a planet directly below a satellite's trajectory. It is also known as a suborbital track or subsatellite track, and is the vertical projection of the satellite's ...
. During the commissioning phase of the mission, the ICESat was placed into an orbit which allowed the ground track to repeat every 8 days. During August and September 2004, the satellite was maneuvered into a 91-day repeating ground track for the main portion of the mission.
Operational history
ICESat was designed to operate for three to five years. Testing indicated that each GLAS laser should last for two years, requiring GLAS to carry three lasers in order to fulfill the nominal mission length. During the initial on orbit test operation, a pump diode module on the first GLAS laser failed prematurely on 29 March 2003. A subsequent investigation indicated that a corrosive degradation of the pump diodes, due to an unexpected but known reaction between
indium
Indium is a chemical element; it has Symbol (chemistry), symbol In and atomic number 49. It is a silvery-white post-transition metal and one of the softest elements. Chemically, indium is similar to gallium and thallium, and its properties are la ...
solder and
gold
Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
bonding wires,
[ ] had possibly reduced the reliability of the lasers. Consequentially, the total operational life for the GLAS instrument was expected to be as little as less than a year as a result. After the two months of full operation in the fall of 2003, the operational plan for GLAS was changed, and it was operated for one-month periods out of every three to six months in order to extend the time series of measurements, particularly for the ice sheets. The last laser failed on 11 October 2009, and following attempts to restart it, the satellite was retired in February 2010.
Between 23 June 2010 and 14 July 2010, the spacecraft was maneuvered into a lower orbit in order to speed up
orbital decay
Orbital decay is a gradual decrease of the distance between two orbiting bodies at their closest approach (the periapsis) over many orbital periods. These orbiting bodies can be a planet and its satellite, a star and any object orbiting it, or ...
. On 14 August 2010, it was decommissioned,
[ ] and at 08:49 UTC on 30 August 2010 it
reentered the atmosphere.
Follow-on satellite
A follow-on mission,
ICESat-2
ICESat-2 (Ice, Cloud, and land Elevation Satellite 2), part of NASA's Earth Observing System, is a satellite mission for measuring ice sheet elevation and sea ice thickness, as well as land topography, vegetation characteristics, and clouds. ICES ...
, was developed by NASA to continue studying polar ice changes, and the biomass and carbon in vegetation.
The satellite was launched on 15 September 2018 aboard a
Delta II
Delta II was an expendable launch system, originally designed and built by McDonnell Douglas, and sometimes known as the Thorad Delta 1. Delta II was part of the Delta rocket family, derived directly from the Delta 3000, and entered service in ...
launch vehicle.
For the period of time in between the two satellites, NASA's
Operation IceBridge
Operation IceBridge (OIB) was a NASA mission to monitor changes in polar ice by utilizing airborne platforms to bridge the observational gap between the ICESat and ICESat-2 satellite missions. The program, which ran from 2009 to 2019, employed v ...
used a
Douglas DC-8
The Douglas DC-8 (sometimes McDonnell Douglas DC-8) is an early long-range Narrow-body aircraft, narrow-body jetliner designed and produced by the American Douglas Aircraft Company. Work began in 1952 towards the United States Air Force's (USA ...
aircraft as a stopgap to measure ice thickness and collect other data.
References
External links
ICESATby NASA's Goddard Space Flight Center
ICESAT/GLAS by the Center for Space Research, University of Texas
Further reading
*
{{Orbital launches in 2003
Earth satellite laser altimeters
Earth observation satellites of the United States
Spacecraft launched in 2003
Spacecraft launched by Delta II rockets
Spacecraft which reentered in 2010
NASA satellites