ICESAT-2

ICESat-2 (NORAD 43613, COSPAR 2018-070A) is an American Earth-observing satellite operated on behalf of NASA and built to extend a decades-long scientific record of polar ice measurements from space. Launched in September 2018, it carries a sophisticated laser altimetry instrument designed to measure changes in ice sheet elevation across Greenland and Antarctica with centimeter-scale precision, while also collecting data on sea ice thickness, land surface topography, forest canopy height, and atmospheric features such as clouds and aerosols. The satellite remains in orbit as of this writing, continuing what was originally planned as a three-year primary mission.

Mission and Purpose

The central scientific motivation behind ICESat-2 is the measurement of ice loss and gain over Earth's polar regions, data that is critical for understanding sea-level rise, climate feedback mechanisms, and the long-term health of the cryosphere. It serves as the successor to the original ICESat mission, which operated from 2003 until 2009, and was designed to close the observational gap that had accumulated in the years since that earlier spacecraft ceased operations.

Rather than relying on radar or passive imaging, ICESat-2 measures surface elevation using laser pulses. Its sole science instrument, the Advanced Topographic Laser Altimeter System (ATLAS), fires rapid bursts of green-wavelength laser light toward Earth's surface and times the return of individual photons with extreme precision. By tracking how long each photon takes to travel down and back, the system can calculate surface height to a level of detail not achievable with older altimetry technologies. This single-photon counting approach represents a substantial advance over the instrument flown on the original ICESat.

Although the mission is classified in the satellite catalog under an unknown mission type and status, its scientific objectives are well-documented in the public literature. Primary among them is tracking year-to-year and seasonal changes in ice sheet mass balance — essentially whether the great ice sheets are gaining or losing ice overall, and at what rate. Secondary objectives include monitoring Arctic and Antarctic sea ice freeboard (the portion of sea ice that protrudes above the waterline), mapping shallow coastal bathymetry where laser light can penetrate clear water, characterizing forest canopy heights and biomass estimates at global scales, and profiling cloud and aerosol layers in the atmosphere. The breadth of these objectives makes ICESat-2 a genuinely multi-disciplinary asset within NASA's Earth Observing System despite its primary identity as a glaciology mission.

Orbit and Tracking

ICESat-2 occupies a low Earth orbit with an apogee of 488 km and a perigee of 482 km, giving it a nearly circular profile with less than 6 km of variation between its highest and lowest points. Its inclination of 92.0° places it in a slightly retrograde, near-polar orbit, allowing the satellite to pass over or near both poles on successive orbits and providing coverage of the high-latitude regions that are central to its science goals. At this inclination, the ground track gradually shifts with each pass, eventually building up a dense, repeating grid of measurement points across Earth's surface.

The orbital period is 94.2 minutes, meaning the spacecraft completes roughly fifteen full orbits of Earth every day. Over its operational life, this repeating ground track pattern allows scientists to return to the same surface locations at regular intervals and detect subtle elevation changes that would be undetectable from a single overpass.

Tracking data for ICESat-2 is maintained under NORAD catalog number 43613. The object is cataloged as a payload — meaning the satellite bus itself, as opposed to any associated rocket bodies or debris — and its international designator, 2018-070A, identifies it as the primary payload of the 70th orbital launch of 2018.

The orbit is relatively compact by the standards of scientific Earth observers, sitting well below the altitude of many commercial communication satellites and well above the drag-dominated region where objects decay within days or weeks. At roughly 485 km mean altitude, atmospheric drag is low enough that the satellite can maintain its orbit for years with only occasional propulsive corrections, but high enough that precise station-keeping is still required to maintain the repeating ground track needed for long-term change detection.

Design and Operator

ICESat-2 was manufactured by Orbital Sciences Corporation, a firm that has produced a wide range of small-to-medium scientific and commercial spacecraft. The satellite has a launch mass of 1,514 kg, placing it in the medium class of Earth-observing payloads. The spacecraft bus was designed to accommodate the demands of the ATLAS instrument, including precise pointing control and a stable thermal environment for the laser and detector systems.

Northrop Grumman Corporation is listed as the satellite's operator in the catalog. This reflects Northrop Grumman's eventual acquisition of Orbital Sciences and its role in supporting satellite operations. The underlying program, however, is a NASA science mission managed through the agency's Earth Science Division, and the data products are distributed publicly through NASA's data archives.

The satellite was launched on September 14, 2018 (Eastern Daylight Time), aboard a Delta II rocket from Vandenberg Air Force Base on the California coast. The Delta II vehicle, one of the most reliable medium-lift launch vehicles in American spaceflight history, made its final flight carrying ICESat-2 to orbit — a fitting capstone for a rocket that had launched numerous NASA planetary and Earth science missions over more than three decades of service. The satellite was deployed into its near-polar orbit shortly after launch.

ICESat-2 was designed with a primary mission duration of three years, with sufficient onboard propellant to sustain operations for up to seven years. This design margin allows for mission extensions should the hardware remain functional, enabling a longer continuous data record than the minimum required to meet core science objectives.

Significance and Current Status

The value of ICESat-2's measurements lies in their continuity with earlier datasets. By combining observations from the original ICESat, from NASA's Operation IceBridge airborne campaign — which bridged the gap between the two satellite missions — and from ICESat-2 itself, scientists have assembled a multi-decade record of ice elevation change across the polar regions. This record has been used to quantify ice sheet mass loss rates in Greenland and Antarctica, to track the thinning and retreat of glaciers, and to monitor the seasonal and long-term behavior of Arctic sea ice.

Beyond glaciology, the ICESat-2 dataset has proven useful in applications its designers anticipated but that have expanded in scope over time. Forest height measurements derived from the satellite's surface returns have contributed to global biomass estimation efforts. Inland water body surveys have used the data to track lake and reservoir levels. The instrument's ability to detect shallow seafloor returns in clear coastal waters has opened possibilities in marine mapping. These secondary applications illustrate how a focused scientific instrument, when placed in a well-chosen orbit with high measurement precision, can generate utility well beyond its primary objectives.

The satellite's near-polar inclination of 92.0° ensures coverage extending nearly to the geographic poles, which is essential for ice sheet science. Unlike sun-synchronous orbits, which are also common for Earth observers and typically have inclinations slightly above 97–98°, ICESat-2's orbit is only slightly retrograde, a choice driven by the need to maximize polar coverage while maintaining a stable, repeating ground track.

ICESat-2 remains in orbit and, based on available tracking data, continues to maintain an orbit consistent with active operations. No reentry or decay date has been recorded in the catalog.

How to Spot It

ICESat-2 is not among the brightest objects visible to the naked eye from the ground. At roughly 485 km altitude and with a mass of 1,514 kg, it presents a modest cross-section to sunlit conditions. However, like all satellites in low Earth orbit, it can occasionally be seen as a steadily moving point of light crossing the sky during twilight hours — after sunset or before sunrise — when the observer is in darkness but the satellite is still illuminated by the Sun.

Favorable passes occur when the satellite's ground track brings it within a reasonable angular distance of your location, and when the geometry places it in sunlight while you are in shadow. Given its 94.2-minute orbital period and near-polar inclination of 92.0°, ICESat-2 passes over most inhabited latitudes multiple times each day, though not every pass will be visible from a given location.

For precise pass predictions, LowEarth's real-time tracking tools use current two-line element sets associated with NORAD 43613 to calculate exactly when and where the satellite will appear in your sky. Observations of the satellite contribute to a broader awareness of what humanity has placed in orbit for the purpose of understanding our changing planet.