Year: 2017

The excellent health and longevity of the Terra platform and its five instruments has led to the enviable problem of deciding how best to manage fuel usage of the platform over the next five years.  The decision will directly impact both the continuity of the Terra science record and the length of time that Terra will remain on orbit.  The Project is looking to better understand the possible benefits to the science community from different fuel use scenarios and welcomes feedback.

The question that poses itself now is whether to use all of the remaining maneuvering fuel to maintain Terra’s current orbit and keep the equator crossing-time at 10:30 AM (within a tight time window of 10:29 AM to 10:31AM local time) which will lead to nearly 3 more years of continuous climate quality data or to use some of the fuel to lower the orbit leading to an earlier re-entry of Terra.  The earlier re-entry decreases the probability that Terra will be impacted by space debris, although all orbiting satellites are at risk of being hit by debris and rely on collision avoidance maneuvers to minimize this risk.  Terra will maintain fuel reserve to perform these maneuvers after lowering or exiting the constellation to minimize risk of collision.

A major impact of lowering Terra’s orbit is a change in its crossing time.  A body of scientists acquainted with Terra’s instruments concluded that a “change in the crossing-time would mark the end of Terra’s ‘climate quality’ data record for trend analysis”. The panel stipulated that the magnitude of the impact would be of the same order as the trends projected by climate models.  The fact that Terra still has five healthy instruments providing a continuous well-calibrated, inter-calibrated, data record led the panel to conclude “that it is of utmost importance to continue this data record while the Terra instruments are performing nearly optimally.”

In order to provide a data set of the best quality for the science community, the Terra Project Science Office, including the five instrument teams, recommended that the current crossing-time be held until fall 2020.  Doing so, would sustain an equatorial crossing time within a two-minute window for an unprecedented 18 years while still allowing a safe exit from the Earth Science Constellation.  The use of fuel to maintain Terra’s crossing-time until fall 2020 leads to a predicted additional 18 years on orbit and a corresponding marginal increase in the probability of a debris impact.  The science possible from a near-constant crossing time for 18 years is unique and viewed to offset the added risks involved from the additional time on orbit.  What is not clear to the Terra Mission, however, is whether there are science applications that would benefit from either a shift in crossing time or an orbit lowering.  The Project is currently searching for possible science benefits from the orbit lowering and plans to hold a panel discussion at the American Geophysical Union’s annual meeting in December, 2017.

The Terra Science Team welcomes any feedback or suggestions as to whether to maintain the current orbit and the long-term data continuity, or lower the orbit, and therefore, shifting the crossing time.

** Note that Terra did not come to maintain a consistent 10:30 am crossing time until 2 years after its launch.

Please leave any feedback or suggestions by contacting us. All comments will be considered in our panel discussion on December 10. Comments left after December 10 will be considered prior to Terra’s next planned inclination maneuver.

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Are you ready for a challenge? Become a geographical detective and solve the latest mystery quiz from NASA’s MISR (Multi-angle Imaging SpectroRadiometer) instrument onboard the Terra satellite. Prize submissions for perfect scores accepted until Wednesday, June 28, at 4:00 p.m. PDT. Happy sleuthing!


Take the quiz here:

The tiny Aleutian island of Bogoslof in Alaska, erupting regularly since December 2016, produced fresh activity on Sunday, May 28, 2017. Bogoslof is a stratovolcano fueled by the subduction of the Pacific Plate under the North American Plate and forms part of the larger Aleutian Arc, which includes more than 60 volcanoes on the Aleutian Islands and the Aleutian Range on the Alaska mainland. Previous to its recent period of activity, Bogoslof had last erupted in 1992, and its above-water surface area was a mere 0.11 square miles (0.29 square kilometers). As of March 11, the most recent data available, the area of the island had tripled to 0.38 square miles (0.98 square kilometers). The event on May 28 produced an ash cloud that reached 40,000 feet (12 km) in altitude, causing the Alaskan Volcano Observatory to issue a red alert for air travel in the area. Volcanic ash can cause major damage to aircraft engines, and the region is close to several major air routes between North America and Asia.

On May 28, 2017, at approximately 2:23 p.m. local time, NASA’s Terra satellite passed over Bogoslof, less than 10 minutes after the eruption began. MISR has nine cameras that view Earth at different angles. It takes slightly less than seven minutes for all nine cameras to view the same location on Earth. On the left, an animation made from the images from the nine MISR cameras, captured between 2:19 and 2:26 p.m., demonstrates how the angled views give a glimpse of the underside of the growing plume of volcanic ash, showing the eruption column widening into the cloud at the top.

Data from MISR’s nine cameras can also be used to calculate the height of the plume, based on the apparent movement of the cloud from one camera to another. On the right, a map of plume height is plotted over the downward-looking image. The top of the cloud was approximately 10,000 feet (3 kilometers) high at this time. Below the image is a scatterplot of the heights, with blue points representing heights corrected by the northwesterly winds reported by the Alaskan Volcano Observatory during the eruption, and red points representing uncorrected heights. Lower points at either side of the plume represent retrievals of the eruption column.

These data were captured during Terra orbit 92786. The stereoscopic analysis was performed using the MISR INteractive eXplorer (MINX) software tool, which is publicly available through the Open Channel Foundation at Other MISR data are available through the NASA Langley Research Center; for more information, go to MISR was built and is managed by NASA’s Jet Propulsion Laboratory in Pasadena, California, for NASA’s Science Mission Directorate in Washington, D.C. The Terra spacecraft is managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The MISR data were obtained from the NASA Langley Research Center Atmospheric Science Data Center in Hampton, Virginia. JPL is a division of the California Institute of Technology in Pasadena.

Credit: NASA/GSFC/LaRC/JPL-Caltech, MISR Team, article by Abbey Nasten