Overall, the TRMM spacecraft body measured 5.1 by 3.7 by 3.0 meters in size with its two solar arrays stretching 14.6 meters from tip to tip. The spacecraft had a launch mass of 3,524 Kilograms including 890kg of hydrazine propellant that was consumed over the course of the mission.
TRMM maintained its orbit until July 2014 when the craft ran out of propellant and began its slow drop towards the atmosphere as drag caused by residual molecules and atoms in the upper reaches of the atmosphere progressively slowed the vehicle down. Luckily, TRMM's successor, the GPM Core Spacecraft - outfitted with the most powerful precipitation radar ever flown - had begun operations in March 2014, giving scientists a few precious months of overlap to compare the data delivered by the two spacecraft and ensure TRMM's record would be continued by the next generation of rainfall satellites.
Over the past week, the predicted time of orbital decay drifted to an earlier time due to a pair of geomagnetic events that saw Earth's atmosphere expand temporarily and speed up the descent rate of the spacecraft.
The two-minute window of uncertainty corresponds to a ground track length of around 900 Kilometers along which orbital decay took place. Therefore, decay occurred between 2,700 and 3,600 Kilometers off the west coast of Australia.
The onset of re-entry normally occurs between 120 and 100 Kilometers in altitude when the spacecraft encounters the dense layers of the atmosphere, initially not slowing down at a fast rate, but already interacting with plenty of molecules that are broken up into atoms and ions leading to plasma forming around the spacecraft which would normally become self-luminous around 104 Kilometers in altitude. Given the extremely high speed of the object, traveling 7.7 Kilometers per second at Entry Interface, air in front of the vehicle is compressed, creating a shock wave layer in which molecules are separated into ions and temperatures rise to the extreme.
Detailed analysis was performed for the TRMM satellite to identify components that could survive re-entry and reach the ground using a sophisticated simulation that uses a model of the satellite Parent Body and all major components to calculate the heat each component can receive during entry to assess its altitude of demise or downrange impact point. The survivability of specific components depends on a number of factors including the component’s material, shape, area to mass ratio and shielding provided by other spacecraft components.
NASA determined that at least 12 components of the TRMM satellite would reach the ground with a cumulative mass of 112 Kilograms, amounting to about 4.3% of the total dry mass of TRMM. These components included the four titanium and steel reaction wheels with a mass of 10.7 Kilograms, a gaseous nitrogen tank made of titanium weighing 14kg, a pair of propellant tanks each 1.0 by 0.81 meters in size, two solar array drive mechanisms with a mass of 11.2kg, and a titanium motor and shaft from one of TRMM's instruments. Other components that may have survived include titanium parts from some of the instruments and some glass lenses. 
Image: Spaceflight101/Google Earth
Yellow Marker: Opening of Entry Window (3:54 UTC) -- Green Marker: Center of Window (3:55 UTC) -- Blue Marker: End of Window (3:56 UTC)
1-5: Debris Impacts for Decay at Window Opening -- A-E: Debris Impacts for Decay at Window Closure Debris Order: 1) TMI Instrument Motor & Shaft - 2) Nitrogen Tank - 3) Main Propellant Tank (x2) - 4) Solar Array Drive Mechanism (x2) - 5) Reaction Wheel (x4)
Its legacy will live on for years to come as its climatological record marked the beginning of a continuous monitoring of global precipitation and the technologies developed for TRMM are still being utilized in Earth Science missions.
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Image: NASA Goddard
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Latest Re-Entry Update
Re-Entry Updates - June 16, 2015
[16:00] USSTRATCOM has issued a corrected TIP Message containing the final TRMM Re-Entry Data:
Orbital Decay (80km): 03:55:00 UTC +/- 1 Minute Location: 19°S 87°E A detailed Debris Field Analysis will be posted here later today. 
Credit: Spaceflight101/JSatTrak
[09:30] There continues to be confusion regarding the orbital decay location of the TRMM Satellite that re-entered early (UTC) on June 16, 2015. USSTRATCOM provided a post-entry TIP Message with a Message Epoch of 6:56 UTC showing re-entry to have taken place at 6:54 UTC at 19°S, 87°E. The time and given location do not match and differ by two orbits.
The location corresponds to a decay time around 3:57 UTC and would place orbital decay within the pre-entry prediction windows from several sources and seems to be the most plausible data point. The time given by USSTRATCOM deviates ~3 hours from the estimates made before re-entry. Interestingly, NASA issued a third location for orbital decay in the Southern Indian Ocean, around 34°S, 87°E. This would correspond to a decay time around 7:01 UTC - after (!) the USSTRATCOM TIP message had already been issued. Furthermore, it is unclear what is shown in the map provided by NASA since the depicted ground trace is much longer than the 2-minute decay uncertainty plus the maximum debris field length. 
Credit: Spaceflight101/JSatTrak
Credit: NASA
[07:05] Confirmation of TRMM Re-Entry.
USSTRATCOM issued a Post Re-Entry Update for TRMM, confirming that the spacecraft re-entered the atmosphere early on Tuesday, June 16, 2015. However, the message within itself includes an error because the given time of re-entry and the provided location of the orbital decay point do not match. The location is given as 87°E 19°S in in the Indian Ocean while the time of re-entry was given as 6:54 UTC, exactly two orbits after the satellite passed the decay location at around 3:57 UTC. Given the earlier re-entry predictions, it is most probable that the given location is correct while the time has been calculated in error. An updated TIP message is being awaited. 
Image: Spaceflight101/Orbitron
[06:15] Odds are that TRMM re-entered a while ago, but without visual observation of re-entry or any negative detections on subsequent passes, there is no way of determining an estimate for the timing of orbital decay. Data will be released by USSTRATCOM later in the day that will allow a detailed analysis of TRMM's re-entry and debris impact locations. Please note the section on how the orbital tracker displayed on this page works.
[05:00] In case TRMM persisted through the end of the re-entry window, observers in the Canary Islands, southern Morocco and Algeria may be able to see the last visible pass of the spacecraft or even witness its re-entry. Although it may have re-entered much earlier as new TLE, TIP Messages or a Decay Message are awaited. 
Credit: Spaceflight101/Google Maps
[04:39] In case TRMM is still in orbit, the satellite would be starting a pass over Mexico at this time, flying from Colima to Tampico before heading over the Gulf and passing over Florida, straight over Ocala and Palm Coast, north of Orlando and Daytona Beach.
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Object: TRMM - Tropical Rainfall Measuring Mission
Origin: U.S./Japan - Spacecraft Dry Mass: 2,634 Kilograms Launched: November 27, 1997 - 21:27 UTC Launch Vehicle: H-II - Launch Site: Tanegashima Space Center Operational Orbit: Circular, 402.5 Kilometers, 35° Latest Re-Entry Predictions (Pre-Entry):
USSTRATCOM: June 16 - 03:49 UTC +/-5 Hours [Issued: 6/16 - 01:28] Spaceflight101: June 16 - 04:18 UTC +/- 2 Hours [Issued: 6/15 - 23:55] Aerospace Corp.: June 16 - 05:55 UTC +/-10 Hrs [Issued: 6/14 - 12:04] Satflare/J. Remis: June 16 - 04:55 UTC +/-3 Hours [Issued: 6/15] TRMM Re-Entry Bands based on Pre-Entry Prediction
Credit: Spaceflight101/JSatTrak
Tracking TLE (via Heavens-Above.com):
1 25063U 97074A 15166.45885502 .03516128 00000-0 48396-3 0 9998 2 25063 034.9363 206.2486 0002991 109.7657 250.3998 16.34007729 1826 
Credit: SpaceFlight101
Credit: SpaceFlight101
Credit: SpaceFlight101
Credit: SpaceFlight101
TRMM over Japan on June 12, 2015
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[04:23] If not down already, TRMM would now be passing over the Pacific Ocean making a visible flyover of the Cook Islands, Bora Bora & Tahiti. Infrared-sensing satellite of the U.S. Military, normally used to detect missile launches, can also be used to track the infrared signature of re-entering spacecraft (larger than CubeSats) to precisely determine their orbital decay position. This data is available to the military in real time, but released through USSTRATCOM significantly later to disguise the capabilities of the infrared-vision satellites in question.
[03:49] Center of the USSTRATCOM Re-Entry Window. If still flying, TRMM would be over the Indian Ocean at this point, approaching Australia for a lengthy passover.
[03:34] Possibly the final visible pass of the TRMM mission is occurring now, stretching from eastern Morocco over Algeria into Libya. Re-Entry near the coming descending node is likely, however, uncertainties are still large. On this ground track, the spacecraft is passing over Africa (Morocco, Algeria, Libya, Sudan, Ethiopia) before flying across the Indian Ocean, heading over Western & South Australia and New South Wales (right over Perth, Adelaide & Canberra).
[03:49] Center of the USSTRATCOM Re-Entry Window. If still flying, TRMM would be over the Indian Ocean at this point, approaching Australia for a lengthy passover.
[03:34] Possibly the final visible pass of the TRMM mission is occurring now, stretching from eastern Morocco over Algeria into Libya. Re-Entry near the coming descending node is likely, however, uncertainties are still large. On this ground track, the spacecraft is passing over Africa (Morocco, Algeria, Libya, Sudan, Ethiopia) before flying across the Indian Ocean, heading over Western & South Australia and New South Wales (right over Perth, Adelaide & Canberra).
Credit: Spaceflight101/Google Maps
[02:50] TRMM's Re-Entry Window is now open. Propagation of its last known orbit places the satellite just below 150 Kilometers in altitude now.
[02:05] TRMM streaks across the night skies of Libya, Egypt and Saudi Arabia. The area of visibility stretches from Benghazi, Libya to Tabuk, Saudi Arabia. Egypt's capital has a 77° elevation pass. There have been no observer reports in over 15 hours and the last orbital data for TRMM is nearly eight hours old.
[02:05] TRMM streaks across the night skies of Libya, Egypt and Saudi Arabia. The area of visibility stretches from Benghazi, Libya to Tabuk, Saudi Arabia. Egypt's capital has a 77° elevation pass. There have been no observer reports in over 15 hours and the last orbital data for TRMM is nearly eight hours old.
Credit: Spaceflight101/Google Maps
[01:28] USSTRATCOM has issued a new TIP Message predicting the orbital decay (80km passage) of TRMM on June 16, 2015 at 03:49 UTC +/-5 Hours. A TIP Message issued at 20:44 UTC had a much smaller uncertainty period of +/- 1 Hour.
[00:38] A visible TRMM pass occurs from Baghdad, Iraq to the south-east to the Gulf of Oman with visibility over southern Iran and the south west of Pakistan.
[00:38] A visible TRMM pass occurs from Baghdad, Iraq to the south-east to the Gulf of Oman with visibility over southern Iran and the south west of Pakistan.
Credit: Spaceflight101/Google Maps
Re-Entry Updates - June 15, 2015
[23:55] USSTRATCOM issued a set of six revised Element Sets from 15166.21456 to 1566.76376 showing slightly different orbits and very different Ballistic Coefficients (1st Derivative of Mean Motion) and second order drag terms than the TLEs that were originally issued at 15166.4589 and 15166.7639. This discrepancy had shown up earlier as TLEs provided by USSTRATCOM yielded a much later decay time when analyzed with GMAT than the time provided in the TIP Messages.
The most recent of the revised TLEs (Epoch: 18:19 UTC) shows TRMM in an orbit of 167 Kilometers vs. the earlier 174 by 176km orbit that can be derived from the previous TLE with identical Epoch.
The most recent of the revised TLEs (Epoch: 18:19 UTC) shows TRMM in an orbit of 167 Kilometers vs. the earlier 174 by 176km orbit that can be derived from the previous TLE with identical Epoch.
Credit: Spaceflight101
[22:40] TRMM will be visible from Iran, Afghanistan, Pakistan and India between 23:08 and 23:16 UTC. New Delhi will have a high-elevation pass.
Credit: Spaceflight101/Google Maps
[22:05] The next visible pass carries TRMM over Chile, Peru, Bolivia and Brazil.
Credit: Spaceflight101/Google Maps
[21:40] TRMM passes over Afghanistan, Pakistan and Tibet, visible from Islamabad and Kabul in the early morning hours. No observer reports from any locations of recent passes have been made up to this point.
[20:45] USSTRATCOM issued a new TRMM Re-Entry TIP Message predicting re-entry for June 16, 2015 at 03:50 UTC +/- 60 Minutes.
[20:40] TRMM will be visible in the evening skies over Brazil starting at 21:05 UTC. The spacecraft will be visible - depending on lighting conditions - from Pres. Prudente, Sao Paulo, Belo Horizonte, Montes Claros, Salvador and a number of other large cities in the south east.
[20:45] USSTRATCOM issued a new TRMM Re-Entry TIP Message predicting re-entry for June 16, 2015 at 03:50 UTC +/- 60 Minutes.
[20:40] TRMM will be visible in the evening skies over Brazil starting at 21:05 UTC. The spacecraft will be visible - depending on lighting conditions - from Pres. Prudente, Sao Paulo, Belo Horizonte, Montes Claros, Salvador and a number of other large cities in the south east.
Credit: Spaceflight101/Google Maps
[19:35] USSTRATCOM issued new orbital elements for TRMM: 174.3 by 176.0 Kilometers, Inclination: 34.937°, Period: 87.99min (Epoch: 18:20 UTC)
[19:20] The next opportunity to observe TRMM will come for China with visibility all the way from the town of Hanzhong to the eastern coast. TRMM can be seen starting at 20:14 UTC, passing over Hanzhong, Shiyan, Xiangyang, Wuhan, Hangzhou and Shanghai among other populated areas.
[19:20] The next opportunity to observe TRMM will come for China with visibility all the way from the town of Hanzhong to the eastern coast. TRMM can be seen starting at 20:14 UTC, passing over Hanzhong, Shiyan, Xiangyang, Wuhan, Hangzhou and Shanghai among other populated areas.
Image: Spaceflight101/Google Maps
[18:30] The next visible pass of TRMM will come for southern Japan at around 18:45 UTC. The spacecraft will be visible from the majority of Kyushu as well as Shikoku. The further east, the longer the pass will be given the current lighting geometry. Tosashimizu will have the best possible viewing (length of pass & elevation).
Image: Spaceflight101/Google Maps
[16:30] USSTRATCOM issued a new TIP Message for the re-entry of the TRMM Satellite predicting re-entry on June 16, 2015 at 4:02 UTC +/- 180 Minutes.
[15:30] The next visible TRMM pass will come at 16:40 UTC for a region from Windhoek, Namibia, to Kabwe, Zambia. TRMM will be visible from central to north-eastern Namibia, south eastern Angola, the north of Botswana and from Zambia, including the city of Lusaka.
[15:30] The next visible TRMM pass will come at 16:40 UTC for a region from Windhoek, Namibia, to Kabwe, Zambia. TRMM will be visible from central to north-eastern Namibia, south eastern Angola, the north of Botswana and from Zambia, including the city of Lusaka.
Image: Spaceflight101/Google Maps
[15:15] TRMM passes over Madagascar in the evening twilight and is visible for most locations on the northern half of the island. No observer reports have been received yet.
[13:50] The next visible pass of the TRMM satellite will come for the island of Madagascar at around 15:14 UTC.
[13:50] The next visible pass of the TRMM satellite will come for the island of Madagascar at around 15:14 UTC.
Image: Spaceflight101/Google Maps
[11:40] New orbital data has been issued for TRMM: 179.8 by 183.7 Kilometers, 34.936° (Epoch: 11:00 UTC)
[11:15] Space Weather forecast models show geomagnetic activity to remain constant from now through TRMM's re-entry.
[11:00] NASA's TRMM spacecraft is expected to re-enter in the next 24 hours after spending the last 17 years orbiting the Earth to deliver unprecedented rainfall measurements that found use in science and operational weather and climate forecasting. The last set of orbital data was released on Sunday (Epoch: 12:04 UTC) and showed the spacecraft in an orbit of 198.5 by 200.0 Kilometers. Since then, TRMM will have fallen further, new orbital data is awaited.
[09:00] Observer reports from Florida suggest that TRMM is tumbling indicated by a flashing motion. TRMM can be seen with the naked eye, check for pass predictions over your location at heavens-above.com.
[11:15] Space Weather forecast models show geomagnetic activity to remain constant from now through TRMM's re-entry.
[11:00] NASA's TRMM spacecraft is expected to re-enter in the next 24 hours after spending the last 17 years orbiting the Earth to deliver unprecedented rainfall measurements that found use in science and operational weather and climate forecasting. The last set of orbital data was released on Sunday (Epoch: 12:04 UTC) and showed the spacecraft in an orbit of 198.5 by 200.0 Kilometers. Since then, TRMM will have fallen further, new orbital data is awaited.
[09:00] Observer reports from Florida suggest that TRMM is tumbling indicated by a flashing motion. TRMM can be seen with the naked eye, check for pass predictions over your location at heavens-above.com.
Tracking TLE (via Heavens-Above-com):
1 25063U 97074A 15165.50311909 .02817259 12734-5 73363-3 0 9990
2 25063 034.9372 213.3338 0001157 095.5853 042.7070 16.27491319 1664
1 25063U 97074A 15165.50311909 .02817259 12734-5 73363-3 0 9990
2 25063 034.9372 213.3338 0001157 095.5853 042.7070 16.27491319 1664
TRMM's Origin & Objectives
The Tropical Rainfall Measuring Mission (TRMM) was initiated as a cooperation between NASA and JAXA (formerly NASDA) within NASA’s Earth Science Enterprise to deliver measurements of precipitation and evaporation in the tropics in order to further the understanding in climate mechanisms and answer the question on how substantial rainfall affects climate patterns on a global scale.
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The need for such a mission was identified in Japan in the 1970s while initial proposals on the American side came in the early 80s followed by a detailed proposal from both agencies. NASA officially invited Japan to join the TRMM project in 1985 leading to the refinement of the science requirements for the mission. In 1988, the agreement between the U.S. and Japan was formalized allowing teams to start development of rainfall measurement instruments. Funding was provided by the U.S. Congress in 1991 and TRMM passed its critical design review in 1993 with the selection of the mission science team in 1994.
The objectives of TRMM included the measurement in the daily variation of precipitation and evaporation in the tropics, the collection of at least three years of data of importance for climatological studies, the generation of accurate estimates of the vertical distribution of latent heating in the atmosphere, the distribution of rainfall products to weather organizations and scientists as close to real-time as possible to allow this unique data to be available for forecasting and weather research. TRMM was expected to provide a better understanding of Earth’s energy and water cycles, shed light on the mechanisms of how global circulation is influenced by tropic rainfall, and deliver data for the improvement of weather and climate forecast models. The mission was also tasked with looking at specific phenomena such as El Nino, the Southern Oscillation and the propagation of the 30-60-day cycles in the tropics. Furthermore, TRMM was a technology evaluation mission as the first spacecraft dedicated to measure rainfall; it also provided the standard for cross-calibration of future rainfall measurement spacecraft. |
Image: NASA/JAXA
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Spacecraft & Instruments
Photo: NASA
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The TRMM spacecraft was built by the Goddard Spaceflight Center and carried four passive and one active instrument. Goddard developed the four passive instruments while JAXA provided the Precipitation Radar. TRMM has a dry mass of 2,634 Kilograms and carried 890 Kilograms of propellants at liftoff to be used over the course of its mission for orbit maintenance. In its launch configuration, the spacecraft measured 5.1 meters in length and 3.7 meters in diameter. Once in orbit, the vehicle deployed its two power-generating solar arrays increasing the spacecraft’s span to 14.6 meters from tip to tip.
The TRMM spacecraft uses a three-axis stabilized platform with a zero momentum bias. The attitude determination system employs a number of sensors for precise attitude determination - an Earth Sensor Assembly, Digital Sun Sensors, Coarse Sun Sensors, a Three-Axis Magnetometer and gyroscopic rate sensors. Attitude control is achieved through the use of Magnetic Torquer Bars and a Reaction Wheel Assembly that provides precise Earth-pointing capabilities, requiring the satellite to make one rotation per orbit to keep the instrument panel facing the planet. TRMM’s propulsion system consists of two hydrazine tanks pressurized with gaseous nitrogen, feeding four roll, pitch and yaw thrusters for a total of 12 thrusters installed on the spacecraft. |
Each of the two solar arrays consists of two panels for a total power-generation of 850 Watts. Communications are handled by an S-Band system that permitted communications via four RF links with the Tracking and Data Relay Satellite System. Command uplink was completed on the 2076.94MHz frequency while data downlink was done at 2255.5Mhz at a data rate of 170kbit/s on average, 32kbit/s in real time mode and 2Mbit/s for data playback, requiring 8.5 minutes of playback per orbit.
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Data from TRMM was
distributed to NASA Goddard and the JAXA Earth Observation Research
Center for ground-based processing and distribution to data users.
The TRMM spacecraft carries a suite comprised of five instruments, three of which were considered the primary instruments of the mission that were needed to fully satisfy the mission objectives. The 465-Kilogram Precipitation Radar (PR) is TRMM’s only active instrument. Developed by JAXA and NICT, the instrument featured an 128-element, two-by-two meter active phased array microwave radar – sending out microwave pulses towards the ground and recording the echo that is strongly influenced by water in the atmosphere and the altitude of water concentration. PR was capable of measuring the three-dimensional rain distribution from the ground to 15 Kilometers in altitude with 250m intervals and a sensitivity of 0.5mm of rain per hour. |
Image: NASA
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The echo measurement consisted of three components – the rain echo, the surface echo and the mirror image echo that extended from 0 to 5km in altitude. Operating at 13.8GHz, the instrument covered a swath of 215 Kilometers and achieved a 4.3km resolution, using an operational pulse repetition frequency of 2,776Hz at a pulse width of 1.6 microseconds in two channels.
The Visible Infrared Scanner, VIRS, is a passive cross-track scanning radiometer that measures the natural infrared emissions in five spectral bands from 0.63 to 12 micrometers for the assessment of cloud and ground radiation. The telescope uses a two-mirror Cassegrain design with a scanning mirror sweeping out the cross-track observation swath that has a width of 720 Kilometers corresponding to a +/-45-degree field of view. The five detectors are co-located on a cooled focal plane assembly, each equipped with its own specific bandpass filter. The 35-Kilogram instrument achieves a two-Kilometer ground resolution at nadir.
The Visible Infrared Scanner, VIRS, is a passive cross-track scanning radiometer that measures the natural infrared emissions in five spectral bands from 0.63 to 12 micrometers for the assessment of cloud and ground radiation. The telescope uses a two-mirror Cassegrain design with a scanning mirror sweeping out the cross-track observation swath that has a width of 720 Kilometers corresponding to a +/-45-degree field of view. The five detectors are co-located on a cooled focal plane assembly, each equipped with its own specific bandpass filter. The 35-Kilogram instrument achieves a two-Kilometer ground resolution at nadir.
Image: NASA Goddard
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TMI, the TRMM Microwave Imager, was built by Boeing Satellite Systems and is a multichannel, dual-polarized microwave radiometer measuring the natural microwave emissions to assess the brightness temperature of the surface and atmosphere that are processed into sea surface temperature, wind speed, water vapor column, cloud water content, and rain rate. The instrument has nine separate total power radiometers to create nine channels making measurements at five discrete frequencies from 10.7 to 85.5 GHz with four channels supporting both, vertical and horizontal polarization, the fifth channel at 21.3GHz only measures vertically polarized radiation.
The instrument covers a swath width of 760km – using a 61cm reflector to collect microwave radiation as part of a conical scanning geometry requiring the mirror to rotate once every 1.9 seconds during which only a 130-degree sector is actively measured. Except for the 85.5GHz channel, all TMI channels provided sufficient overlap between subsequent scans to create a complete strip of data. TMI resolution varies with measurement frequency from 63 by 37 Kilometers to 7 by 5 Kilometers. The Clouds and the Earth’s Radiant Energy System, CERES, is designed to measure the energy exchanged between the sun, Earth’s atmosphere, the surface and clouds, and space. For that, the instrument measures the energy at the top of the atmosphere and its data permits estimates of the energy level within the atmosphere and the surface. Combining CERES data with high-resolution cloud imaging can yield data on cloud distribution, altitude, thickness and the size of cloud particles. Information on the exchange of energy between Earth, Sun and space is essential for gaining an understanding of Earth’s climate system as a whole and for the improvement of climate prediction. CERES measures in three channels, a shortwave range from 0.3 to 5 micrometers, a longwave channel at 0.3 to 100µm and a narrowband window at 8-12µm. The instrument uses thermistor bolometers as detectors reaching a resolution of around 10 Kilometers operating in three modes – along and cross-track modes and a third mode known as rotating azimuth plane in which the instrument scans in elevation to collect radiance measurements from different viewing configurations. |
LIS, the Lightning Imaging Sensor, is a specific instrument for the detection of lightning in the atmosphere to monitor its distribution and variability, its correlation with rainfall and the relationship between lightning and Earth’s global electric circuit. The instrument is an optical staring telescope capable of detecting the position, rate and radiant energy of lightning flashes by obtaining wide-field images that are focused onto a 128 by 128-pixel CCD detector after passing through a narrowband filter of 777.4nm. With a total field of view of 600 by 600 Kilometers, the instrument can pin-point the location of lightning within 5 Kilometers at a temporal resolution of 2 milliseconds. LIS can detect intracloud and cloud-to-ground lighting and its data is useful for many applications including convection studies, storm dynamics assessments and microphysical studies.
TRMM Mission
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In the agreement between NASA and Japan, JAXA was responsible for the launch of the TRMM spacecraft atop its H-IIA rocket. Liftoff took place on November 27, 1997 from the Tanegashima Space Center and TRMM was delivered to its target orbit along with a secondary payload known as Engineering Test Satellite 7 that consisted of two components to complete a rendezvous and stationkeeping demonstration in orbit.
Ten days after launch, TRMM reached its operational orbit at 350 Kilometers and an inclination of 35 degrees. The orbital inclination was selected to provide coverage of the tropics only as rainfall in this area accounts for two-thirds of the total rainfall on Earth. The very low orbital altitude was chosen to ensure weak echoes could be picked up by the Precipitation Radar, the primary instrument of the mission. Given the science requirements for TRMM, an extensive Global Validation Program was started after the spacecraft started operating, involving ten ground validation sites throughout the tropics to provide ground-truth measurements for comparison with TRMM data. Airborne underflight campaigns were completed as part of initial satellite commissioning and throughout the TRMM mission to keep track of the satellite’s measurement accuracy. Within 30 days after launch, data from all five instruments of TRMM became available, but the calibration of all instruments continued for several more months. |
Photo: JAXA
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Nine months into the mission, in August 1998, the CERES instrument suffered a voltage converter anomaly, rendering the instrument useless after less than a third of the primary mission of the TRMM spacecraft.
Over the primary mission of three years, TRMM continued to function as advertised with the exception of CERES and data delivered by the instruments was of the expected quality, allowing scientists to access previously unavailable data to study global climate mechanisms. Additionally, a gradual change of the nature of the mission took place – starting out as a purely scientific mission, TRMM data was slowly integrated into operational applications such as hurricane and cyclone forecasting. The availability of a unique data set from complementary sensors in near real-time proved useful in operational programs such as hurricane modeling and found its way into models of many meteorological agencies around the globe.
Over the primary mission of three years, TRMM continued to function as advertised with the exception of CERES and data delivered by the instruments was of the expected quality, allowing scientists to access previously unavailable data to study global climate mechanisms. Additionally, a gradual change of the nature of the mission took place – starting out as a purely scientific mission, TRMM data was slowly integrated into operational applications such as hurricane and cyclone forecasting. The availability of a unique data set from complementary sensors in near real-time proved useful in operational programs such as hurricane modeling and found its way into models of many meteorological agencies around the globe.
Image: NASA Goddard
TRMM Satellite image of Tropical Cyclone Yasi, 2011
Image: NASA Goddard
Precipitation Radar image of tropical cyclone Magda, 2011
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After the conclusion of the primary mission, efforts began to prolong the life of the TRMM spacecraft by placing it in a higher orbit to reduce fuel consumption for stationkeeping. The spacecraft raised its orbit on August 20, 2001 to reach an orbital altitude of 402.5 Kilometers which was dictated by the pulse repetition rate of the Precipitation Radar. In the new orbit, the spacecraft switched to the backup Kalman filter for attitude determination using gyro data with sun sensor and magnetometer data to estimate 3-axis attitude and gyro rate bias. The backup control was initially expected to yield a degraded attitude accuracy of 0.7° but improvements brought the attitude precision back to the original requirement of 0.2 degrees.
With TRMM gaining importance for operational services, its operation beyond the three-year primary mission was greatly desired, however, the initial plan was to operate the spacecraft until a certain fuel level is reached that would still permit a safe deorbitation of the spacecraft over the Pacific Ocean. Therefore, the mission was only extended until 2004 to leave the required fuel margin. The End-of-Mission date was pushed to 2005 under pressure of weather forecasting centers around the world that had begun to rely primarily on TRMM data. In October 2005, a decision was made to keep operating the spacecraft until fuel exhaustion that, at the time, was expected around 2012. Over the course of its mission, TRMM was joined by other spacecraft that entered orbit to make similar or complementary measurements with TRMM acting as the gold-standard in terms of cross-calibration for data continuation and comparability. Additionally, improvements in data processing and the combination of PR and TMI data led to a list of new objectives being added to the TRMM mission for a range of studies. With TRMM still functional and with sufficient fuel reserves, NASA aimed for a period of overlap between the TRMM mission and the GPM Core Spacecraft (Global Precipitation Measurement), the direct successor to TRMM and the new centerpiece of a constellation of rainfall and cloud-measurement satellites. An overlap between the two would have allowed for a direct comparison of data to ensure proper calibration of GPM data for the continuation of a climatological record beginning with TRMM in 1997. |
GPM slipped from a 2013 to a February 2014 launch, but TRMM continued operating efficiently in terms of fuel expenditure. In preparation for GPM, the TRMM spacecraft switched to the Precipitation Processing System for data processing. With GPM launching in February 2014 and starting initial measurements in March, teams got their highly desired overlap period between GPM Core and TRMM, though TRMM was nearly running on empty.
Some battery issues arose aboard TRMM in early 2014 leading to the shutdown of the VIRS instrument in March.
Pressures within the propulsion system of the TRMM spacecraft dropped below the identified threshold on July 8, 2014 and NASA ended stationkeeping maneuvers, marking the beginning of a slow drop towards the dense atmosphere. However, it was initially expected that TRMM was two to three years from re-entry with a 95% probability issued for re-entry during a window of May 2016 to November 2017. As is now clear, this calculation was off by nearly a year, showing how difficult it is to reliably model orbital decay.
Some battery issues arose aboard TRMM in early 2014 leading to the shutdown of the VIRS instrument in March.
Pressures within the propulsion system of the TRMM spacecraft dropped below the identified threshold on July 8, 2014 and NASA ended stationkeeping maneuvers, marking the beginning of a slow drop towards the dense atmosphere. However, it was initially expected that TRMM was two to three years from re-entry with a 95% probability issued for re-entry during a window of May 2016 to November 2017. As is now clear, this calculation was off by nearly a year, showing how difficult it is to reliably model orbital decay.
Image: NASA Goddard
Image: NASA Goddard
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On October 7, 2014 the last data from the Precipitation Radar was made public as TRMM dropped to an altitude at which cloud data can no longer be observed at a useful quality. When the satellite arrived at an altitude around 350km, its original orbital altitude, PR measurements resumed for a brief period for verification of data and instrument performance.
In March 2015, the final fuel aboard the spacecraft that had been reserved for any debris avoidance maneuvers in the closing months of the mission was depleted. On April 8, the mission was declared as complete and science data collection was ceased. Decommissioning of the spacecraft followed and the transition from science activities to decay monitoring was completed. Re-Entry of the spacecraft is expected in June 2015. "TRMM has been the world’s foremost satellite for the study of precipitation and climate processes in the tropics, and an invaluable resource for tropical cyclone research and operations," says TRMM Project Scientist Scott Braun at NASA Goddard. "Data from TRMM will continue to foster science well after the mission ends, and, when combined with data from the new Global Precipitation Measurement Core Observatory, launched earlier this year by NASA’s partner the Japan Aerospace Exploration Agency, will contribute to a long-term precipitation climate record.” |
Re-Entry Prediction and Risk to Life & Property
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Objects drop out of orbit and re-enter Earth’s atmosphere every day, however, the re-entry of large objects with masses of several metric tons is rather rare, coming about once every year or two.
International agreements have been made in recent years to ensure heavy objects are deorbited in a controlled fashion to avoid risk to the public, but there are are many old, heavy satellites still to re-enter and accidents such as the recent Progress mishap can leave large spacecraft in short-lived orbits. The case of TRMM has been a special one since the spacecraft was launched with a specific plan for a safe deorbitation at the end of its functional mission. It was planned to operate TRMM for as long as possible before allowing its orbit to decay somewhat to set up a retrograde maneuver to sufficiently drop the perigee of the orbit for a targeted re-entry over the Pacific Ocean. |
Photo: NASA (ATV-1)
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A plan was developed for three maneuvers – the first lowering the orbit from 350 to 250 Kilometers, the second lowering the perigee to 150 Kilometers and a third maneuver setting up entry interface at the desired location for a total fuel consumption of 157 Kilograms (with reserves). However, this plan was abandoned in 2005 when the mission of the TRMM spacecraft was extended and it was decided to use up all of the satellite’s fuel for its active mission.
This decision was made by NASA against a National Research Council recommendation of ensuring a safe re-entry of the satellite. However, NASA did not take that decision lightly and performed a risk review in 2002 that identified the risk of a human injury or death caused by TRMM’s uncontrolled re-entry as 1 in 5,000 which is about twice the acceptable casualty risk that is acceptable for a NASA mission under NASA Safety Standard 1740.14.
This decision was made by NASA against a National Research Council recommendation of ensuring a safe re-entry of the satellite. However, NASA did not take that decision lightly and performed a risk review in 2002 that identified the risk of a human injury or death caused by TRMM’s uncontrolled re-entry as 1 in 5,000 which is about twice the acceptable casualty risk that is acceptable for a NASA mission under NASA Safety Standard 1740.14.
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However, weighing the casualty risk of an uncontrolled re-entry against the loss of public safety benefits provided by the cyclone prediction provided TRMM led to a decision of continuing the mission to potentially safe lives over the extended mission of TRMM.
A 2005 NASA Goddard Study titled “Estimating the Benefit of TRMM Tropical Cyclone Data in Saving Lives”using a mathematical model to calculate the potential lives that TRMM data could save concluded: The resulting estimates indicate 100-500 lives are saved annually through the use of TRMM data in tropical cyclone monitoring and forecasting. TRMM is currently in its eighth year of operation and has the potential for another 4-7 years of operation. |
Image: NASA
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To date, there has not been a casualty reported in association with a re-entering man-made object. But there have been cases of re-entries occurring over or near populated areas and remnants of spacecraft are known to survive re-entry. There have been cases of objects from spacecraft being recovered on land or washed ashore if re-entry occurred over the Ocean.
Image: Orbital Debris Quarterly
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A
rule of thumb often used when it comes of the estimation of an
uncontrolled satellite re-entering over land is the distribution of
land and ocean on the surface of the Earth. 75% of the Earth is
covered by water so often a probability of 25% of a satellite hitting
land can be found in the media.
However, the matter becomes more complicated when taking into account the orbital inclination of the satellite that drives the fraction of an orbit spent over land given Earth’s uneven distribution of land as a function of latitude. In a study published by M. Matney in ‘Orbital Debris Quarterly’ the probabilities of satellite re-entry avoiding land was calculated for all orbital inclinations from equatorial to polar orbits. The study evaluated a hypothetical satellite re-entry with a debris footprint of 800 Kilometers in the along-track direction, but no width, or cross track dispersion to simplify the model. |
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The
TRMM spacecraft orbits Earth at an inclination of 35 degrees which
means that debris could fall anywhere between 35 degrees south and 35
degrees north latitude, covering much of the inhabited areas of the
planet, but also passing over the vast areas of the Ocean. It has been
calculated that the probability of debris ending up on land for this
type of orbit is approximately 39%.
More complicating this calculation is the variability of land coverage with an orbit precessing over time. A detailed simulation was run for the TRMM mission to determine land mass coverage as a function of the Initial Longitude of Ascending Node over a 17-day period. This simulation showed that the percentage of a given ground track for TRMM passing over land can vary from 41.97% to 15.47% with a 17-day average of 29.95%. An additional factor taken into account by a 2001 TRMM re-entry analysis was the population density under a spacecraft’s orbit as a function of inclination. This analysis used 1994 average population density data and showed that an orbit with a 35° inclination had the highest average population density under the spacecraft: |
Image: NASA Goddard, 2001 TRMM Workshop
TRMM land Mass Coverage vs. initial LAN in 17-Day Simulation
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Image: NASA Goddard, 2001 TRMM Workshop
Through tracking of the spacecraft and orbit propagation, it is possible to estimate the time and possible location of re-entry in advance, but this calculation is strongly dependent on a number of factors that can not be accurately determined. These factors include the conditions of the atmosphere that drive the speed of orbital decay and are influenced by solar activity that can not be predicted with 100% accuracy. Also, the orientation and attitude rate of the spacecraft plays a major role in the speed of its orbital decay as they influence the drag experienced by the craft.
A good illustration of the difficulty of exact orbital decay modeling is the August 2014 estimate by NASA that showed a 95% certainty of TRMM re-entering between May 2016 and November 2017. Now it is known that this calculation was off by almost one year.
Any re-entry prediction is *always* associated with a window of uncertainty given the unknowns described above. Many media outlets will give the re-entry time and even locations as absolute values, but the truth is that when re-entry is still several days away, the error bar on any prediction can be 24 hours in either direction or more. Even on the day of re-entry, calculations can only narrow down the approximate time and location to within about one orbit of Earth so that areas of risk can be identified and other areas can be excluded.
A good illustration of the difficulty of exact orbital decay modeling is the August 2014 estimate by NASA that showed a 95% certainty of TRMM re-entering between May 2016 and November 2017. Now it is known that this calculation was off by almost one year.
Any re-entry prediction is *always* associated with a window of uncertainty given the unknowns described above. Many media outlets will give the re-entry time and even locations as absolute values, but the truth is that when re-entry is still several days away, the error bar on any prediction can be 24 hours in either direction or more. Even on the day of re-entry, calculations can only narrow down the approximate time and location to within about one orbit of Earth so that areas of risk can be identified and other areas can be excluded.
The Re-Entry Process & Surviving Components
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TRMM started its slow drop towards the atmosphere from an altitude of 402 Kilometers in July 2014, beginning at an altitude almost matching the current altitude of the International Space Station that also has to maintain its orbit through regular engine burns to make up for drag in the upper reaches of Earth’s atmosphere.
Initially, TRMM began losing altitude slowly caused by drag in the upper atmosphere in the form of collisions of the spacecraft with ions and molecules present in the upper reaches of the atmosphere leading to a loss of velocity on the spacecraft that causes the orbital altitude to drop. As the spacecraft enters a lower and lower orbit, drag increases and the speed of orbital decay picks up. One interesting item of note for TRMM is that the spacecraft is still operating to some degree, so it can be expected that it will remain at a relatively stable attitude as it approaches the dense layers of the atmosphere. |
Photo: NASA/ESA (Cygnus)
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In some cases, spacecraft can enter a tumble in the days leading up to entry, but in many cases the craft will enter an aerodynamically stable attitude in the tenuous upper layers of the atmosphere.
Credit: Calsky.com
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The speed of orbital decay will depend on a number of factors, not all of which can be known precisely such as the state of Earth’s atmosphere that can only be estimated based on current solar weather using the 10.7cm radio flux, Kp-Index and space weather forecast models to feed decay simulations. Also, the spacecraft attitude plays a role in the level of drag experienced by the vehicle. Therefore, decay predictions are always associated with an error bar that corresponds to about 20% of the time from the prediction to the predicted decay time.
Over its final days in orbit, TRMM will be tracked by ground-based radars to precisely determine its orbit. The United States operate a tracking system that provides data to the public to allow an independent calculation of the re-entry time. |
When re-entry comes, its position can be calculated from orbital data gathered in the last orbits ahead of the event, but the most precise data will be provided through space-based assets of the U.S. military that can track the signature of spacecraft re-entries and so pin-point their timing and location with high precision.
Photo: NASA/ESA
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As the TRMM satellite drops in altitude, it will approach the dense layers of the atmosphere for its steep plunge. The exact timing of orbital decay depends on the current state of the atmosphere which is known to expand and contract as a result of solar activity. Once hitting the dense atmosphere, TRMM will start feeling the effects of re-entry.
The onset of re-entry usually occurs at an altitude of 120 to 100 Kilometers when the spacecraft enters the dense atmosphere, initially not slowing down at a fast rate yet but already interacting with plenty of molecules in the upper reaches of the atmosphere. Given the high speed of the object, traveling at 7.7 Kilometers per second, air in front of the craft is compressed creating a shock wave layer in which some of the molecules are separated into ions, creating the typical visible plasma layer that can be present even minutes before disintegration starts. |
The Entry Point, as defined by USSTRATCOM and represented in all their data, refers to the spacecraft passing 80 Kilometers in altitude where drag builds up to a destructive force, triggering the onset of the disintegration of the spacecraft structure. The shock wave layer forming just in front of the spacecraft and any separated components leads to considerable heating that causes the incineration of the majority of the spacecraft structure. The mechanical deceleration experienced during re-entry can be up to 20Gs further crushing the structural components and causing the break-up of the spacecraft.
The mechanical energy of a re-entering satellite is ~3.2 x 10^7 J/kg which would be sufficient to easily vaporize the entire satellite if all of this energy were converted into heat entirely absorbed by the satellite structure. However, only a fraction of a satellite’s total energy is converted into heat absorbed by its body and depends on a number of factors such as flight path angle and velocity as well as the properties of the object (shape, area and mass).
The mechanical energy of a re-entering satellite is ~3.2 x 10^7 J/kg which would be sufficient to easily vaporize the entire satellite if all of this energy were converted into heat entirely absorbed by the satellite structure. However, only a fraction of a satellite’s total energy is converted into heat absorbed by its body and depends on a number of factors such as flight path angle and velocity as well as the properties of the object (shape, area and mass).
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Generally,
loose components with a high area to mass ratio such as solar
arrays and antenna reflectors are lost first, becoming detached
from a satellite at an altitude around 100 Kilometers. The main
spacecraft body usually experiences disintegration at an altitude of
68 to 88 Kilometers due to the heat and dynamic loads experienced
during entry.
The survivability of specific components depends on a number of factors including the component’s material, shape, area to mass ratio and shielding provided by other spacecraft components. A generalization that is often found states that aluminum components usually burn up completely unless they have a high area to mass ratio, are shielded by other satellite parts or are released late in the entry process. Titanium or stainless steel spheres (tanks) or solid rocket motor casings have a good probability of surviving and hitting the Earth’s surface. A number of models have been developed over the years to assess the survivability of satellite components and NASA established specific rules for the risk assessment done for every spacecraft re-entry to determine whether uncontrolled re-entry can be accepted as disposal of a satellite at the end of its life. For TRMM a number of studies were conducted by NASA’s Orbital Debris Program Office using the Object Reentry Survival Analysis Tool – a high-fidelity simulation tool that takes into account heat conduction on spheres and cylinders of layered structure, surface chemical heating through oxidation and emissivity that varies with material type. The model of TRMM used in the simulation (referred to as Parent Body) was a 2,632kg aluminum box 5.1 by 3.5 by 3.0 meters in dimensions. |
Image: NASA Goddard, 2001 TRMM Workshop
Image: NASA Orbital Debris Program Office
Delta II Second Stage Pressurant Tank after Re-Entry
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The Parent Object included 36 objects larger than 0.25m in any direction that were modeled as equivalent spheres or cylinders of the predominant material they consist of. Inputs made in the simulation were the integrated heat load received by each component, and the specific heat of ablation of the predominant materials. The simulation yielded the survivability of each component from which a casualty area could be computed using the cross sectional area of each component added to an 0.3m ‘man border.’
Image: NASA Goddard, 2001 TRMM Workshop
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If the cumulative Debris Casualty Area of a specific spacecraft re-entry exceeds 8 square meters, NASA rules require active control of the ground impact points for the debris (i.e. a controlled re-entry). The ORSAT simulation applied to TRMM analyzed 76% of the total spacecraft mass (6% were less than 0.25m in size, 1% was accounted for in gas and residual propellant and 17% were not taken into account as zero risk of survival – cable harness, insulation blankets, plumbing and solar array booms).
The simulation assumed entry interface at 122 Kilometers and breakup at 78 Kilometers with a flight path angle of –0.7° and a relative velocity set at 7350m/s. |
The total debris casualty area (DCA) for TRMM was determined at 12.35m² - violating NASA Safety Standard 1740.14. A controlled re-entry was waived for this mission given the benefit of the continuation of the mission with respect to lives saved by TRMM data versus the increase in risk associated with re-entry.
The following components were identified to survive re-entry:
Other components that were not identified to survive by ORSAT, but have a good chance of reaching the ground include components of the LIS instrument – 0.9kg of titanium and 0.5kg of glass components.
The ORSAT simulation can also provide component demise locations and calculate the downrange travel distance of surviving components to allow a basic estimation of the debris field size.
The following components were identified to survive re-entry:
- TRMM Microwave Imager – Titanium Motor and Shaft – Mass: <20kg – DCA:0.657m²
- 4 Reaction Wheels – Titanium & Stainless Steel, housed in Aluminum - Mass: 10.7kg – DCA: 1.784m² [The reaction wheels consist of a titanium flywheel 35.8cm in diameter and 1.8cm thick with a steel shaft 2.5cm in diameter and 11.5cm long.]
- Gaseous Nitrogen Tank – Titanium, 0.5cm wall thickness – Mass: 14.04kg – DCA: 1.200m²
- 2 Solar Array Drive Mechanisms – Aluminum – Mass: 11.175kg – DCA: 1.640m²
- LBS – Lower Bus Structure – Mass: 416.476kg – DCA: 7.067m² [LBS is 1.8 by 2.44 by 1.67m in size and will not survive in its entirety. It contains, however components that will survive: 2 main tanks 1.0 by 0.81 meters in size with a wall thickness of 0.13cm and a mass of 32.28kg]
Other components that were not identified to survive by ORSAT, but have a good chance of reaching the ground include components of the LIS instrument – 0.9kg of titanium and 0.5kg of glass components.
The ORSAT simulation can also provide component demise locations and calculate the downrange travel distance of surviving components to allow a basic estimation of the debris field size.
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The simulation calls for most satellite components to fully burn up between 50 and 78 Kilometers in altitude and surviving components to impact between 640 and 1,030 Kilometers downrange.
The following downrange travel distances have been determined for surviving components:
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Image: NASA Goddard, 2001 TRMM Workshop
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NASA’s Orbital Debris Program Office conducted a separate study published by R.Smith et. al. in 2004 using an ORSAT simulation with over 200 satellite components accounting for 91% of the total dry mass of the spacecraft. The simulation used the same trajectory and Parent Body properties and calculated the point of demise of each object corresponding to the total heat absorbed by a component (net heating rate integrated over time multiplied by object surface area) becoming equal or greater than the heat of ablation of all object layers.
Image: NASA Orbital Debris Program Office
The simulation showed 12 components to survive re-entry and impact between 534km and 1,010 Kilometers downrange from the orbital decay point. The cumulative debris casualty area was estimated at 11.3 square meters.
From the simulation, a total mass of 112 Kilograms was obtained for all surviving components corresponding to 4.3% of the total dry mass of the spacecraft. From a risk calculation standpoint, this simulation concludes with a 1 in 4,530 chance of human casualty or death as the result of the TRMM re-entry that was then expected to occur in 2009. (Current values are on the order of 1 in 4,200 due to population growth).
Considering all factors, the uncontrolled re-entry of TRMM is associated with more risk than the re-entry of ESA’s GOCE spacecraft in 2014, but less-risky than many of re-entries of the last few years such as UARS, ROSAT, Phobos-Grunt and Progress M-27M.
From the simulation, a total mass of 112 Kilograms was obtained for all surviving components corresponding to 4.3% of the total dry mass of the spacecraft. From a risk calculation standpoint, this simulation concludes with a 1 in 4,530 chance of human casualty or death as the result of the TRMM re-entry that was then expected to occur in 2009. (Current values are on the order of 1 in 4,200 due to population growth).
Considering all factors, the uncontrolled re-entry of TRMM is associated with more risk than the re-entry of ESA’s GOCE spacecraft in 2014, but less-risky than many of re-entries of the last few years such as UARS, ROSAT, Phobos-Grunt and Progress M-27M.
Observing Re-Entry
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As described above, predicting the exact timing of re-entry
is nearly impossible, but the re-entry window that is issued based on orbital
tracking can help when trying to watch the event.
The exact location of re-entry can not be predicted, however a few hours before the event, zones will be excluded. Should you have TRMM passes around the time of final entry predictions that are made on the day of the estimated Re-Entry, you should certainly step outside and look for the spacecraft. Websites like Heavens-Above.com provide a list of passes for any given location on Earth. (Pass Predictions of these websites are based on orbital information that is updated several times per day. On Re-Entry day, the spacecraft's orbit decays rapidly so that these predictions become inaccurate very fast and the time of the start of the pass might vary by several minutes.) In the days leading up to re-entry, TRMM can be seen as a little dot racing across the sky. Possible variation in brightness can indicate tumbling of the spacecraft. When re-entering, the disintegrating vehicle will streak across the sky with a visible plasma tail and glowing debris falling back to Earth. |
Photo: John Arnold / Spaceweathergallery.com
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If you observe the spacecraft in the days leading up to re-entry or catch a glimpse of re-entry, give us a Tweet or send an E-Mail, we are interested in your observation reports and photos! (Please provide an approximate observation location to make analysis of the data possible.)
How the Orbital Tracker works
There often are misconceptions on how tracking websites like n2yo.com work. A common believe is that these ‘real time tracking sites’ indeed show the position of the satellite based on tracking information gathered in real time. This is not the case. The trackers receive a set of orbital elements from which the position of the satellite at any given time is calculated. These orbital elements are generally updated several times per day to show the position of the satellite with reasonable accuracy.
However, with a spacecraft close to re-entry, the fast reduction of orbital period will result in the tracker and the actual position of the satellite to get out of synch between tracking updates. Therefore, it is common that the satellite will appear up to a few minutes before the predicted times according to online observation calculators or trackers. Also, when re-entry comes, online trackers will continue to show the propagated position of the satellite for several hours or even days, although the satellite has long ceased to exist.
However, with a spacecraft close to re-entry, the fast reduction of orbital period will result in the tracker and the actual position of the satellite to get out of synch between tracking updates. Therefore, it is common that the satellite will appear up to a few minutes before the predicted times according to online observation calculators or trackers. Also, when re-entry comes, online trackers will continue to show the propagated position of the satellite for several hours or even days, although the satellite has long ceased to exist.
Update History
Re-Entry Update - June 14, 2015
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Updated: June 14, 2015
Current Orbit: 197.2 x 203.7 Kilometers, 34.95° [Epoch: 11:30 UTC] Latest Re-Entry Predictions: USSTRATCOM: June 16 - 06:37 UTC +/-24 Hours [Issued: June 14 - 09:06] Spaceflight101: June 16 - 12:22 UTC +/- 22 Hours [Issued: June 14 - 13:30] Aerospace Corp.: June 16 - 09:18 UTC +/-17 Hours [Issued: June 13 - 12:29] Satflare/J. Remis: June 16 - 13:59 UTC +/-14 Hours [Issued: June 14] Re-Entry Zone: No Prediction Possible Solar activity and associated geomagnetic response keeps driving the speed of TRMM's orbital decay. Geomagnetic activity is expected to increase late on Sunday, peaking at a Kp Index of 5 which may further speed up the rate of decay, leading to re-entry early on Tuesday, June 16. Re-Entry Zones can not be predicted yet due to the uncertainty of decay predictions, however, it will be possible to narrow down the orbital decay point to a few orbits on Monday so that areas can be excluded. Tracking TLE (via Heavens-Above-com): 1 25063U 97074A 15165.47957304 .02224527 12782-5 60056-3 0 9999 2 25063 034.9520 213.4864 0004937 112.9680 247.1119 16.27052583 1655 |
Credit: Spaceflight101
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Re-Entry Update - June 12, 2015
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Current Orbit: 218.6 x 224.8 Kilometers, 34.94° [Epoch: 09:18 UTC]
Latest Re-Entry Predictions: USSTRATCOM: June 16 - 08:59 UTC +/-48 Hours [Issued: June 12 - 10:14] Spaceflight101: June 16 - 18:44 UTC +/- 34 Hours [Issued: June 12 - 09:30] Aerospace Corp.: June 16 - 07:16 UTC +/-33 Hours [Issued: June 10 - 14:20] Satflare/J. Remis: June 16 - 13:14 UTC +/-30 Hours [Issued: June 12] Re-Entry Zone: No Prediction Possible USSTRATCOM has begun issuing TIP Messages for the TRMM Satellite Re-Entry. Solar activity had been trending up earlier in the week leading to orbital decay to speed up with predictions drifting forward by about 24 hours. On June 12, solar activity was on the increase again and geomagnetic activity is expected to reach a Kp Index of 5 later on Friday and remain elevated throughout the weekend which could further accelerate TRMM's orbital decay. Tracking TLE (via Heavens-Above-com): 1 25063U 97074A 15163.38812917 .01489710 18943-2 80085-3 0 9999 2 25063 034.9399 228.7608 0004660 090.9928 269.1294 16.19210891 1317 |
Credit: Spaceflight101
Credit: Spaceflight101
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Re-Entry Update - June 9, 2015
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Current Orbit: 234.6 x 242.4 Kilometers, 34.94° [Epoch: 16:36 UTC]
Latest Re-Entry Predictions: Spaceflight101: June 17, 2015 - 15:25 UTC +/- 50 Hours [Issued: June 9] Satflare/J. Remis: June 16, 2015 - 03:43 UTC +/-36 Hours [Issued: June 9] USSTRATCOM 60-Day Message: June 17, 2015 [Issued: June 3] Re-Entry Zone: No Prediction Possible Tracking TLE (via Heavens-Above-com): 1 25063U 97074A 15160.69229949 .00895837 46968-3 73392-3 0 9999 2 25063 034.9439 248.2460 0005895 063.8361 065.6467 16.13042772 883 |
Credit: Spaceflight101
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Re-Entry Update - June 7, 2015
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Current Orbit: 243.0 x 252.3 Kilometers, 34.94°
Latest Re-Entry Predictions: USSTRATCOM 60-Day Message: June 17, 2015 [Issued: June 3] Spaceflight101: June 18, 2015 +/- 4 Days [Issued: June 7] Re-Entry Zone: No Prediction Possible Tracking TLE (via Heavens-Above-com): 1 25063U 97074A 15160.69229949 .00895837 46968-3 73392-3 0 9999 2 25063 034.9439 248.2460 0005895 063.8361 065.6467 16.13042772 883 |
USSTRATCOM 60-Day Messages
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Re-Entry Update: June 5, 2015
Current Orbit: 249.3 x 259.5 Kilometers, 34.95°
Latest Re-Entry Predictions:
USSTRATCOM 60-Day Message: June 17, 2015 [Issued: June 3]
Spaceflight101: June 17, 2015 +/- 4.3 Days [Issued: June 5]
Re-Entry Zone: No Prediction Possible
Tracking TLE (via Heavens-Above-com):
1 25063U 97074A 15156.46734194 .00450010 95271-4 53730-3 0 9998
2 25063 034.9450 278.5066 0007686 031.1909 050.5486 16.07253456 206
Latest Re-Entry Predictions:
USSTRATCOM 60-Day Message: June 17, 2015 [Issued: June 3]
Spaceflight101: June 17, 2015 +/- 4.3 Days [Issued: June 5]
Re-Entry Zone: No Prediction Possible
Tracking TLE (via Heavens-Above-com):
1 25063U 97074A 15156.46734194 .00450010 95271-4 53730-3 0 9998
2 25063 034.9450 278.5066 0007686 031.1909 050.5486 16.07253456 206
Re-Entry Update - June 4, 2015:
Current Orbit: 252 x 262 Kilometers, 34.94° [Epoch: 11:15 UTC]
Latest Re-Entry Predictions:
USSTRATCOM 60-Day Message: June 17, 2015 [Issued: June 3]
Spaceflight101: June 18, 2015 +/- 5 Days [Issued: June 3]
Re-Entry Zone: No Prediction Possible
Tracking TLE (via Heavens-Above-com):
1 25063U 97074A 15155.46931630 .00406723 76189-4 51371-3 0 9999
2 25063 034.9449 285.6241 0007697 024.4964 033.9445 16.06361132 48
Latest Re-Entry Predictions:
USSTRATCOM 60-Day Message: June 17, 2015 [Issued: June 3]
Spaceflight101: June 18, 2015 +/- 5 Days [Issued: June 3]
Re-Entry Zone: No Prediction Possible
Tracking TLE (via Heavens-Above-com):
1 25063U 97074A 15155.46931630 .00406723 76189-4 51371-3 0 9999
2 25063 034.9449 285.6241 0007697 024.4964 033.9445 16.06361132 48
