UPDATE 06-06-2025
Multiple stations confirm that NOAA-18 is shut down on APT, S-Band, HRPT transmissions. The NOAA 18 Satellite was fully decommissioned via the shutdown commands at approximately 1740 UTC 06/06/2025
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Deorbiting of the Satellite
NOAA-18, like its legacy Polar-orbiting Operational Environmental Satellite (POES) predecessors, lacks any propulsion systems for major orbital maneuvers, like deorbiting. Consequently, upon decommissioning, these satellites undergo a permanent power-down sequence. This action effectively renders them inert, and they remain in their current orbital parameters as space debris. No further telemetry or operational contact will be established with NOAA-18. So this is the last we will hear from NOAA-18. All power buses are disabled to all sensors, receivers, and transmitters.
As for the decommissioning of NOAA 15 and 19. Not scheduled as of yet.
Between 2015 and 2021, four satellites—NOAA-16, NOAA-17, DMSP F11, and DMSP F13—experienced in-orbit breakups. Investigations, notably the 2023 NOAA-17 report, point to a violent rupture of the onboard Nickel-Cadmium (Ni-Cd) battery packs due to extreme overcharging as the probable cause.
Despite NOAA-16, NOAA-17, and DMSP F11 undergoing decommissioning, which includes disconnecting batteries from charging systems, the overcharging occurred. The NOAA-17 investigation theorized a potential electrical system fault that allowed inadvertent charging through a normally discharge-only pathway. This persistent design flaw risk prompted NOAA to decommission NOAA-18, given the known susceptibility of this spacecraft design to battery overcharging. With the loss of S-band as as the only method to verify command and control responses, the order was given to decommission NOAA 18. If NOAA and the subcontractor operating the satellites, determine that there is an issue with command and control, then I would imagine that the decommissioning of the last two satellites will occur, but as of now that has not happened.
Final Decommissioning Notice
On Wednesday, June 5, 20025, NOAA sent out the final decommissioning notice for NOAA 18.
On May 31, 2025 at 1605 UTC, the NOAA-18 S-band Transmitter 4 (STX4) experienced a power drop from 7W to 0.8W. STX4 is the only remaining transmitter used for up-link (commanding) and downlink (telemetry & global science data from the recorder). Full recovery of the S-Band transmitter and its functionality is not possible, and therefore jeopardizes the ability to ensure safe operation of the spacecraft. Based on NOAA’s requirement to responsibly manage on-orbit assets, NOAA will decommission NOAA-18 on June 6, 2025 between 1733 and 1749 UTC.
NOAA relies on this STX4 system for crucial real-time operations, including confirming commands, receiving telemetry data, and obtaining GACs. However, NOAA is encountering significant challenges because the data being received is extremely noisy and contains errors. This is due to the variable, uncontrolled low power output of 0.8 watts from 7.5 on STX4. The excessive noise makes it very difficult for NOAA to accurately assess the spacecraft’s health and ensure its safety.
NOAA-18 is a legacy Polar Operational Environmental Satellites (POES) satellite and is operated with no performance or latency requirements. Users should transition to NOAA’s Joint Polar Satellite System (JPSS). JPSS provides global observations that serve as the backbone of both short- and long-term forecasts, including those that help us predict and prepare for severe weather events. The five satellites scheduled in the fleet are the currently-flying NOAA/NASA Suomi National Polar-orbiting Partnership (Suomi NPP) satellite, NOAA-20, previously known as JPSS-1, NOAA-21, previously known as JPSS-2, and the upcoming JPSS-3 and JPSS-4 satellites.
UPDATE 06-03-2025
Based on NOAA’s requirement to responsibly manage on-orbit assets, NOAA will commence with decommissioning activities immediately for NOAA-18. The exact date/time of decommission is not yet determined and is pending completion of pre-decommission processes. Users are advised to discontinue use of all NOAA-18 science products immediately.
NOAA has officially initiated the decommissioning activities for the NOAA-18 satellite. This process aims to safely remove the aging spacecraft from active service and mitigate any potential risks, such as the creation of orbital debris.
While the agency has begun the necessary steps, the precise date and time of the satellite’s full decommissioning are not yet finalized. This is contingent upon the successful completion of a series of “pre-decommission processes.” These preliminary steps typically involve:
- System Safing: Disconnecting batteries, disabling transmitters, and depleting propellants (like nitrogen gas) to make the satellite inert and prevent uncontrolled breakups.
- Data Transition: Ensuring that all critical data streams from NOAA-18 are successfully transferred to newer, more advanced satellite constellations, such as the Joint Polar Satellite System (JPSS). NOAA-18, along with NOAA-15 and NOAA-19, has been in an “Extended Life” program, transitioning to a commercial ground system for continued operation as “data of opportunity,” but this will cease.
- Operational Handover: Shifting any remaining operational responsibilities or data product generation to other active satellites or ground systems.
- Final Orbital Maneuvers (if applicable): While not always a de-orbit for end-of-life satellites like NOAA-18 (which will likely remain in orbit but be inert), some decommissioning processes might involve maneuvers to place the satellite in a safer, less congested orbital path.
- Compliance Checks: Verifying that all decommissioning procedures adhere to national and international guidelines for space debris mitigation.
The delay in setting an exact decommission date allows NOAA to meticulously execute these pre-decommissioning tasks, ensuring a smooth transition and minimizing any potential disruptions to weather forecasting and environmental monitoring services.
Please also note the NOAA-18 STX-4 S-band downlink transmitter (dropped from 7 Watts down to 0.8 Watts), which surfaced over the weekend (May 31), and is resulting in considerable imagery degradation. Users are advised to discontinue use of all NOAA-18 products immediately.
Past issues impacting the decision to decommision NOAA-18
1. Reliance on Backup Gyros since 2017: Gyroscopes are crucial for a satellite’s attitude control system, allowing it to maintain its orientation in space and point its instruments accurately. All NOAA-18 MIMU laser gyros have failed; operating RGYRO GYE mode since August 9, 2017. This means that its primary (and likely redundant primary) gyros have failed, necessitating the use of a less robust or less precise system. While this has allowed the satellite to continue functioning, it introduces a degree of instability. Reports indicate estimated yaw errors of ±0.5 degrees, which can lead to geolocation errors at the edges of its imagery, although the data generally remains usable (though not 100%accurate). This reliance on backup systems highlights the satellite’s advanced age and the degradation of its original components.
2. Various Transmitter Failures Over the Years: Transmitters are vital for sending the collected data back to Earth. NOAA-18 has experienced multiple failures in its S-band downlink transmitters. Most recently, in late May 2025, the S-band downlink transmitter (STX-4) failed, resulting in severe image degradation and data dropouts. (Note the S-Band was recovered, but analysis show that the failure point is past and a new failure could happen at any time. This particular failure is a significant factor in the decision to decommission the satellite earlier than initially planned. Previously, it has also had other S-band transmitters (like STX-2/MSB) and Automatic Picture Transmission (APT) transmitters (VTX-2) that have seen issues or changes in their operational status and frequencies over the years.
3. Sensor Failures and Degraded Performance: Beyond attitude control and data transmission, the scientific instruments themselves have suffered. While NOAA-18 carries a suite of instruments like AMSU (Advanced Microwave Sounding Unit), AVHRR (Advanced Very High Resolution Radiometer), HIRS (High Resolution Infrared Radiation Sounder), SARSAT (Search and Rescue Satellite-Aided Tracking), SEM (Space Environment Monitor), MHS (Microwave Humidity Sounder), and SBUV (Solar Backscatter Ultraviolet Radiometer), several have experienced degradation or outright failure. For example, reports have noted issues with AVHRR imagery, which, while still usable, exhibits geolocation errors due to the gyro issues. There have also been mentions of erratic HIRS performance due to a suspected loose lens. The longevity of these instruments has far surpassed their initial design life, making some failures inevitable.
More information on the 3 NOAA satellites:
End Of Life for NOAA 15,18,19?….not so fast…
Expected Steps in Decommissioning a NOAA Satellite
Decommissioning a NOAA-N series satellite (like NOAA-15, NOAA-18, or NOAA-19) involves a series of steps to safely remove the spacecraft from active service and mitigate the creation of orbital debris. This process is guided by national and international space debris mitigation guidelines.
Here are the typical steps involved:
- Transition to “Data of Opportunity” and Commercial Ground System: Before full decommissioning, NOAA-N satellites, particularly those in “Extended Life” programs, may transition from being operationally managed by NOAA to a commercial ground system. This means their data streams might continue to be available, but not as a primary operational product. Users are advised to discontinue operational reliance on their science products.
- Pre-Decommissioning Processes (System Safing): These are crucial preliminary steps to make the satellite inert and prevent uncontrolled breakups. They typically involve:
- Disconnecting Batteries: To prevent potential overvoltage or thermal runaway events.
- Disabling Transmitters: To avoid radio frequency interference with other spacecraft.
- Depleting Propellants (Passivation): This includes venting any remaining propellants like nitrogen gas or hydrazine to remove sources of stored energy that could lead to an explosion or breakup.
- Placing Flight Computers in a Safe State: This might involve putting them into an infinite loop to prevent unintended operations.
- Pointing Solar Arrays Away from the Sun: To further reduce power generation and make the satellite inert.
- Data Transition and Operational Handover:
- Ensuring Critical Data Transfer: All vital data streams from the satellite are successfully transferred to newer, more advanced satellite constellations (e.g., Joint Polar Satellite System – JPSS).
- Shifting Responsibilities: Any remaining operational responsibilities or data product generation are transferred to other active satellites or ground systems.
- Final Orbital Maneuvers (if applicable): While not always a de-orbit for these low Earth orbit (LEO) satellites (which often rely on atmospheric drag for eventual re-entry), some decommissioning processes might involve maneuvers to place the satellite in a safer, less congested orbital path. For LEO satellites, the goal is typically to achieve an orbit that ensures re-entry into Earth’s atmosphere within 25 years. This often means lowering the satellite’s perigee.
- Autonomous Decommissioning Control (ADC): Decommissioning a satellite usually falls to human operators on the ground. However, it’s a tricky business for POES (Polar-orbiting Operational Environmental Satellite) operators because they can only talk to each satellite for a brief 10 to 15 minutes as it passes over a ground station. This short communication window, during the satellite’s 101-minute orbit, might not be enough time to send all the necessary end-of-life commands. Many modern NOAA satellites, including the POES fleet (which includes NOAA-N satellites), are equipped with ADC. This software runs continuously and can automatically execute a series of commands to safely decommission the satellite if it detects serious issues jeopardizing function or control, or if total failure is imminent. This proactive measure minimizes the chance of uncontrolled breakups and debris creation.
- Compliance Checks: Throughout the process, all decommissioning procedures must adhere to national and international guidelines for space debris mitigation, such as those set by the Inter-Agency Space Debris Coordination Committee (IADC) and the U.S. Government Orbital Debris Mitigation Standard Practices.
- Monitoring and Verification: After the decommissioning commands are executed, the satellite is monitored to verify its inert state and ensure it doesn’t pose a risk to other active spacecraft.
It’s important to note that while controlled re-entry into an unpopulated ocean region is the most desirable method for LEO satellites, it may not always be feasible due to fuel limitations or satellite health. Therefore, for many NOAA-N satellites, the end-of-life plan often involves passivation and allowing atmospheric drag to naturally lower its orbit for eventual burn-up in the atmosphere. The primary goal is to ensure the satellite becomes inert and minimizes the risk of creating new space debris.
