International Space Station Alarm Situation Resolved - What Happened Today


Astronauts reentering the U.S. segment.

An alarm went off on the International Space Station indicating there was a leak of some sort on the U.S. segment. It was first thought it could have been an ammonia leak but mission controllers now know it was a false alarm due to a sensor problem.

Please note that when emergency situations occur you can keep up to date on our Special ISS Situation Page. We suggest you bookmark the page.

Here's the updates of today's events in reverse order of when they happened.

3:43 p.m. ET update: The problem seems to have originated from a Multiplexer/Demultiplexer (MDM). The MDM routes multiple streams of data. There appears to have been a unique situation today whereby the data resulted in the MDM sending out an alarm based on data that mimicked an ammonia leak. The crew is returning to normal operations.

3:23 p.m. ET update: The crew opened the hatch to the U.S. segment and returned inside at 2:05 p.m. Central time. Wearing protective masks, Virts and Cristoforetti sampled the cabin atmosphere and reported no indications of any ammonia.

11:12 a.m. ET update: NASA does not believe there was an ammonia leak. There is no indication of ammonia in the U.S. segment. It is believed a series of events triggered the sensor that led to the alarm. NASA is continuing a step-by-step process to get the segment prepared for the crew to head back into the segment this evening. Once an alarm is triggered of this type several systems are taken offline. So a step-by-step protocol must to be adhered to prepare for the return of the crew as systems come back online. No research has been compromised.

Thoughts on the situation by Canadian astronaut and former ISS commander Chris Hadfield:

10:18 a.m. ET update: NASA is still troubleshooting the issue which they believe is a faulty sensor.

Note: This page automatically refreshes every 10 minutes to include new updates.

NASA Statement from 8:55 a.m. ET:

The Expedition 42 crew members are safe and in good shape inside the Russian segment of the International Space Station following an alarm in the U.S. segment at about 4 a.m. EST.

The crew received an update from spacecraft communicator James Kelly that it's starting to look like a false indication, either a faulty sensor or computer relay. Flight controllers are continuing to analyze the situation but for now, there is still no direct evidence that ammonia was leaked into the station atmosphere.

Archived MP3 of ISS false indicator message.

Earlier NASA Statement from 7:48 a.m. ET:

The Expedition 42 crew members are safe and in good shape inside the Russian segment of the International Space Station following an alarm in the U.S. segment at about 4 a.m. EST.

Flight controllers in Mission Control at NASA's Johnson Space Center in Houston saw an increase in pressure in the station's water loop for thermal control system B then later saw a cabin pressure increase that could be indicative of an ammonia leak in the worst case scenario. Acting conservatively to protect for the worst case scenario, the crew was directed to isolate themselves in the Russian segment while the teams are evaluating the situation. Non-essential equipment in the U.S. segment of the station was also powered down per the procedures.

In an exchange at 7:02 a.m. with Expedition 42 Commander Barry Wilmore of NASA, spacecraft communicator James Kelly said flight controllers were analyzing their data but said it is not yet known if the alarm was actually triggered by a leak or whether the situation was caused by a faulty sensor or by a problem in a computer relay box that sends data and commands to various systems on the station.

NASA TV will provide a live update at 7:45 a.m. ET

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