Editing Communications blackout

{{short description|Halt to communication abilities or utilization}}
{{distinguish|radio silence|news blackout}} 

In [[telecommunications]], '''communications blackouts''' are
* a cessation of communications or communications capability, caused by a [[power outage|lack of power]] to a communications [[Facility (telecommunications)|facility]] or to communications equipment.
* a total lack of radio communications capability, caused by [[ionosphere|ionospheric]] anomalies, e.g., during strong auroral activity or during re-entry of a [[spacecraft]] into the Earth's atmosphere.

==Technical failures==
[[Uptime]] being a key goal of most [[communications network]]s, [[uninterruptible power supply| power supplies]] and [[backup generator]]s are typically used to ensure high-reliability power.

Wireless networks may be subject to [[radio jamming]];  wired networks can be physically severed.  [[Network planning and design|Network design]] can also play a role in maintaining communications reliability; depending on the constraints in building a [[fiber-optic]] network, a [[self-healing ring]] topology may be used.

==Spacecraft reentry==
The communications blackouts that affect spacecraft [[atmospheric reentry|re-entering the Earth's atmosphere]], which are also known as '''radio blackouts''', '''ionization blackouts''', or '''reentry blackouts''', are caused by an envelope of ionized air around the craft, created by the heat from the compression of the atmosphere by the craft. The ionized air interferes with radio signals. For the [[Project Mercury|Mercury]], [[Project Gemini|Gemini]], and [[Apollo program|Apollo]] spacecraft, such communications blackouts lasted for several minutes.<ref name=Rogers>{{cite book|title=It's only rocket science: an introduction in plain English|author=Lucy Rogers|publisher=Springer|year=2008|isbn= 978-0-387-75378-2|series=Astronomers' universe: Springer eBooks collection|pages=159–162}}</ref> [[Gemini 2]], for example, endured such a blackout for four minutes, beginning at 9 minutes 5 seconds into the descent.<ref>{{cite book|title=Gemini: steps to the moon|series=Springer-Praxis books in astronomy and space sciences|author=David Shayler|publisher=Springer|year=2001|isbn= 978-1-85233-405-5|pages=183|chapter=Gemini 2}}</ref>

For Apollo missions, the communications blackout was approximately three minutes long.<ref>{{cite book|title=Excel HSC physics|author=Neville Warren|publisher=Pascal Press|year=2004|isbn= 978-1-74125-077-0|pages=23}}</ref> For [[Apollo 16]], for example, pre-advisory data (PAD) for re-entry listed the expected times for re-entry communications blackout to be from 0 minutes 16 seconds after entry interface to 3 minutes 33 seconds after entry interface (a total of 3 minutes 17 seconds).<ref name=Woods>{{cite book|title=How Apollo Flew to the Moon|series=Springer Praxis Books in Space Exploration|author=W. David Woods|publisher=Springer|year=2008|isbn=9780387716756|pages=[https://archive.org/details/howapolloflewtom0000wood/page/354 354, 366]|url=https://archive.org/details/howapolloflewtom0000wood/page/354}}</ref> For the [[Apollo 13]] mission, the blackout was much longer than normal because the flight path of the spacecraft was unexpectedly at a much shallower angle than normal.<ref name=Woods /> According to the mission log maintained by [[Eugene F. Kranz|Gene Kranz]], the Apollo 13 re-entry blackout lasted around 6 minutes, beginning at 142:39 and ending at 142:45, and was 1 minute 27 seconds longer than had been predicted.<ref>{{cite web|title=Did Ron Howard exaggerate the reentry scene in the movie Apollo 13?|author=Joe Pappalardo|date=2007-05-01|url=http://airspacemag.com/need-to-know/NEED-Apollo13.html|work=[[Air & Space]]|publisher=[[Smithsonian Institution]]|access-date=2009-08-13|archive-date=2009-07-29|archive-url=https://web.archive.org/web/20090729092224/http://www.airspacemag.com/need-to-know/NEED-Apollo13.html|url-status=dead}}</ref>

Communications blackouts for re-entry are not solely confined to entry into Earth's atmosphere. They apply to entry into any atmosphere where such ionization occurs around a craft. The [[Mars Pathfinder]] endured a 30-second communications blackout as it entered Mars' atmosphere, for example. The [[Huygens probe]] endured a communications blackout as it entered the atmosphere of [[Titan (moon)|Titan]].<ref name=Rogers />

Until the creation of the [[Tracking and Data Relay Satellite System]] (TDRSS), the [[Space Shuttle]] endured a 30-minute blackout. The TDRSS allowed the Shuttle to communicate by relay with a [[Tracking and Data Relay Satellite]] during re-entry, through a "hole" in the ionized air envelope at the tail end of the craft, created by the Shuttle's shape.<ref name=Rogers />

==Space weather==
{{See also|Solar flare#Radio blackouts}}
Radio blackouts on Earth caused by [[solar flare]]s are measured by the [[National Oceanic and Atmospheric Administration]] on a scale from 1 (minor) to 5 (extreme).<ref name=Rogers /><ref>{{cite web| url = https://www.swpc.noaa.gov/noaa-scales-explanation| title = NOAA Space Weather Scales}}</ref><ref>{{cite web |title=Solar Flares (Radio Blackouts) {{!}} NOAA / NWS Space Weather Prediction Center |url=https://www.swpc.noaa.gov/phenomena/solar-flares-radio-blackouts |website=www.swpc.noaa.gov |access-date=11 November 2021}}</ref>

==Solar position==
{{Main|Sun outage}}
Communications can also be lost when the [[Sun]] is blocking or behind one station in the same line of sight; [[Sun outage]]s periodically interrupt communications with [[geosynchronous satellite]]s.  It is also a common problem for interplanetary [[space probe|space missions]].

==See also==
* [[Sudden ionospheric disturbance]]
* [[Sun outage]]

==References==
{{Reflist}}
* {{FS1037C}}

==Further reading==
* {{cite web|title=SHUTTLE BLACKOUT MYTH PERSISTS|date=2003-03-01|author=Nikki Chandler|url=http://urgentcomm.com/mag/radio_shuttle_blackout_myth/|publisher=Penton Media, Inc.|work=Urgent Communications}}
* {{cite web|title=NOAA Space Weather Scale for Radio Blackouts|url=http://swpc.noaa.gov/NOAAscales/#RadioBlackouts|date=2005-03-01|publisher=NOAA / Space Weather Prediction Center}}

{{DEFAULTSORT:Communications Blackout}}
[[Category:Radio frequency propagation]]
[[Category:Telecommunications engineering]]
[[Category:Technological failures]]