When reading Soyuz 2-1B - Glonass-M Launch Updates on Spaceflight 101, I noticed an interesting photo showing these two red "horns" on the payload fairing (all photos courtesy of the Russian Ministry of Defence, here is an article in Russian, and English translation via Google Translate):

            enter image description here

Their red color and that they don't really look strong enough to withstand acceleration during launch seems to suggest these are to be removed before launch and must be umbilical ports to access Fregat upper stage and the sole passenger - GLONASS-M satellite. This photograph seems to confirm the umbilical port part, as it looks like Fregat and GLONASS-M are being fueled / charged before the rocket is moved into its upright position:

            enter image description here

Then, I've noticed they're still in place after moving Soyuz rocket vertically:

            enter image description here

So this made me really curious;

What purpose do these red "horns" on the Soyuz 2-1B payload fairing serve? Is there more to them than merely being service / umbilical ports, or are they indeed removed before launch? If latter, why would they be still in place as the rocket is moved vertically?

To my understanding, the Fregat upper stage is loaded with 5,350 kg of UDMH + N2O4 (Unsymmetrical Dimethylhydrazine and Nitrogen Tetroxide fuel and oxidizer) long before that, during payload integration, but I'm not sure about GLONASS-M consumables (perhaps cold gas for ACS thrusters?), or if they both require grid power before switching to internal power minutes before launch? Is there any page available where their purpose is explained in more detail?

  • 2
    $\begingroup$ Air-conditioning system hatch? - arianespace.com/launch-services-soyuz/… - pages 85, 59-61 $\endgroup$
    – osgx
    Mar 23, 2014 at 10:44
  • $\begingroup$ @osgx Looks to me like you identified their purpose, could you please write an answer? I've found another photo showing those "horns" removed and cover flaps placed instead of them here: function.mil.ru/news_page/country/more.htm?id=11910794@egNews so it seems the red plastic is just to prevent the rain and fog condensation from entering the payload fairing. What I didn't realize while writing the question is that the service tower is again clamped around the launcher after it's been placed upright, so crew can still remove them (as indicated by their red color that they should be). $\endgroup$
    – TildalWave
    Apr 24, 2014 at 0:36

1 Answer 1


According to http://www.arianespace.com/launch-services-soyuz/Soyuz_Users_Manual_CSG_June06.pdf#page=85 pages 85, 59-61 the red horns are placed exactly over some Air-conditioning system hatches, which are used to stabilize temperature in the fairing.

When Soyuz rocket is transferred, the horns are used to plug air conditioning unit from the transport platform to the fairing.

When the rocked is moved to vertical state, the conditioning may be temporary unplugged (for example, Proton rocket have 4-hours with unplugged air conditioning: http://www.federalspace.ru/464/ "Во время установки РН на пусковое устройство в течение 4-х часов система кондиционирования должна быть отключена от КГЧ. После подвода к РН башни обслуживания работа системы кондиционирования возобновляется.")

The system is finally unplugged several hours before start (again, in case of Proton-K, 2 hours before start - "Система кондиционирования воздуха должна быть отключена за 2 часа до пуска.")

For Soyuz there are some numbers in the linked pdf, page 60 "Table 3.6 Air Conditioning under the Fairing". Several conditioning systems are listed:

  • CARAVAN - 3 hours for moving the rocket from UCIF to Launch pad
  • "None" for 1 hour (mating on LV)
  • "High mode venting" (up to 4 days, when rocket is installed on the LP)
  • "Low mode venting"
    • up to 45 minutes - from H0 -45minutes to liftoff
    • and some more time for aborted launch... seems up to 4 hours, before High mode is connected back.

The red horns are installed at two top intakes of "Low pressure air-conditioning system". There are two more inlets at bottom part of fairing, near the yellow pipes on your second image.

  • $\begingroup$ Some more info in russian: open.ifmo.ru/images/6/63/145181_book.pdf page 173 "*термостатирование КА. Система термостатирования КА размещается на специальной буферной платформе. С этой целью при подготовке РКН к транспортированию к головному обтекателю подводят воздуховоды.... После подстыковки воздуховодов системы термостатирования начинается термостатирование КГЧ. *" $\endgroup$
    – osgx
    Apr 24, 2014 at 1:11
  • $\begingroup$ Proton: "Система термостатирования КГЧ" gorizont-ktrv.ru/… $\endgroup$
    – osgx
    Apr 24, 2014 at 1:15

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