- Mayak (Lighthouse/beacon) or URS truss, mounted on Salyut-7 in May 1986.
Unfortunately, it is not the Sofora Arm, but the predecessor to it.
From EVA's carried out from May 28 1986 to May 31 1986, Cosmonauts Leonid Kizim and Vladimir Soloviyov installed the URS (also known as Mayak) truss on the front compartment of the station, after removing previous experiments.
It is described here:
The cosmonauts then attached the cylindrical 150kg URS space assembly device to the hull outside the airlock hatch.
The URS device deployed a 20kg, 12-to-15-m tubular metal truss held together by hinges and springs. URS was designed and built by the Paton Institute of Electric Welding in Kiev.
Further descriptions are:
The assembly unit was a rather large 150-kilogram cylindrical container, where a sliding hinge-lattice structure made of aluminium and titanium was laid. It could be pulled out of the "barrel" manually, in a semi-automatic mode and completely without human intervention using an electric motor.
A small orange beacon glowed on top of it
A displacement sensor was mounted to record vibrations
Its upper end swayed noticeably. However, this did not frighten the commander, who decided to subject the mast to an unplanned test. Turning his hands over the steps of the staircase directed into space, swaying his whole body, Kizim slowly climbed higher and higher.
After this the experiment was considered over and the truss was disassembled.
This probably accounts for the scarcity of photos and descriptions.
As you can see, the installation position accounts for the limb position in the currently only known photograph of the truss.
The extended space station configuration of Salyut-7, with TKS craft Kosmos 1686 permanently docked, from October 1985 to February 1991.
That aside, the physical description shows the ancestry of the two trusses that ended up on Mir.
So, for those reasons, I think I should not delete all the info below, it is still useful.
Incidentally, this also describes the second time ever that welding was carried out in space, using the same hand held URI device that Svetlana Savitskaya used for the first time in 1984 (First female EVA and first welding in space, outside a spacecraft).
- Information below is for the Sofora truss mounted on Mir.
(At the end I note my interest in pursuing this question)
The description for it is that it is made of titanium nickel - each section 500 x 500 mm, each horizontal section is flat welded with holes for each of the Y sections to go through. I think the truss overall was about 21 sections, made up from a flat pack of 80 pieces.
You can also see the flat corner sections, and the cable that snakes its way down the truss.
It is not the left truss as this is the Rapana arm added in 1993, which is much shorter, and being a test for construction for Mir-2, it is a series of hinged boxes that open out, made of carbon fiber.
Its construction is entirely different from the Sofora arm.
With reference to the @GordonD answer and @OrganicMarble comment, with the Mir photo, taken in 1998:
The truss seen to the right, is not a truss at all, it is just a funny angle of the solar panel mounted on top of Mir.
Either side of that are the Strella cranes.
Laborious construction of the Sofora arm by cosmonauts from flatpacks.
and finally, a really good closer photo of the two truss assemblies.
Reason for update - even after I had finished the answer something still bugged me and I disliked the lower half of the lattice mast - it did not match the close up photo of Mir.
So I looked closer and realised that there was a record of a previous truss, and it was not on Mir.
Then I re-read the OP article, and it specifically mentions Salyut-7.
Then I read the article on http://www.spacefacts.de and I realised I had to update this answer for clarity and the correct answer.