Why is the Russian moon-flight-for-hire booster stage called "Block DM"?

Question

Space Adventures, Inc.'s DSE-Alpha proposal, where two paying tourists will ride a Russian Soyuz with a professional cosmonaut on a circum-lunar flight, depends on hooking up in earth orbit with a booster stage launched on a separate rocket.

In all of the materials I've seen online, this extra stage is referred to as a "Block DM."

Is this booster stage related to the Fregat?

What does the name "Block DM" mean?

Answer 1

Block DM is a derivative of Block D, a rocket stage designed first for the Soviet Moon landing program and then adapted as an upper stage for several launch vehicles.  The transliterated Russian title is "blok," which means "block" in English.  The 'D' is the fifth letter of the Cyrillic alphabet, fitting the stage's original position as the fifth stage of the N-1 launch vehicle.  While it is no longer the fifth stage of the vehicles it now serves, the name stuck.  It is related to the Fregat stage only in that both the Fregat and the Block D/DM stages perform similar functions in their launch vehicles.

The context suggests that "block" connotes something like a building-block, emphasizing the component nature of most multistage launch vehicles.  In contrast, American usage of "block" in aerospace denotes the broadest design generation -- a Block II design, for example, is a major upgrade from a Block I design of the same element.

The 'M' apparently designates a Russian word that conveys the essence of the difference between it and the original design:  chiefly its autonomous guidance system.  The Block DM is most frequently used as the insertion stage to place payloads in geostationary orbit.