Major Locales of the Titan I Complex

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Antenna Terminal

The Antenna Terminal consists of two perpendicular, cylindrical steel structures 16 feet 6 inches in diameter that form a T-shaped junction connecting the two antenna silos.  The floor in this junction is suspended from above by six steel I-beams.  Beneath this floor there is a layer of concrete lining the bottom of the tunnel to provide strength and proper drainage.  AC ducting for guidance equipment and a sump well and pump are located underneath the suspended floor.

The antenna terminal - extremely simplified diagram

An exhaust shaft to the surface 4 feet 6 inches in diameter ventilates the terminal and protects it from blast overpressures with a 3 foot diameter blast valve.  A sump line from the pumps in the terminal purges any water seepage to a seal chamber at the surface.  Both the exhaust vent and sump line exit the terminal from the south wall between the silos.

Antenna terminal - Structural and HVAC details

The antenna silos are two cylindrical concrete structures, 65 feet deep and 27 feet in diameter with a floor at the personnel access level approximately 42 feet below grade and a lower service level at the bottom.  The walls of the silos vary in thickness near the cap where they are heavily reinforced both to withstand blast forces as well as internal loads from support structures for the door rams and antenna assembly.  Below these reinforced sections the walls are 15 inches thick with heavy steel reinforcement.


The lower level contains an access ladder and lighting along with a sump well and sump pump to purge any water that may enter the terminal.  This lower area exists largely to accommodate the very long (around 4 stories, or ~40 feet!) hydraulic cylinder running up the very center of each silo upon which the guidance antennas are raised to the surface.


Terminal room - Side aspect showing floor and HVAC layout.  This structure mated with the vertical antenna silos and antenna tunnel to interconnect the three areas.


Antenna terminal exhaust vent stack - Side aspect


The silos are protected by two doors about 3 foot 9 inches thick with an embedded ethylene glycol system to provide radiant heat to prevent snow and ice from accumulating on the doors and hindering their operation.

Antenna silos - Side aspect

The antenna terminal housed support equipment and controls for the silo doors and antennas as well as racks of equipment, guidance systems and heating, ventilating and air conditioning systems for the terminal, silos and equipment racks.


Heating and cooling units were housed on an upper platform and ductwork was routed under the floor and up through the bottom of each equipment cabinet to provide cooling.  Ventilation ducting supplied to the antenna silos has special butterfly-type blast valves to prevent a blast entering the terminal when the silo doors are open.


Isometric diagram of antenna terminal


Note that this diagram bears many structural deviations from the "As-built" operational complexes.  Two examples shown here are the smaller bottom sections of the silos and the extra convolution in the exhaust stack.  These were not present in the Lowry Titan I bases. 


Isometric Cutaway of Antenna Silo in the lowered and raised positions 


The twin antenna silos house the radar dome antennas for tracking and guiding the missile along its trajectory.  There were 2 antennas to provide redundancy in case of failure since without a guidance antenna the entire site could be rendered useless without a means to control the missiles.  As an added measure of redundancy the Titan I system had the ability to "hand off" guidance and control of any missile at any complex in the squadron or wing to allow it to be guided remotely.


That is, if critical failures of say, the guidance antennas of one site brought it off alert, any other site could use their own Control Center and antennas to launch and guide the missile so they would not be left dead in the water.


Cutaway of the antenna terminal - This is a pretty close representation of the actual Lowry bases' construction though the details are a bit rough.


Each silo is protected by a set of massive two-leaf concrete doors which would shield the antennas in their hardened state.  The antennas themselves consist of a radome radio dish enclosed within an inflatable canvas dome which is expanded by a blower (squirrel cage type fan) when in use.


When needed, an antenna would be raised to the surface hydraulically on its platform.  Only one antenna would be raised at any one time to prevent both being disabled in an attack.  The antenna was raised on a single hydraulic ram that extended over 20 feet below the floor level of the silo.  The antenna itself and much of it's support equipment was suspended on a hanging platform that could move and sway to suppress shock.  Hung from 6 six incredibly strong cables with massive shock-absorbing springs, the whole antenna assembly was designed to shake and bob a tremendous amount without sustaining damage.


Once the antenna was raised to the surface, it was locked solidly in place by a hydraulic mechanism to ensure its accuracy in tracking and guiding the missiles.  When guidance operations are in progress, a moving radio antenna will simply not do.


Construction photo of antenna silos showing the first few pours completed and forms in place.  Note the curved section of form resting at the lower right and the crane boom visible at the upper left.  The crane was used to position the massive forms and for other heavy lifting.

Photo courtesy of Fred Epler




The antenna terminals were constructed using the same method as the rest of the more shallow silo-type structures like the equipment terminals, entry portal and propellant terminals.  First the whole area was excavated to a depth of about 48 feet and once the proper depth and leveling was achieved, the base slab was poured and the remaining structure built using successive concrete pours and reinforcement until complete.


Once a section of concrete was cured and sealed and any interconnecting tunnels and structures were complete and water-proof expansion joints were installed, the entire construction was re-buried using the excavated earth which was then laboriously compacted to prevent (insofar as was possible-- see the antenna tunnel section for details on the perils of backfilling) settling and movement of the soil and underground structures-- a very undesirable outcome.


Backfill was added in a step-wise fashion in most cases where soil was added and compacted around the newest completed section.  The following photo shows the silos already buried to a depth of about 23 feet.


Making progress - the antenna silos are really taking shape as workers ready the forms for the next pour.  Notice the tunnel liner jutting into the photo on the left.  Later this liner will be mated to the larger terminal structure and sealed.


The walls were built up using forms in about 8 foot sections to encase steel reinforcing bars in between.  When a section was properly set, the next section was started, re-bar first, and then the forms moved to enclose the next pour.  In this way the structure grew upward until the final pour was ready: the doors.


Progressing nicely - this shot of site 724-B shows the terminal structure mated to the silos and the backfill completed up to level of the personnel tunnel.  There are about 25 feet more to be added to each silo at this point.  The remaining pours will be much thicker and add structure to support the antenna platforms and rams for the doors.

Photo courtesy of Fred Epler


Cold Colorado weather hinders concrete work at 725-C.  Silo A's cap appears to be complete in this photo (no doors yet, however) but silo B has at least 1 or 2 more pours before the doors can be added.


Frigid weather posed major challenges for contractors in states with more inclement winter weather such as Colorado where concrete had to be heated prior to pouring and then warmed with diesel heaters while it set to prevent freezing.

Photo courtesy of Fred Epler


Forms for the final cap pours are in place awaiting either warmer weather or further preparations for winter concrete work.


The silo doors were rather interesting in their construction.  Each were comprised of a dense mesh of heavy steel reinforcing bars and high-strength concrete and weighed around 100 tons.  As such, they were not something that could be constructed off-site and installed in the antenna silos.  Instead, each was constructed in place, right there on top of the silos.


The massive, solid steel hinge pins and trunnion assemblies (hinge bearings) were installed, rebar was measured, cut, bent, placed and welded* and forms were constructed and positioned on the silo caps.  This also included the installation of piping that snaked back and forth inside the doors to facilitate radiant heating for snow and ice removal.  Once the forms were complete, concrete was poured right around the hinge pins, rebar, piping and all.


After the forms were removed, the two separate leaves of the door were broken free using hydraulic jacks and opened.  After the doors were opened, the four hydraulic rams were installed and tested.


*In typical construction, most steel reinforcement is constructed into a latticework using wire to tie the bars together.  This is fine for most applications, but the specifications for the Titan I complex called for "continuous reinforcement" which meant that rebar was welded together instead of just tied with wire, adding a far greater strength to the concrete pours as a single large mass.


Completed silos with one set of doors poured.  Next, hinge plates will be installed at the corners of the doors.


The silo doors are complete and opened and awaiting installation of the hydraulic rams while construction work continues inside.  Most of the backfill operation is also complete in this area.

Photo courtesy of Fred Epler


A closer look: Still no rams on the doors and there's still some backfill to be done at this site

Photo courtesy of Fred Epler


Still awaiting a closing mechanism, the doors are temporarily secured from accidental closure by steel cables in this photo as work continues.


A nearly completed silo with doors closed at Lowry 724-A

Photo courtesy of Fred Epler


Silo at 724-B with antenna installed and raised and door rams in place.  Notice the concrete structure in the lower center of the photo.  This is the seal chamber where purged sump water discharges from.

Photo courtesy of Fred Epler


724-A with silo B antenna raised and silo A on its way up.  The rest of the complex is still in the throes of construction in the background.

Photo courtesy of Fred Epler


Here you see the focus of the antenna terminal and in fact, the 2nd most important part of a Titan I complex after the missile itself: The Western Electric Missile Guidance Set AN/GRW-5.  Evolved from naval guidance systems, the AN/GRW-5 MGS consists of (in the context of the Titan I weapon system) the guidance set itself, the antenna protecting and elevating set-- the hardened silos and the hydraulic platform that raises the antennas to the surface-- a testing and checkout set to maintain, diagnose and exercise the system and ensure proper function, a missile guidance computer set and missile-borne guidance equipment on board each Titan I.


A very complex system indeed, the antennas pictured here are like the tip of the iceberg that is the complete Missile Guidance Set developed by Bell Telephone Laboratories; a radio-inertial missile guidance and tracking package representing, at the time, some of the very latest in technology and miniaturization in solid state electronics.


A closer look at the raised antenna with its inflatable canvas shroud.  A small blower keeps the dome inflated during operation. For safety, extendable railings ring the antenna platform for use during maintenance.


Inside the radome antenna is a dish-shaped radar receiver/transmitter that moved about the axes of azimuth and elevation to acquire and maintain radio contact with the missile or ground-based test set.


Unknown persons at 724-A antenna platform, showing the inflatable dome.  Here you can see a section of railing raised in the "working" position.

Photo courtesy of Fred Epler

A handsome Tech Order illustration showing a nice clear view of the antenna and silo doors

So far we've looked at the construction of the antenna terminals but we've seen little of the interior.  In the next section we'll go underground and see how the antenna terminal really looks on the inside, both now and as it once was.


Click the link below to see the antenna terminal, or explore elsewhere at the Main Map.



Antenna Terminal Cont.


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