In order to effectively pull this one off, I am envisioning establishing this totally new complex (NASA/NSA/DoD should thrive on this part because, it's simply going to cost plenty). This new complex would consist of a fairly large round hub structure (1000 meters worth), designed so as to allow for a substantial multi-use roof top airport along with nearly unlimited vertical expansion. This relatively massive public hub complex will spawn three primary secure wings, equally configured for future vertical expansion. One of these wings may become the NASA/CD empire (including NSA/DoD), another wing will formulate the GASA Space Sciences and Technologies (SST) campus, and the third Enterprise wing will be primarily focussed upon the privet/commercial enterprise entities. Thus all three wings will have full access to and privileges associated with the central (public) hub services and accommodations, as well as benefit from association with the master overall security and collective technologies amassed under one complex.
Roof top airport for multiple (fleet) helicopters as well as accommodating other vertical takeoff and/or short takeoff/landing capable airships (Ospreys will be restricted to the furthest possible NASA/CD pavilion area). The adjoining floor (below the roof/flight deck) will act as that of an added penetration buffer zone, comprised of general facilities management offices, various internal support systems, air-transport related issues as well as various logistics support related functions, plus further security technologies. Obviously the roof top airport could facilitate off-loading troops as well as safely evacuating thousands within minutes.
The first 10 (above ground) fully occupied stories are those to be established as nearly bullet/bomb proof. Including the management/security and airport levels, the required vertical exposure that would comprise the primary hub structure (including the 10 primary stories) may approach 60 meters.
The first 10 stories are also to provide the necessary foundation so as to support and sufficiently integrate, as to accommodate nearly unlimited vertical expansion. There will also be a minimum of 10 stories situated below ground, where this fortified foundation shall cover a diameter of 1500 meters.
The bulk of the above ground structure shall be comprised of cor-10 or better alloy steels, and further insulated to sufficiently withstand a sustained 2500°F environment.
Windows will become structural elements, comprised of proven multi layered elements, incorporating high temperature (nuclear flash blocking) mylars, inch thick polycarbonate layers as well as tempered safety plate glass having first been alloy steel mesh reinforced. All together comprising an overall thickness of nearly 4" worth of essentially none-void solid laminate(s). Possibly a sufficient projectile such as a modern tank traveling at perhaps 100 knots could partially penetrate this, but not entirely because the maximum distance between vertical structural's would be insufficient for the body of that tank to pass without having to further deal with the massive external/internal cor-10 alloy steel framework of the building. An attack via fully loaded aircraft would inflict minimal penetration, and the resulting fire would become mostly that of an external threat, and thereby not sufficiently weaken the impact exposed steal infrastructure.
In addition, the most secure operations will be situated (inboard) clearly away from the perimeter.
The core elevator cluster shall be that which is established within an independent free-standing structural entity. At the center of this elevator cluster will house secure conduits, ventilation and multiple escape routing. This central (75 meter) core will also be widely protected on top by an added structure, comprised of a thick (missile attack rated) 100 meter diameter, multi layered alloy and insulated dome/shield of defensive structural composite roof elements.
This complex will perform and exist as a self sufficient power utility, capable of exporting surplus power. The primary power may potentially be delivered by dual sub-rooftop situated (compact) multi-fueled 70MW turbines, plus another 10MW of internal backup will be highly protected by those units being situated deep within the vaulted foundation. Other technologies such as fuel cells as well as nuclear (preferably French technology) may otherwise be accommodated within the sub-foundation considerations. External utility power interface will merely act as the third backup. All essential fuels will be those tanked sufficiently (50 meters) below ground as well as sufficiently capped via reinforced concrete.
Internal fresh water wells and reservoirs as well as wast treatment will be fully contained within the greater property site.
Besides independent wing elevators/escalators, there will be three massive hub perimeter elevators that will each perform as structurally independent (free standing yet properly interfaced within the hub structure) as well as being passenger rated at 10 tons and cargo rated at 20 tons each.
In addition to the interior stairways, there will be three additional large perimeter exit stairways, each of those will exist as structurally independent entities, accommodating a minimum of 10 abreast plus dual handicap ramps.
Do to the overall simplistic design, it's robust caricature, geometric openness as to being fully surveyed and thereby easily monitored from internal forces and technologies, makes for a truly capable and if necessary self sufficient (doomsday) complex, one which would be difficult to infiltrate or inflect damage upon. The very nature of the robust foundation(s) along with the initial 10 (above ground) stories being so over constructed as though to support an additional 120+ stories, insures that all foreseeable future needs (expansions) are to be met without compromise. The NASA/CD divisions may establish their own underground network as well as entrance/exit prerogatives.
Should this complex be situated near any launch sites, the site elevation chosen may be considered being as high as reasonably possible. Launching hundreds of tons into space obviously takes mass quantities of energy as well as dollars, and the higher the initial event is, the greater amount of delivery/payload may be accomplished per ton of fuel as well as obviously per dollar. Because of the substantially improved reliability of the initial launch phase, being sufficiently inland should also be reviewed as a lessor challenge from weather related considerations, as well as far better security from foreign aggression threats that could arrive unexpectedly by air, sea or under-sea.
I only mentioned the above because of our crack NSA/DoD talents have recently demonstrated their ability to precisely knock out "RED CROSS" and "Northern Alliance" depots, and as of yet seemingly unable to detect, let alone prevent, strikes within our own country. This is clearly where our high technology is just that, too damn high to hear those all around us saying exactly what they intend to be doing to us.