Rotating building houses a telescopeAn astronomical instrument now in various stages of design and fabrication will be mounted in a space frame poused in a revolving building 54 ft high, 43 ft wide and 63 ft long.

The instrument, known as a mul- tiple-mirror telescope (MMT), will be lo­cated on the summit of Mt. Hopkins, near Tucson, Ariz.

The scientific project is a joint ven­ture of the Smithsonian Astrophysical Observatory, Cambridge, Mass., and the University of Arizona, Tucson. This instrument may be a prototype fo r—* much larger instruments of from 400 to

^ 600 in. in equivalent diameter, accord­ing to Howard Simpson, of Simpson Gumpertz & Heger Inc. (SGH), the Cambridge, Mass., consulting engineer­ing company that did the conceptual studies and the detailed preliminary de­sign of the optical support structure.—The instruinent. to_have with an ef­fective aperturec^TL76)n., will be used as a general-purpostrfelescope. Basic to the power of the instrument are the six mirrors symmetrically arranged around the 30-in. guide telescope, and which give the instrument its name, multiple-

Pirror telescope.The M M T concept involves the accu­

rate superposition o f images from sev­eral primary mirrors to achieve the ef­fective light-gathering area of a single, much larger primary, mirror. The array of smaller mirrors, more easily manu­factured and much lower in cost than a large single mirror, will let the telescope approach the aperture and resolution of the most powerful existing telescopes, but with much less structural weight.

To achieve the required precise alignment, the relative static deflections between optical support points of the supporting structure could be no more than 0.002 in. and the natural fre­quencies no.less than 25 cf)s.

Standard shapes used. The design employs standard structural shapes or mechanical tubing to which bars or plates will be attached for field adjust­ments of certain member areas. This will allow correction for the difference between the actual and nominal stiff­ness of independent load paths.

Best accommodating the require-

Kts was a box-like, steel space truss a high stiffness-to-weight ratio, optical support structure, 26 ft

high and 23 ft across the trunnion axis, will weigh 90,000 lb, including all op­tics, a weight considerably rcduced by

i

- , * 3 I,

if'J) ■v/.iytV ,n j .y"

VrEttR MILLIMETER WAV35 TELESCOPI

•MEMO it f 8

fr ; * r .I

J_____“ 3 I

~*v

* '4

Model, (above), of space frame for a telescope, and, at right, ren­dering of rotating building hous­ing Instrument and its mount.

the method of constructing the six pri­mary mirrors. These units will employ new, lightweight honeycomb construc­tion of fused quartz, which will cut the weight of each from 4,000 to 1,300 lb.

For the optical support structure, the designers plan use of 8-in. wide flange shapes for members supporting the pri­m ary m irror cells an d 14-in. wide flange shapes for the trunnion plane. Longitudinal trusses and braces will consist of 4 and 6-in. square structural tubing and 6, 8 and 12-in. round struc­tu ral tub ing . Most jo in ts will be welded, but the designer provided for a number of bolted connections.

The supporting structure is not de­signed to position the optics to the re­quired optical tolerances alone. Final precision will be provided by an active- optics system involving servo control of the secondary mirrors. The structure, however, must be of sufficient precision to allow the active optics to function within its effective range.

Preliminary design of the structure was governed by four factors that, if not controlled, would adversely affect optical performance: gravity loading, vibrations, temperature and wind. De­sign for effects of variation in gravity loading was simplified by the decision to use an azimuth-elevation mount rather than a more conventional equa­torial mount for the telescope.

Rotating building. The structure hous­ing the M M T will rotate plus or minus 270 deg on tracks placed on a 34-in.- thick foundation slab cast on bedrock. The rotating structure permits place­ment of control and service rooms adja­cent to the telescope, a feature a con­ventional astronomical dome docs not permit, because most of the area at the

observing level is used as swing space for the telescope.

The building’s exterior walls, de­signed to withstand storm winds with gusts up to 140 mph, are trussed verti­cally. Gravity loads are carried to four hydrostatic bearings by the exterior wall trusses and by 4-ft-deep plate gird­ers located below the first floor. W ind loads are transferred to the exterior wall trusses by the concrete floors, which act as diaphragms. The exterior wall trusses, in turn, transfer the load to the hydrostatic bearings and to the lat­eral support points.

Lateral wind loads occurring during operation of the instrum ent are deliv­ered by horizontally m ounted two- wheel bogies on the inside face of a 43- ft inside diameter, 5-ft high, circular contact wall. During storm conditions, lateral loads will be delivered to the wall by hydraulic pistons mounted on the floor of the building.

The exterior walls are all metal sid­ing, except for those directly shielding the telescope chamber. The walls of this area are steel-faced sandwich panels with polyurethane cores. These panels were chosen because of their low ther­mal mass and good thermal insulation, qualities desirable in maintaining accu­rate temperature control in the tele­scope chamber.

A sliding, biparting steel shutter, shaped like an inverted L, opens the wall and roof of the telescope chambcr to allow viewing. The shutter also is clad with steel-faced sandwich panels.

Wallace, Floyd and Ellenzweig, Inc., Cambridge, .Mass., is the architect, with SGH as the structural engineer.

Completion of the M M T and its building is planned for summer, 1976.

1 : ...j

/TV !.... > C? T' r #

.. t : ^ i < i f

\./ \z„ / i h - t e o . c • vS-rd?- *v/- * i ' L 5 ~ u v oj $ 4 -.— > I |— j~ L i Q " H . 3 / ~ S j J ° °H * <2ry\ j '- i J ) ( f f l r j

S\n\psc>n 6i<mj>4rt£ -/ AAjt’r Jg^ £

- - r ...

|V .7h - iC P

*-r—j----

V— — ■ --------- - i

: ± 2 < ] 0 ' ^ .

<^T*UVt l/'L.iL ^ ' / .’ I £?_ ..;

fc 'R f/

T

7 ? - i 4 r > . .

*v» jb r c V i C -C

r r p .*"1 ^ 4 —4....•+.....-

‘ ^ </• A '^ c t c ........._!— i—.'_4-..-l.... ..... t •■».." ■ • ■ t { ; ! I : , ; ; :' I ' ; { '

Q jm d L <2'pA A ^^?{ ( r y V U ^ JL \ ^ cA r - A :^

- M n jg ^ 7 -

4dzLk-..q%lj - tpt,»C.r ijyjj <£

3 Vv ̂ i>

4U

/ 2 - 3 7 5 ,£ 0 °

'l& o^zoo

fa rfyfKsW■ f

j f i - t i c t n t vm7 - o

.....£ k v > / ' > / ':i i i j z i j : $ KLcn'l ;....i . j .....L. ISOS ? x . L i .....I...-!.. I V 'c y &

4 l ' ^ -L : ....I.... ;....£ -5 y

# jD