Repairing the Hubble Space Telescope

By Keith McNeill

The Mission

Model photo In December 1993 NASA undertook one of the most daring space missions ever to be attempted. At stake was NASA's reputation and according to some the very existence of manned spaceflight in the US. The Hubble Space Telescope was launched in 1990 and was acclaimed as the greatest tool to astronomers since Galileo invented the telescope! Unfortunately it soon became clear that it was not operating as it should and the scandal of the now famous spherical aberration of the primary mirror became apparent. Also, various other problems soon arose including solar panels which expanded and contracted far more than expected when the HST entered and exited sunlight, causing "jitters" throughout HST.

Model photo It was always planned that the telescope should be maintained periodically by visiting teams of astronauts on servicing missions. Indeed HST was specifically designed to be astronaut friendly and was equipped with easily replaceable modular scientific Instruments, 69 metres of handrails and 31 footholds to aid astronauts in servicing tasks. Therefore the first servicing mission was charged with the task of replacing the solar arrays and installing corrective optics to fix the primary. mirror problem. As the mission was being planned a host of other problems cropped up, including three of the six gyroscopes malfunctioning, magnetometers which required replacing, blown fuses and an upgrade to the computer memory. As a consequence the mission was expanded to include five spacewalks (Entra Vehicular Activities or EVAs), four astronauts alternating two at a time on each EVA. Due to the fuel and oxygen requirements of the mission only one shuttle orbiter of the fleet was capable of supporting the servicing flight. This was Endeavour, the orbiter constructed as a replacement for the ill-fated Challenger, destroyed in 1986.

Model photo On 2 December 1993 Endeavour roared into orbit on mission ST8-61, the payload bay packed with repair equipment, and over a period of eleven days the crew rendezvoused with the Hubble, carried out five EVAs, during which they completed all the scheduled tasks, and released a vastly improved HST into orbit. The mission was closely followed by the news media around the world and the only problem arose when one of the solar arrays refused to retract and had to be jettisoned by Kathy Thornton during the second EVA.

About a month after Endeavour landed at Kennedy Space Center, astronomers revealed that NASA's hard work had not been in vain and that the new Wide Field Planetary Camera (WF/PC II) and the COSTAR (Corrective Optics Space Telescope Axial Replacement) device were producing excellent results. Indeed it is claimed that the Hubble Telescope now produces pictures as close to the theoretical limit of the optics as possible.

The Models

Model photo I had previously built several space shuttle kits, but this mission fired my imagination and I decided to upgrade my previous attempt at a 1/72 shuttle. My old one was the worst for wear so I decided to start again. The model I chose was the 1/72 Revell kit which sports more surface detail than the Monogram version. As there is no kit available of the Hubble Space Telescope (due to the publicity I'm sure someone will release such a kit [ed. note: Someone has: Skilcraft #74638 is currently in production.]), I was obviously going to have to scratchbuild the HST along with the packed payload bay. Extensive research was patently a "must" for such a model. Photographs were readily available from the mission which originally launched the H8T in 1990, but the payload bay proved to be a much greater problem. Luckily several astronomy magazines published photographs from the mission and TV coverage provided good clear views of the payload bay from various angles. These gave me a good idea of relative sizes and positions in the bay. I was also fortunate to obtain several NASA photographs taken during STS-61 shortly after beginning the project which confirmed my earlier research. At this point I should modellers that this project took me three months to complete. Hopefully this article will shorten the procedure somewhat.

Space Shuttle Endeavour

Model photo The basic shape of the Revell kit is excellent with only a small change to the length of the payload bay required. This should be lengthened to 254mm, the extra length being derived from the rear where there is a rather large bulkhead thickness between the bay and the tail. This should be filed back until the tailfin almost meets the payload bay. The only other changes I made to the overall shape was to alter the flaps so that they were slightly raised (in weightless conditions they tend to rise up).

I shall dwell only briefly on some of the other 40 odd modifications I made to the kit, but would refer the reader to reference material and specifically David Jenkin's Aerofax Datagraph 5 book "Rockwell International Space Shuttle" which is full of detailed photographs.

Before cementing the two halves of the orbiter I drilled out two holes on the nose to simulate the star trackers used for navigation. Also I upgraded the cockpit area. Proof of how cramped the shuttle cockpit is, came when I attempted to install seven 1/72 crew members! Luckily in zero-G they can be stuck to the roof and in odd corners! Although most wouldn't be visible I painted them to represent the real STS-61 crew. Hence one is a women, one is bald and three have moustaches!

I dispensed with the clear window parts as they seemed rather thick and replaced them with thin clear plastic from a soft drinks bottle. The shape of the overhead windows was altered by rounding off the corners. Also the windows facing the payload bay required major surgery as they are too far apart. The side facing hatch window was drilled out and Kristal Kleer applied.

The tail fin was removed as I wished to install the newly added drag chute system which is basically a box located at the point where the underside of the tail meets the shuttle. The base of tail was flattened (fig 1). The tail would be cemented in position near the end of the construction sequence.

The payload bay itself requires major modification. The one criticism I would make of Revell would be that for a kit of this size there was ample opportunity for good detail. However this is not the case. First of all the bay should be lengthened as per the orbiter. This can easily be accomplished with plastic card. At the forward end there are located two Provisional Storage Assemblies (tool chests basically). Two rectangular shapes (see fig 2) should be cut out and backed with plastic card. If constructed as per the instructions the payload bay would be level with the sides of the orbiter. This is not the case in reality and a 5mm strip should be removed from the length of the payload bay on both sides (fig 1) The unsightly Remote Manipulator System attachment point should also be removed and the resultant gap backed with plastic card and filled.

The payload bay can now be glued in position making sure that it is below the lip of the shuttle's sides (or sills as they are known). It should now be lined with kitchen foil with a gap in the foil towards the rim (fig 1). The bulkheads should be similarly covered. Next, ribbing should be applied to the bay (also fig 1).

The tail fin can now be attached and any gaps filled. Even although there is much still to be done, It is at this point that it is best to paint the model. With reference to photopraphs the orbiter's colour scheme is relatively straightforward, with all of the underside covered in black heat resistant tiles and most of the upper side in white tiles. Actually as Endeavour is the newest orbiter in the fleet, most of these white tiles have been replaced with woven blankets which are easier and less time consuming to apply. As mentioned at the beginning of this article the model is covered with a nice tile moulding and no attempt was made to try to alter this and duplicate the blanket pattern. The wing leading edges are protected by grey panels, as is the nose, and the tail fin is edged black tiles (see photos).

None of the shuttle kits on the market have markings for Endeavour as all were released prior to the Challenger accident. Therefore I had to make up the name using rub down Helvetica Medium typeface. The name Endeavour is displayed either side of the crew cabin and the E in Endeavour is 4mm in height (I used old Chartpak lettering as I could not find equivalent Letraset of the correct size, although I understand this is no longer generally available). For the starboard wing I used Letraset 28pt. no. 725.

The kit decals include two gold squares which are meant to represent the umbilical connections at the aft end of the orbiter. These should be discarded and instead the connections can be replicated using various sizes of Letraset black circles (see photos).

All other decals can be applied as per the instructions. However a large US flag (from the spare decals box) needs to be placed on the right hand side of the rear bulkhead. Having left the decals to dry the whole model was sprayed with matt varnish.

Detailing the Payload Bay

As mentioned previously, the main drawback to this kit is the lack of detail in the large payload bay. This therefore involves a great deal of scratchbuilding as not only the standard features of every orbiter have to be built but also the payload specific to the Hubble repair mission, which as luck would have it is one of the most complex payloads ever carried into orbit by a shuttle.

I shall start at the forward bulkhead. The airlock hatch was fashioned from a 16mm diameter tank hatch which was cemented in position 12mm from the bottom of the bulkhead. Two dark brown "poles" were placed either side of the hatch and just below and between the payload bay facing windows a 5mm diameter circle of plastic card was attached. This represents the manual winch which would be used in the event the payload bay doors could not be closed. There are eight tiny cylindrical "door stops" placed around the edge of bulkhead and these can be made from plastic rod. Next come the handrails. These are located on both forward and aft bulkheads. When building previous shuttle models, I found that the handrails were always the most difficult thing to get right. Not only do they have to be at the same level, but in the case of those running the length of the payload bay, they have to be in a straight line. I solved this to my satisfaction by using 00 Lineside Fencing. This type of fencing has horizontal bars while the vertical posts are moulded onto the rear of these. If the fencing is laid flat, It is supported by about Imm from the surface by the vertical posts, in effect becoming low handrails. It is then only necessary to cut single spans from the length of fencing. The payload bay handrails were used the opposite way (as they are intended to be used) but not disconnected from the lower horizontal bar. This second one was glued directly below the lip of the outside of the payload bay sill so that only the handrails protruded. The payload bay sill handrails are of three types namely, those with two, three or four uprights. To achieve this it is just a matter of cutting away the fencing after the required upright. Figure 3 hopefully makes all of this clearer.

A TV camera is located at each corner of the payload bay. These were fashioned from plastic strip with a cross section of 3mm x 3mm. The cameras, which are 6mm in length are wrapped in gold chocolate foil, the top surface being covered with chrome Bare Metal Foil.

To aid the translation of astronauts on EVA, there is a guide wire running down the length of each side of the payload bay just outside the handrails. Very light weight fishing line was used for these.

The robot arm, or Remote Manipulator System as it is known, which comes with the kit can be dispensed with as it is too spindly. Plastic tubing 4mm in diameter was used. As I wished to have a working arm for photographic purposes I articulated the individual lengths by way of tongue and groove joints which were pinned with a small length of plastic rod. The lengths of the RMS sections are 88mm, 98mm, 8mm and 18mm. This last section is made up of 11mm of the 4mm diameter tubing and the end effector (which does the grappling) which is 5mm in diameter (7mm long). Cameras similar to those in the payload bay were attached just above the elbow joint and on the end effector. The RMS rests were fashioned from off cuts of thick plastic card (fig 4) and glued in position in the payload bay.

It is necessary to remove all detail from the kit payload bay doors. Also the doors should be lengthened to accommodate the altered payload bay. Although the kit states that the radiator panels should be attached to the doors this makes them far too thick and quite out of scale. The radiator panels in fact are only deployed when the heat from the generated by the orbiter and its payload is too great for the Flash Evaporator System. Normally that only occurs on Spacelab missions. Therefore it is safe to ignore these kit parts. However the doors are still too thick. I got around this problem by thinning all the edges of the doors. This gives the appearance of the radiators in the stowed position. Three vertical panel lines were scored at equal distances in each of the doors. Although in reality the payload bay doors have a chrome finish they never look chrome in photographs of orbiters in space. They tend to take on a bluish silver look. I therefore tinted some silver paint with Humbrol blue. After the paint was allowed to dry pencil lines running the length of the doors were drawn at 2mm intervals. The doors were not cemented to the shuttle until the very end.

The Propulsion Systems

The three large main engines are relatively accurate although seen from end on are far too thick and obviously need pared down. The two Orbital Manoeuvering System engine bells should be consigned to the spares box as they are completely inaccurate. I used 1/144 shuttle main engines as when all detail are removed from these are the right size and shape. Likewise the four small vernier engines of the kit should be put to one side. These engines should be replaced with 5mm diameter, 3mm long plastic tubing. There are ten small Reaction Control Thrusters (RCS) located on each OMS pod and these required hollowing out with a drill. The holes were backed with scrap plastic card. Similarly the various RCS thruster openings in the nose of the shuttle can be opened up, although I decided against this as they are moulded with rather deep cavities.

The OMS pods themselves are straightforward until it comes to the painting. Both sport a distinctive black chequered pattern where they receive the greatest heat during re-entry (fig 5). This pattern was obtained by using black squares from a Letraset symbol sheet. I found this best to do before attaching the pods to the model.

Finishing off the Shuttle

Finally to the last few details. The shuttle carries a Ku-band antenna at the forward starboard side of the payload bay. Upon opening of the payload bay doors this is rotated out into the operational position. The antenna is used both for communication purposes (it is this antenna which transmits most of the TV the public sees, through a Tracking and Data Relay Satellite, positioned 22,300 miles over the Equator to Houston) and also as a radar for rendezvous operations.

The main dish was made from a 13mm diameter parabolic dish I found in the spares box and was painted satin black. The feed horn was attached by three small pieces of plastic rod. The dish was attached (not glued) by 1 pin to a rectangular piece of 60 thou plastic card which was covered with chrome foil. This allowed it to move to provide a bit of variety to the photos (fig 6).

Finally, small hinges for the doors were placed along each of the payload bay sills, and at each point where the payload bay door panel lines are located, a small U-shaped item (fig 1 again) was glued in place. These were made from HO gauge train brake couplings.

The Payload

Now comes the hard bit! Or at least it was for me as I had to calculate not only the various sizes and shapes of the individual items which make up the STS-61 payload but also their relative positions. To help me with this I took some still photos from the TV coverage of the EVA·. Especially useful were views from the elbow camera of the RMS when positioned high above the payload bay. I also made extensive use of NASA's press kit for the mission which contains line drawings of the various containers etc. I have reproduced these for this article, the items being from front to rear of payload bay;-- Solar Array Carrier (SAC) (fig 7), Orbital Replacement Unit Carrier (ORUC) (fig 8) which holds five containers and the Flight Support System (FSS) (fig 9). It is the FSS upon which the Hubble is berthed.

I will not cover the payload in depth as the afore-mentioned figures are self evident and contain the pertinent dlmensions. Also figure 2 shows the layout of the payload bay. Unfortunately I came across this Lockheed drawing only after I had painstakingly completed this part of the model. Luckily I was not too far off in my calculations (which makes a change). All the items were constructed from laminated plastic card with the exception of the HST berthing ring (diameter of 29mm) which came from the spares box, the Tool Box (fig 10) (again the spares box) and the shuttle pallet which comes with the kit. This had all protrusions removed and 20thou plastic card was used to line both the inside of the U-shape and also front and back.

All items of the payload with the exception of the Tool Box and the IMAX camera are covered in gold foil. However most TV images and photos from the mission show this foil as appearing mid to dark brown depending on the sun angle. I therefore covered these items in a chocolate wrapping foil that approximates to this colour.

As I was depicting the model after completion of the last EVA I added the old solar panel the crew would bring back to Earth. This was constructed from plastic rod and glued into position on the SAC.

Various other items such as the foot restraints (seen in figs 7 and 10) were added. Also of note was an IMAX camera at the rear of the payload bay pointing up at the HST whilst berthed. This took some excellent footage, some of which is included in the latest IMAX film "Destiny in Space". Handrails of varying lengths were added to the various containers and small NASA and contractor logos were clipped from a magazine and glued in position on the relevant containers. For much of the above detail, it is best to consult photographs to obtain the best positioning.

Finally, astronauts Musgrave and Hoffman used two large framework devices to remove and replace the Wide Field Planetary cameras. These were constructed from plastic rod (see fig 11) and are stowed on the port side of the ORUC.

All the payloads were superglued into the payload bay. However care has to be taken to ensure that the glue does not fog the foil. As my HST was going to be removable, the berthing ring of the FSS was left off at this stage in order that it could be made compatible with the Hubble. Obviously if you intended the HST be permanently attached to the orbiter then it would be possible to glue HST directly onto the berthing ring. My ring had three prongs which like the real thing locate into corresponding attachment points (in this case three holes) on the base of the Hubble.

Building the Hubble Space Telescope

Model photo The Hubble itself is of a fairly simple construction. The telescope consists of two cylinders, one 59mm in diameter (75mm long) the other 44mm in diameter (110mm in length). Figure 12 is a scale drawing of the HST and as such can be used to extract dimensions from. I initially thought all I would have to do was order these from EMA Plastruct. However they do not have tubing of the required diameters, so I had to find them elsewhere. The large diameter cylinder was made from a map tube wrapped with 20thou plastic card to bring it up to the necessary diameter. The smaller tube was obtained from a desk tidy.

The bottom cylinder contains all the scientific equipment and the primary mirror and will hereinafter be referred to as the Aft Shroud. The smaller diameter tube contains the secondary mirror and light shield and I will refer to it as the Light Shield.

Both ends of the Aft Shroud were sealed with plastic card and the underside had three holes drilled to accomodate the berthing ring. Also circling the top of the Aft Shroud are 21mm x 15mm plastic rectangles (see fig 12 again).

Before cementing both tubes together I drilled directly through the Light Shield, a couple of millimeters from one of the ends. A piece of hollow plastic tubing (inside diameter of 4mm) spanned the gap and was superglued in place. A 3mm diameter, 17mm length of brass tube was inserted through this internal support and again superglued in position, making sure there was an equal length protruding from each side of the tube. This brass rod will take the solar panels.

The Light Shield should now be glued centrally to the Aft Shroud. Placed around the front of the telescope on the Aft Shroud are small boxes which contain some of the electrical equipment for the HST. These stop at the solar array boom (see fig 12).

The solar arrays were constructed from aluminium rod and I0thou plastic card. The panels are actually blue in colour on one side and ochre on the other and are also translucent. However most of the photographic evidence shows them glowing orange in space conditions. I therefore decided to paint them an orange/brown colour and the pattern of the panels were picked out with yellow Extradecal lining. Four millimeter brass tubing was used for the Bistem cassette (the solar panels unroll from this - see fig 13) of each array and this was slipped over the protruding brass rod of the telescope and allowed to turn freely. A little packing may be necessary to stop the array spinning.

The Aft Shroud of the HST has a highly reflective chrome surface. This was achieved by using Bare Metal Foil Chrome (available at most good model shops). This must, however be polished before applying as an oxidised surface will most likely be present. This surface is covered in rivets and presented somewhat of a problem until a fellow modeller came up with a solution. Using the template in fig 14 and a steel rule, I carefully ran my power tool with a small circular saw along the lines. The teeth of the saw leave small indentations which mimic the rivets perfectly. You should try this technique out first on a spare bit of foil before using it on your newly polished surface. It took four attempts before I was happy with the result. The foil should then be carefully wrapped around the cylinder and buffed into place. Here the rivets may disappear somewhat. It is a fine balance between indenting the foil so much that it tears when removed from its backing sheet and the rivets disappearing upon burnishing. Located at the front of the telescope of the rectangular Wide Field Planetary Camera. This was just a 34mm x 13mm rectangle piece of 20thou plastic card. A similar sized piece of bare metal foil needs to be removed to allow this to be glued into place.

The Light Shield has five rings around the lower part which was accomplished with plastic rod (fig 12 again) and is covered with silver chocolate foil. The high gain antennae (which I planned to be be deployable) were made from plastic rod and 20mm diameter parabolic dishes (again from the spares box). Each rod was pushed into a slightly larger diameter plastic tubing (tongue in groove style) and a pin inserted which allowed freedom of movement.

Detailing the HST

Unlike several previous satellites which NASA retrieved and repaired the HST was designed to be grappled by the RMS for servicing (and indeed was deployed in this manner) and two grapple fixtures are prominent on the front of the telescope just above the small equipment bays. These were simply constructed from 9mm plasticard circles and tiny off-cuts of plastic rod.

Circling the upper tube (at the position of the five rings) are located rod-like antennae (four in total) each 54mm in length and placed at an angle of approximately 130 degrees.

When the HST was launched in 1990 in the payload bay of Discovery, it was held firmly to the bay by four trunnion pins (attachment points). Two are located near the top of the telescope and are held 10mm out from the telescope by four V-shaped struts. This allows for the smaller diameter at this part of the telescope and aligns these trunnion pins with those further down on the Aft Shroud of the Hubble. All four trunnion pins are in the form of a circular piece of plastic with a cord removed i.e. truncated at one side (see fig 15). The lower ones have a 5mm length of rod protruding from the centre.

The Hubble Telescope is covered in yellow/orange handholds and the best that can be recommended is that photographs are closely studied for the placement of these. In fact there are so many that holding the model becomes increasingly difficult and you may want to avoid adding these until the very end.

I intended assembling the Aperture Door so that it could open and close and this was accomplished with the aid of a tiny hinge. Alterntively a piece of sticky tape could be used instead (this would probably be an easier option actually). However I found that the model does not photograph well with the door open, so mine now stays permanently closed. Figure 12 shows the size and shape of the door which was fashioned from 20thou Plasticard. This was also covered with chrome Bare Metal Foil. Directly below the WF/PC camera are two black ellipses. On the actual spacecraft these are openings for two of the three star trackers which keep the HST pointing directly at its target. However in all but the closest of photographs these just appear to be solid black ellipses, and therefore I decided just to simulate these with black decals. Finally, the front of the telescope bears the NASA and ESA logos. The NASA "worm" as it is known, is in red and this necessitated painting a spare grey NASA decal. The ESA decal also comes with the shuttle kit (it's meant to be used on the Spacelab included in the kit).

The Hubble Space Telescope can now be mounted in its proper place in the payload bay of space shuttle Endeavour, thus completing a project which celebrates one of NASA's most daring and successful shuttle missions.