For many years now Baader Planetarium has been asking me from time to time to put on paper my experiences with observatory domes which I had to deal with during my life as an active observer and user of observatories. I finally wanted to fulfill this wish and have summarized my experiences here
... I'd like to say a few words about my background:
My amateur astronomical and technical experience with classic observatory domes began in 1967 when I joined the Berlin Wilhelm Foerster Observatory (WFS).
Im Laufe weniger Jahre – neben Sternwarten- und Planetariumsveranstaltungen – wurde ich dort so etwas wie ein "freiberuflicher" technischer Mitarbeiter. Ich habe dort bis zum Ende meines Studiums Ende 1987 eng mit Werner Nehls (Witte & Nehls, Konstrukteur die legendären Regulus Montierung) und Bernhard Wedel (dem damaligen technischen Leiter der WFS) lange und intensiv zusammen gearbeitet. So war ich oft an Wartungsarbeiten der großen 12m Askania- und den beiden kleineren Kuppeln der WFS beteiligt.
In the time of a few years - in addition to observatory and planetarium events - I became something like a "freelance" technical assistant there. Until the end of my studies at the end of 1987, I worked closely together with Werner Nehls (Witte & Nehls, designer of the legendary Regulus mount) and Bernhard Wedel, the technical director of the WFS at that time. I was often involved in maintenance work on the large 12m Askania domes and the two smaller domes of this public observatory in Berlin (West).
For almost 20 years I was the 1st president of the public observatory "Geschwister Herschel e.V." in Hanover and during this time I also took care of the 5m- and the 3m domes of the club.
In this period also a complete removal of both domes because of construction work of the water tank on which the domes stand and the following complete reconstruction of both domes.
My private experiences with domes from Baader Planetarium
My first experiences with a Baader dome go back to the early 80's, when I bought a 2.1 m Baaderdome from an astro friend as a "second" or "third" owner and set it up in my garden on a self-made wooden base.
The 2.1 m dome - without electric drives - fulfilled its function for years without problems until my wife and I planned a very spacious conversion of the complete upper floor of our house in 1997.
In 1998 a 2.6 m Baader "Classic Dome" was installed on the roof. The dome was preassembled by me and friends - after a short description of the company Baader - without problems in the garden (picture see above) and then put on with a truck crane on the prepared substructure.
Discover this dome installation also on our World Map
The base is almost square, because in my opinion this floor plan is much more practical than the normal cylindrical base from Baader, because it offers a plenty of space for cupboards and/or racks to store accessories without limiting the use of the telescope.
Access to the dome is via a normal door, accessible from the roof terrace, with a staircase with a normal slope, which allows larger telescopes of high weight to be comfortably brought into the dome. A dome access of this kind was important to me, because I already had many different - also large - telescopes in the dome in operation for adjustment and testing. Normally, access to the attic is via a steep, fold-out scissor staircase - and this is not practical.
The brick instrument pillar - filled with pre-annealed quartz sand - stands on the intermediate reinforced concrete ceiling to the basement in my wife's workroom exactly above a partition wall on the ground floor.
Due to the roof mounting, the dome is quite high above the ground (approx. 8m) and every 5 years it is necessary to clean it from the outside. In the years, mosses and lichens settle down, to say nothing of the many "bird's shit", the dome looks then simply ugly and dirty, by its high position it is also visible from a distance. Also here the square substructure is of great advantage, because one can move safely around the dome from the outside when cleaning the dome. Cleaning is done with clear water, to which something "Meister Proper" or a similar cleaning agent is added.
The dome was retrofitted in 2008 with an azimuth motor for the dome rotation, the slide gate is operated manually via the chain drive, since I am not a big friend of possibly failing end-switches. Except for occasional spraying of the chain with bicycle chain oil, the dome has now been running perfectly for over 20 years and without any further maintenance.
The only problem I had at the beginning was the formation of condense water inside the dome under specific weather conditions, mainly in winter. This is probably due to the fact that the 2.6 m dome is not double-walled. As far as I know the Baader domes from 3.2 m diameter are double-walled and also the smaller models are delivered double-walled on request, so that condensation is excluded.
To avoid a permanent electrical or chemical dehumidification, the small window of the dome base is a gap wide open. The condensation water problem was solved and as a further advantage I already have outside temperatures in the interior when opening the dome for observation.
In many years between 1990 and 2004 I had access to two more Baader "classic dome" domes. One stands near Saarbrücken (3.2 m) and the second in Switzerland in the Bernese Highlands (2.6 m). At the location in Switzerland, the problems are low temperatures, sometimes down to -20 degrees, and a lot of snow. However, if the dome was free of snow and ice, there were no problems during operation. How it looks with both domes today I cannot say, because the contact to the owner was broken off some time
Further in 2003 I built together with a friend in Hannover a Baader 2.6 m "classic dome" on a square substructure. The construction also went without any problems and as far as I know the dome runs without any problems since the construction. Due to the low height above the ground, the dome parts were mounted one after the other directly on the rotating ring.
My professional experiences
In the same year I got the order to plan and build a complete observatory for the German owner of a guest farm in Namibia. Rooisand Desert Ranch is a typical Namibian guest lodge and is located at the edge of the Namib Desert, directly below the famous Gamsberg, Namibia's Table Mountain.
Due to my many good experiences with Baader domes in Germany and Swizerland, only the purchase of a Baader dome came into question for me, moreover there were no serious alternatives to the company Baader at that time - perhaps with the exception of domes from the USA. A 3.2 m "classic dome" was chosen. The ordered telescope configuration consisted of a large Astro Physics 1200 GTO mount on which a hand-selected Celestron C14, a 150mm Zeiss APQ refractor and a small Zeiss AS 80/840mm telescope were mounted.
Discover this dome installation also on our World Map
The dome assembly took place in autumn 2004 with the help of the lodge staff and ran perfectly like the Baader domes, which I had assembled until then. However, sometimes - as a studied German engineer - my heart almost stopped when the team put the dome on the approx. 7m high substructure, because it was too expensive for the lodge owner to order a big truck crane over 200 km from Windhoek.
The instrument, respectively the dome was built so high to get over the air layers near the ground, which are heated during the day for better seeing conditions.
The dome has a motorized azimuth drive, the motor of the shutter drive was omitted because of "my end switch phobia", also because the dome should be operated by normal lodge personnel.
Since the construction of the dome in 2004 I am responsible for the maintenance of the Rooisand dome and at least once a year on site. What should I say? It has been running smoothly and maintenance-free for 15 years now.
The only disadvantage is the cylindrical substructure. We have there in the dome two normal desk containers for storing accessories, but there is always too little space and they are always in the way.
It is no comparison at all to the square substructure of my 2.6m dome in Germany. Even if there are only 2 observers in the dome - there is never enough space for relaxed working.
The special requirements of the dome on Rooisand include the extremely dry air over months of the Namibian winter with an air humidity of often only around 10 to 15%. The dust- and water-repellent rubber parts of the seals in the azimuth of the dome and on the side of the slide gate are still soft and flexible in 2018 as they were on the first day of 2004.
- Months of sunshine - 12 hours during the day - with a high proportion of UV radiation have not managed to cause any visible damage to the outside of the dome in 15 years.
- Anyone who has ever experienced a rainstorm in the Namibian rainy season knows what this means. It "pours" out of buckets and you are reminded of the history of the great Flood. The Baader dome is absolutely waterproof, we have never had water in the dome.
- Another problem in autumn and spring are violent drop winds from the Gamsberg, which carry a lot of sand and dust particles with them. It would be presumptuous to say that the dome would be absolutely dustproof, that it is not and it can also be.
- Since summer 2013, a 17" PlaneWave Astrograph with an open tube is installed and a cleaning of the main mirror was not necessary so far. This may speak as a reference for the seals. The optics in the other two domes, which I maintained in Namibia (see below), often look different.
Further domes from other brands in Onjala
The Rooisand Lodge was sold in 2011 together with the dome to a Namibian architect. The telescopes and the mounting remain with the old owner and the dome accommodated for 2 years only an old Vixen Atlux mount and a Celestron 11.
At the beginning of 2013 the new owner decided to buy a new instrument combination and since summer 2013 there is an Astro Physics 1600 GTO, equipped with the 17" PlaneWave Astrograph, a 130mm Zeiss APQ and a TEC 110mm FL refractor. The observatory is mainly used for "public star-gazing" for lodge guests, but can also be rented by experienced amateur astronomers for their own observations.
The original instrument combination from Rooisand (1200 GTO, Zeiss APQ and C14) was stored in Windhoek and was bought in 2012 by the owners of the Onjala guest lodge through my intermediary. In the same year I got also the order to rebuild the telescope for "public stargazing".
The requirements of the lodge owners were that there should be enough space for groups of 6 to 10 people around the telescope, i.e. rather a classic observatory. A correspondingly large sliding roof house was out of the question for the owners, because this did not correspond to their ideas of an " astronomical observatory ".
The dome had to have a diameter of about 4 meters and for cost reasons (there was a fixed budget) the purchase of a classic Baader 4 meter dome was out of question. At the end of 2012, the building site on the lodge site was determined and two domes of 3 and 4 m diameter (I had negotiated for myself a place for a private observatory) were ordered from a co-supplier of the company Baader.
Both domes were delivered at the beginning of 2013 in a ship container in Namibia and transported then from the port in Walvis Bay on a special truck to Onjala Lodge.
The two dome buildings were built in spring 2013 by the construction team of Onjala Lodge according to my plans and at the beginning of May the assembly of the domes was started, which was completed after only 4 days.
Meine experiences after 6 years of operation in comparison to Baader "Classic Domes"
Disadvantages of the 3 and 4 metre dome compared to the Baader 2.6 and 3.2 metre domes..
The first disadvantage is already apparent during the planning phase for the domed buildings. The Baader domes have a flap underneath the shutter, which, when open, offers a clear view almost to the horizon.
The domes of the other supplier have (presumably for construction reasons ?) installed a fixed part that cannot be opened at this point. The 3m dome has a height of 0.9m and the 4m dome has a height of 1.4m. The disadvantage here is that the telescopes have to be set up higher by this amount in comparison to the Baader domes, and even higher if parallel telescopes are mounted on the mount and both telescopes should be able to observe both east and west at a certain horizon height.
This causes problems in the 3m dome with the height of the floor and the access to the interior, in the 4m dome a 2m high staircase is necessary for observation. Please note that I am not talking here about remote observations, but about visual observations as they are common on a classic folk astronomical public viewing.
The shutter slide of the Baader dome opens beyond the zenith, which the other supplier unfortunately does not. The problem is here with the geographical latitude of approx. south 23 degrees that the highlights of the Namibian winter sky (center of the Milky Way) and also all planets and also the moon run approximately through the zenith and are practically not observable to their highest positions over the horizon.
Probleme with the 3m dome of the competitor:
- After only three years, the side guide rolls of the shutter slide of the 3m dome had practically disintegrated and had to be replaced (picture right), the base of the rolls was already completely rusted (picture left)
- the base of the dome is not exactly round despite careful assembly, so that the assembly of the azimuth motor had to be dispensed with and the dome has to be turned manually
- The radius of curvature of the shutter slide is not uniform, therefore not all guide rollers are engaged at the same time, there is a permanent risk of tilting and blocking of the shutter slide when opening or sliding (especially in the upper position)
- we had a complete failure of the control electronics of the dome's slide gate motor in 2015 with a following expensive repair and maintenance
- bad seals, after heavy thunderstorms in the Namibian rainy season there is always water on the dome floor
Problems and remarks on the 4m dome of the competitor:
- the interior paint of the dome parts is thin and uneven (also on the 3m dome)
- Even during the assembly of the individual dome parts, running defects occurred on three of the 16 azimuth rollers. The track rollers were supplied with single axis without ball bearings, the axes were simply broken by the load of the dome segments. The problem here is that they cannot be changed without lifting the complete dome with a crane
The shutter slide is driven by a toothed wheel and a kind of perforated strip which is mounted in the middle of the shutter slide and in which the teeth of the toothed wheel engage and open or close the shutter slide depending on the direction of rotation of the motor.
The problem here is that the radius of curvature of the shutter gate is obviously not uniform. This means that in certain positions of the gate valve the gear wheel raises and pushes it upwards, in other positions there is far too much play between the gear wheel and the perforated tape. This easily leads to mechanical vibrations of the complete bearing of the drive motor, which is only screwed into the glass-polyester laminate with 6mm thickness of the dome and there is a danger that the threads will tear off due to the motor vibrations. The motor with the gear wheel must be readjusted relatively frequently in order to minimize these vibrations. Further problems were
Further problems were:
- two defective end-switches of the shutter gate !!!, one above and one below,
- bad seals, water in the dome all the time. At the beginning 20 to 30 litres after heavy rain, after 5 years of sealing work the problem seems to be solved.
due to the wide distance between the dome and the up-and-over shutter, we have problems with birds - every year again - flying in and building their nests in the dome (see also the pictures and descriptions). The whole thing results in a lot of dirt and "bird shit". Also this problem we solved to a large extent with an electronic "bird fright".
- Within half a year the Zeiss APQ and the C14 were clearly contaminated by fine-grained, quartz-containing sand and dust (see picture below).
To be honest, the telescope apertures were rarely covered during this period. Nevertheless, the pictures clearly show that the sealing of the 4m cup-pel must be better, especially if the dome will be remote controlled without intention of investing in remote-controlled telescope covers.
In comparison to the 3m dome, the control electrics of the 4m dome for the azimuth rotation and the shutter slit have been running smoothly and trouble-free for 5 years now.
The domes are now 5 years old and I assume that many of the defects described here have been corrected with new domes from the supplier. In the meantime we have solved some problems by " handicrafts ", e.g. the problem of the gate valve drive described above. At the places with too much clearance between the punched tape and the drive pinion, washers were inserted between the screw connection of the punched rail and the slide gate to better adjust the distances.
The Advantages of the competitor domes in contrast to domes of the company Firma Baader are:
- an "opulent" slit width: with the 3m dome it is 1m and with the 4m dome " satisfying " 1.4m,
- in comparison to Baader domes a very low purchase price, and
- in our case a very good supply of spare parts - even after years - of the supplier.
The domes of the co-supplier cannot be seen in competition with the "classic domes" of the company Baader. They are - with a little bit of craftsmanship - an alternative to a garden house observatory, as many amateurs using today. Ultimately, the purchase price decides what can be delivered.
About the author: Wolfgang Paech
Dipl. Ing. Wolfgang Paech has been practicing astronomy for more than 50 years. In addition to his many experiences with observatory domes of all kinds, his core areas are the Sun and the Moon. On the german Website www.chamaeleon-observatory-onjala.de you will find a complete moon atlas, recorded with his standard technique. But even in terms of Deep-Sky and Planetary imaging, as a veteran astrophotographer for many years, nobody can fool him.
The 50+ years of amateur astronomy with many other areas, such as the restoration of historical amateur telescopes, polar light trips and much more are prepared on his private german website at www.astrotech-hannover.de.