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Telescope Fabra ROA Montsec: a new robotic wide-field Baker-Nunn facility

Octavi Fors1,2
 
 

 
 
ABSTRACT
 
 
A Baker-Nunn Camera (BNC),  originally installed at the Real Instituto y Observato- rio de la Armada (ROA)  in 1958, was refurbished and robotized. The new facility, called Telescope  Fabra ROA  Montsec (TFRM), was installed at  the Observatori Astronomic del Montsec (OAdM).
The  process  of refurbishment is described  in  detail.   Most of the steps of the re- furbishment project were accomplished by purchasing commercial  components, which involve  little posterior engineering  assembling  work.   The  TFRM is a  0.5m  aperture f/0.96  optically modified BNC, which offers a unique  combination of instrumental spec-
ifications:   fully robotic  and  remote  operation, wide-field of view (4. 4ª4. 4), moderate limiting  magnitude  (V19.5 mag),  ability  of tracking  at  arbitrary right  ascension  (α) and declination (δ) rates,  as well as opening  and closing CCD shutter at will during  an exposure.
Nearly  all  kind  of image  survey  programs can  benefit  from  those  specifications. Apart from other  less time consuming  programs, since the beginning  of science TFRM
operations we have  been  conducting  two  specific and  distinct  surveys:   super-Earths
 

1 Observatori Fabra, Reial Acad`emia de Ci`encies i Arts de Barcelona. Rambla dels Estudis, 115. 08002. Barcelona.

Spain.

2 Departament d’Astronomia i Meteorologia and Institut de Ci`encies del Cosmos (ICC), Universitat de Barcelona

(UB/IEEC). Mart´ı i Franqu´es 1. 08028. Barcelona. Spain.

3 Real Instituto y Observatorio de la Armada. Plaza de las Marinas s/n, 11110. San Fernando (C´adiz), Spain.

4 Clear Sky Institute Inc., USA

5 Hygga Innovative Technologies Inc., Norway

 
transiting around  M-type dwarfs stars, and geostationary debris in the context of Space Situational  Awareness  / Space  Surveillance  and  Tracking (SSA/SST) programs.  Pre- liminary  results for both  cases will be shown.
 
 
Subject  headings:  Telescopes:  individual(Baker-Nunn Camera) - Surveys  - Planets and satellites:  detection - Astrometry:  individual(Space debris)
 
 
 
1.     INTRODUCTION
 
With the launch  of Sputnik 1 in the fall of 1957 and  other  pioneering  artificial satellites few months later,  the early  Space Age was born.  As a solution for optically tracking these new satel- lites, the Smithsonian Institution designed and constructed a new kind of telescope:  the Baker-Nunn Camera (BNC)  (Henize  1957).   The  effort  invested  in such  challenging  project  yielded  a cutting edge prototype, both  in terms  of technology  and  optics  specifications  in that epoch.   As a result of those outstanding specifications,  the BNC was able to achieve satellite positional measurements with a  typical accuracy  of 2′′  for one  single  station.  It is in  the context of the International Geophysical  Year,  that these measurements allowed to determine for the first time important geo- physical  quantities, such as the upper  atmosphere drag in satellites orbits, the Earth flattening, the radial  distribution of Earth mass, etc.
 
In order  to maximize  the satellites coverage  and  minimize  the positional measurement error, a family  of 21 BNCs  were manufactured  in two  releases  and  placed  all over  the world  spanning in longitude.  In  1958 one of them was installed at  ROA  (see Fig.  1),  in San  Fernando (C´adiz), southern Spain.
 
With the upcoming  of new  satellite tracking technologies on  the early  80s,  a  new  kind  of facilities called Ground Based-Electro-Optical Deep Space Surveillance  (GEODSS) (Jeas & Anctil
1981) were designed,  manufactured and  installed, so that the BNC  program became  obsolete and was cancelled.  The  BNC in San Fernando was donated to ROA,  where it was maintained inactive but in excellent state of conservation.
 
We report here on the refurbishment process of the BNC at ROA, renamed as Telescope Fabra ROA  Montsec (TFRM). The  new telescope designation stands for the two partner institutions of the consortium:  Reial  Acad`emia  de Ci`encies  i Arts  de Barcelona  (RACAB) - Observatori Fabra, and Real Instituto y Observatorio de la Armada (ROA),  as well as the observing  site: Observatori Astronomic del Montsec (OAdM). In summary, the differences between the original  BNC at  ROA and  the TFRM are:  a new motorized equatorial mount, the substitution of the photographic film with a CCD as a detector, the addition of corrective optics to flatten the CCD field of view (FoV), and the control software which commands every device of the observatory and formalizes the robotic concept by scheduling  the observing  tasks to be executed every night.
 
In  § 2 we present  in detail  the refurbishment  process  step-by-step  with  a description  of the
 
specifications  of the original  BNC  at  ROA  given in § 2.1, the specifications  of refurbished TFRM
in § 2.2, and  the observing  site in § 2.3.  In § 2.4, the reproducibility of the refurbishment process for other  BNCs is evaluated.
 
In § 3 we show the observational capabilities of the TFRM. In particular, some demostrative results  of the system  performance are  given  in  the context  of an  exoplanet  survey  and  a  space debris  survey.   Other programs such  as surveying  the Space  Situational Awareness/NEO-segment (SSA/NEO), or monitoring GRBs,  γ-ray  binaries,  AGNs,  blazars,  etc.  are also discussed.
 
In  § 4 we summarize the refurbishment  project  and  TFRM  performance after  one  year  of science  operations.  We  also  discuss  the know-how  accumulated during  the process,  and  lessons learnt in view of improving  reproducibility for other  inactive BNCs.
 
 
 
2.     REFURBISHMENT PROCESS
 
The  Telescope  Fabra ROA Montsec (TFRM) is a consortium that was created to develop and operate a refurbished BNC (see http://www.am.ub.edu/bnc for updated details).
 
An extensive refurbishment project was conducted using the BNC originally  installed at ROA, which  successfully  culminated in the TFRM, a wide-field  CCD  facility with remote  and  robotic capabilities.  In several  aspects,  our  refurbishment  project  learnt from the previous  experience  of the Automated Patrol Telescope  (Carter et al. 1992), the Phoenix  BNC (Law et al. 2002), and the Rothney Astrophysical Observatory (RAO)  BNC (Mazur  et al. 2005).  We placed  special emphasis on the last one, as two of us (RB-G  and MTM)  performed  a number of research  stays at RAO and one of us (MJM), participated in the refurbishment of the RAO BNC.  This  allowed us to be more innovative with a number of parts of the project (see § 2.2), and sped up the learning  curve of those parts which were identical. In addition, another refurbishment project for the Indian  BNC,  called ARIES  (Gupta et al. 2005), was planned.
 
However,  it is worth noting  that, as far as we know,  none  of the refurbished BNCs  have  the ability of being robotically and/or remotely  commanded. Among others,  this is the most important difference between those and  our BNC.
 
 
 
2.1.     Specifications of pre-refurbished BNC
 
The Baker-Nunn Camera is named  after the two pioneering  engineers responsible  for its optical and  mechanical design, Dr.  James G. Baker  and  Joseph Nunn,  respectively.
 
Optically,  the BNC  was designed  as an f/1  system  with  0.5 m three-element  lenses corrector cell, and  a 0.78 m diameter  primary spherical  mirror  (i.e.  modified  Schmidt  telescope).  The  two outside surfaces  of corrector cell are spherical,  while the other  four inner  ones are aspherical. The four  aspherics  are  not  different  each  other,  but identical  in pairs.   The  main  difference  between the BNC and  a classical Schmidt system is that the inner  aspherical surfaces  have more refractive power, which is necessary  for a system as fast as f/1.  This,  however,  adds aberrations that must be accounted for.  To correct this chromatic aberration Dr.  Baker  made use of a combination of exotic glasses:  Schott KzFS-2  and  Schott SK-14 for the outer and  inner  elements, respectively.  And,  as with  a Schmidt  camera,  the focal surface  is non-planar.  Along  this  near  spherical  focal surface ran  a 55 mm  wide Cinemascope photographic  film providing  a roughly  30 x5   FoV.  The  optical prescription of the original  BNC can be found in Table  1, as described  in Baker  (1962).  A drawing of the optical layout for such prescription is shown in Fig. 2.
 
Mechanically, the BNC  was designed  to sit on a triangular base.  As seen in Fig.  1, mounted on that base  there  was a 360   rotating fork.  A gimbal  ring  was mounted  over  this  fork,  so that it could  rotate ±80   in elevation.  The  optical  tube assembly  was mounted  on the center  of the gimbal  ring.  The  tube could  be motor  driven  ±70◦  in a 2nd  elevation  axis that is 90◦  to the 1st elevation  axis.  Although complex  in design,  this balanced  alt-alt-az mount could be positioned to track across any angular  direction in the sky - a necessity for early satellite tracking programs.
 
When  in  observing  mode,  the film was  supplied  from  a  large  film canister attached to the telescope, stretched over the focal surface,  exposed  and  then reeled into a take-up canister on the opposite side of the telescope.  Two synchronized, rotating shutters allowed for the trailed images to be chopped and  timestamped with data  provided  from the BNC signal clock.
 
The  primary mirror  was suspended inside  its cell following an  innovative design,  which  was pioneering  before  the upcoming  of active optics in  the 80s.   As  seen  in  Fig.  3,  the mirror  cell employed  a series of cylindrical  counterweights  and  a ’floating’ mirror  which  was coupled  to the focal surface  through 3 Invar  rods.  These  features  helped  the BNC maintain focus throughout its entire pointing range  and  over a large range  of temperatures.
 
Perkin  & Elmer  Corp.   was the contractor and  manufacturer for the optical grinding,  polish- ing, and  figure testing.  Boller & Chivens  manufactured the mechanical parts, and  performed  the assembly  and  final testings.
 
As a result of the outstanding optical and mechanical designs and the excellent manufacturing process mentioned above,  an extremely high set of optical and mechanical specifications  were met. In particular,  it was guaranteed  that 80% of encircled  energy  of incoming  light  from UV to deep red was projected within a 20µm spot size throughout the 30 x5  FoV covered by the photographic film.
 
 
 
2.2.     Specifications of post-refurbished  BNC
 
On September 23rd of 2009, the (partly) refurbished BNC saw first light at the ROA during  a test of its mount and assessment of the corrector and lens quality.  The first images were taken under non-ideal  conditions:  urban   light polluted skies,  unpolished 50cm  outermost lens,  non-recoated mirror,  and  uncollimated optics. Despite these drawbacks, the quality of the first images was very promising.  These  results were then reconfirmed  with the first technical light at  the final observing site (Observatori Astronomic del Montsec, OAdM),  which was performed  on September 11t2010, after mirror  recoating, outermost lens repolishing  and preliminary collimation of the optical system. As seen in Fig. 4, the quality is excellent giving the instrument a great  deal of scientific potential.
 
A few days  later,  on 16 Sep 2010, the TFRM was inaugurated (Fors  et al. 2010a,b).   Fig.  5 shows the observatory as it looks now, after conclusion  of the refurbishment project.  As a result of this work,  the TFRM offers a unique  combination of instrumental specifications,  namely:  a large FoV  (4. 4ª4. 4),  scale of 3.9′′ /pixel, a moderate limiting  magnitude  (V19.5 mag),  the capability of tracking  at  arbitrary α  and  δ rates,  and  the ability  to command the CCD  camera  shutter at will during  an exposure.  All-in-all,  together with its robotic  and  remote  operations, the TFRM is strongly suited to conduct observational survey  programs (see § 3).
 
The  refurbishment process can be summarized in the following steps:
 
2.2.1.     Mount  modification
 
As described  in § 2.1, the original  mount design of the BNC had 3 rotational axes (alt-alt-az). For  reasons  of reliability  and  operatibility,  it was  decided  to convert  the mount  to a 2-axis
setup.  In deciding  how to proceed,  we considered  approaches that had  been  successfully  applied during  other  BNC refurbishments:
 
 
1.  the Automated  Patrol Telescope  removed  the original  azimuth  base,  built a new  pier  and tilted the yoke in accordance with the site latitude,
 
2.  the RAO BNC kept the original azimuth base and tilted this according  the latitude for setting the α axis.  In addition, the fork was cut so that original altitude axis is now used as declination axis.
 
 
The first option is convenient because of its simplicity, specifically for low to moderate latitude sites, where  the installation of a yoke-mounted BNC  would  be feasible.  However,  it also imposes restrictions when observing  areas  close to the celestial pole.  On the other  hand,  the second alter- native  requires  a major  (and  more expensive)  transformation of the fork.  However, it would be the natural choice for a high  latitude site where  the first approach would  not  be feasible  due  to the possibility of tube-mount interference.
 
Apart from our moderate latitude site, an additional reason  led us towards the first approach: the azimuth fork in early BNCs (like APT  and TFRM) was supported by a simple manual  bearing assembly.  Later  BNCs designs (like the RAO’s),  however,  incorporated a motorized, side-loadable
 
 
bearing  assembly  which  could  be driven  while inclined.   Finally,  the mount was modified  with an adjustable  inclination range  of ±5 , which  spans  the latitudes  of the ROA,  testing  site,  and  the OAdM,  the final observing  site.
 
Other refurbished mount alternatives such as operating in alt-azimuth or buying  a new mount were discarded because  of operational difficulties and  cost, respectively.
 
Once  the BNC  mount was  converted to equatorial mode,  both  α  and  δ axes  needed  to be motorized such that they could be commanded from the control computer.  As the newly modified α axis lacked a gearing  mechanism, a new 180-teeth gear was machined. A design identical to the original  gear  in  the new  δ axis  was  chosen.   In  addition, a new  worm  screw  for the α  axis  was machined as a copy of the δ worm screw, which was already  present in former  orbital axis.
 
The mount conversion  and the manufacture of the α gear was performed  by Talleres  Yeste S.L. (Cadiz,  Spain).
 
Finally,  NEMA-234  brushless  motors  controlled by BearingEngineers AVS digital servo drives were  installed on  the α  and  δ axes.   The  telescope closed-loop  motion  was  completed with the following devices:
 
 
1.  two 25-bit Heidenhain ECN 225 absolute angle encoders  directly installed on each axis shaft and  interfaced via a TCP/IP Heidenhain EIB-741  unit,
 
2.  a Pro-Dex  PC48  Multi-Axis Motion  Controller board  plugged  on the control computer.  A number of devices  of the observatory (α  and  δ motors,  focus drive,  etc.)  can  be controlled from this board,
 
3.  a Meinberg  LANTIME M200/GPS time server  which  allows to synchronize  and  timestamp UTC  time  on whatever observatory device  via  NTP  protocol  with  an  accuracy  of ±0.1 ms (limited by CAT6  LAN latency).
 
 
 
2.2.2.     New precise  spider and focus system
 
A key aspect of the retrofit process is the fabrication of the enclosure  and  spider  assembly  to house the CCD camera  and the focus system. All of which sits inside the Baker-Nunn camera  tube. Because  of the f/1 nature of the BNC,  a ±10µm repeatability or better focus is required  to fully realize the resolution inherent in the optical system.
 
The  solution to these requirements was as follows:
 
 
1.  a preliminary design for a tilt/rotate camera  support assembly  was provided  by MJM based on his experience  with the refurbishment of the RAO BNC.
 
 
2.  the final, optimized design  was developed  and  fabricated by Moreno  Pujal  S.L. (Barcelona, Spain),  as can  be seen in Fig.  6.  This  consists  on a steel  vane  assembly  that attaches to a central  focus housing.   That is a cylindrical  steel  shell containing  the focus mechanics  and motor.  The  CCD camera  housing  is attached to the end of a triple-contact focusing ram.  At the bottom of the CCD  housing  a cell keeps the meniscus  lens at  the prescribed distance to the CCD  chip.   The  whole assembly  is attached to four spider  vanes  which  are  attached to the TFRM midtube section.  Further, precise  alignment of the camera  with respect to the optical  axis of the telescope  is performed  using  rotational and  tip-tilt adjusters  installed  in the midtube section.  These adjusters have a tip-tilt resolution of 3µm, a rotational resolution of 43′′ , and  radial  resolution of 63µm.
 
 
A remarkable feature  of the design specified by Moreno Pujal  S.L. is the capability of removing the central focus and  CCD  housings  without touching the spider  vanes.   This  requirement helps ensure  optimal aligment of the whole assembly  when the central cylinder  needs to be removed  for maintainance.  Operational experience  since Sep 2010 indicates that such a specification  has been met:  for the four times that the cylindrical  housing has been removed  for upgrading purposes,  only small  variations on the collimation of the system were noted  upon  reassembly.  This  means  that relatively few hours  have  been  needed  for recollimation after dismantling/reassembling the BNC camera  housing  unit.
 
Another critical specification  was that the spider  vanes  and  focus system be as athermal as possible.   In  other  words,  with  an  f/1  system  we could  not  afford  to have  focus changes  larger than ±10µm due to temperature changes,  difference in telescope attitude, etc.  The  focus stability after two years  of science  operations has  shown  outstanding performance:  not  only  is the focus adjustment unnecessary during  a given night, but we have  realized  that focus can be maintained unchanged during  months with no loss in faintest object detection.
 
Finally,  the inclusion  of two  baffles between  the meniscus  and  CCD  shutter and  the coating of the internal sides of the CCD housing  with an special ultra-black material (MagicBlack, Acktar Inc.)   serves  for  minimizing  the background level  and  eliminating ghost  images  due  to internal reflections.
 
 
 
2.2.3.     Optics  refiguring
 
The  original  Baker-Nunn 30 x5  FoV  required  a curved  focal surface.   With the commercial CCD detector used for this refurbishment, a focal plane  was mandatory. This  new design required the manufacture of three new elements:  a bi-convex  field flattening lens,  a meniscus  lens,  and  a plano-plano colour  filter.  In addition,  both  the outermost  surface  of the 50 cm corrector  cell and the primary mirror  had  to be repolished  and  recoated respectively to get maximum throughput of the system.
 
 
As a result, this corrected design yielded an f/0.96  modified BNC system with a 4. 4ª4. 4 (more than five degrees diameter) FoV which comfortably placed more than 80% of the ensquared energy within a 20µm spot.  At the extreme field point (3. 125), the ensquared energy falls to just over 65% within 20µm.
 
To accomplish  this, the following general  requirements were specified to Malcolm  J. MacFar- lane, the engineer  hired  to perform  the optical design:
 
 
1.  the focus surface  must be flat, which is not  the case of the original  BNC design.
 
2.  the geometric  distortion  of the camera  must  be less than 10µm  (0.03%)  at  the edge of the field.
 
3.  the flat field size must be 6. 25 in diameter.
 
4.  the useful spectral region is 450-1100 nm.
 
 
A final  design  was  accomplished with the specific parameters in  Table  2.   This  design  was inspired by the work which Dr.  MacFarlane had already  done for the RAO BNC with the addition of a more stringent requirement on geometric distorsion.  In order  to meet the distortion requirement and  to obtain similar  encircled  energy  figures  as  the original  Baker  prescription, the use  of an unusual material (CaF2 ) for the field flattener and  an elliptical surface  on the mensicus  corrector were required. A drawing  of the optical layout for such corrected prescription is shown in Fig. 7.
 
The  fact  that the field flattener  has  to be placed  as close as 0.65 mm  to the CCD  chip  and that it is made  of calcium  fluoride  introduces some  restrictions in  the cooling  rate  of the CCD dewar.  However, the flattener was designed  thin enough  to reach  thermal equilibrium without any significant risk of breakage.  In addition,  an antireflection coating  was applied  to both  surfaces  of the flattener lens.
 
The meniscus lens was required  to correct for the astigmatism introduced by the field flattening lens.   To  do so, the optical  design  placed  that element  far  from  the focus plane  and  outside  the CCD camera  body.  With such a fast optical system, however,  this means  that the diameter of the meniscus  lens  becomes  large  (180 mm).   In  addition  to correcting  for astigmatism,  the meniscus corrector was also designed  to correct for barrel  distortion.  To accomplish  this, the meniscus  lens has deep surfaces  - one of which is ellipsoidal.  Also, an antireflection coating  was applied  to both surfaces  of the lens.
 
Because  of the many  observational programs to be  conducted  with  the TFRM, the use  of a filter is desirable.   Johnson interference filters were early  discarded because  of the unavoidable chromatic aberration with the great  incidence angle of the f/0.96  beam.  Therefore, a coloured glass filter had to be chosen.  Since original  BNC optics was not  optimized for blue wavelengths and the inferior efficiency of the CCD in this part of the visible spectrum, a yellow glass filter with a cutoff
 
 
 
Table  1.    Optical design for the pre-refurbished Baker-Nunn Camera.
 
 
Surface
 
Comment
 
Curvature radius  (mm)
 
Thickness (mm)
 
Diameter (mm)
 
Glass
 
1
 
Corrector 1
 
-13754.100
 
26.54
 
508
 
KzFS-2
2
 
-2589.784
49.2
508
 
3
Corrector 2
-2988.818
14.25
508
SK-14
4
 
+2988.818
49.2
508
 
5
Corrector 3
+2589.784
26.54
508
KzFS-2
6
 
+13754.100
944.8
508
 
7
Primary mirror
-1016.167
-520.65
760
Mirror
8
Focus
-508.001
 
50a
Film
 
a 50mm  is the width of the film.  However,  the field is corrected over a 300 mm  diameter surface  to allow for imaging  with a 50 mmª300 mm strip of film.
 
 
 
 
Table  2.    Optical design for the post-refurbished Baker-Nunn Camera.
 
 
Surface
 
Comment
 
Curvature (mm)
 
Thickness (mm)
 
Diameter (mm)
 
Glass
 
Object
 
 
0
 
1
Corrector 1
-13754.1
26.54
508
KzFS-2
2
 
-2589.784
49.2
508
 
3
Corrector 2
-2988.818
7.125
508
SK-14
4
Stop
7.125
508
SK-14
5
 
+2988.818
49.2
508
 
6
Corrector 3
+2589.784
26.54
508
KzFS-2
7
 
+13754.1
344.8
508
 
8
CCD  camera  shadow
600
200
 
9
Primary mirror
-1016.167
-406.5262
671.8549a
Mirror
10
Meniscus  lens
-152.11
-12.624
180
Fused  silica
11
Ellipsoidal surface b
-146.887
-78.87521
166
 
12
Filter
-3.01752
100
K5
13
 
-15
100
 
14
Field  flattenner
-210.4949
-5.05206
64
CaF2
15
 
+822.5282
-0.65
64
 
Image
Focus
 
52.38919
 
 
a Diameter of illuminated circle for a 5  FoV.
 
b Conic constant of ellipsoidal  surface=0.06049±0.0005 mm.
 
frequency  of 475 nm (Schott GG475)  was found to be the best choice.  Again, antireflection coating was applied  to both  surfaces  of the filter.
 
In summary, the redesign  layout consisted on the focus surface  being  flattened by means  of adding  a positive lens very close to the CCD and a meniscus  lens somewhat further from the focus plane.  This latter element provided  correction for the astigmatism introduced by the field flattener. In order  to keep the field flattener from introducing unacceptable aberrations, it was necessary  to place it 0.65 mm from the focal plane.
 
Furthermore, in order  to increase  the throughtput of the system, the transparency and  reflec- tivity of the outermost 50 cm surface of the corrector cell and the primary mirror,  respectively, had to be improved.
 
The  exterior  50 cm  lens  element  of the corrector  cell is made  of KzFS-2,  which  is a  highly hygroscopic  glass.   As a result, during  the years  the BNC  was  inactive and  exposed  to ambient humidity,  the transparency  of this  element  decreased  significantly.  This  decrease  in transparency was also observed  to occur,  to one degree or another, in other  BNCs  which did not  have  in origin a protective plate  of the corrector cell. This  is the case of the APT  (Carter et al. 1992).
 
A repolishing  of the outermost spherical  surface  was sufficient to restore the original  trans- parency. In addition, in order to protect the lens from humidity damage in the future, the outermost surface  was coated  with MgF2   layer.   In Fig.  8 the evident transparency improvement due  to the repolishing  operation can be appreciated.
 
Despite being sealed within the tube, the aluminized surface of the mirror  had lost much of its reflectivity. Because  of this, it was necessary  to recoat  the surface of the mirror.  Given the special characteristics of BNC  system (with mirror  being  difficult to remove  from  tube), a very  durable reflective coating  was chosen over other  criteria.  The coating  Diamond-BriteTM  from H.L.Clausing Inc.  (Illinois,  USA) was chosen for its durability.  In Fig. 9 the increase  of mirror  reflectivity before and  after the recoating operation is shown.
 
The  manufacture of the field flattener lens, the CCD  filter,  and  the repolishing  of outermost
50 cm  lens  were  performed  by  Harold  Johnson Optical  Laboratories Inc  (California, USA).  The manufacturance of the ellipsoidal meniscus was conducted by Tucson  Optical Research  Corporation Inc (Arizona, USA). Mirror  recoating was performed  by H.L.Clausing, Inc.
 
For  the case of lens repolishing  and  mirror  coating  their original  prescription  parameters  in Table  1 were not  modified.  Regarding the field flattener lens, CCD  filter and  ellipsoidal  meniscus, the comparison of the as-built optics with the theoretical prescription show that all these surfaces were manufactured well within the design tolerances (see Table  3).
 
Star testing of the optical system, post-refurbishment, shows that the acquired  images are, for the most part, free from  obvious  aberrations (Fig.  10).   Furthermore, it can  be seen that image quality (as measured by point spread  function) is consistent with increasing  field angles.  Note that the image in the figure has not  been calibrated (bias,  dark  and  flatfield)  in order  to make sure the
 
 
Table  3.    Comparison of as-built new corrective optical surfaces  with theoretical prescription
values.
 
 
Surface a
 
Parameter
 
Prescribed value  (mm)
 
Tolerance (mm)
 
As-built value  (mm)
 
Meniscus
 
 
 
 
10
Convex  curvature
-152.1292
±0.25
-152.110
11
Concave  curvature
-146.920
±0.25
-146.887
11
Fringe  irregularity b
1
5
 
10 & 11
Axial thickness
12.700
±0.10
12.624
Filter
12 & 13
 
Thickness
 
2.99974
 
±0.10
 
3.01752
Field  flatte
14
ner
Curvature  1
 
-210.4624
 
±1.0
 
-210.49488
15
Curvature  2
+823.0108
±1.0
+822.5282
14 & 15
Axial thickness
5.05206
±0.10
5.00126
 
a Surfaces  numbers as noted  in Table  2.
 
b Number of fringes on the aspheric  surface  as visible on a Zygo interferogram over a 2′′  diameter centered area.
 
 
displayed  stellar surfaces  are the ones which the optic system project over the chip.  Note  the two circular  scratches can be seen on the upper  right and  lower left corners.
 
After repolishing and coating with MgF2 , the 3-lens corrector was tested to have a 69% through- put. The  meniscus,  field flattener, and  filter are all coated  with BBAR  coatings  with a reflectivity of about 1% (on average)  at each surface.  So, the transmission for these three elements totals 94%. The mirror  was coated  with Clausing’s  Diamond  BriteTM coating  which has a stated reflectivity of
97%. So, in total, 63% of the incoming  light reaches  the chip.
 
 
 
2.2.4.     Custom  CCD  camera
 
Our  custom design CCD  was based  on the production prototype PL16803  from Finger  Lakes Instrumentation  (FLI)  Inc.  (New York,  USA),  as can  be seen in Fig.  11.  Its main  specifications are:  4096x4096 9µm-pixel  Kodak  16803 chip, 60% QE at 550nm, 9-11 e- readout noise, 1 MHz and
8 MHz readout  speed  at  16-bit  digitization  rate,  the camera  electronics  and  sensor  chambers are sealed with noble gas to keep the moisture out.
 
Aside  from the above  specifications,  the CCD  camera  inside  the TFRM tube had  a number of requirements  specific to this  project.   For  example,  the field flattener  lens and  the filter  must be placed  inside the camera  body.  In addition, conventional cooling by exhausting warm  air from inside the tube is not  an option.  Therefore, a recirculating liquid cooling system was implemented by  FLI,  Inc.   Finally,   compactness of the CCD  camera  dimensions  (6.2-inchª6.2-inch) was  also essential for fitting it into its spider  housing.  At the time of purchase, the PL16803  was found  to be the smallest  large-format commercial  CCD  camera  which  met  our  requirements.  A small  size was essential for our application to minimize  the size of spider  and  CCD  assembly,  and  therefore, the obscuration over the image.
 
After taking stock and  custom specifications  into account,  FLI,  Inc.   was  found  to be  the commercial  manufacturer which best balances  willingness of performing  this custom design, quality of product and  reasonable cost.
 
Positioning the field flattener element within the camera  body  was one of the most critical aspects of the project.  The  prescription of the refigured  optics (see § 2.2.3) required  the flattening lens to sit 0.65 mm from the CCD  sensor.  Besides,  the filter-sensor distance is such that the filter had  to be placed  as the camera  vacuum  chamber window.
 
The  procedure followed to assemble  the corrective optics was supervised  by one of us (MJM) and performed  by FLI.  It was a complex sequence  of precise measurements of the level of different parts of the camera  and  optics to be assembled.   From  here,  a few µm accurate positioning of the flattener lens and  filter with respect to the CCD sensor could be derived.  The  measurements were taken with a standard micrometer depth gauge while working  on a flat granite table.
 
One of the ’extreme’ characteristics of this optical system is the large angle (60 ) light cone
 
 
at  focus.  The  result is a required  shutter diameter that increases  very quickly  with distance from the focal plane.    Unfortunately for us,  most commercial  shutters are  simply  too small  to allow unobscured imaging  with our camera  system.  And, the requirement become even more stringent if the backfocal distance is to be kept within a reasonable range.  As a result, a large aperture shutter had to be considered.  This device had to guarantee reliable performance as well as mechanical and electrical stability, given the unattended nature of the TFRM. The  CS90 model from Uniblitz Inc. (New York,  USA),  with an aperture of 90 mm,  was selected.  FLI assembled  the shutter internally to the PL16803  camera  body,  which  had  to be modified  to accommodate the larger  diameter  of the shutter. As part of the shutter integration process,  FLI  provided  for both  auxiliary  and  USB triggering of the shutter. Although the TFRM LAN latency  could, in theory, provide  a CCD image
timestamp  precision  of ±0.1 ms,  the electrical  and  mechanical uncertainties  of the CS90 shutter
decrease  the precision  to about 100 ms.
 
Although the CCD camera  consumes  a small amount of power (40 W), one should  note  that it is stored inside two cavities: its housing  in the spider  assembly  and the tube. If conventional air cooling was employed,  turbulence within the tube would result - possibly decreasing  image quality. As an alternative solution,  our camera  was designed  to accommodate liquid  cooling.  At the time of purchase, the FLI  design  was innovative in commercial  cameras  and  has  shown  a performance of typically  +15  better cooling than the air  option  in the same  camera.   In addition,  the use of one cooling method does not  preclude  the other  with this camera.   The  liquid  cooling option can accommodate a large amount of heat  transfer from the camera  to the outside environment.  Should the liquid cooling fail, air cooling can take its place.  This,  of course, would come at the expense of image quality and cooling efficiency. As a coolant, we use a 25% solution of propylene  glycol in dis- tilled water.  This is recirculated and maintained at a constant temperature by a ThermoCUBETM , Solid State Cooling,  Inc.  chiller.  The  ThermoCUBETM  can be remotely  controlled and  monitored by the observatory control computer.
 
 
 
2.2.5.     Reinforced glass-fiber enclosure
 
The  TFRM and  rest of observatory devices are installed in a new enclosure  specially  built for this purpose.   The  enclosure  has been designed,  manufactured and  assembled  by GRPro Precision Manufacturing,  Inc.   GRPro has  extensive experience  in  astronomical enclosures,  like  the ones machined for SuperWASP (North and  South) projects which  were  source  of inspiration for our design (Pollacco  2007).
 
The TFRM 12 m x 5 m x 4.5 m reinforced  glass-fiber enclosure is modular and allows a portable installation.   It has  turned out to be  robust in  all  kinds  of adverse  weather conditions with no mechanical failures.  As seen in Fig. 12, the facility has a sliding roof which, when opened,  it leaves the TFRM uncovered  and  ready  to observe.   The  rest  of the building  is dedicated to the control room.    The  South  wall  can  be  folded  down  by  90 ,  so that the TFRM can  observe  up  to 13elevations.
 
 
The roof and South wall are moved by means of an hydraulic pump  which activates a mechan- ical chain,  in the case of the former,  and  an hydraulic arm  in the case of the latter.  In case of a power failure, backup  24 Vdc batteries allow the system to close the enclosure.  Start and end points of motions  are monitored by means  of mechanical limit switches which stop the motor  supply.
 
A  Vaisala  MAWS100  meteorological  station was  installed  at  the communication tower  of OAdM.  This  station is composed  by a WXT520  multisensor and  two DRD11A  precipitation sen- sors.  This  guarantees continuous monitoring of enviromental conditions from the control software via TCP/IP protocol.
 
In order  to introduce redundancy in meteorological recordings  and  gain  safety in the overall TFRM operation, an independent set of sensors (two DRD11A  for precipitation, one for humidity, and  one for daylight) were connected to a watchdog system located  at  the enclosure.
 
In  contrast to control software which  is running on a computer arquitecture, the watchdog system is a stand-alone electronic device which runs  off of backup  battery power.  In the case of a crash of the control computer software, the watchdog will secure the facility by closing the enclosure roof and  ram  when sunrise  or a weather alert occur.
 
 
 
2.2.6.     Observatory  control  and scheduling  software
 
A  state-of-the-art  observatory control  software  based  on  a  client-server  architecture  via  a Instrument-Neutral Distributed Interface (INDI)  device communication protocol  was created and developed  by one of us (ECD)  (Downey  2011),  who contributed  to this  refurbishment  project  as a consultant.  All the devices in the TFRM observatory communicate with their client and  servers via INDI  protocol,  which  is designed  to control  a distributed  network  of devices in either  remote or robotic  fashion.  All communication uses TCP/IP sockets for reliable  distributed operation.
 
Among  other  interesting  features   of INDI,  we  highlight  the ability  of clients  to learn  the properties of a particular device  at  runtime using  introspection.  As a result, implementation of clients and  devices are decoupled  which is crucial  for code maintainance of both  sides of a control software.  Also,  the protocol  is XML-based  for passing  parameters back  and  forth in a compact efficient format.  Typical  bandwidth requirements for monitoring and  control of all  observatory functions (except camera  images) are on the order of a few tens of kbps, so even simple voice-grade modem  connections are sufficient for routine remote  operation.
 
Whenever INDI detects any of several conditions considered  dangerous for further observations to continue it issues  a weather alert.  This  includes  excessive  wind  speed,  humidity, detection of rain,  hail and  snow, high levels of electrostatic atmospheric activity, and  low UPS  battery power. When  an  alert is issued  the system automatically closes the enclosure  roof and  ram.   The  INDI configuration contains a parameter that allows adjusting the length  of time an alert will remain  in effect after any or all causal  factors have returned to normal.
 
 
INDI drivers  were developed  for all devices at the observatory which need active command or record.   Drivers  are written in ANSI C for the Linux  operating system.  Within each driver  is the code that implements  the desired  functionality  for one, and  only one, INDI  device.  Some drivers only provide  services, such as target prediction. Other drivers  control hardware. Drivers  may also communicate with other  drivers.  The INDI architecture places no restrictions on what  a driver  can do.  The  only requirement is that it responds  to INDI messages  that arrive  on its stdin stream for its device and  that it generates valid INDI messages from its device on its stdout stream.
 
Clientslike  drivers,   may  do  anything they wish  so long  as  they communicate valid  INDI messages  over  the socket  with  which  they  connect  to an  indiserver.   Otherwise  clients  can  be GUIs, command line programs, daemons  or other  process roles and  may be written in any desired language.   Java language  was chosen for the development of INDI GUIs clients, so that maximum portability and  consistency across platforms (Linux  under  KDE  o Gnome,  Windows  and  Mac OS) was assured.
 
A short description of INDI clients follows:
 
 
1.  I-INDI  (stands  for Interactive-INDI)  provides  remote  command and  monitoring  capability for all observatory systems except the CCD  camera.  See in Fig. 13 snapshots of some of the I-INDI windows for the global status of most important devices, and control of environmental variables, telescope pointing and  pointing model.
 
2.  S-INDI  (stands for Sheduled-INDI) allows to dispatch robotic  operations, whose observing blocks were previously  written in XML format. Using S-INDI you define the INDI commands you want to execute, define the target and any additional constraints for the observation, then the S-INDI  device  driver  will decide  the best  time  to perform  the request.   Many  requests may  be pending  simultaneously and  the S-INDI  driver  will always  attempt to perform  each of them at  the best possible time.
 
3.  CCD-INDI  commands the CCD camera  in a remote  fashion.  It can also read and write FITS files from and  to disk.  It is intended only as a basic camera  control and  image display  tool. It is not  intended to compete with very elaborate control and  processing  tools.
 
4.  ANSI C language  was chosen for the development of simple command line clients. These were conceived  for the purpose  of implementing complex  environmental conditions decisions  via high-level  scriptable languages  (Perl,  Python or bash)  that can be scheduled  on the crontab of the observatory control computer.
 
 
 
2.3.     Observing site
 
The  TFRM was installed at the Observatori Astronomic del Montsec (OAdM), in the Catalo- nian  Pre-Pyrenees, whose WGS84  coordinates are:  φ = 42. 0516 N, λ = 0. 7293 E, and  h = 1570 m HMSL.  To  date,  the OAdM  is pioneered  by the Consorci  del Montsec, an  institution run  by the Catalonian Government.  The observatory is located  at the Montsec d’Ares mountain, 50 km South of the central Pyrenees, in the province  of Lleida (Spain). The  site was chosen after a site-testing campaign.  The  OAdM  also hosts the 0.8 m Joan Or´o Telescope,  named  in honour  of this famous Catalonian researcher.
 
The  installation  of the TFRM at  OAdM  resulted  in a number of infrastructure  upgrades to the facility  as a whole:  stable  power  line,  a 100 Mbps  Internet access via fiber optics  cable,  and enhanced security fence.
 
 
 
2.4.     Reproducibility  of the refurbishment  process
 
Including  the TFRM, four BNCs have already  succesfully refurbished, and another one (ARIES
in India)  is in process.
 
This  demonstrates  that the combination of the current  synergies  between  information tech- nologies,  devices  control  electronics,  and  control  software  advances  enable  the upgrading of this kind  of telescopes  into  a  facility  with  unique  specifications  and  great  scientific  potential.   From the originally  manufactured 21 BNCs,  there are still a good number that are inactive but in good shape,  which could benefit from a refurbishment project like ours.
 
Furthermore,  in  the case  of TFRM, a  number of steps of the refurbishment  project  were accomplished by  purchasing commercial  components, which  involve  less cost and  little posterior engineering  assembling  work.
 
 
 
3.     ONGOING SURVEYING PROGRAMS
 
3.1.     Transiting  exoplanets
 
The  large FoV of the TFRM, together with its moderate aperture and  robotic  nature, allows for  the efficient  detection  of exoplanets  by  means  of transit measurements  with  high  signal-to- noise ratio  in the appropiate magnitude range.  The suitability of such an instrument for exoplanet research  was confirmed  earlier  by the APT  during  their UNSW  Extrasolar  Planet Search  during the period  of 2004-2007 (Christiansen et al. 2008).  The  subsequent catalogue  that they produced shows that refurbished BNCs can accomplish  millimagnitude photometry at least up to V14 mag.
 
In order  to confirm the APT  performance, the TFRM observed  a predicted transit of WASP-
37b,  a  known  exoplanet, in  a  completely unsupervised robotic  mode  on  8 Apr  2011.   The  first transit-like signatures of WASP-37b were detected by SuperWASP-N survey  (La Palma) between March and June in 2008 and 2009, and by SuperWASP-S survey (South Africa) during  2008 June to July and 2009 March to July. The transit lightcurve spanned about 4.5 hours (see Fig. 14).  Transit
 
 
analysis  was carried  out by Holger Voss using the reduction software described  in Voss (2006).  The photometric performance shown by the TFRM was outstanding:  differential photometric precision of 4.3 mmag  for WASP-37b (V12.7 mag),  and 3 mmag  for stars of similar  magnitude.  Aside from the excellent  precision,  what  is most  relevant  is that, if WASP-37b were unknown, TFRM would
have detected it as an exoplanet candidate on the very first night of observation, i.e., like a real-time detection without the need of further phase-folded  data  points of posterior nights.
 
Other known exoplanets transits were observed by TFRM, all of them in the 12 mag<V<14.5 mag range,  with similar  photometric precisions  in all cases.
 
Irwin et al. (2009) proposed  an interesting alternative observational approach which has been executed by the MEarth project. In order  to maximize  the probability of detection of rocky super- Earths in  the Habitable  Zone  (HZ),  MEarth is photometrically  monitoring  a  sample  of 2000
M-type stars, which  have  been  pre-selected.  MEarth operates 8 telescopes f/9 Ritchey-Chretien with  a field of view of 25 x25   each.   Due  to this  limited  FoV  (0.17  square  degrees),  this  project can  only  monitor  a single  star per  telescope  at  a time.   Despite  this  limitation  on the efficiency of the survey,  only in 3-4 years  of full operation, it has  been  able  to detect  the first  super-Earth (GJ1214b) with this new pre-selected strategy survey  (Charbonneau et al. 2009).
 
As mentioned in Fors et al. (2010a), the 19.4 square degrees TFRM FoV is the most remarkable feature  of this telescope.  This,  combined  with the fact that a 30-second exposure  typically contains
20.000  stars with  SNR>5  (V<15.5 mag)  and  a photometric  precision  better than 10 mmag  (3-
4 mmag typically for V down to 13-13.5 mag), means that the telescope has a significant probability in detecting new exoplanets by transit technique.
 
Since December  2011, and in collaboration with the team of Dr. Ignasi Ribas  (ICE-CSIC), the TFRM began to survey a pre-selected series of fields, with an input catalog similar to MEarth’s (Reid et al. 1995; Hawley  et al. 1996; L´epine & Gaidos  2011), in search  of super-Earths around  M-type stars.  The  survey  was  called  TFRM-PSES (TFRM-Preselected Super-Earths Survey).    TFRM- PSES  monitors  a number of M0 to M5-type  catalogued targets comprised  in several  fields with sufficient frequency  each night, and  in the range  of 9.0 mag<V<15.5 mag.  M targets per field dis- tribution spans  from  6 to 16, with  a global  median  value  of 8.   However,  up  to 23 out of more
60 fields contain  more  than 13 M targets:  typically  14 and  15, and  16 in one case.   Note  this  is the main  difference between MEarth and  TFRM-PSES: on one hand,  while in MEarth each single telescope monitors one star per CCD  field, TFRM-PSES captures approximately 8 times as many stars per field which,  therefore, increases  survey  efficiency.  On the other  hand,  the higher  number of telescopes in MEarth compensates the former  said.  Finally,  that TFRM-PSES magnitude limit of V=15.5 mag  could  be increased,  but then the frequency  of measurements would  be less, which would penalize  efficiency when recording  possible transits.
 
In particular,  as seen in Fig.  15 the coverage  of the TFRM-PSES survey  to 5 Apr  2013 was such that 48 of the 60 catalogued fields were observed  at least once.  The median  number of epochs is 12, and  the total number of covered  fields per night including  repetitions is 635.
 
 
Preliminary results with respect to the photometric precision  and  exoplanets detection prob- ability of TFRM-PSES survey  were presented in Fors  et al. (2012).  This  study showed  that pho- tometric  precision  down  to 5 mmag  is achieved  in  the range  of 11.0 mag<V<14.0 mag.   A more in-depth study of the TFRM-PSES performance and  subsequent detections is in process  of publi- cation.
 
A by-product result of TFRM-PSES survey is the detection of new variables  stars. Although we cannot  provide detailed statistics of detection, a good example is the WASP-37b transit observation formerly  presented:  in 4.5 hours  of photometric  measurements  of all the objects  in the 4. 4ª4. 4
FoV, ten new variable  stars of different types and  magnitudes were detected.
 
 
 
3.2.     Space debris
 
Among  other  TFRM capabilities, its 4. 4ª4. 4 FoV,  the telescope tracking at  arbitrary α and δ rates,  and  the CCD  shutter commanding at  will during  the exposure  are  extremely  useful  for the participation  in Space  Situational  Awareness  / Space  Surveillance  and  Tracking (SSA/SST) observational programs.
 
The  TFRM’s   large  FoV  is suitable to survey  the entire visible  geostationary belt from  its location.  In fact, with TFRM we can cover twice our entire visible geostationary belt in a 12 hours night.  The best method to track and detect objects close to the geostationary orbit (GEO) is with the telescope stopped, i.e.  in a Earth-fixed Reference  System.  So the background stars will appear as trails with length  proportional to the exposure  time and the objects in the GEO belt will appear as quasi-point-like sources.  A good example  of the TFRM’s  detection capability in a single image is the Fig. 16, where in half FoV there are easily identifiable 8 GEO  objects (two inside the same circle forming  a constellation) among  the trailed background stars.
 
Furthermore, the telescopes capability of tracking at  arbitrary α and  δ rates  jointly with the software control, permits the tracking of objects in any kind of orbit even Low Earth Orbits (LEO), by simply  entering its Two Line Elements (TLEs) in the INDI target property.
 
Commanding the CCD  shutter at  will during  the exposure  could be very useful for surveying the sky looking for objects in any kind  of orbit.  This  observing  approach allows to cut the object trails  while  the sidereal  tracked  exposures  are  timestamped.   Nevertheless,  this  method  has  not been tested yet.
 
The  TFRM’s   collaboration in  the SSA/SST international  effort  develops  in  two  different projects:   the European Space  Agency  (ESA)  program and  the International Scientific Optical Network (ISON)  survey.
 
TFRM is one of the Spanish  assets that is involved  in the ESA  SSA/SST Preparatory Pro- gramme  (2009-2012).  Telescopes  and radars  from other  European countries also participate in this project.
 
 
During 2011 TFRM took part in the third ESA CO-VI 7-day observational campaign. This was an experimental satellite tracking campaign using European facilities, aimed to determine how accu- rately  existing telescopes can work together to track objects in geosynchronous orbits.  The satellite positions of every asset were submitted to the coordinating office at European Awareness  Research Laboratory for Space (Early-Space), which reported the global results of the campaign (Fru¨h et al.
2011).  Systematic observations of different GEO  satellites were conducted by TFRM to determine
1137 satellite  angular  positions,  and  partial TFRM results  were presented  (Montojo  et al. 2011). We estimate  our  astrometric  precision  in the GEO  satellites  angular  coordinates to be below 0. 5 in both  coordinates.
 
In  order  to test our  data  quality, orbit determination from  the angular  measurements was carried  out using  the Orbit Determination Tool  Kit (ODTK) software package,  from  Analytical Graphics, Inc.  (AGI).  As an  example,  in Fig.  17, we show 2-sigma  (95%)  uncertainties  obtained over the MSG2 satellite, with 175 angular  measurements along 4 nights in which the satellite was not  maneuvered.  The  mean  uncertainties in the classical  elements, i.e., semiaxis,  eccentricity and inclination, are of the order of 12 m, 1.8·106  and 1. 5·104 , respectively.  It is worth mentioning that during  this campaign the TFRM was still in commissioning  period and the GEO  objects reduction process  was performed  using  a non-automated and  non-optimized software based  on SExtractor. Nowadays  we can take advantage of the advanced and fully automated reduction software APEX-II developed  by Vladimir  Kouprianov (Pulkovo Observatory).
 
At the time  of writing  the TFRM is about  to participate  in  the imminent  upcoming  ESA
campaing “CO-VI  Optical Observations for Space Surveillance  and Tracking Test and Validations”.
 
The  International Scientific Optical Network (ISON)  is a civilian  non-governmental project devoted  to space debris research  and space situation awareness.  TFRM is collaborating with ISON in its sistematic survey  of the GEO  Protected Zone since 2011 (Agapov  et al. 2011).   Positional measurements  are  derived  using  advanced trailed  image  reduction  techniques  included  in APEX- II  sofware  (Devyatkin et al.  2010).   As  a  result  of this  collaboration, the TFRM is one  of the sensors that contributes to the completeness of the objects without Two-Line-Element data  of ESA’s DISCOS  database, as stated at  the last “Classification of Geosynchronous Objects Report” issued by ESA (Floher  2012).
 
Currently TFRM is observing  routinely and  can detect an average  of 400 GEO  objects tracks per night with an accuracy  better than 0. 5 in both  coordinates and  a limit magnitude of 16 mag. Furthermore, the TFRM team is in the process of improving  the limit of detection towards fainter GEO objects (Fors  et al. 2010c).  Typically in a 12 hour night the TFRM is measuring around  2800 positions of 320 different objects.
 
A good  example  of the TFRM’s  capabilities  in  the SST  field was  the early  detection  after the MSG-3 (Meteosat  10) satellite  launch.   This  GEO  satellite  was on its way after  lifting  off on an  Ariane  5 at  21:36 UTC  on  Thursday, 5 July from  Europe’s  Spaceport  at  the Guiana  Space Centre  in Kourou,  French  Guiana.  The  MSG-3  was first  detected  by  TFRM on the night  of 12
 
 
July, during  our routine collaboration in the ISON geosynchronous space survey.  Three  tracks (see Fig. 18) were detected over the night with the automatic GEO  objects detection software APEX- II. With additional follow-up observations from other  telescopes of ISON network, an initial orbit determination was performed  by ISON  before  the satellite TLEs  were published, and  the results showed that the satellite was indeed the MSG-3, which was drifting East at 3  per hour rate.  Hence, it was caught maneuvering to its final 0  longitude expected geostationary slot.
 
 
 
3.3.     Other observational programs
 
A number of other  observational programs can benefit from TFRM specifications.
 
One is the collaboration in the Space Situational Awareness/NEO-segment (SSA/NEO). The TFRM will also be one of the assets  involved  in the ESA  SSA/NEOs segment.   NEOs  are  small solar system bodies whose orbits bring  them close to Earth and which represent a potential threat to the Earth. The  NEO segment of the European SSA System will perform  observations of NEOs, predict their orbital evolution and impact risk, store observational and calculated data, issue NEO information, news releases and impact warnings and support NEO mitigation measures.  Concerning NEO  observations, ESA is planning to scan  every  night  the complete  visible sky with  the aim to detect objects which are only visible when they are close to Earth.
 
In  the same  context  of SSA/NEO, the TFRM has  the capability  to contribute  significantly to the international effort of surveying  and  monitoring the population of NEOs:  the observations of NEOs  by  TFRM includes  imaging  asteroids at  low solar  elongation (an  area  usually  poorly searched) in collaboration with the NESS project, led by Dr.  Alan  R. Hildebrand (University of Calgary) that will use the NEOSSat microsatellite to continuously search  in this near-Sun region.
 
The  similarities between the SSA/NEO and  TFRM-PSES survey  strategies make  that one program can partially benefit from other’s  data. Furthermore, other  survey  programs related with the search  of Solar  System objects, like main  belt asteroids, comets, KBOs,  and  TNOs  are  also partially compatible.
 
Another program which  was initiated  is the optical  monitoring  of γ-ray  binaries.   The  final aim is to study how the relativistic wind of the young non-acreating pulsar  affects the circumstellar envelope in γ-ray  binaries  through optical photometric variability. Preliminary observations in the case of HD 215227 were presented in Paredes-Fortuny et al. (2012).
 
Finally,   other  alert programs, such  as  GRBs,  SNs,  novae,  blazars,   and  other  transients in general  can be allocated with the proper  observational strategy.
 
 
4.     DISCUSSION
 
A Baker-Nunn camera  has been refurbished to operate with a large-format commercial  CCD camera  in remote  and  robotic  modes.   A night  view of the TFRM ready  to observe  is shown  in Fig. 19.
 
The  refurbishment project included  several  steps, such  as modification of the mount into a motorized equatorial type, manufacture and  installation of a new precise spider  and  focus system, optics refiguring  for  flattening the CCD  focal  plane,  customization of CCD  camera,   new  rein- forced  glass-fiber  enclosure  with sliding  roof and  folding  down  South wall,  and  new observatory control and  scheduling  software among  others.   Most of these steps were executed by the authors. When  required, specialiazed  external  personnel  was hired  (spider  manufacture,  CCD  customiza- tion, reinforced  glass-fiber  enclosure).   The  rest of work was carried  out by purchasing commercial components and  assembling  them with little engineering  time.
 
The  performance of the TFRM was shown  by two different survey-type programs:  millimag- nitude precise photometry of exoplanets transits, and  geostationary debris  in the context of Space Situational Awareness  / Space Surveillance  and  Tracking (SSA/SST) programs.
 
All-in-all,  the acquired  know-how  and  the research  return of the new refurbished facility fully justifies the cost involved  in the project, which is affordable  even for small research  institutions or Universities.
 
Furthermore, a number of other  BNCs are still inactive and stored in good conditions, ready to be refurbished. With the usual decrease of cost when replicating a project, the TFRM refurbishment project could be applied  to such BNCs,  and  enable  in a short term basis (1-2 years)  each of these telescopes in a scientific useful facility.
 
 
This  effort  was  supported  by  the Ministerio  de  Ciencia  e  Innovacio´n  of Spain  (AyA2008-
01225  and  others), and  by  Departament  d’Universitats,  Recerca  i Societat  de  la  Informaci´o  of the Catalonian Goverment  (several  grants).    We  acknowledge  Alan  R.  Hildebrand and  Robert D. Cardinal for sharing  their RAO  BNC  experience  with us,  which  was highly  beneficial  for the proper  development  of TFRM. This  project  has  benefited  from  the wise advise  of Ignasi  Ribas, Don Pollacco  and  Juan Carlos  Morales,  as well as from the data  analysis  expertise of Holger Voss and Vladimir  Kouprianov. Authors also acknowledge  Daniel del Ser, and Albert Rosich and Estela Mart´ın-Badosa for their help in several  figures generation with Python and  ZEMAX,  respectively. Orbit Determination Tool Kit (ODTK) Analytical Graphics, Inc.  (AGI)  is a licensed software used by ROA in collaboration with the Instituto Nacional  de T´ecnica Aeroespacial  (INTA).
 
 
 
REFERENCES
 
Agapov  V., Molotov  I. & Kouprianov V. 2011, private communication
 
 
Baker,  J.G. 1962, U.S. Patent 3,022,708
 
Carter, B. D.,  Ashley,  M. C. B.,  Sun,  Y.-S.,  & Storey,  J. W.  V. 1992, Proceedings of the Astro- nomical  Society of Australia, 10, 74
 
Charbonneau, D., Berta, Z. K., Irwin,  J., et al. 2009, Nature, 462, 891
 
Christiansen, J. L., et al. 2008, MNRAS,  385, 1749
 
Devyatkin, A. V., Gorshanov, D. L., Kouprianov, V. V., & Verestchagina, I. A. 2010, Solar System
Research,  44, 68
 
Downey,  E. C. 2011, Clear  Sky Institute, Inc.:  INDI Control System Architecture
 
Fors,  O., et al. 2010a, Pathways Towards Habitable Planets, ASP  Conference  Series, 430, 428
 
Fors,  O., et al. 2010b, Advanced  Maui Optical and Space Surveillance  Technologies  Conference,  50
 
Fors,  O., Nunez,  J., Otazu, X., Prades, A., Cardinal, R. D. 2010c, Sensors,  10, 3, 1743
 
Fors,  O., et al. 2011, Advanced  Maui Optical and  Space Surveillance  Technologies  Conference,  19
 
Fors,  O.,  et al. 2012, CoolStars17,  the 17th  Cambridge Workshop on Cool Stars,  Stellar  Systems and  the Sun
 
Floher,  T. 2012, Issue 14 Rev. 1 of Classification of Geosynchronous Objects, 17, 116
Fru¨h, C. et al. Proceedings of ESA European Space Surveillance  Conference,  WPP-321 (2011) Gupta, K.  G.,  Yadav,  R.  K.  S.,  Bangia,  T.,  Kumar, T.  S.,  & Sharma, N. 2005, Bulletin  of the
Astronomical Society of India,  33, 414
 
Hawley,  S. L., Gizis, J. E., & Reid,  I. N. 1996, AJ,  112, 2799
 
Henize, K. G. 1957, S&T, 16, 108
 
Mazur,  M.J., Cardinal, R.D.  & Hildebrand, A.R.   2005, Final  Report  for Baker  Nunn  Telescope
Retrofit, Defence Research  and Development Canada, Ottawa, Contractor Report CR 2005-
040, 116 pp.
 
Irwin,  J., Charbonneau, D., Nutzman, P.,  & Falco,  E. 2009, IAU Symposium, 253, 37
 
Jeas, W. C., & Anctil, R. 1981, Military Electronics Countermeasures, 7, 47
 
Law, B., et al. 2002, Proc.  SPIE,  4836, 119
 
Law, B., et al. 2006, Advanced  Maui Optical and  Space Surveillance  Technologies  Conference,  87
 
L´epine, S., & Gaidos,  E. 2011, AJ,  142, 138
 
 
Montojo, F. J., et al. 2011, Proceedings of ESA European Space Surveillance  Conference  2011
 
Paredes-Fortuny, X., Ribo, M., Fors,  O., & Nu´n˜ez, J. 2012, AIP Conference  Proceedings, 1505, 390
 
Pollacco,  D.  2007, private communication
 
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Voss, H. 2006, PhD  thesis, University of Berlin
 
 
This  preprint was prepared with the AAS  LATEX macros v5.2.
 
Fig.  1.— Baker-Nunn Camera at  ROA in 1958.
 

Fig. 2.| Layout of original Baker-Nunn Camera design as defined in Table 1. Axial rays are
blocked by curved focal surface.
 

Fig.   3.— Mirror  cell with  six cylindrical  counterweights  and  a ’floating’ mirror  which  is coupled to the focal surface  through 3 Invar  rods.  When  the pointing or the temperature of the telescope change,  the BNC maintains focus throughout its large FoV.
 

Fig.   4.— Top:  First 70 sec exposure  technical  image  of M31 taken  at  TFRM on September  11,
2010.  Note  the huge  FoV  of the CCD  (4.4 x4.4 ).  Bottom:  Full  resolution  detail  of spiral  arm area.
 

Fig.  5.— Foreground: TFRM at OAdM. Sliding roof half open and south gabling wall fully open. Robotic  refurbished BNC inside.  Background:  Joan Or´o Telescope,  also inside OAdM.
 

Fig. 6.| Left: 3D CAD layout of the design for the spider vanes and CCD focus system. In
the central cylindrical housing, from top to bottom, the focus motor, the CCD camera, its 90 mm
shutter, and the meniscus hold by eight red-coloured bolts are shown. At the right hand side of
the mid tube: tip-tilt adjuster is shown. Right: Finished midtube with spider vanes and CCD
housing.
 

Fig.  7.— Layout of the corrected Baker-Nunn Camera design coinceived  for the TFRM as defined in Table  2. Axial rays are blocked  by spider  central obstruction.
 

Fig.  8.— Outermost lens before (left) and  after (right) repolishing.
 

Fig.  9.— Primary mirror  before (left) and  after (right) recoating.
 

Fig.   10.— A quantitative plot  of achieved  post-refurbishment point spread  function (PSF) as a function of field angle.  Each encircled star on the top image is plotted in a 30ª30pixels 3D surface. From  these, there does not  appear  to be significant image degradation with increasing  field angle.
 

Fig.  11.— Finger  Lakes Instrumentation Inc.  (FLI)  ProLine  16803 CCD  with field flattener lens, filter,  and  glycol recirculating cooling system.  Uniblitz  CS90 90 mm  shutter and  front  of camera
cover were removed.  Courtesy of FLI.
 
Fig.  12.— TFRM reinforced  glass-fiber  enclosure  installed at  OAdM,  with sliding roof and  South gabling  wall.
 

Fig.  13.— Four  windows  of I-INDI  for TFRM remote  control.  Upper left:  Main  window  which summarizes the status of critical devices and  circumstances.  Upper right:  Environmental vari- ables, both  instantaneous values and their plot versus time. Lower left: Manual  telescope control. Lower right:  Pointing model with up to 13 coefficients and  plot  of reference  stars and  errors.
 

Fig.  14.— WASP-37b transit lightcurve observed  by TFRM on Apr  8th  2011.  Note  that the left and right baseline is not completely spanned because that corresponds to a single-night observation.
Photometric precision  is 4.3 mmag.
 

Fig.  15.— Left:  Catalogued fields with  M dwarfs  to be observed.   Right:  Fields  with  M dwarfs already  observed.
 

Fig.  16.— A 10s exposure  taken with the TFRM where 8 GEO  objects (two inside the same green circle forming a constellation) and another object in a lower orbit are easily identifiable among the trailed background stars. Only  half of the TFRM FoV  is shown.  The  orientation of the image  is
North-leftwards and  East-upwards.
 

Fig.   17.—  Uncertainties in  the position of the MSG2  satellite, at  2 sigmas  (95%)  and  in  RIC coordinates.   2-Sigmas  Intrack in  red  solid  line.   2-Sigmas  Radial  in  blue  solid  line.   2-Sigmas Crosstrack in black dashed  line.  It is clearly  noticeable the characteristic increasing  of the Intrack uncertainty during  daytime.
 

Fig.  18.— Three tracks of MSG-3 satellite (point-like features) imaged by TFRM, while the satellite orbit was maneuvering East at  3  per hour.
 

Fig.  19.— Night view of the TFRM observatory.
 

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