sign in sign up
<<
Home , 38628 Huya, Occultation

CALIBRATION FOR MOBILE PLATFORMS: FIRST RESULTS

MIREL BIRLAN1,2, ADRIAN SONKA1,3, DAN ALIN NEDELCU2,1, MUGUREL BALAN˘ 4, SIMON ANGHEL1,3, CONSTANTIN PANDELE4, MARIUS TRUSCULESCU4, CLAUDIU DRAGASANU4, VASILE PLES¸CA5,6, COSTIN HEDWIG GANDESCUˆ 5,6, COSMIN BANIC˘ A˘ 5,6, TUDOR GEORGESCU7 1Institut de Mecanique´ Celeste´ et des Calculs des Eph´ em´ erides,´ CNRS UMR8028, Observatoire de Paris, PSL Research University 77 av Denfert-Rochereau, 75014 Paris Cedex, France Email: [email protected] 2Astronomical Institute, Romanian Academy 5-Cut¸itul de Argint, 040557 Bucharest, 3Faculty of Physics, Bucharest University 405, Atomis¸tilor Street, 077125 Magurele,˘ Ilfov, Romania 4Institute of Space Science 409, Atomis¸tilor Street, 077125 Magurele,˘ Ilfov, Romania 5Wing Computer Group SRL 19D, sos Virtut¸ii, 060042 Bucharest, Romania 6Faculty of Electric Engineering, Politehnica University 313, corp EA, Splaiul Independent¸ei, 060042 Bucharest, Romania 7Elcos Proiect SRL 24C, str Blandes¸ti,ˆ 060042 Bucharest, Romania

Abstract. New data are required continuously for improving the ephemerides of Near- Objects (NEOs) and artificial objects orbiting around Earth. Rapid response optical assets are ideal for the accomplishment of surveillance and tracking of these ob- jects. The increasing importance is addressed to because of the increasing of space activities during the last decade. The article continues the development of con- cept and realization of a mobile optical asset (Birlan et al., 2018) which will be used for both artificial objects and Near-Earth Object observations. Here we present one solution using the same mount for two pointing simultaneously the same region of the celestial sphere. Observational tests were performed for 1998 NU, artificial Astra 1N, the C/2018 Y1(Iwamoto), and the of Trans-Neptunian Object (38628) Huya. Key words: Observations – Telescope – Near-Earth Object – Artificial .

1. INTRODUCTION

A significant hazard for space and terrestrial human infrastructures is repre- sented by , and space debris. Human space activity increased tremendously the number of artificial objects and consequently the space junks in governed by Earth gravity field. Several models concerning the evolution of

Romanian Astron. J. , Vol. 29, No. 1, p. 23–33, Bucharest, 2019 24 Mirel BIRLAN et al. 2 satellite population were developed during the time; one of the most known (Kessler and Cour-Palais, 1978) states on so-called Kessler syndrome and predict an evolu- tion of space debris population where their in is high enough that the collisions could set off a cascade. Efforts of observational surveys for detecting and cataloguing NEOs achieved a completeness of 99% for the objects with a diameter larger than 1 kilometer (Michel, 2013). However this proportion is estimated toward a lower limit of 90%∗. The completeness of discoveries is still far from its goal for asteroids smaller than 1km in diameter. Nowadays, the catalog of NEOs contains 20 000 objects. Among them, more than 1 900 objects are classified as Potentially Hazardous Asteroids (PHAs). NEOs and space debris are deeply influenced by gravitational perturbation of Earth and Earth- system. Their irregular shape contribute also to the tumbling or chaotic spin. As a consequence, their coefficient of chaoticity, expressed either by Lyapunov time (Dumitru et al., 2017) or other parameters (Galushina and Sambarov, 2017; Nedelcu et al., 2014) is very important. Thus, their dynamical evolution (ob- ject ephemeris) could be predicted only for short period of time. The surveillance and tracking of these objects is crucial for orbital evolution and the fine tuning of dynamical parameters into their long-term evolution of orbit. During the last years a concept of mobile optical asset for artificial objects and Near-Earth Object observations has been developed inside a Romanian consor- tium (Birlan et al., 2018). The asset will answer to a requirement of recording new and high accuracy astrometric measurements for artificial satellites, space debris and NEOs in order to refine their osculating elements. The article presents the retained solution for the final version of this concept. Optical tests of telescopes and the mount have been performed inside the Astronomi- cal Institute of the Romanian Academy (IAU Code 073) and are be briefly presented.

2. DESIGN OF MOBILE ASSET AND ITS OPTICAL DETECTORS

Several concepts were declined for the mobile asset following the requirements presented in Birlan et al. (2018). One of the newest designs is presented in Figure 1. The container is splitted in two isolated parts, the optical asset and the technical compartment respectively. The rectractabile roof allows lifting the optical system. The container take profit of an exit door for its technical part and the ventilation slits. Autonomous electrical power allows the charging of batteries for the night observations. A weather forecast station is also present, and additional solar panels are installed as alternative power charge of the batteries.

∗http://cineo.jpl.nasa.gouv/stats 3 Telescope calibration for mobile platforms: first results 25

Fig. 1 – Design of mobile asset into a quasi-final stage of development of concept. The container is splitted into a technical part isolated from the observational one which contains optical components.

3. TELESCOPES AND CAMERAS

Crude initial idea was to start with an optical device which can be used for both satellite and NEO tracking and surveillance. Initial simulations for telescope (Birlan et al., 2018) shows that this solution might be feasible in theory, using a 0.6m telescope with large 2◦x2◦ of field of view. Market prospection made it as an evidence that this solution might be hard to be attained. Thus, we reconsidered our ideas throughout a double optical system. In this new design, our choice was oriented to a large (around 0.5m telescope) asset with reasonable field of view (300 – 600) and a relatively small one (0.3 – 0.4m telescope) with large field of view (around 2◦x2◦). The choice of telescopes was for 0.5m telescope RiDK500 f/7 (T05 in this article), and the 0.35m telescope RH350Veloce (T03 in this article) produced by Officina Stellare. T05 is a relatively low and compact telescope with a field of view of about 600x600. The coated optics allow optimal response in the visible 26 Mirel BIRLAN et al. 4 domain. T03 is a compact instrument having a field of view (FOV) of 1.7◦x1.7◦. The ratio between FOV of T03 and T05 is approximately four. Technical solution for the mount was the L600 Alt-Az one provided by Planewave. The Direct drive mount allows an remarkable speed of movement up to 50◦/s. This mount allows to assist both telescopes and the pointing precision falls into our tech- nical requirements. The acquisition of images will be done by two 4x4k pixel matrices: sCMOS FLI Kepler4040 will be used for T03 while FLI ProLine1803 will record the images of T05. In order to be tested both telescopes and mount, the benchmark was organized using facilities of the Astronomical Institute of the Romanian Academy (IAU Code 073). Thus, the mount and telescopes were installed for at least three months on one of pillars inside the institute. This solution allows a flexible schedule and the easiness of access to telescopes for their fine tuning.

4. RESULTS

During February and March 2019 optical systems were tested in the condition of routine work. Thus, the telescopes were pointed toward several azimuths and elevations, for very short, short, and long exposures. The mount was used in both diurnal and differential tracking and the commissioning of mount ends in March 2019.

4.1. OBSERVING NEA 1998 NU

Several NEOs were scheduled and observed after the final benchmark installa- tion of optical components. Part of the consortium members have a long experience in observing NEOs in a routine program (Birlan et al., 2016; Sonka, Gornea, and Bir- lan, 2018) but also as a target of opportunity when the NEO graze the Earth (Sonka et al., 2017; Gornea et al., 2018). Figure 2 presents a mosaic of two images of NEO 1998 NU. The exposure time was 60 seconds for both images, and the dotted square in the mosaic represents the region where the images of the two telescopes overlap. 1998 NU has an apparent of 14.5 and its signal allows clearly the identification of the object.

4.2. OBSERVING ARTIFICIAL OBJECTS

During March 2019 several observational campaigns for recording artificial satellites were performed. These observations were used for both astrometric mea- surements and stress test for the assembly of mount plus telescopes. 5 Telescope calibration for mobile platforms: first results 27

Fig. 2 – Asteroid 1998 NU observed during the night of March 4, 2019. The wide field image is presented on left side. The region inside the dotted square was recorded by the 0.5m telescope and presented on the right side of the mosaic. The asteroid 1998 NU has a visual magnitude of 14.5 and is shown by the arrow. The asteroid is visible in both images.

Two images recorded for the geosynchronous satellite Astra 1N are presented in Figure 3. Astra 1N was launched in August 6, 2011 from French Guiana (Kourou) into a geosynchronous orbit in an orbit with the semi-major axis of 42 165km and zero inclination. The satellite complete its period in 1 436.1 minutes. The surface of the satellite together with its solar panels is around 30m2. Its nominal life should be 15 years. The satellite was recorded for short exposure times, namely 5s for T03 telescope and 10s for T05 one. The paradigm of observing satellites on low Earth orbit (LEO) and medium Earth orbit (MEO) is the same, except that the technical constrains of tracking are more strict. More tests of observing these categories need to be done for the routine observation program.

4.3. DETECTION LIMIT

One of the key factors to fulfill the requirements of our projet is the estimation of magnitude limit for both T03 and T05. For this objective, we keep in mind that our benchmark is not placed into a very good environment for observational astron- omy. Indeed, the Astronomical Institute is located inside the city, into a zone with vegetation, with an altitude of about 100m. However, this benchmark is essential as the first step, for future calibration of telescopes when the mobile asset will be tested 28 Mirel BIRLAN et al. 6

Fig. 3 – Images recording the geosynchronous satellite Astra 1N using both telescopes. These images show also other artificial objects in the vicinity of Astra 1N. The differential tracking was performed, thus geosynchronous satellites are point source objects, while the are trails in both right and left images. in better astroclimatic conditions. In order to determine the limiting magnitude of stellar sources in our telescopes, we acquired short and long exposure images of targets situated at a low airmass. During these tests, we determine the saturation level, the signal-to-noise ratio and the detection limit. We used as reference the magnitudes of NOMAD catalog (Zacharias et al., 2005). Results of these tests are presented in Table 1. The weather conditions were relatively good, with low humidity (20–50%) and the seeing was estimated to 2.800. The observations were made for a region of the sky located at a topocentric hight of 68◦ (an airmass around 1.1). For the T05 telescope the image taken using 10s of exposure time shows that the stars brighter than R=7.4 are completely saturated. The same test for an exposure time of 60s shows that the stars below R=9.4 are also saturated. As it can be seen in Table 1, the detection limit occurs around R=16.2 for an exposure time of 10s and to R=17.5 for an exposure time of 60s. The detection limit can reach R=20 for a stack of 600s. In the case of T03, the detection limit is R=17 for an image obtained using and integration time of 60s. The limitation imposed by the quality of the sky in Bucharest makes our estimations in a first attempt to characterize the optical system. It is however important to mention that these measurements could be extrapolated for an average quality of sky over Romania. Thus, we expect to improve with at least one magnitude the performance of this system. 7 Telescope calibration for mobile platforms: first results 29

Table 1 Synthesis of tests for T05 and T03 telescopes during the night of February 25, 2019. The tests were made at relatively large heights using both single and series of images

T05 Texp(s) Obs Type Heigh(◦) Mag(R) SNR 10 single 1x10 68 10.2 165 10 single 1x10 68 11.8 78 10 single 1x10 68 13.7 11 10 single 1x10 68 15.4 8 10 single 1x10 68 16.2 5 60 single 1x60 68 11.7 168 60 single 1x60 68 12.2 148 60 single 1x60 68 13.9 57 60 single 1x60 68 14.7 36 60 single 1x60 68 15.9 10 60 single 1x60 68 16.7 7 60 single 1x60 68 17.5 4 600 stack 20x30 78 15.5 105 600 stack 20x30 78 16.0 87 600 stack 20x30 78 16.4 59 600 stack 20x30 78 17.2 43 600 stack 20x30 78 18.2 12 600 stack 20x30 78 18.8 9 600 stack 20x30 78 19.7 4 T03 60 single 1x60 65 11.5 198 60 single 1x60 65 12.9 82 60 single 1x60 65 14.2 22 60 single 1x60 65 14.8 13 60 single 1x60 65 16.5 6 60 single 1x60 65 17.0 4 30 Mirel BIRLAN et al. 8

4.4. LONG EXPOSURES, TRACKING ON COMET C/2018Y1(IWAMOTO)

The optical asset was also tested in the condition of long time tracking on the same object. The sky conditions are not ideal while the benchmark is inside the city, thus very long exposures have no relevance. Thus, we tested the ability of telescopes plus mount to track for a long time the same region on the sky. During February 25, 2019 the comet C/2018 Y1 (Iwamoto) (Jaeger et al., 2019) was tracked using the system T03 plus T05. The results of this run is presented in Figure 4. This slice of the mosaic presents eight individual images stacked on the comet C/2018 Y1. The presence of coma and comet tail is visible in the enhanced contrast of the slice (bottom of mosaic in Figure 4).

Fig. 4 – Slice of stack of images containing the comet C/2018 Y1 (Iwamoto) for a total exposure time of 480 seconds. The stack is composed by eight individual images of 60 seconds. The run was made on February 25, 2019 around 16h40mUT, when the comet was at 0.558 AU from Earth. 9 Telescope calibration for mobile platforms: first results 31

4.5. OCCULTATION OF TNO (38628) HUYA On March 18, 2019 a prediction of an occultation by the Trans-Neptunian Object (38628) Huya was computed†. The star ID:4352829408946665600 of Gaia DR2 catalog has a magnitude of H=9.4. The object (38628) Huya belongs to the category (objects having -like orbits). The system was tuned in order to have relatively high speed records. Thus, the event was recorded with 4.1–5.2 seconds of sampling counting an exposure time of 2s of individual images plus the readout between frames. As seen from Bucharest, the occultation occurs for an airmass between 2.0 and 2.1.

20

15

10

Magnitudedrop

5

(38628) Huya

0

0.0350 0.0355 0.0360 0.0365 0.0370 0.0375 0.0380 0.0385 0.0390

Date - 2458560.5 (days)

Fig. 5 – Occultation of star ID:4352829408946665600 by the TNO (38628) Huya.

Compared to the prediction, the occultation band over Earth for this event oc- curs slightly shifted to Romanian territory; however this prediction is remarkable while it benefits of the accuracy of position of star given by Gaia catalog (Lindegren et al., 2018). The result of occultation is presented in Figure 5. The star completely disappeared, thus the flux of star drop to zero (the background level). We confirm the occultation since at least 10 frames show no signal of the occulted star. Thus, the crude estimation of time of occultation is (50 ± 5) seconds. The magnitude drop

†http://lesia.obspm.fr/lucky-star/occ.php?p=15372 32 Mirel BIRLAN et al. 10 is very rapid, within the sampling of our records thus the information of ingress and egress are very small (if exists!) inside the signal of individual images.

5. CONCLUSION

This article presents the stage of concept and realization of a mobile optical asset (Birlan et al., 2018) which will be used for both artificial objects and Near-Earth Object observations. Technical solution for optical asset was to use two telescopes (namely T03 and T05) on the same mount in order to fulfill the requirements of this project. Successful tests were performed for asteroid 1998 NU, artificial satellites Astra 1N, the comet C/2018 Y1(Iwamoto), and the occultation of Trans-Neptunian Object (38628) Huya. All measurements are inside the nominal parameters for which the project was developed. Thus, the detection limit for single exposures of 60s can be R=17 and R=17.5 for T03 and T05 respectively. New observations are ongoing for the astrometric calibration of system camera plus telescope.

Acknowledgements. This scientific study was supported by the grant of the Romanian National Authority for Scientific Research, Program for research – Space Technology and Advanced Research - STAR, project number 465.

REFERENCES

Birlan, M., Nedelcu, D.A., Sonka, A., Popescu, M., Dumitru, B.: 2016, Observations for Secure and Recovery Near-Earth Asteroids. Romanian Astronomical Journal 26, 25 – 33. Birlan, M., Plesca, V., Gandescu, C.H., Nedelcu, D.A., Balan, M., Banica, C., Pandele, C., Sonka, A., Georgescu, T.: 2018, Observational asset for Near-Earth Objects, artificial satellites, and space debris: an assessment of concept. Romanian Astronomical Journal 28, 67 – 77. Dumitru, B.A., Birlan, M., Popescu, M., Nedelcu, D.A.: 2017, Association between meteor show- ers and asteroids using multivariate criteria. Astron. Astrophys. 607, A5. doi:10.1051/0004- 6361/201730813. Galushina, T.Y., Sambarov, G.E.: 2017, The dynamical evolution and the force model for asteroid (196256) 2003 EH1. . Sp. Sci. 142, 38 – 47. doi:10.1016/j.pss.2017.04.019. Gornea, A.I., Sonka, A.B., Birlan, M., Anghel, S.: 2018, Photometric Observtions of Near-Earth Asteroid 2018 GE3. Bulletin 45, 315 – 316. Jaeger, M., Prosperi, E., Vollmann, W., Naves, R., Campas, M., Hasubick, W., Donati, S., Camilleri, P., Oey, J., Groom, R., Stranger, K., Kadota, K., Abe, H., Seki, T., Rodriguez, D., James, N., Cortes, E., Rinner, C., Kugel, F., Bryssinck, E., Diepvens, A., Lindner, P., Dangl, G., Gaitan, J., Gaiyan, J., McCormick, J., Carstens, R., Felber, T., Paul, N., Lutkenhoner, B., Prystavski, T., Bell, C., Buczynski, D., Suzuki, M., Gonzalez, J., Carson, P., Pascoli Observatory, G., Bacci, R., Gerhard, C., Grazzini, L., Iozzi, M., Tombelli, M., Ditz, P., Vandenbulcke, G., Soulier, J.F., Ikemura, T., Sato, H., Nohara, H., Denneau, L., Tonry, J., Heinze, A., Weiland, H., Flewelling, H., Stalder, B., Fitzsimmons, A., Young, D., Erasmus, N., Flynn, R.L., Jacques, C., Pimentel, E., Barros, J., Acosta, A., Sofia, A., Silvia, A., Farfan, R., Wells, G., Bamberger, D., Pratt, A.R., Williams, G.V.: 2019, 11 Telescope calibration for mobile platforms: first results 33

COMET C/2018 Y1 (Iwamoto). Minor Planet Electronic Circulars 2019. Kessler, D.J., Cour-Palais, B.G.: 1978, Collision frequency of artificial satellites: The creation of a debris belt. J. Geophys. Res. 83, 2637 – 2646. doi:10.1029/JA083iA06p02637. Lindegren, L., Hernandez,´ J., Bombrun, A., Klioner, S., Bastian, U., Ramos-Lerate, M., de Torres, A., Steidelmuller,¨ H., Stephenson, C., Hobbs, D., Lammers, U., Biermann, M., Geyer, R., Hilger, T., Michalik, D., Stampa, U., McMillan, P.J., Castaneda,˜ J., Clotet, M., Comoretto, G., Davidson, M., Fabricius, C., Gracia, G., Hambly, N.C., Hutton, A., Mora, A., Portell, J., van Leeuwen, F., Abbas, U., Abreu, A., Altmann, M., Andrei, A., Anglada, E., Balaguer-Nu´nez,˜ L., Barache, C., Becciani, U., Bertone, S., Bianchi, L., Bouquillon, S., Bourda, G., Brusemeister,¨ T., Bucciarelli, B., Busonero, D., Buzzi, R., Cancelliere, R., Carlucci, T., Charlot, P., Cheek, N., Crosta, M., Crowley, C., de Bruijne, J., de Felice, F., Drimmel, R., Esquej, P., Fienga, A., Fraile, E., Gai, M., Garralda, N., Gonzalez-´ Vidal, J.J., Guerra, R., Hauser, M., Hofmann, W., Holl, B., Jordan, S., Lattanzi, M.G., Lenhardt, H., Liao, S., Licata, E., Lister, T., Loffler,¨ W., Marchant, J., Martin-Fleitas, J.M., Messineo, R., Mignard, F., Morbidelli, R., Poggio, E., Riva, A., Rowell, N., Salguero, E., Sarasso, M., Sciacca, E., Siddiqui, H., Smart, R.L., Spagna, A., Steele, I., Taris, F., Torra, J., van Elteren, A., van Reeven, W., Vecchiato, A.: 2018, Gaia Data Release 2. The astrometric solution. Astron. Astrophys. 616, A2. doi:10.1051/0004-6361/201832727. Michel, P.: 2013, Physical properties of Near-Earth Objects that inform mitigation. Acta Astronautica 90, 6 – 13. doi:10.1016/j.actaastro.2012.07.022. Nedelcu, D.A., Birlan, M., Popescu, M., Badescu,˘ O., Pricopi, D.: 2014, Evidence for a source of H chondrites in the outer main . Astron. Astrophys. 567, L7. doi:10.1051/0004- 6361/201423949. Sonka, A.B., Gornea, A.I., Birlan, M.: 2018, Photometric Monitoring of PHA (3122) Florence. Ro- manian Astronomical Journal 28, 79 – 86. Sonka, A.B., Gornea, A.I., Anghel, S., Birlan, M.: 2017, Photometric observations of Near Earth Asteroid 2012 TC4. Romanian Astronomical Journal 27, 223 – 231. Zacharias, N., Monet, D.G., Levine, S.E., Urban, S.E., Gaume, R., Wycoff, G.L.: 2005, VizieR Online Data Catalog: NOMAD Catalog (Zacharias+ 2005). VizieR Online Data Catalog 1297.

Received on 5 April 2019