Launch and commissioning of the PAMELA experiment on board the Resurs-DK1 satellite

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1 Available online at Advances in Space Research 41 (2008) Launch and commissioning of the PAMELA experiment on board the Resurs-DK1 satellite M. Casolino *, P. Picozza, On behalf of the PAMELA collaboration INFN, Structure of Rome Tor Vergata and Physics Department of University of Rome Tor Vergata, Via della Ricerca Scientifica 1, I Rome, Italy Received 9 January 2007; received in revised form 21 May 2007; accepted 23 June 2007 Abstract PAMELA is a satellite borne experiment designed to study with great accuracy cosmic rays of galactic, solar, and trapped nature in a wide energy range (protons: 80 MeV 700 GeV, electrons 50 MeV 400 GeV). Main objective is the study of the antimatter component: antiprotons (80 MeV 190 GeV), positrons (50 MeV 270 GeV) and search for antimatter (with a precision of the order of 10 8 ). The experiment, housed on board the Russian Resurs-DK1 satellite, was launched on June, 15th 2006 in a km orbit with an inclination of 70. The detector consists of a permanent magnet spectrometer core to provide rigidity and charge sign information, a Time-of- Flight system for velocity and charge information, a silicon tungsten calorimeter and a neutron detector for lepton/hadron identification. An anticounter system is used off-line to reject false triggers coming from the satellite. In self-trigger mode the calorimeter, the neutron detector and a shower tail catcher are capable of an independent measure of the lepton (e + + e ) component up to 2 TeV. In this work we focus on the first months of operations of the experiment during the commissioning phase. Ó 2008 Published by Elsevier Ltd on behalf of COSPAR. Keywords: Cosmic rays; Antimatter; Satellite-borne experiment 1. Introduction * Corresponding author. address: Marco.Casolino@roma2.infn.it (M. Casolino). The Wizard collaboration is a scientific program devoted to the study of cosmic rays through balloon and satellite-borne devices. This involves the precise determination of the antiproton (Boezio et al., 1997) and positron (Boezio et al., 2000) spectrum, search of antimatter, measurement of low energy trapped and solar cosmic rays with the NINA-1 (Bidoli et al., 2001) and NINA-2 (Bidoli et al., 2003) satellite experiments. Other research on board Mir and International Space Station has involved the measurement of the radiation environment, the nuclear abundances and the investigation of the Light Flash (Casolino et al., 2003) phenomenon with the Sileye experiments (Bidoli et al., 2001; Casolino et al., 2006c). The PAMELA experiment is a satellite-borne apparatus devoted to the study of cosmic rays, optimized for the detection of the antiparticle component. The system is the main scientific payload of the Resurs-DK1 satellite, primarily devoted to Earth observations. PAMELA has been in data acquisition mode at the time of writing for more than 9 months with all systems working within expected parameters. 2. Scientific objectives PAMELA aims to measure in great detail the cosmic ray component at 1 AU (Astronomical Unit). Its 70, km orbit makes it particularly suited to study items of galactic, heliospheric and trapped nature (Casolino et al., in press). Versatility and detector redundancy allow PAMELA to address at the same time a number of different cosmic ray issues ranging over a very wide energy range, from the trapped particles in the Van Allen Belts, to electrons of Jovian origin (Casolino et al., 2008), the study of the antimatter component of cosmic rays and the composition and spectra of solar particle events (Casolino et al., 2006a). The study of the antiparticle component (p, /$34.00 Ó 2008 Published by Elsevier Ltd on behalf of COSPAR. doi: /j.asr

2 M. Casolino, P. Picozza / Advances in Space Research 41 (2008) e + ) of cosmic rays is the main scientific goal of PAMELA. A long-term and detailed study of the antiparticle spectrum over a very wide energy spectrum will allow to shed light over several questions of cosmic ray physics, from particle production and propagation in the galaxy to charge dependent modulation in the heliosphere to dark matter detection (Hooper and Silk, 2005; Hisano et al., 2006; Lionetto et al., 2005). Also cosmological issues related to detection of a dark matter signature and search for antimatter (PAMELA will search for He with a sensitivity of 10 8 ) will be addressed with this device. 3. Resurs-DK1 satellite The Resurs-DK1 satellite (Fig. 1) is the evolution of previous military reconnaissance satellites flown during in the years It was developed by TsSKB Progress plant 1 in the city of Samara (Russia), in cooperation with NPP OPTEKS, OAO Krasnogorskiy Zavod, NIITP and NTsOMZ (Russia s Science Center for Remote Sensing of Earth). 2 The spacecraft is three-axis stabilized, with axis orientation accuracy 0.2 arcmin and angular velocity stabilization accuracy of /s. The spacecraft has a mass of about 6650 kg, height of 7.4 m and a solar array span of about 14 m. It is designed to provide imagery of the Earth surface for civilian use and is the first Russian non-military satellite with resolution capability of.0.8 m in composite color mode. 3 The imaging system has a coverage area at 350 km of km, obtained with oscillation of the satellite by ±30 in the cross-track direction. Onboard memory capacity is 769 Gbit. The RF communications for the payload data are in X-band at GHz with a downlink data rate of 75, 150 and 300 Mbit/s. PAM- ELA data amounts to about 16 Gbyte/day, sent to ground and processed in NTsOMZ station in Moscow, where also the data analysis and quicklook procedures for PAMELA are performed. 4. Detector description PAMELA is housed in a pressurized container located on one side of the Resurs, as shown in Fig. 3. The Al container has 2 mm thickness in the field of view, an inside diameter of about 105 cm with a semi-spherical bottom and a conical top. In the twin pressurized container is housed the Arina experiment, devoted to the study of the low energy trapped electron and proton component. PAMELA is constituted by a number of highly redundant detectors capable of identifying particles providing charge, mass, rigidity and beta information over a very wide energy range (Picozza, 2007). The instrument (Fig. 2) is built around a permanent Observations are performed in three bands ( lm, lm, lm) each with m resolution to produce a composite color image. magnet (Adriani et al., 2003) with a microstrip tracker (TRK: 6 double sided planes) providing rigidity and sign of charge information. A scintillator system (S1,S2,S3: six layers arranged in three planes) provides trigger, charge and time of flight (b) information (Barbarino et al., 2003). Hadron/lepton separation is performed with a 44 plane silicon tungsten calorimeter (Boezio et al., 2002) (CALO: 16.3 radiation lengths, 0.6 interaction lengths). A shower tail catcher and a neutron detector (Galper et al., 2001) at the bottom of the apparatus (S4 and ND, respectively) increase this separation detecting the number of neutrons produced in the hadronic and electromagnetic cascades. The neutron detector is also employed to measure the neutron field in Low Earth Orbit and in case of solar particle events. An anticounter system (Orsi et al., 2006;Pearce, 2003) (AC) is used to reject spurious events in the off-line phase. Around the detectors are housed the readout electronics, the interfaces with the CPU (Casolino, 2006) and all primary and secondary power supplies. Total weight of PAMELA is 470 kg; power consumption is 355 W, geometrical factor is 21.5 cm 2 sr. The detector is capable of identifying protons (in the energy range 80 MeV 700 GeV), electrons (50 MeV 400 GeV), antiprotons (80 MeV 190 GeV), positrons (50 MeV 270 GeV) and nuclei up to Z = 8 up to.100 GeV. The calorimeter can also function in self-trigger mode to perform with the aid of the neutron detector an independent measure of the lepton (e + e + ) component up to 2 TeV (Galper et al., 2001). A more detailed description of the data acquisition and handling can be found in (Casolino, 2006; Casolino et al., 2006b). 5. Integration, launch and commissioning Pamela was integrated in INFN Rome Tor Vergata clean room facilities; tests involved first each subsystem separately and subsequently the whole apparatus simulating all interactions with the satellite using an Electronic Ground Support Equipment. Final tests involved cosmic ray acquisitions with muons for a total of about 480 h. The device was then shipped to TsKB Progress plant, in Samara (Russia), for installation in a pressurized container on board the Resurs-DK satellite for final tests. Also in this case acquisitions with cosmic muons (140 h) have been performed and have shown the correct functioning of the apparatus, which was then integrated with the pressurized container and the satellite. The detector was then dismounted from the satellite and shipped by air to Baikonur cosmodrome (Kazakstan) where the final integration phase took place in The Soyuz-U rocket was launched from Baikonur Cosmodrome Pad 5 at Site 1, the same used for manned Soyuz and Progress cargoes to the International Space Station. Launch occurred on June 15th 2006, 08:00: UTC with the payload reaching orbit after 8 min. Parking orbit had a semimajor axis of 6642 km. Final boost occurred on June 18th 2006 when the orbit was raised with two

3 2066 M. Casolino, P. Picozza / Advances in Space Research 41 (2008) Fig. 1. (Left) Scheme of the Resurs-DK1 satellite. PAMELA is located in the pressurized container on the right of the picture. In the center panel it is possible to see the container in the launch position and in the extended (cosmic ray acquisition) configuration. In the right panel it is possible to see a photo of the satellite in the assembly facility in Samara. The picture is rotated 180 to compare the photo with the scheme. The dashed circle shows the location of PAMELA pressurized container in the launch position. engine firings to a semimajor axis of 6828 km. The maneuver was completed before 17:00 Moscow time. The transfer orbit resulted in a height increase from km to km, with the apogee of the lower orbit becoming perigee of the final orbit. Also inclination of the satellite (Fig. 4) was increased from to In the same Fig. 2. (Left) Photo of the PAMELA detector during the final integration phase in Tor Vergata clean room facilities, Rome. It is possible to discern, from top to bottom, the topmost scintillator system (S1, S2, S3), the electronic crates around the magnet spectrometer (TRK), the baseplate (to which PAMELA is suspended by chains), the black structure housing the Si-W calorimeter (CALO), S4 tail scintillator and the neutron detector (ND). (Right) scheme approximately to scale with the picture of the detectors composing PAMELA.

4 M. Casolino, P. Picozza / Advances in Space Research 41 (2008) Fig. 3. Photo of PAMELA in the final integration phase with Resurs-DK1 satellite in Baikonur cosmodrome. PAMELA is being integrated in the right pressurized container. The integration was performed with PAMELA in the launch position, with the top pointing nadir. Figure it is also possible to see long-term variations of 0.1 in a period of 5 months due to the oblateness of the Earth. To compensate for atmospheric drag, the altitude of the satellite is periodically reboosted by vernier engines. To perform this maneuver the pressurized container housing PAMELA is folded back in the launch position, the satellite is rotated 180 on its longitudinal axis and then engines are started. Reboost frequency depends from orbital decay, due to atmospheric drag. Up to December 2006 the activity has been low with two small Solar Particle Events in summer and three larger events generated by sunspot 930 in December, so there has not been the need to perform this maneuver so far. In Fig. 5 is shown the value of the angle (Beta angle) between the orbital plane and the Earth Sun vector. This value should vary with a 1-year periodicity but the oblateness of the Earth causes to precess with a higher frequency. The position of the orbital plane affects the irradiation and temperature of the satellite, which is for instance always under the Sun for high values of the absolute value of beta. These thermal excursions are greatly reduced in the pressurized container of PAMELA thanks to the cooling loop with a fluid at a temperature of which maintains the temperature of the detector relatively low and reduces fluctuations within some degrees. As already mentioned Resurs-DK1 oscillates on its longitudinal axis when performing Earth observations: a detailed information of the attitude of the satellite is provided to the CPU of PAMELA in order to know the orientation of the detector with precision of.1. Position and attitude information of the satellite are provided to PAM- ELA CPU via a 1553 interface (used also for Command and Control) and are based on the GLONASS (GLObal Inclination (deg) /05/ /07/ /08/ /10/ /11/2006 Time Fig. 4. Inclination of Resurs satellite as a function of time. The final boost after launch increased inclination of the satellite. It is possible to see secular oscillation of.0.1 and short-term (daily) variation of Fig. 5. Beta angle of satellite. The inclined orbit of the satellite and the oblateness of the Earth result in the precession of the node line resulting in a faster oscillation of the angle.

5 2068 M. Casolino, P. Picozza / Advances in Space Research 41 (2008) from the satellite: the satellite conducted two photographic sessions, lasting 5 s each. On September 15, 2006, Roskosmos announced that testing of the spacecraft was successfully completed on that day and State Commission planned to convene on September 21, 2006, to declare the satellite operational. On September 22, 2006, Roskosmos confirmed that the spacecraft was declared operational as scheduled. Commissioning of the experiment proceeded in parallel with Resurs-DK1 and mostly consisted in a fine tuning of the observational parameters of PAMELA and the on board software, optimizing time and schedule of downlinks to maximize live time of the instrument. 6. In flight data Fig. 6. Counting rates of PAMELA (Hz) as a function of time. Navigation Satellite System), similar to the GPS positioning system. On June 22, ground control successfully tested the Geoton-1 optical-electronic system and the Sangur-1 data receiving and processing system, according to Roskosmos. On June 23, 2006, NTsOMZ received first images PAMELA was first switched on June, 26th 2006: A typical behavior of the acquisition of the device is shown in Fig. 6. The three panels show the counting rate of the three planes and correspond to particles of increasing energy: S11*S12 is triggered by 36 MeV protons and 2.5 MeV e, S21*S22 requires protons and electrons of 9.5 and 63 MeV, respectively, and S31*S32 requires protons and electrons of 80 MeV and 50 MeV (lower energy particles may penetrate the detector from the sides and increase the trigger rate). The higher energy cut is evident in the counting rate of the scintillators: the first SAA passage, corresponding to the easternmost passage is absent in the S3 counting rate. The other two passages in the SAA saturate several times the ADC counting rate of the S1 scintillator but not the other two scintillators. This is consistent with trapped particle models (Gaffey and Bilitza, 1994) considering the power law spectrum of trapped particles in the SAA and the size of the two scintillators. Outside the SAA it is possible to see the increase of particle rate at the geomagnetic poles due to the lower geomagnetic cutoff. The highest rates are found when the satellite crosses the trapped components of the Van Allen Fig. 7. Ground track of PAMELA with counting rate of S11*S12 trigger. Note the particle rate increase in the South Atlantic Anomaly.

6 M. Casolino, P. Picozza / Advances in Space Research 41 (2008) Fig. 8. Counting rates of main trigger of PAMELA ((S11*S12)*(S21 + S22)*(S31 + S32)), corresponding to (p P 80 MeV, e P 50 MeV). Fig. 9. b = v/c of particles measured with PAMELA (Y-axis) as a function of geographic latitude (X-axis). It is possible to see how particles with lower beta are only visible at the geographic poles due to lower particle cutoff. Only high rigidity particles are found at the equator. Particles with negative beta are mostly due to albedo protons. The high flux region in the 40:0 range of latitudes and low b is due to particles trapped in the South Atlantic Anomaly. Albedo trapped particles are also visible in the b < 0 range. Colour scale represents rigidity coming from the tracker. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this paper.) Belts. In Fig. 7 is plotted the same trigger rate as a function of the ground track of PAMELA, showing the inclination of the orbit of satellite and the particle rate increase in the polar and South Atlantic regions. The pause in the acquisition at the equator are due to the calibration of the subdetectors usually performed during the ascending phase to avoid crossing the radiation belts. In Fig. 8 is shown PAMELA world particle rate for the trigger counter requiring that particles cross at least on scintillator in each plane (S1, S2, S3) and corresponding to P50 MeV e and P80 MeV protons. It is possible to see the high flux of the trapped protons in the South Atlantic anomaly and the geomagnetic cutoff effect on galactic particles. Particle rate increases close to the magnetic poles and decreases close to the equator. This trigger threshold is too high to show the contribution of trapped electrons, which have a maximum energy of 7 MeV and are visible only using topmost scintillators (Casolino et al., in press). In Fig. 9 is shown the plot of particle b = v/c measured from the Time-of-Flight system as function of the geographical latitude. Particles with b < 0 are albedo events, mostly protons since low energy albedo electrons interact with the calorimeter and are absorbed without triggering the system. Slower (low b) particles are more abundant at highest and lowest latitudes where the geomagnetic cutoff is lower. At the equator most par-

7 2070 M. Casolino, P. Picozza / Advances in Space Research 41 (2008) ticles have b. 1 since a higher energy is required not to be deflected by the geomagnetic field. In the plot are also visible protons trapped in the SAA in the latitude region 45 to 0. Trapped particle population is composed of mostly E MeV protons, with lowest particles trapped at lower latitudes for the orbits considered. Also albedo trapped particles are visible at the same latitude range. Color code (visible in the online version) indicates particle rigidity as measured from the tracker. The b. 1, low rigidity band due to electrons, not observable in the b. 1 range since albedo electrons shower in the calorimeter. 7. Conclusions PAMELA was successfully launched on June 2006 and is currently operational in Low Earth Orbit. The satellite and the detectors are functioning correctly. It is expected that data from PAMELA will provide information on several items of cosmic rays physics, from antimatter to solar and trapped particles. References Adriani, O., Bonechi, L., Bongi, M., et al. The magnetic spectrometer of the PAMELA satellite experiment. Nucl. Instr. Meth. Phys. Res. A 511, 72 75, Barbarino, G.C., Boscherini, M., Campana, D., et al. The PAMELA time-of-flight system: status report. Nucl. Phys. Proc. Suppl. B 125, , Bidoli, V., Canestro, A., Casolino, M., et al. In orbit performance of the space telescope NINA and Galactic cosmic-ray flux measurements. Astrophys. J. 132, , Bidoli, V., Casolino, M., De Pascale, M.P., et al. Isotope composition of secondary hydrogen and helium above the atmosphere measured by the instruments NINA and NINA-2. J. Geophys. Res. 108 (A5), , Boezio, M., Carlson, P., Francke, T., et al. The cosmic ray antiproton flux between 0.62 and 3.19 GeV measured near solar minimum activity. Astrophys. J. 487, , Boezio, M., Carlson, P., Francke, T., et al. The cosmic-ray electron and positron spectra measured at 1 AU during solar minimum activity. Astrophys. J. 532, , Boezio, M., Bonvicini, V., Mocchiutti, E., et al. A high granularity imaging calorimeter for cosmic-ray physics. Nucl. Instr. Meth. Phys. Res. A 487, , Bidoli, V., Casolino, M., Morselli, A., et al. In-flight performance of SilEye-2 experiment and cosmic ray abundances inside the Mir space station. J. Phys. G 27, , Casolino, M., Bidoli, V., Morselli, A., et al. Dual origins of light flashes seen in space. Nature 422, 680, Casolino, M. The PAMELA storage and control unit. Adv. Space Res. 37 (10), , Casolino, M., Altamura, F., Basili, A. Cosmic ray observation of the heliosphere with the PAMELA experiment. Adv. Space Res. 37 (10), , 2006a. Casolino, M., De Pascale, M.P., Nagni, M., Picozza, P., et al. YODA++: a proposal for a semi-automatic space mission control. Adv. Space Res. 37 (10), , 2006b. Casolino, M., Bidoli, V., Minori, M., et al. Relative nuclear abundances inside ISS with Sileye-3/Alteino experiment. Adv. Space Res. 37 (9), , 2006c. Casolino, M., Picozza, P., Altamura, F. et al. Launch of the space experiment PAMELA. Adv. Space Res., in press, doi: / j.asr Casolino, M., Di Felice, V., Picozza, P. Detection of the high energy component of Jovian electrons at 1 AU with the PAMELA experiment. Adv. Space. Res. 41, , Gaffey, J., Bilitza, D. NASA/National Space Science Data Center trapped radiation models. J. Spacecraft Rockets 31 (2), Available from: < Galper, A.M. et al. Measurement of primary protons and electrons in the energy range of ev in the PAMELA experiment. In: Proc. 27th Int. Cosm. Ray Conf., Hamburg, OG , Hisano, J., Matsumoto, S., Saito, O., Senami, M. Heavy wino-like neutralino dark matter annihilation into antiparticles. Phys. Rev. D 73, , Hooper, D., Silk, J. Searching for dark matter with future cosmic positron experiments. Phys. Rev. D 71, , Lionetto, A.M. Morselli, A. Zdravkovic, V. Uncertainties of Cosmic ray spectra and detectability of antiproton msugra contributions with PAMELA, JCAP , Available from astro-ph/ Orsi, S., Carlson, P., Lund, J., et al. The anticoincidence shield of the PAMELA space experiment. Adv. Space Res. 37 (10), , Pearce, M., Carlson, P., Lund, J. The anticounter system of the PAMELA space experiment. In: Proc. of the 28th Int. Cosm. Ray Conf., Tsukuba, Japan, OG 1.5, , Picozza, P., Galper, A.M., Castellini, G. et al. PAMELA A Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics, astroph/ Astrop. Phys., 27 (4), , 2007.