DSP (Double Star Project)
Double Star is a joint ESA (European Space Agency) / CNSA (China National Space Administration) project to study the effects of sun radiation on Earth's space environment (i.e., magnetosphere in geospace), in particular the 'magnetotail', where storms of high-energy particles are being generated. The DSP mission consists of two spacecraft, each designed, developed, launched, and operated by CAS/CNSA (Chinese Academy of Sciences/China National Space Administration). The orbital design of the two minisatellites considers a so-called mini-cluster with one spacecraft in near-equatorial- and the second spacecraft in polar orbit. DSP is in fact providing new measurements in key regions of the magnetosphere. The coordinated and simultaneous measurement capability of DSP with ESA's Cluster-II mission from various perspectives promises an optimum exploitation in observation returns. In China, the two spacecraft missions are referred to as TC (Tan Ce), meaning Explorer. The science objectives of DSP are to: 1) 2) 3) 4)
• Provide high-resolution field, particle and wave measurements in several important near-Earth active regions which have not been covered by existing ISTP (International Solar-Terrestrial Physics Program) missions, such as the near-Earth plasma sheet and its boundary layer, the ring current, the radiation belts, the dayside magnetopause boundary layer, and the polar region
• Study magnetic reconnection at the magnetopause and in the magnetotail. Investigate the 3-D small and mid-scale structures and the magnetic reconstruction in the boundary layer of the magnetopause - making use of different interplanetary conditions and to study the disturbance processes that transfer to the ionosphere
• Study and understand the trigger mechanics of magnetic storms and substorms, their role in the global response, and the processes of magnetotail and ionospheric processes
• Study of the temporal and spatial variations of magnetospheric particle storms in order to understand the processes/phenomena of particle acceleration, diffusion, injection, precipitation, and up-flowing during particle storms.
Background: In 1992, the Chinese approached ESA with a proposal to establish a Data and Research Center in Beijing for Europe's Cornerstone Cluster mission. A cooperation agreement to this effect was signed on Nov. 25, 1993. - In the time frame 1997/99, the Chinese DSP mission, under definition at the time, was presented to ESA and eventually accepted/integrated into an international cooperation agreement with ESA's Cluster-II mission, following successful discussions of CAS/CNSA and with the member agencies of Working Group 2 of IACG (Inter-Agency Consultative Group). A formal ESA/CNSA cooperation agreement was signed on July 9, 2001.
Double Star is the first major collaboration between Europe and China on a scientific space mission. The coordination of Double Star with Cluster extends to the reuse of many Cluster ideas: a) seven of the eight European instruments on the two DSP spacecraft are copies of instruments on Cluster-II, b) the re-use of the Cluster science operations centre to coordinate operation of the European payload, and c) re-use of Cluster software for dissemination of data products. Most importantly, the European teams working on Double Star are largely drawn from the Cluster teams and thus have a long and successful history of working together. In addition, the DSP mission is also employed in support of IACG campaigns. 5)
The two DSP satellites were designed and built by DFHSat (DFH Satellite Co. Ltd.), a manufacturing/operating unit of CAST (Chinese Academy of Space Technology), Beijing, using the CAST968 bus. Each S/C is spin-stabilized with a cylindrical structure of size 2.1 m diameter and 1.23 m in height with two 2.5 m experimental rigid booms and two axial telecommunication antenna booms (the magnetometers are boom-mounted). The total mass of each minisatellite is 330 kg at launch (payload mass of 30 kg). Electrical power is provided by surface-mounted silicon solar cells. The total solar array has a size of 6.33 m2, providing a power of 260 W (BOL) and 210 W (EOL). NiH2 batteries (four modules) of 36 Ah capacity are used for the night phase of the orbit. The attitude control system orients the spin axis of the S/C normal to the ecliptic plane. The spin rate is 15 rpm; the S/C pointing accuracy is <5º with a pointing knowledge of <0.5º. All onboard communication/processing is provided by a CAN (Controller Area Network) bus; the payload communicates via a MIL- STD-1555B bus with CAN. Mission design life: >18 months for the near-equatorial S/C, and >12 months for the polar S/C. 6)
Figure 1: Illustration of the DSP spacecraft in its launch configuration (image credit: ESA)
Figure 2: Artist's view of deployed DSP spacecraft (image credit: ESA)
Figure 3: Cutaway view of the DSP spacecraft (image credit: CAST)
The RF communication (TT&C and payload data) is provided in S-band. The uplink data rate is 1 kbit/s; the downlink data rates are: 256 bit/s and 2048 kbit/s for the TT&C functions, and 16 kbit/s, 128 kbit/s, or 1.024 Mbit/s for the payload data (the selected downlink rate is dependent on the orbital distance between the S/C and the ground stations). The CCSDS protocol is used for payload data transmissions. An on-board data storage capacity of 2 Gbit is provided.
Launch DSP-1: The launch of the equatorial DSP-1 spacecraft, also referred to as TC-1 (Tan Ce-1, meaning ”Explorer-1” in Chinese), took place Dec. 29, 2003 from the Xichang Launch Center, China, using a Long March 2C/SM launch vehicle.
Launch DSP-2: The launch of the polar spacecraft, DSP-2 (TC-2), took place on July 25, 2004 from the Taiyuan launch site in China, using a CZ-2C/CTS launch vehicle. The launch provider was the China Great Wall Industry Corporation.
Orbits of the DSP spacecraft:
The two DSP orbits are being synchronized with those of ESA's four Cluster satellites so that all six spacecraft are studying the same region of near-Earth space at the same time. This orbital configuration will enable scientists to obtain simultaneous data on the magnetic field and population of electrified particles in different regions of the magnetosphere.
Orbit of the equatorial satellite DSP-1 (TC-1): HEO (Highly-elliptical Earth Orbit) with a perigee of 565 km and an apogee of 78,970 km (~12 RE), inclination = 28.5º, Kepler period of 21 hours (Note: due to an over-performance of the upper stage the apogee is about 12 000 km more than expected). This orbit enables the payload to observe the Earth's huge magnetic tail, the region where particles are accelerated towards the planet's magnetic poles by a process known as reconnection. Note: DSP-1 is also referred to as DSP-E (meaning equatorial).
Orbit of the polar satellite DSP-2 (TC-2): HEO with a perigee of 700 km, an apogee of 39,000 km, and an inclination of 90º; Kepler period = 11.74 hours. Its instruments will concentrate on the physical processes taking place over the magnetic poles and the development of auroras. It is expected to operate for at least one year. Note: DSP-2 is also referred to as DSP-P (meaning polar).
Figure 4: Schematic of DSP orbits (image credit: ESA)
Figure 5: Illustration of Double Star orbits in relation to Cluster-II (image credit: ESA)
Figure 6: Earth's magnetosphere with the orbit of the TC-1 spacecraft (yellow) and the Cluster satellite quartet (in red) in May 2004 (image credit: ESA)
Status of DSP mission:
Unfortunately, contact with Double Star TC-2 spacecraft was not reestablished by the end of 2009, which marks the end of the predicted operational DSP mission lifetime. The Chinese and European operations, project science and instrument teams have initiated the archiving phase of the mission. 7)
• The TC-2 spacecraft was operational as of 2008. Then, from August 2008 onwards, TC-2 lost the ability to demodulate the signal. The RF signal was still received after that time which means that the spacecraft was still sending information but this information was not properly encoded onboard. - There was hope to restore the ability to decode the signal again after the eclipse season in November 2008. However, there was no success so far (up to May 2009). The Chinese operators continue trying to recover the spacecraft in the prevailing non-eclipse season. 8)
• The TC-1 spacecraft was decommissioned on Oct. 14, 2007 when it reentered the Earth's atmosphere and disintegrated. TC-1 provided almost 4 years of operational service - yielding new perspectives concerning the boundaries of the magnetosphere and the fundamental processes that are playing a role in the transport of mass, momentum and energy into the magnetosphere. 9)
• The DSP mission is operating nominally as of mid-2007. The European Payload Operation System, which coordinates the operations for the seven European instruments, is running smoothly. Data are acquired using the VILSPA-2 ground station in Spain and the Beijing and Shanghai stations in China. 10)
In October 2007, TC-1 will enter Earth's atmosphere. The Chinese (CSSAR) have confirmed the intention to continue operations of TC-2. For ESA, operating only TC-2 will be much simpler because it involves only two instruments instead of seven and VILSPA-2 will not be needed for the smaller volume of data.
• In Nov. 2006, ESA approved a 9 months extension of ESA involvement in the Double Star Programme (DSP) operations from 1 January 2007 to 30 September 2007. Operations of DSP-1 are expected to end in Sept. 2007 with a reentry of the spacecraft into the atmosphere. 11) 12)
• Using coordinated observations of the CNSA/ESA Double Star and ESA/NASA Cluster missions in Sept. 2006, a team of European and US scientists revealed new features of magnetic reconnection at the Earth's magnetopause. These results improve our knowledge on how, where and under which conditions the solar wind manages to penetrate the Earth's magnetic shield on the flank of the magnetosphere. 13)
• In the summer of 2005, the ESA Science Program Committee approved an extension of the DSP mission until the end of 2006. The two spacecraft and their instruments are operating nominally.
• During the largest geomagnetic storm of 2004, the redundant attitude computer failed on TC-1 spacecraft. Now both spacecraft have non functioning attitude computers. The consequences are no attitude control of the spacecraft. Fortunately, both spacecraft are spinning at 15 rpm and are therefore stable. A slow drift of the spin axis is observed about 0.9º per month on TC-1 and 1.5º per month on TC-2. This means that there should not be problems up to end of nominal mission lifetime (July 31, 2005).
• The TC-1 spacecraft was declared ”operational” in March 2004 following the initial commissioning phase after launch. 14)
• The TC-2 spacecraft was declared “operational” as of April 18, 2005.
The following instruments are provided by ESA: ASPOC, FGM, HIA, PEACE, STAFF/DWP, and NAI. The other instruments are provided by CAS (Chinese Academy of Sciences), they were designed and developed by CSSAR (Center for Space Science and Applied Research) of CAS, Beijing. Both spacecraft carry the sensor complement as outlined in Tables 1 and 2. Each instrument is built by a team under the leadership of a PI (Principal Investigator).
Table 1: Summary of instruments and some instrument parameters on TC-1
Table 2: Summary of instruments and some instrument parameters on TC-2
ASPOC (Active Spacecraft Potential Control):
ASPOC is flown on TC-1. PI: K. Torkar, IWF (Institut für Weltraumforschung), Graz, Austria. Objective: control of the S/C potential and to ensure the measurement of the low energy . The science objectives are to:
• Reduce positive potentials of the satellite
• Ensure the accurate measurements of low energy ions of HIA and LEID
• Ensure the accurate measurements of low energy electrons of PEACE
• Study of the temporal and spatial variation of low energy ions, and of low energy ions based on the data of HIA and PEACE
• Study of the interaction between spacecraft and ambient plasma.
Figure 7: The ASPOC instrument (image credit: ESA)
ASPOC prevents a buildup of positive electrical charge on the spacecraft by emitting indium ions into space. The instrument mass is 1.54 kg for electronics box + harness, and 1.9 kg for two emitter modules with cover. The total size is: 187 mm x 157 mm x 170 mm. Instrument power = 2.4 W; beam species = In+; atomic mass = 113,115 amu; energy range of 5 to 9.5 keV; current = 50 to 80 µA (max); typical is 15 µA. Opening angle with a direction of ±15º (half maximum) along the spin axis. The data rate is 0.13 kbit/s. The instrument design life is 32,000 h at 10 µA. 15)
Figure 8: 6. Electric block diagram of Double Star ASPOC (image credit: ESA)
FGM (Flux Gate Magnetometer):
FGM is flown on TC-1 and TC-2. PI: C. Carr of IC (Imperial College), London, UK for FGM on TC-1. PI: T. Zhang, IWF, Graz, Austria for FGM on TC-2 (there are two non-identical FGMs per spacecraft). The objective is the measurement of the 3-D magnetic field vector and its spatial variation with high time resolution. The specific science objectives are to:
• Measure the thickness of the plasma sheet near the Earth during the period of magnetic quiet as well as magnetic activity
• Study of the evolution of the three vector components of magnetic field in a substorm and the position of the inner-edge of the plasma sheet during magnetic field di-polarization
• Study of the acceleration process and transmission of the upflowing oxygen ions in the magnetosphere near Earth. Combining of the data with Cluster II, study the reconnection of the magnetic field in the plasma sheet region near Earth
• Study of the variation of magnetic fields in regions of radiation belts during substorms, as well as current ring and plasmasphere analysis
• Study of the variation of the shape and position of cleft in various interplanetary magnetic field conditions
• In different interplanetary magnetic field conditions, study of the variation of the shape and position of cleft
• In different interplanetary magnetic field conditions, study of the position variation of the magnetopause at dayside, and study of the processes of flux transfer events as well as reconnection of the magnetic field in the magnetopause boundary layer at dayside.
The FGM instrument is mounted on a boom of 3.5 m length, it has a total mass of 2.736 kg, and a size of 98 mm x 51 mm x 30 mm. Its measurement range is from -65,536 nT to +65,504 nT. The power consumption is 2.46 W, the data rate is 3.2 kbit/s in vector mode and 0.05 kbit/s in background vector mode. In addition, there is a Low Mass Fluxgate magnetometer of size: 30 mm x 30 mm x 30 mm. The size of the electronic units is: 126 mm x 110 mm x 110 mm.
PEACE (Plasma Electron And Current Experiment):
PEACE is flown on TC-1 and TC-2. PI: A. Fazakerley, MSSL (Mullard Space Science Laboratory) of UCL (University College London), Dorking, UK. PEACE consists of a set of two instruments: LEFA = Low Energy Electron Analyzer. The instrument is a spherical electrostatic analyzer with a FOV of 180º x 3.8º. The second instrument, HEFA (High Energy Electron Analyzer), is a troidal electrostatic analyzer with a FOV of 360º x 4.6º. The Cluster spare instrument has been split into two instruments: one sensor is on board the equatorial spacecraft and the other is on board the polar spacecraft.
The objective to detect electrons in the energy range from 1eV to 26 keV in the upper ionosphere, the plasmasphere, the auroral acceleration region, the cusp/cleft, and in the near-Earth plasma sheet. The detected electrons in these regions play an important role in the dynamics. The science objectives are to:
• Study of the dynamic processes of the upper ionosphere, in particular the temporal- spatial variation of the electrons during the magnetic storm and substorm. Also study of the instabilities and the inhomogeneity in the upper ionosphere.
• Study of the temporal-spatial variation of the electrons in the plasmasphere, as well as the coupling process of the electrons in the ionosphere and the plasmasphere.
• Investigate the processes of acceleration and precipitation of the electron in the polar region, polar wind transfer process to the magnetosphere, the electron behavior in the magnetosheath transfer process to the cusp/cleft and high latitude boundary layer in different interplanetary conditions.
• Study of the dynamic process of electrons in the near-Earth plasma sheet, including instability, heating, acceleration, injection, diffusion and precipitation of electrons.
Figure 9: The PEACE instrument (image credit: MSSL)
PEACE has an instrument mass of 6.018 kg, power consumption of 4.713 W (max. of 8.457 W); the measurement ranges are: LEEA (Low Energy Electrostatic Analyzer) = 1 eV - 1 keV; HEEA (High Energy Electrostatic Analyzer) = 30 eV-26 keV; the instrument size is: DPU: 252 mm x 126 mm x 160 mm; LEFA: 304 mm x 143 mm x 137 mm. The temperature range is -10º to +40ºC. The data rate is 3.54 kbit/s in normal mode and 15.98 kbit/s in burst mode.
HIA (Hot Ion Analyzer):
HIA is flown on TC-1 only. PI: H. Rème, CESR (Centre d'Etude Spatiale des Rayonnements), Toulouse, France. HIA measures the energy spectrum and 3-D ion distribution in the upper ionosphere, the plasmasphere, the ring current, the near Earth plasma sheet and the dayside magnetopause boundary layer. Specific science objective are to:
• Study the spatial and temporal variation of the distribution of the ions at the upper ionosphere
• Study the spatial and temporal variation of the ions, ion instabilities and the wave-particle interaction at the plasmasphere as well as the variation of the location of the plasmapause during a magnetospheric substorm and magnetic storm
• Study the acceleration and transport processes of the upflowing O ions towards the plasmasphere
• Study the acceleration and injection towards the ring current of the hot ions at the near Earth plasma sheet during the magnetospheric substorm
• Study the transport process of the ions through the dayside LLBL (Low Latitude Boundary Layer) towards the magnetosphere; study of the 3-D construction and temporal variation of the hot ions during the magnetic reconnection and FTEs (Flux Transfer Experiment) at the magnetopause boundary layer.
The HIA instrument has a measurement range of 5 eV to 30 keV; the mass is 2.65 kg, the size is 330 mm x 142 mm x 120 mm, the power consumption is 2.5 W. The energy distribution (FWHM) is 18%; the time resolution is 62.5 ms (for 2-D measurements) and 4 s for 3-D measurements. The angular resolution is 5.6º x 5.6º; the dynamic range is 104 to 2x1010. The data rates are: 2.135 kbit/s or 13.162 kbit/s.
Figure 10: The HIA instrument (image credit: ESA)
HID (Heavy Ion Detector):
HID is flown on TC-1 and TC-2. PIs: Y. Zhai and J. B. Cao, CSSAR, China. The objective is the measurement of ions in the energy range from 10 MeV (He) to 8 GeV (Fe) and an atomic number from 2 (He) to 26(Fe). Specific science objective are to:
• Detect and study the component, energy spectrum and flux of heavy ions of galactic cosmic rays
• Detect and study the component, energy spectrum and flux of heavy ions of solar cosmic rays
• Detect and study the component, energy spectrum and flux of heavy ions of radiation zone
• Detect new component of heavy ions with medium and high energy in magnetosphere.
The instrument has a mass of 2.2 kg, a power consumption of 1.2 W, and a size of 150 mm x 120 mm x 170 mm; full angle = 60º; measurement range = 10 MeV (He+) to 8 GeV (Fe); dynamic range = 0-105 s; sampling interval = 1 s; temperature range = +5ºC to +25ºC; data rate = 0.32 kbit/s. Continuous instrument operation.
HEED (High Energy Electron Detector):
HEED is flown on TC-1 and TC-2. PIs: W. Zhang and J. B. Cao, CSSAR, China. The objective is to detect electrons in the energy range of 100 keV to 10 MeV. Specific science objectives are to:
• Study the spatial and temporal variation of the distribution of the radiation belt electrons during the magnetospheric substorm and magnetic storm
• Study the acceleration mechanism of the high energy electrons in the near-Earth magnetosphere during CMEs (Coronal Mass Ejections)
• Study the precipitation processes of the high energy electrons as well as the attitude and latitude distribution of their flux during the magnetospheric substorm and magnetic storm
• Study the spatial and temporal variation of the high-energy electrons at the near-Earth plasma sheet as well as their injection towards the radiation belt and ring current regions.
The instrument has a mass of 2.2 kg, power consumption of 1.2 W, and a size of 150 mm x 120 mm x 170 mm. The geometric factor is 0.1105 cm2 sr; the opening angle is 40º. The electron measurement range is from 150 keV to 6 MeV; the temperature range is from +5º to +25ºC; the data rate is 0.32 kbit/s. Continuous instrument operation.
LEID (Low Energy Ion Detector):
LEID is flown on TC-2 only. PIs: Q. Ren and J. B. Cao, CSSAR, China. It measures the low energy ions in the range of 30 eV to 40 keV. LEID is used to detect the energy spectrum, distribution function and differential flux of ions with low and medium energy in regions of auroras, cleft and polar cap. Specific science objective are to:
• Study the transmission process and acceleration mechanism of upflowing ions in the auroral ionosphere
• Study the transmission process of upflowing ions from the cleft ionosphere both to the high-latitude magnetopause boundary layer and to the magnetopause boundary layer at the dayside
• Study the transmission process of magnetosheath ions through the cleft and the high- latitude magnetopause boundary layer to ionosphere and plasma sheet
• Study the transmission process of polar wind ions into the magnetosphere.
The LEID instrument has a mass of 3.1 kg, size of 330 mm x 150 mm x 130 mm, power consumption of 2.9 W, and a data rate of 1 kbit/s.
HEPD (High Energy Proton Detector):
HEPD is flown on TC-1 and TC-2. PIs: J. Liang and J. B. Cao, CSSAR, China. The objective is the energy measurement in the range of 1 - 1000 MeV. Specific science objectives are to:
• Study the energy spectrum and of the flux of solar cosmic rays (solar proton events) and galactic cosmic rays at the near-Earth magnetosphere; especially, study the time variation and distribution with height and latitude of the protons of solar cosmic rays during the period of substorm and magnetic storm
• Study the processes of time and space variation of the protons of radiation belts during the periods of substorm and magnetic storm
• Study the variation process of the protons of radiation belts during the period of solar proton events
• Study the processes of solar-cosmic-rays protons from the cleft, the polar cap and the auroral zone to low-ionosphere, and the causes that influence the processes of the ionosphere in the polar region.
The instrument has a mass of 2.2 kg, a power consumption of 1.2 W, and a size of 150 mm x 120 mm x 170 mm. The geometric factor is 0.1105 cm2 sr; the opening angle is 40º; the measurement range is 1-1000 MeV; dynamic range = 0 - 105 s; sampling interval = 0.33 s; temperature range = +5º to +25ºC; data rate = 0.32 kbit/s; continuous operation of instrument.
LFEW (Low Frequency Electromagnetic Wave) Detector:
LFEW is flown on TC-2 only. PIs: Z. Wang and J. B. Cao, CSSAR, China. The objective is to detect the frequency in the range from 8 Hz to 10 kHz in the various regions of the magnetosphere. Specific science objectives are to:
• Study the generation mechanism and propagating characters of low frequency electromagnetic waves at the plasmapause region, and the acceleration/diffusion and precipitation processes of the particles
• Study the instabilities, exciting processes of the low frequency electromagnetic waves (electrostatic ion cyclotron wave, low hybrid wave, etc.) in the auroral and cusp regions, and their accelerating effects on the upflowing ions (H+, O+ and He)
• Study the exciting mechanism of low frequency electromagnetic waves (including magnetic pulsation, Alfven wave, low hybrid wave) in the plasma sheet and the plasma sheet boundary layer during the magnetosphere substorm and magnetic storm; its relations with the magnetosphere substorm; and the heating, acceleration and diffusion processes of ionospheric upflowing ions and plasma sheet thermal ions interacting with these waves.
The instrument has a mass of 4 kg, a power consumption of 5W, and a sensor size of 25 mm (diameter) x 240 mm x 300 mm; the electronic unit size is: 150 mm x 180 mm x 200 mm. The measurement range is from 8 Hz to 10 kHz; the data rate is 3 kbit/s.
STAFF/DWP (Spatio-Temporal Analysis of Field Fluctuations) / (Digital Wave Processor):
STAFF/DWP is flown on TC-1 only. PIs: N. Cornilleau-Wehrlin, CETP (Centre d'etude des Environnements Terrestre et Planetaire), Velizy, France, and H. Alleyne, Sheffield University, UK. The objective is to detect the energy spectrum, the 3-D distribution and the differential flux of the energetic particles (including electrons, protons and O ions) in the radiation belt, ring current, near-Earth plasma sheet and in the dayside LLBL. Specific science objectives are to:
• Study the spatial and temporal variation of the distribution of the energetic particles at the near-Earth plasma sheet, and to explore the acceleration, diffusion, injection and precipitation processes of the energetic particles at the near earth plasma sheet during the magnetospheric substorm
• Study the spatial and temporal variation of the low energy electrons and protons at the radiation belt during the magnetospheric substorm and magnetic storm
• Study the acceleration process of the high energy electrons in the near-Earth magnetosphere during CMS
• Study the acceleration and transport processes of the upflowing O ions in the near- Earth magnetosphere
• Study the spatial variation process of the protons/O ion ratio at the ring current during a magnetic storm.
A magnetometer at the end of a 3.5 m long boom looks at waves (rapid variations in the magnetic fields), particularly in regions where the solar wind interacts with the magnetosphere. Low-frequency data are analyzed on the ground, while the magnetic components of the higher frequency waves are processed onboard. It also has a particle correlator that enables variations in the electron population around the spacecraft to be compared with the wave measurements.
Figure 11: Illustration of the STAFF/DWP instrument
The STAFF/DWP instrument has a mass of 5.6 kg and a power consumption of 4.5 W. The particle measurement ranges are: Electrons = 20 keV - 400 keV; Protons = 40 keV - 1500 keV; Helium = 40 keV - 150000 keV; Oxygen = 40 keV - 4000 keV. Mass classes: 1, 4, 12-16, 28-56 amu. FOV (Field of View) = ±3ºx 180º(IIMS), = ±17.5º x 180º (IES); Angular coverage: Polar(range/interval) = 180º/12 (IIMS), = 180º/9 (IES). The instrument size is: 351 mm x 200 mm x 208 mm; the data rates are: 1.024 kbit/s, or 4.627 kbit/s.
NAI (Neutral Atom Imager):
NAI is also referred to as NUADU (Neutral Atom Detection Unit), flown on TC-2 only. PI: Susan McKenna-Lawlor, STI Ltd., National University of Ireland, Co. Kildare, Ireland. It provides the global imaging of the inner magnetosphere by means of the ENA (Energetic Neutral Atoms) imaging technique, which is of special importance for the ring current. The instrument is based on an instrument flying on ESA's Mars Express mission. The Swedish Institute of Space Physics (IRF) participated in the development of NUADU. 16)
Specific science objectives are to:
• Measure the temporal and spatial variation of particles, and the dynamics in the ring current, the radiation belt and the near-Earth plasma sheet, in comparison with the data of some in-situ instrument.
• Study the global distribution and changing process of the ring current particles during quiet times and storm times
• Study the global distribution and changing process of the low energy particles in the radiation belt during quiet times and storm periods
• Study the global structure change of the near-Earth plasma sheet during quiet times and storm times, including the thickness and inner boundary
• Study the triggering and developing process of geomagnetic storm and substorm by means of the global image of the plasma sheet and ring current.
The NAI instrument has a mass of 3.13 kg, a power consumption of 4.0 W, and a size of 287 mm x 142 mm x 111 mm. The instrument comprises an array of solid state detectors to measure the ENA flux in the energy range 15 - 300 keV. The data rate is 4.9 kbit/s in normal mode and 78 kbit/s in burst mode.
Figure 12: Illustration of the NUADU (or NAI) instrument (image credit: ESA, IRF)
Table 3: Overview of the major observation zones of the two constellations
DSP ground segment:
The DSP spacecraft are monitored and controlled by CSSAR (Center for Space Science and Applied Research), Beijing, China.
There are two ground receiving stations, one located near Beijing (70 km northeast of the city in Miyun County, 11 m dish antenna), the other near Shanghai (100 km southwest of the city, 25 m antenna dish). In addition, the ESA station at Villafranca, Spain, receives DSP payload data directly (VILSPA-2). CSSAR is collecting the data from Beijing and Shanghai while ESOC is collecting the data from Villafranca.
As a part of the DSP Ground Data System, the EDDS (European Data Disposition System) has two main tasks:
• Mirroring the Double Star raw data from China to Europe
• Providing access to the raw data to the European instrument teams and data centers.
The raw data, acquired by the three ground stations, are decommutated and ordered by instruments by the Chinese DSAS (Double Star Science Application System). These data are then sent to the IWF data system (EDDS) in Graz, Austria, where the PI teams can access them on-line. After arrival at the PI institute, the data are processed and the summary (SP) and prime parameters (PP) are produced and sent to the DSDS (Double Star Science Data System). DSDS consists of four National data centers that distribute SP and PP data to the scientific community. The four centers are located at: 17)
• CSSAR, Beijing, China; CSSAR is providing the operation of DSAS (Double Star Science Application System)
• IWF (Institut für Weltraumforschung), Graz, Austria; IWF is providing the EDDS function
• RAL (Rutherford Appleton Laboratory), Didcot, UK; RAL is providing the EPOS (European Payload Operations Service) function. RAL is also providing the Double Star Data Management System (DDMS) and the Double Star Data System quick-look facility (DSDSweb)
• French DSP Data Center, at CNES, Toulouse, France.
Figure 13: The Double Star Science Data System
1) Y. L. Lin, J. R. Cai, Z. X. Liu, J. Wu, et al., ”Double-Star Project - One of the on-going Chinese Space Research Missions on Space Weather,” 52nd IAC, Oct. 1-5, 2001, Toulouse, France, IAA-01-IAA.6.3.01
2) B. Gramkow, P. Escoubet & the Double Star Team, P. Bond, K. Bergquist, ”East Meets West in Near-Earth Space - Double Star ,” ESA Bulletin No 118, May, 2004, pp. 23-30
6) Spacecraft information was provided by Lihua Zhang of CAST, Beijing, China
7) Information extracted from ESA Bulletin Nr. 141, Feb. 2010, p. 65 -- under the heading: “Programs in Progress: Status at end December 2009,”
8) Information provided by Philippe Escoubet of ESA (ESA Cluster Mission Manager) in May 2009
12) “Programs in Progress: Double Star,” ESA Bulletin No 129, Feb. 2007, p. 72, URL: http://www.esa.int/esapub/bulletin/bulletin129/bul129_pip.pdf
13) “Double Star and Cluster witness pulsated reconnection for several hours,” Oct. 3, 2006, http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=40340
14) “No. 2 - First Double Star spacecraft declared ready for operations,” March 18, 2004, http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=34876
15) K. Torkar, H. Arends, W. Baumjohann, C. P. Escoubet, A. Fazakerley, M. Fehringer, G. Fremuth, H. Jeszenszky, G. Laky, B. T. Narheim, W. Riedler, F. R¨udenauer, W. Steiger, K. Svenes, H. Zhao, “Spacecraft potential control for Double Star,” Annales Geophysicae, Vol. 23, pp. 2813-2823, 2005, URL: http://www.iwf.oeaw.ac.at/fileadmin/publications/dsp_aspoc/torkar_et_al_2005a.pdf
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.