The Potential of VSOP2
WEI ERHU, LIU JINGNAN, YAN WEI
Coverage of the tracking network
The ground tracking station is to receive and record observation data from satellite, to measure the position, movement velocity and orbit parameters of the satellite. And it is an important factor to guarantee the successful observation, so it is necessary to establish tracking stations and use advisable technique to complete these tasks. Mainly, VSOP2 system use K waveband to track and observe the satellite.
There is no material about the tracking stations for VSOP2, so tracking stations for VSOP will be used in the simulation, which are Usuda in Japan (10 m caliber), Green Bank in USA (14 m caliber) and other three DSN (Deep Space Network) stations of NASA (Goldstone in USA, Tidbinbilla in Australia and Madrid in Spain, all 11 m caliver).
Results and analyses
The simulation gives the dynamic and real-time coverage result of satellite and shows the report of coverage time. According to the simulate results, the total coverage time of VSOP2 satellite by tracking stations is 151875.737 seconds. The shortest coverage time is 2944.578 seconds in Usuda and the longest one is 22135.337 seconds in Green Bank. The percentage of coverage time of each tracking station is shown in Fig4. These results are improved by comparing with VSOP (VSOP’s coverage instance in the same time is shown in Fig 5.The total coverage time is 130764.923 seconds). These improvements are attributed to the new design of satellite structure and orbit.
Percentage of VSOP and VSOP2 by tracking network is respectively 85.37% and 86.39%, excluding the overlapped parts of coverage. For VSOP2, the coverage time of satellite by tracking station can be improved obviously from the example of Tidbinbilla and Madrid. But the coverage time of some stations, such as Green Bank, is shorter than VSOP. VSOP2 is designed to observe radio source in the south sky, so the coverage time of high latitude station is shorter.
If more tracking stations all over the world are added, the situation will be improved. In a word, the ability of coverage time of VSOP2 by tracking station is improved.
The baseline formed by observation station and VSOP2 satellite
The formula of radio telescope angular resolution is θ′′= λ/D.ρ′′ (1) in which θ is angular resolution, λ is the wavelength of radio wave received by telescope, D is the length of baseline.
According to the formula (1), the length of baseline is a crucial factor to influence SVLBI angular resolution when the wavelength of radio source is invariable. High angular resolution caused by long baseline will be useful for geodetic applications.
Although the length of SVLBI baseline of VSOP2 is extended, actual baseline formed by observation station and VSOP2 satellite is the guarantee of interferometry. To consider its applications in China, several Chinese radio telescopes will be selected in the simulation. There is a radio source in the simulation too. The observing time and the number of baselines formed by observation station and VSOP2 satellite will be analyzed.
The selected radio telescopes are located in Beijing, Shanghai, Kunming, Urumqi and Guizhou. The diameter of telescope in Beijing Shanghai and Urumqi is 25 m, in Kunming is 40 m and in Guizhou is 500 m. The latter two are being established now. The selected radio source’s code is HR-7745, its right ascension is 20h18m56s and declination is -47°42´39˝, located in the south sky.