|
|
RUSSIANSPACE ASTROMETRIC MISSIONTHE PROJECT OF RUSSIAN SPACE INTERFEROMETER OSIRIS |
|
|
OPTICAL LAYOUTEven in the absence of atmospheric effects it is only Michelson interferometer that can provide submillisecond accuracy of position measurements. The Michelson interferometer can be used to measure the angle between the interferometer base and the star. In order to avoid the problem with identifying the position of the interferometer base the design with two-base interferometer with matching bases is proposed. This two-base design guarantees the microsecond accuracy for a measurement of the arc length between two celestial objects.
OSIRIS arc-measuring instrument consists of two identical interferometers, sharing the common base. Each is pointed to a different star, the arc between these stars is what is being measured. Identical telescopes compress the starlight into the narrow beams that recombine and interfere on the detectors (see the scheme). In order to obtain the clear interference fringes, the pointing accuracy must be so high that it requires an autonomous star-tracking by every telescope. They, therefore, are all equipped with the individual coarse (not shown) and fine pointing systems (14).The starlight, gathered by the primary mirror (1), is reflected onto the secondary mirror (3), which sends it in a narrow beam through the array of mirrors into the delay line (6-7). If the instrument's optics were ideal, the beam could then be sent directly to the beam combiner (16). Since they are not, and there is a need for the correction of aberrations and distortions in the optics, the beam is routed first through the diffraction integrator (13,15), containing the light receiver (14) of the telescope's fine pointing system as well. Finally, the prism (17) and the lens (18) send the combined beam to the detector (19), whereupon the interference fringes in each of operational wavebands form. |
