We report an outline and a current status of developing a small, all-aluminum made telescope for Nano-JASMINE.
Nano-JASMINE is a nano-size astrometry satellite that will demonstrate some key technologies required for
JASMINE (Japan Astrometry Satellite Mission for Infrared Exploration) in a real space environment and will
measure absolute positions of bright stars (z ≤ 8 mag) with accuracies about 1 milli-arcsecond in a few years
mission. It has a Ritchey-Chretien type telescope with a 5-cm effective aperture, a 167-cm focal length and a field
of view of 0.5x0.5 degree. The telescope only occupies a volume about 15x12x12 cm, and weighs two kilograms
or less. Almost all of the structures and the optical elements of the telescope, including two aspherical mirrors
three flat mirrors and a dual-angled flat mirror that combines the beam from a relative angle of 99.5 degrees into
the primary mirror, are made out of aluminum alloy, being figured by diamond turning machines. The Bread
Board Model (BBM) of the telescope was now measured to be achieving a diffraction-limited performance at
We introduce a Japanese plan of infrared(z-band:0.9μm) space astrometry(JASMINE-project). JASMINE is
the satellite (Japan Astrometry Satellite Mission for INfrared Exploration) which will measure distances and
apparent motions of stars around the center of the Milky Way with yet unprecedented precision. It will measure
parallaxes, positions with the accuracy of 10 micro-arcsec and proper motions with the accuracy of ~ 4microarcsec/
year for stars brighter than z=14mag. JASMINE can observe about ten million stars belonging to the
bulge components of our Galaxy, which are hidden by the interstellar dust extinction in optical bands. Number of
stars with σ/π < 0.1 in the direction of the Galactic central bulge is about 1000 times larger than those observed
in optical bands, where π is a parallax and σ is an error of the parallax. With the completely new "map of the
bulge in the Milky Way", it is expected that many new exciting scientific results will be obtained in various fields
of astronomy. Presently, JASMINE is in a development phase, with a target launch date around 2015. We adopt
the following instrument design of JASMINE in order to get the accurate positions of many stars. A 3-mirrors
optical system(modified Korsch system)with a primary mirror of~
0.85m is one of the candidate for the optical
system. On the astro-focal plane, we put dozens of new type of CCDs for z-band to get a wide field of view. The
accurate measurements of the astrometric parameters requires the instrument line-of-sight highly stability and
the opto-mechanical highly stability of the payload in the JASMINE spacecraft. The consideration of overall
system(bus) design is now going on in cooperation with Japan Aerospace Exploration Agency(JAXA).
The current status of the nano-JASMINE project is presented. Nano-JASMINE - a very small satellite weighing
less than 10 kg - aims to carry out astrometry measurements of nearby bright stars. This satellite adopts
the same observation technique that was used by the HIPPARCOS satellite. In this technique, simultaneous
measurements in two different fields of view separated by an angle that is greater than 90° are carried out; these
measurements are performed in the course of continuous scanning observations of the entire sky. This technique
enables us to distinguish between an irregularity in the spin velocity and the distribution of stellar positions.
There is a major technical difference between the nano-JASMINE and the HIPPARCOS satellites-the utilization
of a CCD sensor in nano-JASMINE that makes it possible to achieve an astrometry accuracy comparable to that
achieved by HIPPARCOS by using an extremely small telescope.
We developed a prototype of the observation system and evaluated its performance. The telescope (5cm)
including a beam combiner composed entirely of aluminum. The telescope is based on the standard Ritchey-
Chretien optical system and has a composite f-ratio of 33 that enables the matching of the Airy disk size to three
times the CCD pixel size of 15μm. A full depletion CCD will be used in the time delay integration (TDI) mode
in order to efficiently survey the whole sky in wavelengths including the near infrared.
The nano-JASMINE satellite is being developed as a piggyback system and is hoped for launch in 2008. We
expect the satellite to measure the position and proper motion of bright stars (mz < 8.3) with an accuracy of 1
mas, this is comparable to the accuracy achieved with the HIPPARCOS satellite.