Hipparcos

For a satellite that seemed plagued with problems from the start, the small Hipparcos satellite has made large contributions to the measurement of astronomical distances by making much more accurate stellar parallax measurements than could be made from Earth.

The Hipparcos satellite contains a small 29-cm mirror designed to measure the positions of stars very accurately. It's parallax measurements are at least 10 times greater in accuracy than measurements from the Earth's surface. It's mission was to measure accurate distances of nearly a million stars out to a distance of 200 parsecs.

An important contribution of Hipparcos was to make precision parallax measurements of 273 Cepheid variables, 2 of them not previously observed. Since the Cepheids are one of the keys to astronomical distance measurement, this improvement in accuracy has far-reaching consequences.

Launched in August 1989 by the European Space Agency, "Hipparcos successfully observed the celestial sphere for 3.5 years before operations ceased in March 1993. Calculations from observations by the main instrument generated the Hipparcos Catalogue of 118,218 stars charted with the highest precision. An auxiliary star mapper pinpointed many more stars with lesser but still unprecedented accuracy."(ESA) 1989年8月由欧洲空间局发射的“Hipparcos”成功观测了3.5年，直到1993年3月停止运行。主要仪器的观测数据生成了包含118,218颗恒星的Hipparcos星表，这些恒星以最高精度进行了测绘。辅助的恒星测绘仪还以较低但前所未有的精度定位了更多的恒星。

Hipparcos, courtesy ESA Hipparcos， courtesy ESA

Reference:
European Space Agency Hipparcos site

Hipparcos Measurements of Cepheid Variables

An important contribution of the Hipparcos satellite was to make precision parallax measurements of 273 Cepheid variables, 2 of them not previously observed.

Reference:
European Space Agency Hipparcos site