"In 2010, the VLBA will begin a long-term program to determine the complete 3D structure of the Milky Way by measuring parallaxes with 10 mas accuracy or better to ~ 400 high-mass star-formation regions."
In order to achieve the stated accuracy it is is necessary to use together the radio telescopes which are as distant as possible.
https://science.nrao.edu/facilities/vlba
"In 2010, the VLBA will begin a long-term program to determine the complete 3D structure of the Milky Way by measuring parallaxes with 10 mas accuracy or better to ~ 400 high-mass star-formation regions."
In order to achieve the stated accuracy it is is necessary to use together the radio telescopes which are as distant as possible.
http://www.vlba.nrao.edu/sites/