ИСТИНА

The space radio telescope RadioAstron has an ultra-stable hydrogen maser frequency standard on board, which offers a unique opportunity for testing the gravitational redshift effect. The accuracy of the anticipated experiment, taking into account the hydrogen maser's stability and accuracy, can reach a value of ~10^{-6}, which is 100 times better than the result of the GP-A mission. However, the lack of a specially designed on-board communications subsystem degrades this value by several orders of magnitude. We discuss the possibilities for overcoming this issue and present some results of the developed techniques.