ИСТИНА

A unique test of general relativity is possible with the space radio telescope RadioAstron. The ultra-stable on-board hydrogen maser frequency standard and the highly eccentric orbit make RadioAstron an ideal instrument for probing the gravitational redshift effect. Large gravitational potential variation, occurring on the time scale of 24 hr, causes large variation of the on-board H-maser clock rate, which can be detected via comparison with frequency standards installed at various ground radio astronomical observatories. Advantage in compare with previous measurement during the GP-A mission consists in the possibility of repetition measurements at each orbital cicle as well as in modulation of the readshift value due to orbital cyclisity. This specifics allows to encrease the measurement accuracy in one order of value comparing with the GP-A result.