Theoretical analysis on the analytic expression of space VLBI ground-space baseline time delay shows that a minimum number of 3 radio sources is necessary for GEDEX parameters adjustment.

• 对空间VLBI地-空基线时延的解析表达式分析表明，空间VLBI天文测地参数的联合平差要求每次实验至少观测3颗射电源。