International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / As Mobile Satellite Communication Systems (MSCS), such as INMARSAT, Iridium, Globalstar, ICO, et al, are emerging, the feasibility analysis of MSCS using for spacecraft TT&C data transmission have been studied by many space agencies and scientists. In this paper, the usability of MSCS’s low data transmission for modern spacecraft is analyzed. The availability of existing and near future MSCS are reviewed briefly in terms of orbital coverage, data transmission rate, EIRP, adaptability and so on. The special problems to be resolved are discussed such as compensation for high Doppler frequency shift, provision of user spacecraft EIRP, antenna beams steering of user spacecraft, use of advanced modulation scheme.