Current frequency allocations for non-geostationary mobile-satellites (NGSO-MSS) are all below 1 GHz, a very crowded portion of the radio frequency spectrum. To the extent that feeder links to satellites in that service can use frequencies in bands above 1 GHz, the demand for additional spectrum below that point will be lessened. Feeder links can use higher bands that would be less desirable, or even unusable, for service links to the large number of small, low-power, user terminals with low-gain antennas envisaged for this service. Two possible bands above 1 GHz, 1390–1393 MHz and 1429–1432 MHz, are close to the 1400–1427 MHz band that is important to two passive (non-radiating) science services. To the extent that out-of-band emissions from NGSO MSS systems can be reduced to levels acceptable to the science services, the efficiency of use of orbit and spectrum resources can be increased. Copyright © 1999 John Wiley & Sons, Ltd.