Description of Satellite types

Satellite systems may be classified according to orbit altitude as follows:

• GEO - geostationary earth orbit, approx altitude:  35 000 km

• MEO - mid-altitude earth orbit, approx altitude:   10 000 km

• LEO - low earth orbit, approx altitude:   <1 000 km

LEOs can be further sub-divided into Big LEO and Little LEO categories. Big LEOs offer voice, fax, telex, paging and data capability, whereas little LEOs offer data capability only, either on a real-time direct readout ('bent pipe') basis, or as a store-and-forward service.  

Since the satellite footprint decreases in size as the orbit gets lower, LEO and MEO systems has required larger constellations than GEO satellites in order to achieve global coverage and avoid data delays. However, less energy is generally required for LEO and MEO satellite communication because of the shorter average distance between transmitter and satellite. Some systems implement several high-gain antennas to generate ‘spot beams’ and so reduce the requirement of the mobile to have a complex antenna and/or high output power. There is another trend towards much smaller and cheaper satellites: microsats,minisats, picosats nanosats, and even femtosats — credit-card-sized satellites.  Due to the commercial forces which are driving the implementation of the new systems, many will primarily focus on land masses and centres of population, and will not offer truly global or polar coverage. These systems will not in general be acceptable for global ocean monitoring.

Furthermore, while the technical capabilities for the new systems do currently exist, delays are inevitable due to problems with spectrum allocation, licensing (in each country where the service will be offered), company financing, and availability of launch vehicles and ground stations. 

It is unlikely that all of the planned systems will overcome all of these hurdles. Indeed, major financial difficulties have hit a number of systems, including Iridium, Orbcomm and Globalstar.

Mergers are becoming increasingly common, as market reality forces system planners to cut their losses and pool resources.

From a technical point of view, some new systems do offer significantly enhanced capabilities compared to traditional carriers. Potential advantages include two-way communication, more timely observations, and greater data rates and volumes. Some systems are also proving to be considerably less expensive and more energy efficient than traditional channels. However, dangers will exist for data buoy users of most systems, in that they will generally be small minority users of the system, with consequent lack of influence in regard to pricing. The arrangements for data distribution are also unlikely to be tailored towards data buoy applications, in particular those that require data insertion onto the GTS.