Global Positioning System Reference
In-Depth Information
is that these services have quality information included so as well as knowing
where something is, it will also be possible to know the accuracy and integrity of
the broadcast information, providing a legal guarantee of the system's quality.
This is an important benefit if monetary transactions or safety critical activities are
dependent on the raw information. The following is the proposed list of Galileo
services as listed by the European Space Agency (ESA) [8].
•
Open access (free to air);
•
Commercial, high performance with fees (encrypted);
•
Safety of life (guaranteed accuracy);
•
Public regulated service (for government agencies, encrypted);
•
Search and rescue (includes two-way communications system for
beacons).
Although one might consider the idea that the various GNSS systems would
be competing, in fact it could lead to a situation where the benefits are greater than
the sum of the parts. Provided reasonable receiver compatibility is possible (i.e.,
many parts of a multisystem receiver would be common or shared), overall a user
could expect vastly better coverage and availability for the much greater numbers
of satellite measurements that can be used in calculations:
•
GPS, 24 satellites;
•
Galileo, 30 satellites;
•
GLONASS, 24 satellites.
Clearly, the future of GNSS is dependent on launch technology and its costs.
All quasi-governmental space projects are expensive but involve a degree of
politics including maintaining strategic technological capabilities and support for
the aerospace and defense sectors. In spite of a general move towards the
civilianization of GNSS, other agendas are present.
Perhaps the wild card may be the emerging business of space tourism and the
concept of cheap reusable spacecraft. It may be possible to use these craft as
launch platforms for low Earth orbit microsatellites. Microsatellites [9] have been
developed and involve short-lived, low specification, small “disposable” satellites
that may be launched in high numbers at very modest costs. It is feasible that an
“Internet in the sky” may be deployed using microsatellites within a decade, and it
is likely that these will also serve as positioning, imaging, and environmental
sensing devices. Signal strengths could be large and in building coverage more
feasible than with conventional GNSS.
