Would a GNSS need a backup?

Abstract

No navigator likes to be totally dependent on only one navaid-it is an article of faith for many that there should always be a backup system. Several systems have been put forward as possible backups for a GNSS but they seem to have originated more in a generalised feeling that there ought to be one rather than a dispassionate examination of what is involved. GPS/Galileo are radical departures from any previous concepts of radio navigation aids and a full-blown GNSS is an even more radical proposal. There is a good deal more involved than simply engineering and technical matters. There are the questions of who controls them; what the customer interface is; who certifies them for use in safety-related situations; and what legal recourse there is. On the answers to these questions depends whether a backup is needed and if so what form it should take. It is found in this paper that for many non-critical users there is no need for a backup, and that others who may be involved in safety-critical situations already have a backup in the form of their current systems. It is also found that in fact it may be extremely difficult to compose a GNSS in the form it is generally given; that is, a combination of GPS, Galileo and perhaps Glonass. The problem lies not in on the engineering side, but in matters of legality and the sovereignty of individual nations. For these reasons it is concluded that the development or implementation of a new system purely to act as a backup for a GNSS is not necessary.