where

"n"

integer number of orbits required to bring the satellite to the

position in the circular

"m"

degrees from its starting point.

An example of such a manoeuvre is provide by Daly, Ref 2.  Cosmos 1885 was given a

velocity change on 21 September 2024 such as to decrease its period by almost 8

minutes and then to carry out 21 orbits along the elliptical path, allowing the space craft

to accomplish the 90 degree phase movement in 10 days.  It is clearly demonstrated

that the GLONASS satellites are capable of rapid manoeuvering within the orbit. 

GLONASS spacecraft have  enough  fuel  on board  to accomplish manoeuvres several

times: Cosmos 1779 traversed 45 degrees of arc on three separate occasions.  Clearly

spacecraft in the orbital arc which fail can quickly be replaced by another spacecraft. 

This flexibility would give GLONASS an advantage during the operational phase where

one would expect in orbit spares to be in place and ready to cover for any

malfunctioning  units.

A different control philosophy appears to be used by the Russians to control GLONASS

satellite to the US control of GPS.  Whereas GPS satellites are precisely controlled to

follow the same ground track each day, GLONASS does not repeat unlit 17 days.  The

result is that GPS appears to have a large number of control manoeuvres than

GLONASS and must therefore carry more fuel and have a more complex control

network. 

A.7   SPACECRAFT DESCRIPTION

GLONASS spacecraft similarly to Cicada, have significantly shorter lifetime than US

equivalents.  Lifetimes have increased over the programmes life, see below, from under

two years to currently approaching 5 years. 

The Russians have announced that from 1995 a modified upgraded satellite will be

deployed. There are several stages planned in the programme, Ref 1.  The current

GLONASS satellite has a mass of 1300 kg which will rise in 1995 8 to 1480 kg mostly

due to increased fuel load.  Minor modifications will be made to the Proton launch

system with a reduction to two satellites per launch.  Improvements will be made to the

attitude control systems, clocks  and ground systems.  The result is an increase in

navigation accuracy  and time.  In addition differential corrections with respect to

Universal time and system time scales of GPS and GLONASS are planned to be

transmitted. 

The second stage of system development GLONASS M is scheduled for deployment

after 2000.  (It is confusing that some Russian writers refer to the stage one upgrade as

GLONASS M).  The upgrade will include autonomous satellite using inter satellite

measurements to solve the ephemeris problem and improved lifetime for the solar

arrays.  Inter satellite measurements will be made in the optical and radio bands and

communications provided for navigation data exchanges.Autonomous operation for 60

days without degradation is specified.  The main error is caused by the extrapolation of

A 6