Other Satellite Navigation Systems - Understanding GPS: Principles and Applications - page 601

seconds, 2.5 10 −13 at 1 day [1, 15]. Appendix B contains

a detailed description of the Allan variance and its applicability to satellite
navigation.

× 10 −12 at 1 hour, and 5 ×

11.1.5.2 GLONASS-M
In 2003, the Russians began launching the new GLONASS-M spacecraft, where
“M” stands for Modified . The GLONASS-M is a modernized version of the
GLONASS spacecraft using more modern electronics and supporting a number of
new features. Although the first launch occurred in 2003, GLONASS-M is an older
spacecraft design, first conceived in the early 1990s but not sufficiently funded until
2001. GLONASS-M continues the design practice of housing the satellite electron-
ics in a heavy pressurized gas-filled vessel, similar to the original GLONASS space-
craft design. The older design requires the continued use of the expensive Proton
launch vehicle to launch a set of three satellites into orbit. As a result, the Russians
plan only to build and launch a total of 10 to 12 GLONASS-M satellites over the
next several years to act as a gap-filler until they complete the design and produc-
tion of the next generation of satellites, GLONASS-K. The GLONASS-K spacecraft
is projected to be much smaller and half the weight, thus reducing program costs
significantly [9-12, 16-18]. The GLONASS-M has a number of new features. These
include:

1. Improved navigation performance. GLONASS-M carries a more accurate
satellite clock (Allan variance of 10 −13 at 1 day), a better attitude control

system, and intersatellite navigation links (incorporated after the second
GLONASS-M satellite). These features will improve user PVT accuracy by
reducing errors in measurements of time and ephemeris calculation [9-12,
16-18].
2. Longer lifetime. GLONASS-M carries an increased propellant loading,
improved onboard batteries, and modernized spacecraft electronics. These
features support a longer design-lifetime of 7 years [9-12, 16-18].
3. Improved navigation signals. This feature will add a second civil modulation
on L2 signal and capability to shift the signals from channels

1×

12. The
addition of a second civil frequency will allow civil users to make
ionospheric corrections, thus improving accuracy. The additional channels
will allow the Russians to fulfill international commitments to move the
navigation signals out of the radio astronomy frequency band. In addition,
the satellite will carry filters, which will remove out-of-band emissions in the
1,610.6-1,613.8-MHz and 1,660.0-1,670.0-MHz radio astronomy bands
[9-12, 16-18].
4. Improved navigation message. This feature will transmit corrections
between GPS and GLONASS time to facilitate joint use; navigation data
authentication information every 4 seconds; navigation age-of-data
information; and warnings about the future adjustment of the GLONASS
time scale with leap-second correction [9-12, 16-18].

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