Supplementary memorandum submitted by
The Royal Academy of Engineering (SAGE 33a)
VULNERABILITY OF
THE GALILEO
SATELLITES TO
EXTREME SPACE
WEATHER EVENTS
You recently invited The Royal Academy of Engineering
to give evidence to the House of Commons Science and Technology
Committee inquiry on extreme space weather events along with the
impact of solar storms on the mobile telephone network. Professor
Paul Cannon FREng appeared as our witness: his additional comments
on both issues are set out below.
GALILEO
You asked for additional information regarding
the vulnerability of the Galileo satellites (as opposed to the
GPS satellites) to extreme space weather events.
Both satellite constellations are/will be in
medium earth orbit (MEO) and as such they are exposed to high
energy electrons and very high energy solar particle events, both
of which can have a deleterious impact on satellites. The GPS
satellites are of military origin and we can expect that they
have been "hardened". The Galileo constellation is,
however, a civilian system and so is being designed in accordance
with usual space engineering practice. That means that the satellites
will be designed, with some margin, to operate over their design
lifetime while subjected to a standard model of the high energy
particle environment. This environmental specification is based
upon measurements conducted since the start of the space era,
rather than a major Carrington event. The detailed design requirements
will be held by the European Space Agency (ESA). As part of the
government's assessment of the vulnerability of national infrastructure
to major solar storms, it may be appropriate for these specifications
to be reviewed by expert authority.
Both the GPS system and Galileo systems operate
at similar frequencies and consequently the impact of the solar
storm on the radio signals will be very similar. It is very possible
that combined GPS and Galileo receivers will be somewhat more
resilient to these propagation impairments by virtue of the special
separation of the signal paths from the satellites to the ground.
IMPACT OF
LOSS OF
GPS/GALILEO SIGNALS
ON MOBILE
PHONE NETWORKS
Timing
It is our understanding that neither the GSM
standard (2G) nor the wideband code division multiple access (CDMA)
standard (3G) as implemented in the UK are dependent on GPS timing
for their operation. Base stations operate asynchronously and
timing in the backhaul network is distributed through the communications
protocols.
The situation is very different in the USA,
where, GPS timing is deeply integrated into the US (CDMA) standard
known as IS95. Again, there is no GSM (2G) GPS dependency. The
Academy also understands that GPS timing is employed to deliver
against FCC requirements on 911 (emergency) localisation of mobile
users.
In conclusion, the US mobile network appears
to be vulnerable to the loss of GPS timing, and the UK network
seems to be resilient—but we would expect the Government
to check these understandings given the importance of the mobile
network to the UK infrastructure.
Solar Radio Bursts
There is documented evidence that Solar Radio
Bursts (SRBs) can detrimentally affect GPS systems for a period
of ~20 minutes. We have already indicated that the mobile telecommunications
system in the UK is not dependent on GPS.
It has been suggested, however, that SRBs can
affect the performance of mobile phone networks by increasing
the noise floor in the system and causing an increase in the dropped
call rate. The effect should be most evident if the base station
antenna is pointing at the sun (ie antennas pointing to the east
and west and when an SRB occurs at sunrise or sunset respectively).
The effect is probably small—it has not
been possible to find any reports of wide scale effects resulting
from the Dec 2006 SRB (the largest on record).
Should you require further information, please
do not hesitate to contact the policy team at The Royal Academy
of Engineering.
Philip Greenish
The Royal Academy of Engineering
23 November 2010
| 
