HC 498 - Scientific advice and evidence in emergencies

Memorandum submitted by Professor Clive Dyer
(SAGE 05)

Please find enclosed my submission concerning solar storms concentrating on radiation hazards to spacecraft and aircraft.

I am writing to you in my private capacity and not as a member of any particular company or body and the views expressed are mine and not necessarily that of any company with which I have been associated. However I believe that these views are well founded and backed up by peer-reviewed research publications in the open literature. I am happy to provide further advice and papers if required. I trust that the following summary biography illustrates my credentials in this area.

Following degrees at Christ’s College Cambridge and Imperial College London I have spent some forty years in the aerospace industry mainly researching radiation environments and their effects on electronics and personnel. After positions with NASA Goddard Space Flight Center, USA and the Royal Naval College Greenwich I spent most of my career at Farnborough where the Royal Aircraft Establishment has evolved to become QinetiQ. There I founded and developed a research team to study radiation environments, effects and hardening and became Senior Fellow and Chief Scientist(Space). The initial emphasis was on Space Systems but in the late 1980s I was one of the first to identify potential problems for avionics and this aspect has steadily grown. I am co-author of several standards including the IEC TS62396 standard for SEE in avionics. I have published some 167 papers in the open literature including 35 on aircraft radiation environments and effects. I retired from full-time employment at QinetiQ in 2008 but continue to supply consultancy in my areas of expertise. In July 2010 I was honoured with "The Radiation Effects Award" of the IEEE Nuclear and Plasma Sciences Society.

I hope that this submission is useful to the committee.

Clive Dyer

Professor Clive Dyer, MA (Cantab.), PhD (Lond.), DIC.

Inquiry into Scientific Advice and Evidence in Emergencies: (iii) Solar Storms

Submission on Radiation Hazards to Spacecraft and Aircraft

1. Introduction

Solar storms comprise bulk emissions of high speed ionised gas (coronal mass ejections), which take a day or two to reach earth where they disturb the earth’s magnetic field, and/or acceleration of particles to high energies which take a matter of minutes to arrive at earth leading to a radiation hazard and ionisation of the upper atmosphere. These storms can produce a range of effects on technological systems and could in extreme situations lead to an emergency situation. Such effects include:

i) Disruption of the National Grid from geomagnetic storms;

ii) Disruption of communications due to ionospheric disturbances;

iii) Disruption of global positioning signals from satellites due to ionospheric disturbances;

iv) Damage or down time of key satellites caused by enhanced levels of ionising radiation;

v) Dose to air crew and passengers and disruption to avionics due to enhanced ionising radiation from solar particle events.

Of course a sinister synergy of all the above would lead to the most severe emergency and this could indeed occur from a sequence of solar storms over several days. However, in this submission I will concentrate in items iv and v as they are my major area of expertise and in the case of v, in my opinion, the least appreciated and understood.

2. Radiation Effects on Spacecraft

During certain solar storms energetic protons and heavier ions are accelerated and arrive at earth within about 10 minutes with the enhanced levels lasting from hours to days. In addition major geomagnetic storms can lead to enhanced levels of trapped electrons in the radiation belts. Both types of environment enhancement are significant at key orbits such as geosynchronous orbit, used by communication and broadcast satellites, and at orbits used by global positioning systems.

The effects of such radiation on spacecraft range from cumulative dose and damage, such as solar array degradation, to more immediate problems from electrostatic discharge or single particle induced upsets in on-board computers and memories.

Although the experience of the space industry is extensive, engineering mistakes are still made and losses and outages still occur in extreme events. Most systems are specified to the worst radiation levels measured since the beginning of the space age. However this experience is limited and more severe events have occurred historically, such as the Carrington event of 1 September 1859. In addition modern microelectronics is becoming increasingly susceptible to individual particles of radiation (single event effects-SEE) due to their higher density and performance requirements.

In general there is good international communication on understanding environments and effects. However commercial operators will always limit the degree of hardening to that which they consider to be cost-effective. For critical systems there is a need for greater communication and understanding to safeguard the infrastructure. At present initiatives tend to be bottom-up from concerned scientists.

3. Radiation Effects on Aircraft and Air Crew

Solar storms can disrupt communications and navigation signals to aircraft due to the disturbed ionosphere. In addition certain events can lead to enhanced levels of ionising radiation at aircraft altitudes. Again synergy of such effects in conjunction with ground level problems is a recipe for an emergency.

The earth’s atmosphere in conjunction with the geomagnetic field provides considerable protection against both cosmic rays and solar particle events. However the protective layer of the atmosphere is reduced to about one third at normal subsonic cruising altitudes and to one tenth at supersonic altitudes leading to background radiation levels that are 300 to 1000 times higher than at sea level. As a result air crew are the most highly exposed occupation with long haul crew receiving typically 4 to 6 milliSieverts (mSv) per year [1], the upper level being limited by guidelines accompanying the current legislation [2]. The milliSievert is a measure of effective radiation dose which is used to assess the probability of long term effects such as cancer. By comparison the average sea level dose is 2 to 3 mSv per year (from both rocks and cosmic rays) while medical diagnostic doses range from 0.004 mSv for a dental X-ray to 0.06 mSv for a chest X-ray.

A small but very important subset of solar particle events can generate particles of sufficient energy to enhance radiation levels at aircraft altitudes [3]. Because they are also detectable by ground level monitors (in general large area neutron monitors) these are frequently referred to as ground level events (GLEs). While increases at ground level can be up to a factor 50 (as measured at Leeds on 23 February 1956), increases at flight altitudes can be 1000-fold leading to effective dose rates of several mSv/hr, hence exceeding annual flight limits in one flight if no avoiding action is taken [4]. In this regard it should be noted that in Europe the general public and pregnant air crew are restricted to 1 mSv per year and 1 mSv per term of pregnancy respectively. FAA guidelines further limit exposure in pregnancy to no more than 0.5 mSv in a month. If the geomagnetic field is not disturbed there is a steep gradient of dose with respect to magnetic latitude and such problems occur only with high latitude flights. However this includes flights on some of the most densely populated routes, such as from UK and Europe to North America and Japan. Fortunately such large GLEs are rare and it is estimated that about 6 events since 1942 (the start of ground level monitoring) would have exceeded the 1 mSv legal limit for an example flight from London to Los Angeles at 39000 feet [5]. Indirect evidence of solar particle radiation from ice core samples shows that the 1859 event could have been 4 times worse than any of these [6]. If the geomagnetic field is highly disturbed when the particles arrive, then much lower latitudes can be exposed. Indeed the 1859 event could have given significant exposure down to the tropics. Fortuitously the growth of civil aviation has been accompanied by a quieter sun. However there was a wake- up call on 20 January 2005 when a major GLE gave a factor 50 increase in the Antarctic region corresponding to effective dose rates of 3 mSv/hr at cruising altitudes. Fortunately for aviation this was very short lived and localised, northern hemisphere rates being an order of magnitude lower.

Another problem that has become increasingly evident since about 1990 is the effect of radiation on avionics via the single event effects mechanism mentioned above. There is now a considerable body of evidence of upsets in flight systems and hard failures in certain electronics [7]. These have been shown to correlate with cosmic ray fluxes [8] but fortunately during this time no very large ground level events have occurred. For such events significant numbers of upsets could occur in a single flight leading to possible flight hazards [9]. For example an autopilot system was found to upset on average every 200 flight hours and return control to the pilot. If a major GLE had occurred before this problem was eventually fixed such an upset could have occurred every hour making safe flight very difficult. Upsets from cosmic rays are now starting to be considered in accident investigations [10]. Technical specifications to account for and limit radiation hazards in avionics have been available since 2006 [11, 12] but it is not clear that they are universally applied and there is plenty of pre-2006 equipment in flight.

At present there are no viable methods for predicting GLEs and the exposure of aircraft. Ground level monitors are diminishing in number and by the time such information reached aircraft it would be too late as maximum rates are reached in a matter of 10 minutes or so. Attempts are made to estimate the dose received after the event but even here the accuracy is limited by the lack of information, typically to about a factor 2. Concorde (and supposedly all aircraft operating above 49000 feet) was compelled to carry a radiation warning monitor [2]. However this has not been extended to other aircraft despite the fact that subsonic routes at high latitude are in fact more exposed than Concorde due to the latitude effect exceeding the influence of the higher altitude [4].

Many pilots would like to carry monitors to measure their radiation environment and warn of enhancements and this is reflected in a recent letter (25 September 2009) to the European Commission from the European Cockpit Association (ECA), which represents more than 38000 commercial pilots. They make a number of recommendations on controlling exposure to air flights of which the following are relevant to solar particle events:

At present there appears to have been no movement by government bodies to accommodate these recommendations.

There are currently solar particle event warnings from US NOAA and FAA but these are based on satellite measurements of much lower energy particles. It is not clear what notice is taken of them and if it is there is likely to be over-reaction and unnecessary grounding of flights as there are many more low energy events affecting spacecraft than there are high energy events affecting aircraft (about 10:1).

There is clear need for government action and international agreement to protect aircraft and crew. The situation is somewhat analogous to the recent "volcanic ash" emergency, where there was apparently a lack of monitoring and a lack of agreed fly/no-fly criteria. Only with further action will there be a balance between safety on the one hand and unnecessary economic chaos from the widespread grounding of flights on the other. The aviation industry has been fortunate since 1956 but the Sun’s history will one day repeat itself.

4. Government Advice and Preparedness

In relation to the 5 questions posed by the Committee my opinions with respect to the above hazards are as follows:

1. The hazards and risks are as above and have largely been identified by basic research. Sometimes the relevant industry will admit to problems following probing by scientists and allow sufficient flight data to prove their cause. However often there is a cloak of commercial sensitivity. In my opinion the Government is totally unprepared for such an emergency.

2. Use of advice in this area is extremely limited. A Cosmic Ray Advisory Group was once established (by DfT and CAA) to consider the implementation of air crew dose legislation. However this appears to have been abandoned without any ongoing methodology for dealing with solar particle events.

3. Major obstacles arise from fragmentation of knowledge across a wide variety of bodies. Government needs to ensure joined-up thinking and coordination. There appears to be very little power to enforce anything. There are too many vested commercial and departmental interests. The situation has not been helped by the commercialisation of research activity over the last decade with consequent lack of objective advice to government.

4. There appears to be no strategic coordination at all.

5. International coordination is extremely important. Scientists communicate well at the research level but this does not appear to be reflected in coordination between legislative bodies. There is a lack of UK support for ESA Space Weather activities which limits UK influence.

References

[1] L Lindborg, D T Bartlett, P Beck, I R McAulay, K Schnuer, H Scraube, F Spurny, "Compilation of measured and calculated data: A report of EURADOS WG5," May 2004.

[2] Joint Aviation Authorities (JAA) JAR-OPS 1.390 Cosmic Radiation, 2001.

[3] C.S.Dyer , A. J. Sims, J. Farren , and J. Stephen, Measurements of solar flare enhancements to the single event upset environment in the upper atmosphere, IEEE Trans. on Nucl . Sci., 37 , 1929-1937, Dec. 1990.

[4] Clive Dyer, Fan Lei Alex Hands, Peter Truscott, "Solar particle events in the QinetiQ atmospheric radiation model," IEEE Trans. Nucl. Sci. vol. 54, no.4, 1071-1075, 2007.

[5] P. Lantos, N. Fuller, "History of the solar particle event radiation doses on-board aeroplanes using a semi-empirical model and Concorde measurements," Radiation Protection Dosimetry, Vol. 104, no. 3, pp. 199-210, 2003.

[6] M A Shea, D F Smart, K G McCracken, G A M Dreschhoff, H E Spence, "Solar proton events for 450 years: The Carrington event in perspective," Adv. Space Res.,Vol. 38, pp. 232-238, 2006.

[7] J. Olsen et al., "Neutron-Induced Single Event Upsets in Static RAMs Observed at 10 Km Flight Altitude," IEEE Trans. Nucl. Sci., 40, 77, (April, 1993).

[8] E. Normand, "Correlation of In-flight Neutron Dosimeter and SEU Measurements with Atmospheric Neutron Model," IEEE Trans. Nucl. Sci., 48, 1996 (2001).

[9] C. S. Dyer, F. Lei, S. N. Clucas, D. F. Smart, M. A. Shea, "Solar particle enhancements of single event effect rates at aircraft altitudes," IEEE Trans. Nucl. Sci., vol. 50, No. 6, pp. 2038-2045, Dec. 2003.

[10] Australian Transportation Safety Bureau (ATSB) Transportation Safety Report, Aviation Occurrence Investigation AO-2008-070, Interim Factual No 2, "In-flight upset 154 km west of Learmonth, WA 7 October 2008," Nov. 2009.

[11] R Edwards, E Normand, C Dyer, "Technical standard for atmospheric radiation single event effects (SEE) on avionics electronics," 2004 IEEE Radiation Effects Data Workshop Record, IEEE 04TH8774, pp 1-5, 2004.

[12] International Electrotechnical Commission, Process Management For Avionics –Atmospheric Radiation Effects –Part 1: Accommodation of atmospheric radiation effects via single event effects within avionics electronic equipment, IEC TS 62396-1, 2006.

Professor Clive Dyer, MA (Cantab.), PhD (Lond.), DIC.

5 September 2010