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GEOSHAFT OBJECTIVES

The Geostationary Spacecraft Hazard and Anomaly Forecasting Tool (GEOSHAFT) is a Java based web application designed to provide real-time space radiation threat information.

GEOSHAFT aims to provide useful information on the level of this hazard as an aid to spacecraft operators. It provides users with improved hazard indicators for the internal charging process.:

Daily averages of >2MeV electron flux, every 5 minutes. This is a general indicator and simply packages NOAA data in a more timely way.

Currents estimated through the shielding around a component. This is most useful where the site of ESD is known or suspected. However, a default typical spacecraft skin thickness may be used as a general indicator.

Maximum electric field estimated in a material. This is most useful where both the site of the ESD and the material involved are known or suspected. However, a typical common default material, known to be at risk from this process may be used as a general indicator.

Delivery method: Hazard levels via web page and alerts by e-mail User control of alert levels, shielding and material properties

The service also aims to provide realistic forecasts up to 1 day into the future.

GEOSHAFT Pilot Space Weather Service David J Rodgers, Karen A. Ford and Keith A Ryden

(Space Department, QinetiQ, Farnborough, Hampshire GU14 0LX, UK)(e-mail: djrodgers@space.qinetiq.com)

AbstractInternal dielectric charging is one of the main space weather hazards to spacecraft electronics. This occurs when electrons at high energies, typically >0.5MeV and usually in the outer radiation belt, penetrate surface materials and are deposited in underlying dielectrics. The charging that results leads to electrostatic discharges which may cause temporary upsets or permanent damage to electronic components. In geostationary orbit electron flux increases of a factor 1000 in a few hours are not unusual and spacecraft in this highly populated orbit are at high risk. The GEOSHAFT prototype space weather service aimed to provide improved information on the level of this hazard as an aid to geostationary spacecraft operators. Products of the service are: running 24-hour average of >2MeV electron fluxes, modelled charging current and modelled dielectric electric field. A numerical technique was also used to provide short term forecasts up to 24 hours ahead.As part of the prototyping activity, the service was run for a year. During this time, comments were sought from users and improvements were made. Users who agreed to take part in this activity were New Skies NV and Paradigm Ltd. At the end of the study the device performance was assessed. The service was found to be reliable, particularly after the initial period. The effectiveness of using charging current and >2MeV electron flux as an anomaly indicator was demonstrated. Good correlation was found between anomalies and the running 24-hour mean of >2MeV electron flux and better predictions were obtained with the calculated current. The numerical flux predictions were not as successful as expected and operational problems associated with of time-tagging the data were suspected. At the end of the study, the two users considered that there was a need for a space weather service addressing satellite anomalies. However, one user had not experienced problems of internal charging and so had not found the service very helpful. The other user did not find that the service fitted into operational procedures. Hence neither user derived sufficient benefit from the service that was produced and future developments are seen as an essential step in continuing the service.

INTRODUCTION

Spacecraft in the highly populated geostationary orbit suffer from the effects of internal charging as a result of space weather. There is a potential for anticipating anomaly occurrence from the fact that the internal charging process is quite slow (typically more than 1 day). In addition, once a vulnerable system or component has been identified, there is the possibility of anticipating future anomalies by a more physics-based approach, using deposited current or electric field as hazard indicators. This is the rationale behind the GEOSHAFT service.

SERVICE EVALUATIONGood pointsCharging current can be shown to be a better hazard indicator than fluence. Below, we compare two thresholds in fluence and current that were set to produced 80% successful anomaly prediction and 20% false alarms respectively for a geostationary satellite.

80% successes 20% false alarms

BUSINESS PLANFor GEOSHAFT a sustainable business plan has to be based on an improved service Market:

~ 320 geostationary satellites, ~ 60 systems, 6 multiple European systemsSystem options – In-house web service, Hosted web service or jointly hosted with related space

weather servicesCosts £

Funding models•Subscription £5k/u/yr•Public service £77k over 3 years

Comparisons with other similar services•NOAA SEC, NASA’s ‘SpaceWeather.com’, IPS in Australia, BAS SatRisk and IRF Lund are non-subscription, also SPENVIS currently.•Satellite Users Interference Reduction Group ~ $15k/u/yr

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Access to data and plots

Nowcast/Forecast

Fluence histogram giving recent history and short-term prediction

Archive retrieval

Electron fluence, charging current and electric field can be plotted and data exported.

Flux >2MeV Current Flux >2MeV CurrentThreshold 2.54e6 cm-2s-1 2.6e-9 A/m2 7.53e6 cm-2s-1 3.15e-9 A/m2

Success (event) 17 (81%) 17 (81%) 8 (38%) 13 (62%)Miss (event) 4 (19%) 4 (19%) 13 (62%) 8 (38%)Success (non-event) 697 (65%) 773 (72%) 859 (80%) 859 (80%)False alarm 376 (35%) 300 (28%) 214 (20%) 214 (20%)

Using the calculated current as a predictor led to a reduction in false alarms for the same positive success rate and an increase in positive success rates for the same false alarm rate.

Bad pointsIn practice, forecast accuracy of >2MeV daily fluence was significantly poorer than that achieved during the testing of the prediction model on historical data. It is speculated that the large number of data gaps in the assessment period may be the cause of this but other causes, such as non-stationary data and problems with data time-stamps may have had an effect.

Web StatisticsMonitoring of web hits and origin of users is crude due to the actvities of search engines and the complex routing of the internet. 76% of hits were from the USA. The majority of these are believed to be search engines. Around 5 hits per day are estimated to be genuine.

User Feed-backNew Skies NV and Paradigm Ltd participated in the evaluation.

Cost of anomalies•Engineering time dealing with space weather anomalies

–New Skies - 1½ months of engineer effort per year for the 5 spacecraft–Paradigm - 3 months of engineer effort per year for fleet

•Disruption to service: – New Skies - < 6 or 7 mins not serious, but >10-15 mins a problem

•Documentation for insurance (typically 2%/year premium)

Value of existing GEOSHAFT to users (~ zero)•New Skies – no internal charging anomalies•Paradigm – mature fleet, no new anomalies, interest in longer-term forecasts for operations•Neither user looked at current or electric field•Nevertheless an improved service would have value

Both users wanted additional capabilities to make the service sufficiently useful, e.g.•Local time dependence, multiple spacecraft at once•More user-friendly anomaly correlation

•Also no perceived value in having European space weather capability per se

GEOSHAFT WEB SERVICE

The GEOSHAFT web site (http://geoshaft.space.qinetiq.com/geoshaft/) has been publicly available during this study with an additional private area available via registration.

Welcome Page

Step Persistence NRMSE Model NRMSE Skill-factor6 hours 0.226 0.141 0.3812 hours 0.385 0.229 0.4124 hours 0.605 0.344 0.43

TSAR forecast performance assessment

Set-up Recur. Data Business Market. Total

In-house 35k 16k 0k .5k /u/yr 12k 99.5k

Hosted 31k 16k 0k .5k /u/yr 6k 101.5k

Joint 33k 10k 0k .25k/u/yr 6k 80.25k

PROSPECTIVE IMPROVEMENTSWithout changes the existing GEOSHAFT service is too limited. New requirements are for:

• Local time mapping• Multiple satellites visible at once• Easier customisation of shielding, no fields• Automated anomaly comparisons

Being part of global service makes sense financially and practically for users

New Data sources• Higher spectral resolution for better internal charging calculations feasible• More GEO monitors would improve predictions and local time mapping• Extension to MEO• New, sophisticated detectors on GSTB/Galileo • Galileo itself would be a major new user• Europe could become the principal provider of MEO spacecraft hazard information.[1] D.J.Rodgers, K.A.Ryden, G.L.Wrenn, P.M.Latham, J. Sørensen and L.Levy, An Engineering Tool for the Prediction of Internal DielectricCharging, 6th

Spacecraft Charging Technology Conference, AFRL-VS-TR-20001578, 1 September 2000[2] D.J.Rodgers, S.N.Clucas, C.S.Dyer and R.J.K.Smith, ‘Non Linear Prediction of Relativistic Electron Flux In the Outer Belt' Advances in Space Research, Vol.

31 No. 4

The service accesses,and processes data from NOAA’s GOES spacecraft and makes calls to two programs:

•DICTAT [1] to calculate electric field and charging current within a shielded dielectric. •TSAR [2] to perform prediction using radial basis functions.