Adv.SpaceRes. Vol. 22, No. 1, pp.29-38.1998 Published by Elsevier Science Ltd on behalf of COSPAR Printed in Great Britah 0273-1177/98$19.00+0.00
Pergamon PII: SO273-1177(97)01097-l
SPACE WEATHER: THE EFFECTS ON OPERATIONS IN SPACE M. A. Shea and D. F. Smart Geophysics Directorate, Phillips Laboratory, 29 Randolph Road, Hanscom AFB, Bedford, MA 01731-3010, U.S.A.
ABSTRACT The major solar-term&l perturbations that occur& during the 22ud solar cycle have increased our awareness of theefibctsofspaceweather. Anoverviewofthecausesofsameofthesedisturbancesandtheensuing~~~for opera&m in space are described. These include problems associated with communications, Ilavigatioq solar cells, spacecrai? ekctronics, satellite positions aud radiation to manned space vehicles. Also discussed are the effects of the ever present galactic cosmic radiation. Examples of defhutive problems that were encotmmed during specific time Published by Elsevier Science Ltd on behalf of COSPAR periodsarepreseuted. INTRODUCTION
The observation of an uuusual method oftelegaph operations was reported in the Aunual of Scientific Discovery, 1860. As uoted by Stewart (1861), kkgmph lutes were operated entirely with induction cmrents during the major gemage& storm that followed the famous cartingtan flare of September 1859. Telegraph operators between Bostoq Massachusetts and Portland, Maine in the Uuited States seut a series of messages includiug routine telqraphic busiuess back aud forth using only the i&&u curmts duriug the period of strong aurora. This was p&ably the first report that magMospheric eueqy supported a unumunication system. In fact the telegraph operators reported that the signal was stumger using the induction curmts thau when using the batteries. On 27 and 28 February 1942 the British anti&craft gun layin radars working on a 4.2 meter wavelength were jaznwd. TheBritishWarDe~mhm& mkmtmd&ly umcemed, assigued J.S. Hey, a scientist working with the
Heynoticedthatthejammingwascmfiuedtothe maxmumleflbcttowardthesull. uponiuquirytotheRoyalGreemvichobseMltoryhe1eamed thatahugesuuapotgroupwasuearthecemalmeridiauofthesuu. FromthisHeyconcl~thatsolarradio emissiouwasrespousibleforthisjamming. Hiswritteureportwasimme&telyclassifiedasamiliterysemtaud was uot declassiiied uutil atter the war (Love& 1987). In July 1946 the headhum of a [email protected]
DC mmpaper blazed an aunounm of major HF radio . . ccmmm&mproblems. These~~~wareassociatedwiththesolarproton~tof25July1946and subqueutgmuagMicdi&&mce. Jn1973aDSCSsatellkhadauuuumm&d modechaugeiuitssolarpower array. This~wasnotdiscovenduntilthepowcrlevelwastoolowtobereversad,andthe~~failed. Duriq a 12-mouth period in 1980 and 1981, the PAVE PAWS over-the-horizon radar system detmted 17 signals ~oouM~~intsrpntedas~-~ballisticmissilee;~falsesigoalswert~~to”clu#er” duriugaumrala&vity. X-raymd~amma-rayradiatioufkomthe24April 1984majorsolarflarewasthesourceof ~~ioniPtionontheNllit~afHPrthrarultiaginatanpararyloesofhigh~communication ~thegrormdaadtheaircraft~~~~bctwsentheunitadscatssandc~. JnMarch 1991 the North Americau Defense Conmumd (NORAD), which tracks objects orbitiug Earth, kmpomily “lost” morethan200objects~theircatalogasaresultofdragintheupper~p~. Theiufxeaseindragisadirect result of atmospheric heating which iucreases the density at the altitude of the orbiting object. The problems 29
M. A. Shea and D.
awxiated with the Canadian ANIK geovchronous communication satellites in January 1994 received considerable publicity. The chain of “cause and ei%ct” could be linked to the transit of a coronal hole on the sun, A month later, the television signal being transmitted between Norway and Japan was ~~~p~ just as the last member of the Japanese ski-jumping team was competing for a medal. Again, there was a link with solar phenomena,
All of these happenings are examples of disruptions that occur when the natural environment is perturbed by some form of solar-terrestrial phenomena. In this paper we discuss some of the phenomena that can lead to difficulties for systems dependent upon a relatively quiescent spatial environment for optimum operation. Examples of problems that occurred during some of the mjor ~~-~~~ events of the 22nd solar cycle are given. THE SOLAR SOURCE AND DEFINITIVE EFFECTS It is often difficult to believe that the energy source causing perturbations to our technology and other problems at Earth is located -150 million km away. Figure 1 illustrates the time profile of solar emissions that transfer energy to Earth. I
1 1 la3oloo
ENERGY (ME’/) SOLAR
6 I MIN
I I tOMIN
TIME Fig. 1. Time
I: II I I t&zRzl
SCALE OF SOLAR EFFECTS
scale of solar effects at 1 Astronomical Unit.
Ma& solar flares, no matter where they occur on the visible solar disk, can seriously disrupt the sunlit ionosp~re, The arrival of solar X-rays at the top of the sunlit ionosphere is usually the initial indication of solar activity that may severely influence the terrestrial environment. Traveling at the speed of light the additional ionization added by these photons can disrupt point-to-point high frequency radio communioations. This phenomena, historically called the sudden ionospheric disturbance (SID), has been associated with solar flares for more than half a century. Solar Xmy~~~~af~~~~s~~h~. Airline pilots are o&n told tbat a major solar flare may occur dur& their projected flight time - not because the flare itself is important but because the effkts on the ionosphere may disrupt communications to ground control locations. The 3B/X13 solar flare at 2356 UT on 24 April 1984 was an intense X-my and gamma-ray event, This long duration X-ray event was responsible for increased ionization leading to the temporary loss of high-frequency ~~~tio~ to President Reagan%aircraft over the Pa&c Ocean. Concurrent with X-ray emission, solar activity often emits radio noise. Similar to X-rays, travelling with the speed of light, radio emission can also interfere with communications and radar systems on the sunlit side of Earth. For rwons such as these, it is important to be able to predict the occurrence of major solar flares and the expected magnitude and duration of the X-ray and radio emission.
Fig. 2. Conceptual figure of phese and amplitude change of VLF waves during a polar-cap absorption event. TDRS-1 Attitude Control Memory Upeta
Year Fig. 3. Single event upsets per week experienced by TDRS-1 and the weekly average >50 MeV proton flux measured by the ODES spacecraft. This figure illustrates that the number of attitude control memory upsets increases during solar proton events. The “bursty spikes” in the SEU rate during 989, 1991 and 1992 occurred when the solar proton flux was extremely high. (Figure courtesy of DC. Wil inson, NGDC, NOAA.)
M. A. Shea and D. F. Smart
the solar particle flux intensifies,the probabilityincreasesthat a nuclear &emotion in the sensitive vohune of a semiconductorwill resuit in a “singleevent upset’. ht this case the energeticprotons (or heavier nuclei) bombard a spacecraftand penetrate into the structure to excite charge carriers in the active volume of sensitiveeleotronicchips. These events may change the state of a digital logic element(i.e. change the conten&of the ~0~) or may cause a circuit to latch up permanentlyin a bad state. The memorychip in the attitude control system of the geosynchronous orbiting TDRS-1 satellite is particularly susceptibleto single event upsets. Figure 3 illustratesthe number of single event upsets experienced by TDRS-1 aud the weekly averages of the >50 MeV proton flux as measured by the GOES spacecraft during the past ten years. The “burstyspikes”evidentin 1989, 1991,and 1992 are during periods when major solar proton events occurred. Spacecraft baving rad-hard chips in their electronics are less likely to experiencethese single-eventupsets. However,the cost of producingthese rad-hard chips is significantand may not be as cost effectiveas error detectionand correctiontechniquesor spacecraftoperators who can rapidly interveneif a satelliteexperiencesan unexpectedanomalythat may adverselyand rapidly affect operations. As
The anomaliessufferedby two CanadianANIK spacecraftin late January 1994receivedconsiderablepublicity in the press. In this case there were no reports of so~-~e-~~ ~~~0~ to the aerospace en~ro~~t at 1735 UT on 20 January and 0210 UT on 21 January when the problems were encountered. However,there was a period of enhanced flux of high energy electrons (> 1 MeV) for seven days prior to these anomalies. During this period excess electrons might have been depositedwithin insulatingmaterial. When the euergy deposition from the excess electronsis sufficient to generate an electric field that exceedsthe breakdownstrength of the material, then a pulsed dischargemay occur. The resulting electromagueticpulse may be “pickedup” by other circuits such as a command processor. When these e~~~us signals bud fkom the plasma discharge are injected into the system, unpredictableresults may occur (Violetand Frederickson,1993). The commandprocessor might respond by turning off the spacecraft, or by igniting a thruster, or, as in the case of the ANIK spacecraft,a.tKbcting the momentumwheel control circuitry. The charge storage and pulsed discharge, called “deep dielectric chargi&’ or “bulk charging”, were identifkd as the cause of the ANK anomalies(Bakeret al., 1994). So~-~ ph~orn~ impacted Japanese sport enthusiastson the eveningof 22 February 1994 during the Winter Olympic Games Just as the last man on the Japanese ski j~p~ team was ~~~0~ to leap his way iuto the record books, the television signal being relayed from Norway to Japan via the BS-3a geosyn&ronous orbiting satellite was interrupted. This disruption, which contmued for 50 minutes, occurred during a complex period of solar~~~p~~~~~~~a~~~~ 0 109 UT on 20 February. The solar a&ivity was related to a major solar proton event with the second highest peak flux of > 10 MeV protons recorded during the 22nd solar cycle. A storm sudden commencement(SSC) was recorded at 0901 UT on 2 1 February followedby a geomagneticstorm with KP values of 7+. The anomaly aE&ting the JapaneseBS3a spacecrafk on 22 February 1994 was originally believedto be a “singleevent upset” since it occurred ai& this unusual and complex solar-terrestrial activity. However,for appro~ly two weeks prior to 22 February, there was another period of enhanced flux of high-energy (Z 2 MeV) electrons at g~~c~~ous orbit. It is now believed that the problems on the BS3a spacecraft can be attributedto the accumulated effect of the enhanced high-energy electronflux.
Fig. 4. Top: solar-wind speeds for January 1994. Bottom: daily average E > 1 MN electron fluxes at t-6, (Adapted from Baker et al., 1994.)
Space Wenther: Operations
There is a related solar phenomena associated with an enhanced electron fhix in the magnetosphere that comimies for several days during otherwise relativelyquiescentperiods. The efkct starts with the passage of a coronal hole across the visible solar disk. Coronal holes are known to be the source of highqeed solar+vind streams. When the highspeed solar-wind stream reaches Earth energy is tn&ermd from the interplanetary medium to Ea&s magnetoestablishing the necessary eonditmns for generating large fluxes of high energy electrons. The sPhe=, high-speed solar-wind stream can continue for several days (Baker et al., 1994); the resulting enhanced high-energy electron flux in the magnetosphere increases the possibility of excessive bulk charging in geosynchronous satellites (Frederickson et al., 1992). During solar minimum conditions these coronal holes give rise to the 27day recurrency in the high-speed solar wind at Earth and subsequent increase in electron flux at geostationary orbit. Figure 4 illustmtes the average solar-wind speeds and the daily average electron fluxes during January 1994. Solar protons can also degrade solar cell performance, severely limiting the lifetime of the spacecraft. The Japanese TV satellite BS-3a, the same one that experienced a signal interruption in February 1994, lost solar power panel output during the March 1991 events. During these same events the power panel outputs on the GOES-6 and GOES-7 satellites degraded by about 0.2-0.3 amps, roughly equivalent to the degradation in performance expected from a two to three year exposure to the radiation at g~s~c~onous orbit. There was significant power-panel output degradation on the GOES spacecraft for other mjor proton events of the 22nd solar cycle including the events of August-October 1989 and March 1990 (Allen and Wilkinson, 1993).
SOLAR-INDUCED GEOMAGNETIC DISTURBANCES For many events the plasma contained in the coronal mass ejection dominates the solar energy outflow. When the associated solar activity occurs near the central meridian of the sun, the plasma may envelope Barth imparting a tremendous amount of energy in human terms to the magnetosphere. Major solar activity near the central meridian of the sun associated with a large solar proton event is most likely to be associated with a fast moving coronal mass ejection that will ultimately intersect Earth (Shea and Smart, 1996). A fast moving interplanetary shock may intersect Earth’s ensphere within one or two days after the associated solar activity gene~~g a “storm sudden ~~~~t” @SC) to the geomagnetic field as measured by magnetometers. If the interplanetary magnetic field has a southward component at the time of the shock arrival, a major geomagnetic storm will occur presenting another set of problems for operations in space.
NORMAL GEOMAGNETIC CONDITIONS
SEVERE GEOMAGNETIC DISTURBANCE
Conceptuai view of solar proton access to the northern polar regions during normal quiescent Fig. 5. conditions (left) and during disturbed conditions when the aurora1 oval is displaced equatorward (right).
M. A. Shea and D. F. Sman
The &media& efkct of a major geomagnetic disturbance is the equatorward displacemem of the auroral oval. Coals and navigation difBcukies, previously con&red to the polar regions, may now be prevalent at mid and even low h&&s depending upon the reduction in the geomagnetic cutoff rigidities. Since very large geomgwtic stmms ofken occur while a solar proton event is still in progress, particle access is no longer con&red to the polar regions as illustrated in Figure 5. This influx of higher energy particles to lower L values than under quiescent dtiolls can interfere with spacecraR and systems operating in these regions. Major geomagnetic storms also result in heating and expansion of the atmosphere, causing sign&ant perturbations in low-abitude satellite orbits. The increased drag on objects in low altitudes can pose additional cons&a& to operations in space. The North Amerkan Defense Command ~0~) maintains a catalog of these low-bide objects which must be updated after every major geomagnetic storm. The effect of increased drag on low-altitude spacecraft must be rapidly ascertained to facilitate aecumte spacecraft tracking. The efibcts of satellite drag must also be included when cakxrlating the re-entry of the Space Shuttle. LONG TERM SPACE WEATHER EFFECTS Space weather also includes the ability to forecast the solar cycle and the phenomena depemh& upon this long term variation in solar activity. Solar flares and associated solar emissions are most prevalent during a seven year period around solar ~~. Geomagnetic disturbances are related not only to the randomly occurring coronal mass ejections which are most prevalent during maximum solar aotivity, but also to the more regularly occurring corotating structures during the declining years of the cycle. A reliable prediction of the activity expected during fbture solar cycles would greatly aid in selection of the optimum time for the launch of low altitude orbiting spacecraft such as the Solar Maximum Mission (SMM) and the Hubble Telescope. The l&time of these satellites is greatly dependent upon satellite drag. The underestimatiou of the activity expected in the decline of the 20th and the start of ~e21stsoiarcycleledtofhep~reentryofSKnABin 1979. GA.LACTlC COS~C RAYS The intensity of galactic cosmic rays is modulated inversely proportional to the solar activity cycle. These highenergy particles also cause interfbrenee to technological systems. They can generate memory upsets in semiconductors on a global basis for low-altitude spacecmtt in addition to producing random upsets on other spacecraft. The random upsets on the TDRS-1 satellite from gala&c cosmic rays are illustrated in Figure 6. The number of anomalies shown per week are in the top panel which is identical to the top panel of Figure 3. The middle panel indicates the galactic cosmic ray intensity recorded by the neutron monitor at Deep River, Canada ~~~ this period. The solar aotivity cycle, typically identified by the smo&hed sunspot number, is shown in the [email protected]
~~of~~~~~cycle~~s~by~o~r~~d~~en~berof SEUs that is correlated with the galactic cosmic radiation. When the gala& cosmic radiation decreased during the rising portion of the solar [email protected]
cycle, the number of SEUs decreased. As the solar cycle approached solar minimum conditions after 1991 with a corresponding increase in the galactic cosmic radiation intensity, the number of single event upsets also started to increase. The “bursty spikes” in the number of single event upsets during the ~~ phase of solar activity are r&ted to solar proton events as discussed previously and ilhrstmted in Figure 3. High-energy cosmic rays can also inter&e with spaceerafk orientation. A sate& such as the Hubble telescope relies on specific stars for guidance. A high-energy cosmic ray can generate Cerenl~~ light or induce scintiWions in the guidance optics. The attitude control of this and similar spacecraft in geosynchronous orbit using star sensors for orientation must be camfully monitored. During high+nergy (>50 MeV) solar proton events, the star sensors on geosynchronous orbii spacecraft are particularly vulnerable to this type of interfbrence.
Year Fig. 6. Top: TDRS-I Attitude control anomafies per week (also shown in Figure 3). Center: The galactic cosmic ray intensity recorded by the neutron monitor at Deep Rivar, Canada. Bottom: The solar activity cycle as identiffed by the smoothed sunspot number. (Figure courtesy of D.C. Wilkinson, NGDC, NOAA.)
RADIATIONDOSE Both solar protons and galactic cosmic rays contribute to the radiation dose at shuttle and aircraft altitudes. The space shuttle mission STS-28 in August 1989 masured noti bv radiation for most of its time in orbit. However, an intense solar proton event commencedon 12 August impartingsolar protons >400 MeV to the upper mid-lathde region of Earth. STS-28, in a ~-~~~ orbit, rem&xi an increase in radiath dose as the spm shuttle orbited over the North Atlanticandsouthof Australia (~1~~ et al., 1994). Solar pro&mand galactic cosmic rays also contribute to radiation dose at high altitudes, particularly in thq polar to air crews, particularly pemmel akgned to high-m routes. The background mgions. msisofcomxm ~froan~ccosmicradiatian~be~~asafunctionof~pathand~~. ThechIco* su~ctnulsportisequippadwitha~~moaitorthatalertsthe~tcrewintheeventofan~solar protonevent. TheJemonitorswereactiMltedatthe”waming”l~l~thesolarproton~in1989. The radiation dosage experiencedby passengerson the Concordeflight between France aud the United States during the 29S~1989relativisticsolarpr~eveadwasestimatedtobeequivalanttotheradifftiandoseofonechwtXray. This was the largest highumgy (i.e. rhtivistic) peak flux solar proton evmt since 23 Febnmry 1956.
Table 1 presents calcul&ms of the amount of radiation expeckd from cosmic rays on three transoceanic aire& rninimum(~thegalacticcosrnic~ionisatthe~~~),~aadatsolat ~~~~~ ~~~~~~c~c~~~at~ ~~). The North Atlantic flights are ~-1~~ ~~~~c~~c~~~~~. ~S~F~~~~S~~~p~y~ eqworial route over which the shielding efht of Earth’sgmnqwtic field significantly reduces the amount of galacthcQsmicradigtionparticularlyduringsolar~ conditious. AisostumlistheradiatianexpectedmaIl [email protected]
,000&ct. ~~u~thccoacorde~esathigh~~,thedecnaseintimebetweesrP~and [email protected]
results in a slightly lower dosa8e fkomgalactic cosmic radiation. These values have been calculated [email protected]
the CARI program prepared by the US FederalAviationAgency (O’Brienet al., 1992)assuming an hour climb to cruisir~ altitude and an hour descent. These dose data are given in sieverts, the new scientific inter&id (SI) unit of biologicallyef3kche absorbedradiation. Since the doses are small, the micro Sv is a convenientunit. (1 Sv =1Gytimesdoseequi~~Q;iSv=100~~
M.A. Shea and D.F. Smart
Table 1. Examples of Cosmic Radiation Dose on Transoceanic Flights
Route. Cruisimr Altitude. Duration
Radiation Dose Solar Minimum solar Maximlml
London to Washington 37,000 Feet, 7 hours, 55 minutes
36.2 Micro Sv
22.9 Micro Sv
Paris to Washington 37,000 Feet, 8 hours, 35 minutes
39.3 Micro Sv
25.2 Micro Sv
Paris to Washington 55,000 Feet, 4 hours via the Concorde
34.5 Micro Sv
20.1 Micro Sv
San-Francisco to Sydney 37,000 Feet, 14 hours, 30 minutes
38.1 Micro Sv
33.0 Micro Sv
EFFECTS IN SOLAR CYCLE 22 There was a plethora of solar proton events in solar cycle 22 reminiscent of solar cycle 19 during the Jntemational Geophysical Year. Most of these events occurred between March 1989 and June 1991 with a “final” large event in February 1994. These events have given us a unique opportunity to ascertain the effects of the environment on various systems in space. A list of some of the e&cts to systems in space that occurred during the March 1989, October 1989 and March 1991 solar-terrestrial events is presented in Table 2. Each of these events were di&rent. The March 1989 period was a series of intense X-ray flares and soft spectra solar proton events coupled with major geomagnetic disturbances with mid and low-latitude amoral effects. The October 1989 sequence of activity produced more solar proton fluence at Earth at energies greater than 10 MeV than was measured for all the solar proton events that occurred during the entire 2 1st solar cycle. There were four intense X-ray flares and three relativistic solar proton events from 19 to 30 October. Agam mid and low-latitude auroral activity was reported during the major geomagnetic disturbances of 20 and 26 October. The event in March 1991 was entirely different. The powerful and fast interplanetary shock that impacted Earth resulted in the creation of a new inner radiation belt that was detected not only by various spacecraft such as CRRES but also by dosimeters onboard the Space Shuttle (Mullen, et al., 1991; Blake, et al., 1992; Badhwar and Bobbins, 1996). Many other periods of disruptive solar-terrestrial activity have occurred during the 22nd solar cycle. A description of many of these events and the effects to both spatial and ground-based systems is given by Allen and Wilkinson (1993). CURIOUS EFFECTS Some curious efkcts have been reported during times of geomagnetic disturbances. For example, police in the state of [email protected]
U.S.A. received radio reports from half a continent away (i.e. from California state patrohnen). People have also reported automatic garage doors mysteriously opening during geomag&ic phenomena. Boththese [email protected]
could be from radio signals “displaced” by increased ionization.
Table 2. Examples of Space Environment Impact During Specific Periods Examples of Space Ewironme& Impw#du~
Lwanoqtagoson6alld13Mareb. Satclliwtumblingon8and9Marcb. Gxnmunieations circuit anomaIy on GOES-7 on 12 March. Loss of imagery and ~~~~ on GOES-7 on 13 March. Three low-altitude NOAA polar orbiters and a DMSP polar orbiter had trouble unloading torque probably due to large changes in the ambient magnetic field. Japanese telecommunications satellite CS3B failed on 17 March. MARECS-1 satellite experienced operational problems. seriesofsevencommerc ial geostationary satellites had many problems ma&an&g operational attinuk. These mquired 177 mamral operator ~~~~ to stay within specifications. This is more than usually required during one year. GMS3 satellite suffered severe scintillations on 23 March with temporary loss of data transmission. SMM spacecraft dramatically dropped in altitude. Examples of Space En~ro~~t
Impact during October 1989
TDRS-1 experienced 50 RAM “hits” on 19120October. Space hardemd electronics on TDRS-2 and TDRS-3 experiencedsingle event upsets. A&orwts on the shuttle ATLANTIS reportedseeing “lightflashes” as energeticprotons penetrated the optic nerves. Microwave tran&t& unit switched “off’ several times on polar orbiter. Signikmt GOES-5, GGES-6, and GOES-7 solar panel power output degradation. Commercialsatellites report4 power panel degnuh&on and a total of 137 single event upsets. Significant increase in mdiation levels inside MIR space station. Examples of Space En~~~~t
Impact during March 1991
MARECS-1 satellite tkiled on 25 March. Permanent power degmdanon on GOES-7 decreasing satellite lifetime by two to three years. NOBAD experienced a significant dispkcement of 200 objects fkom spatial catalog. Japanese TV satellite BS3a lost power panel output. NOAA 11 and DMSP experienced tic attitude control problems. L-band amplifier on a geostationary satellite fails. Radiation belt modified thereby at%ting spacecraft that pass through this region. Reports of 37 single event upsets from six geosynchronous satellites.
When discussing “systems“, the biological system of the homing pigeon is [email protected]
upon the geomagnetic field to fly to its de&nation. There is a large loss of homing pigeons if pigeon races are held during major WC distmba~~ There were many reports of homing pigeons that were disoriented and lost during the August 1972 gscrmagneticaetivity. Finally, GPS satellites are now beii used to locate indivniual cars and to plot routings to various destinations. nkMehasbeena~tKWsr~rtofan~~useofthesesatellitestodetermineedistanoebecweenagotf~ and the hole during golf toumaments. Someday we may hear that a golfer will place the blame of a missed shot to space weather instead of meteorological weather.
M. A. Shea and D. F. Smart
SUMMARY It is ~ssible to uniquely quantify the ~~~~~y induced problems that systems in space envier since most problems are interrelated in a complex manner. For example spacecraft anomalies can occur fi-om solar particle or galactic cosmic-ray intetierence; solar particle interference occurs randomly primarily during the maximum yeas of sunspot activity; galactic cosmic-ray interference, also occurs randomly with a rate that is solar cycle dependent. Communication problems occur during any phenomena that increases the ionization in the ionosphere. These include solar X-ray, solar gamma ray and solar radio emissions as well as solar particle and geomagnetic disturbances. There is an expression that says “The only constant in life is change.” As our technology changes, problems with the spatial enviromnent will change. Throughout this process we will continually learn more about the solar-terrestrial system. For this reason it is important to be able to understand and predict, as accurately as necessary, the environment in which various systems operate. Predicting solar-terrestrial phenomena is still in its i&&y. The ef%ts of space weather on systems in space, as we experience them today, can only help improve the accuracy of predicting the ~~o~~t in which ~rno~s space systems will operate. REFERENCES Allen, J.H., and D.C. Wilkinson, Solar-terrestrial Activity A&cting Systems in Space and on E$arth, in SolarTerrestrialPre~ctio~ - IV, e&ted by J. Hruska, M.A. Shea, D.F. Smart, and G. He&man, Vol. I, pp. 75, U.S. Department of Commerce, NOAA, Boulder, 1993. Badhwar, G.D., and D.E. Robbins, Decay Rate of the Second Radiation Belt, Adv. Space Rex, 17, (2)15 1, 1996. Bailey, D.K., Polar Cap Absorption, PlanetaryandSpace Science, 12,495,1964, Baker, D.N., S. Kanekal, J.B. Blake, B. Kle&er, and G. Rostoker, Satellite Anomalies Linked to Electron Increase in the -here, EOS, 75,40 I, 1994. Blake, J.B., W.A. Kolasinsi, R. W, Fill& and E.G. Mullen, Injection of Electrons and Protons with Energies of tens of MeV into L < 3 on 24 March 1991, Geophys.Res. L&t,, 19,821,1992. Frederickson, A.R., E.G. Holeman, and E.G. Mullen, Characteristics of Spontaneous Electrical Discharging of Various Insulators in Space Radiations, IEEE Trans. Nucl. Sci., 39, 1773, 1992. Golightly, M.J., A.C. Hardy, and K. Hardy, Results of Time-resolved Radiation Exposure Measurements Made during US. ShuttIe Missions with a Tissue Equivalent Proportional Counter, Adv. Space Res., 14, (10)923, 1994. Lwell, B., The emergence of radio as&onomy in the U.K. after World War II, Quart.J Roy. Astron. Sot., 28, 1, 1987. Mullen, E.G., M.S. Gussenhoven, K. Ray, and M. Violet, A double-peaked inner radiation belt: Cause and Effect as Seen on CRRES, IEEE Trans. on Nucl. 5X, 38,1713,199 1. O’Brien, K., W. Friedberg, F.E. Duke, L. Snyder, E.B. Darden, Jr., and H.H. Sauer, Extraterrestrial Radiation Exposure of Air Crews, in Pr~ee~ngs of the TopicalMeeting on NewHotizons in ~d~a~on Protec~on and shielding, AmericanNuclear Society, Inc., La Grange Park, Illinois, 403, 1992. Shea, M.A. and D.F. Smart, A Summary of Major Solar Proton Events, Solar Phys., 127,297-320, 1990. Shea, M.A., and D.F. Smart, Solar Proton Flues as a Function of the Observation Location with Respect to the Parent Solar Activity, Adv. Space Res., 17, No. 4/5, (4/5)225-(4/5)228, 1996. Smart, D.F., and M.A. Shea, Solar Proton Events During the Past Three Solar Cycles, Journal of S’cecrqP and Rockets,26,403-415, 1989. Stewart, Phil. Trans. RoyalSac. London, 11,407, 1861. Violet, M.D., and A.R. Frederickson, Space Anomalies on the CRRES Satellite Correlated with the bvironment and Insulator Samples, IEEE Trans. Nucl. Sci., 40, 1512, 1993.