Proceedings of the Workshop - United Nations Office for Outer ...

MAINTAINING THE SPACE ENVIRONMENT 203Spillover of radio wavesAstronomy needs for its research observations on allwavelengths which are accessible to present daytechnology. They extend from very hard x-rayradiation at the short end to the entire spectrum ofradio waves. The radio signals which are received fromcelestial bodies in our own and other galaxies areexceedingly fa int. Large radio telescopes are neededfor their detection but the dimensions of the antennashave a limit given by technology of about 100 mdiameter. Still larger dishes can be built in fixedpositions, such as a valley in Arecibo, Puerto Rico,which hosts a parabolic dish of 300 m diameter. Onthe other hand, radio astronomy has become anextremely important branch which brings uniqueknowledge on very distant celestial bodies. For thisreason, selected frequency bands have been allocatedby the International Telecommunication Union, ITU,to radio astronomy. Most of the bands are quitenarrow, just covering important spectral lines, someare shared with other services but all are very close tobands used for strong telecommunication signals.Radio waves are carriers of telecommunications,an extended and highly lucrative application of spacetechnology, used for broadcasting television, mobiletelephones and navigation systems for ships andaeroplanes. The ITU is swamped with requests forassignments o f new bands. It happens sometimes thattelecommunication signals, or side lobes, spill over intothe radio astronomy bands drowning the feint signalscompletely.The following recommendation, addressed toUNISPACE III, is proposed:Support should be expressed to the principle o freserving necessary frequency bands fo r futureresearch o f distant natural sources o f radio signals,and to their protection from spill-over.Pollution by lightThe strongest pollution of the night sky comes fromsources on the ground, such as street lights oradvertising. A local but potentially highly harmful lightpollution is caused by space debris reflecting sunlight.Most wide-angle astronomical photographs show todaytraces made by space debris. These traces may destroyor compromise the value of observations which may beunique or impossible to repeat. Astronomy wouldbenefit from all measures which are taken to reduce theamount of debris. Moreover, designers of spacecraftshould avoid placing reflecting surfaces on the outsideof spacecraft which produce specular reflections. Asan example, Iridium satellites provide short flashes oflight, mostly exceeding the brightness of planets.Sensitive astronomical light detectors aimed at faintlight sources could be destroyed if illuminated by anIridium flash. The flashes are not rare events. On everyspot on the globe they occur up to 4-5 times a night. Itis a beautiful sight but may cause losses to science.The matter was treated at the IAU-COSPAR SpecialEnvironmental Symposium “Preserving theAstronomical Sky”, held last week.The following recommendation should be adopted:The principle o f preserving the dark night skysuitable fo r astronomical research should be takeninto account in planning space missions.ConclusionThis session is a unique opportunity to informUNISPACE III of the views o f the IISL on questionsconnected with the maintaining of the spaceenvironment in a state suitable for future spaceactivities. Another such opportunity might have to waituntil the next UN conference on space, i,.e., somefifteen years. Therefore the recommendations adoptedhere could deal also with matters of a long perspective.Commentary PaperG. LafferranderieMr Chairman, Madame Rapporteur, ProfessorWilliams, Professor Perek, Ladies and Gentlemen,