Constraints on a scientific project

Print edition : October 24, 1998

The National Centre for Radio Astrophysics has finally signed with Iridium an agreement that will provide some protection to its Giant Metre wave Radio Telescope from radio interference.

AFTER many months of negotiations, the National Centre for Radio Astrophysics (NCRA) and Iridium LLC, a subsidiary of Motorola, the telecommunications giant, have signed a Coordination Agreement that will provide the Giant Metre wave Radio Telescope (GMRT) located near Pune, some protection from radio interference caused by Iridium's satellite-based global mobile telephone services. The GMRT is one of the world's most powerful radio telescopes.

The agreement, valid until January 2006, was signed by Vijay Kapahi, Director of the NCRA, and James G. Ennis, Iridium's counsel, after its details were worked out by the NCRA, Iridium LLC and the Wireless Planning and Coordination (WPC) office of the Government of India. In wireless lingo, coordination refers to an understanding between agencies so that when a particular satellite is on a radio telescope's horizon, the satellite company will switch off in accordance with a pre-arranged time and date schedule.

The five-page agreement guarantees that:

* By restricting its transmissions every day between 12 midnight and 6 a.m., Iridium will protect the GMRT from any harmful interference from its satellites whenever the GMRT is used to make observations in the OH band of 1610.6 to 1613.8 megahertz (MHz).

* Radio astronomers will be able to make interference-free observations of rare targets such as comets and supernovae outside this "protected" time slot;

* For the next generation of satellites beyond January 1, 2006, Iridium has agreed to take steps to minimise the emission of "spurious" signals from its satellites at all times of the day; and

* If the GMRT considers it necessary to augment its own system in order to achieve an acceptably low level of interference, Iridium will find ways and means to meet the cost.

The low-cost parabolic dish of the Giant Metre wave Radio Telescope located near Pune. The restricted access to the 1610.6 to 1613.8 MHz band is a double misfortune to the GMRT.-VIVEK BENDRE

Although the Coordination Agree-ment was signed on September 22, it is dated May 19, 1998. Iridium India's vice-president (technical operations), T.K. Sridharan, told Frontline that "all technical basics have been resolved" and that the delay was only about "a matter of semantics" which was being resolved by lawyers.

While agreeing that the Iridium systems will cause problems to radio observations, Sridharan argued that "there is no real issue until 1999 since the GMRT does not even have all the requisite equipment to begin operations. Even after it is installed it will take a few years to become fully operational." This explains why the NCRA-Iridium agreement will be in effect until 2006 whereas the Arecibo Observatory in Puerto Rico, which has the world's largest telescope, has opted for an annual review of its deal with Iridium.

The basic problem between radio astronomers and Iridium arises out of the closeness of the bandwidths allotted to them. There is a bandwidth difference of only 8 MHz between the two. This will result in Iridium's signals often interfering with the signals received by radio telescopes. Radio astronomers worldwide have been unhappy with the technical design of the Iridium systems which do not provide for non-interference with radio telescopes operating in radio frequencies near the 1612 MHz band (Frontline, April 17, 1998).

The International Telecommunica-tions Union (ITU), the organisation that assigns wavelengths and radio bands worldwide, has allotted the band 1610.0 to 1626.5 to mobile satellite service providers, such as Iridium, in which downlinks (transmission of signals downwards) between 1613.8 and 1626.5 MHz have a secondary allocation. Radio astronomers have a primary allocation in the 1610.6 to 1613.8 MHz band. A secondary allocation permits the use of a band with the proviso that no harmful interference should be caused to and no protection be asked from primary users. Thus the ITU agreed in 1992 to the use of neighbouring bands for mobile satellite communications, with the proviso that radio astronomical observations would be fully protected.

All communication satellite networks plan to use frequencies near the 1612 MHz radio band for uplinks (sending signals from the ground to space). However, Iridium, with a chain of 66 communication satellites, faces criticism because it plans to downlink on the same frequency. According to Sky and Telescope, an astronomy journal, "Iridium's design seems destined to introduce unintended transmissions into the OH band."

The OH band is one of the most important bands for radio astronomy. It falls in the 1610.6-1613.8 MHz band. OH, the hydroxyl radical, is abundant in space and so is seen as a tracer in observations of the universe. OH radicals are found in the dark clouds of gas and dust in interstellar space. Such clouds are believed to be the sites of star formation; hence their importance to radio astronomers.

Although the ITU is the body that makes radio regulations, according to Kapahi, "it works largely on the goodwill of the parties involved" as far as their implementation is concerned. However, Kapahi believes that one positive development in recent times has been that astronomers have "agreed to work collectively on all aspects related to the protection of radio astronomy observations and to lobby for radio astronomy with their respective administrations and policymakers."

DESPITE the settlement, astro-nomers working on the GMRT system will be functioning under certain constraints. By March 1, 1999, the interference levels that should be filtered and the duration of this process will be decided by Iridium. Sridharan says that "this level will not be the same as that asked for by astronomers."

A major problem is that although radio astronomy has primary allocation in the 1610.6 to 1613.8 MHz band, radio astronomers will be able to use this band only between midnight and 6 a.m., when traffic on the Iridium system is expected to be low. Elaborating on the loss to radio astronomers, Arecibo's Dr. Chris Salter told Frontline: "Arecibo especially will feel this time restraint since it is one of the most heavily oversubscribed in terms of telescope observation proposals. The existence of Iridium will put a severe constraint on our ability to conduct the research proposed by the global user community."

An advertisement for Iridium's satellite phone service.-

The rapid increase in the commercial use of radio waves for communication needs has resulted in an overcrowding of bandwidths. Radio astronomers, more than any other users, are particularly affected. They are passive users of the system - they only receive, and never send, signals. They install large and expensive pieces of equipment which are extremely sensitive because they have to listen to signals that could have been generated millions of light years away. Any man-made disturbances can swamp these faint signals. And as Kapahi puts it, "shut a window to observe the universe." It appears that radio astronomers were not vigilant although the potential threats from the Iridium systems were known since 1992.

Speaking in defence of the scientific community, Kapahi says that Motorola had initially assured scientists that it would work in a non-interfering manner. "It only became clear to us in 1995 or 1996 that Iridium would not be able to do so." The original Iridium design apparently had filters meant to cut-off out-of-band emission. These were later dropped. Scientists theorise that this was meant to reduce the weight of the satellites. Quoting an article published in the August 1998 issue of Nature, Kapahi says, "I believe the European Science Federation has recently signed an agreement with Iridium on behalf of all radio astronomers in European countries, which appears to bind Iridium to improving its system for the next generation of satellites after January 2006."

In the specific instance of the GMRT, the restricted access to the 1610.6 to 1613.8 MHz band is a double misfortune. The GMRT is acclaimed in the scientific world for its low-cost parabolic dish. This indigenous design is now viewed as a blueprint. Although the GMRT was originally designed to operate in six different frequency bands between 38 MHz and 1420 MHz, the flexibility of this design allowed scientists to extend its operations to the higher frequency bands of 1610.6 to 1613.8 MHz. So, although Kapahi reasons that "in India it became clear a year ago that with some additions and modifications, the GMRT would be able to make useful observations in this band although the telescope was primarily designed to observe in a number of frequency bands below 1400 MHz" there is no doubt that the GMRT design will not be used to its full potential.

Kapahi says that although Indian astronomers are "unhappy that there will be time restrictions for observations in the O* band, the compromise solution is considered acceptable under the circumstances because only a small fraction of the GMRT would be used for observations in this band. The GMRT would be used extensively by astronomers in six other frequencies."

Preferring to take a positive stand on the issue, he says that the need of the moment is "to strike a balance" and to recognise that "communications services are important for development."

However, he is firm in his defence of radio astronomy. "Radio astronomy has made significant contributions to the development of technology. The large antennae systems, low-noise amplifiers and receivers... have clearly had a beneficial impact on daily life."

Kapahi's views are echoed by Salter, who says: "If all pure-science related research were to be stopped, we would be halting the growth of the pool of knowledge from which the most exciting future developments will come... Knowledge that is gained by the relatively low-cost radio astronomical research is priceless, unique and is the property of the whole world. In contrast, commercial ventures such as Iridium, while indisputably providing valuable services to many, are driven by the profit motive of a relatively small body - on a global scale - of people."

Kapahi concludes: "It would indeed be sad if, in order to meet our commercial and developmental requirements today we condemn our future generations to a frog-in-the-well kind of existence, incapable of exploring the universe beyond planet earth."

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