IF Neil Armstrong had taken a mobile phone to the Moon, it would have shone
like a beacon. After the Sun and the Milky Way, it would have appeared back on
Earth as the brightest source of radio waves in the Universe. Fortunately for
radio astronomers trying to pick out faint signals from the cosmos, no one is
yet planning to take cellphones to the Moon. But developments in communications
closer to home are posing an increasing threat. Commercial interests want to get
their hands on more and more of the radio spectrum, and this worries people like
Derek McNally of University College London. If the companies get their way, he
says, 鈥渞adio astronomy could be dead within 10 to 15 years鈥攁 quarter of a
century at the outside鈥�.
McNally is an astronomer with a special interest in the gas and dust between
stars. He became aware in the late 1980s of the severity of the interference
problem while serving as general secretary of the International Astronomical
Union (IAU), the world governing body of astronomy. Now he is trying to alert
his fellow astronomers to the seriousness of the threat. 鈥淲e鈥檙e in danger of
completely blinding ourselves to the cosmos,鈥� he says. 鈥淯nless astronomers
commit more time, effort and money to safeguarding their science, I鈥檓 afraid
they may not be doing astronomy much longer.鈥�
Human interference is becoming worse in almost every region of the
electromagnetic spectrum. Everyone knows about streetlights that blot out the
constellations for city dwellers and affect the skies for tens of kilometres
around. But now other types of radiation are being affected as well. The handful
of infrared 鈥渨indows鈥� through which Earth-bound astronomers peer into the
Universe are now being obscured by CFCs and other infrared-absorbing molecules
in the stratosphere. And it is only a matter of time before communications
companies begin to exploit shorter radio wavelengths, and invade the preserve of
the relatively new and hugely productive area of millimetre-wave astronomy.
Advertisement
But the science most under threat at present, says McNally, is radio
astronomy. 鈥淭he situation is potentially disastrous,鈥� he says. Though radio
interference is generated by a huge range of sources, from television stations
to microwave ovens, it is the threat of interference from space that is really
worrying. Several companies are planning to put constellations of satellites in
low-Earth orbit to provide global coverage for mobile phone users.
Frequency clash
The Iridium consortium, which includes Motorola and Cable & Wireless,
intends to launch 66 satellites that will broadcast and receive at a frequency
of around 1624 megahertz. This happens to be very close to the 1612 MHz
frequency of the common hydroxyl radical (OH), whose 鈥渕aser鈥� emission contains
information about regions where stars are being born. 鈥淚t鈥檚 inevitable that the
Iridium signal will spill over into neighbouring frequencies,鈥� says Mark
McKinnon, an expert in radio interference at the National Radio Astronomy
Observatory (NRAO) at Greenbank, West Virginia.
Iridium illustrates perfectly one of the major problems faced by radio
astronomy. Currently, 2 per cent of the radio spectrum is reserved for the
exclusive use of radio astronomers by the International Telecommunications Union
(ITU), an arm of the UN. However, spurious emissions from powerful transmitters
often leak into the protected bands from outside, overwhelming the weak signals
from deep space.
Radio astronomers are still smarting from the GLONASS fiasco. When Russia
launched GLONASS, its Global Navigation Satellite System, in 1982, it was
supposed to be transmitting over a region 10 MHz wide. In fact its signals were
spreading over 100 MHz. It was not until a decade later that Russia agreed to
suppress its unwanted transmissions鈥攁 case of glasnost
influencing GLONASS. Even so, the changes are not expected to be completed until
the next century.
Meanwhile, radio astronomers still want to be able to gain some access to the
98 per cent of the spectrum for which they have no exclusive right. Radio
astronomy has moved on considerably since it was allocated its frequencies by
the ITU more than thirty years ago. 鈥淎t the time, we couldn鈥檛 possibly have
known all the frequencies that would turn out to be important,鈥� says Jim Cohen
of the Nuffield Radio Astronomy Laboratory at Jodrell Bank. A case in point is
the 1612 MHz frequency of OH. 鈥淓veryone thought the principal OH spectral lines
were at 1666 and 1667 MHz,鈥� says McNally. 鈥淣obody dreamt that OH would emit
intense maser light at 1612 MHz.鈥� For this reason, 1612 MHz falls within a
鈥渟hared鈥� radio astronomy/commercial band, which explains why the ITU had no
qualms when it allocated the nearby 1624 MHz frequency to Iridium in 1992.
鈥淚n the past, we had no problems because radio astronomy was always first
into a new region with the detection techniques,鈥� says Cohen. 鈥淣ow everyone else
is there and we face uncontrolled interference.鈥�
The problems of radio astronomers today are likely to be the ones their
colleagues in millimetre-wave astronomy will face tomorrow. Currently,
astronomers have the spectrum below a wavelength of about 3 millimetres to
themselves. But powerful commercial operations are showing an interest in the
region because short wavelengths offer the large bandwidth necessary for
relaying huge volumes of data around the world.
Bill Gates of Microsoft already has a scheme, called Teledesic, to girdle the
globe with more than 800 satellites that would transmit and receive at
sub-millimetre wavelengths. The irony is that the receivers and antennas needed
to exploit the region commercially will be available within a decade thanks to
technological advances made by astronomers. Simply launching so many satellites
would cause headaches for Gates. 鈥淗e will need the present total launch capacity
of the world,鈥� says McNally. 鈥淏ut who is to say that a scheme like it won鈥檛
become a reality?鈥�
Then there are the millimetre-wave applications that pose a more immediate
threat to astronomy. For instance, car manufacturers are now testing radar
systems designed to help drivers avoid collisions, and they could be on the road
within a decade. Such systems would affect astronomy sites near roads. What鈥檚
more, meteorologists want to put satellites into orbit with downward-looking
radars to probe the clouds and atmosphere. 鈥淚t鈥檚 a case of one science blinding
another,鈥� says McNally. 鈥淚 suppose you could call it friendly fire.鈥�
Millimetre-wave astronomers will have to argue their case when the ITU carves
up the millimetre and sub-millimetre spectra some time after 1997. 鈥淭he region
is unbelievably rich in the spectral lines of interstellar molecules, and nobody
knows all the lines which are going to become important,鈥� says McNally. 鈥淲hen
you take into account the fact that those lines are red-shifted to longer
wavelengths in distant galaxies, it鈥檚 clear that protecting even 2 per cent of
the spectrum will not be enough.鈥�
Even so, he says, there are those in the commercial world who think the 2 per
cent of the radio spectrum protected for astronomy is already too much. 鈥淭hey
say we should pay for the bandwidth we use like everyone else.鈥� But the cost
would be huge. 鈥淟ast year, when the US government auctioned off bits of the
radio spectrum which it had formerly used, it charged $1 million a
megahertz,鈥� says McKinnon. 鈥淭his year the price is $10 million.鈥�
One solution to the interference problem that seems obvious would be to do
astronomy in space. Already, X-ray and gamma-ray telescopes have been placed
above the atmosphere. But, says McNally, space debris could wreck sophisticated
space observatories. The far side of the Moon remains a possibility. But setting
up an observatory there would be extraordinarily expensive, and because of the
Moon鈥檚 low gravity, any dust stirred up during construction work could take
years to settle.
Cosmic tractors
Back on Earth, astronomers are currently working on two fronts to protect
their interests. The first is strictly local. 鈥淚t鈥檚 up to each observatory to
ensure there is minimal interference from the surrounding 10 miles or so,鈥� says
Malcolm Longair of the University of Cambridge. 鈥淎t our own Mullard Radio
Astronomy Observatory, we had a particular problem with unsuppressed tractors.
They looked just like pulsars.鈥�
In the US, the NRAO has been uniquely successful in protecting its interests
by negotiating a radio-quiet zone which covers 34 000 square kilometres鈥攁n
area larger than Belgium鈥攁round its Greenbank site. It must be notified
about all new applications for transmitters, or modifications to existing
transmitters in the zone, and there are strict limits on how much power can be
transmitted at particular frequencies.
McKinnon freely admits that radio astronomers must recognise commercial needs
and cooperate with local people. As an example of such cooperation, he cites a
recent incident when some colleagues were tuned to the highly red-shifted
spectral line of atomic hydrogen in a remote galaxy. The line, at 753 MHz, was
at the same frequency as Channel 61, one of eight TV stations whose interference
is picked up at Greenbank. 鈥淚 telephoned the station鈥檚 engineer in Nashville at
2 am and he was kind enough to turn off the transmitter,鈥� says McKinnon. 鈥淭hey
got no complaints, as far as I know, so perhaps nobody was watching.鈥�
Optical astronomers, too, recognise the need for constant vigilance. 鈥淚t鈥檚 a
never-ending struggle,鈥� says Katie Pilachowski of the National Optical Astronomy
Observatories at Kitt Peak, Arizona. In the past, astronomers at Kitt Peak have
been successful in persuading nearby cities, such as Tucson, to change to street
lighting that minimises light pollution. But the new threat, says Pilachowski,
is from commercial lighting鈥攕ecurity lighting, illuminated billboards and
lighting at sports arenas and shopping malls. 鈥淲e have to recognise that
commercial lighting is necessary and work with the lighting industry to make
more energy-efficient lights,鈥� she says.
Global efforts
The local efforts of observatories like Kitt Peak and the NRAO to protect
their interests are being complemented by a global effort by the astronomical
community. This is the second front. The IAU has a commission dedicated to
lobbying for international agreements to protect observatory sites. Radio
astronomers are already pressing for measures that would control broadcasts from
space. For instance, McKinnon and his colleagues are working with Motorola to
make sure Iridium鈥檚 emissions have a minimal impact on radio astronomy.
Even so, McNally is convinced that his colleagues are not doing nearly
enough, which is why he has sounded a warning in no less an arena that The
Quarterly Journal of the Royal Astronomical Society (vol 37, p 129). 鈥淚
expect to get a lot of flak from my colleagues,鈥� he says. 鈥淏ut failure to grasp
the nettle now may lead to the ultimate extinction of astronomy.鈥�
No one denies that there is a major problem, though there are those who
disagree with McNally鈥檚 assessment of how serious it is. 鈥淵ou can take the
strength of Derek鈥檚 remarks and divide them by two or three,鈥� says Longair. 鈥淗is
scenario of the death of astronomy is at the ultimate negative end of the scale
of possibilities but there鈥檚 no denying we have a problem.鈥�
According to McKinnon, most astronomers are not facing up to the problem.
鈥淭hey simply don鈥檛 want to think about interference,鈥� he says. 鈥淎t NRAO, the
pressure is to deliver working instruments and to find out interesting things
about the Universe.鈥� What鈥檚 more, says McKinnon, the kind of work he
does鈥攎onitoring interference around NRAO鈥攊s looked down on by some
astronomers. 鈥淚鈥檝e had people say to me: `What are you wasting you career on
that stuff for?鈥� 鈥� he says. 鈥淵ou get tenure by doing astronomical research, not
by doing research to protect the research. Until that changes, we鈥檙e in
迟谤辞耻产濒别.鈥�
The astronomical community should spend a lot more time and money on
safeguarding the future of its science, says McNally. He is talking about
significant sums, perhaps as much as 1 per cent of the research budget going
into efforts to protect the research. The first step, he says, is to quantify
the problem. 鈥淲e鈥檙e not going to be taken seriously unless we can be precise
about the level of interference we鈥檙e getting across the electromagnetic
spectrum, how often it occurs, and so on.鈥� The next step is to press for a UN
agreement that protects the electromagnetic spectrum. 鈥淲e need it to have the
status of a global resource like the tropical rainforest,鈥� he says. 鈥淭hat will
allow us to mount legal challenges against the companies planning to broadcast
from space.鈥�
McNally also believes that astronomers must get the public on their side, and
here they have not been doing themselves any favours. 鈥淲e鈥檝e spent too much time
pointing out the mind-blowing power of astronomical objects like quasars and
radio galaxies,鈥� he says. 鈥淲hat we need to emphasise is how incredibly faint
their light is when it arrives on Earth and how terribly vulnerable we are to
even the weakest manmade interference.鈥�
McNally is convinced that everyone, not only astronomers, will lose out if we
inadvertently blind ourselves to the cosmos. 鈥淓ven people who are not interested
in astronomy will resent not being able to see the spectacle of the night sky,鈥�
he says. And he is convinced that vital information needed to understand the
problems besetting the Earth may be found elsewhere in the Universe. He cites
the examples of carbon dioxide on Venus, which warned us about the danger of a
runaway greenhouse effect, and dust on Mars, which warned us of the peril of a
nuclear winter, not to mention the astrophysics of stars, which determine the
abundances of elements on Earth. 鈥淲e simply cannot afford to cut ourselves off
from the Universe,鈥� says McNally. 鈥淚f the human race loses its cosmic
perspective, we are lost.鈥�