Technology Leaps Shape Satellites of Tomorrow [LOR/GSTRF references]
awgnet.com
JOSEPH C. ANSELMO/WASHINGTON
Revolutionary technologies on the horizon promise to dramatically
improve the capabilities and costs of tomorrow's spacecraft. But in
a departure from the past, it will be commercial markets, not
governments, that define what these new systems will look like. In
this special report, Aviation Week & Space Technology editors
outline some of the most promising technology trends and how
they could alter the space landscape over the next two decades.
The report also takes in-depth looks at four of those technologies:
space inflatables, on-board processing, phased array antennas and
flywheels.
Ever since the
small Sputnik
satellite sent chills
through the
Western world in
October 1957,
aerospace
engineers have
been working to
design more
capable satellites.
Over the years,
larger and larger
spacecraft have
evolved, with
ever-growing
power and
communications
capacity. The
U.S. National
Reconnaissance
Office (NRO)
now operates
mammoth
intelligence
spacecraft on the
order of 15 tons,
while commercial
geosynchronous
spacecraft have
grown to 5 tons.
But things may
come full circle in
the next two
decades as
satellites come
down in size for
low-Earth orbit
(LEO) and
medium-Earth
orbit (MEO)
applications.
Scientists are
envisioning a
return to
Sputnik-sized spacecraft, but this time as highly- sophisticated
processors. Each satellite would possess massive computing power and
interconnect with dozens or even hundreds of similar craft to provide
blanket coverage of the Earth at all times, be it for telecommunications,
intelligence monitoring or scientific observation.
The much smaller spacecraft would dramatically reduce launch costs,
which today average about half the price of a satellite. And they would
be largely autonomous and self- correcting, eliminating much of the need
for ground control.
Visions of basketball-sized spacecraft elicit excitement in government
labs. But in the commercial sector, where looking more than 10 years
into the future is considered folly, two diverse patterns have emerged.
Geosynchronous spacecraft
continue to grow in size to
meet increased bandwidth
and power requirements.
Just last week, Space
Systems/Loral announced
plans for a modular 25 kw.,
150 transponder satellite
bus. Dubbed "20.20," the
bus would have a dry
weight of 2,500 kg. (5,500
lb.).
On the other hand,
commercial LEO and MEO
spacecraft used for voice
and data communications are shrinking. A 16-beam Globalstar mobile
telephone satellite, for example, weighs just 1,000 lb. and its payload
uses only 1.1 kw. of power.
What is clear is that a number of new technology advances are within
reach which should vastly lower the cost of utilizing space during the next
10-20 years. Major advances are in the works in areas such as on-board
processing, reconfigurable antennas, power systems, chemical
propulsion, inflatables, laser communications and robotics.
"We have been moving along the path of evolutionary technology and
have reached a plateau. The time is now ripe for revolutionary
technologies," said USAF Col. Pedro Rustan (Ret.), previously director
of smallsat development for the NRO and the Ballistic Missile Defense
Organization's Clementine program and now general manager of the
commercial Ellipso venture.
In a paradigm shift, development of many of those technologies will be
driven more by the needs of consumers than governments.
In the U.S., most of today's spacecraft advances were born out of the
Reagan defense buildup of the 1980s--particularly the Strategic Defense
Initiative--and, as recently as 1995 technology development, was still
government-led, Rustan said. The Iridium project, for example, leveraged
military technology for its constellation of low-Earth-orbit mobile
telephone satellites.
But 21st Century projects, such as Teledesic's $9-billion-plus "Internet in
the sky," are forging ahead with research tailored to meet commercial
requirements. The trend is likely to grow even stronger. According to
projections by Futron Corp., all of the robust growth in the space market
will come from the commercial side, while the government market will
remain flat for the foreseeable future.
"The government cannot outspend the commercial space industry," said
Rustan. "They will fund the technology whether the government wants it
or not. Government is no longer the controlling factor."
Though the U.S. still holds an enviable lead in satellite technology,
Europe is pushing to catch up. And Japan is undertaking basic research
in satellite communications, especially optical communications, and
pursuing development of robotics and automatic docking for space
platforms.
Some technology areas that will be key to 21st century satellites are:
On-Board Processing, Power and Communications. Satellite makers
are beginning to produce the first civil products in which signal
processing, whether to filter and route data, or to actually regenerate data
on board the spacecraft, are starting to appear.
Two principal drivers are at work. Satellites are being transformed so
customers only pay for services they use when they use them. And
spacecraft builders are anticipating the Internet will usher in a new era for
mobile communications, whether that means instant communications with
the office or downloading a movie anytime, anywhere. "On-board
processing will be the big breakthrough in satellite technology in the next
10-15 years," predicts Jean Broquet, director of R&D at Matra Marconi
Space.
The computer revolution is playing a major role. On the ground, the cost
of computing has gone down by a factor of 1 million during the last two
decades. C. Paul Robinson, president and director of Sandia National
Laboratories, said he sees no major impediments to achieving a further
reduction of similar magnitude over the next 20 years.
Expanding on-board capacity requires power--lots of it--as evidenced
by Loral's new plans for a 25-kw. satellite. "The key constraints on
satellites are power, power, power, weight and size," said Brian
Clebowicz, the operational leader for digital electronics at Hughes Space
& Communications. He envisions nearly unlimited demand for signals
processing.
Advanced flywheel technology could provide longer life for power
systems and more compact energy storage than chemical battery systems
(see p. 67). And work is underway to increase the amount of sunlight
solar cells are able to harness.
Hughes' Spectrolab, Tecstar and Encore are working under U.S.
government sponsorship to try to develop solar cells that could retain
37-40% of the Sun's energy, well above the experimental 26% peak that
companies have achieved to date. Spectrolab President Dieter Zemmrich
said basic physics will limit improvements of solar cells to the 40% range.
After that, he expects efforts will focus on improving the overall efficiency
of spacecraft power systems.
In the communications area, phased-array antennas, with electronic
agility that allows them to be reconfigured in orbit, are already in the
works for next-generation commercial spacecraft. The combination of
commercial market demand and advances in antenna design, materials,
production processes and solid state electronics has broken down cost
barriers (see p. 65).
Miniaturization. More than a few researchers are envisioning fleets of
interconnected microsatellites (10-100 kg.) and nanosatellites (under 10
kg.) in the not-too-distant future. William C. Tang, chief of
microelectromechanical systems (MEMS) research at the Jet Propulsion
Laboratory, envisions "drastically smaller" spacecraft in 5-10 years and
fleets of 1-kg. satellites within 10-20 years (AW&ST Sept. 7, 1998, p.
141).
A team at NASA's Goddard Space Flight Center is aiming to develop a
fleet of 10-kg. satellites to simultaneously study interactions between the
Sun and Earth from different vantage points. The team hopes to launch
up to 100 spacecraft at once into highly elliptical orbits in 2007.
A project at Sandia is attempting to develop a nanosatellite that integrates
microsystems, MEMS and photonics technology, performs significant
efficiency improvements in photovoltaics, batteries and structures, and
utilizes laser communications. The goal is to launch a spacecraft in 4-5
years that can perform a "significant mission" related to Sandia's role in
detecting nuclear proliferation. "Anyone today could put up a 10-kg.
satellite that does nothing," said Jeff Kern, principal investigator for the
project. "Our goal is to get into the realm to use these very small satellites
independently or in groups to perform the functions done [today] by
much larger satellites."
Some industry observers believe Japan could take a leading role in
MEMS technology because of its expertise in micro-electronics. But to
date, the Japanese have failed to apply their knowledge in the field to
commercial spacecraft.
Inflatables. Space inflatable technology languished in the conceptual
phase until a L'Garde inflatable antenna experiment was tested on the
space shuttle in May 1996. Inflatables could enhance
miniaturization--allowing satellites to be boxed into small packages for
lower-cost launches--but also would enable the deployment of giant
space structures such as 1,000-ft. antennas (see p. 60).
Space applications are diverse, ranging from solar array struts to antenna
reflectors, solar concentrators, pressurized habitats and ultimately optical
telescope mirrors (an application that interests the NRO).
One L'Garde idea calls for NASA's Arise spacecraft to use a 25-meter
(82-ft.) inflatable antenna to make radio interferometry observations of
stars (see cover). The spacecraft also would utilize inflatables to deploy
and support its solar arrays.
Optics. The use of optical, or laser, communications offers the
potential of transmitting many times more data than today's RF
communications, which are limited to about 3-5 gigabits per sec. "We
have some [experimental] satellites up now that are running at 30
megabits/sec. data rates," said Sandia's Robinson. "I suspect we'll be the
better fraction of a terabit [1 trillion bits/sec.] in 15 years."
Though great pointing accuracy is needed, there are no major hurdles to
using lasers for spacecraft-to-spacecraft communications. Teledesic, for
example, is planning optical links to connect its 288 satellites.
Communications between space and Earth are more problematic,
however, because of atmospheric conditions such as clouds that interfere
with laser pulses. Last summer, the NRO awarded a contract to TRW to
build GeoLITE, a spacecraft dedicated to studying--and presumably
overcoming--those obstacles. Launch is set for 2001.
In Europe, Alcatel Space is already looking beyond the Silex optical
experiment that was orbited last year on board the Spot 4 spacecraft
(AW&ST Mar. 31, 1997, p. 51). The company is working on a new
system that would allow intersatellite links at transmission rates of several
gigabits per sec., compared to 50 megabits/sec. for Silex. Terminal mass
is expected to be about 20 kg., one-tenth that of Silex.
Meanwhile, Matra Marconi Space is focusing its research on ultra-stable
materials, such as silicon carbide, which are critical in many optical
applications, including communications.
Propulsion. Electric propulsion, pioneered in space by the former
Soviet Union in 1965, offers greatly reduced propellant weight over
traditional chemical systems. Commercial spacecraft builders in the U.S.
and Europe are utilizing electric propulsion for stationkeeping, but so far
have shunned its use for orbital transfers which, because of minuscule
thrust, can require as much as 200-300 days to travel from low-Earth
orbit to geosynchronous orbit.
But that problem could be significantly mitigated within 5 years by power
advances, according to Rob Jankovsky, who leads Hall thruster
development at NASA Lewis Research Center. "If we had 50 kw. on a
spacecraft we could do LEO to GEO transfers with all-electric
propulsion in less than a month," he said.
Jankovsky's team recently tested a Hall truster that surpassed 1 newton
of thrust--enough to make the orbital transfer in 30-60 days. Similar
research efforts are also underway in Europe.
Robotics. Work is underway to develop constellations of robotic
spacecraft that can communicate with one another, hand off information,
take action independent of human input, and even repair themselves.
Robinson envisions constellations of micromachines as small as
basketballs, baseballs, or even marbles. Such systems could constantly
stare at a target area 24 hr. a day, seamlessly handing off responsibility to
the next spacecraft.
A key wild card, however, is whether commercial operators of fixed
geosynchronous spacecraft will ultimately migrate to low- and
medium-orbit spacecraft to take full advantage of the potential
revolutionary technologies offer. Many see little economic reason to
change, opting instead to take advantage of incremental improvements in
power and transponder capacity. It is those doubts that make it hard to
pinpoint exactly when the Sputnik-like spacecraft will return.
European Editor Michael A. Taverna contributed to this story from
Paris.
© January 25, 1999, The McGraw-Hill Companies Inc.
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