In
the realm of space exploration, nearly everything seems large: from enormous
space shuttles and rockets, and the booming explosions that accompany the crafts
at liftoff, to the sizeable planets and objects of study. Even costs can be
colossal, with the average price tag of getting objects into orbit at about
$22,000 per kilogram. Bigger, however, is not always better, say some scientists
working to design, construct and test the next generation of space satellites.
Three birthday-cake-sized microsatellites are working together to explore Earth’s magnetic fields, as shown in this artist’s depiction of NASA’s Space Technology 5 (ST5) mission, which launched in March. Small technologies are allowing scientists to launch small satellite clusters, which can collect data simultaneously at multiple points in space. All images are courtesy of NASA.
Technologies similar to those that have helped cell phones reach diminutive sizes over the last decade now allow researchers to push satellites toward a similar trend. Not only are these small satellites less expensive to produce and launch, but they also have strength in numbers.
By clustering together small Earth-observing satellites, scientists can make measurements not obtainable with larger individual satellites. In addition to collecting weather data on Earth, the small satellites can also reveal new information about “space weather,” which includes the sometimes harmful effects of energetic particles from the sun interacting with Earth’s magnetic field.
Strength in numbers
In October 1957, the Soviet Union launched Sputnik 1, the world’s first artificial satellite, which was a sphere 58 centimeters across that weighed 83.6 kilograms. The United States followed suit in January 1958, and launched Explorer 1, which measured 203 centimeters long (including the rocket) and weighed only 13.9 kilograms. (Science instruments aboard Explorer 1 discovered the presence of radiation belts around Earth.) As the complexity of satellite missions grew, however, so too did satellite size and weight — the space-based telescope Hubble, for example, which launched in 1990, measures 13.2 meters across and weighs 11,110 kilograms.
Over the last decade, however, the trend has been to develop smaller satellites that maintain high levels of capability and work in concert to accomplish a task. Such satellites — called minisatellites, microsatellites, nanosatellites, picosatellites or even femtosatellites, depending on their sizes (see sidebar) — are the future of space technology, says Martin Sweeting, chief executive of Surrey Satellite Technology Ltd., an enterprise company created by the University of Surrey in Guilford in the United Kingdom. The near future will see a “considerable increase” in the use of small satellites to carry out tasks previously only done by large and expensive satellites, Sweeting says.
At the request of NASA and the National Oceanic and Atmospheric Administration (NOAA), the National Academy of Sciences tasked a committee to begin a study in 1995 to determine the feasibility and advantages of small satellites (between 100 and 500 kilograms) for Earth-observing missions. The report, The Role of Small Satellites in NASA and NOAA Earth Observation Programs, published in 2000, determined that while small satellites are not likely to entirely replace traditional larger satellites, the smaller versions offer opportunities for low-cost missions and alternative launching techniques.
Accordingly,
NASA recently set out to test newly developed miniature technologies in the
harsh environment of space so they can be incorporated into future missions.
On March 22, NASA launched a rocket from Vandenberg Air Force Base in Santa
Barbara County, Calif., carrying three microsatellites that are part of the
Space Technology 5 (ST5) mission. Each craft weighed only about 25 kilograms
and measured about 50 centimeters across — approximately the size of a
large birthday cake and four to five times smaller than an average NASA satellite.
Rather than working independently, the three satellites will work together.
A support structure flung each ST5 mission microsatellite like a Frisbee into its final orbit around Earth in April, as depicted in this still shot from an animation. Scientists on Earth could engage microthrusters aboard each satellite and make small adjustments to its position.
“Data from the three spacecrafts together gives you a whole that’s greater than the sum of its parts,” says Candace Carlisle, ST5 deputy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Md. Such constellations of individual satellites simultaneously take measurements at different points of space and could change the way scientists study Earth and its surroundings.
The more satellites, the better the data, says Art Azarbarzin, project manager of ST5 at Goddard. Several multi-satellite missions currently orbit Earth, including the U.S.-Taiwan satellite cluster Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), which launched April 14 to collect temperature and other weather-related data. COSMIC’s six satellites, each measuring 103 centimeters by 16 centimeters and weighing 70 kilograms, are profiling in 3-D the humidity, temperature, pressure and electron density in Earth’s atmosphere. Data from the COSMIC constellation will almost triple the amount of real-time, high-resolution data available for weather forecasts and research, according to estimates released by the University Corporation for Atmospheric Research in Boulder, Colo.
If the number of satellites in a constellation increased to 100, for example, then “the accuracy of the forecasting would be much better,” Azarbarzin says. Placing weather satellites all over the globe could collect temperature data from all sides of Earth and at different altitudes and provide better resolution of data for models, he says.
“Forecasting weather for the everyday person who deals with the weather, would be a lot more accurate in the future if they use this technology and this concept around Earth,” he says. But the small-satellite technology could also prove useful for making forecasts for cosmic weather predictions off the planet.
Stormy weather
On Oct. 31, 2003, a charged wind of solar particles destroyed two satellites, disrupted radio communications and knocked out power to tens of thousands of people. This “Halloween storm” was a result of space weather, caused by changes on the sun.
Such space weather events also can bombard astronauts with radiation and can mingle with the Earth’s magnetic field to produce the colorful and dynamic light of the aurora, as well as to induce large currents in power lines and cause transformer failures that can lead to widespread power outages. Thus, scientists are continually trying to improve the accuracy of space weather predictions (see Geotimes, October 2005).
Previous attempts to understand these events from single-satellite measurements failed to determine if magnetosphere disturbances occur in time, space or both, says Robert Strangeway, the director of ST5 contributions from the University of California in Los Angeles (UCLA). Multi-satellites, however, are gaining ground.
On Aug. 5, 2004, the European Space Agency’s (ESA) Cluster mission — a group of four, 2.9- by 1.3-meter crafts at 1,200 kilograms each — measured a magnetic disturbance area that spanned 30,000 kilometers. Based on their weight, these crafts fall under the category of large satellites, but they represent the first time that the “true extent” of a disturbance has been measured, and the feat was only possible by using multiple satellites, according to an ESA press release. This success helped spur interest in using satellite clusters to understand space weather, including ST5.
ST5 was planned as a prototype technology mission for future NASA missions, including the launch of 50 small satellites to study Earth’s magnetosphere. The Magnetospheric Constellation Mission (MagCON), as the 50-satellite mission was called, has since been delayed because of funding cuts, but the mission is still under consideration, Carlisle says.
Still, the primary mission of ST5 remains to test the new, small technologies that compose the magnetometers, which take measurements of Earth’s magnetic field. With magnetometers aboard a constellation of satellites, scientists may be able to discern the changes to the magnetosphere in 3-D and better understand processes affecting Earth’s magnetosphere. Testing ST5’s constellation of three satellites is the “first step” toward decreasing size and increasing performance of future multiple satellite missions, Carlisle says.
A tiny test
In addition to the magnetometers, smaller-than-ever components that scientists are testing onboard each satellite during the ST5 science mission include a transponder (which communicates data back to Earth), a battery, thrusters and solar panels. The technologies aboard ST5’s swarm of three satellites are “the smallest we know of that have this level of capability,” Carlisle says.
Additionally, the mission is testing a new support structure that, once in orbit, hurled the three ST5 satellites away, sending them spinning like Frisbees. The design provided a simple way of propelling each satellite into positions that would eventually line up between 40 and 200 kilometers apart and fall into orbit around Earth’s poles. Uncertainty existed, however, about exactly where the launch vehicle would place the satellites. NASA scientists were able to use tiny thrusters to make some minor adjustments to a wayward satellite that released too low to nudge it back into alignment.
Next, each self-contained satellite extended a boom with a magnetometer attached. In April, when each satellite was correctly positioned in polar orbit around Earth, the magnetometer became the key device collecting measurements of Earth’s magnetic field during ST5’s 90-day science mission.
A team led by Strangeway at UCLA took three years to build the magnetometers. The university has built magnetometers for more than 35 years for missions that include Apollo 15 and 16 in the early 1970s. Each mission required magnetometers built to meet NASA specifications, but the magnetometer for ST5 was “the smallest we’ve had to build for spaceflight,” Strangeway says.
The magnetometers, like most small satellite parts, are designed from Earth-based technologies. The key, Sweeting says, is to take these “commercial off-the-shelf” terrestrial technologies developed for industrial and leisure markets — such as the smaller and more powerful microelectronics for mobile phones, digital cameras and nanotechnologies — and adapt them for use in space.
But in space, without Earth’s protective atmosphere, the radiation environment is “nasty,” Strangeway says, and the huge amount of radiation that strikes the crafts every year can cause them to malfunction. That’s why lag time exists between when Strangeway and colleagues identify key components in Earth technologies and when it actually migrates into small satellite technology. It takes time to make each technology “flight qualified,” he says, which includes finding new designs and manufacturing processes for components, as well as shielding them from radiation.
Time will tell whether UCLA’s magnetometers can take the heat, but the first data received indicated that the devices on all three satellites “are in great shape,” Strangeway says, “and we’re looking forward to doing some pretty new science with it.”
Costs and tradeoffs
The
2000 National Academy report speaks to the idea that small satellites do not
ensure that the mission itself, along with its cost, will also be small. The
report notes that Earth-observing missions with a large constellation of small
satellites “may cost a great deal, even though the individual satellites
may cost little.”
An engineer at Goddard Space Flight Center in Greenbelt, Md., examines a tiny magnetometer, which measures energetic particles in space that interact with Earth’s magnetic field. Built by scientists at the University of California in Los Angeles, the sensor (seen here at the end of the boom) weighs only 75 grams (0.16 pounds) and is part of NASA’s ST5 mission.
The launch of three ST5 satellites together aboard a Pegasus XL rocket cost NASA $30 million, for example, less than what it would have cost to launch three satellites separately. The total cost of the ST5 mission, however, including research, technology and launch, totaled $130 million. Still, one goal of a technology demonstration like ST5 is to absorb the overhead costs of miniaturizing technology so that new tools are available for use on future missions at lower cost, Carlisle says.
Surrey Satellite Technology sees a growing market in developing small satellites, says Sweeting, the company’s chief executive. The company takes research carried out at universities (for Earth-observing satellites) and develops small satellites for commercial, civil and military applications. The company’s main customers include emerging space countries, such as Algeria, South Korea and Turkey, that want to own and operate their own satellites, as well as existing space countries, such as the United States, France and China, that want a satellite for a specific task built more quickly and at a lower cost than traditional-sized satellites, Sweeting says.
For now, though, manufacturing satellites in general is only “modestly profitable,” Sweeting says, with demand currently highest for civil and military use. Most manufacturers likely pull in about a 5 to 10 percent net profit margin, Sweeting says.
But as satellites decrease in size, they became cheaper and more adaptable, as well as better able to incorporate up-to-date electronics over shorter timescales, Sweeting says. He expects such advantages will lead to an increased interest in small satellites, including satellites that produce services such as GPS and communications, which bring in higher revenues, he says.
Small satellites for large Earth-observing clusters will see price reductions mostly in launch costs. Smaller satellites mean more of them can be launched on a single, smaller launch vehicle, which is one of the “major drivers” in the cost of a mission, Carlisle says. “If we can get two for one, then we’re in better shape,” Strangeway adds.
But while the move from launching single satellites to three at a time is “a step in the right direction,” going from building instrumentation for three at a time to 50 at a time requires manpower to increase by a factor of 10, as well as an assembly-line process to build hardware, Strangeway says. “We’re not at that stage yet.”
Making satellites ever smaller also comes with tradeoffs between size, power and capability, Carlisle says. To fit NASA’s ST5 specifications, UCLA scientists had to build hardware that ran on 7 volts, about one-quarter of the amount of power allowed for average space hardware they build.
In addition to power restrictions, small spacecraft have a limit on the amount of hardware they can hold, no matter how advanced the technologies. For example, the James Webb Space Telescope — a space-based, infrared telescope planned for launch as soon as 2013 — will have some ST5 technologies in its design, Azarbarzin says, but it will remain a large 6.5 meters across, due to its power requirements and the size of the mirror needed to collect light.
“There will still be certain missions or services that will require large satellites,” Sweeting says. But with the 90-day ST5 mission demonstration, scientists want to show that small technologies running on less power are capable of collecting research-quality data on the grandest of scales.
Hansen is a staff writer for Geotimes.
Links:
"New flare for space weather prediction,"
Geotimes, October 2005
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