NASA’s Goddard Space Flight Center’s Spectrum Management office is a hidden guardian for space communications activities, protecting the crucial, yet finite, spectrum Goddard needs to launch missions, conduct science and explore the universe.
Without the office managing Goddard’s invisible communications assets, the spectrum could be auctioned off to the highest bidder or used inappropriately, substantially limiting NASA’s critical ability to communicate with spacecraft and operate science instruments.
What is Spectrum?
“Spectrum” is a generic term encompassing the various frequencies of electromagnetic waves, including radio waves and light.
Space data is traditionally transported over radio waves. Because a finite amount of radio frequencies exists, spectrum must be prioritized to serve the country’s and the world’s most crucial interests.
NASA communications range from around 50 hertz to 200 gigahertz, enabling NASA missions to track hurricanes and wildfires, detect masses in the universe, determine ocean levels and soil moisture content, monitor solar activities and more.
When data travels through radio waves, those waves (or frequencies) are spread out (or modulated) to accommodate the data volume; transporting more data requires more space (and therefore more frequencies, or greater bandwidth).
NASA is also testing and developing technologies that utilize frequencies in the light portion of the spectrum, which are not as limited in availability as radio waves.
Imagine you are driving from one city to the next and as you approach the city border, your radio starts to produce static noise. This is the result of frequency interference.
In much the same way, communications to and from space can experience interference if frequencies or spacecraft are too close together. Interference can also occur if two spacecraft have (or appear to have) the same endpoint. So if two spacecraft on Mars were looking at Earth, two different ground antennas that were far apart could appear to be the same point.
Here are a few ways to mitigate interference:
- Different frequencies: Isolate communications by using different frequencies, if available.
- Physical space: Position spacecraft to be physically far apart or have visibly different endpoints. The second solution is harder to accomplish when spacecraft are far away from Earth.
- Time management: Allocate turns for different spacecraft (or science instruments) to transmit data along a particular frequency.
If one of these strategies is unavailable, spectrum managers must employ other mitigation techniques.
Role of the Spectrum Management Office
Goddard’s Spectrum Management office, housed within the Exploration and Space Communications Projects Division in Greenbelt, Maryland, serves many roles.
Spectrum managers keep track of all spacecraft coming out of Goddard, ensuring their needs concerning bandwidth (width of frequency modulation), data rates and regularity of communications are met.
One major responsibility is to prevent interference using the tactics mentioned above. In one method, spectrum managers allocate certain bandwidths to specific types of compatible space users (see Image 3). For example, NASA’s Tracking and Data Relay Satellites, a fleet of data relay spacecraft, facilitate communications to the International Space Station in the Ku-band.
Spectrum managers also model and compare a spacecraft’s planned communication times and frequencies with all known users (within and outside of NASA) to make sure there is no interference, a process that can take months. This is necessary because no project or mission has an exclusive right to use any frequency. Spectrum is shared by many users, so all communications links must be individually analyzed and authorized.
The spectrum team assigns frequencies after considering how often and with which systems spacecraft need to communicate. The team constantly monitors usage requests around the world to protect assigned spectrum through the entirety of a mission’s lifespan. This helps not only to ensure that no other spacecraft or outside organizations jeopardize NASA missions by causing spectrum interference, but also to make sure NASA’s usage protects other authorized operators.
Most of NASA’s bands have historically been reserved for space agencies, but many commercial users have been trying to buy the spectrum for private use, including diversifying cellular bands and retrieving imaging information from space (such as maps and weather data) for sale.
While spectrum can be shared, sharing is only feasible if it is used in technically compatible ways. NASA works to protect its spectrum usage from constraint by other users – both domestic and international – that may not be compatible with existing and future NASA missions.
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By Seema Vithlani
NASA's Goddard Space Flight Center, Greenbelt, Md.