Small Satellites a Big Deal for Remote Sensing
Remote sensing satellites are getting smaller, lighter and less expensive thanks to advances in micro technology. By leveraging commercial off-the-shelf electronics, lighter materials and efficient processes, manufacturers are decreasing costs and creating affordable opportunities for diverse data collection. Satellites that are right-sized to meet the requirements for specific missions carry a variety of payloads for academic, government and commercial applications, including greenhouse gas monitoring, maritime tracking and messaging, and multispectral Earth imaging. Continuing efforts to miniaturize components without sacrificing functionality support the proliferation of small satellites.
The State of the Satellite Industry Report 2017, published by the Satellite Industry Association in June, reports that the number of satellites launched from 2012 to 2016 increased 53 percent over the previous five years, averaging 144 per year, due mostly to small/very small (less than 1,200 kilograms)satellites in LEO (low Earth orbit). This is encouraging news for the satellite industry and all geospatial information users. Complete and frequent coverage of the Earth complements and adds to the remote sensing options currently available from traditional large satellites, and aerial and terrestrial assets.
What is a Small Satellite?
The definitions for small spacecraft are not fixed. However, the term focuses on spacecraft less than 180 kilograms. According to NASA, minisatellites are 100-180 kilograms, microsatellites are 10-100 kilograms, nanosatellites are 1-10 kilograms, picosatellites are 0.01-1 kilograms and femtosatellites are 0.001-0.01 kilograms. Robert Zee, director of Space Flight Laboratory (SFL) in Toronto, Canada, uses the following ranges to categorize SFL’s platforms: 1-10 kilograms for a nanosat, 10-100 kilograms for a microsat and 100-500 kilograms for a smallsat.
Small satellites are spacecraft less than 180 kilograms, according to NASA.
Source: University of Toronto Space Flight Lab
To put this in perspective, DigitalGlobe’s WorldView-4 weighs around 2,500 kilograms and is 5.3 meters tall-by-2.5 meters across, not including the solar arrays. This large satellite collects 31-centimeter resolution panchromatic imagery and 1.24-meter resolution multispectral imagery, while delivering a horizontal accuracy of 4 meters CE90 (circular error 90 percent) at nadir. Although size has performance advantages, there is a cost/value tradeoff to be considered by users with limited budgets. Less expensive smallsats are an option for applications that do not require the highest possible resolution and accuracy.
SFL follows a philosophy of designing and building satellites that are the “right” size for the application. Micro technology supports building a smaller, cheaper platform around the payload, so most of the resulting mass consists of the sensors. “Quality at low cost is our focus, and we always try to improve quality without driving up the cost,” Zee says. “We follow a small team approach, which includes great talent, robust design, parts qualification and implementation including customer input. Clients come to SFL needing a small satellite to carry a specific payload. They expect an operational mission that meets their requirements.”
Earth imagers on smallsats are inherently constrained by physics — optics determine resolution, and the aperture size and focal length are limited by the size of the sensor. “Ground sample distance (GSD) is different than resolution and the two should not be interchanged,” Zee explains. “One-meter GSD is not 1-meter resolution; only with the latter can you distinguish items of 1-meter size on the ground. Resolution will continue to be a differentiating factor between aerial, large satellites and small satellites in the foreseeable future.”
However, constellations of lower-resolution imaging satellites have a role to play in meeting goals of frequency and coverage. “There are other companies pursuing a business model based on mass producing inexpensive nanosats and launching large numbers of them in groups,” Zee says. “Some fraction of them will work; however, the constellation needs frequent replenishment of assets to avoid having gaps in the data.”
Micro Technology Expanding its Reach
To address some of the challenges faced by smallsat users around positional accuracy, SFL focuses on developing high-performance ground-tracking capability. Several missions currently flying are returning ground-tracking accuracy within 0.2-0.3 degrees with a star tracker and basic sensors; this can be improved to approximately 10 arcseconds with more complex gyros and added cost.
Building large satellites with the micro philosophy will help bring costs down, but they are still extremely expensive to launch, especially to attain a specific orbit. Most smallsats piggyback on other scheduled launches, and they cannot choose a specific orbit. There is hope that SpaceX’s partially reusable launch vehicles may be able to reduce launch costs in the future.
“There will always be a role for every size satellite, but the real question is how much it costs,” Zee says. “The smaller the satellite, the lower the cost to build and launch. If you have a 100-kilogram satellite, you are looking to pay in the single millions for launch, not $60 million, so developments in the launch industry will have a major impact on the expansion of smallsats.”
Diverse Data Collection
Applications for smallsats are numerous. They are appropriate to use in many areas of science, atmospheric monitoring, ship tracking, airplane detection and Earth observation. There is not one specific area where smallsats will displace existing methods of data collection. It is more likely that they will be used in conjunction with other assets to compile a more complete picture than is currently available.
For example, an aircraft can carry more weight than a smallsat, which translates to larger sensors, more powerful optics and higher resolution Earth observation data. However, there are significant costs involved with mobilizing and operating an airplane or helicopter, and the area of interest may be restricted by no-fly rules or military conflicts. Hazardous weather can also ground aircraft, and the volume of data collected is limited by the number of hours in the air and the sensor’s swath, as compared to constellations of satellites intended to be collecting continuously all around the globe.
There are also high costs — hundreds of millions of dollars — connected to the design, manufacturing and launch of large satellites, with the corresponding benefits of tasking, direct downlink, accuracy and high-quality data. Cost has created a natural barrier to entry in this market, which the more affordable smallsats help break down.
In general, large-area collection that requires frequent revisits may be most appropriate for smallsats, while small-area collection with less frequent revisits and high resolution makes sense for aircraft. At this time, aerial assets continue to have an advantage in the architecture, engineering and transportation markets. Large satellites play an important role in global and large-area collection and monitoring due to their capacity to reliably provide large volumes of data at high resolution. Resolution and coverage areas are competing quantities, so the right-size sensor doesn’t always mean the highest resolution.
Impact on Aerial Mapping
Aerial mapping companies are closely watching the development of the smallsat industry. To stay ahead, digital aerial camera manufacturers continue to improve the quality of data and increase the volume of data collected in a variety of forms such as nadir, stereo, oblique and wide-angle. As aerial cameras continue to evolve, software and processing capabilities also are changing to keep up with demand.
“As an aerial mapping provider/buyer, we need imagery, elevation data and other data to do our work,” says Andy Dougherty, president of Continental Mapping Consultants. “We use data from minisats, drones, aerial, mobile, whatever is the best asset to accomplish what our customer needs. Microsats add to the abundance of data available, and they fill requirements that now go unmet.”
The increasing number of smallsats, along with the lower prices of imagery and associated products, has encouraged some users to think about leveraging the opportunities offered by real-time access and how it can be more useful than static maps.
“Business and transportation applications can benefit from live mapping, and this will be the norm in the next five years,” Dougherty says. “Traffic, weather, accidents will be updated on a live map along with predictive analytics. Smallsats, drones and the Internet of Things (IoT) will enable live mapping with frequent data collection. Continental already integrates multiple sensors and builds a ‘common operating picture’ for clients, and we are always open to new sources of information.”
Continental is keeping pace with the changing industry by implementing accelerated processing and obtaining the newest technology. Nvidia has helped with efficiently processing large data sets in-house and in the cloud. In anticipation of autonomous driving, Continental is also building infrastructure and operations to be able to meet detailed asset mapping requirements for departments of transportation.
“We anticipate continuing to use aerial imagery for very high-resolution, dense urban datasets,” Dougherty says. “However, smallsat data may be useful for filling gaps in projects with less rigorous requirements, and for other applications. With frequent revisits, the smallsat constellations could be the first to detect problems such as wildfires and oil spills, allowing them to ‘tip and cue’ other remote sensing and aerial assets for further investigation.”
Smallsat Data Adds to the Geospatial Picture
As supporting micro technologies continue to develop, manufacturers of small satellites, such as Space Flight Laboratory, will design smaller, less expensive platforms around increasingly high-functioning sensors for a variety of applications.
Companies that use aerial, ground and satellite data are encouraged by the potential of adding small satellite imagery to their selection of tools. New commercial assets create more data choices and competition, which creates opportunities for the whole industry.
“Continental is excited to be a member of the geospatial community as awareness of how geospatial information can be used to support decision making grows,” Dougherty says. “By accessing multiple assets and integrating improved information, our customers are getting answers to questions they’ve been asking for quite a while.”