LIVERMORE, Calif. (Lawrence Livermore National Laboratory PR) — The population of human-made satellites orbiting Earth has skyrocketed over the past 60 years. Launches nearly doubled from 2016 to 2017, and a significant contributor to this growth has been the development and implementation of small satellites that are easier and less expensive to build and more cost efficient to launch than conventional ones. Today, the hottest destination for these spacecraft is low-Earth orbit (LEO)—in the range of a few hundred kilometers above the planet’s surface.
Nanosatellites, a class of small satellites weighing between 1 and 10 kilograms (kg), have become increasingly popular because of their lower cost and ease of construction—made possible through standardization. Cube satellites, called CubeSats, are a common type of nanosatellite comprising a modular framework of cube-shaped building block units (U) that measure 10 centimeters (cm) per side, about twice the size of a Rubik’s cube. For comparison, the spherical Sputnik—the first artificial satellite in orbit—measured 58 cm in diameter and weighed 83.6 kg.
CubeSats typically comprise two main parts: a payload and a bus, the latter of which provides the structure, command and control, communication, power, navigation, and maneuvering systems for the spacecraft. Lawrence Livermore’s first involvement with CubeSats was developing optical imaging payloads for the Space-Based Telescopes for the Actionable Refinement of Ephemeris (STARE) project to monitor space debris. (See S&TR, April/May 2012, Launching Traffic Cameras into Space.) Since then, the Laboratory has continued to advance CubeSat technology and strengthen the institution’s space program. Through this work, Lawrence Livermore is embarking on new technological frontiers, from enhancing sophisticated optics and telescope designs to developing its own bus platform.
STARE-ing into Space
Consisting of derelict satellites, rocket boosters, and parts from spacecraft, pieces of space debris range in size from too small to be tracked to larger than a softball and can travel at speeds exceeding 25,000 kilometers per hour. Tens of thousands of these objects are tracked and considered lethal, and collisions, intercepts, and catastrophic failures continually increase the amount of debris. In 2009, for example, the inoperable Cosmos 2251 satellite collided with the privately owned Iridium 33 satellite over the Arctic at a closing speed of 12 km per second, breaking into more than 2,000 pieces of trackable debris. More recently, in 2015, astronauts aboard the International Space Station nearly collided with a fragment from a defunct weather satellite.
Although simple laws of physics govern the path of an orbiting object, variations in solar radiation and perturbations from the gravitational pull of the Sun, Moon, and Earth make determining the exact positions of any single object, let alone thousands, rather tricky. Satellites in LEO also experience drag from Earth’s upper atmosphere. Ten years ago, a team from Livermore, consisting of engineers, physicists, and computer scientists, began studying how to improve detecting and tracking objects that threaten space operations. Funded by the Laboratory Directed Research and Development (LDRD) Program, their approach to space situational awareness (SSA) included using high-performance computing to analyze and simulate the trajectories of space debris and the results of hypervelocity collisions between satellites. The team applied improved orbital predictions with optical and radiofrequency observations to develop their model.
Building on this modeling effort, Livermore began a partnership to build a series of three CubeSats (STARE-A, -B, and -C) and launch them into LEO at approximately 700 km. The CubeSats were designed to investigate methods for better protecting operational satellites from fates similar to Iridium 33. Livermore was responsible for developing the telescopes as part of the optical imaging payloads. Each CubeSat telescope had a diameter of 8.5 cm, weighed less than 1 kg, and took up about 1U of space.
Whereas STARE-A and -B used a conventional telescope design with independent primary and secondary mirrors for viewing distant objects, the (unlaunched) STARE-C configuration was the first to feature a new monolithic optic, an approach that combines the primary and secondary mirrors into a single element. The idea stemmed from the dual-surface monolith that Livermore scientists helped develop for the Large Synoptic Survey Telescope. (See S&TR, September 2017, The Widest, Deepest Images of a Dynamic Universe.)
In 2014, a team led by Livermore physicist Wim de Vries partnered with the U.S. Air Force and commercial bus provider Tyvak to develop the 3U GEOstare-1 CubeSat. This satellite, and the subsequent GEOstare-2, also incorporated a monolithic telescope design and tested new concepts for SSA missions. Imagery of Earth and the Moon collected by GEOstare-1 during checkout operations validated the telescope’s performance. “GEOstare-1 launched in January of 2018,” says De Vries. “We’re already done with the experiment, which produced beautiful data and validated all the ideas that we had.” Scheduled to launch in 2019, GEOstare-2 is twice the size of its predecessor. The 6U CubeSat will carry a narrow-field-of-view color imager and a wide-field-of-view panchromatic imager mounted side-by-side to fulfill its SSA mission.
Building a Next-Generation Bus
Once in orbit, bus failures prevented both STARE-A and STARE-B from becoming operational, so neither could be evaluated in space. Instead of launching STARE-C, the partners moved in new directions. Livermore again focused on telescope payloads but also began work on a new bus design. In 2014, a team lead by Livermore engineer Vincent Riot, in collaboration with colleagues at the Naval Postgraduate School and under sponsorship from the National Reconnaissance Office, created the CubeSat Next Generation Bus (CNGB) architecture. The bus design featured flexibility; transparency; and mechanical, electrical, and software standardization. Although initially defined for a 3U CubeSat, CNGB is scalable to larger configurations. Darrell Carter, lead Livermore mechanical designer for CNGB, notes, “We used the lessons learned from STARE-A and STARE-B to guide our designs and ensure we could easily and reliably mount, test, and unmount components as needed.”
To provide the most design flexibility and efficient integration of payloads, the framelike structure—a lattice reminiscent of an Erector Set toy—was designed with 4 perforated rails running the length of the CNGB structure. The rails are fastened together by 16 crossbars, and the payload and other components mount to these rails. The widely used vehicle Controller Area Network (CAN) interface handles the electricity and data signals. To support a broad range of computing platforms, the bus includes the Space Plug-and-Play Avionics (SPA) software interface.
“This work represents the building blocks for one sector of the Laboratory’s space program,” says Bill Bruner, a senior advisor for Livermore’s Space Science and Security Program (SSSP). “For years we have built instruments and optics for others. Now, thanks to a boost from our work with the National Reconnaissance Office, we are also providing bus platforms that can deliver different services for sponsors depending upon their needs.”
With the new Livermore bus design in place, in 2016 the team began partnering with NASA Goddard Space Flight Center to develop the payload and the U.S. Air Force to provide a way to launch the spacecraft. Using CNGB, the final size of the CubeSat, called MiniCarb, is 6U. Once in orbit at 500 km, MiniCarb will be used to monitor atmospheric gases. “This work represents the first time that we are launching a Livermore-developed spacecraft,” says Riot, who also leads Livermore’s MiniCarb team. “It’s a proof of concept for our bus design, but we are also conducting important science with a NASA payload.”
Building satellites inexpensively requires an innovative approach. MiniCarb was built for only $500,000 by using commercial parts that have limited lifespans in the harsh environment of space. Costs were further managed by assembling the satellite under a clean hood as opposed to in a clean room. Some of the prelaunch testing even occurred outdoors. Says Riot, “It’s a cost–schedule–performance tradeoff.” CNGB has realized the goal of cost efficiency whereby a second one would only cost a few hundred thousand dollars more to produce, take a year to build with minor modifications, and incorporate upgraded technologies and capabilities. Quick iteration of the “design–build–test–fly” cycle is the key to obtaining performance and reliability.
As with other CubeSats, MiniCarb relies on GPS and star tracking to determine its exact location and orientation. Similar to other modern satellites, MiniCarb rotates around and refines its aim using three continuously spinning reaction wheels.
Power is generated by two trifold solar panels, stored in 6 lithium batteries, and delivered by a software-controlled distribution system. This entire power system is one of Lawrence Livermore’s key innovations for CubeSats. For data transmission and other telemetry, MiniCarb uses a modem from Iridium Communications, Inc., to connect to the company’s network of satellites in orbit. In seconds, the network relays communications back and forth to an Iridium ground station linked to Livermore’s spaceflight control center.
To ensure MiniCarb can withstand the various hazards in orbit and promote its successful operation, all systems are tested and verified prior to launch as part of NASA’s Technical Standards Program. To help the satellite survive the harsh space environment, a bright, coppery-orange thermal blanket regulates the payload’s temperature as MiniCarb’s orbit causes a swing from 5°C to 45°C.
MiniCarb on a Mission
On May 8, 2018, NASA installed a 4U laser heterodyne radiometer (LHR) into Livermore’s CNGB to complete the MiniCarb CubeSat. By collecting sunlight that has passed through slices of Earth’s upper troposphere and lower stratosphere, LHR can detect the amount of sunlight absorbed by methane (CH4) and carbon dioxide (CO2). Absorption spectra are then used by scientists to measure the concentrations of these greenhouse gases.
For LHR to work, it must mix the incoming sunlight with laser light of a wavelength that corresponds to the absorption peaks of the gases. Advancements in technology and the increasing availability of laser components enabled the design of an existing ground-based LHR to be miniaturized for use in MiniCarb. The key to the LHR instrument development was finding the solid-state, distributive feedback laser tunable to around 1,640 nanometers.
Unlike typical ground-based LHRs that cannot distinguish between gas concentrations at different altitudes, or current remote-sensing, atmospheric satellites that point directly to the ground, MiniCarb will have a better vantage point. With the atmosphere positioned between a direct line of sight from the Sun to MiniCarb, the orbiting LHR can take multiple measurements as the CubeSat orbits. Each measurement slices through a different altitude, providing key details about the concentrations of greenhouse gases within the atmosphere.
The launch of MiniCarb will mark the first time an LHR enters space and the first use of a CubeSat to measure CH4 and CO2 simultaneously. NASA scientist Emily Wilson leads the LHR design and MiniCarb’s science mission. She says, “Compared to other types of commercial instruments, LHR gives a better-quality measurement because of its higher spectral resolution.” Favorable angles occur twice per orbit—the best measurement positions occur during sunrise and sunset from the CubeSat’s point of view. MiniCarb must rotate between observations at these two positions. MiniCarb records two series of scans each time it circles Earth. Up to five scans are completed per position, with each scan lasting about a minute and collecting approximately a hundred data points.
After MiniCarb’s three-month mission, its orbit will naturally decay over about two years and then burn up in Earth’s atmosphere so as not to add to the collection of already defunct satellites in space. Of the approximately 4,800 satellites in orbit, less than half of them are operational.
Small Satellites, Big Potential
The successful launch of MiniCarb will mark the first time a CubeSat bus built by the Laboratory is delivered to space. It will also represent the maiden voyage and operation of NASA’s innovative LHR instrument. Scheduled for no earlier than May 2019, MiniCarb will be put into space as part of an Earth-to-orbit rideshare. It will be a Department of Defense Space Test Program mission launched by VOX Space on a Virgin Orbit LauncherOne vehicle. Such partnerships make splitting the cost for a ride to space much more affordable.
Branching out with new mission concepts, improved optical payloads, and other technological advances, CubeSat projects contribute to both basic science and national security endeavors and have helped shape the broader Laboratory space program and mission. Mike Pivovaroff, the program leader for SSSP, adds, “The Laboratory’s strength is looking at a sponsor’s mission, separating it into basic requirements, and then doing the architectural studies, which regularly require high-performance computing. The focus of our integrated team is to provide a cost-effective solution for getting the best data for the sponsor.”
The research and development efforts have also enabled Livermore to expand its space technology expertise, which can be further applied to existing programs at the Laboratory. “For example, what if our additive manufacturing group produces a breakthrough structural element that can be used as an antenna, and scientists want to fly the element to space because it supports underlying missions,” says Pivovaroff. “We are now in a position to bring these efforts together in a vertically integrated way.”
Through a strong understanding of the principles that guide operations in orbit, development of innovative instruments, and research and design that promotes the realization of more cost-effective spacecraft, Livermore’s space program is embarking on something extraordinary. CubeSat by CubeSat, the Laboratory is demonstrating that small modular satellites are just the beginning of big scientific breakthroughs.