Cooperative Constellations: Resilient, Persistent, and Flexible Satellite Systems

Michael Pivovaroff (14-SI-005)

Abstract

Space remains vital to our national security, but the evolving strategic environment increasingly challenges U.S. space advantages. The nation's space capabilities allow our military to see with clarity, communicate with certainty, navigate with accuracy, and operate with assurance. The U.S. is reliant on the advantages afforded by an active space program, but internal and external forces threaten the nation's ability to continue operations in this once-benign environment. For this project we focused on developing enabling technologies for synoptic (frequent-view) and multi-static (multi-view) space missions. We (1) developed a low-cost, powerful facility to perform ground-based, optical space situational awareness; (2) developed algorithms applicable to satellite-based star trackers, geo-location, space object identification, and maintaining space situational awareness catalogs; (3) developed, implemented, and optimized efficient algorithms to choose the appropriate orientation of a satellite to tailor how it moves through the tenuous atmosphere present in low earth orbit; (4) modeled, fabricated, and experimentally validated the performance of a family of monolithic optics designs; and (5) developed a nanosatellite-based capability to monitor methane concentrations in the atmosphere in partnership with NASA Goddard Space Flight Center in Greenbelt, Maryland. In addition to our partnership with NASA Goddard, we developed partnerships with a number of federal agencies, universities, research institutions, and U.S. industry, including Millennium Space Systems in El Segundo, California; Rochester Institute of Technology in Rochester, New York; and Southern Research Institute in Huntsville, Alabama. This project also spawned a number of internally and externally funded efforts.

Background

The challenges facing the U.S. in space were well captured in a 2013 speech by Doug Loverro, Deputy Assistant Secretary of Defense for Space Policy, when he noted that although U.S. space capabilities were allowing the U.S. military to see with clarity, communicate with certainty, navigate with accuracy, and operate with assurance, those capabilities were being provided in an increasingly congested, contested, and competitive space environment. Furthermore, Loverro commented that space programs are, by their very nature, expensive, and that poorly planned past approaches to space programs had trapped the country in a "vicious cycle" of delayed capability, mounting cost, and increased risk. Loverro's observations concisely captured the motivation for our project. Since 2013, the security environment for national security space has only become more challenging and dangerous. The increasing challenges the U.S. faces and the willingness of senior leaders and decision makers to discuss threats from Russia and China—topics previously not discussed in the open—are evident from two widely viewed television programs: “The Battle Above” on 60 Minutes in April 2015 and “CNN Special Report: War in Space: The Next Battlefield” on CNN in November 2016.^1,2

When we started our project, we originally envisioned a multi-prong research and development program containing four broad categories of tasks in which we would: (1) fly STARE (Space-based Telescopes for Actionable Refinement of Ephemeris) pathfinders to validate modeling and simulations tools and conduct experiments; (2) explore active and passive techniques to control nano- and micro-satellites; (3) develop enabling technologies for synoptic (frequent-view) and multi-static (multi-view) missions; and (4) analyze threat posed by foreign micro-satellite development efforts. This work plan underwent several key modifications during the lifetime of the project. First, Task 4 was eliminated because it was deemed more appropriate to perform the all-source intelligence analysis within this task in a different venue. Next, although the second STARE pathfinder satellite was launched in November 2013, there was unfortunately never any communication with it. A post-mortem analysis by Boeing (headquartered in Chicago, Illinois), which manufactured the Colony II bus (the core satellite “backbone”) provided to LLNL by the CubeSat Office in the National Reconnaissance Office, revealed several fatal flaws in the Colony II design. Boeing was never able to develop mitigations and fixes with high enough reliability, so the CubeSat Office recommended no additional flights of Colony II vehicles. This satellite failure, because of the faulty bus manufactured by Boeing, prevented us from pursuing many of the investigations we had planned. For example, we could not validate models of how to passively fly satellites, because we had no way to experimentally verify the techniques with a functioning satellite. Thus, most of our research efforts and accomplishments focused on the third task: developing enabling technologies for synoptic and multi-static missions.

Scientific Approach and Accomplishments

Ground-Based Optical Space Situational Awareness Test Bed

To support the identification, tagging, and tracking of LLNL-controlled spacecraft such as the STARE pathfinders, our team developed a low-cost, powerful facility to perform ground-based optical space situational awareness in a repurposed solar observatory at Lawrence Livermore. Figure 1 shows the robotically controlled precision mount and two telescopes that comprise the basis for this capability.

This instrument supported the likely optical identification of the HORUS 3U CubeSat (the second STARE pathfinder, launched in November 2013) and allowed our team to verify that the spacecraft had deployed from the CubeSat dispenser. Figure 2 shows data from this measurement campaign.

During the later part of our project, we used this facility to acquire on-sky data from monolithic optics to validate their performance and to acquire additional data sets to test space situational awareness algorithms, including advanced methods for performing metric observations.

Advanced Methods for Performing Metric Observations and Astrometric Calculations

We developed algorithms and techniques that allow fast and reliable processing of optical observations of resident space objects, such as debris or satellites, in a variety of orbital regimes. These algorithms can support a number of missions including: satellite-based star trackers, geo-location, space object identification, and maintaining space situational awareness catalogs.

Advanced Algorithms for Astrodynamics and Passive Satellite Flying

The potential benefits of using small satellites are expected to increase if they are operated in groups or constellations. Examples of these benefits include: (1) using multiple, simultaneous viewing of the same target to provide additional context or dimension information; (2) maintaining surveillance or tracking of an object for a longer period of time than from a single satellite (typically only about five minutes from low Earth orbit); and (3) providing an imaging or sensing capability with a virtual aperture much larger than can fit in a single, small satellite, by using a synthetic-aperture imaging technique. Unfortunately, because of third-body gravitational forces, solar radiation pressure, and other perturbing forces, the satellites will drift apart if no control mechanism is employed to maintain the formation. In our project, we focused on developing methods for assembling a group of small satellites into a formation and then maintaining that formation for the duration of the mission.

Our accomplishments included developing, implementing, and optimizing efficient algorithms to choose appropriate orientation of a satellite to tailor how it moved through the tenuous atmosphere present in low Earth orbit.³ We also developed algorithms for efficiently processing space-object metric observations. These methods were benchmarked against data acquired from a variety of sources, including observations with the LLNL-based space situational awareness ground system. We also developed efficient mathematical and computational techniques to calculate a six-degree-of-freedom propagator to accurately represent a satellite's motion through space. The six-degree-of-freedom technique includes calculating and using the three positional vectors and three orientation angles to determine the process orientation, velocity, and position of a satellite, and how gravity, the atmosphere, and other factors that influence how those vectors change as a function of time. Finally, building upon the algorithms developed for producing metric observations, our team developed and implemented new techniques for determining astrometric solutions. This type of calculation can be used for determining the absolute position of a satellite, with respect to an inertial coordinate system like the galactic latitude and longitude system.

Spacecraft Technologies: Monolithic Optics

A major focus area of our work was a comprehensive exploration—modeling, fabrication, and experimental validation of performance—of the monolithic optics concept. The monolithic optics approach relies on advances that U.S. industry has made in producing high-quality optics and the availability of high-purity, low-inhomogeneity fused silica. Using these building blocks, our team conceived a new configuration of a classic Cassegrain telescope design. Traditionally, the primary and secondary mirrors are made of two different substrates held with respect to one another via a metering structure. For monolithic optics, a single piece of fused silica holds both the primary and secondary mirror surfaces. This design is more compact and robust than a traditional Cassegrain telescope and ideally suited for small satellite payloads.

We created a family of designs spanning (1) different aperture diameters from 10 cm to 100 cm, (2) different wavelength regimes from visible wavelengths as low as 400 nm to mid-infrared wavelengths as large as several millimeters, and (3) different fields of view from diffraction-limited performance with very long focal lengths with fields a view just a fraction of a degree in diameter to shorter focal-length, non-diffraction designs with fields of view several degrees in diameter. We built several prototype systems and explored and optimized different baffling schemes through extensive laboratory testing. These tests were performed at dedicated facilities as well as at a custom test facility built at LLNL.

Spacecraft Technologies: 6U CubeSat (Nanosatellite) Development

During the second half of this project, we began a partnership with NASA Goddard Space Flight Center to develop a nanosatellite-based capability to monitor methane concentrations in the atmosphere. The partnership was premised on the idea that each institution would independently support research efforts at their home organizations, coordinate the overall project goals and objectives, and integrate capabilities into a single prototype spacecraft that could eventually fly.

Goddard has made historical investments in laser heterodyne instruments to monitor atmospheric methane. This technique is the basis of the scientific payload. Independent of our work here, LLNL was funded by the National Reconnaissance Office’s CubeSat Office to develop a government architecture for nanosatellite buses. This externally funded research involved the design, fabrication, and testing of a 3U (31 × 10 × 10 cm) satellite bus. We leveraged that experience to design and optimize a 6U (31 × 20 × 10 cm) satellite bus that could accommodate a miniaturized heterodyne laser instrument. For the Measuring Atmospheric Gas Using Small Satellites (MiniCarb) project, we used some of the algorithms described above to develop an initial operational concept for how to operate the satellite during each 90-minute orbit through low Earth orbit and over the course of an entire day. The objective was to maximize science observations while ensuring reliable transmission of data to ground station, thermal and power management, and altitude control. Figure 3 shows an engineering rendering of the satellite and an example of some of the orbital studies performed.

Partnerships

One of the goals of this LDRD was to develop partnerships with other federal agencies, universities, research institutions and U.S. industry. We were very successful in this area, both enhancing our own research efforts with expertise and capabilities unique to each of our partners, as well as establishing strong collaborations that continued after this project ended. Above, we described the partnership with NASA Goddard Space Flight Center on the MiniCarb project. The development of MiniCarb continues, and the plan for the Lawrence Livermore and NASA teams is to complete the spacecraft, launch it, and then operate it and perform scientific observations for a year. The two research teams have already submitted one joint proposal and will look for additional opportunities in the future.

Millennium Space Systems, a small aerospace firm, is an example of one of the companies driving the renaissance of the U.S. satellite industry. Millennium has delivered inexpensive but very capable systems to several key U.S. government sponsors. We partnered with Millennium, and our project supported LLNL’s contributions to this effort.

We also funded researchers at Rochester Institute of Technology to use their expertise in accurately modeling terrestrial and space scenes by, for example, generating imagery of deserts and dense urban environments that account for realistic reflections off the surfaces and materials present in those landscape. We then used these realistic simulations to test and improve algorithms and evaluate the effectiveness of our monolithic optical designs. This partnership with Rochester allowed us to help two U.S. Air Force officers formulate Masters and Ph.D. thesis projects. The success of the work performed by the Rochester faculty under this project has lead to collaborations on additional LLNL projects.

Southern Research Institute, a not-for-profit research institute, has significant experience developing leading-edge technologies for aerial-based intelligence, surveillance, and reconnaissance. This institute assessed that the compactness and robustness of monolithic optics would make them ideal candidates for unmanned aerial platforms. Southern Research Institute regularly performs measurements on the NASA WB-57 platform, and they helped provide access to us to fly a monolithic optics payload in 2015. This measurement campaign was very successful, and provided the first color video imagery obtained at altitude using monolithic optics.

Impact on Mission

Our research is directly aligned with the Laboratory's strategic focus area in cyber security, space, and intelligence and is also relevant to LLNL's strategic focus area in energy and climate security, through measurement of pollutants in the upper atmosphere.

Conclusion

Due to re-scoping of our project, most of our research efforts and accomplishments focused on the development of enabling technologies for synoptic (frequent-view) and multi-static (multi-view) missions. Our accomplishments included the development of (1) a ground-based optical space situational awareness test bed, (2) advanced methods for performing metric observations and astrometric calculations, and (3) advanced algorithms for astrodynamics and passive satellite flying. We also modeled, fabricated, and experimentally validated the performance of the monolithic optics concept and, in partnership with NASA Goddard Space Flight Center, developed a nanosatellite-based capability to monitor methane concentrations in the atmosphere. These accomplishments led to a number of expanded collaborations. As a result of our work on advanced algorithms and hardware concepts, several U.S. government sponsors have funded programs to deploy and adapt these capabilities for their specific missions.

References

1. Turner Broadcasting System, Inc., "CNN special report: War in space: The next battlefield." Cable News Network. (2016). http://www.cnn.com/videos/tv/2016/11/23/exp-cnn-special-report-war-in-space.cnn
2. CBS Interactive Inc., "The battle above." 60 Minutes. (2015). http://www.cbsnews.com/news/rare-look-at-space-command-satellite-defense-60-minutes/
3. Pertica, A. J., and M. J. Pivovaroff, Cooperative constellations: Persistence, resilience and flexibility for space systems. (2016). LLNL-PRES-715095.

Publications and Presentations

• Ammons, S. M., Feasibility of laser communications for 3U satellites. (2016). LLNL-PRES-66448.
• Bauman, B., Preliminary design of 18cm F/16 monolithic optic. (2016). LLNL-PRES-664482.
• Bauman, B., et al., LLNL monolithic optical systems. (2016). LLNL-PRES-664391.
• Nikolaev, S., Implementing Hough/Radon transform on NVIDIA Jetson TK1 board. (2014). LLNL-TR-664136.
• Pertica, A., Monolithic optical payloads for nano-satellites. (2016). LLNL-PRES-664483.
• Pertica, A. J., and M. J. Pivovaroff, Cooperative constellations: Persistence, resilience and flexibility for space systems. (2016). LLNL-PRES-715095.
• Pertica, A. J., et al., Monolithic optics characterization and testing. (2016). LLNL-PRES-666363.
• Pivovaroff, M. J., The Importance of LDRD in creating LLNL's space program. (2016). LLNL-PRES-717683.
• Pivovaroff, M. J., The importance of LDRD in creating LLNL's space program, version 2. (2016). LLNL-PRES-717698.