The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket experiment enables hard-X-ray solar observations with high angular resolution, high energy resolution, and high sensitivity using the direct imaging method. The fourth flight, FOXSI-4, aimed for the first-ever focusing imaging spectroscopic observation of a medium to large solar flare in hard X-rays and launched in spring 2024 as part of NASA's sounding rocket solar flare campaign. For resolving structures in the footpoints and the loop-top of a solar flare, the hard X-ray telescopes, which consist of focal plane detectors and Wolter-I mirrors, are required for high angular resolution of 3 arcseconds with high-count-rate photon detection. We developed wide-gap CdTe Double-sided Strip Detectors (CdTe-DSDs) for the hard X-ray focal plane detector, which achieved an energy resolution of 1 keV (FWHM) and a high position resolution of 30 mu m with high detection efficiency. We also developed a new onboard data acquisition (DAQ) system with a Raspberry Pi, an FPGA board SPMU-001, and a SpaceWire interface for controlling all CdTe-DSDs and realizing fast readout of the observation data whose counting rate is estimated to be 5000 counts per second. The observation data is written in a 128 MB data ring buffer region for temporary storage. The software in the Raspberry Pi controls each detector by the commands from a ground-based computer and simultaneously reads the data at 0.6 Mbps for storage in the DAQ. Some essential data for operation, for example, light curves, energy spectrum, and the status of the DAQ system, is sent to the ground-based computer through the onboard control system.

Satellites in low-Earth orbit have complex missions involving various time-dependent attitude requirements. For instance, a satellite must point an antenna toward a ground station to communicate with Earth and point its solar panels toward the Sun to collect power. At the same time, the mission of a satellite may make certain attitudes desirable or unacceptable. These complex constraints on a satellite's control design can be dealt with succinctly by Signal Temporal Logic (STL) specifications. In this work, we leverage the robustness degree metric on STL expressions---quantifying the degree to which an STL specification is satisfied by a signal--- and formulate an optimization problem that maximizes the robustness degree to generate control trajectories for the small satellite IMPRESS. We utilize the smooth approximation of robustness degree and use a gradient-based optimization framework to generate these control trajectories. The proposed approach is validated on simulated data for a mission scenario involving communication with ground stations and maintaining onboard power.

This paper presents a method to improve mission performance for Cube Satellites (CubeSats) with scientific missions. The proposed approach proactively plans slew maneuvers which trade mission objectives against power constraints. There are many scientific CubeSat missions which require pointing a sensor payload at a target in space. During the design phase of these missions there exists a trade-off between ambitious missions with many pointing targets, and hardware cost. In the past, many CubeSats have used naive event-triggered mode switching-e.g. slewing towards a ground station for downlinking only when it becomes visible rather than in advance-which serves to reduce the total amount of scientific data transmitted to the ground over the mission lifetime. In this work, we develop a mission planning method that maximizes data volume downlinked over attitude history. We formulate the optimization problem as an integer program over the space of attitude histories and subject to battery level constraints. The optimal solution is an attitude sequence that can be used as a reference for a low-level controller to track. We demonstrate the approach using simulated data for the upcoming CubeSat EXACT, which has a celestial scientific target in addition to requiring ground-pointing for data transmission and Sun-pointing for power. Extensions of the work to benefit the related CubeSat IMPRESS are also discussed. Using the quality metric of total data volume received on the ground, we demonstrate the effectiveness of this approach in maximizing downloaded science data while maintaining the battery within operating limits.

This work demonstrates a high-level mission planning method for maximizing data output from a pair of scientific CubeSat missions. The proposed approach identifies the optimal sequence of attitude maneuvers to perform in order to maximize total downlinked data over the mission, while considering constraints on available power. Many scientific satellite missions consist of at least three target attitudes: pointing solar panels towards the Sun for power, pointing an antenna towards a groundstation to transmit data, or pointing a payload towards a point of scientific interest. While careful mechanical design of the mission may enable all three (or more) target attitudes to be achieved simultaneously in certain cases, in general a decision must be made about which target to point to at what time in order to optimally achieve mission objectives and satisfy mission constraints. In this work, we develop a mission planning method that maximizes the volume of data downlinked to the ground over the mission time horizon while respecting constraints on battery level. The optimization problem is posed as an integer program over the space of attitude trajectories and subject to battery constraints. The solution of this problem is an attitude sequence that can be used as a reference for a low-level attitude controller to track. Previous work on this problem suffered from slow solution time for complex mission scenarios which constrained the realism of simulations performed for validation, so in this work we build on our prior approach by leveraging more advanced pruning and search methods to improve optimizer efficiency. We demonstrate the proposed approach on two CubeSats: IMPRESS and EXACT, both currently in design and sharing many mechanical specifications. Both CubeSats are controlled by low-bandwidth actuators and have three main attitude targets: the Sun for power, the Crab Nebula or the Sun the scientific mission, and ground stations for communication. Using simulated orbit data, we show the effectiveness of this method in squeezing mission performance out of both CubeSats while maintaining on-board power. Additionally, the proposed method can run faster than real-time for time horizons of several orbits, enabling a high level of autonomy in orbit

The FOXSI-4 sounding rocket will fly a significantly upgraded instrument in NASA's first solar are campaign. It will deploy direct X-ray focusing optics which have revolutionized our understanding of astrophysical phenomena. For example, they have allowed NuSTAR to provide X-ray imaging and IXPE (scheduled for launch in 2021) to provide X-ray polarization observations with detectors with higher photon rate capability and greater sensitivity than their predecessors. The FOXSI sounding rocket is the first solar dedicated mission using this method and has demonstrated high sensitivity and improved imaging dynamic range with its three successful flights. Although the building blocks are already in place for a FOXSI satellite instrument, further advances are needed to equip the next generation of solar X-ray explorers. FOXSI-4 will develop and implement higher angular resolution optics/detector pairs to investigate fine spatial structures (both bright and faint) in a solar are. FOXSI-4 will use highly polished electroformed Wolter-I mirrors fabricated at the NASA/Marshall Space Flight Center (MSFC), together with finely pixelated Si CMOS sensors and fine-pitch CdTe strip detectors provided by a collaboration with institutes in Japan. FOXSI-4 will also implement a set of novel perforated attenuators that will enable both the low and high energy spectral components to be observed simultaneously in each pixel, even at the high rates expected from a medium (or large) size solar are. The campaign will take place during one of the Parker Solar Probe (PSP) perihelia, allowing coordination between this spacecraft and other instruments which observe the Sun at different wavelengths.