A CubeSat is, by definition, a 10 cm cube with and a total mass less than or equal to 1.33 kg. The exponential increase in CubeSat interest in its nearly two-decade-long existence can be attributed to a few primary factors. The CubeSat design is a well-defined standard, allowing universities to quickly implement a CubeSat program and integrate it into its curriculum. Having a standardized launch platform, called a P-POD, allows the CubeSat community to request for launch opportunities, typically as secondary payloads on commercial flights, long before the internal design of any CubeSat is finished.
NASA and NSF have both started research programs that fund CubeSat missions for scientific objectives. Dr. Barjatya was funded as an instrument PI on the NSF DICE mission and has been recently funded on the NASA LLITED mission. Both of these are dual 1.5U CubeSat missions.
Brief introductions and a few pictures for each of these missions is provided in the accordions below.
Mars’ interaction with the solar wind is unique among the planets because it does not have any intrinsic magnetic field. Instead, it has a nonhomogeneous crustal magnetic field and an induced magnetic field due to its ionosphere. ESCAPADE is a recently selected (2019) NASA SIMPLEX mission for Phase A/B study. With unprecedented two-point plasma measurements, ESCAPADE will untangle temporal from spatial variability and definitively map out the transfer of energy and momentum that leads to ion and sputtering escape, enabling a much more reliable extrapolation of escape rates to early Mars. Thus, this mission will help us understand the rate at which Mars lost its atmosphere. The mission PI is Dr. Rob Lillis from Space Sciences Laboratory at University of California, Berkeley. Dr. Barjatya is a Co-Investigator providing in-situ thermal plasma measurement instrumentation.
SAIL is providing a suite of Langmuir probes consisting of a Planar Ion Probe, a Multi-Needle Langmuir Probe and a floating potential probe. These instruments will collectively provide absolute electron and ion density and relative spacecraft charging potential. The instruments will also provide measurements of integrated EUV flux in the solar wind.
The mission is on schedule to hold its Preliminary Design Review in July 2020. Further details of the ESCAPADE Langmuir Probe suite will be provided as the mission progresses and meets scheduled milestones.
The Low-Latitude Ionosphere/Thermosphere Enhancements in Density (LLITED) CubeSat mission is a recently funded (2017) NASA HTIDs program. It is a three-year grant with two 1.5U CubeSats with a one-year on-orbit mission life. Each CubeSat will host an ionization gauge (IG), planar ion probe (PIP) and GPS radio occultation sensor (GPSRO). The mission is to provide both ionosphere and thermosphere measurements related to the Equatorial Ionization Anomaly (EIA) and the Equatorial Temperature and Wind Anomaly (ETWA). The EIA and ETWA are two of the dominant ionosphere/thermosphere interactions on the low-latitude duskside. While the EIA has been extensively studied both observationally and with modeling, the ETWA is less well-known since observations are infrequent due to a lack of suitably instrumented spacecraft at appropriate altitudes. LLITED will, for the first time, provide coincident high-resolution measurements of the duskside ionosphere/thermosphere at lower altitudes that will characterize and improve our understanding of the ETWA, provide insight into the coupling physics between the ETWA and EIA, and increase our knowledge of the duskside dynamics that may influence space weather.
SAIL will design, build, calibrate and deliver the Planar Ion Probe (PIP), which is a gold-plated planar Langmuir probe based in the ion saturation region. PIP is depicted as the gold rectangle on the top plate of the LLITED CubeSat in the image above. The top plate will be within a few degrees of the RAM direction. PIP will provide absolute ion density for the LLITED science mission.
Planar Ion Probe Salient Features:
- Total 17 cm2 electronics board
- 4 x 6 cm sensor plate with 1 cm wide guard electrode
- Low mass components: instrument PCB 9 g, sensor 10 g, envelope 27 g
- Power draw of 125 mW at nominal ion density (2 x 10^11 m-3)
- Power draw of 250 mW at maximum ion density (2 x 10^13 m-3)
- Instrument boot-up time ≤ 350 ms
- Design resolution (noise floor resolution):
- Better than 10% precision throughout the four decades of measurement
More details about the mission can be found in the Small Satellite Conference Proceedings paper on LLITED. And more information on the PIP instrument can be found in the MS Thesis of Liam Gunter.
Funded by the NSF CubeSat and NASA ELaNa programs, the Dynamic Ionosphere CubeSat Experiment (DICE) mission consists of two 1.5U CubeSats that were launched into an eccentric low Earth orbit on Oct. 28, 2011. Each identical spacecraft carries two Langmuir probes to measure ionospheric in-situ plasma densities, electric field probes to measure in-situ DC and AC electric fields, and a science-grade magnetometer to measure in-situ DC and AC magnetic fields.
Dr. Geoff Crawley from Astra was the mission PI. The satellites were built at Space Dynamics Laboratory under the guidance of program manager Chad Fish and Deputy PI Dr. Charles Swenson. Dr. Barjatya from SAIL was the Instrument PI on the Langmuir probes.
Given the tight integration of these multiple sensors with the CubeSat platforms, each of the DICE spacecraft is effectively a “sensorsat” capable of comprehensive ionospheric diagnostics. The use of two identical sensors at slightly different orbiting velocities in nearly identical orbits permits the de-convolution of spatial and temporal ambiguities in the observations of the ionosphere from a moving platform. In addition to demonstrating nanosat-based constellation science, the DICE mission is advancing a number of groundbreaking CubeSat technologies, including miniaturized mechanisms and high-speed downlink communications.
A comprehensive paper on DICE mission has been published in Space Science Reviews.
DICE is primarily an exploratory Space Weather mission. Several important research questions regarding Storm Enhanced Density (SED) were the focus of the DICE mission, specifically the physical processes responsible for the two features of SEDs: SED plume and SED bulge. But beyond the ambitious science, the CubeSat technology innovation in DICE was also state-of-the-art. This included a high-data-rate S-band radio, a total of 10 complex deployable booms, the first dual-constellation of satellites trying to do science and so on.
DICE had two 1.3 cm diameter gold-plated spherical Langmuir probes that were deployed from the top and bottom of the CubeSats on scissor booms. To avoid adverse spacecraft charging events, the probes were biased in the ion saturation region at -7 volts. The Langmuir probes were typically sampled at 35Hz but also had the capability to be sampled at 70Hz in "science mode." Deploying the two probes 180 degrees apart guaranteed that at least one of them would be out of the wake. SAIL has published a paper on complicated wakes around CubeSats in Journal of Spacecraft and Rockets.
The figure below shows three orbits of the two DICE CubeSats (named Yahtzee and Farkle) overlaid on each other. Farkle was following Yahtzee for 26 minutes in the same orbital plane. The plot shows in-situ observed ion density at the same physical location, 26 minutes apart in time. Measurements like this show the power of doing CubeSat constellations wherein is possible to do spatial and temporal measurements of plasma parameters.
