1. Undergraduate
Nano
Ionospheric
Temperature
Explorer
| Wyatt Helms |Sujan Kaphle | Glen Kissel | Ryan Loehrlein| Zack Snyder |
ABSTRACT
The Undergraduate Nano Ionospheric Temperature Explorer (UNITE) 3U CubeSat has been designed and built by an all undergraduate team at the University of Southern Indiana as part of NASA’s Undergraduate Student Instrument Program – 2 (USIP-2). The mission of UNITE is to calculate plasma properties in the lower ionosphere using data from a Langmuir Plasma Probe, to measure temperatures in the interior and on the skin of the CubeSat to compare with a student-developed thermal model, and to carefully track the orbital decay, especially near re-entry, using an onboard GPS unit. Following deployment from the International Space Station in early 2019, UNITE will orbit the Earth for about 450 days. Its Globalstar-based communication system allows nearly 24-hour coverage of the mission, which is complemented by a student-designed mobile app, allowing mission monitoring from one’s smartphone. Transmissions have been structured to provide intense data collection the first week of the mission, followed by more modest collection until the CubeSat reaches altitudes below 300 km, where the magnetometer will be sampled to confirm stabilization in the ram direction of the passively stabilized vehicle. Frequent Langmuir Probe and GPS sampling and transmissions will occur below 225 km, even up to re-entry, allowing valuable data collection in the Extremely Low Earth Orbit region. An exploded view of the CubeSat is shown.
Mu-Metal Rod
Mission Objectives
Conduct Space Weather Measurements in the lower ionosphere using a Langmuir Plasma probe.
Measure Exterior and Interior Temperatures of the spacecraft for comparison against the thermal simulation model.
Track Orbital Decay of the spacecraft in the lower ionosphere and during the final hours of re-entry.
Expected Results
Langmuir Plasma Probe Expected Results:
# of plasma particles: 3 x 102 cm3 to 5 x 106 cm3
Plasma temperatures: 400 K to 2500 K
Temperature Sensor Expected Results:
Temperatures from -30 C to 34 C
Orbital Decay Expected Results
Able to reconstruct orbit below 150 km where Two Line Element is in Error
Langmuir Probe Antenna
Batteries
Command Board
EPS
Ballast Mass
Langmuir Probe
AsteRx-m GPS
Duplex
Fins
Duplex Antenna
Horizon Sensor
Simplex Antenna
Temp Sensor (x8)
Magnetometer
PCB
Solar Cells
GPS Antenna
Flight/ Ground Software
Mission Control on
the Go
Integration and Testing
Command Board
Global Positioning System
Printed Circuit Boards
The GPS subsystem is designed to provide PVT (Position, Velocity, and Time) data during the flight mission. The GPS was carefully designed to interface with the Command Board (CB) via a transmission (TX) line. The CB will utilize the altitude from the GPS to determine which mode of operation to be in. The PVT packets will also be sent to the Ground Station (GS) for further processing and calculations. Once the UNITE team receives the GPS PVT data it will then be used to obtain the orbital elements to replicate the satellites orbit. The information will be further analyzed by inputting the raw PVT data into Systems Tool Kit (STK) to see how simulation portfolios in STK vary from the actual orbital element calculation. Through the UNITE mission the GPS subsystem has been evaluated through extensive testing scenarios.
Two different Printed Circuit Boards (PCBs) were designed for this project. The first design is capable of holding 8 Spectrolab UTJ 28.3 % efficient solar cells and the other design can hold 6 Spectrolab UTJ solar cells. A time intensive process was involved to attach each of the solar cells to the PCB. The team had to attach a grounding tab to the back of each solar cell by using Silver Epoxy. Once the tab was placed on the solar cell it was immediately placed in an oven for 3 minutes to cure the epoxy. RTV was then placed onto the PCB and spread evenly across the surface. The solar cells were than placed and soldered down. The team was successfully able to fabricate 4 solar panels for the UNITE mission. Countless designs and revisions were tested before arriving at the final Solar Panel Design.
A major component of UNITE is the student-designed and -populated printed circuit board. Designated as the Command Board, this unit features a PIC24FJ256GA106 microprocessor, a digital-to-analog converter, a temperature sensor, and an auxiliary power circuit. The Command Board was designed using Eagle PCB software, manufactured by Sunstone Circuits, populated at USI’s Applied Engineering Center, and separately tested in the UNITE flowbench. The auxiliary power circuit on the UNITE Command Board takes the +5 V power supply from the NSL EPS, and converts it to -9 V, -5 V, and +9 V also making it possible for the command board to sweep voltages between -4.5 V and +4.5 V. These supplies are used in UNITE’s Magnetometer and Langmuir Plasma Probe. Another feature of UNITE’s Command Board is the data scaling circuits. These are used for most of the scientific instruments to scale the signals into a range that the microprocessor can read.
The UNITE CubeSat team has reached the sought after milestones for the year. The team was able to perform an end-to-end integration, environmental testing, and day in the life testing. The environmental testing mainly consisted of performing a thermal bakeout/thermal-Vacuum testing on all the internal/external components. This test was performed at Morehead University where the satellite was subjected to temperature cycles ranging from 45C to 6C. During this temperature cycle profiles a vacuum of 9.0 x 10-6 Torr was being pulled. Likewise, thermal bakeout of the external solar arrays was conducted at University of Illinois at 70C followed by solar array, c.g., MOI, and magnetometer test. Vibration test was performed at ETS with NanoRacks. Each axis of the CubeSat was subjected to a sine sweep prior to and after the random vibration parameters. No major anomalies were detected during these test.
Instead of the traditional Mission Control Center, the UNITE team decided to take a mobile approach to mission operations. Making use of the Globalstar network instead of a singular ground station, UNITE’s flight software is able to continuously gather data and transmit it to the ground, offering near realtime measurements of its instruments. Therefore, Mission Control On-The-Go, a proprietary mobile app, seemed like the best way to take advantage of regular data downlinks. The app will offer commanding capabilities as well as detailed data measurements and graphs representing conversions of UNITE’s sampled instruments’ output.
UNITE’s mission and data gathering flight software was developed almost completely in-house and was designed to handle its variety of instruments as well as capitalize on its connection to the Globalstar network. The software was written in the C programming language using the MPLab X IDE and built to run on a Microchip PIC24FJ256GA106 microcontroller. UNITE, by design, can run autonomously, switching through altitude-dependent modes for the entire length of it’s mission; however, it is also capable of responding to commands sent by the UNITE team from the ground. Each mode (Interim, Stabilization, Science, and Reentry) is built to run a different stage of UNITE’s mission, each with a different data/operational focus.