Morehead State's Lunar IceCube 6U CubeSat is on its way to the Moon! According to NASA GSFC, Lunar IceCube made contact with NASA's Deep Space Network's Goldstone 24 dish after deployment as part of the Artemis mission.
Lunar IceCube utilizes a Pumpkin two-wing, 126-cell solar array with each wing individually articulated via Pumpkin's DASA, a kind of Solar Array Drive Assembly (SADA) that incorporates a rad-hard H-bridge designed by GSFC. Solar array power feeds into Pumpkin's EPSM1 power system, to which two Pumpkin BM2 batteries are connected to give a total of 200Wh of reserve power. MSU designed a custom tabbed-style 6U CubeSat chassis as the structure.
The EPSM1 was chosen for this mission because of its ability to handle the difficult load that the on-board cryocooler for the BIRCHES instrument presents, and because Lunar IceCube needs a lot of power to operate its thruster as it transits from Earth orbit to a lunar orbit. Lunar IceCube is in group "A" below:
Of note is the fact that Lunar IceCube and several other CubeSats were integrated onto the Artemis LV in the fall of 2021; Lunar IceCube was not afforded the opportunity to top off its batteries a year later. When inhibited by their separation switches, the Li-Ion cells in the Pumpkin BM2 batteries experience the same self-discharge rate as bare 18650 cells manufactured with Li-Ion cell chemistry (typically around 1.5% per month). Despite the 15-month storage time and being outside for several weeks prior to the Artemis 1 launch, the all-Pumpkin power system weathered the conditions just fine, and Lunar IceCube's initial commissioning appears to have gone smoothly. Additional BM2 features like automatic cell balancing and heaters will come into play over the lifetime of the Lunar IceCube mission.
From its current orbital position around Earth -- where it is subjected to considerable radiation -- Lunar IceCube will take another six months to reach the moon and begin its lunar capture maneuvers.
Because of a third-party delay, one of Pumpkin's 12U buses has undergone ground-based testing for several months longer than originally planned. This has presented the opportunity to fine-tune Pumpkin's GUTS flight software for enhanced performance. Because this 12U program only purchased one radio (the Flight Model), Pumpkin's software team developed a suite of tools to ensure reliable radio communications without having 24x7 access to the flight hardware.
As part of our testing, a ground-based Engineering Model is used to first validate GUTS, and then new code releases code make their way to the Flight Model. One of the critical GUTS components is the radio service that implements the CCSDS protocol over a commercial S/X-band radio. In order to test the radio service without access to the S/X-band radio, Pumpkin wrote a radio simulator. In the real-time performance plot below, the radio service (running on a Pumpkin 1GHz BeagleBone Black (BBB) SBC in a Pumpkin RS3) is communicating with the radio simulator (on a Xeon-based desktop PC) over a 100Mbps Ethernet link.
By using the simulator to develop and fine-tune the simulator, GUTS's CCSDS radio service can now deliver continuous throughput as high as 45Mbps (limited by the BBB SBC). While the actual radio may limit on-orbit performance, this test setup demonstrates the current upper bound of GUTS' radio service's performance in the existing 12U SUPERNOVA architecture. Further optimizations may raise the radio service's performance even further.
At the end of the cold-temperature BM2 battery testing mentioned in the previous blog post, the BM2 was allowed to rest. This simply means that the overall power system was not drawing any power from the BM2, and the BM2 was fully charged to its terminal voltage (16.2V in this particular test). The resulting cell voltages illustrate the efficacy of the cell balancing algorithm -- there's a maximum spread across the four cells of 5-10mV.
The BM2 intelligent battery module includes an active battery balancer that automatically seeks to equalize the voltages of all two (2S4P) or four (4S2P) cell groups in the BM2's total of eight 18650-size Lithium-Ion cells. The balancer is active when the battery is charging and when the charge current has dropped below a prescribed limit.
Most Li-Ion batteries cannot be charged at temperatures below 0ºC, and the BM2's LG MJ1 cells are no exception. The BM2 cell heaters for this cell chemistry automatically enables the heater at 5ºC as the temperature drops and disables it once the temperature rises to 7ºC.
As part of low-temperature testing being performed at Pumpkin, a neat telemetry capture came up this evening. The thermal chamber is set to -5ºC, the BM2's heater was in the default AUTO mode, and the charging current into the BM2 was limited to 1A to simulate a wimpy charger. The cell heaters consume around 8W; battery energy is 100Wh.
As the heaters turn on and off, the current flowing into the cells decreases and increases, respectively (because charge + heater current is limited to 1A). Each time the charge current increases, the cell voltage increase with it, but individually. The telemetry capture shows the four individual cell voltages as the BM2 approaches its final pack voltage. You can see the active cell balancing in cell 2 (the purple trace): it started out around 20mV higher than cell 4 (the yellow trace), but within 45 minutes of all of the cells charging, these two cell voltages have converged. All four cell voltages will converge further as the BM2 continues operating like this. The cell balancing is slow but effective; we typically see mismatches of under 5mV across four cells, when the balancing algorithm is allowed to run its course.
The cell balancing, cell heaters and real-time telemetry (and nearly 100 other data points) are available to all BM2 users as standard features of each BM2.
After over 13 years of holding prices constant, inflation and the global supply chain (GSC) crisis have finally forced Pumpkin's hand. Chips that were easily available in 2019 for $4 are now costing $65, if you can find them. So it was with great reluctance that we raised our prices today.
We will honor the older pricing until May 31 for those customers who have received quotes or contacted us with pricing between Jan. 1 and April 8. For all other customers, the new pricing takes effect immediately.
Did you know that Pumpkin also develops and sells a unique RTOS that is targeted for MCUs with small memory footprints? All of Pumpkin Space's microcontroller-based modules utilize a Microchip PIC24E MCU, with Salvo as the foundational RTOS. In these applications, Salvo enables event-driven, priority-based tasks to run on the MCU in a highly decoupled manner.
Pumpkin is not the only Salvo RTOS user -- today we received an email from a company whose products you are likely to see when visiting a large world-wide fast food chain:
Salvo is still great, in no uncertain terms, for our application on dsPIC it's been a God-send. We build 40,000 dsPIC33
boards a year, and at present 35,000 ship with Salvo running on them. Harold F.
While there is a learning curve associated with learning an RTOS, once learned, the benefits of the structure that the RTOS brings to an application are substantial. And a carefully-crafted RTOS like Salvo can easily be configured to have zero impact (yes, zero!) on the real-time responsiveness of the application.
In 2009-2011, Pumpkin developed and delivered a series of twelve 3U-sized CubeSats to the National Reconnaissance Office (NRO) -- these were the Colony I buses. These 3U CubeSat-size buses had fixed and deployable panels, a full 3-axis ADACS with coarse sun sensors and a magnetometer, an 8051-based C&DH processor, multiple batteries and over 1000cc of payload volume. The NRO distributed Colony I buses to various organizations ranging from the Naval Research Lab (NRL, with their QbXI & QbXII CubeSats) to USC's ISI, with its Aeneas CubeSat.
Yesterday, a group of Students at USC ISIS's SERC delivered another Colony I-based CubeSat, this one to Vector Launch, Inc. This CubeSat is called GalacticSky-1, and its Colony I heritage is clearly visible.
It's interesting to reflect on how versatile the Colony I design turned out to be. In the intervening ten years, Pumpkin has greatly increased the capability of its 3U buses, and in doing so, added more payload volume, processing power, electrical power, battery energy, and sensors. That's now Pumpkin's MISC 3 family, and is ideally suited to IoT and other missions.
Read more about GalacticSky-1 in USC Viterbi's news release.
Sometime in the not-too-distant future, one of thousands of Pumpkin SUPERNOVAs is likely to fall back to Earth. Some time will pass, and someone will find it, in a field, resting, its payload long gone, and yet seemingly unscathed due to its robust construction.
Almost unscathed -- if you look closely, one of the SAP cover screws (made from 18-8 SST) burned up on rentry, and the -ZA1 SAP cover has worked itself loose ...