After a 7 year endeavor, Capitol Technology University is pleased to share with you the final report on our CACTUS-1 payload project, headed by professor Alex (Sandy) Antunes with a leadership team involving over 30 students throughout the course of the project. This massive endeavor demonstrates the brilliant and collaborative nature of the Capitol community, as students from various majors and skillsets came together to launch this payload into space.
Thank you to Professor Antunes for writing and sharing the following report with Capitol!
The Coordinated Applied Capitol Technology University Satellite-1 (CACTUS-1) mission is a tabbed 3U CubeSat involving two technology demonstrations built entirely by undergraduate students. The primary payload, TrapSat, uses aerogel to capture and profile micrometeorites and microdebris to collect data for cleanup of low-Earth orbit (LEO), and is the first CubeSat-based orbital debris detector to be flown in LEO. The secondary payload demonstrates commanding via internet as an innovative cost-saving communications and command subsystem for gathering scientific data. We integrated CACTUS-1 across majors into our curriculum to serve as a flagship project, both for hands-on training of STEM students and to increase engagement and visibility of our program to better serve as a STEM pipeline, particularly useful as a significant portion of our student population comes from underserved communities.
Our prior work had a Technology Readiness Level (TRL) of 4, “Subsystem validation in laboratory environment” and during payload development we moved to TRL 5, “Subsystem component validation in relevant environment,” through our multiple high altitude balloon missions and summer ballistic sounding rocket flights. Preparing then flying in low Earth orbit aimed for us to reach TRL 7, “System prototyping demonstrated in operational environment- space.” We supported CACTUS-1 development at Capitol Technology University through our existing program incorporating classroom work, senior projects, and both internally and Maryland Space Grant Consortium funded internships.
The TrapSat payload, our scientific payload, captures orbital debris microparticles of space dust or broken satellite debris. Tackling space debris is a timely problem for our age. We use the exotic material called Aerogel to capture it. Aerogel is very fragile, so our students designed then implemented 3D printing to make the custom 'holder' for the Aerogel capture material. The 2 Aerogel capture bays are covered with mylar to block light, and the Aerogel is imaged by a side-mounted camera illuminated by LEDs to observe the depth and shape of the captured debris impact craters. Their 3D structure and side-imaging capture camera was successfully validated on multiple RockSat sounding rocket flights. The TrapSat CPU and flight software uses Python on a Raspberry Pi.
To test new communications modes, we implemented Smartphone-to-Satellite communications. Our student teams built an interface to use your smartphone to communicate with and command the satellite. They tested this "Hermes" module on a sounding rocket before putting it onto our CACTUS-1 CubeSat. Hermes is its own stand-alone module with separate solar panels and power bus, so we're flying 2 satellites that are independent, bolted onto the same 3U+ baseplate. Hermes has flown on multiple platforms.
From a structural point of view we're using CubeSat Tabs instead of Rails. This is new enough that we had to fabricate, then donate a test bed to Morehead State University in return for using their test facilities (run by the co-inventor of the CubeSat).
We built this for less than $35,000, or about 1/10th the usual cost of a university satellite build, all funded via the Maryland Space Grant Consortium (MDSGC) (https://md.spacegrant.org/). To benefit the community, we released our hardware and design guides as Open Source. Our CAD designs, circuit boards, and most other materials are available to the community under an open source license so that other student teams can benefit from our work. We also funded an intern via MDSGC to write up a "Cookbook" on how to build your own satellite, and put everything up on the learn/share/work site GitHub (DOI: 10.5281/zenodo.5780181).
EDUCATION ACCOMPLISHMENTS:
Our payloads are student-designed and student-operated, and expand student opportunities in the frontiers of space research. Creating real missions inspires our future engineers. CACTUS-1 was Capitol's first CubeSat mission, building off existing high altitude balloon payload projects. Our students operated in multi-major multi-disciplinary teams with a strong systems engineering structuralism to iteratively invent and improve their designs. CubeSat development at Capitol was funded through and integrated into the astronautical engineering curriculum, so these projects also educated future engineers.
We see deploying our CubeSat into space as the capstone to their work, and the many stages working towards launch as a part of their curricula as undergraduate engineering, computer science, and cybersecurity students. CACTUS-1 addressed Capitol’s educational goals in training the next generation of engineers, provided potential technology transfer from our institute back into NASA and to other universities through our release (under the open Creative Commons license) of our 3 CubeSat 'cookbooks' plus our High Altitude Balloon (HAB) handbook. While Capitol faculty and all CACTUS-1 advisors share their experience working on space missions, teaching students about risk reduction and good operations practices, by receiving a launch opportunity for CACTUS-1, students gained new hands-on insights into the space industry.
CubeSat development was fully integrated into the curricular and extra-curricular structures in Capitol Technology University’s Astronautical Engineering (AE) program. Three of the courses taught by the Principal Investigator directly supported the Capitol CubeSat program. AE-205 CubeSat Engineering focused on the building, integration, and testing of working design models. CT-206 Scripting Languages developed the pool of programming talent in languages needed to complement CubeSat instrument design and flight software. Students in AE-463 Space Systems Engineering Simulation & Modeling worked on interdisciplinary team-based projects to design, integrate, and test full lifecycle-secure satellites using a CubeSat simulator mission model. Students were also encouraged to undertake independent studies to explore advanced techniques.
There was also departmental support for clubs in which students work on CubeSat development, including the Capitol Amateur Radio Club and VelcroSat Team. All Capitol students were welcome in these groups regardless of major, so AE students joined with electrical engineers, computer scientists, and information security managers to tackle real world challenges with faculty support.
Capitol provided institutional support in the form of on-campus internships in the Balloon Payload Program, which focuses on high altitude balloon testing of CubeSat models, and the Space Flight Operations Training Center (SFOTC), where students practiced and executed ground control using a satellite simulator provided by the Hammers Company. Capitol’s work supported NASA Objective 2.4: “Advance the Nation’s STEM education and workforce pipeline by working collaboratively with other agencies to engage students, teachers, and faculty in NASA’s missions and unique assets,” with minimal investment by NASA.
Finally, Capitol is a small, not-for-profit university that serves many traditionally under-represented populations and first-generation college students. With funding from NSF’s S- STEM program, Capitol offers a scholarship and retention program for high-need, high-ability students. Real projects improve student retention, and building actual payloads for high altitude balloon launches and prospective orbital flights improves STEM engagement for all learners. Capitol students involved in CACTUS-1 are constantly improving their skills and gaining knowledge about flight payload, bus, and operations exploration. CACTUS-1 was also a flagship project highlighted frequently on the Capitol website, blog, and in recruiting material.
TECHNOLOGY ACCOMPLISHMENTS
Our technology was successfully validated in prior sounding rocket flights. However, we have been unable to command the actual CACTUS-1 satellite. The CACTUS-1 orbital build of the HERMES communications payload did not return data for our flight. The HERMES smartphone-to-satellite communications protocol was previously validated in multiple sounding rocket flights, and as Iridium modems have been flown in space, should be considered for future flights.
For the science payload of TrapSAT, we obtained images during sounding rocket tests of upper atmospheric particles captured during the sounding rocket flight, which were then analyzed with an electron microscope. This provides a technical validation of the TrapSAT aerogel detector, as well as its launch survivability.
Similarly, 3D printed plastic parts for custom components (such as our Aerogel holder) worked for our sounding rocket flights and, given our flight issues were entirely comms-related, are a valid technology for creating flight components for future CubeSats.
We can neither validate nor invalidate our use of a Raspberry Pi for flight use; while the Raspberry Pi has worked well for sounding rockets, we used a different underlying PCB design and different flight software and, due to lack of successful comms, can make no statement on the reliability of this aspect of CACTUS-1.
While earlier CubeSats use a ‘rails’ design, where the CubeSat structure fits within 4 rails that require precise tolerances to fit into the canister, our CACTUS-1 design uses the newer ‘tabbed’ design, where the CubeSat sits on a flat plate that is milled to high tolerance. The tabbed design has less risks in deployment and is easier to fabricate to the tolerances required. Our deployment was able to validate ‘tabs’ as working, as
CACTUS-1 did successfully deploy from the launch vehicle. We therefore recommended tabs as the structural choice for any future CubeSats.
SCIENTIFIC ACCOMPLISHMENTS
Due to not being able to establish reliable communications sufficient to issue ground commands, we do not have scientific data from CACTUS-1. Because we validated the payloads via sounding rocket flights, however, we did obtain data from both payloads in the space environment. From this, we suggest future missions should fly a TrapSAT particle detector to obtain orbital microparticle and microdebris measurements (as discussed in our 2014 AAS talk, in references below).
IMPACT
The project initiated in 2014 with our pre-CubeSat preparations and extended into 2021 as our cybersecurity students use CACTUS-1 in its current "hard to reach" communications state as a challenge to learn signal theory and satellite communications. Over that time, 32 students were directly involved in CACTUS-1, and CubeSat development at Capitol influenced and improved multiple courses across our multiple engineering and computer science majors for our roughly 500 undergraduate students.
CACTUS-1 was impactful in terms of student hands-on experience as well as in developing technology towards NASA goals. The NASA technology goals our mission aimed at included Objective 1.5, “Ascertain the content, origin, and evolution of the solar system”, through prototyping our Aerogel capture technology in the TrapSat module, and Objective 1.7: Maturing crosscutting and innovative space technologies, through the Hermes communications and control system. Both technologies were proven successful in the sounding rocket test flights during CACTUS-1 development, though again our inability to establish command and control of CACTUS-1 itself is a disappointment. As an engineering (rather than science) school, however, the build was the core of the project, and in that regard our primary impact has been the educational benefit.
Primarily, we note that our work supports Objective 2.4: “Advance the Nation's STEM education and workforce pipeline”, with minimal investment by NASA. We are a small not-for-profit university who serves under-represented populations-- in particular students who are the first from their family to graduate-- including our need-based NSF funded Capitol Scholars Program. We find real projects help greatly with student retention, and building actual payloads for high altitude balloon and prospective orbital flights helps with STEM engagement for all learners. Our students are constantly improving and moving forward in our flight payload, bus and operations exploration with CACTUS-1 and the CSLI launch opportunity was ideal for education and motivate our students over the 3 year development period and 2 year wait-for-launch ground development period, as well as with our cybersecurity extended mission.
32 undergraduate students directly worked on some aspect of CACTUS-1. Two of those students continued working on CACTUS-1 as part of their Master’s degree, and at least four others started a technical Master’s program within a year of graduating from Capitol. 19 publications and posters were generated by CACTUS-1 work. 15 of the publications had undergraduate students as first author. 11 undergraduate students were first author on a paper or publication, and 19 students were either lead or co-author on a poster or publication. 31 of the students are employed or engaged in the engineering field as their current job (the 32nd student is a librarian). We consider CACTUS-1 an educational success in terms of student outcomes, student publications, and student post-graduation job success, as well as a strong centerpiece of our curricula for the 2014-2021 window.
DEVELOPMENT CHALLENGES
The primary development challenges we faced were FCC licensing, testing of the newer 'tabbed' CubeSat structure, and student teaming issues due to launch delays.
The FCC licensing process is its own technical specialty, separate from engineering, and was beyond our in-house capability. Without the support of TriSept (the launch broker) that could have been a serious impediment, but they did a great job of contracting Mark Miller as an advisor/liaison to make the FCC licensing proceed.
We had budgeted for creating the CubeSat and using a virtual fit check, but because we chose the newer ‘tabbed’ format, had to create or find a suitable test canister for the fit check (whereas all the other payloads in the manifest used the older ‘rails’ design, for which the launch broker was able to obtain test canisters). Fortunately, Planetary Systems in Maryland (near us) agreed to let us use their tabbed canister, test tools, and facility (during Covid) to complete this requirement. The physical fit check ended up being essential to correct a millimeter-sized discrepancy that hindered door deployment, which was fixed onsite (using a hand-held Dremel!) by our student so that we successfully fit.
We also had to fabricate a vibration plate suitable for tabbed designs so that we could fulfill the vibration and thermal bakeout testing. This was an unexpected design and cost as well, which we accomplished. Morehead State University’s program was generous enough to grant us access to their test facility, and in return we left the tabbed test stand and provided them with the design schematics so they could support this format for future missions.
Launch delays were problematic in terms of student teaming. As an undergraduate-focused project, our ConOps as a formal plan has always been hindered by not knowing when the launch would be and thus which students would be still be available, which is why we anticipated playing catch-up in training everyone. But if we'd trained everyone 2.5 years ago for ground ops... they'd all be graduated and we'd have to re-do it anyway. So we waited for launch... and waited. The original students (a mix of all majors) graduated and moved into successful careers. Our launch date arrived, slipped, arrived again. But once we had a fixed launch date, a new cadre of students stepped up to learn how to communicate with and send commands to CACTUS-1, and hopefully get some data back down.
MISSION CHALLENGES
CACTUS-1 has not had successful commanding, though SatNOGS reports beacon pulses are received, and as a result we have no scientific data but are using the satellite as a testbed for our cybersecurity program. We have attempted but have not successfully contacted CACTUS-1 yet at 434.03MHZ. Our initial ground station used a transmitting system at the lower power end of our allowed power, but upgrading to higher power command still did not enable us to issue commands. We did not have a beacon mode in our license plan-- only active commanding, so as to comply with FCC shut-down requirements (we erred on the side of caution, probably overly cautious). But for safety, if no commands are received in 14 days CACTUS-1 will 'beacon' for 1 day, so even if our ground station transmit is weak we should get health & safety (H&S) packets (at 434.03MHz) via our ground listening partners at that time (and every 14 days after). Our secondary (and completely separate) payload "Hermes" was not able to effectively communicate via Iridium during its 2-week operational window.
These are somewhat mitigated by reports via the SatNOGS network that they have detected our ‘health and safety’ packets, but not with sufficient clarity that we are able to extract the data. Because our FCC license is valid for two years, we have transferred CACTUS-1 student usage from our engineering group to our cybersecurity group. As a corollary, Capitol students are receiving help from the Aerospace Village/GrayHat cyber not-for-profit to assist with this. So there is hope with the extended mission.
LESSONS LEARNED
Almost all of our lessons learned for future missions involve a more robust communications (‘comms’) design. We enumerate these lessons below. In addition, we have provided a 'Cookbook' of lessons learned and made it available under a Creative Commons open source license for other teams to use (DOI: 10.5281/zenodo.5780181)
(1) Include a constant beacon mode, despite how difficult that is for negotiating with the FCC licensing.
(2) Have better packet handling & error correction for lossy comms. Related-- teams should assume comms will be lossy or weaker than nominal, and design their commanding accordingly, versus optimizing commanding for a presumed normal operations.
(3) Use amateur band instead of experimental band, so other ground stations can operate as ground stations and issue commands. Because our FCC license only allows ground stations listed in the license, we lose the ability to legally ask local HAMs, AMSAT stations, etc. to assist in reaching our satellite.
(4) Use a dual-frequency radio design for up/down to avoid interference and provide redundancy.
(5) If we were to design now, we would put in a COTS CubeSat Globalstar board $800 incl license, but that hardware didn't exist at the time we passed our Flight Readiness Review (FRR).
(6) Next mission, do onboard autonomous data analysis and send results as text data, instead of sending the larger raw images.
We are still learning more about CACTUS-1 due to its reduced communications, and are using the difficulty in contacting CACTUS-1 as an excuse to train up a new cadre of students on space communications and space cybersecurity, so that CACTUS-1 continues to be part of our student learning and curricula.
ANECDOTAL INFORMATION
As a student-conceived, student-led, and student-build mission, we’d like to share quotes from our student leads. From lead designer R. Pierce Smith, "For me the most rewarding part was building the payload – that’s when I really started to get that sense of doing something really incredible,” he says. “We built our power board from scratch to save money. We made a lot of our stuff rather than buying it off the shelf. For example, we made our own USB cables.”
Smith also comments on how work was painstaking and labor-intensive. “You have to make sure each small component works. You have to pair up components and see if they work together, then repeat with another pair of components. It can get tedious. But towards the end of it, when you’re actually putting it all together -- that’s really fun.”
We also appreciate the support we received from the CubeSat community. In particular, Professor Bob Twiggs and Professor Chuck Conner of Morehead State University were of great assistance in testing as well as being supporting mentors early in the project inception. Their advice and Morehead State's test facility were core to CACTUS-1 reaching the launchpad. Similarly, Jason Armstrong in his role of Integration Manager for Elana XX was a great source of information and support, and Mike Miller of Sterk Solutions guided us through FCC licensing. Finally, none of this would have been possible without the support of the Maryland Space Grant Consortium.
Student engineer Georgios Giakoumakis adds, “The most exciting thing about this project is that you’re always learning new skills. You won’t repeat the same thing twice. You get to work with amazing people on a mission that offers incredible learning experiences that you can’t really find anywhere else.” Finally, quoting advice on CACTUS-1 from Jerry Buxton of RadFxSat-2 AMSAT.us, “I see two kinds of people who succeed in their missions: Winners, and Learners. The ELaNa XX mission teams are all successful!”
PUBLICATIONS
(Note with the exception of the Antunes items, all publications have our undergraduate students as first author). Antunes, A., Horvath, M., Johnson, A., Smith, R.P., Odigwe, C. & Schrenk, R. (2017). Integrating an Open Source CubeSat. AAQ Conf 2017, https://aaq.auburn.edu/sites/default/files/workshops/2017/Presentations/Antunes.pdf
Antunes, A., Schrenk, R., Bormanis, M., Walters, A. & White, T. (2014). Profiling near-Earth debris using picosatellites. AAS 224, http://adsabs.harvard.edu/abs/2014AAS...22410701A
Antunes, A., Schrenk, R., Gesterling, C. & Weideman, N. (2015). Quality Assurance via Successive HAB Flights. AAQ Conf 2015, https://aaq.auburn.edu/sites/default/files/workshops/2015/Presentations/07.pdf
Antunes, A., Walters, A., Bormanis, M. & Schrenk, R., (2014). Constrained Multi-Altitude Design Using 3-D Printed CubeSat Shells. AIAA SciTech.
Capitol Technology University (2017). 3D Printing the Final Frontier. Hack A Day, https://hackaday.com/2017/12/18/3d-printing-the-final-frontier/
Hansen, C. (2016). Hermes: CACTUS-1 Quality Assurance Testing. AAQ Conf 2016, https://aaq.auburn.edu/sites/default/files/workshops/2016/Posters/Hansen.pdf
Hansen, C. & Ho, A. (2015). Hermes Rocksat-X Flight QA Testing. AAQ Conf 2015, https://aaq.auburn.edu/sites/default/files/workshops/2015/Posters/poster05.pdf
Hastings, I. (2019). The High Altitude Balloon (HAB) Handbook. DOI: 10.5281/zenodo.5780181
Ho, A. (2016). Quality Assurance for CubeSat Mission. AAQ Conf 2016, https://aaq.auburn.edu/sites/default/files/workshops/2016/Presentations/Ho.pdf
Horvath, M.G., Johnson, A. & Antunes, A. (2017). Student Built Prototype Ground Station. AAQ Conf 2017, https://aaq.auburn.edu/sites/default/files/workshops/2017/Posters/Horvath.pdf
Horvath, M., Pittman, J., Mabson, M. & Walters, A. Using AI to improve spacecraft automation. AAQ Conf 2018, https://aaq.auburn.edu/sites/default/files/workshops/2018/Horvath.pdf
Murray, C. & Smith, R.P. (2017). Mission Quality Assurance: Virtualizing Design. AAQ Conf 2017, https://aaq.auburn.edu/sites/default/files/workshops/2017/Posters/Murray.pdf
Petrov, A. & Schrenk, R. (2015). TRAPSat: Trapping space debris with Aerogel Prototype Satellite. AAQ Conf 2015, https://aaq.auburn.edu/sites/default/files/workshops/2015/Posters/poster08.pdf
Rodriguez, J. & Antunes, A. (2018). Newcomers Guide to CubeSats (CubeSat Cookbook Vol 2). DOI: 10.5281/zenodo.5780181
Schrenk, R., Strittmatter, M., Walters, A. & Jagarnath, M. (2017). Crawl-Walk-Run-Fly! AAQ Conf 2017, https://aaq.auburn.edu/sites/default/files/workshops/2017/Posters/Schrenk.pdf
Schroen, E. (2019). Common Electrical Power System for Small Satellites (CubeSat Cookbook Vol 3). DOI: 10.5281/zenodo.5780181
Smith, R.P. (2018). Engineering Guide - CACTUS-1 Design Documentation and Future Guidance (CubeSat Cookbook Vol 1). DOI: 10.5281/zenodo.5780181
Smith, R.P., Murray, C. & Walters, A. (2018). Project Aether: Small Universities and Quality Assurance. AAQ Conf 2018, https://aaq.auburn.edu/sites/default/files/workshops/2018/Murray.pdf
Stormer, R.A. III (2019). PuzzleSat. DOI: 10.5281/zenodo.5780181
Acknowledgements
Specific citations and history for CACTUS-1 are given for each component as follows:
CACTUS-1 proposals and mission overviews: A. Antunes, R. Schrenk, R. P. Smith, A. Walters, R. Maharaja, M. Horvath
Hermes payload (on Cactus only-- for Hermes sounding rockets, see Maharaja) by C. Murray, E. Schroen (power Board design), Carlos Del Cid, R. Maharaja, P. Smith, IP rights retained by R. Maharaja
Trapsat payload by R. Schrenk, K. Moore, Z. Richards, M. Strittmatter, A. Walters, R. P. Smith, IP rights retained by R. Schrenk
3U++ Tabbed Frame: by R. P. Smith, R. Schrenk, provided under an open hardware license
Pi-CPU/Health & Safety Boards: by R. P. Smith, A. Antunes, provided under an open hardware license
Power bus: by R. P. Smith, G. Auvray, C. Odigwe, A. Antunes, R. Schrenk
Solar: (Added this because power and solar have different aspects (i.e. licensing to use) by R. P. Smith with assembly help from George Gieomekis, Marcus Bailey, Sam Lawson, Nick Keller, Sarah Sharpe, Alex English, Nick Aniello, Chris Finch
Passive Magnetics: by E. Routhier, B Reese , R. P. Smith with help by Ian Hastings, Christina Williams
Flight software by A. Antunes with help by Randy Powell, Zalika Dixon, and thanks to Alan Cudmore for useful discussion on his “PiSat” concept
Thermal blankets by R. Schrenk with help by Sarah Sharpe, Marcus Bailey, and George Giakoumakis
Comms: by M. Horvath, A. Johnson, A. Antunes
Burn wire, foot switches, inhibits, ports, and subsystems not mentioned: considered either part of the above, part of the general Cactus mission, or not sufficiently novel to merit publication or separate enumeration.
Ground team: Mark Horvath, Charis Houston, Devon Marshall, Seth Dickerson
Full list of high-level support (addendum): Alex Antunes, Angela Walters, Rishabh Maharaja, Marcel Mabsen, Patrick Stakem, Alan Cudmore, Dave McComas, Suzanne Strege, Alison Evans, Cinnamon Wright
Full list of students (addendum): Pierce Smith, Ryan Schrenk, Nathan Weideman, Mark Horvath, Alec Johnson, Chris Murray, Sarah Sharpe, George Giakoumakis, Marcus Bailey, Xavier Guzman, Marissa Jagernath, Chukwuma Odigwe, Keegan Moore, Zack Richard, Jamil Ahmed, Gary Visser, Joshua Joseph, Eric Ruthier, Sean Mullin, Christina Williams, Nick Aiello, Randy Powell, Mikus Bormanis, Christel Gesterling, Zalika Dixon, Mike Stritmatter, Josh Hernendez, Ralph Stormer III, Dan Whiteside, Bryce Reese, Charis Houston, Devon Marshall, Seth Dickerson, and others.