AggieSat2 was tasked with collecting two orbits (180 minutes) of DRAGON GPS data and returning the data to the ground. The data were not required to be from two consecutive orbits.
LONESTAR Program Review
AggieSat Lab, in partnership with the University of Texas at Austin, developed a series of 4 pairs of satellites for NASA Johnson Space Center’s Low earth Orbiting Navigation Experiment for Spacecraft Testing Autonomous Rendezvous and docking program. The LONESTAR program is currently scheduled to be an eight year program, with the final (4th) pair of satellites in this series (LONESTAR Mission 4) demonstrating Autonomous Rendezvous and Docking capabilities. The first three satellite pairs (LONESTAR Missions 1-3) will demonstrate technologies required to attain the ARD demonstration. This means the first three satellite pairs will be required to test the sensors, computers, navigation system, control system, communications system, GPS, etc., that will need to fly on LONESTAR Mission 4.
AggieSat2 was one of two satellites developed for LONESTAR Mission 1, and its mission was to test a novel dual-GPS system (dubbed DRAGON) engineered by the Johnson Space Center (JSC) Aeroscience and Flight Mechanics Division (AFMD). The other satellite of the pair, named Bevo-1, was from the University of Texas at Austin. Collectively, these satellites were known as DRAGONSAT payload, and they flew aboard the Space Shuttle Endeavour on STS-127 (launched July 11th, 2009).
AggieSat2 was a picosatellite, a small version of the satellites developed for the Air Force University Nanosat competitions, and had several essential mission requirements. Primarily, AggieSat2 served as a bus for the NASA provided DRAGON GPS unit. After deployment from the Space Shuttle Picosat Launcher (SSPL) mounted in the Space Shuttle Orbiter’s cargo bay, AggieSat2
was scheduled to separate from Bevo-1 via spring loaded antennas and ready itself to begin data collection. In the weeks following deployment, AggieSat2 would try to independently record and downlink 180 minutes of raw GPS data as commanded by the mission control team. The mission can be considered a success after this information has been completely received by the ground control station and delivered to AFMD. Students working on the AggieSat2 mission in the process will obtain the unique experience of planning and carrying out a co-operative mission to satisfy the requirements set forth by
NASA’s JSC (through delivery). The AggieSat2 team will continue this unique experience as they plan and carry out the operations segment of the mission.
NASA, Texas A&M, and the University of Texas embarked on the LONESTAR Autonomous Rendezvous and Docking Campaign in 2005. NASA tasked the two schools with three cooperative missions to test ARD technologies and techniques, and a fourth an ARD demonstration. The satellite pair, AggieSat2 and Bevo-1, comprised the first of these missions. Students from both schools formed the Mission Systems Engineering Team (MSET) to define mission requirements and shape the beginnings of the campaign. At this early stage, the mission was comprised of both GPS data and crosslink data taking
sessions between the two satellites. Realities of design and size would play a role in iterating this preliminary design during the course of the program. The Preliminary Design Review showcased the initial configuration and designs of both spacecraft for the AggieSat2/Bevo-1 mission. Lab students provided the briefings in front of NASA managers. NASA approved AggieSat2 for continued payload processing as part of the STS-127 payload. Texas A&M students briefed the shuttle safety review board at NASA Johnson Space Center in relation to mission critical items (such as electrical, RF and physical interfaces) and their impact on safe shuttle operations. Key topics at this review included the passive magnetic attitude systems and their effects on GPS reception, and the separation interfaces between Texas A&M and the University of Texas.
By this time, the mission had matured into a more robust, two orbit GPS data taking flight which involved redundant operations of the Texas A&M and University of Texas satellites. This refocusing was the result of trade studies and lessons learned from prototyping by the students on both teams. The Critical Design Review during October 2008 covered the final designs for the major subsystems of AggieSat2. This review was held at NASA Johnson Space Center.
Texas A&M students developed and built a functional replica of the Oceaneering Space Systems SSPL launcher to conduct a series of air bearing floor tests to prove the satellites could separate without interference. The series was 100% successful. Texas A&M and the University of Texas joined forces to test interfaces between the two cubesats. Each satellite featured inhibit pins and spring loaded antennas which were used to provide separation energy at deployment. The student team, with the assistance of mentor Joe Perez, spent long hours in the lab painstakingly assembling and testing these components. Additionally, all subsystem components, such as electrical power system or command and data handling, were integrated together into a final, working, flight unit. From December 2008 to February 2009 Texas A&M assembled and checked out the components of the flight unit AggieSat2 spacecraft.
Texas A&M delivered the AggieSat2 flight unit in February 2009 to Oceaneering Space Systems in Houston, Texas where it was integrated with the University of Texas Bevo-1 satellite and the SSPL launcher unit. During this time, final safety information was approved by the shuttle safety boards at JSC for flight. During these test, functional tests were completed continually. A shorting problem, induced by the last vibration axis, was discovered and corrected. Soon after, the spacecraft was deemed in good health and approved to ship to the Cape. Soon after delivery in March, AggieSat2 underwent combined vibration testing at NASA Johnson Space Center’s test facilities. The spacecraft went under a three axis vibration series to simulate the effects of a Space Shuttle launch. AggieSat2, BEVO-1, and the SSPL launcher were processed at NASA’s Space Station Processing Facility prior to installation in Space Shuttle Endeavour in Orbiter Processing Facility 2. Texas A&M lab members followed the AggieSat2 flight unit to Kennedy Space Center in March to perform one last aliveness test prior to integration with the Shuttle. Atlantis flew on STS-125, without need of rescue, and successfully maintained the Hubble Space Telescope for the last time.
In April, STS-127 Endeavour, with AggieSat2 on board, was rolled out to Pad 39B at Kennedy Space Center to serve as rescue shuttle for Atlantis on STS-125. At 39A, the primary payload for STS-127, the Japanese Exposed Facility, was installed and prepped for a 13 June launch. May, after rescue duty for Atlantis, Endeavour and AggieSat2 were rolled around to Pad 39A at Kennedy Space Center in final prep for STS-127. The AO-51 amateur radio satellite was received from near Panama, and heard through the Eastern United States and onto Canada in the first integrated RF and tracking test of the new facility. In late June, when AggieSat2 deployed from Endeavour, this station was seeking to receive flight telemetry and data. After approximately three months of preparation, the AggieSat2 ground station made its first satellite contact on 8 June.
NASA closed the payload bay of Endeavour for the last time. AggieSat2 was GO and ready for launch on 13 June 2009 at 7:17 a.m. Despite these delays, Lab members were elated at the liftoff; with many present during the launch in Florida. Additionally, those who were unable to travel to Florida gathered at the AggieSat Lab on campus at the Munnerlyn Building in College Station to witness the launch on NASA Television. After 5 launch scrubs, AggieSat2 finally launched aboard Space Shuttle Endeavour on attempt 6. Space Shuttle Endeavour took off at 5:03 p.m., central time, on a 16 day mission to the International Space Station to add an additional component to the Kibo Laboratory. Endeavour was dogged by a leaky seal on the fueling plate for liquid hydrogen on the Shuttle’s orange External Tank and a string of stormy Florida afternoons.
The AggieSat2 spacecraft, Texas A&M University’s first free flying spacecraft, operated for 230 days in low earth orbit from its release from STS-127 Endeavour on 30 July 2009 until its de-orbit on 17 March 2010. This mission was the first in a four-mission campaign, named LONESTAR (Low Earth Orbiting Navigation Experiment for Spacecraft Testing Autonomous Rendezvous and Docking), partnering the Aeroscience and Flight Mechanics Division at NASA Johnson Space Center (JSC), Texas A&M, and the University of Texas at Austin (UT) to promote space engineering education as well as research into novel, low-cost autonomous rendezvous and proximity operations techniques. The first-mission requirements were to operate the Global Positioning System (GPS) receiver built by NASA JSC called DRAGON (Dual RF Astrodynamic GPS Orbital Navigator). AggieSat Lab developed a 5” cubesat for this first flight, with UT building a similar spacecraft, called Bevo-1. Launch integration and engineering mentorship for the program was provided by MEI Technologies and Oceaneering Space Systems (OSS).
AggieSat2 and Bevo-1 were launched together from the payload adapter/launcher, (Department of Defense Space Shuttle Payload Launcher, SSPL) and were designed to push apart and separate completely from each other for independent operations. However the separation was incomplete and this hindered communications through antennas which were partially captive within the UT spacecraft. AggieSat2 was heard by amateurs over Europe ~20 minutes after its release. After significant upgrades to boost signals to and from the ground station and adjustments in procedures, AggieSat Lab established basic operational capabilities with AggieSat2. While the downlinking of data volumes intended for the DRAGON GPS unit was limited, the spacecraft remained functional collecting data throughout its ~7 months in orbit, and the team and NASA JSC learned much about the DRAGON system and its operation on-orbit in its feed-forward to future missions. The team maintained communications and consistent, albeit reduced, operations with AggieSat2 during this time and learned valuable lessons about real time spacecraft operations. AggieSat2 was last heard ~4 hours before its de-orbit. The flight program began in late 2005. Students at Texas A&M and UT developed preliminary campaign and first mission requirements in a joint group called the Mission Systems Engineering Team (MSET).
Throughout 2006 and 2007, design development continued. Actual prototyping and initial flight construction occurred throughout 2008. Early 2009 was spent solving documentation and technical problems, conducting testing on flight designs with the help of mentors and facilities at NASA JSC, MEI, and OSS, and participating in NASA Space Shuttle safety reviews. Students delivered the flight unit to OSS facilities by late February, and the spacecraft, paired with its UT counterpart, was delivered to Kennedy Space Center in early March. AggieSat2 spent time with Space Shuttle Endeavour at Pad 39B handling rescue duty for Atlantis’ flight to Hubble, and finally travelled to Pad 39A for launch on STS-127 on 15 July 2009. Operations were conducted for 230 days by Texas A&M students operating a Texas A&M developed ground station facility. Including the complications, AggieSat2 was a good mission and case study for student satellite programs. AggieSat Lab students have responsibility and control over engineering decisions, design, hardware, and testing when developing a mission. Students work in an environment that encourages in-house designs wherever possible to maximize the student’s practical learning. The mission experience has given participating students their first taste of the sheer detail and diligence required to complete a flight program successfully and has given a complete end to end experience for most of those participants. The AggieSat Lab flight program offers very distinct lessons learned. AggieSat2 proved elements that survived long term in orbit; and highlighted areas where there is a need for increased attention to detail and care in documentation, integration and testing, and time management. AggieSat Lab is looking forward to applying these lessons learned to future flight programs with the NASA JSC and UT partnership. With its first flight experience, the Lab is looking to build experience in attitude control, expanded power, expanded communications, and other spacecraft infrastructure to complete campaign requirements while continuing to educate students with real flight programs.
In addition to those mentioned above, the authors are grateful to ALL the students involved with AggieSat Lab; amateur radio operators world-wide for help with operations; Lockheed Martin for its support; PM&AM Research and SpreadSheetWorld for their partnership, and Professor Greg Huff in Electrical Engineering at Texas A&M for help with antennas.