NASA Ames Suborbital Flight Communication

While the barriers to space flight have been reduced due to the privatization of launch vehicles, two large hurdles remain for those seeking to conduct research in space: orbit-to-ground communication, and reentry recovery. Our work seeks to reduce these barriers through research in these areas.

Communication costs can be reduced by using consumer satellite phone modems, specifically the Iridium Core 9523, to give satellites in low Earth orbit (LEO) access to a constant internet connection. Satellites and other devices operating at or below LEO and equipped with such a module would be able to stream data to Earth without the need for users to apply for frequency licenses, while also eliminating the need for prohibitively expensive radio equipment.

Additionally, our research looks to solve the current lack of recoverability of small satellites. Through the development of a Tube Deployed Reentry Vehicle (TDRV), we will allow satellites a means of surviving reentry so that equipment can be reused, or physical samples collected and returned to Earth.

Continuing work started by the Technical Education Satellite (TechEdSat) research group led by Marcus Murbach at NASA-ARC, we are utilizing the Iridium satellite constellation to communicate with satellites in LEO. The TechEdSat team has demonstrated that Iridium modules such as the 9602 Short Burst Data (SBD) transceiver are fully functional in orbit and are able to communicate with the Iridium constellation. The next step in this research is to develop a carrier module for the Iridium Core 9523 modem that adapts the core for use in a cube satellite. The Iridium Core supports a 2.4 kbit/s data stream compared to the 9602’s 340-byte packets. The 9523 is currently used in NASA’s Reentry Breakup Recorder (REBR) to transmit reentry data while falling at sub-sonic velocity post-reentry. As such, we believe the 9523 shall also operate normally in LEO and provide a stable data connection.

The NASA-ARC TechEdSat group has also been working to develop a three-stage Small Payload Quick Return (SPQR) device designed to return small payloads from the ISS back to Earth in a temperature and pressure-controlled environment. The middle stage of this device is developed under this project and consists of the TDRV.

=Project Background= A multi-year project, the goals of this research team have been incrementally furthered by each successive design team over the course of nearly five years. Due to the highly ambitious nature of this project, it is likely this project will be continued for several years into the future before it is flight-ready. This section outlines the prior work done by past senior design teams and NASA.

NASA Ames TechEdSat Group
Led by Marcus Murbach at NASA Ames Research Center, the Technology Education Satellite (TechEdSat) research group seeks to develop and test technologies to help increase access to space research, and to enable the reentry recovery of small satellites and payloads. Their main goals are to test and improve use of Iridium Communications modules in low Earth orbit (LEO) to reduce communication costs, and the development of a Small Payload Quick Return (SPQR) device under their Sub-Orbital Aerodynamic Re-entry Experiments (SOREX) flight series. Ultimately, the group seeks to 'evaluate, demonstrate, and validate new technologies' before they are used on a larger scale in space. The TechEdSat group has had a longstanding relationship with the University of Idaho, traditionally hosting UI student interns and sponsoring a Capstone design project each year.

SPQR Device
The SPQR device consists of three primary stages designed to allow the recovery of small payloads or satellites from orbit. The current goal for the SPQR is to allow sample return from the ISS, with eventual use being geared towards landing small probes and rovers on Mars. The TechEdSat group is currently testing the first stage of the device, the Exo-Brake drag device. Several TES satellites have been equipped with various Exo-Brake designs to test their de-orbiting abilities. Work on the latter stages of the device has been passed to teams at various universities such as the University of Idaho and San Jose State University.

The SPQR first stage consists of an Exo-Brake equipped vehicle that is released from either the ISS or a larger satellite. At a pre-determined point, or upon receiving a de-orbit command, the Exo-Brake is deployed, rapidly slowing the vehicle and guiding reentry over a specified location. Once thermal reentry begins, the Exo-Brake stage is completed, and the TDRV is released. The TDRV uses a conical drag device to withstand hypersonic reentry and to slow its descent. Low-altitude testing and design of the TDRV is the focus of the University of Idaho student groups. After reentry is completed, a guided parafoil is deployed which actively guides the payload to a target landing site.

Iridium Modem Testing
Iridium Communications maintains what is currently the largest consumer satellite communication constellation in a 100-minute orbit around Earth. These satellites communicate with an assortment of consumer devices and modules on the L-band spectrum. The satellites then use a 20-30GHz back-haul to communicate with one of four Iridium ground stations, which relay messages from individual devices to the internet. The end result is global, pre-licensed data coverage. As the ISS deploys research satellites at a lower 90-minute orbit, such satellites can hypothetically use consumer Iridium modules to communicate as they are under the orbit of the Iridium constellation. The TechEdSat group has shown not only is this possible, but they have proven that Short Burst Data (SBD) over the Iridium network can be sent from satellites in LEO to a server on the ground reliably. The next step in their research is to switch from using Iridium's relatively simple 9603 module to the Core 9523. Unlike the 9603, the 9523 can support a full dial-up internet connection, in addition to RUDICS, allowing for a live, streaming internet connection rather than short data bursts. Achieving a live data stream from a satellite would vastly improve data collection and allow for the possibility of active control from a ground computer. However, no orbital tests of the 9523 have been conducted as no platform exists for integrating a Core 9523 into a cube satellite.

Team GPS (Guided Parafoil System) 2014-2015

 * Team GPS Wikipage

One of the most successful groups to date, team GPS successfully built and tested a working guided parafoil system capable of steering itself to a programmed GPS coordinate location during descent. Team GPS has been the only team tasked with developing the final stage of the SPQR system to date, however their designs have yet to be replicated onto any latter team's TDRV. Team GPS was also the only team to actively use both Iridium and XBee modules in their electronics system.

Team Rocket 2016-2017

 * Rocket Wikipage

In 2016, Team Rocket focused on the development of a carrier module for the Iridium 9523 Core to allow for its eventual integration into a cube satellite. Their primary objectives were as follows: Create a carrier PCB for the Iridium 9523 Core Develop and Arduino library for the 9523 Using an NAL A3LA-RS Iridium module, test software to establish a dial-up connection

Rocket was ultimately only able to accomplish a few of their goals, primarily the creation of a prototype carrier board. Their notes and SCUBEE testing indicate their PCB is not functional and does not properly interface with the 9523. However, team Rocket made significant progress with software development, creating the base for what team ACOM would use the following year.

Team ACOM (Advanced Communication Device) 2017-2018

 * ACOM Wikipage

In 2017, Team ACOM was tasked with several goals aimed at advancing several aspects of the SPQR device and associated projects. Their primary objectives were as follows: Develop software for the Raspberry pi to allow use of the Iridium 9523 as a dial-up modem Create a remote server to send data to using the 9523 Create and test a mesh network using ZigBee 900MHz radio modules Create and test fly a prototype TDRV device

ACOM was ultimately only able to accomplish a few of their goals, primarily the creation of a prototype TDRV and initial testing of basic software for the Iridium 9523. The TDRV prototype was 3-D printed using PLA plastic and drop-tested in the ASUI Kibbie Dome. Reports indicate the Iridium had difficulty sustaining satellite contact was was never able to initiate a dial-up connection. However, it appears short-burst-data (SBD) messages were able to be sent. No electrical hardware was created.

=Project Goals= Picking up where teams ACOM and Rocket left off, this project was split into two primary directives: the development of a carrier module for the Core 9523 for use in a cube satellite, and the further testing and development of the TDRV. As per the SCUBEE System Requirements document, the main project objectives were precisely defined as:  This project shall develop the hardware and software required to achieve a live network connection from a cube satellite in low earth orbit to a remote ground-based server using the Iridium Core 9523 satellite communication module.   This project shall also further develop and optimize the Tube Deployed Re-entry Vehicle, a three-stage re-entry vehicle launched from an orbital payload at the Von Karman altitude. </li>

=TDRV Development= The primary goal of the SCUBEE mechanical design team was to develop a fully functioning tube deployed reentry vehicle (TDRV). The TDRV serves to deliver payloads from space to Earth, surviving the harsh conditions experienced upon reentry. TDRV design, although sparsely investigated, must meet several criteria for optimal performance. The reentry vehicle must be designed to deploy from tube dispensers similar to those found on the International Space Station (ISS), and, once deployed, must fall to Earth and survive reentry conditions up to Mach-5 (hypersonic flow). Once reentry is complete, the TDRV must self-stabilize and fall orthogonal to the Earth’s surface. Successful completion of all criteria illustrates optimal conditions for small payload return to Earth. A finished prototype and production ready design could become instrumental to small satellite research as well as interplanetary exploration. Preliminary drop test data indicates proper construction and stabilization of SCUBEE’s TDRV prototype.

Existing Design Analysis
While team ACOM's work validated the use of descent arrestors for drag force breaking, their design did not provide adequate stabilization during descent, and successful arrestor deployment was highly dependent on the drop orientation of the TDRV. These were the two problems our team set out to solve.

Based on the test performance of the ACOM TDRV, the following design changes were proposed based on general aerodynamic assumptions: Shorten descent arrestors to reduce drag, thus increasing velocity and stability</li> Increase arrestor angle of attack to further increase velocity and improve stability</li> Improve arrestor material from felt to nylon to reduce back-end mass</li> Place hard-stops on strut ring to keep arrestor from laying against the TDRV body to increase probability of successful deployment</li>

Additional changes were proposed to improve ease of construction, usability, and aerodynamics, as detailed in the following diagram:

Revision and Simulation
Re-design of the TDRV began by creating a new CAD model in Solidworks based on the existing ACOM files. However, the new design files use global variables to define critical dimensions. This allows for the TDRV design to be easily scaled so the it can be sized for each return payload or launcher system. This also allows for rapid simulation of design variations using ANSYS to determine the aerodynamic impact of changing key angles and dimensions via CFD.

CFD Modeling
Computational Fluid Dynamics modeling (CFD) was used to simulate the TDRV in free fall in atmosphere after thermal reentry at sub-sonic speeds. ANSYS software was used in conjunction with Solidworks models to determine the centers of pressure and mass for each TDRV design, and the drag coefficient of each design. To be stable, the center of mass must be ahead of the center of pressure, with the stability being proportional to the distance between the centers. A low drag coefficient was also desired to reduce heating. Ultimately, ANSYS was used to simulate the effect of different descent arrestor angles on the TDRV terminal velocity and center of pressure. To facilitate timely simulation, the TDRV model and fluid velocity was scaled by 90% to reduce calculated surface area.

Zero-Degree Arrestor Modeling
To test the effect of increasing the arrestor surface area, the arrestor was modeled at a deployment angle of zero-degrees, or perpendicular to the body of the TDRV. The above images show the presence of a high-pressure/low-velocity region on the surface of the arrestor, indicative of a aerodynamic instability and greatly increased drag. Instability can be determined by seeing the lack of a confined, low-pressure zone behind the descent arrestor. This model suggested a less aggressive angle of attack needed to be used.

Twenty-Degree Arrestor Modeling
While team ACOM's design of an approximate thirty-degree angle of attack worked, it was desired to increase the terminal velocity of the TDRV to improve stability. As such, a twenty-degree model was simulated. The above images show the formation of a teardrop shaped low-pressure zone behind the descent arrestor, indicating a stable design. Additionally, the high-pressure region in front of the arrestor was reduced, further increasing stability. Based on this simulation, it was decided to begin testing a twenty degree design alongside thirty and zero degree designs to verify the ANSYS models.

Control System Development
The control system designed by team ACOM used a Raspberry Pi single board computer (SBC) to log GPS data and interface with the Iridium 9523 NAL A3LA-RS module to report data. As a backup tracking system a stand alone APRS radio module with an integrated GPS and battery would be attached to the balloon. While this design offered a surplus of computational power, there were several drawbacks to this system: The control system did not fit in the TDRV </li> The primary data reporting system was the experimental payload rather than a proven technology such as a 900MHz radio or APRS link</li> This design did not have the ability to separate the TDRV from a balloon or other platform, preventing accurate fall testing</li> No orientation sensors were included in the design to allow the flight behavior of the TDRV to be studied</li>

A conversation with NASA determined that a re-design was needed in order to facilitate better tracking and flight data logging of TDRV test flights and to include the Iridium 9523 at a later date once it was fully functional on the ground. The proposed system had the following requirements: Record real-time flight data including velocity, orientation, acceleration, altitude and air region pressure to enable flight analysis</li> Integrated battery management and power distribution</li> Relay position via APRS radio with the ability to eventually integrate the developed Iridium 9523 module</li> Control release of the TDRV from the carrier vehicle and potentially control the release of additional drag devices such as a parachute or the descent arrestors</li>

Based on these criteria, the above block diagram was created outlining the major components and functional blocks of the proposed controller. Rather than being controlled by a Raspberry Pi, the controller is centered around a Teensy 3.5 microcontroller as the TechEdSat group is experienced with its use and it offers the required computational power to process and store live data as it is a ARM Cortex-M4 microcontroller operating at 120MHz. The Teensy 3.5 board also offers 5V and 3.3V I/O signal tolerance and has a built-in micro SD card holder, satisfying the data storage requirement. A 7.4V LiPo battery was selected to resemble the 8V battery system used in the TES satellites. To ease assembly and reduce design complexity, Sparkfun breakout boards were selected to satisfy the sensing requirements of the controller. The following sensors and devices were selected to satisfy the mission requirements: Venus 638 GPS Module: Offers high altitude measurements and high-frequency sampling at lower altitudes. Commonly used by high-altitude balloon teams.</li> MPL3115A2 Altimeter: Barometric altimeter with I2C interface. Capable of centimeter resolution.</li> MPU-6050 Inertial Measurement Unit: Combination 3-axis gyroscope and accelerometer with an integrated Digital Motion Processor Engine (DMP). Allows off-loading of pitch, yaw, roll, acceleration, velocity, and other orientation calculations from CPU to boost sampling rate. </li> <li>HX1 Radiometrix: APRS (Automated Packet Reporting System) 144.39MHz amateur radio band module with 300mW broadcast power. Allows for APRS packets containing GPS and sensor data to be sent every 1-2 minutes. Module requires FCC licence to operate.</li> A system block consisting of motor drivers and feedback mechanisms was also included to allow for the control of servos and linear actuators required to deploy the TDRV and other drag devices. This portion of the design was never fully flushed-out as detailed in the 'Test Variant' section. The key idea behind this design was to allow for the eventual integration of the Iridium 9523 Carrier into the TDRV and to allow for additional sensors and actuators to be connected to the module as needed. As such, mating connectors to the 9523 Carrier board are specified, and all the sensors are able to share a single I2C bus. A serial bus allows data to be sent to the Iridium from the Teensy, emulating the TES satellite infrastructure.

Test Variant
Due to time constraints and TDRV delays, a test variant of the TDRV control system was designed and constructed, rather than the full system. The key differences between the test variant and original design are as follows: <li>No data transmission ability. The APRS radio was not included to reduce cost and was deemed unnecessary as it became evident high-altitude testing of the TDRV would not occur in the immediate future. </li> <li>No Iridium Module integration ability. Connections to the Iridium Carrier board were not included as the software development for both the Iridium carrier and control system fell behind schedule. The Iridium was also deemed too high value an asset to include on preliminary tests of the TDRV. </li>

A two-layer PCB was designed and professionally manufactured after initial breadboard development. However, this PCB did not function and was replaced with simple milled PCB made at UI. The final control system was capable of sending sensor and GPS readings to a connected computer, but not standalone data logging. Further software development is required to enable data logging to the built-in micro SD card.

TDRV Construction
The new TDRV design was built using 4" diameter 1/4" wall aluminum stock tube, which was professionally milled down to a 1/8" wall thickness to reduce weight. The nosecone, end cap, and strut ring were then 3-D printed out of PLA. Multiple strut rings were printed to test each of the simulated angles of attack, and multiple replacement nosecones were also created. All pieces were friction-fit together and secured with an exterior band of electrical tape. The drag device was a piece of cut rip-stop nylon sewn to aluminum spars bolted to the plastic strut ring. The only payload was a personal GoPro camera which was used to record flight video and basic velocity and acceleration measurements. The GoPro was fit into the nosecone of the TDRV. No external tie-points were included to allow the connection of the TDRV to a launch vehicle.

TDRV Breakdown: <li>Body: 1/8" wall aluminum tube</li> <li>Nosecone: 3D additive printed PLA</li> <li>End Cap: 3D additive printed PLA</li> <li>Strut Ring: 3D additive printed PLA</li> <li>Arrestor Struts: 1/4"x1/2" aluminum bar stock</li> <li>Arrestor: Ripstop nylon</li> <li>Weight: Approximately 4 pounds</li>

Testing
Two test sessions in the University of Idaho Kibbie Dome were conducted during the final weeks of the project to match the testing conducted by team ACOM. No other tests were conducted. During the tests, the TDRV was fitted with a GoPro camera and was hand-dropped from the maintenance catwalks in the Kibbie Dome. Not all components were replaced between tests, and the drop height was only approximated. From the GoPro data, velocity and acceleration graphs were produced from each drop trial. Prior to testing, the terminal velocity of the TDRV was estimated using basic area calculations in SolidWorks. Before the test, the terminal velocity for the twenty-degree descent arrestor was estimated to be 15 m/s. The final test velocity was measured to be 17.5 m/s, validating the SolidWorks model.

Future Work
The final design of the TDRV must be able to survive hypersonic reentry through Earth's atmosphere, which requires materials and techniques that simply exceed the ability and budget of the university, let alone a senior design team. The TDRV would need to be made of a shell thousandths of an inch thick from exotic alloys to reduce weight and heat resistance. The nose cone would need to be made of ablative heat-shielding materials, and the descent arrestor would be made of carbon fabrics with composite struts to survive the extreme heat of reenty. As such, the future role of this team's successors is to design and prove the aerodynamic model though constructing and testing low-cost test models using high-altitude balloons and high-speed wind tunnels to prove that an expensive flight-ready TDRV would be successful. These models will also allow for integration and testing of any control electronics, which unlike the TDRV itself could be fully designed and built by a senior design team, then integrated into a NASA-built TDRV.

To meet this goal, future teams will need to adapt the current TDRV design to accept a drop device to allow for high-altitude testing. Additionally, the control electronics must be completed with some sort of remote data transmission system in place to enable tracking and recovery. Due to the cost of an Iridium modem, it is recommended the 9523 Core not be flown until multiple test are conducted with consistent data indicating a high probability of survival and recovery. To increase survival, a late-deployment parachute would need to be added to the TDRV. This parachute would consist of some type of deployment mechanism, controlled by the TDRV control electronics, ejecting a parachute from the rear of the TDRV after it has passed a set altitude. It is desired that the TDRV hit the ground as slowly as possible, yet have a rapid descent rate to reduce drift distance during flight. Future teams should collaborate with or consist in part of VAST team members to facilitate high-altitude balloon testing.

In short, the main focus of the 2019-2020 senior design team regarding the TDRV should be to complete the work started by team SCUBEE by designing a drop mechanism for the TDRV, and building and testing the originally designed control electronics. Once this is completed, a parachute can be added to the TDRV, and its physical design can begin to be optimized. Later teams can then work on repeatedly testing the TDRV using sounding rockets or balloons in collaboration with NASA and integrating the Core 9523 Iridium Modem.

=Iridium 9523 Development= The primary goal of the SCUBEE electrical and software design team was to develop a carrier module for the Iridium 9523 Core satellite communications modem to allow for the core to be integrated into the existing standardized electronics payload used on each TechEdSat cube satellite. Such a carrier module would allow for a dramatic improvement in bandwidth by swapping the satellite from 340-byte short burst data (SBD) packets to a full 2.4 kbit/s data stream. However, the reason this was not already done is the enormous leap in technical complexity the 9523 requires compared the currently used Iridium 9502 modem. As the Core 9523 can sustain a live internet connection, it requires much more power at various voltages compared to the 9502's single 5V input, in addition to a full 9-wire RS-232 interface to a microcontroller that must host a full TCP/IP stack. While prior teams had worked to develop hardware and software to achieve this goal, none had yet been fully successful at either creating a working carrier module or the code to run such a device. SCUBEE was the first team to fully develop a working carrier module in hardware, but was unable to complete and test a working software library to control the Core 9523.

Future Work
The library was designed to use a simple command/response packet system.

The library was designed to provide four modes of operation:
 * OFF, where the modem is disabled;
 * RAW, where all data packets are sent directly to the modem;
 * SBD, where all data packets are converted into Short-Burst Data packets, which is the format currently used; and
 * TCP, where all data packets are streamed over a TCP/IP connection, which is the primary goal of this project.

Two versions of the library were created. The first version is designed for use on a microcontroller and is optimized to use as little memory as possible. The second version is designed to run on a computer and provides debugging information to assist  future software development.

GitHub Repo

=Team Members= Left to Right: Hunter Barnett Major: Computer Science Biography: Hunter Barnett is a computer science student from southern California. His interests include writing software for embedded devices and retro consoles.

Avery Brock Major: Electrical Engineering Biography: Avery Brock is an electrical engineering student from the Seattle area. When not busy with classes he enjoys developing his own projects ranging from Jacob's ladders to IoT devices. His primary interests are aerospace and robotics and hopes to pursue those topics for his master's degree.

Yi Yang Major: Electrical Engineering Biography: Yi Yang is an electrical engineering student. She is from China.

Hunter Kanniainen Major: Mechanical Engineering Biography: Coming from Vancouver, Washington, Hunter Kanniainen is a mechanical engineering student with a strong focus on design and analysis. Hunter has designed robotic components for Dr. Joel Perry’s BLUE SABINO project as well as completing an internship at NASA’s Ames Research Center. At NASA, Hunter designed test components for small satellites and used FEA analysis to determine their effectiveness in application. Hunter is returning to NASA to work full time after graduation in 2019.

Tim White Major: Mechanical Engineering Biography: Tim is a mechanical engineering student at the University of Idaho and has a passion for prototyping, problem solving and intersecting business and engineering products. He plans on getting his MBA after his undergraduate program.

=Additional Documentation=

Presentations:

! scope="col" width="width:20em;" |Result ! scope="col" width="width:20em;" |Notes
 * 1999
 * Deep Space 2
 * Test martian soil samples, and communicate results back to earth.
 * Failure
 * &mdash;
 * 2014-15
 * Unknown
 * Unknown
 * Ongoing
 * Documentation lost; taken over by Team inSPACE.
 * 2015-16
 * Near Space Engineering
 * Design a test board for suborbital satellites.
 * Ongoing
 * Taken over by Team ROCKET.
 * 2016-17
 * Satellite Development
 * Improve communications between flight experiments and ground stations.
 * Ongoing
 * Taken over by Team ACOM.
 * 2017-18
 * ACOM
 * Improve communications between flight experiments and ground stations.
 * Ongoing
 * Taken over by this project.
 * }
 * ACOM
 * Improve communications between flight experiments and ground stations.
 * Ongoing
 * Taken over by this project.
 * }