Cubesats are revolutionizing space and remote sensing research because their compact size and low cost coupled with the explosion of powerful OEM electronics has made it feasible to explore new areas of research which were cost prohibitive in the older satellite model.
The need to quickly setup or re-establish a secure cellular network in an emergency or combat zone is critical to mission success. Other proposals have addressed trying to establish such a network using drones or balloons. The reasons why Cubesats would be preferable to other proposed solutions include protection against enemy interference, freedom from weather difficulties, and higher altitudes ensuring greater coverage and no obstruction from line of sight obstacles, a significant barrier to communications in urban areas.
The solution would be divided into the following subsystems:
1) A central communications base station operated by trained military communications specialists. They will be able to monitor the existing network, including connecting with still operational civilian cell towers. Mobile substations that could be placed at high vantage points, monitor collected data, and apply prediction and optimization algorithms to forecast probable civilian movements and optimal locations for aid stations and supply depots.
2) Civilians with commercial cell phones will have apps loaded on cell phones which will provide GPS and movement data and receive text messages and updated maps that will provide additional information on critical centers where civilians have gathered like hospitals or houses of worship, the best evacuation routes and areas to avoid.
3) The Cubesats will use self-organizing network technology to amplify and repair the existing civilian cellular infrastructure and provide civilians with a secure,encrypted, real-time channel to communicate with USSOCOM commanders.
We are proposing a 3U unit reserving a 1U block for our phased array antenna. .5U for our data processing and encryption unit. and 1.5U for ADACS, power and flight control
The mission objectives of United States troops are drastically changing. The USSOCOM spends more time than ever in peacekeeping missions around the world. This presents our commanders in the field with a vastly different set of challenges from more traditional conflicts. Communications, logistics, and strategy are all greatly complicated when the commander has to take into consideration the movements, needs, and safety of thousands, or maybe even millions, of unarmed and untrained civilians.
Cubesats combined with the social media technology can provide a means for civilians to communicate via a secure VPN with commanders of peacekeeping forces, providing location, group size, movement plans and needs. Previously the vast deluge of 140 character messages would be useless to users looking for a coherent picture of the civilian situation. But recent advances in machine learning and natural language processing allow us to create a fully automated system capable of analyzing thousands of individual text messages with locations and produce a coherent map of the civilian densities and movements over a broad area. This information is vital to field commanders and NGO aid workers trying to craft a strategy that is capable of both defeating the enemy and protecting the refugees. It is also notoriously difficult to obtain this data in the chaos of the modern battlefield. Commanders could also utilize the system to provide a real-time map of areas for refugees to avoid, possible evacuation routes , and drop sites where medical aid, food, shelter, and other necessities can be set up for maximum effect.
The antenna design requires 2.9 W for the antenna subassembly the majority of that being used by the 4 Skyworks SE2568U RF Power amplifiers. The Cubesat processor is a standard 32-bit ARM Cortex-M3 based MCU ,which draws under 200 mW . An additional 300 mW resistive heating unit was added to compensate for the processor's high minimum temperature requirement outlined below under thermal consideration. For a 3U satellite using standard GaAs solar cells power generation of 6.9 W is expected. With a total power draw of our system at 3.43 W, that leaves over 3.5 W surplus. For a significant part of the Cubesat orbit, the satellite will not be above the coverage area. That will allow the unit to conserve power and recharge its batteries, essential to providing 24 hours of continuous operation.
All components picked for the design have a thermal operating range from-40 to +85 deg C. This is within mission parameters. The only exception is the Cortex microprocessor which has a lower temperature range of -10 deg C. As outlined above, weight and power was budgeted for extra insulation and heating to overcome this and keep our MCU at optimal temperature.
The 24. GHz 802.11b specification, upon which we are basing our design, has a specified data transfer rate of 11 Mb/s. Using a mature and robust standard ensures our ability to build the system with commercially available OTS components. With an orbital altitude of 200 km, the range of transmission will vary between 200 km directly overhead to 1000 km at the horizon. As detailed in the attached paper, we will have a link surplus of 5.93 dB with a 10 dB link margin in the best case but a margin of only 1.1 dB in the worst case. Additional satellites will be able to allow Cubesats to hand off transmission before they reach this area. The base station unit will have to handle scheduling satellite links to optimize network robustness and quality of service.
The 802.11 standard offers great flexibility. Mature software libraries for voice, text, image transmission and data encryption are readily available. Assuming that we can achieve 70% of the 11 Mb/s spec bandwidth, we have many options to determine which transmission schemes will be optimal. Detailed discussions with USSOCOM commanders and NGO aid workers will be essential to building an architecture that is both robust and gives all end-users the information they need to act swiftly and decisively in a crisis.
Due to the nature of our phased array antenna, lower-cost magnetometers may be sufficient for orienting the Cubesat so that the antenna unit is always facing planet-side. The ability to quickly steer and adjust our beam pattern via software controls instead of mechanical servos will save power and greatly improve the system stability. The reduced power and control signal requirements can free up resources for other system functions.
A single Cubesat will not be able to provide 24/7 coverage of an area unless multiple satellites are employed. Periodic coverage would still provide communications benefits and would allow the individual units to go into sleep mode when not over the crisis zone. But to increase the coverage area,operation time and Quality-of-Service multiple satellites will have to be deployed. The key system software can be updated as needed from the base unit as individual Cubesats come online. Mobile base stations can also be deployed to help augment the network.
The power, navigation and data processing units can be built with commercial off the shelf(COTS) components. The 2x2 helical phased array antenna unit is currently in the design phase. Further work will be required to prototype and test the design. Deeper details on the antenna design are in the attached paper by Kameron LaCalli.
