Satellites are a fantastic piece of equipment that accomplished and enhanced the lives of many humans. Each satellite has a unique mission and specialized instruments that provide data back to Earth from space which could be weather, science or provide information for national security. The effects it has on our lives could be modern day conveniences, such as television, telephones, navigation, business, weather or even climate and environmental monitoring. But the question is what kind of instruments are on satellites, and how is this information processed and passed down to the user on Earth. Depending on the mission satellites are in different orbit to provide various information to users.
One satellite is called New Horizon which has a goal of understanding the Kuiper’s belt and the transformation of the solar system. The satellite is powered by a “Radioisotope Thermoelectric Generator (RTG) given the depth of space it will travel, far away from the sun where solar power generation would require extremely large solar arrays” (Spacecraft Overview, n.d.). Each RTG contains pellets of a mixture of Plutonium PU-236,238,239,240,241 and other isotopes with the Actinium group. The Plutonium is held in a titanium structure which provides stiffness and low thermal conductivity. The RTG provides a better and reliable source of power to the satellite for the deep space missions.
The communications system provides for the command uplink and telemetry and data downlink. The RF System is comprised of an RF antenna assembly, redundant amplifiers, redundant, Oscillators, and the uplink/downlink cards within the two Integrated Electronics Modules. The forward antenna has a high-gain antenna measures 2.1 meters, medium gain measures 30 centimeters and one low gain which can function to a distance of 1 AU for mission phase and commissioning. The High Gain Antenna is able to deliver downlink data at a rate of 600bit/s for the playback of Pluto data, will be able to receive commands up to a distance of 50AU or beyond.
[bookmark: _Hlk2152788] The Command and Data Handling functions is the timekeeping, command management, science and engineering data management, autonomous system recovery, safing data storage and transmission, . “New Horizons collected so much data which is stored two 32-Gbit hard drives and it takes 16 months to send it all the data back to Earth. During a normal mode of operation, only one Integrated Electronics Modules (IEMS) remain fully powered as a primary controller, and the other is a standby mode, and the RF Uplink receives a command within the IEM. “The C&DH software completes a real-time analysis of the telemetry delivered by all subsystems and takes action in case of an off-nominal situation” (Spacecraft Overview, n.d.).
Thermal Control System is a significant consideration because the mission would take it to the coldest places in the solar system. The approach was to use the heat that it produces like a thermos as it is already in the vacuum of space. “The multilayer insulation blankets are designed to retain the thermal radiation emitted inside the spacecraft body by the various electronics to keep the spacecraft at an operating temperature between 10 and 30 degrees Celsius” (Spacecraft Overview, n.d.). The 18 layers of Dacron is a polyester fiber (a condensation polymer from ethylene glycol and terephthalic acid), sandwiched in aluminized Mylar plastic film and Kapton polyimide film.
New Horizons Navigation and Attitude determination use sensors that determine its orientation by calculating the solar, Earth and Pluto vectors for the relevant mission phases to communicate with Earth. “It is outfitted with two Star Trackers, sun sensors and a dual-redundant Inertial Reference Platform to precisely determine its orientation in space and minimize body rates for scientific observations” (Spacecraft Overview, n.d.). It also combines Sun Pulse and Fine Sun Sensors, which delivers data on spin-rate and help during attitude acquisition. “Fine Sun Sensors cannot detect stars like the star trackers, but are built to detect the position of the sun with high precision which will be used in case of a spacecraft safe mode to point the antennas at Earth since the Earth and Sun vectors will be very similar once the spacecraft is at great distance to Earth” (Spacecraft Overview, n.d.).
The propulsion & attitude control system uses hydrazine which operates in a blowdown mode meaning it is pressurized with helium and holds 77 kilograms of propellant. It has 16 thrusters which operate in five thruster banks, which four make up a single bank and are the main propulsion system that delivers 4.4 Newtons of thrust and the other twelve are arrange in a bank of four each and deliver 0.8 Newtons of thrust. “The 4.4N thrusters are arranged in pairs, one is pointed to the –Y axis for delta-v maneuvers while the second pair provides thrust on the +Y axis and is angled 45° to the Y-Z plane to minimize plume impingement on the High Gain Antenna, reducing their overall propulsive effect, though they are still usable to provide redundancy and the ability to generate thrust in both spacecraft directions” (Spacecraft Overview, n.d.).
The Space-Based Infrared System (SBIRS) is a system intended to meet the United States space surveillance needs of the 21st century to provide missile warning and missile defense battlespace awareness, and technical intelligence missions. The satellites are in a geosynchronous earth orbit and sensors on satellites in highly elliptical orbit with ground-based data processing and control. “SBIRS replaces the Defense Support Program that saw its last launch in 2007 after nearly four decades of operation, starting out in the days of the Cold War when potential missile threats reached a peak”.
SBIRS data can detect missile launches, and compute the trajectory of missiles and impact and provides data to missile defense systems. “The GEO spacecraft bus consists of a militarized, radiation-hardened version of the Lockheed Martin A2100 spacecraft, providing power, attitude control, command and control, and a communications subsystem with five separate mission data downlinks to meet mission requirements, including system survivability and endurability requirements” (Force, 2015). The A2100 modular design is capable of generating 15kW in its standard configuration. SBIRS uses “A pair of two-panel Gallium-Arsenide solar arrays deliver around 3kW of power to the satellite with a 100 Amp-hour battery in charge of power storage”.
The propulsion system uses mixed oxides of nitrogen and hydrazine with pressurized helium. The main engine is a LEROS-1c and has an operational thrust of 458 Newtons and can vary between 386 and 470 Newtons depending on the inlet pressure. “Attitude control during propulsive phases and station keeping maneuvers are accomplished by smaller attitude control thrusters and reaction wheels serve as the primary attitude actuator during nominal satellite operations”. There is also the use of a Star Tracker and Earth/Sun sensors with a pointing accuracy of 0.05 degrees or better. SIBRS GEO-5 system will use the scalable space inertial reference unit (Scalable SIRU) for sensor pointing/stabilization and attitude control.
LANDSAT-8 is a series of satellites that collect data and imagery used by agriculture, education, business, science, and government. “The Landsat Program provides repetitive acquisition of high-resolution multispectral data of the Earth’s surface on a global basis, with the data from Landsat spacecraft constitute the longest record of the Earth’s continental surfaces as seen from space”. It also provides for land use planning, disaster response and evaluation and monitoring of water use, which began with the first series of satellites in 1972. “Landsat 8 measurements directly serve NASA research in the focus areas of climate, carbon cycle, ecosystems, water cycle, biogeochemistry, and Earth surface/interior”. It is in a near-polar, sun-synchronous orbit, and complete fourteen orbits per day and a complete coverage every sixteen days.
The satellite uses the Landsat Data Continuity Mission (LDCM), “a collaboration between NASA and the U.S. Geological Survey, will provide moderate-resolution measurements of Earth’s terrestrial and polar regions in the visible, near-infrared, short wave infrared, and thermal infrared’ (P.Taylor, 2019). The Payload Interface Electronics (PIE) receives the sensor and housekeeping telemetry, calibration data and image processing. “The daily command load covers the subsequent 72 hours of operations with the commands for the overlapping 48 hours overwritten each day” (USGS, n.d.). Landsat-8 observatory sends data file by its X-band Earth-coverage antenna, at a rate of 384 Mbps and uses an S-band uplink providing encrypted data rates of 1, 32, and 64 kbits/s. The Landsat ground stations are located in Sioux Falls, South Dakota; Alice Springs, Australia; Neustrelitz, Germany; Gilmore Creek, Alaska; and Svalbard, Norway.
Landsat uses standard off the shelf solar panels, and since it is in a Sun Synchronous, it only needs one solar to provide power. “The ADCS (Attitude Determination and Control Subsystem) employs six reaction wheels, three torque rods, and thrusters as actuators, and attitude is sensed with three precision star trackers (2 of 3-star trackers are active), a redundant SIRU (Scalable Inertial Reference Unit), twelve coarse sun sensors, redundant GPS receivers (Viceroy), and two TAMs (Three-Axis Magnetometers)” (Kramer, n.d.). The instruments it carries are the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS). “These sensors both provide improved signal-to-noise (SNR) radiometric performance quantized over a 12-bit dynamic range. (This translates into 4096 potential grey levels in an image compared with only 256 grey levels in previous 8-bit instruments.)” (USGS, n.d.).
As fantastic Satellites are, they accomplish many tasks and provide vital information to many people. Each satellite has a unique mission and specialized instruments that provide data back to Earth from space which may be weather, science or provide information for national security. The effects they have on our lives to provide modern day conveniences or much-needed information, such as television, telephones, navigation, business, weather or even climate and environmental monitoring. Depending on the satellite’s mission various users may rely on the information for a simple thing or to save a life. But what will the next generation of satellite bring to us in the future, this is up to the young space minded child that will be the next inventor with new ideas.
Reference
- Command, A. F. (2003, March). U.S. Air Force Fact Sheet. Retrieved from Fact Sheet: http://www.au.af.mil/au/awc/space/factsheets/dmsp.htm
- Force, U. A. (2015, Nov 23). Space Based Infrared System. Retrieved from U.S. Air Force: https://www.af.mil/About-Us/Fact-Sheets/Display/Article/104549/space-based-infrared-system/
- Kramer, H. J. (n.d.). Landsat-8 / LDCM (Landsat Data Continuity Mission). Retrieved Feb 22, 2019, from Earth Observation Resources: https://directory.eoportal.org/web/eoportal/satellite-missions/l/landsat-8-ldcm
- NOAA. (2018, June 13). Defense Meteorological Satellite Program (DMSP). Retrieved from NOAA: https://www.ospo.noaa.gov/Operations/DMSP/index.html
- P.Taylor, M. (2019, Feb 20). Landsat Science. Retrieved from NASA: https://landsat.gsfc.nasa.gov/landsat-8/
- Rienzi, G. (2015, July 17). How exactly does New Horizons send all that data back from Pluto? . Retrieved from HUB: https://hub.jhu.edu/2015/07/17/new-horizons-data-transmission/
- SBIRS Satellite Overview. (2013). Retrieved Feb 23, 2019, from Spaceflight 101: http://spaceflight101.com/spacecraft/sbirs/
- Spacecraft Overview. (n.d.). Retrieved Feb 2019, 2019, from Spaceflight 101: http://spaceflight101.com/newhorizons/spacecraft-overview/
- USGS. (n.d.). Data and Tolls. Retrieved Feb 2019, 2019, from U.S.Department of the INterior: https://landsat.usgs.gov/landsat-8-l8-data-users-handbook-section-2
