D-SAT CubeSat mission — demonstration of a decommissioning device
The increasing population in space of defunct satellites and other man-made debris is an issue that is getting strongly the interest of legislators, agencies and industry. In order to guarantee a safer and sustainable access to orbit, it is necessary to stop the systematic non-operative defunct satellites concentration increase in orbit. This seems to be feasible with an approach based on a preventive debris removal solution, whereby a dedicated and independent de/re-orbiting propulsion system is installed on the satellite prior to launch allowing a safe and quick decommissioning of the spacecraft before it will become a debris. 1) 2) 3)
Today both the industrial and scientific space communities agree that effective SDM (Space Debris Mitigation) measures are necessary in order to maintain future space activities below an acceptable level of risk. LEO (Low Earth Orbits), especially, together with the other upper orbits are getting more and more crowded and the space industry strongly depends on how the issue of space debris is effectively managed.
Space Agencies introduced dedicated activities as the Clean Space Initiative of ESA, which is setting a clear roadmap towards the development of building blocks enabling the compliance of SDM requirements on future satellite platforms ; 4) the activities of the Orbital Debris Program Office of NASA, which was the first organization to develop orbital debris mitigation policy and guidelines already back into the 90s and now focusing the efforts on modeling, measurement, protection, mitigation and reentry issues ;5) the activities of JAXA's Space Debris managed by the Innovative Technology Research Center . 6) Together with governmentally backed programs, there is a relevant number of activities that are proceeding as private initiatives on a commercial, quasi-commercial or private institutional basis.
End-of-life disposal technologies are under development and testing, which can be divided into both passive:
• electromagnetic tethers: low mass, low volume, negligible power but no possibility of a controlled re-entry, non-compliance with regulations for large satellites, operationally complex, long time monitoring required. Not working if the satellite gets defunct.
• drag augmentation (e.g. sails, balloons, booms): low mass, low volume, negligible power but no possibility of a controlled re-entry, non-compliance with regulations for large satellites, operationally complex, only suitable altitudes below 600 km, long-time monitoring required, low TRL, increased impact probability with debris. Not working if the satellite gets defunct.
• electric propulsion: medium mass, low volume, space proven but low impulse (no controlled reentry), not compliance with regulations for direct re-entry of space vehicles, operationally complex, long time monitoring required, high power needed. Not working if the satellite gets defunct.
• liquid propulsion: medium mass, medium volume, already available on most spacecraft, space proven but very complex system, large mass and volume if controlled reentry has to be provided, high power needed.
• solid propulsion: medium mass, low volume, space proven, low level of complexity, high thrust, relevantly low impact on spacecraft design but mass impact on the spacecraft and no re-ignition possible.
Within this context, the company D-Orbit Srl of Como, Italy, is commercializing a unique device for satellite direct and controlled decommissioning called D3 (Dedicated Decommissioning Device). 7) 8) 9)
In view of current launch rates, D-Orbit suggests the embodiment of an on-board dedicated decommissioning device in satellites, named D3. A device using an independent system based on solid propulsion technology seems a practical and efficient option and can be implemented using current technologies. Such a device has the following features: it works even if the satellite is malfunctioning or death; it is compliant with ESA and NASA standards on safety; it is single point of failure free (except for the motor); it is reliable for the entire life of the satellite; it is scalable and adaptable to different kinds of missions.
D-SAT program - a challenge: In order to achieve and demonstrate the technology maturity and demonstrate space experience, D-Orbit decided to perform an in-orbit demonstration of such a device. The constraints on costs and mass led the company to work on the system miniaturization and to end up with the decision of manufacture a real satellite with the less volume and mass possible, with a fully and functional decommissioning device. The result was the design and development of a nanosatellite, D-SAT, based on a 3 Unit CubeSat standard. D-SAT will be launched in 2017 and after two months of nominal operations in orbit the Decommissioning Device will be activated and D-SAT will reenter the atmosphere in a safe and direct way, burning up because of the atmospheric drag over a predefined uninhabited area of the globe.
The main reasons why the company decided to invest in D-SAT project are:
• demonstrate the Decommissioning Device technology, which is the core business of the company, thanks to a full controlled-quick and safe re-entry of a LEO satellite through the D3 as an effort to demonstrate TRL 9 (Technology Readiness Level-9).
• gain visibility and boost the company brand
• create opportunities and increase cooperation and collaboration with other companies
• gain capabilities in nanosatellite manufacturing, validation and testing, both software and hardware
• gain experience in satellite operations
• gain capabilities in dealing with explosive materials and safety laws and regulations for storage, handling and transportation
• gain experience on the integration logistics of the Decommissioning Device in view of its use for other applications
• increase the space community awareness on space sustainability and the threat of space debris on space missions
• let the general public know about space debris and the potential risk at which all the satellite services are exposed
• let the satellite commercial operators know about D-Orbit technology they may use to increase their satellite lifetime in orbit, decrease complexity of the decommissioning phase, avoid collisions in orbit and eventually properly dispose the satellite avoiding extra costs.
The D-SAT mission is the first example of a CubeSat adopting a solid propellant motor for active deorbiting services at the end of its mission. The decommissioning device is installed in a 3U CubeSat, with the objective to remove the satellite from its service orbit through a controlled atmospheric reentry path.
The project started in 2014 and was initially financed by D-Orbit internal investments and from December 2015 part of D-SAT project has received funding from the European Union's Horizon 2020 research and innovation program.
With reference to Figure 1, the main phases of the mission are: (1) D-SAT is loaded in the launcher, (2) D-SAT is deployed in a LEO orbit of 500 km altitude; (3) completed the LEOP operation, D-SAT performs the SatAlert, DeCAS and AtmoAnalyzer experiments, (4) completed the mission, D-SAT executes the firing maneuver controlled and commanded by ground, (5) the decommissioning maneuver location is high over the Atlantic Ocean to minimize the risk for people and assets during the atmospheric entry.
Figure 1: Illustration of the D-SAT mission phases (image credit: D-Orbit)
In order to identify, collect and understand the applicable requirements, and identify the best integration, test campaigns and transportation logistics, an extensive work was done in closed collaboration between the nanosatellite owner, D-Orbit, the solid rocket motor manufacturer, Bayern Chemie GmbH, Aschau am Inn, Germany, and the Launch Service Provider, Tyvak International. First of all, the EES (Electro Explosive Subsystem) and the solid rocket motor were individually qualified. These qualification test programs were based on major safety standards, as the ECSS (European Cooperation for Space Standardization), the Military Standard (MIL-STD-1576) and the Eastern-Western Range (EWR 127-1), the SMC-S-016 and related standards. Secondly, the satellite Qualification Model was tested in an inert configuration, to optimize the program scheduling and minimize costs. Finally, the satellite Flight Model went through the acceptance test program, which was identified merging ground handling, transportation, safety, launcher and CubeSat International Standard requirements.
D-SAT is a nanosatellite designed on the 3U+ CubeSat standard with a mass < 4.5 kg. The satellite has been designed to maximize the reliability and consequently the mission success. Therefore D-SAT main functions are single point of failure free. Thanks to this valuable characteristic, D-SAT differs from the majority of current CubeSats and it may represent an innovative design model in the nanosatellite development.
Figure 2: Illustration of the D-SAT 3U CubeSat (image credit: D-Orbit)
D-SAT spacecraft is constituted by two identical units, called Unit 1 and Unit 2 (Figure 3). In cruise conditions, Unit 1 acts as "Master", which plays the role of the CubeSat platform, while the Unit 2 acts as "Slave", playing the role of the satellite payload.
In nominal operation the Unit 1 carries on all typical features of a platform; it is responsible of housekeeping, ADCS (Attitude Determination and Control Subsystem), energy charging and power distribution and radio communication with ground. In the meantime, the Unit 2 acts as "Slave", playing the role of the Unit deputed to the decommissioning function. Before the decommissioning phase, the control is transitioned to the Slave Unit, which provides a maneuver-suitable attitude, a stabilizing spin motion and finally the deorbiting maneuver.
Figure 3: D-SAT block diagram (image credit: D-Orbit)
Both Units interface with the EES (Electro Explosive System) and the motor, thus if needed they are both fully capable to assume the role of Master or Slave. Thanks to the D-SAT architecture, the decommissioning function, consisting of a quick, reliable and safe deorbiting of the D-SAT spacecraft, is possible even if one of the two units is malfunctioning or dead.
The D-SAT nanosatellite includes the following components:
• 2 CubeSat-class systems, called Unit 1 and Unit 2, each containing:
- one on board computer OBC
- one interface board
- one S-band antenna
- one UHF radio module
- AOCS actuators (magnetorquers) and sensors (magnetometers, sun sensors, gyroscope)
- one EPS (Electric Power Subsystem) including batteries and solar arrays.
• A GPS receiver to accurately track the reentry trajectory after the decommissioning maneuver
• A spin wheel to impart angular momentum about the z-axis of the satellite, for passive stability during fire
• An EES comprehensive of the EED, the electric "Firing Circuit" and mechanical "Safe and Arm Device" part
• A solid propellant motor.
As of June 2016, the QM (Qualification Model) is now subjected to the qualification tests following the Launch Service Provider requirements (Figure 4).
Figure 4: Photo of the D-SAT QM during the qualification spin test (image credit: D-Orbit)
Launch: The launch of the D-SAT nanosatellite as a secondary payload is scheduled for Q2 2017 on board of a PSLV launcher from SDSC (Satish Dhawan Space Center) SHAR, the main launch center of ISRO on the south-east coast of India, Sriharikota.
Orbit: Sun-synchronous orbit, altitude of ~ 500-600 km.
D-SAT Test Campaigns:
D-SAT Test philosophy: D-SAT FM (Flight Model) baseline acceptance test plan at satellite level consists of a set of acceptance tests performed in the spacecraft inert configuration, meaning that, inside the EES and the SRM (Solid Rocket Motor), the hazardous materials have been substituted with equivalent inert materials (Figure 5); the EES contains an Electro Explosive Device not containing explosive powder and similarly the SRM contains an inert initiator powder and inert propellant cartridge.
Figure 5: D-SAT inert EES and SRM subsystems (image credit: D-Orbit)
The test and integration approach with hazardous subsystems is reported in the block diagram of Figure 6. The test consist of random and sine vibration compliant with the launcher user guide and thermal vacuum basing on SMC Standard SMC-S-016 . After the tests, D-SAT is partially disassembled to integrate the Flight subsystems previously accepted at subsystem level. After reassembling D-SAT, a functional test is performed to verify a correct integration. Finally, D-SAT integration in the P-POD and functional tests after integration are performed. 10) 11)
Figure 6: D-SAT FM acceptance approach (image credit: D-Orbit)
EES (Electro Explosive Subsystem): An EES, designed with a SRM (Solid Rocket Motor) directly integrated with an igniter, EED (Electro Explosive Device), shall be controlled with a dedicated system that integrates several inhibits. With a deep investigation on the common standard related to EESs is clear that the most used standard is MIL-STD-1576, which was written in 1984, but always used. The MIL-STD-1576 lists several requirements on EES design for space application (manned mission or not) and many of these are focused on the safety aspect. The main functions of the EES are:
• Avoid an inadvertent ignition of the EED – 4 electrical inhibits: 3 controlled by command and 1 based on pyrotechnical chain status
• Avoid the ignition of SRM caused by an inadvertent ignition of the EED
• Monitoring of the state of the EES (safe state of arm state)
• Contain the gas generated by an inadvertent ignition of the EED.
Test Philosophy and tests performed: The test plan is a tailoring of SMC-S-016 and MIL-STD-1576. The tailoring was done in order to be compliant with cost and time schedule imposed by a typical CubeSat mission. The strategy in the tailoring is based on performing the most critical tests on the single critical components, the EED. The testing phase is composed by two sequential phases (design verification and qualification), for each of these are foreseen: environmental tests (thermal and vibration) and fire tests integrated with the motor, in order to demonstrate the full functionality of the EES directly with the SRM:
• Fire test – The coordination between D-Orbit and Bayern Chemie teams allowed to perform the fire tests integrated with SRM during its design verification/qualification path:
- 1° phase – during design verification, the pyrotechnical chain, that connect the EED with the SRM, was tested to high and low temperature (-30°C and +71°C) directly with the SRM
- 2° phase – during qualification, the assembly of pyrotechnical chain, the EED and the firing circuit was tested on the SRM at high and low temperature (-34°C and +71°C).
The tested unit are in inert configuration, with an inert EED; this is necessary for programmatic constraints (budget and scheduling). The EED is already subject to a qualification program performed by the manufacturer.
Each produced unit is subject to an acceptance test program:
• Functional test after production – Inert configuration
• Environment test (random vibration and thermal cycle) – Inert configuration
• Integration of EED and functional test.
Each EED is subject to its own acceptance program performed by the manufacturer.
Design verification program: The design verification program is executed in order to acquire confidence on the EES design. The tailoring of the test program is based on standards SMC-S-016, MIL-STD-1576 and EWR-127-1 satisfying budget constraints and the worst-case approach on test levels. The firing tests are executed with a reduced version of EES, in order to replicate the pyrotechnical chain. In these tests, D-Orbit verified the functionality of the chain EES+SRM+EED at low and high.
Test Results: The test executed on EES had positive results. The firing tests executed during the verification and qualification of SRM had positive results; all EES produced had passed the acceptance test.
SRM (Solid Rocket Motor) subsystem: The configuration of the D-SAT rocket motor was chosen to be a cartridged propellant case where the propellant grain is case-bonded to a steel cartridge that is surrounded by the rocket motor housing. This design has the advantage that the propellant cartridge can be handled and transported independent and separate from the nozzled motor housing.
The propulsion unit consists of a solid propellant rocket motor with a caliber of 97 mm and total length of 122 mm. The main features are:
- Minimum total delivered impulse: 740Ns @ -30 °C soak temperature
- Maximum Thrust: 450 N @ +71 °C
- Soak temperature range for qualification: -34 °C, +71 °C
- Nominal burn-time: 3.2 s
- Fully military qualified
- Total motor mass: 0.9 kg
- Propellant mass: 0.3 kg
- MEOP (Maximum Expected Operative Pressure): 70 bar
- Specific impulse (vacuum): 2613 m/s
- Throat diameter: 7.5 mm
- Nozzle expansion ratio: 20
- Web fraction: 64%.
Figure 7: Design drawing of the D-SAT solid propellant rocket motor (GRZ-650-20223-0000-A), image credit: D-Orbit
Test philosophy and test performed: The D-SAT Motor Test Firing and Qualification Program was designed in order to qualify the rocket motor step by step, in order to assess the performance in terms of motor ignition behavior, motor burn characteristics and general motor performance. and drive the test program (Ref. 11). 12) Therefore, the test-firing program is composed by the following program phases including nine motor test firings:
- Functional: Two motor test firings at -30°C and +71°C soak temperature with fresh motors
- Verification: Three motor test firings at -30°C, +20°C and +71°C soak temperature with motors that went through the verification test program.
Qualification: Four motor test firings, two at -34°C and two at +71°C soak temperature, with motors that went through the full ageing, thermal and mechanical qualification program.
Functional Test Program: As part of the Functional test program, two motor test firing including the EES Static Firings were performed in order to assess the design performance as a preparatory step before carrying out the Verification and Qualification test programs.
Verification Test Program: As part of the Verification Phase, the three Verification Motors went through a pre-qualification program that used fresh, i.e. not artificially aged, D-SAT rocket motors. The program is listed in detail in Table 1.
Table 1: D-SAT SRM verification test program
Qualification test program: At the beginning of the qualification phase, four propellant cartridges were first artificially aged for an equivalent shelf life of 4 years (accelerated ageing at a constant temperature of 62°C for 25 days). After the integration of the aged propellant cartridges, the four D-SAT Qualification Motors went through the Qualification Program listed in Table 2.
Table 2: D-SAT SRM qualification test program
Test Results: All D-SAT motor test firings conducted after the Function, Verification, and Qualification Phases were completed with successful ignition of the solid rocket motor. The registered performance showed full compliance with all qualification and performance requirements.
The minimum and maximum operating motor pressure at -34°C and +71°C soak temperature, respectively, result to be 47.1±1.5 bar and 63.5±1.5 bar. The maximum thrust at +71°C soak temperature was determined to be 483±21 N. The measured burn times are in a range from 2.62±0.13 s to 3.55±0.05 s.
In summary, the D-SAT motor test firings do not only show good results in terms of comparison with the assumptions and results of internal ballistics and structural FE calculations, but also in terms of a reliable and fast-response ignition behavior. This is actually true for all applied initiator and EES/initiator combinations and in terms of a smooth and repeatable pressure and thrust evolution.
D-SAT transportation: The transport of the D-SAT spacecraft presented some issues related to the included components and the classification of the device. The transportation of the satellite requires asking a formal evaluation to the European body in relation to classification products, i.e. Bundesanstalt für Materialforschung und -prüfung (BAM). Another issue related to the transport is regarding the authorizations needed to export the device from the European Union. The needed authorization and declarations are associated to the TARIC (Integrated Community Tariff) code. All the listed documents have to be collected and presented to the customs.
The actual transportation of the D-SAT spacecraft is assigned to an international forwarder with expertise in transport of space application devices.
Experiments: (SatAlert, DeCAS, DAA)
During its mission, together with the Decommissioning Device In-Orbit Demonstration, D-SAT will host different scientific experiments: in the cruise phase, D-SAT will carry out the "SatAlert" experiment, developed together with the CNIT (Consorzio Nazionale Interuniversitario per le Telecomunicazioni) and after the fire, during the reentry trajectory through the atmosphere, the DeCAS and the Atmo-Analyzer experiments will be performed (Ref. 3).
When a disaster happens, the delivery of alerts to the population is a key element to prevent tragic consequences and increase the efficiency of the planned reaction to the event. The SatAlert Experiment is a part of the standardization activity devoted to the definition of MAMES (Multiple Alert Message Encapsulation protocol over Satellite) for the delivery of alerts to the population in the case of a disaster. The MAMES main objective is the definition of an extensible multiple alert message encapsulation protocol for alert messages transport over satellite links. In particular MAMES provides a means for encapsulating one or more differently formatted alert messages [e.g. CAP (Common Alert Protocol) , unstructured text, image, paging protocols, DeCAS messages]. 13)
The SatAlert experiment aims to verify the transmission setup of MAMES messages from the MAMES Alert Provider to the MAMES Alert Receiver. The experiment consists in the generation and transmission of a MAMES ALERT message, from an Earth station to satellite, which will process and broadcast the received message back to Earth. In order to validate the process, two separate Earth stations for satellite beacon tracking will be implemented. The main ground station will be located in Lomazzo (Italy) at D-Orbit's premise and it will be responsible for the generation and transmission of the MAMES Messages and also for the reception and decapsulation of them; while a second ground station located in Florence (Italy) will only receive and decapsulate MAMES messages (Figure 8).
Figure 8: SatAlert experiment overview (image credit: D-Orbit)
DeCAS (Debris Collision Alerting System) Experiment
In Earth's orbit, there are about 13,000 objects. For most of them, the disposal will be through the reentry into the atmosphere as required by international agreements between agencies in different countries. (i.e NASA Safety Standard 8719.14 - Process for Limiting Orbital Debris, Ref. 13). With the new satellite technologies and the advent of space tourism, SV reentries in the atmosphere are expected to rise considerably over the next few years. Today we are forced to close airspace supposedly concerned with these reentries (with strong economic impact) and to live moments of uncertainty and apprehension. The fragmentation of a space vehicle (satellite or spacecraft) during reentry to the Earth can be planned or accidental, as in the case of Columbia. The debris that is generated, whose position is always uncertain, can be very dangerous to the population and to high-risk industrial plants (i.e. nuclear power plants) and to the civil and military aviation (a fragment more than 300 gr causes loss of aircraft). Knowing the location and the extent of the debris (or danger area), as well as its dynamics, allows to secure and notify all potentially interested parties in time. This leads to a need for aerospace safety of a system able to determine the exact condition of explosion / fragmentation of Space Vehicle and to send an early warning to the users potentially affected by transmitting the dynamics of Danger Area to all interested users and providing the elements to "suggest" to pilots an initial escape heading to avoid danger area.
The patented DeCAS device is small in size and lightweight based on the principle of the black box of the aircraft and it uses space technologies already tested for data broadcasting. It works as a "smart fragment" which can autonomously determine its own position during reentry and which knows its relative location in the projected hazard area which has been pre-computed on ground and/or its data are used directly from a ground station to determine the Dangerous Area. It is fitted into or on the vehicle during the construction phase remaining in a dormant status until it activates by itself at the moment of fragmentation of space vehicle sending information about its location (which corresponds to the space debris area). - Hence the DeCAS system aims to inform both the air traffic and the population of an imminent danger due to the fall of space debris caused by controlled or uncontrolled reentry of the space vehicle on which it is mounted. It is useful both in the launch phase (detachment and reentry of the various stages of combustion) and in the reentry phase.
The D-SAT mission will have the capability of the DeCAS system on board, thus allowing the latter to make its first in-orbit validation test. With D-SAT in orbit, an uncontrolled re-entry will be simulated by sending to D-SAT a trigger message which in turn will generate a message towards the ground with the necessary parameters to define its footprint. Once the message is received by the ground stations, it will be processed by a special software, which will calculate the position of the footprint and will make a prediction of the time and the area of impact on the ground.
Once the danger area will be defined, the DeCAS message will be encapsulated, uploaded to the satellite and broadcasted to ground by the MAMES protocol. This second phase has the aim to verify the possibility of using an emergency protocol for the transmission of DeCAS messages that allows their validation and authenticity.
The third aim of this mission is to simulate a network of ground stations able to receive the signal, process it and transmit the information to all potential customers and agencies. To achieve this purpose, Aviosonic has partnered with companies and government agencies, which will provide facilities capable of receiving the signal and process it with the software that will be provided to them. The success of D-SAT mission is fundamental for Aviosonic because it will open the way to the second phase of the system development and to the drawing-up of preliminary agreements for its marketing.
DAA (D-Orbit Atmosphere Analyzer), also referred to as Atmo-Analyzer Experiment, is a sensor developed by D-Orbit able to analyze and retrieve atmospheric data during its reentry through the atmosphere and send them to specific fixed or mobile ground stations. During the reentry phase, DAA will retrieve atmospheric data during the satellite descent, and post processing analysis of the raw data will produce valuable data for customers. Among the main users for DAA data will be insurance companies, weather agencies and telecommunication companies that are interested in measuring scientific data in the MLT (Mesosphere and Lower Thermosphere) region. The DAA major competitive advantage is the type and quality of data collected. DAA is being developed in the scope of the European Space Agency's Business Incubation Center (ESA BIC) in Portugal and has been granted SME (Small and Medium sized manufacturing Enterprise) Instrument Phase 1 from the European Commission, benefiting from both business and technical support. In this first version, DAA will measure temperature, GPS signal and the magnetic field during D-SAT descend towards Earth.
1) Alessio Fanfani, Simone Brilli, Matteo Trotti, Angelo Dainotto, Elena Toson, Alexander Weigand, Fabio Nichele, "Launch of a 3 Unit CubeSat with integrated propulsion system: D-SAT qualification, acceptance and transportation logistics," Proceedings of the 67th IAC (International Astronautical Congress), Guadalajara, Mexico, Sept. 26-30, 2016, paper: IAC-16-B4.6B.8
2) "D-Sat mission brochure," D-Orbit, URL: http://www.deorbitaldevices.com/wp-content
3) Elena Toson, Alessio Fanfani, Luca Simone Ronga, Piermarco Martegani, Luca Rossettini, "D‐SAT Mission: an In‐Orbit Demonstration of a Solid Propellant Satellite Decommissioning Device," Proceedings of the 4S Symposium: `Small Satellite Systems and Services,' Valletta, Malta, 30 May – 3 June 2016
4) "Clean Space," ESA, 2016, URL: http://www.esa.int/Our_Activities/Space
6) Seishiro Kibe, "JAXA's Space Debris Related Activities : Mitigation, R&D," 2013, URL: http://www.stardust2013.eu/Portal
7) Luca Rossettini, "D-Orbit Solutions for our Future,"10th ESA Workshop on ADCSS (Avionics, Data, Control and Software Systems), ESA/ESTEC, Noordwijk, The Netherlands,Oct. 18-20, 2016, URL: https://indico.esa.int/indico/
8) E. Toson, S. Antonetti, M. Trotti, L. Ferrario, L. Rossettini, "A Satellite Dedicated Decommissioning Device based on Solid Rocket Motor Technology, 6th EUCASS (European Conference for Aeronautics and Space Sciences) 2015. 29 June - 3 July, Krakow, Poland
9) "D3 Technical Sheet," D-Orbit, URL: http://www.deorbitaldevices.com/wp-con
10) "User Manual - Interface Requirements for launching Auxiliary satellites in PSLV", 15 December 2014, PSLV_UsersGuide_20141215
11) SMC Standard SMC-S-016, "Test requirement for launch, upper-stage and space vehicles",Space and Missile Systems Center Standard, Air Force Space Command, 5 September 2014, URL: http://everyspec.com/USAF/USAF-SMC/download.
12) "Eastern and Western Range. Range Safety Requirements", EWR 127-1, URL: https://snebulos.mit.edu/projects/refe
13) "Process for Limiting Orbital Debris," NASA Technical Standard, STD-8719.14A, Approved: 2011-12-08, Change 1 approved: 2012-05-25, URL: http://www.hq.nasa.gov/office
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).