Ho'oponopono (Hawaiian for “To Make Right”)

Quick facts

Overview

Ho‘oponopono (Hawaiian for “To Make Right”)

A Radar Calibration CubeSat Mission

Ho‘oponopono (“to make right” in the Hawaiian language) is a 3U CubeSat mission developed by students of the University of Hawaii, Honolulu (M¿noa), HI, USA. The development of the nanosatellite was the basis for the University of Hawaii’s participation in the AFOSR (Air Force Office of Scientific Research) UNP-6 (University Nanosat-6 Program), kickoff in Jan. 2009, a rigorous two-year satellite design and fabrication competition.

The design of Ho‘oponopono went through a six-level review process (Proposal Merit Review, Systems Concept Review, Systems Requirements Review, Preliminary Design Review, Critical Design Review, Proto-qualification Review) that was judged by DoD, NASA, and industrial reviewers. Throughout these reviews, Ho‘oponopono’s design was judged on its technical merit, educational merit, and feasibility. Independent design evaluations were also held with review boards consisting of engineers from Northrop Grumman Aerospace Systems and InDyne Inc. ^{1) 2)}

In January 2011, the student team of the University of Hawaii won 3^rd prize in the UNP competition, awarded by AFRL (Air Force Research Laboratory) and AIAA. Ho‘oponopono was also selected by NASA as a participant in its CubeSat Launch Initiative for an upcoming launch. ^{3) 4) 5)}

Ho‘oponopono is a collaborative project of the University of Hawaii (UH) and the USAF (United States Air Force). UH is providing the satellite, while the USAF is furnishing the payload suite consisting of a C-band transponder, GPS unit, and associated antennas, all housed in a 3U CubeSat form factor.

The objective of the mission is nothing less but to continue a long-existing radar calibration service, provided currently with a microsatellite (RADCAL) and with a payload suite on a meteorological mission (DMSP-15) — with a sensor complement on a nanosatellite mission.

The nominal success criteria call for the following capabilities:

• Demonstrate the collection of accurate (< 5 m) ephemeris data

• Provide radar calibration information at an average rate of five radar ranges every day for 1 year.

One of the most notable aspects of the Ho‘oponopono project is that while it is faculty-guided, it is predominantly student-driven. In fact, undergraduate students have led the development efforts for all seven of UH’s eight CubeSat projects to date.

Background

To accurately identify and track objects over its territories, the US military must regularly monitor and calibrate its 80 plus C-band radar tracking stations distributed around the world. Unfortunately, only two calibration satellites are currently in service, and both have been operating well past their operational lifetimes. Losing either satellite will result in a community of users that no longer has a reliable means of radar performance monitoring and calibration.

Although radar calibration methods have existed for many years, satellite calibration has numerous advantages over these other methods. A boresight tower, for example, lacks the dynamic characteristics of an orbiting satellite, making it an unrealistic target. Aircraft targets, while dynamic, are limited in calibrating multiple radar stations simultaneously. Multipath problems are essentially eliminated with satellites due to their high elevation angles as well.

Since 1968, there have been five US satellites with RPM (Radar Performance Monitoring) payloads aboard: GEOS-2 (Geodetic Earth Orbiting Satellite-2) of NASA (launch Jan. 11, 1968), GEOS-3, also known as GEOS-C of NASA (launch April 9, 1975), GEOSAT (launch March 12, 1985, RADCAL of DoD, and DMSP F-15 of DoD.

• RADCAL (Radar Calibration microsatellite), an axially symmetric, gravity-gradient stabilized spacecraft with a launch on June 25, 1993, was the first satellite dedicated to RPM with the objective of providing calibration data for numerous DoD (Department of Defense) C-band radar systems distributed around the world. To carry out these calibrations, RADCAL carries two C-band transponders, a dual-frequency Doppler beacon transmitting at 150 and 400 MHz, and a tracking, telemetry, and control unit. In an effort to standardize the procedures required to make use of a GPS-based system as a backup orbital determination system, two Trimble TANS Quadrex, non-military GPS receivers were also put onboard as a secondary, experimental payload.

Commissioned under a one-year contract-to-launch schedule, RADCAL is currently (2011) operating over 15 years past its expected lifetime and has had higher power degradations over the years, making it more evident that a replacement system will soon be needed. RADCAL orbit: 757 km x 887 km, inclination = 89.6º.

• DMSP-15, a meteorological spacecraft of DoD/USAF, was launched Dec. 12, 1999. In 2011, the mission is operating eight years beyond its expected lifetime.

In total, 13 DoD tri-service agencies, NASA, and international major range organizations located in 23 geographic locations, supporting 109 radars and 80 plus user programs, are supported by RADCAL and DMSP F-15. This high volume of users, coupled with the likelihood of the current RADCAL satellite failing any day, further motivates the need of a replacement system.

The US JSpOC (Joint Space Operations Center) at VAFB, for example, is a RADCAL beneficiary whose calibration needs are crucial given that its Space Situational Awareness Operations Cell maintains space data and performs satellite screenings for all man-made objects orbiting Earth to mitigate satellite collisions.

Spacecraft

The Ho‘oponopono project uses a 3U CubeSat form factor with a standard size of 10 cm x 10 cm x 34 cm and a mass of ~ 3.5 kg. The original RADCAL microsatellite had a launch mass of 95 kg and identical mission objectives. Additional advantages of Ho‘oponopono’s CubeSat implementation include significant reductions in development and launch cost (Ref. 1).

The nanosatellite design consists of the following 6 subsystems:

• ADCS (Attitude Determination and Control Subsystem)

• COM (RF communications)

• EPS (Electrical Power Subsystem)

• C&DHS (Command and Data Handling Subsystem)

• STR (Structure)

• PLD (Payload). Note: The PLD is described separately under sensor complement.

Figure 6 is a functional block diagram of Ho‘oponopono’s subsystems showing their electrical connectivity through a common system bus.

ADCS: The nanosatellite uses the Earth’s gravity field to point its COM and PLD antennas in the nadir direction via a deployable gravity-gradient (GG) boom and attached endmass (Figure 4). Unlike active-control schemes, gravity-gradient stabilization methods do not require a feedback control loop to adjust control torques to meet pointing objectives and therefore consume little power and do not require the design of a controller. A passive attitude control system design therefore tends to be simpler than an active one. However, a downside to GG stabilization is that a deployable element is required, which introduces reliability concerns and requires extensive testing.

A 1 m deployable GG boom with an 80 g aluminum endmass has been developed and successfully deployed in a 1 g environment. Modifications to this 1 m boom design are planned for the flight unit to allow the GG boom to have a 3 m extension, augmenting Ho‘oponopono’s pitch and roll inertia by over 200 times the retracted inertia about the pitch and roll axes to approximately 1.2 kg m².

Preliminary results indicate that this increase in inertia sufficiently reduces the nadir pointing error. Special consideration was taken to ensure the GG boom tether does not blossom due to vibration and to ensure little friction in the GG boom reel during extension.

For attitude determination, Ho‘oponopono uses an Invensense ITG3200 three-axis gyro to measure rotation rates, a Honeywell HMC5843 magnetometer to measure the magnetic field at the location of the satellite, and six OSI Optoelectronics S-100 photodiodes that act as sun sensors. Much of the development of the Kalman filter used to carry out these measurements is based on previous work done in this area.

RF Communications

The COM subsystem includes a Microhard MHX2420-FT S-band radio with associated patch antenna and an AstroDev Neon-1 (Ne-1) UHF beacon with a quarter-wave monopole antenna. The COM subsystem is one of three subsystem PCBs in the PCB (Printed Circuit Board) stack, the other two being the PLD and EPS subsystem PCBs. The PCB stack is connected through the system (SYS) bus, which is a 120 pin PC-104 connector. The block diagram of the COM subsystem is shown in Figure 7 with the COM components in blue and supporting C&DHS components in orange.

The radio and beacon is controlled by the supporting hardware of C&DHS, which includes the Microchip dsPIC33F microcontroller24, Texas Instruments (TI) TCA9539 I/O expander25, TI SN65HVD233 CAN driver26, and the Microchip SST25VF032B flash memory27. The dsPIC33F microcontroller controls the beaconing of SYS health data through the Ne-1 and the receive/transmit of data through the MHX2420. The MHX2420 receives uplinks of radar interrogation schedules as well as command and control data while transmitting collected GPS ephemeris data and satellite state of health.

The COM, PLD, and SYS level requirements are the lead driving factors of the design. The COM subsystem requirements include having inhibits that prevent RF emission before deployment with a 45 minute delay, supporting sufficient uplink and downlink margins for all mission data elements, adhering to all spectrum licensing requirements, and ceasing all radio transmission at end of life.

The MHX2420-FT is a 2.4 GHz frequency-hopping spread-spectrum radio. It operates in the 2.4–2.4835 GHz range, and outputs 1 W of RF power with a required supplied voltage of 5 VDC28. COM operates the MHX2420 radio at a link rate of 57.6 kbit/s to ensure adequate data bandwidth for the collected PLD GPS data.

The COM subsystem features four onboard antenns:

• a C-band quadrifilar helix antenna, which is used by the onboard transponder to transmit a >100 peak power pulse in response to a radar interrogation

• a GPS antenna for collecting ephemeris data

• an S-band microstrip patch antenna for downlinking mission data

• a UHF antenna for beacon purposes.

EPS (Electrical Power Subsystem)

The EPS is designed to meet the power requirement needs of the various COTS (Commercial-Off-The-Shelf) components distributed throughout Ho‘oponopono’s system bus. The ability to activate the Herley MD2000C-1 transponder five times per day, along with the transponder’s 7 W power requirement, were driving factors to implement a large power margin as well. A block diagram of Ho‘oponopono’s EPS is shown in Figure 8.

Power is generated through use of Emcore 609147-BE Triple-Junction Monolithic Diode (BTJM) solar cells with 28% efficiency. This relatively new photovoltaic technology offers improved radiation hardness while reducing the required surface area coverage and increasing the potential mission lifetime as well. Six solar cells are distributed along three of Ho‘oponopono’s four lateral faces. A 2.4 GHz deployable patch antenna, mounted to the remaining lateral face, limits the surface area to fit four cells, for a total cell count of 22. The cells along each solar panel are arranged in pairs that are wired in series. These pairs are then all connected in parallel, as shown in Figure 9.

The output from each solar panel is fed to a Maxim MAX1709 DC/DC converter with 90% efficiency, which is integrated on the inside of each panel. The output from the MAX1709 converter is controlled using its feedback pin and a Maxim DS3901 variable resistor, whose voltage divider resistance values are chosen to provide a constant 4.35 VDC. This output voltage powers a MAX8934D Li+/Li-Poly linear battery charger.

The battery charger, which features temperature-monitoring capabilities during periods of charging and discharging, provides a range of voltages (3–4.35 VDC) and has three output options. The ‘Always-On Linear Regulator Output’ pin provides a constant 3.3 VDC with 30 mA, which powers the EPS dsPIC33F microcontroller. The ‘System Supply Output’ is the other pin that is used to output either a regulated (3–4.2 VDC) Li-Poly battery voltage or a regulated 4.35 VDC.

The RAW output voltage from the MAX8934D battery charger is fed to three converters to provide 3.3 VDC, 5 VDC, and 28 VDC, and also supplied to the system bus for distribution to COM, PLD, and ADCS. The Texas Instruments TPS62046 DC/DC converter outputs 3.3 VDC and has a maximum output current of 1.2 A. The MAX1709 DC/DC converter boosts the RAW voltage up to 5 VDC with a maximum output current of 5 A. Two TPS61175 DC/DC converters are cascaded in series to provide the 28 VDC and 7 W required for the Herley MD2000C-1 transponder module.

The EPS Microchip dsPIC33F microcontroller, when used in normal operations, is able to implement peak power tracking through control of the DS3901 variable resistor. Further research is needed to determine the necessity for peak power tracking. In the event that the EPS batteries discharge to non-operational levels, the dsPIC33F maintains control by operating the satellite system in a “power save” mode until the batteries charge to a nominal level.

Power is stored using 15 COTS Tenergy Li-Polymer 3.7 V 1150 mAh batteries. These batteries are spot welded together in parallel and provide 3–4.2 VDC, depending on their level of discharge, with a storage capability of 62 Wh.

C&DHS (Command and Data Handling Subsystem)

The architecture is based on CSI (CubeSat Stackable Interface) of UH which was developed to provide a cleaner EPS subsystem. CSI minimizes the need for a complex wiring scheme to distribute voltages across a PCB stack by providing standardized voltages across a common bus. CSI uses the PCI-104 standard, that not only provides a robust connection, but also fits within a 1U CubeSat form factor.

A key feature of CSI is the option to place addressable I/O expanders on each board in the stack to be accessed by an I²C bus, which allows for remote access for a multitude of I/O in the system. The further addition of on/off switches controlled by this I/O expander allows for a remote power management system that is controlled by two lines across CSI as shown in Figure 10.

CSI also supports four levels of data communication. At the lowest level, 32 digital I/O pins allow for point-to-point communications between devices on the bus. Four UART channels form a secondary level of point-to-point communication. The main communication bus uses CAN (Controller Area Network) for robust data transfer. CAN uses an arbitration system that minimizes collisions on the network and also allows for low-power data transfer by taking advantage of differential signaling. CSI also supports USB channels that are not used in Ho‘oponopono.

The CAN bus allows multiple nodes to communicate using a wait-on-send approach. There are predetermined time slots in which a transfer can occur, and at the beginning of these time slots is an arbitration period in which each device on the bus wanting to transmit sends its message identifier. In arbitration, if two or more devices wish to start a transfer at the same time slot, each device will start transmitting its arbitration sequence and the higher priority message will be sent. Each message type has its own unique label in arbitration ensuring that no collisions will occur.

The C&DHS relies on supporting component hardware to maintain control of each subsystem. C&DHS’s component ICs (Integrated Circuits) include: the Microchip dsPIC33F microcontroller, Texas Instruments (TI) TCA9539 I/O expander, TI SN65HVD233 CAN driver, and the Microchip SST25VF032B flash memory. The microcontroller selected from the Microchip dsPIC33F family is the dsPICFJ128MC804 which has an on-chip flash program memory of 128 kByte, supports one I²C, two UART, and two SPI (Serial Peripheral Interface) digital communication peripherals. This microcontroller also supports an enhanced CAN module that has up to eight transmit and up to 32 receive buffers.

TI TCA9539 I/O expanders each have a low standby-current consumption of 3 µA while also each featuring 18 5 V tolerant I/O ports. Using the I²C protocol, these I/O expanders give the EPS microcontroller remote access to all of its I/Os across the CSI bus. Selected to operate in especially harsh environments, the TI SN65HVD233 CAN drivers provide transmit and receive capabilities between the differential CAN bus and CAN controllers, with signaling rates up to 1 Mbit/s. Ho‘oponopono’s CAN drivers manage the robust CAN bus ensuring a clean bus for data transfer between the subsystem microcontrollers. The C&DHS has two Microchip SST25VF032B flash memories, featuring a four-wire, SPI-compatible interface, having each 32 Mbit of flash memory.

An important aspect of the C&DHS is the ability to ensure sufficient data storage as this is the driving factor in Ho‘oponopono’s mission. The primary payload data is the GPS ephemeris that will be stored on Microchip SST25V032B memory chips. These flash memory chips, in conjunction with the Microchip dsPIC33F’s internal memory, allow 64 Mbit of data to be stored which, in the extreme case of each GPS packet being 847 bytes, allows 9904 packets to be stored. At a GPS ephemeris collection rate of 30 seconds per packet, Ho‘oponopono can store up to 3.4 days worth of data.

The C&DHS software is based on a four-level programming model for the subsystem microcontrollers distributed across the CSI bus.

The first level, starting at the base of Figure 11, is the core features layer. The core features for the dsPIC33F microcontroller include power modes, clock frequency, setup of I/O ports, interrupts, real time clock and calendar (RTCC), and analog to digital conversion (ADC). Next, moving up one level to the protocols layer, the UART, I²C, CAN, and SPI protocols are developed in software to be callable functions. These functions are called upon by the driver layer that is developed for the COM radio, PLD GPS, TCA9539 I/O expanders, voltage, current, and temperature monitors, and the SST25VF032B flash memory. The driver layer tells the protocols how to function based on parameters such as data rate and I/O setup. The final programming layer is the application layer, and includes task queue, operation modes, and command and data handling. The application layer is developed uniquely for each of the subsystem microcontrollers.

Nanosatellite structure (STR)

From a general standpoint, the structural subsystem of Ho‘oponopono must fulfill the basic requirements of a satellite structure, namely surviving launch loads and the on-orbit environment. Being a 3U CubeSat, the structural subsystem must match the CubeSat form factor, allowing it to be deployed from the P-POD. Accordingly, the overall structural envelope and mass properties were made to conform to the Cal Poly standard. Beyond these requirements, the satellite structure is responsible for providing appropriate mounting points both internally and externally for the other subsystems.

The 3U CubeSat structure is custom made (the Pumpkin Kit structure didn't meet the mounting requirements). The basic chassis design consists of four walls: two are flat and two are bracket-shaped, having right angle tabs where the flat walls attach to hold the two sides together. End brackets enclose the CubeSat structure. The structural design was performed primarily via SolidWorks CAD.

All structural components were milled out of 6061-T6 aluminum except the deployable patch antenna cradle hinge, which was machined out of brass for solderability. For the larger and more intricate parts, such as chassis walls and brackets, a CNC mill was used. Some smaller parts were machined by hand for the engineering design unit, with the intention of machining all flight parts on a CNC machine.

Launch

On Nov. 20, 2013 (01:15 :00 UTC), the Ho‘oponopono nanosatellite was launched as a secondary payload from the MARS (Mid-Atlantic Regional Spaceport) on Wallops Island, VA on a Minotaur-1 vehicle of OSC (Orbital Sciences Corporation). The launch was part of the ORS-3 (Operationally Responsive Space-3) enabler launch mission. The primary payload on this flight was STPSat-3. ^{6) 7) 8)}

Ho‘oponopono was manifested on ELaNa-5 for a launch in November 2013 as part of the SpX-3 Dragon CRS-3 (Commercial Resupply Services-3) payload aboard a SpaceX Falcon-9 vehicle to the ISS. ⁹⁾

In January 2011, NASA announced that Ho‘oponopono was one of 20 CubeSats selected to fly as an auxiliary cargo onboard rockets planned to launch in 2011 and 2012 as part of the ELaNa (Educational Launch of Nanosatellite) program.

Orbit: Near-circular orbit with an altitude of ~330 km and an inclination of 51.6º.

Secondary Payloads: The secondary technology payloads on this flight consist of 26 experiments comprised of free-flying systems and non-separating components (2 experiments). ORS-3 will employ CubeSat wafer adapters, which enable secondary payloads to take advantage of excess lift capacity unavailable to the primary trial. ^{10) 11)}

NASA's LSP (Launch Services Program) ELaNa-4 (Educational Launch of Nanosatellite-4) will launch eight more educational CubeSat missions. The ELaNa-4 CubeSats were originally manifest on the Falcon-9 CRS-2 flight. When NASA received word that the P-PODs on CRS-2 needed to be de-manifested, LSP immediately started looking for other opportunities to launch this complement of CubeSats as soon as possible. ¹²⁾

ORS and CubeStack: ¹³⁾

• ORS (Operationally Responsive Space) partnered with NASA/ARC and AFRL to develop & produce the CubeStack

• Multi CubeSat adapter provides “Low Maintenance” tertiary canisterized ride capability

• ORS-3 Mission: Will fly 2 CubeStacks in August 2013. This represents the largest multi-mission launch using a Minotaur I launch vehicle (26 free flyers, 2 experiments).

The CubeStack adapter structure is a design by LoadPath and Moog CSA Engineering. ¹⁴⁾

Sensor Complement

The PLD (Payload) subsystem consists of a Herley MD2000C-1, a non-coherent transponder module that has a volume and mass of 13.8 cm³ and 425 gram, respectively. It operates using 22–32 VDC, and has an internal power supply that stabilizes transient voltages to the normal operating range. The transponder operates between 5.4–5.9 GHz, and is connected to a QHTF99R-5768 C-band quadrifilar helix antenna from the Antenna Development Corporation (Figure 16). The block diagram of the PLD subsystem is shown in Figure 6.

The PLD subsystem also includes a NovAtel OEMV-2 L1/L2-F GPS unit and an Antcom 1.9G1215A-XSO-2 antenna; these are used for GPS data collection. The GPS unit, which runs on 3.3 VDC and has a mass of 56 g, is integrated on a printed circuit board (PCB) with a dsPIC33F microcontroller.

Ground Segment

Once the Ho‘oponopono nanosatellite is in orbit and pointing nadir within the required accuracy, the calibration process can take place. For the sake of simplicity, the entire process is described in two parts: the mission transponder operations and ephemeris data collection (Ref. 4).

• The mission transponder operations begin with a radar station making a calibration request to the RADCAL coordinator at VAFB (Vandenberg Air Force Base). VAFB then generates an interrogation schedule that is sent to Ho‘oponopono’s ground station for uplinking. Creating interrogation schedules is crucial to ensure the transponder is not activated more than the five interrogations per day allotted by Ho‘oponopono’s power budget. The timing for the interrogation is derived using Two-Line Element set calculations that help the station estimate when and where Ho‘oponopono will pass. Once Ho‘oponopono is within line-of-sight of the radar station, the interrogation process takes place.

• The ephemeris data collection occurs simultaneously and starts with Ho‘oponopono using its zenith-facing GPS antenna to collect GPS data, which is then downlinked to Ho‘oponopono’s ground station and made available to VAFB and NGA (National Geospatial-Intelligence Agency). The GPS orbital data is then processed by the NGA and made available to a select group of users on the Internet, including the radar station requesting calibration.

The radar station can then correlate the ephemeris and transponder-interrogation data and to quantify how accurate their system is at identifying Ho‘oponopono’s position, and implement its calibration algorithms as needed.

References

1) Larry K. Martin, Nicholas G. Fisher, Windell H. Jones, John G. Furumo, James R. Ah Heong Jr., Monica M. L. Umeda, Wayne A. Shiroma, “Ho‘oponopono: A Radar Calibration CubeSat,” Proceedings of the 25th Annual AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 8-11, 2011, paper: SSC11-VI-7

2) Nick Fisher, “A Radar Calibration CubeSat,” Calpoly Summer Workshop, Logan, UT, Aug. 8, 2010, URL:  http://mstl.atl.calpoly.edu/~workshop/archive/2010/Summer/14%20-%20Fisher%20-%20Radar%20Calibration%20CubeSat.pdf

3) “Engineering team wins third place in national nanosatellite competition - Satellite also selected for upcoming NASA launch,” Feb. 25, 2011, URL: http://www.hawaii.edu/news/article.php?aId=4204

4) Larry K. Martin, Nicholas G. Fisher, Windell H. Jones, Monica M. L. Umeda, John G. Furumo, James R. Ah Heong Jr., Toy Lim, Wayne A. Shiroma, “Radar Calibration Using a Student-Built Nanosatellite,” Proceedings of the Advanced Maui Optical and Space Surveillance Technologies Conference, Wailea, Maui, Hawaii, September 13-16, 2011, URL: http://www.amostech.com/TechnicalPapers/2011/Poster/MARTIN.pdf

5) Larry K. Martin, Nicholas G. Fisher, Toy Lim, John G. Furumo, James R. Ah Heong Jr., Kelson A. Lau, Cam V. Chau, Darryl M. McKinley, Andy M. Morishita, Andy H. N. Pham, Wayne A. Shiroma, “Cost-Effective, Rapid Design of a Student-Built Radar Calibration Nanosatellite,” AIAA Reinventing Space Conference, Los Angeles, CA, May 7-10, 2012, paper: RS2012-2012-3001

6) “Orbital Successfully Launches Minotaur I Rocket Supporting ORS-3 Mission for the U.S. Air Force,” Orbital, Nov. 19, 2013, URL: http://www.orbital.com/NewsInfo/release.asp?prid=1876

7) Patrick Blau, “Minotaur I successfully launches STPSat-3 & record load of 28 CubeSats,” Spaceflight 101, Nov. 20, 2013, URL: http://www.spaceflight101.com/minotaur-i-ors-3-launch-updates.html

8) Roz Brown, “Ball Aerospace's STPSat-3 to Fly Solar TIM Instrument for NOAA,” BATC, July 19, 2012, URL: http://www.ballaerospace.com/page.jsp?page=30&id=478

9) Garret Skrobot, “ELaNA - Educational Launch of Nanosatellite,” 8th Annual CubeSat Developers’ Workshop, CalPoly, San Luis Obispo, CA, USA, April 20-22, 2011, URL:  https://web.archive.org/web/20190716170813/http://mstl.atl.calpoly.edu:80/~bklofas/Presentations/DevelopersWorkshop2011/21_Skrobot_ELaNa.pdf

10) Peter Wegner, “ORS Program Status,” Reinventing Space Conference, El Segundo, CA, USA, May 7-10, 2012, URL: https://web.archive.org/web/20150423114038/http://www.responsivespace.com/Papers/RS2012/SPECIAL%20SPEAKERS/Dr.%20Peter%20Wegner/Dr.%20Peter%20Wegner.pdf

11) Joe Maly, “ESPA CubeSat Accommodations and Qualification of 6U Mount (SUM),” 10^th Annual CubeSat Developer’s Workshop, Cal Poly State University, San Luis Obispo, CA, USA, April 24-25, 2013, URL: http://www.cubesat.org/images/stories/workshop_media/DevelopersWorkshop2013/Maly_MoogCSA_ESPA-SUM.pdf

12) Garrett Lee Skrobot, Roland Coelho, “ELaNa – Educational Launch of Nanosatellite Providing Routine RideShare Opportunities,” Proceedings of the 26^th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 13-16, 2012, paper: SSC12-V-5

13) “CubeStack: CubeSat Space Access,” 9th Annual Spring CubeSat Developers’ Workshop, Cal Poly State University, San Luis Obispo, CA, USA, April 18-20, 2012, URL:  http://mstl.atl.calpoly.edu/~workshop/archive/2012/Spring/27-Maly-CubeStack.pdf

14) Joe Maly, “6U Mount for CubeSats on ESPA,” CubeSat 9th Annual Summer Workshop, Logan UT, USA, August 11-12, 2012, URL:  https://web.archive.org/web/20160914101344/http://mstl.atl.calpoly.edu/~bklofas/Presentations/SummerWorkshop2012/Maly_6U_ESPA_Mount.pdf

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(eoportal@symbios.space).