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CSSWE (Colorado Student Space Weather Experiment)

Spacecraft    Launch   Mission Status    Sensor Complement   References

The CSSWE is 3U CubeSat configuration nanosatellite mission being designed and developed by students at the University of Colorado at Boulder (CU-Boulder) under the direction of faculty and staff. The objective of the science mission is to address fundamental questions pertaining to the relationship between solar flares and energetic particles. These questions include the acceleration and loss mechanisms of outer radiation belt electrons. The goal is to measure differential fluxes of relativistic electrons in the energy range of 0.5-2.9 MeV and protons in 10-40 MeV. This project is a collaborative effort between the Laboratory for Atmospheric and Space Physics (LASP) and the Department of Aerospace Engineering Sciences (AES) at the University of Colorado, which includes the participation of students, faculty, and professional engineers. 1)

In December 2009, the CSSWE project received NSF (National Science Foundation) funding to address fundamental questions pertaining to the relationship between solar flares and energetic particles. 2) 3) 4)

Background: The science goal is the study of the phenomenology and range of processes active on the sun and in the radiation belts. CMEs (Coronal Mass Ejections) are very large structures (billions of tons of particles) containing plasma and magnetic fields that are occasionally expelled from the sun into the heliosphere. This violent solar activity is the cause of major geomagnetic disturbances, reflected by the space weather, during which the trapped radiation belt electrons have their largest variations. There is a strong correlation between CMEs and solar flares, but the correlation does not appear to be a causal one. Rather, solar flares and CMEs appear to be separate phenomena, both resulting from relatively rapid changes in the magnetic structure of the solar atmosphere.

Solar flares are very violent processes in the solar atmosphere that are associated with large energy releases ranging from 1022 J for sub-flares, to more than 1032 J for the largest flares. The strongest support for the onset of the impulsive phase is due to magnetic reconnection of existing or recently emerged magnetic flux loops6. Reconnection accelerates particles, producing proton and electron beams that travel along flaring coronal loops.

Some of the high-energy solar particles, referred to as SEPs (Solar Energetic Particles), escape from the sun to produce solar energetic particle events. The CCCWE mission will measure these SEPs with the REPTile (Relativistic Electron and Proton Telescope integrated little experiment) instrument.

SEP measurements are important for space weather applications because of their direct effects in Earth's ionosphere and on man-made systems in space. SEP and CME particles enhance the ionosphere, primarily at high latitudes. These ionospheric changes lead to a myriad of space weather consequences, such as degradation or even disruption of communications, degradation in the accuracy of the highly relied upon GPS (Global Positioning System) measurements and surges in the power lines on the ground that could lead to widespread blackouts.

Earth's radiation belts are usually divided into the inner belt, centered near 1.5 earth radii (RE) from the center of the Earth when measured in the equatorial plane, and the outer radiation belt that is most intense between 4 and 5 RE (Figure 1). These belts form a torus around the Earth, and many important orbits go through them, including those for GPS satellites (MEO) and spacecraft in GEO and in highly inclined LEO.

The science goals of the CSSWE mission are to study:

• How flare location, magnitude, and frequency relate to the timing, duration, and energy spectrum of SEPs reaching Earth

• How the energy spectrum of radiation belt electrons evolve and how this evolution relates to the acceleration mechanism.

To accomplish these goals CSSWE has a requirement for a minimum of 3 months of science operations based on expected flare and geomagnetic storm frequency. The first month of operations will be utilized for systems stabilization and check out.


Figure 1: Schematic cross section of the trapped radiation belts surrounding Earth (image credit: NASA)

Legend to Figure 1: The inner and outer Van Allen belts are shown in blue and purple. The two yellowish crescents represent trapped energetic heavy nuclei that originated in the local interstellar medium, though their intensity is much lower than inner and outer belts. The white lines represent Earth's magnetic field lines, approximated as a dipole. The orbit of the polar-orbiting SAMPEX (Solar Anomalous Magnetospheric Particle Explorer) satellite of NASA (launch July 3, 1992) is indicated.



CSSWE is a LEO (Low Earth Orbit) nanosatellite mission to measure outer belt electrons and SEP protons to study outer belt processes, the relationship between events and solar flares, and these particles' effects on the lower thermosphere.

The nanosatellite features a 3U CubeSat form factor design with a size of 10 cm x 10 cm x 34 cm and a mass of ≤ 4 kg. The design uses surface-mounted triple junction solar cells of Emcore with 28% efficiency. Eight cells are located on two of the 3U sides, and six cells are located on the remaining two 3U sides, with no cells on the two 1U sides on the ends of the CubeSat.

The CSSWE team opted to use the 3U solid wall structure provided by Pumpkin Inc., San Francisco, CA.


Figure 2: Internal and external views of the CSSWE nanosatellite (image credit: CU-Boulder)


Figure 3: Block diagram of the CSSWE spacecraft (image credit: CU-Boulder)

ADCS (Attitude Determination and Control Subsystem): The objective of ADCS is to align the nanosatellite to within ±15º, of the Earth's local magnetic field within 7 days of launch. To meet these requirements, a simple PMAC (Passive Magnetic Attitude Control) system will be used. The subsystem consists of a permanent bar magnet in combination with hysteresis rods. The bar magnet interacts with the local magnetic field to torque the spacecraft toward the local magnetic field direction. As the spacecraft progresses in its orbit, the local magnetic field induces a changing magnetic moment in the hysteresis rods. The soft magnetic material of these bars will lag behind the field, creating a damping torque on the system.

PMAC has been shown to reach a steady state oscillation of the spacecraft about the changing local magnetic field lines of ±15º or less, which is more than adequate to meet the science pointing requirements of CSSWE. The PMAC system requires no power and very little mass (<50g).


Figure 4: The PMAC system orients the nanosatellite to Earth's magnetic field lines throughout each orbit (image credit: CU-Boulder)

A magnetometer is included for ADCS to determine the relative angle between REPTile's look direction and the local magnetic field. The HMC5843 3-axis magnetometer has been chosen, with a resolution of 7 milli Gauss (mG). The location of the magnetometer, bar magnet, and hysteresis rods within the spacecraft have been set in an effort to minimize the magnetic noise.

C&DH (Command & Data Handling) subsystem: The C&DH subsystem is the intelligence unit of the autonomous nanosatellite. It controls and communicates with all the subsystems on board collecting the science and housekeeping data. The functional requirements of the C&DH subsystem are:

1) Command the REPTile instrument to take science data

2) Receive science data from the REPTile instrument

3) Gather housekeeping data from all on-board subsystems

4) Perform the FDC (Fault Detection and Correction) function

5) Send science and housekeeping data to the COMM subsystem

6) Receive commands from the ground station.

The C&DH subsystem has 3 major components: motherboard, processor, and RTOS (Real-Time Operating System) software. The hardware selected for the C&DH subsystem consists of a two-component system offered by Pumpkin Inc. (CubeSat Kit). The pluggable processor is a new architecture developed by Pumpkin which allows the customer to select a processor from a range of choices which can be directly plugged into the motherboard. 5)

The motherboard provides command and data handling using a pluggable 16 bit MSP430F2618 low-power microcontroller (PPM A3). Given +5 volt input, the flight module provides +5 and +3.3 V, function timers, launch switches, latchup and over current protection, a Secure Digital (SD) memory card socket for mass storage, an on-board low dropout regulator and reset (watchdog) supervisor, and supports a wide range of transceivers.

The Salvo Pro RTOS is a cooperative RTOS designed expressly for very-low-cost embedded systems with severely limited program and data memory. This has been selected after a comprehensive trade study considering the complexity, foot-print etc. There are three major communication protocols being used on-board: full duplex SPI (Serial Peripheral Interface), half duplex I2C and AX.25.


Figure 5: Block diagram of the C&DH subsystem (image credit: CU-Boulder)

EPS (Electrical Power Subsystem): The nanosatellite uses 28 PV triple junction solar cells distributed among its 4 long (3U) sides, with an effective area of 763 cm2. An average power of 6.75 W is provided. The solar cells are linked in 2 serial and 3 parallel (2s3p) and or 2 serial and 4 parallel (2s4p) configurations, where two cells connected in series provide 4.6 V to the power system. A BCR (Battery Charge Regulator) is used for the battery assembly. Two Li-ion batteries have a storage capacity of 14.8 Whr. The battery cells are connected in series to supply between 6 and 8.4 V (nominally 7.4 V) to the power system.

Downstream from the battery assembly are two buck converter circuits, each built around the LT3480 DC/DC converter IC. One of these circuits converts the battery voltage to 3.3 V, and the other converts it to 5 V. These voltages are made available to all other electrical subsystems, with solid-state switches to protect against overcurrent conditions and passive LC low-pass filters to protect against transient electrical behavior originating in the converter circuits. A 350 V bias is also provided to each REPTile detector individually via a COTS DC/DC converter module, the EMCO Q04-5 converter.


Figure 6: Block diagram of the EPS (image credit: CU-Boulder)

COMM (Communications subsystem): A half-duplex communication scheme is used with two deployable steel-tape monopole antennas connected together with a 180º hybrid for RF communications. This dual monopole configuration has been tested, and exhibits a gain pattern very close to that of a dipole. A GMSK (Gaussian Minimum Shift Keying) modulation chip has been selected to be the heart of the communications board, the SX1231.

The COMM microcontroller (µC) interfaces the C&DH subsystem with a GMSK modem and sends all data received by the C&DH to the GMSK modem to be modulated and transmitted to the GN (Ground Network). The nanosatellite uses a MSP430 microcontroller for the COMM and C&DH subsystems, which enables a common programming environment and reduces interface complexity.

The transceiver operates in the UHF band at 433 MHz (amateur band), which allows cooperation with any number of amateur ground stations across the globe. The transmission data rate is 9.6 kbit/ in downlink and uplink. 6) 7)

The ground station antenna is a M2 MCP436CP30 cross polarized 42 element yagi antenna with a gain of 14.15dBdc.


Figure 7: Block diagram of the COMM subsystem (image credit: CU-Boulder)

Thermal control subsystem: Thermal control is accomplished via Kapton tape on all exposed (non-solar cell covered) areas of the CubeSat. The passive attitude control system uses the magnetic torque of a bar magnet against the earth's magnetic field and a set of hysteresis rods to align the satellite to within 15º of the local magnetic field.


Figure 8: Timeline of mission development phases (image credit: CU-Boulder, Ref. 3)


Launch: The CSSWE nanosatellite was launched as a secondary payload on Sept. 13, 2012 within NASA's ELaNa-6 initiative. Launch vehicle: Atlas-5-411 of ULA (United Launch Alliance), launch site VAFB, CA. 8) 9)

The primary payload on this flight, referred to as NROL-36,(National Reconnaissance Organization Launch), were two NRO/MSD (Mission Support Directorate) classified spacecraft, namely NOSS-36A and NOSS-36B. 10) 11)

Orbit of all secondary payloads: Elliptical orbit of 790 km x 490 km, inclination = 65º.

Mission title


CubeSat size

CINEMA (CubeSat for Ions, Neutrals, Electrons, & MAgnetic fields)

UCB (University of California, Berkeley)


CSSWE (Colorado Student Space Weather Experiment)

University of Colorado at Boulder


CP5 (Cal Poly CubeSat 5)

California Polytechnic State University


CXBN (Cosmic X-ray Background Nanosatellite)

MSU (Morehead State University)


Table 1: Summary of secondary payloads manifested on ELaNa-6 (Ref. 11)

Next to the NASA sponsored secondary payloads in Table 1, there are additional secondary payloads sponsored by NRO/MSD as shown in Table 2 (containing all secondary payloads).


Launch Sponsor

CubeSat Name



Mass (kg)


1 & 8




3U, Qty 2






Aerospace Corp., El Segundo, CA

1U, Qty 2


Technology Demo




Aerospace Corp



Technology Demo




USC, Marina Del Ray, CA



Cargo Tracking




LLNL, Livermore, CA



Space Debris Mitigation




Univ of Colo/NSF



Space Weather


NASA/LSP (Launch Services Program)


Morehead State University and Kentucky Space



Space Weather




CalPoly, San Luis Obispo, CA



Debris Mitigation




NSF/UCB Berkeley



Space Environment

Table 2: NROL-36/OUTSat CubeSat manifest with 8 P-PODs 12)

The launch of all CubeSats is being conducted in a new container structure, referred to as NPSCuL (Naval Postgraduate School CubeSat Launcher). This new dispenser platform was designed and developed by students of NPS (Naval Postgraduate School) in Monterey, CA, to integrate/package P-PODs as secondary payloads.

NRO refers to all 11 secondary (or auxiliary) CubeSat payloads on NROL-36 as the OUTSat (Operationally Unique Technologies Satellite) mission using for the first time the NPSCuL platform as a container structure for the 8 P-PODs. 13)


Figure 9: Photos of the integrated OUTSat P-PODs in the NPSCuL platform (left) along with the proud NPS students (left), image credit: NRO, NPS

Early mission timeline: CSSWE will be deployed with a standard P-POD (Poly Picosatellite Orbital Deployer) and will initially be tumbling at an unknown rate and attitude. Sufficient power will be available after two orbits to power up the C&DH subsystem and deploy the stowed communications antennas. Over the first 14 days the passive magnetic attitude system will align the CubeSat with the local magnetic field. During this time the batteries will continue to charge. Once a sufficient state of charge has been achieved the communications beacon will be initiated. This beacon will be initiated no later than 36 hours after launch for early operations and tracking.


Figure 10: Schematic view of the early mission timeline for CSSWE (image credit: CU-Boulder)



Mission status:

• December 13, 2017: A 60-year-old mystery regarding the source of some energetic and potentially damaging particles in Earth's radiation belts is now solved using data from a shoebox-sized satellite built and operated by CU Boulder students. 14)

- The results from the new study indicate energetic electrons in Earth's inner radiation belt—primarily near its inner edge—are created by cosmic rays born from explosions of supernovas, said the study's lead author, Professor Xinlin Li of CU Boulder's LASP (Laboratory for Atmospheric and Space Physics). Earth's radiation belts, known as the Van Allen belts, are layers of energetic particles held in place by Earth's magnetic field.

- The team showed, during a process called "cosmic ray albedo neutron decay" (CRAND), cosmic rays entering Earth's atmosphere collide with neutral atoms, creating a "splash," which produces charged particles, including electrons, that become trapped by Earth's magnetic fields. The findings have implications for understanding and better forecasting the arrival of energetic electrons in near-Earth space, which can damage satellites and threaten the health of space-walking astronauts, said Li.

- "We are reporting the first direct detection of these energetic electrons near the inner edge of Earth's radiation belt," said Li, also a professor in CU Boulder's aerospace engineering sciences department. "We have finally solved a six-decade-long mystery."

- A paper on the subject was published in the Dec. 13 issue of Nature. The study was funded primarily by NSF (National Science Foundation). 15)

- Soon after the discovery of the Van Allen radiation belts in 1958, both American and Russian scientists concluded CRAND was likely the source of high-energy protons trapped in Earth's magnetic field. But over the intervening decades, no one successfully detected the corresponding electrons that should be produced during the neutron decay.

- The CubeSat mission CSSWE (Colorado Student Space Weather Experiment) houses a small, energetic particle telescope to measure the flux of solar energetic protons and Earth's radiation belt electrons. Launched in 2012, CSSWE has involved more than 65 CU Boulder students and was operated for more than two years from a ground station they built on the roof of a LASP building on campus.

- The instrument on CSSWE, REPTile (Relativistic, Electron and Proton Telescope integrated little experiment), is a smaller version of REPT, twin instruments developed by a CU Boulder team led by LASP director and Nature paper co-author Daniel Baker that were launched on NASA's 2012 Van Allen Probes mission.

- "This is really a beautiful result and a big insight derived from a remarkably inexpensive student satellite, illustrating that good things can come in small packages," said Baker. "It's a major discovery that has been there all along, a demonstration that Yogi Berra was correct when he remarked ‘You can observe a lot just by looking.'"

- "These results reveal, for the first time, how energetic charged particles in the near-Earth space environment are created," said Irfan Azeem, a program director in the NSF's Division of Atmospheric and Geospace Sciences. "The findings will significantly improve our understanding of the Earth-space environment," Azeem said. "It's exciting to see NSF-funded CubeSats built by undergraduate and graduate students at the center of a significant scientific discovery."

- Other study co-authors include researcher Hong Zhao of LASP; graduate student Kun Zhang of CU Boulder aerospace engineering sciences; Richard Selesnick of the Air Force Research Laboratory at Kirtland Air Force Base in New Mexico; Quintin Schiller of NASA's Goddard Space Flight Center in Greenbelt, Maryland; and Michael Temerin of the University of California, Berkeley.

• As of Dec. 22, 2014, the capacity of CSSWE's batteries have degraded extensively; as a result CSSWE cannot be powered by them. It is not clear if CSSWE can be powered exclusively by the solar cells. Currently, CSSWE does not have enough power capacity to receive or transmit data. Although the flight mission may be at an end, data analysis and modeling continue on a dataset that consists of 3.5 million points covering ~2 years (Ref. 16).

• In October 2014, CSSWE is continuing to extend the mission well beyond four times the expected lifetime. CSSWE is currently cycling between SCIENCE mode (no beacons) and SAFE mode (beacons), so listening HAM operators have a good chance of hearing beacons. 16)

- LASP's CSSWE is communicating in the 70 cm band using antennas on the roof at 9.6 kbit/s (most common data rate). The spacecraft has collected ~160 MB of data to date.

Recovery of the mission in June 2013: On 7 March 2013, communication with CSSWE was lost due to a latch up event in the radio. With no onboard ability to hard-reset the radio, nothing could be done. Fortunately, a battery draining anomaly occurred in June, causing the entire system to power cycle. This cleared the latch up in the radio and on 18 June 2013 communications were reestablished. The automated ground station did not stop listening for CSSWE during this 3 month period. The health of CSSWE checked out, and is presently collecting science data again. 17)

- Despite the hiatus, the CubeSat was healthy enough to return to science mode (no beacons).


Figure 11: Overview of the CSSWE development and operations (image credit: CU-Boulder)

• The CSSWE nanosatellite was launched on Sept. 13, 2012; it has been operational until March 7, 2013 when the project lost contact with the spacecraft. In late March, the project is still trying to establish the contact again (however, the chance is getting smaller). 18)

The clean measurements from REPTile reveal the detailed structures and dynamic variations of MeV electrons in both outer (L = 3–8) and inner (L = 1–2) radiation belts, as shown in Figure 12. In conjunction with similar measurements (not shown here) from the Van Allen Probe mission at low inclination, the measurements show that (1) outer belt electrons are dynamic with continuous pitch angle scattering, (2) inner belt electrons are more stable, mostly confined to the equatorial region, and (3) lower energy electrons (0.5–1.7 MeV) can penetrate deep into the radiation belt slot region (L = 2–3) and even the inner belt region during geomagnetically active times (there was a geomagnetic storm during 8–9 October, 2012). REPTile also provides clean measurements of energetic protons. 19)

The success of this mission shows that clean measurements of energetic electrons and protons in the near earth environment are achievable with a nanosatellite that is designed, built, tested, calibrated, and operated by students. CSSWE also exemplifies the value of nanosatellite missions in providing, at low cost, important scientific measurements complimentary to larger missions such as the Van Allen Probes.

• The CSSWE project is studying violent activity in the solar atmosphere. Students are monitoring incoming CSSWE data from a ground station at LASP to study how particles released during solar flares affect Earth's radiation belt. 20)

• In January 2013, preliminary data were provided of the electron and proton flux, focusing on the first 20 days of science. 21)

The primary 3-month science mission was completed on January 05, 2013. The project is now in the extended mission phase, focusing more on data analysis and modeling. A number of engineering challenges had to be overcome to achieve such clean measurements under the mass, volume, and power limits of a nanosatellite. The CSSWE is also an ideal class project, involving over 65 graduate and undergraduate students and providing training for the next generation of engineers and scientists over the full life-cycle of a satellite project.


Figure 12: Preliminary data of the electron flux, focusing on the first 20 days of science (image credit: CU-Bolder)

Legend to Figure 12: The image shows the first 20 days observations of the electron fluxes in different energy channels, color-coded in logarithm, and sorted in L-value, which can be viewed as the equatorial radial distance in units of Earth radii for the same magnetic field line if Earth's magnetic field can be approximated as a dipole (bottom).


Figure 13: Preliminary data of the proton flux, focusing on the first 20 days of science (image credit: CU-Bolder)

• On December 13, 2012, the CSSWE nanosatellite was 3 months on orbit. The project acquired already 68 days of science data. Most of the data coincided with periods when the RBSP (Radiation Belt Storm Probes), now renamed to the Van Allen Probes, were also taking science measurements. Students working on CSSWE, are judiciously processing REPTile data, looking for conjunctions with the Van Allen Probes that could provide clues on the dynamics of the radiation belts. 22)

- The first science results of CSSWE were presented by Xinlin Li, the PI of the CSSWE Project, at the annual AGU (American Geophysical Union) conference in San Francisco, CA. 23)


Figure 14: Illustration of RBSP mission HEO and CSSWE LEO orbits (image credit: CU-Boulder)

• October 26, 2012: The REPTile instrument of CSSWE has been taking data for ~three weeks. The project is getting a great picture of the dynamics of Earth's radiation environment. 24)

• October 4, 2012: For the first three weeks of spacecraft commissioning, the project team has been monitoring system health and watching the spacecraft align with Earth's magnetic field. All housekeeping data looks nominal. On Oct. 4, the spacecraft was into Science Mode which started the commissioning phase for the science instrument. In science mode, CSSWE stopped beaconing to prevent contamination of the instrument measurements. 25)

• Three hours after launch, the CSSWE nanosatellite was deployed from its P-POD. Two hours later, the fishing line keeping the antenna coiled, was burned through, the antenna deployed, and CSSWE started beaconing. Amateur radio operators heard the beacon over Europe, and other places around the world on Sept. 13, 2012. Then, on Sept. 14, the nanosatellite flew over the LASP ground station and the project team was able to hear the beacons for the first time. 26)



Sensor complement: (REPTile)

REPTile (Relativistic Electron and Proton Telescope integrated little experiment)

The REPTile instrument provides the following functions:

- It measures the outer belt electrons, both trapped and precipitating to study how the low rate and energy spectrum of the Earth's outer radiation belt electrons evolves.

- It monitors the SEP protons associated with solar flares to study how flare location, magnitude, and frequency relate to the timing, duration, and energy spectrum of SEP protons that reach Earth.

- It measures electrons in 3 differential and 1 integral energy channel. Protons are measured in 4 differential channels.

REPTile is a small (6.05 cm in length and 6 cm in diameter), low-mass, and low-power article detector capable of measuring relativistic outer radiation belt electrons in the energy range of 0.5 to > 3 MeV and solar energetic protons from 10-40 MeV.

The instrument is a scaled down version of the instrument, which is being built at LAST (Laboratory for Atmospheric and Space Physics) for NASA's RBSP (Radiation Belts Storm Probes) mission in the LWS (Living with a Star) program. 27) 28) 29)


Figure 15: Cutaway view of the REPTile instrument (image credit: CU-Boulder)

The REPTile instrument design is based on GEANT4 (Geometry and Tracking toolkit 4) simulations, which statistically determine the interaction of relativistic particles and matter. The REPTile instrument has a 52º FOV (Field of View) which benefits from alignment orthogonal to the Earth's local magnetic field, about which charged particles spiral.

GEANT4 is used to simulate particle behavior in instrument materials:

- Used to obtain a detector efficiency

- Used to determine energy thresholds for particle determination

- When combined with geometric factors and expected particle fluxes (e.g. AE8-max or empirical flux data), efficiencies are used to determine signal and noise count rates.


Particle detection sequence of the REPTile instrument electronics:

1) Particle produces signal in detector

2) Detector signal amplified by CSA (Charge Sensitive Amplifier)

3) Signal further amplified by NIA (Non-Inverting Amplifier)

4) Signal is compared to references to determine if electron or proton

5) CPLD (Complex Programmable Logic Device) determines the energy bin

6) Store bin counts at given temporal resolution in PIC (Peripheral Interface Controller).

The REPTile instrument is a loaded-disc collimated telescope designed to measure energetic electrons and protons with a signal to noise ratio of two or greater. The instrument consists of a stack of four solid-state doped silicon detectors manufactured by Micron Semiconductor. The front detector has a diameter of 20 mm, while the following three are 40 mm across. Higher energy particles penetrate deeper into the detector stack and, as they do, they generate electron-hole pairs in the doped silicon. A bias voltage is applied across each detector to accelerate the loosened electrons to an anode, where they are collected and measured by instrument electronics. Using coincidence logic, the electronics determine which detectors the particle impacted, and thus the energy range of the particle.


Figure 16: Flight instrument during integration; the collimator is facing down in the image, and the back plate not yet attached, so the fourth detector in the stack is visible (image credit: CU-Boulder)

Figures 15 and 16 illustrate the instrument geometry and various components. The detector stack is housed in a tungsten (atomic number Z=74) chamber, which is encased in an aluminum (Z=13) outer shield. The materials were chosen based on a combination of their ability to shield energetic particles and minimize secondary electron generation within the housing. Tantalum (Z=73) baffles within the collimator prevent electrons from scattering into the detector stack from outside the instrument's 52º FOV and give the instrument a geometric factor of 0.52 sr cm2. Tantalum is used because it strikes a balance between stopping power and relatively low secondary particle generation.

The instrument and its response to energetic particles have been modeled using GEANT4, a software tool developed at CERN (European Organization for Nuclear Research) to simulate the passage of particles through matter. The current instrument shielding has been shown in GEANT4 to stop all electrons with energies < 10 MeV and protons up to 85 MeV from penetrating through the outer casing and reaching the detectors from directions other than the collimator aperture. The 0.5 mm thick beryllium foil at the front of the detector stack acts as a high-pass filter, stopping all electrons < 400 keV and protons < 8 MeV. This determines the cutoff energy on the lowest energy channel, and mitigates saturation of the detectors from the high count rates of lower energy particles.


Figure 17: REPTile electronics block diagram (image credit: CU-Boulder)

The instrument will measure electrons in four energy bins: 0.5-1.5, 1.5-2.2, 2.2-2.9, and >2.9 MeV. Protons will be measured and binned into four differential energy channels of 8.5-18.5, 18.5-25, 25-30.5, and 30.5-40 MeV. The total instrument mass is 1.25 kg, with a cylindrical envelope of 4.6 m (diameter) x 6.0 cm (length).


Figure 18: Electrical block diagram of the REPTile instrument and the related CSSWE subsystems (image credit: CU-Boulder)


1) Scott Palo, Xinlin Li, David Gerhardt, Drew Turner, Rick Kohnert, Vaughn Hoxie, Susan Batiste, "Conducting Science with a CubeSat: The Colorado Student Space Weather Experiment," Proceedings of the 24th Annual AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 9-12, 2010, SSC10-XII-8, URL:

2) "CU Students to Build Tiny Spacecraft to Observe 'Space Weather' Environment," December 29, 2009, URL:

3) "CSSWE - Colorado Student Space Weather Experiment," URL:

4) CSSWE homepage, URL:

5) Muralikrishna Nallamothu, David Gerhardt, Drew Turner, "The Colorado Student Space Weather Experiment (CSSWE) - Command & Data Handling," 2010 Summer CubeSat Developer's Workshop, Logan,Utah, August 8, 2010, URL:

6) Xinlin Li, Scott Palo, Shri Kanekal, Rick Kohnert, Gail Tate, Vaughn Hoxie, David Gerhardt, Lauren Blum, Quintin Schiller, "The Colorado Student Space Weather Experiment (CSSWE) - CSSWE COM System," 9th Annual Spring CubeSat Developer's Workshop, Cal Poly State University, San Luis Obispo, CA, USA, April 18-20, 2012, URL:

7) Xinlin Li, Scott Palo, Rick Kohnert, David Gerhardt, Lauren Blum, Quintin Schiller, Drew Turner, Weichao Tu, Nathan Sheiko, Christopher S. Cooper, "Colorado Student Space Weather Experiment: Differential flux measurements of energetic particles in a highly inclined low Earth orbit," Dynamics of the Earth's Radiation Belts and Inner Magnetosphere, Geophysical Monograph Series, Vol. 199, edited by D. Summers et al., pp. 385-404, 2012, AGU, Washington, D. C., doi:10.1029/2012GM001313.

8) "2012 in Spaceflight," Wikipedia, URL:

9) "Atlas V launches on classified Flight to orbit NROL-36 Payload," Spaceflight 101, Sept. 14, 2012, URL:

10) Travis Willcox, "Office of Space Launch Atlas V Aft Bulkhead Carrier& Operationally Unique Technologies Satellite," 8th Annual CubeSat Developers' Workshop, CalPoly, San Luis Obispo, CA, USA, April 20-22, 2011, URL:

11) Garret Skrobot, "ELaNA - Educational Launch of Nanosatellite," 8th Annual CubeSat Developers' Workshop, CalPoly, San Luis Obispo, CA, USA, April 20-22, 2011, URL:

12) Guy Mathewson, "2012 CubeSat Workshop, OSL's Vision & Mission," 9th Annual Spring CubeSat Developer's Workshop, Cal Poly State University, San Luis Obispo, CA, USA, April 18-20, 2012, URL:

13) Travis Willcox, "Office of Space Launch Atlas V Aft Bulkhead Carrier & Operationally Unique Technologies Satellite," 9th Annual Spring CubeSat Developer's Workshop, Cal Poly State University, San Luis Obispo, CA, USA, April 18-20, 2012, URL:

14) Jim Scott, "How a student satellite solved a major space mystery," University of Colorado Boulder, 13 Dec 2017, URL:

15) Xinlin Li, Richard Selesnick, Quintin Schiller, Kun Zhang, Hong Zhao, Daniel N. Baker, Michael A. Temerin, "Measurement of electrons from albedo neutron decay and neutron density in near-Earth space," Nature Letter, Published online:13 December 2017, doi:10.1038/nature24642, URL of abstract:


17) Information provided by James Mason, PhD candidate at the University of Colorado/LASP, Boulder, CO.

18) Information provided by Xinlin Li, PI (Principal Investigator) of the CSSWE project at LASP (Laboratory for Atmospheric and Space Physics) of CU-Boulder.

19) Xinlin Li, Scott Palo, Rick Kohnert, Lauren Blum, David Gerhardt, Quintin Schiller, Sam Califf, "Small Mission Accomplished by Students—Big Impact on Space Weather Research," Space Weather, Vol. 11, No 1-2, doi:10.1002/swe.20025, 2013, URL:

20) "Student-built satellite studies solar storms," LASP Space Newsletter, Issue 2, Feb. 2013, URL:


22) "First Results Debuted at AGU," CU-Boulder, Dec. 13, 2012, URL:

23) Xinlin Li, S. E. Palo, R. Kohnert, D. Gerhardt, L. W. Blum, Q. Schiller, D. L. Turner, W. Tu, "First Results from Colorado Student Space Weather Experiment (CSSWE): Differential Flux Measurements of Energetic Particles in a Highly Inclined Low Earth Orbit," AGU Fall Meeting, San Francisco, CA, December 3-7, 2012

24) "3 weeks of science data," CU-Boulder, October 26, 2012, URL:

25) "On Orbit: Week Three – Entering Science Mode," CU-Boulder, Oct. 4, 2012, URL:

26) "First Beacons Received," CU-Boulder, Sept. 14, 2012, URL:

27) Quintin G. Schiller, Abhishek Mahendrakumar, Xinlin Li, "REPTile: A Miniaturized Detector for a CubeSat Mission to Measure Relativistic Particles in Near-Earth Space," Proceedings of the 24th Annual AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 9-12, 2010, paper: SSC10-VIII-1, URL:

28) S. E. Palo, X. Li, D. L. Turner, D. Gerhardt, R. Myers, T. Redick, J. Tao, "REPTile: A relativistic electron and proton detector small enough to meet CubeSat requirements," VKI (Von Karman Institute for Fluid Dynamics) QB50 Workshop, Brussels, Belgium, Nov. 17-18, 2009

29) Lauren W. Blum, Quintin G. Schiller, Xinlin Li, "Characterization and Testing of an Energetic Particle Telescope for a CubeSat Platform," Proceedings of the 26th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 13-16, 2012, paper: SSC12-VIII-4, URL:

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 (

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