PhD - The Open University (2012 to 2014) - JSPS Summer Fellowship

McEntaffer Group History

McEntaffer Group (University of Iowa (2014 to 2016) and Penn State University (2016 to present)

PhD

Development of CCD and EM-CCD technology for high resolution X-ray spectrometry

PhD thesis

J. TUTT, 2012, "DEVELOPMENT OF CCD AND EM-CCD TECHNOLOGY FOR HIGH RESOLUTION X-RAY SPECTROMETRY", PHD THESIS, THE OPEN UNIVERSITY, UK

Abstract:

This thesis discusses the development of Charge-Couple Device (CCD) and Electron Multiplying CCD (EM-CCD) technology for high resolution X-ray spectroscopy.  Of particular interest is the spectral resolution performance of the devices alongside the optimisation of the quantum efficiency through the use of back-illuminated CCDs, thin filter technology and improved passivation techniques.  The early chapters (1 through 5) focus on the background and theory that is required to understand the purpose of the work in this thesis and how semiconductors can be used as the detector of high resolution X-ray spectrometers.  Chapter 6 focuses on the soft X-ray performance of three different types of conventional CCD using the PTB beamline at BESSY II.  The results show that there is degradation in spectral resolution in all three devices below 500 eV due to incomplete charge collection and X-ray peak asymmetry.  The Hamamatsu device is shown to degrade faster than the CCD30-11 variants and this is attributed to the thickness of the active silicon (>50 μm) in the device and also its thicker dead-layer (~75 nm) which is found by evaluating the device’s soft X-ray QE).  The charge loss at the back-surface generation/recombination centres is also investigated and is found to be higher in the Hamamatsu device, again due to its thicker dead-layer.  Chapter 7 is an investigation of the Modified Fano Factor which aims to describe the spectral resolution degradation that is expected when an EM‑CCD is used to directly detect soft X-rays.  The factor is predicted analytically, modelled and then verified experimentally allowing EM-CCD performance over the soft X-ray range to be predicted with high levels of confidence.  Chapter 8 is a detailed look into work completed for the phase 0 study of the off plane X-ray grating spectrometer on the International X-ray Observatory.  The work includes a detailed contamination study, effective area analysis, the pointing knowledge requirement and the use of filters to minimise optical background.

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The Open University (2012 to 2014)

High-speed EM-CCD camera system - Thin filter study

High Speed EM-CCD camera system

Photos from the test at the B16 beamline at the Diamond Light Source can be found here

Many X-ray imaging detectors, from medical diagnosis to the examination of energy levels in atoms, are based on the same technology as found in digital cameras. Most X-rays pass straight through these Charge Coupled Devices (CCDs) and CMOS detectors and it is therefore necessary to use a thicker detector (e.g. CMOS hybrid) or a scintillator. However, current methods produce detector systems with limited performance: CMOS-hybrid technology requires intricate features limiting the minimum pixel size and spatial resolution, whilst the readout speed of CCD-based systems is limited by higher noise levels.

Over recent years an STFC funded concept study was completedon a novel photon-counting detector. The Electron-Multiplying (EM) CCD was designed for low light level imaging such as night-time surveillance or night-vision. The EMCCD differs from the standard CCD through the addition of a "gain register". By multiplying the signal by thousands, the effective read noise of the device can be reduced to the sub-electron level, allowing operation at very high speeds. If a scintillator is coupled to an EM-CCD then this low effective noise allows analysis of single photon interactions (photon counting), providing higher resolution imaging and energy discrimination.

The small area (8mm x 8mm) scintillator-coupled EM-CCD operated at 2fps, limiting potential applications. Further developments are required to transfer this technology and expertise to the marketplace. 

We aim to produce a large area, high speed X-ray detector module, making use of the now commercially available highspeed electronics developed from the STFC funded 'Lucky Imaging' at the Institute of Astronomy, Cambridge. By coupling a fibre-optic taper to a larger area EM-CCD, an increase in area of over 44 times is possible. It is envisaged that a series of modules will then be formed into an array, creating a much larger system. We also aim to test the suitability of the scintillating fibre-optic (SFO). Whilst the SFO has largely been ignored for use with a CCD due to lower light output, it has a highly structured form, minimising the signal spread. With the EM-CCD's ability to apply gain to the signal, it is expected that a high-resolution integrating system may be produced. 

In comparison to previous detectors, the expected performance of the new module will give a higher resolution, faster speed (increasing beamline throughput), higher effective dynamic range through higher maximum flux before saturation and higher detection efficiency, higher signal to noise and operation at higher temperatures. The projected specifications of the module will provide these substantial benefits to users, including allowing higher throughput in the beamline facilities and shutter-less performance, providing the high speed of the low resolution 'pixel detectors' and the high resolution of the low speed CCD systems. 

Through the production of a proof of concept prototype module, not only will this technology be opened up to the marketplace, but the range of applications for the EM-CCD will be dramatically expanded, opening new markets for this device. 

This detector is aimed towards applications at synchrotron facilities such as macromolecular crystallographysurface diffraction or small-angle scattering techniqueshigh energy X-ray diffraction andphase-contrast imaging. Applications in medical imaging may also be envisaged for a larger array of modules.  To transfer this technology and expertise to the marketplace, we propose to build a proof of concept module with the support of e2v technologies, a leading designer, developer and manufacturer of high performance imaging sensors.

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Image of a fly taken at the diamond light source. A dead fly was placed in the x-ray and the transmitted x-rays were converted into optical photons using a scintillator and then focused onto an EM-ccd

Thin filter study

To maximise the performance of an X-ray instrument you need a detector with a high Quantum Efficiency (QE) in an environment with a low light background.  Unfortunately, the environment that X-ray detectors operate in have a large amount of stray-light that will cause an increase in the detector background.

To counter this increase in background, the detector can be coated with a thin optical filter of aluminium coupled with an insulator (typically magnesium fluoride or silicon dioxide).  This study is designed to measure the effect that the thickness of the aluminium and insulator has on the overall detector QE.  A thicker filter will reduce the optical stray-light background detected compared to the thinner one, but it will also cause a drop in QE of the instrument.

By evaluating the effect that different filters have on stay-light and QE, better models can be developed to aid decisions on filter thickness in future X-ray missions.

So far I have been able to test two EM-CCDs (e2v CCD97) using the PTB beamlines at BESSY II to get a baseline performance for detectors with no filters over the 50 eV to 1.9 keV energy range.  Later in the year I hope to have thin filter covered EM-CCDs to compare with these results.

The Reflection Grating Spectrometer (RGS) on XMM-Newton

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JSPS Summer fellowship, Osaka, Japan  (11th June 2013 to 21st August 2013)

The JSPS Summer Program is implemented as a component of the JSPS Postdoctoral Fellowship for Research in Japan. It provides opportunities for young pre- and post-doctoral researchers from North America and Europe to receive an orientation on Japanese culture and research systems and to pursue research under the guidance of host researchers at Japanese universities and research institutes over a period of two months during the summer.

JSPS seeks cooperation from its overseas partners in recruiting candidates for the program. In implementing this program, our overseas partners are the National Science Foundation (USA), British Council (UK), Centre National de la Recherche Scientifique (France), Deutscher Akademischer Austauschdienst (Germany), the Canadian Embassy in Japan (Canada), and the Swedish Foundation for International Cooperation in Research and Higher Education (Sweden).

Please click on a bullet point for more information

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McEntaffer Group History

The McEntaffer group formed at the University of Iowa in 2008 under Randall McEntaffer. In July 2016 the group then moved to The Pennsylvania State University and continued its research.

THE MCENTAFFER GROUP IN MAY 2017 - FROM LEFT TO RIGHT - DANIEL YASTISHOCK, FABIEN GRISE, BEN DONOVAN, JAMES TUTT (IN PICTURE), RANDALL MCENTAFFER, DREW MILES, TYLER STEINER, NINGXIAO ZHANG, JAKE MCCOY, TED SCHULTZ, ROSS TEDESCO, STEVEN

The Water Recovery X-ray Rocket (WRXR)

A NASA press-release about WRXR can be found herephotos related to the mission can be found here, and the YouTube channel for the sub-payload SuGRE-1 can be found here

The WRX-R mission targets the Vela Supernova Remnant (SNR) and measures soft X-rays emanating from this region. The Vela SNR was created when a star, >10 times the mass of the Sun, collapsed and then exploded as a Supernova, the final stage of stellar evolution. Supernova explosions are one of the most energetic events in the Universe, and play a role in recycling material within galaxies. They are responsible for the creation and distribution of elements such as, oxygen, silicon, neon, iron, nickel, and magnesium among others, into the interstellar medium, thereby providing source material for the next generation of stars, planets, and even organic chemistry. The explosions are rarely seen in action, but evidence is left behind as Supernova Remnants. Ejected material from the explosion travels at high speeds and the shockwave sweeps up interstellar material along the way, continuing to heat it to temperatures as high as 10 million Kelvin. Hotter temperatures lead to the emission of higher energy electromagnetic radiation, such as X-rays, from the SNR. WRX-R measures soft X-rays with an energy range of 0.25- 0.8 kilo electron Volts (keV), focusing on emission lines for ions of Oxygen6+, i.e. Oxygen lacking six of its eight electrons, O7+ (seven of eight electrons missing) and Carbon5+ (five of six electrons missing). The data will show how much of each constituent is present, and allow scientists to derive information about the conditions in the Vela SNR such as the temperature, density, chemical composition, and ionization state. Using these characteristics they will also be able to estimate the shock velocity near the SNR limb, the age and type of the SNR, the energy of the supernova, and the mass of the progenitor.

On the night of the 4th April 2018, WRXR was successfully launched from the Reagan Test Site, Roi Namur, Kwajalein Atol, Marshall Islands.

The NASA WRX-R Principal Investigator Professor Randall McEntaffer takes us through X-ray astronomy, why use a sounding rocket and the science of the Water Recovery X-ray Rocket mission
Engineer Ted Schultz of Penn State University introduces us to the NASA Sounding Rocket programme and explains the different stages of a sounding rocket flight. Please subscribe! For mission progress please check out our Twitter feed @SUGRE_1

The Water Recovery X-ray Rocket is a re-flight of the OGRESS payload after a significant upgrade. The hardware on OGRESS worked perfectly, but a large background signal was detected during the flight which swamped the X-rays from Cygnus. The background signal was attributed to the high electric field generated by the GEMs detectors used on OGRESS. This upgraded flight will replace the GEMs detectors with a Hybrid CMOS Detector (HCD).

The GEMs detectors on OGRESS were originally chosen as it was possible to cover a large proportion of the focal plane (100 mm x 100 mm on two different channels) with detector at an affordable price. The HCD detector that will be used on WRXR is smaller than the GEM detectors (35 mm x 35 mm) and only a single channel will be used. This loss in effective area due to losing a channel will be partially recovered through the use of new off-plane gratings. These gratings are larger than the OGRESS gratings (100 mm in the groove direction and 110 mm in width) and will be operated at a shallower graze angle (2.2 degrees vs 4.4 degrees). This makes the gratings more efficient.

The second channel that was used on OGRESS is being replaced with a lobster eye experiment that is being developed by the Czech Technical Institute in Prague and Rigaku. This instrument is made up of two different optical systems. The first is a 1D focusing system where a single lobster eye optic focuses X-rays in 1D onto a TimePix detector. The second optical system contains two lobster eye optics and focuses X-rays in 2D onto a focal plane that is ~1.3 meters away.

THE LOBSTER EYE INSTRUMENT IN FLIGHT ASSEMBLY STATE

Also on the WRXR payload is an instrument being developed by Dynamic Imaging Analytics (DIAL) in the UK. The first part of the instrument is designed to image dust in a micro-G environment (samCAM) and the second is an outreach experiment called SuGRE-1. SuGRE-1 plans to test novel 3D imaging techniques by tracking the trajectory and interaction of objects and particles in a micro-gravity environment (sculptures designed by school and college students).

For WRXR, I am leading the team that is co-aligning the off-plane reflection gratings into a module to replace the OGRESS gratings. A series of mirrors to direct the diffracted X-rays onto the HCD are also being developed and my team will lead that alignment effort. In addition I am the lead mechanical engineer for WRXR and assist the lead system engineer.

Related papers

  • Miles - 2017 - An introduction to the water recover x-ray rocket
  • Stehlikova - 2017 - Hard X-ray Vela supernova observation on rocket experiment WRX-R
  • Daniel - 2017 - X-ray Lobster Eye all-sky monitor for rocket experiment

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CAD OF WRXR SHOWING THE OPTICS (WIRE GRID COLLIMATOR), TELESCOPE VOLUME AND DETECTOR. THE LOBSTER EYE EXPERIMENT THAT IS BEING DEVELOPED IN COLLABORATION WITH RIGAKU AND THE CZECH TECHNICAL UNIVERSITY IN PRAGUE IS ALSO SHOWN.

LEFT - THE WHOLE ROCKET PAYLOAD OF WRXR WITH THE LOCATION OF THE SCIENCE PAYLOAD SHOW. RIGHT - A ZOOMED IN SECTION ON THE SCIENTIFIC PAYLOAD

The Off-plane Grating Rocket Experiment (OGRE)

I work with a group at the University of Iowa, run by professor Randall McEntaffer, that is working on a sub-orbital rocket mission (OGRE). The payload of this mission is designed to test the effectiveness of off-plane gratings in a high resolution soft X-ray spectrometer.  The goal of the mission is to show that such an instrument could improve understanding of shock fronts in supernova remnants and find the WHIM.  My primary responsibility is to oversee the specification, design, fabrication, testing and launch of the X-ray CCD camera intended for the mission.  In addition I assist in the integration and testing of the rocket spectrometer optics. A CAD model of the electronics section has been developed by XCAM and a CAD model of the X-ray optic has been developed by Will Zhang and his team from GSFC.

CAD image of the proposed ogre electronics section. the 4 em-ccd cameras are housed in the triangular chamber so that they can be evacuated and cooled. the right model shows a cutaway of the electronics section so that the inside of the boxes can be seen

CAD model of the x-ray optic for ogre. This optic is being developed by a team out of goddard space flight center being lead by will zhang. the optic uses polished silicon, aligned into parabolic and hyperbolic pairs, to focus incident x-rays. it is an example of a wolter-i optic.

Related Papers

  • Lewis - 2017 - The simulated spectrum of the OGRE X-ray EM-CCD camera system
  • Chan - 2017 - Kinematic alignment and bonding of silicon mirrors for high-resolution astronomical x-ray optics
  • Zhang - 2017 - Monocrystalline silicon and the meta-shell approach to building x-ray astronomical optics
  • Riveros - 2017 - Progress on the fabrication of lightweight single-crystal silicon x-ray mirrors
  • Lewis - 2016 - Development of the x-ray camera for the OGRE sub-orbital rocket
  • Riveros - 2016 - Progress on the fabrication of high resolution and lightweight monocrystalline silicon x-ray mirrors
  • Zhang - 2016 - Lightweight and high-resolution single crystal silicon optics for x-ray astronomy
  • DeRoo - 2013 - Pushing the boundaries of x-ray grating spectroscopy in a suborbital rocket
  • McEntaffer - 2013 - First results from a next-generation off-plane X-ray diffraction grating
  • Allured - 2013 - Analytical alignment tolerances for off-plane reflection grating spectroscopy
  • Bautz - 2012 - Concepts for high-performance soft X-ray grating spectroscopy in a moderate-scale mission
  • McEntaffer - 2011 - Development of off-plane gratings for WHIMex and IXO
  • Cash - 2011 - X-ray optics for WHIMex: the Warm Hot Intergalactic Medium Explorer

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The Off-plane Grating Rocket for Extended Source Spectroscopy (OGRESS)

Photos from the OGRESS sub-orbital rocket can be found here

The OGRESS sounding rocket payload is capable of moderate spectral resolution (E/ΔE ~ 10-40) between 0.3 – 1.2 keV, while providing FOV large enough to fully encompass nearby diffuse sources. OGRESS’s optical system is identical to that of CODEX , The Extended Off-plane Spectrometer (EXOS), and the Cygnus X-ray Emission Spectroscopic Survey (CyXESS). The payload consists of two nearly-identical spectrographs. Light for each spectrograph is collected by passive focusers consisting of a stack of wire grids which sculpt a converging beam. Each focuser feeds into an array of off-plane gratings located ~2 meters from the detectors. The spectrum is collected by Gaseous Electron Multiplier (GEM) detectors. The position of the detectors relative to the spectrum provides the only difference between the spectrographs. This instrument is capable of generating high-resolution spectra of large diffuse sources such as the Cygnus Loop and Vela SNRs. OGRESS will observe the Cygnus Loop SNR. Cygnus is a high-surface brightness annular soft X-ray source. It is a middle aged (5-8 kyr) shell-type SNR with most emission coming from a ring-like area fitting comfortably into OGRESS’s FOV. It is ~540 pc distant in the constellation Cygnus, spanning ~3° x 3°. Our observations of Cygnus will determine its dominant emission mechanism in the soft X-ray bandpass and the equilibrium state and elemental abundances of the plasma. 

On the morning of the 2nd May 2015, OGRESS was successfully launched from White Sands Missile Range, New Mexico, USA.

Related Papers

  • Rogers - 2017 - Gaseous electron multiplier gain characteristics using low-pressure Ar/CO2
  • Rogers - 2015 - First results from the OGRESS sounding rocket payload
  • Rogers - 2013 - The OGRESS sounding rocket payload
  • Zeiger - 2011 - The CODEX sounding rocket payload
  • Oakley - 2011 - A Suborbital Payload for Soft X-ray Spectroscopy of Extended Sources
  • McEntaffer - 2008 - Soft X-Ray Spectroscopy of the Cygnus Loop Supernova Remnant

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Grating Alignment at Penn State University

The grating alignment method developed at the University of Iowa was found to have some flaw. The first, and major concern was that the grating position was shown to be highly dependent on the temperature in the room while the epoxy was curing. If the temperature changed, so would the position of the grating.

 PLOTS SHOWING HOW THE PITCH (LEFT) AND ROLL (RIGHT) OF THE GRATING CHANGED OVER TIME WHEN THERE WAS A SMALL TEMPERATURE CHANGE IN THE CLEANROOM. SMALL CHANGES IN TEMPERATURE CAUSED MEASURABLE CHANGES IN PITCH AND ROLL

PLOTS SHOWING HOW THE PITCH (LEFT) AND ROLL (RIGHT) OF THE GRATING CHANGED OVER TIME WHEN THERE WAS A SMALL TEMPERATURE CHANGE IN THE CLEANROOM. SMALL CHANGES IN TEMPERATURE CAUSED MEASURABLE CHANGES IN PITCH AND ROLL

Better temperature control is imperative if we are to precisely control the alignment of the gratings. To control the temperature, a Praecis temperature control ATCU-5 unit was purchased. This unit is able to control the temperature in the enclosure to 50 times better than the control of the room.

Further upgrades are also planned to the Shack-Hartmann Sensor which will be replaced with an interferometer and to the module motion control which will be completed using a hexpod. These upgrades will not be in place for the WRX-R grating alignment campaign, but will be operational for OGRE

The tolerance on the alignment of the grating for WRX-R are loose enough that the setup used in Iowa can be used. The tolerances are loose as WRX-R is a diffuse spectrometer and so high resolving power will not be possible.

Related papers

  • Donovan - 2018 - X-ray verification of an optically aligned off-plan grating module

CAD showing the new alignment setup being used at penn state university. the new setup will be used to align gratings for WRXR

Grating Alignment, Resolution and Diffraction Efficiency - pre 2017

The major research that is being performed at the University of Iowa involves the development of off-plane X-ray diffraction gratings. These gratings are densely ruled to maximise the dispersion of the X-rays, radially grooved to match the convergence of a focusing optic, blazed to preferentially diffraction the X-rays to one side of the specular reflection position (zero-order) and closely packed to maximise effective area. 

As part of this work, I have developed a setup in a CAD program (Solidworks) that can be used to align the closely packed gratings in pitch, roll, yaw, x, y and z dimensions.  To do this we utilize the unique ability of a hexapod to access all 6 of the degrees of freedom that we require.  The pitch and roll of the grating is measured using a theodolite and Shack-Hartmann sensor, the yaw is measured using the diffraction of an optical laser from an optical grating on the X-ray grating and x, y and z is constrained through kinematic mounts.

This setup is under construction in the lab and first testing of aligned gratings should occur in early 2016.

 CAD OF THE GRATING ALIGNMENT SETUP DEVELOPED AT THE UNIVERSITY OF IOWA

CAD OF THE GRATING ALIGNMENT SETUP DEVELOPED AT THE UNIVERSITY OF IOWA

UPDATE: The setup was constructed and 4 off-plane reflection gratings were co-aligned into a grating module. The alignment of these gratings to one-another were tested at the Stray-light facility at Marshall Space Flight Center in mid-2016 and they were shown to be co-aligned within the errors of the experiment. The gratings were then put through vibration testing and re-measured to ensure they could survive launch. Again, within the errors of the experiment, the gratings were co-aligned. Finally, the module underwent thermal cycling testing and survived. A paper on this work is in the final stages of being written.

 IMAGES SHOWING THE GRATING ALIGNMENT TESTING COMPLETED AT MARSHALL SPACE FLIGHT CENTER. THE LIFT IMAGE SHOWS THE OPTICS USED TO FOCUS THE LIGHT ONTO OUR ALIGNED GRATINGS TOGETHER WITH THE GRATING MODULE. THE FOUR MIDDLE IMAGES SHOW DIFFRACTED ORDERS FROM EACH OF THE FOUR GRATINGS TESTED AT MARSHALL SEPARATELY AND THE RIGHT IMAGES SHOWS THESE LINES SUPERIMPOSED OVER EACH OTHER.

IMAGES SHOWING THE GRATING ALIGNMENT TESTING COMPLETED AT MARSHALL SPACE FLIGHT CENTER. THE LIFT IMAGE SHOWS THE OPTICS USED TO FOCUS THE LIGHT ONTO OUR ALIGNED GRATINGS TOGETHER WITH THE GRATING MODULE. THE FOUR MIDDLE IMAGES SHOW DIFFRACTED ORDERS FROM EACH OF THE FOUR GRATINGS TESTED AT MARSHALL SEPARATELY AND THE RIGHT IMAGES SHOWS THESE LINES SUPERIMPOSED OVER EACH OTHER.

Grating resolution has been tested and shown to be >3000 (E/dE) at the stray-light facility at Marshall Space Flight Center (USA) and at the MPE PANTER facility (Germany).  The PANTER test was the first to test two gratings co-aligned to each other in the converging beam of a Silicon Pore Optic (SPO) provided by cosine (Netherlands). Photos of the test performed at PANTER can be found here

 CAD OF THE ACTIVE GRATING ALIGNMENT MODULE - ACTUAL PHOTOS FROM THE PANTER TEST CAN BE SEEN  HERE

CAD OF THE ACTIVE GRATING ALIGNMENT MODULE - ACTUAL PHOTOS FROM THE PANTER TEST CAN BE SEEN HERE

Grating diffraction efficiency is tested using the PTB EUV reflectometer at BESSY II in Germany.  Their highly tuneable pencil X-ray beam is used to measured the diffraction efficiency of single gratings between 300 eV and 2000 eV in 50 eV steps across all visible diffracted orders.  Photos taken at this facility can be seen here.

Related Papers

  • Donovan - 2018 - X-ray verification of an optically aligned off-plan grating module
  • Tutt - 2016 - Diffraction Efficiency Testing of Sinusoidal and Blazed Off-Plane Reflection Gratings
  • Allured - 2015 - Optical and x-ray alignment approaches for off-plane reflection gratings
  • Peterson - 2015 - Off-plane x-ray reflection grating fabrication
  • Marlowe - 2015 - Performance testing of a novel off-plane reflection grating and silicon pore optic spectrograph at PANTER
  • Miles - 2015 - Diffraction efficiency of radially-profiled off-plane reflection gratings
  • McEntaffer - 2013 - First results from a next-generation off-plane X-ray diffraction grating

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Lobster Eye Optics

As part of a collaboration between our group at the University of Iowa and a Czech institution, we have been able to adapt our soft X-ray beamline to be able to test a Lobster Eye optic system.

Related Papers

  • Dániel - 2017 - X-ray Lobster Eye all-sky monitor for rocket experiment
  • Stehlikova - 2017 - Hard X-ray Vela supernova observation on rocket experiment WRX-R

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Telemetry

As part of the OGRESS payload, the group has had to develop an understanding of telemetry using the IRIG106 chapter 10 telemetry standard.  A primer of the work that was done can be found in this paper.

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