The paper presents the variations of space radiation (primary and secondary galactic cosmic rays (GCR) absorbed dose rate in silicon and flux) measured during the first-ever commercial suborbital flight of the Virgin Galactic (VG) SpaceShipTwo Unity on 29 June 2023. A Portable Dosimeter-Spectrometer Liulin-CNR-VG is used. It is developed in the Space Research and Technology Institute, Bulgarian Academy of Sciences (SRTI-BAS) under a scientific contract with National Research Council of Italy (CNR), Italy. Liulin-CNR-VG size is 63х54 × 23 mm. Its weight is 0.092 kg. During the first part of the SpaceShipTwo flight, up to 14.4 km, the dose rate rises from 0.058 μGy h-1 up to 2.5 μGy h-1. Above the altitude of 30 km, the dose rate falls to 2.2 μGy h-1, while the dose to flux ratio increases to values about 1.0 nGy cm2 particle-1. The latter confirms the outcomes of previous balloon experiments, i.e. the change of the composition of the radiation field of the GCR and secondary radiation source from predominantly light particles as electrons, pions and muons towards heavier particles as protons and neutrons. On the descending part of the flight, one maximum in the flux and dose rate curves is obtained as Regener-Pfotzer maximum (R-PM). The flux calculated by the moving avervage is equal to 1.2 cm-2 s-1 and the dose rate is equal to 2.9 μGy h-1 at an altitude of 13 km. These values are well in line with those expected in conditions of relatively high solar activity, such as during the flight. The dose rates measured by Liulin-CNR-VG are in good agreement with other Liulin data, such as those recorded during balloon flights in 2005 and 2015 and civil aviation flights. The calculated total equivalent dose rate during the VG SpaceShipTwo flight is 7.46 μSv for 1.22 h. This reveals that there is a very small radiation risk for the pilots and astronauts flying at the VG SpaceShipTwo up to 85.1 1 km altitude.

The dosimeter Liulin-MO for measuring the radiation environment on board the ExoMars Trace Gas Orbiter (TGO) is a module in the Fine Resolution Epithermal Neutron Detector (FREND). A number of solar energetic particle (SEP) events were observed in Mars orbit from July 2021 to 2024 during the increasing phase and close to the maximum of the 25th solar cycle activity. The results from the SEPs measurements obtained in 2021-2023 by Liulin-MO have been previously reported. Here we present the LiulinMO results from the observation of the radiation parameters of the SEP events during January- October 2024. The most powerful SEP event registered up to now in TGO orbit started on 20 May 2024. The maximum dose rate during this SEP event has been 2800 f 280 mu Gy h-1 and the maximum particle flux - 383 f 19 cm-2 s-1. The total event lasted for about 64 hours up to 24 May with a long tail of increased dose rates and fluxes. The total dose from SEPs for the 64 hours of the main phase of the SEP event was 24.7 f 2.5 mGy. The total dose from SEPs during this event is equal to the dose from the galactic cosmic rays (GCR) received for about 200 days at this phase of solar cycle 25. The total dose from all SEPs during January - September 2024 is 36.6 mGy (in Si), which is approximately equal to the dose received from GCR for the same period. The observations of SEPs in Mars orbit are compared to the observations during the same periods of proton fluxes measured by the GOES satellite in Earth orbit. The results show that some of the SEPs observed in Mars orbit, excluding the biggest SEP events of 20-24 May and 05-07 September, are also seen in the GOES proton fluxes data. SEP events recorded both in Mars and Earth orbits are related to coronal mass ejections (CMEs) observed by the SOHO and STEREO A coronagraphs. The paper shows that responsible for most of the SEP events registered both in the Liulin-MO data and in the GOES proton fluxes data are halo CMEs. The paper also shows that the sources of the three most powerful SEP events in Mars orbit - those of 20 May, 23 July and 05 September - are halo CMEs from the far side of the Sun. Some of these CMEs are associated with major X class far-side flares. Long-term investigations of the GCRs radiation parameters in Mars orbit show that in August 2024 (the last month of our data with no recorded SEP events) the dose rate was 6.5 f 0.65 mu Gy h-1 and the particle flux - 1.4 f 0.07 cm-2 s-1. These values are about 40 % of the corresponding maximal values measured by Liulin-MO during the solar cycle 24 minimum in March 2020. The above results show the importance of long-term measurements (at least during a full solar cycle) of the radiation conditions in Mars vicinity. Such measurements will make it possible to obtain the data necessary for the planning of future manned and robotic missions, as well as for the selection of the best time interval in the solar cycle for a manned flight to the planet.

The Liulin-SET spectrometer, developed at the Space Research and Technology Institute of the Bulgarian Academy of Sciences, was integrated with the Automated Radiation Measurements for Aerospace Safety (ARMAS) Flight Module Number 9 (FM9). The ARMAS FM9 was developed by Space Environment Technologies (SET) in Pacific Palisades, California, USA. Inclusion of the abbreviation “SET” in the name of the instrument underlined that this spectrometer was developed especially for the Space Environment Technologies (SET) ARMAS FM9 mission.ARMAS FM9 was launched on February 19, 2022 with the Northrop Grumman-Antares rocket from NASA's east coast launch facility in Virginia and operated externally on the Japanese Experimental Module of the International Space Station (ISS) for 216 days, from March to December 2022. During this period, it measured the ionizing dose and flux of three radiation components: (1) Galactic Cosmic Rays (GCR), (2) Inner Radiation Belt (IRB) energetic protons in the South Atlantic Anomaly (SAA) region, (3) Outer Radiation Belt (ORB) energetic electrons in the high-latitude regions of the ISS orbit. This paper presents the analysis of the Liulin-SET data and compares it with data from other four Liulin type instruments that worked on the ISS between 2001 and 2016.

Nnuclear spectrometers and/or dosemeters using photodetectors is proposed and investigated. Visible light pulses with different intensity and duration are used for irradiation of the detector instead of nuclear radiation sources. The calibration procedure is described in detail. Experimental results with a dosemeter for aerospace applications are presented and discussed.

The radiation risk radiometer-dosimeter (R3D)-R2 instrument was situated outside the Russian segment of the International Space Station (ISS) and inside the ESA EXPOSE-R2 facility in the period November 2014 - January 2016. We detected a penetration of the relativistic electrons below L=2.5 in the recovery phase of the magnetic storm after 18 March 2015. In the period March 18-28 2015, the lower boundary of L=1.8 was reached. The relativistic electrons at low L disappeared on March 28, 2015. The magnetic storm on 25th of June 2015 again generated relativistic electrons' fluxes from the Outer Radiation Belt (ORB) at the L values below 2.5. The ORB enhancement on July 4 2015 emphasized them again. In this specific case, the minimal L values reached L=1.6. Almost all disturbances in the Disturbance Storm Time (Dst) index from July 11th, 2015 until January 1st, 2016 generated new portions of relativistic electrons in the L-values below 2.5. They existed for few days and disappeared until the next Dst disturbance.

•Investigated are the radiation conditions in Mars orbit from May 2018 to June 2022.•Observed are 5 solar particle events (SPE) in Mars orbit in July 2021-March 2022.•The dose, dose equivalent and flux during SPE held15–19 February 2022 are biggest.•SPE recorded in Mars orbit are related to solar activity and coronal mass ejections.•Agreement of the flux time profiles measured by different detectors in Mars orbit.

The data from two Bulgarian-German instruments with the basic name "Radiation Risk Radiometer-Dosimeter" (R3D) are discussed. The R3DR instrument worked inside the ESA EXPOSE-R facility (2009-2010), while R3DR2 worked inside the ESA EXPOSE-R2 facility (2014-2016). Both were outside the Russian Zvezda module on the International Space Station (ISS). The data from both instruments were used for calculation of the neutron dose equivalent rate. Similar data, obtained by the Russian "BTNNEUTRON" instrument on the ISS are used to benchmark the R3DR/R2 neutron dose equivalent rate. The analisys reveals that the "BTNNEUTRON" and R3DR/R2 values are comparable both in the equatorial and in the South Atlantic Anomaly (SAA) regions. The R3DR/R2 values are smaller than the "BTNNEUTRON" values in the high latitude regions. The comparison with the Monte Carlo simulations of the secondary galactic cosmic rays (GCR) neutron ambient dose equivalent rates (El-Jaby and Richardson, 2015, 2016) also shows a good coincidence with the R3DR/R2 spectrometer data obtained in the equatorial and high latitude regions.

The dosimeter Liulin-MO for measuring the radiation environment onboard the ExoMars TGO is a module of the Fine Resolution Epithermal Neutron Detector (FREND). Here we present results from measurements of the charged particle fluxes, dose rates and estimation of dose equivalent rates at ExoMars TGO Mars science orbit, provided by Liulin-MO since May 2018. The period of measurements covers the declining and minimum of the solar activity in 24th solar cycle and the inclination phase of the 25th cycle. Particular attention is drawn to the observation of the solar energetic particle (SEP) events in July, September and October 2021, February and March 2022 as well as their effects on the radiation environment on TGO during the corresponding periods. The SEP event on 15-19 February 2022 is the most powerful event observed in our data. Compared are the time profiles of the particle fluxes and count rates measured by Liulin-MO and the neutron detectors of FREND during these events. The data for SEP events on TGO in July 2021-March 2022 contribute to the details for the solar activity at a time when Mars is on the opposite side of the Sun from Earth.

The paper presents the space radiation extreme events observed with Liulin type instruments. The following events, characterized by fast increase of the dose rate were classified as extreme: solar energetic particles (SEP) events, relativistic electron enhancements (REE) and burst type REE in the outer radiation belt (ORB). We compare the dose rates data from 4 SEP events in 1989, 2012, 2015 and 2022, 2 REE events in 2010 and 2015 and 1 burst type REE in 2015. All data were selected to cover periods of 6 hours and 30 minutes that are the average continuation of the extra vehicle activities (EVA) on the ISS. The time intervals were chosen to coincide with the maximum of the observed dose rates during different events. Only the REE1 event data was chosen simultaneously with real EVA-1 of STS-131 astronauts on April 9 2010. The dose rates data in the inner and the outer radiation belt maxima measured by RADOM instrument in 2008 at about 3,000 and at about 20,000 km altitude, respectively, are compared with the extreme events data.

The EXPOSE-R2 experiment was carried out by the European Space Agency on board “Zvezda” module of the ISS. The R3DR2 device was one among the EXPOSE-R2 instruments. The semiconductor detectors were sensitive elements of the R3DR2 device that permit to measure radiation doses behind thin shielding. The results of this experiment are freely available now. We used them to analyse variations in the radiation environment at ISS altitude in the Earth’s outer radiation belt. SINP MSU carried out a similar experiment on board The “Lomonosov” satellite. One of its devices DEPRON instrument includes semiconductor detectors. The detectors were similar in design to those in the R3DR2 instrument. The analysis showed the presence of significant enhancements in dose rate. The dose rate of such enhancements reached the level of 28.8 mGy/h according to R3DR2 data and 106.5 mGy/h according to DEPRON data. However, the total dose rate of single enhancements did not exceed 0.8 mGy according to R3DR2 data and 1.6 mGy according to DEPRON data. Comparison with geomagnetic conditions showed that such enhancements are observed mainly during periods of geomagnetic disturbances. The obtained information may be used to estimate the level of radiation impact in the region of the Earth’s outer radiation belt.

On 29 October 2018 at 13:08 Japanese Standard Time was successfully launched the Greenhouse gas Observing SATellite (GOSAT-2) from the JAXA Tanegashima Space Center. Piggypack with the GOSAT-2 satellite in a circular (623 km), polar synchronous orbit was launched the 22 kilogram mass satellite Ten-Koh (http://kit-okuyama-lab.com/en/ten-koh/), developed in Kyushu Institute of Technology by Prof. K. Okuyama, Chief Scientist of the Spacecraft. Ten-Koh satellite is observing low Earth environment (LEO). The primary purpose is to provide valuable data for future development of satellites or operation. Ten-Koh's primary science instrument is the Charged Particle Detector (CPD) developed at the Prairie View A&M University, and NASA Johnson's Space Center of Houston, TX, USA. Principal Scientist of this payload is Prof. P. Saganti (https://www.pvamu.edu/raise/space-payload/charged-particle-detector-2018/) . Principal Engineer of the CPD project is S. D. Holland (formerly with NASA-JSC and currently with Holland-Space LLC, Houston, TX, USA). IKIT-BAS received a request from Prof. Saganti to develop a Liulin type instrument to be part of the CPD payload. Scientists from IKTI's Solar-Terrestrial Physics Department have developed and handed three units per the request (engineering, flight, and operational models) of the instrument named "Liulin Ten-Koh". These instruments are similar to the RADOM instrument, which worked in 2008-2009 on the Indian moon satellite Chadrayaan-1 [12]. This paper describes the flight model, "Liulin Ten-Koh Saganti" instrument and the standard sources radiation tests, which were performed during the calibrations in the laboratory of IKIT-BAS. As of this writing, Ten-Koh spacecraft is making polar orbit passes as expected at about 623 km altitude and at 98 degree inclination with very healthy telemetry data as received by several ground stations across the world. The first received data from "Liulin Ten-Koh Saganti" instrument of the Ten-Koh spacecraft are presented. The available at this moment galactic cosmic rays (GCR) L-value profiles of the dose rate and the dose to flux ratio (D/F) from 11 December 2018 are compared with the R3DE profile at ISS. In addition, the integral "Liulin Ten-Koh Saganti" instrument LET spectrum from 11 December 2018 is compared with spectra from other instruments, measured in and out of the Earth magnetosphere.

ExoMars is a joint ESA - Rosscosmos program for investigating Mars. Two missions are foreseen within this program: one consisting of the Trace Gas Orbiter (TGO), that carries scientific instruments for the detection of trace gases in the Martian atmosphere and for the location of their source regions, launched on March 14, 2016; and the other, featuring a rover and a surface platform, with a launch date of 2022. In March 2018 TGO was inserted into circular Mars science orbit with a 400 km altitude. The dosimetric telescope Liulin-MO for measuring the radiation environment onboard the ExoMars TGO is a module of the Fine Resolution Epithermal Neutron Detector (FREND). Here we present recent results from measurements of the charged particle fluxes, dose rates and estimation of dose equivalent rates at ExoMars TGO science orbit, provided by Liulin-MO dosimeter. The obtained data from May 2018 to December 2019 show that: 1) Increase of the dose rate, dose equivalent rate and flux is observed during this period, which corresponds to the increase of galactic cosmic rays (GCR) intensity during the declining of the solar activity. Measurements in two perpendicular directions along axes X and Z of TGO show that the average fluxes for the period are 3.08 cm(-2) s(-1) and 3.18 cm(-2) s(-1), the average dose rates are 352 +/- 35 mu Gy day(-1) and 366 +/- 36 mu Gy day(-1), the average dose equivalent rates are 1.6 +/- 0.33 mSv day(-1) and 1.65 +/- 0.34 mSv day(-1); 2) There is slight dependence of the flux distribution on the Martian latitude and longitude; 3) Data from two independent instruments is also evaluated and compared to: good agreement between the GCR count rates time profiles from Liulin-MO, neutron detectors of FREND and High Energy Neutron Detector (HEND) onboard Mars Odyssey orbiter is observed. The comparison between simulations of dose rate carried out with OLTARIS tool using the GCR model of Matthia et al., 2013 and Liulin-MO measurements during the transit to Mars and on the high elliptic orbit show that the measured dose rate behind the shielding of the detectors of Liulin-MO is about 25% higher than the simulated values. The data obtained confirm the worsening of the radiation conditions in the interplanetary space. Our evaluations show that with respect to the values measured during TGO transit to Mars (April-September 2016) in December 2019 the particle flux in the free space has increased at least by 16% and the dose rate - by 23%. The GCR dose rate in free space during the minimum of 24th solar cycle, based on Liulin-MO data is significantly higher than the dose rate measured by CRaTER instrument onboard Lunar Reconnaissance Orbiter during the minimum of 23rd cycle.

The article presents the first attempt to analyze data obtained simultaneously by the Russian BTN and Bulgarian R3DR instruments, flown in 2010 on the “Zvezda” module of the International space station (ISS). Both instruments have well established sensitivity against gamma radiation. This was verified in space, when the Russian spacecraft Soyuz TMA-16, initially docked to the aft port of the “Zvezda” module, was relocated to the zenith-facing port of the “Poisk” module on January 21, 2010. This maneuver brings a gamma ray source in the angle of view of both the BTN and R3DR instruments. The comparison of the data, after the relocation, for the first channels of the spectrometers reveals that they are elevated. This situation continues till March 18, 2010 when Soyuz TMA-16 spacecraft was undocked from the ISS and landed. The final part of the paper, investigate the decrease of the R3DR instrument dose rates in the region of the South Atlantic anomaly (SAA), generated by the additional mass of the Soyuz TMA-16 spacecraft.

The paper presents the solar modulation of the long-term galactic cosmic rays (GCR) flux and dose rates variations, observed during 14 space experiments by 10 Bulgarian build Liulin-type spectrometers (LTS) (Dachev et al., 2015a). They worked in near Earth space and in the interplanetary radiation environment between January 1991 and January 2019. Data were collected by LTS in the low Earth orbit (LEO) in the L range between 4 and 6.2 or outside the magnetosphere. The major advantage of the data sets are that they are obtained by the electronically identical LTS. The Liulin measurements of about monthly averaged flux and dose rate data are compared with the monthly values of the modulation parameter, reconstructed from the ground based cosmic ray data (Usoskin et al., 2017). A good correlation between the two data sets is observed. The most important achievement of the paper is that for the first time a proof of the solar modulation of the long-term variations of the monthly averaged dose rates is obtained. These long-term experimentally obtained dose rate data could be used for modeling of the GCR space radiation risks to humans in the near Earth radiation environment. Parallel to the long-term dose rate varitions, the monthly averaged flux variations are also presented.

Ten-Koh is a 23.5 kg, low-cost satellite developed to conduct space environment effects research in low-Earth orbit (LEO). Ten-Koh was developed primarily by students of the Kyushu Institute of Technology (Kyutech) and launched on 29 October 2018 on-board HII-A rocket F40, as a piggyback payload of JAXA's Greenhouse gas Observing Satellite (GOSAT-2). The satellite carries a double Langmuir probe, CMOS-based particle detectors and a Liulin spectrometer as main payloads. This paper reviews the design of the mission, specifies the exact hardware used, and outlines the implementation and operation phases of the project. This work is intended as a reference that other aspiring satellite developers may use to increase their chances of success. Such a reference is expected to be particularly useful to other university teams, which will likely face the same challenges as the Ten-Koh team at Kyutech. Various on-orbit failures of the satellite are also discussed here in order to help avoid them in future small spacecraft. Applicability of small satellites to conduct space-weather research is also illustrated on the Ten-Koh example, which carried out simultaneous measurements with JAXA's ARASE satellite.

Two Liulin type spectrometers performed measurements of the energetic particles flux outside the International Space Station (ISS) in 3 long-term periods between 2008 and 2016. The linear regression analysis is performed of 1053 averaged per day South-Atlantic anomaly (SAA) proton flux measurements from the daily Dst index. The data reveal that the SAA flux dependence from the Joule heating in the high latitudes and respectively from the neutral atmosphere density, isn't observed only in the time of the magnetic storms. This is a permanent, continues process influencing the SAA fluxes all the time. The data, obtained during the two magnetic storms in 2010 and to powerful storms of March and June 2015, were used to find and classify the following short-term magnetic storm effects: 1) The SAA proton flux maximum and area show strong decrease during the main phase of the magnetic storms. The protons losses can be caused by the collisions with the storm-enhanced neutral oxygen atoms. This hypothesis is proved by a comparison with the prediction by the NRLMSISE-00 model global neutral Oxygen density; 2) Increase of the proton flux, in the presence of solar energetic protons, is observed during the storm sudden commencements (SSC); 3) An enhanced flux of relativistic electrons is recorded in SAA during the recovery phase of the magnetic storms at L-values higher than 1.7. They migrate from the outer radiation belt. Their presence was proved by the analysis of the energy deposition spectra.