BTN-Neutron space experiment onboard International Space Station First stage of the experiment using BTN-M1 instrument

Project Objectives Вверх

BTN-M1 scientific instrument is designed for BTN-Neutron experiment for fast and thermal neutron studies onboard Service Module within Russian Orbital Segment of International Space Station (ISS). Further information on ISS is available at http://www.energia.ru/energia/iss/iss.html

BTN-Neutron space experiment is aimed to study spatial and temporal distribution of neutron fluxes in the near-Earth space, and during solar flares in particular. Expected results will greatly improve our understanding of the physical processes that end up with neutron generation during solar flares. They will also help us to estimate neutrons' contribution to the total radiation dose which the cosmonauts are exposed to during extravehicular activities.

Neutrons in the near-Earth space are born when galactic and solar cosmic rays interact with Earth's upper atmosphere, as well as when cosmic rays and particles from terrestrial radiation belts irradiate the ISS, and in powerful solar flares. Neutron registration in the ISS orbit would help to determine the neutron fluxes' dependence on geographical coordinates and ISS altitude, on the current state of terrestrial magnetosphere and atmosphere, and on solar activity.

To achieve these goals, the instrument should be capable to measure the following physical parameters in orbit around the Earth:

  • neutron fluxes in wide energy range starting from 0.4 eV to fast neutrons with energies up to 10 MeV;
  • gamma-ray radiation in energy range from 60 keV to 10 MeV.

The data obtained during the experiment would allow:

  • to develop a physical model of the Earth's atmospheric neutron albedo with regard to its dependence on measuring point's longitude and latitude, time and illumination conditions, atmospheric parameters;
  • to develop a physical model of neutron background in ISS vicinity with regard to different flight conditions;
  • to develop a physical model describing charged and neutral particles generation during solar flares;
  • to solve supplementary scientific tasks that are:
    • simultaneous registration of solar protons and products of their interactions with terrestrial and martian atmospheres. This can be done with the help of BTN-M1 working synchronously with HEND instrument onboard Mars Odyssey spacecraft in orbit around Mars. Solar flares are detected in the same time near the Earth and Mars, thus improving the reliability of registration and making data more informative (information includes energy spectrum and time profile of the flare, features of the radiation propagation in the interplanetary medium, etc);
    • simultaneous registration of gamma-ray bursts in orbits around the Earth and Mars allows one to apply triangulation method to estimate the direction towards GRB sources, and observe GRB afterglows in other energy ranges together with other space and ground-based observatories;
    • to study radiation hardness of new scintillators, whose samples are placed inside electronics unit of the instrument and then are delivered back to the Earth. These scintillation materials are intended for use in future space experiments, among others, for following stages of BTN-Neutron experiment.

Operation Principle Вверх

BTN-M1 exploits principle of detecting neutrons and gamma-rays born or scattered in Earth's atmosphere and within construction elements of ISS, as well as those coming from the Sun or other space sources.

This instrument is essentially a spectrometer with four independent neutron detectors. Three epithermal neutron detectors (SD, MD, and LD in the Fig. 1) are proportional gas counters with 3He and the fourth high energy neutron detector (SC in the Fig. 1) is made from C14H12 stilbene crystal placed inside active anticoincidence shield made from CsI:Tl3+ crystal.

Design and Mount Вверх

Equipment used for the experiment:

  • BTN-MD detection module (built by IKI) — HEND flight unit № 2 (https://np.cosmos.ru/hend-en.html), modified according to specific requirements for ISS equipment and placed into special BTN-MF mounting box (built by IKI),
  • additionally developed BTN-ME electronic module (built by IKI),
  • set of cables to connect modules inside and outside ISS (built by RSC Energia),
  • special frame to place BTN-MD detecting module on the outer surface of Zvezda Service Module (built by RSC Energia).

Detecting module includes HEND flight unit №2 (Fig. 1) placed into BTN-MF truss, which provides mechanical vibroinsulated mounting of BTN-MD, sockets for electrical connecting with ISS cable system, and supports thermal regime using thermal radiators and vacuum shield thermal insulation (Fig. 2).

Fig. 1. Scheme of the HEND instrument used as BTN-MD detecting module (SD — small 3He detector, MD — medium 3He detector, LD — large 3He detector, SC — scintillation detector)

Fig. 2. BTN-MD module assembled with BTN-MF truss with radiators, covered by temporary insulation

 

Scientific tasks of the experiment required that axis of scintillator of BTN-MD module was normally pointed to zenith. Additionally, there were specific requirements concerning instrument storage inside ISS, its mounting and unmounting by cosmonauts in space suits. So the special assembly equipment was designed by RSC Energia specialists, combining special bracket (fig. 3), intermediate (transition) platform, and three quick-release locks, to which BTN-MD+BTN-MF assembly was mounted.

Fig. 3. External BTN-MD module assembled with the truss (1 — BTN-MD, 2 — truss, 3 — arm, 4 — quick-release latches, 5 — cables, 6 — temporary protective cover)

 

BTN-ME electronics module (Fig. 4) is designed to match HEND electrical interfaces to those of service systems of Service Module within ISS Russian Orbital Segment, including:

  • power supply interface;
  • command and control interface;
  • telemetry and scientific data interface;
  • time signals translation interface.

Fig. 4. BTN-ME module

 

BTN-ME also contained special boards (Fig. 5) with detector's assemblies (PDS) which include crystals that can be possibly used in future scintillators((LaBr3):Ce3+, (LaCl3):Ce3+, (Lu0.5Y0.5)AlO3:Ce3+, (Lu0.7Y0.3)AlO3:Ce3+, (Lu0.7Y0.3)AlO3:Ce3+, (Lu2SiO5):Ce3+, (YAlO3):Ce3+) and passive dosimeters to study radiation resistance of scintillators and their potential use in the next stages of BTN-Neutron space experiment. PDSs, after having been exposed in orbit for no less than 6 months, were delivered to the Earth to study scintillators' degradation under space radiation.

Fig. 5 BTN-ME module internal structure (left — PDS boards with crystals to be tested and dosimeters, right — electronic boards)

 

BTN-M1 equipment was delivered to ISS in October 2006 on board Progress № 358 cargo ship.

It was mounted and turned on in November 2006 – February 2007 by crew members of the 14th long-duration expedition — Russian cosmonaut Mikhail Tyurin and the US astronaut Michael Lopez-Alegria.

BTN-MD module was placed at the station's outer surface and mounted to the 2331 and 2333 handrails of Zvezda Service Module (Russian Orbital Segment of ISS, Fig. 6 and 7).

Fig. 6. Detector module is being mounted outside Zvezda Service Module

Fig. 7. ISS overview and BTN-M1 detector module location on the outer side of Zvezda module

BTN-ME module was placed inside the station (Fig.8).

Fig. 8. BTN-ME module location. BTN-ME module is fastened to the handrail 244 with 4 plastic wire fixed at the construction elements

Starting from February 2007, BTN-M1 aboard ISS has been working normally transmitting scientific and telemetry data.

Main Parameters Вверх

Mass : BTN-MD 6.4 kg
BTN-ME 3.4 kg
Power consumption : BTN-MD 8.7 W
BTN-ME 3.4 W
Dimensions : BTN-MD 245 x 280 x 330 mm
BTN-ME 255 x 265 x 115 mm
Energy range : from 0.4 eV to 15 MeV (neutrons)
from 60 keV to 10 MeV (gamma rays)
Time resolution : 0.25–256 sec
Working temperature range : from −40 to +50 degrees Celsiusо
Telemetry volume : 3 Мb per day
Warranty period : 5 years

Developers and co-executors Вверх

Funding organization ― Open Joint-Stock Company S.P. Korolev Rocket and Space Corporation Energia (RSC Energia).

Primary contractor, space experiment organizer, and instrument designer ― Space Research Institute of the Russian Academy of Sciences (IKI RAS).

Principal Investigator ― Dr. Igor Mitrofanov.

Works on BTN-Neutron theme from 2002 to 2006 with regard to BTN-M1 scientific equipment development (design, building, testing, calibrating, delivery to the customer, complex testing, delivery, and testing at Baikonur) were led on the basis of the contract №828 from March 15, 2002 with RSC Energia.

Works on BTN-Neutron project from 2006 to 2010 (operating, scientific and telemetry data storing and processing) are led on the basis of the contract №1173 from October 15, 2007.

 
S.P. Korolev Rocket and Space Corporation Energia
(Korolev, Moscow distr.)
Funding organization. Hydrolab testing and crew trainings. Instrument testing on complex ISS testbed. Experiment support onboard ISS in operation control, scientific data receiving and telemetry data processing.
Joint Institute for Nuclear Research
(JINR, Dubna, Moscow district)
Participation in BTN physical scheme development, numerical modeling of BTN counting parameters; preparation for and calibrations of the device' units on natural (isotopic) and artificial (generator) neutron sources.
A.A. Blagonravov Institute for Engineering Science of the Russian Academy of Sciences
(IMASH, Moscow)
Development of mathematical model of instrument mechanical structure; participation in the development of testing facilities for BTN instrument in compliance with the Funding organization requirements; development of mechanical test programs for the instrument; support of the instrument testing.
Joint-Stock-Company «Specialized scientific research institute for instrumentation engineering»
(SNIIP, Moscow)
Electronic scheme design development for scintillation tract for fast neutron registration.
N.M. Fedorovsky All-Russian Scientific Research Institute for Mineral Raw Materials
(Moscow)
Scintillation unit development for fast neutrons registration.

First results Вверх

BTN-M1 measurements made from February 2007 up to now were used to map neutron fluxes in ISS vicinity and radiation dose accumulation rate, which helped to estimate radiation environment at the station and to study dependence of upper atmosphere neutron albedo on charged particle flux in the magnetosphere.

As the additional task of the experiment on gamma-ray bursts registration, gamma profiles obtained by the CsI:Tl3+ detector (time resolution 1 sec and 0.25 sec) are analyzed and compared with data obtained by the instruments onboard other spacecraft.

Since most neutrons are generated due to galactic cosmic rays interactions with terrestrial atmosphere (as it is for BTN-M1 onboard ISS) or with Martian surface (for HEND onboard Mars Odyssey), galactic cosmic rays trends, related to solar activity variations in 2007–2008, were estimated, using variations in albedo neutron fluxes at Solis Planum subequatorial region on Mars and equatorial and circumpolar regions of the Earth.

 

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