| 1. |
- Alaniz, Monica, et al.
(författare)
-
The SQUID sounding rocket experiment
- 2011
-
Ingår i: Proceedings of the 20th ESA Symposium on European Rocket and Balloon Programmes and Related Research. - : European Space Agency. - 9789290922643 ; , s. 159-166
-
Konferensbidrag (refereegranskat)abstract
- The objective of the SQUID project is to develop and in flight verify a miniature version of a wire boom deployment mechanism to be used for electric field measurements in the ionosphere. In February 2011 a small ejectable payload, built by a team of students from The Royal Institute of Technology (KTH), was launched from Esrange on-board the REXUS-10 sounding rocket. The payload separated from the rocket, deployed and retracted the wire booms, landed with a parachute and was subsequently recovered. Here the design of the experiment and post fight analysis are presented.
|
|
| 2. |
- Alday, Juan, et al.
(författare)
-
New constraints on Ganymede's hydrogen corona : Analysis of Lyman-alpha emissions observed by HST/STIS between 1998 and 2014
- 2017
-
Ingår i: Planetary and Space Science. - : Elsevier. - 0032-0633 .- 1873-5088. ; 148, s. 35-44
-
Tidskriftsartikel (refereegranskat)abstract
- Far-ultraviolet observations of Ganymede's atmospheric emissions were obtained with the Space Telescope Imaging Spectrograph (STIS) onboard of the Hubble Space Telescope (HST) on several occasions between 1998 and 2014. We analyze the Lyman-alpha emission from four HST campaigns in order to constrain the abundance and variation of atomic hydrogen in Ganymede's atmosphere. We apply a forward model that estimates surface reflection and resonant scattering in an escaping corona of the solar Lyman-alpha flux, taking into account the effects of the hydrogen in the interplanetary medium. The atmospheric emissions around Ganymede's disk derived for the observations taken between 1998 and 2011 are consistent with a hydrogen corona in the density range of (5-8) x 10(3) cm(-3) at the surface. The hydrogen density appears to be generally stable in that period. In 2014, Ganymede's corona brightness is approximately 3 times lower during two observations of Ganymede's trailing hemisphere and hardly detectable at all during two observations of the leading hemisphere. We also investigate extinction of Ganymede's coronal emissions in the Earth's upper atmosphere or geocorona. For small Doppler shifts, resonant scattering in the geocorona of the moon corona emissions can effectively reduce the brightness observed by HST. In the case of the 2014 leading hemisphere observations, an estimated extinction of 80% might explain the non-detection of Ganymede's hydrogen corona. Geocoronal extinction might also explain a previously detected hemispheric difference from Callisto's hydrogen corona.
|
|
| 3. |
- Andersson, L, et al.
(författare)
-
Electron signatures and Alfven waves
- 2002
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 107:A9
-
Tidskriftsartikel (refereegranskat)abstract
- [1] We identify two distinct electron populations associated with Alfven waves in the Freja data set using the high time resolution state of the art electron detector. One of the populations, detected together with an Alfven wave, is field-aligned and can be seen as trapped within the wave. The other electron population is detected before the wave and consists of electrons which have left the wave at a point with a velocity higher than the local Alfven speed. In the paper, the electrons leaving wave are modeled for different density profiles and are compared with the observed data. Depending on the density profile, the model can produce the same energy-time and pitch angle-time dispersion that is observed in the Freja data. The conclusion of the paper is that the Alfven wave can explain the observed particle signatures. It is shown that the Alfven wave acceleration can create electron signatures similar to inverted-V structures. The density distribution along a flux tube has an important role in the type of particle signatures that can be detected at low altitudes.
|
|
| 4. |
- Archer, Jenny, et al.
(författare)
-
Dynamics and characteristics of black aurora as observed by high resolution ground-based imagers and radar
- 2011
-
Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 32:11, s. 2973-2985
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution, multi-spectral data from the ground-based low-light auroral imager ASK (Auroral Structure and Kinetics) are used to characterize the fine structure of black aurora. Sixteen events comprising sheared and unsheared black arcs, as well as black patches and rings, constitute the analysed dataset. Simultaneous measurements of emissions caused by high- and low-energy precipitation make it possible to relate the characteristics of different black structures to the energy of the precipitating electrons. The reductions of high-energy particles versus low-energy particles in the black regions compared to the diffuse background are investigated for the different forms of black aurora. Two separate mechanisms have been suggested to cause black aurora. The larger reduction of high-energy precipitation within the fine-scale black structures discussed here favours a magnetospheric mechanism that blocks high-energy electrons from being scattered into the loss cone. European Incoherent SCATter radar (EISCAT) electron density profiles are available for one of the nights, and are compared to the optical measurements.
|
|
| 5. |
- Arriaga, I., et al.
(författare)
-
SMILE - A miniaturized fluxgate magnetometer
- 2007
-
Ingår i: 18TH ESA SYMPOSIUM ON EUROPEAN ROCKET AND BALLOON PROGRAMMES AND RELATED RESEARCH. ; , s. 569-572
-
Konferensbidrag (refereegranskat)abstract
- The SMILE (Small Magnetometer in Low-mass Experiment) instrument is a miniaturized digital fluxgate magnetometer that combines a miniature triaxial sensor with volume compensation with digital data processing implemented in a single FPGA. This report presents first results of numerical simulations of the sensor. We also discuss the digital solutions used in SMILE.
|
|
| 6. |
- Ashrafi, M., et al.
(författare)
-
Modelling of N(2)1P emission rates in aurora using various cross sections for excitation
- 2009
-
Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:6, s. 2545-2553
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of N(2)1P auroral emissions from the (4,1) and (5,2) bands have been made at high temporal and spatial resolution in the region of the magnetic zenith. The instrument used was the auroral imager ASK, situated at Ramfjordmoen, Norway (69.6 N, 19.2 E) on 22 October 2006. Measurements from the European Incoherent Scatter Radar (EISCAT) have been combined with the optical measurements, and incorporated into an ionospheric model to obtain height profiles of electron density and emission rates of the N(2)1P bands. The radar data provide essential verification that the energy flux used in the model is correct. One of the most important inputs to the model is the cross section for excitation to the B-3 Pi(g) electronic state, as well as the cross sections to higher states from which cascading into the B state occurs. The balance equations for production and loss of the populations of all levels in each state are solved in order to find the cascade contributions. Several sets of cross sections have been considered, and selected cross sections have been used to construct "emission" cross sections for the observed bands. The resulting brightnesses are compared with those measured by ASK. The importance of specific contributions from cascading is found, with more than 50% of the total brightness resulting from cascading. The cross sections used are found to produce a range of brightnesses well within the uncertainty of both the modelled and measured values.
|
|
| 7. |
- Balmer, G., et al.
(författare)
-
ISAAC : A REXUS STUDENT EXPERIMENT TO DEMONSTRATE AN EJECTION SYSTEM WITH PREDEFINED DIRECTION
- 2015
-
Ingår i: EUROPEAN ROCKET AND BALLOON. - 9789292212940 ; , s. 235-242
-
Konferensbidrag (refereegranskat)abstract
- ISAAC - Infrared Spectroscopy to Analyse the middle Atmosphere Composition was a student experiment launched from SSC's Esrange Space Centre, Sweden, on 29th May 2014, on board the sounding rocket REXUS 15 in the frame of the REXUS/BEXUS programme. The main focus of the experiment was to implement an ejection system for two large Free Falling Units (FFUs) (240 mm x 80 mm) to be ejected from a spinning rocket into a predefined direction. The system design relied on a spring-based ejection system. Sun and angular rate sensors were used to control and time the ejection. The flight data includes telemetry from the Rocket Mounted Unit (RMU), received and saved during flight, as well as video footage from the GoPro camera mounted inside the RMU and recovered after the flight. The FFUs' direction, speed and spin frequency as well as the rocket spin frequency were determined by analyzing the video footage. The FFU-Rocket-Sun angles were 64.3 degrees and 104.3 degrees, within the required margins of 90 degrees +/- 45 degrees. The FFU speeds were 3.98 m/s and 3.74 m/s, lower than the expected 5 +/- 1 m/s. The FFUs' spin frequencies were 1.38 Hz and 1.60 Hz, approximately half the rocket's spin frequency. The rocket spin rate slightly changed from 3.163 Hz before the ejection to 3.117 Hz after the ejection of the two FFUs. The angular rate, sun sensor data and temperature on the inside of the rocket module skin were also recorded. The experiment design and results of the data analysis are presented in this paper.
|
|
| 8. |
- Belyayev, Serhiy, et al.
(författare)
-
Digital fluxgate magnetometer : design notes
- 2015
-
Ingår i: Measurement science and technology. - : Institute of Physics Publishing (IOPP). - 0957-0233 .- 1361-6501. ; 26:12
-
Tidskriftsartikel (refereegranskat)abstract
- We presented an approach to understanding the performance of a fully digital fluxgate magnetometer. All elements of the design are important for the performance of the instrument, and the presence of the digital feed-back loop introduces certain peculiarities affecting the noise and dynamic performance of the instrument. Ultimately, the quantisation noise of the digital to analogue converter is found to dominate the noise of the current design, although noise shaping alleviates its effect to some extent. An example of magnetometer measurements on board a sounding rocket is presented, and ways to further improve the performance of the instrument are discussed.
|
|
| 9. |
- Belyayev, Serhiy, et al.
(författare)
-
Effect of second harmonic in pulse-width-modulation-based DAC for feedback of digital fluxgate magnetometer
- 2018
-
Ingår i: Measurement science and technology. - : Institute of Physics Publishing. - 0957-0233 .- 1361-6501. ; 29:4
-
Tidskriftsartikel (refereegranskat)abstract
- Digital fluxgate magnetometers employ processing of the measured pickup signal to produce the value of the compensation current. Using pulse-width modulation with filtering for digital to analog conversion is a convenient approach, but it can introduce an intrinsic source of nonlinearity, which we discuss in this design note. A code shift of one least significant bit changes the second harmonic content of the pulse train, which feeds into the pick-up signal chain despite the heavy filtering. This effect produces a code-dependent nonlinearity. This nonlinearity can be overcome by the specific design of the timing of the pulse train signal. The second harmonic is suppressed if the first and third quarters of the excitation period pulse train are repeated in the second and fourth quarters. We demonstrate this principle on a digital magnetometer, achieving a magnetometer noise level corresponding to that of the sensor itself.
|
|
| 10. |
- Bergström, Rasmus, et al.
(författare)
-
SCATTERING OF RADAR WAVES ON AEROSOLS IN PLASMAS
- 2015
-
Ingår i: EUROPEAN ROCKET AND BALLOON. - 9789292212940 ; , s. 87-94
-
Konferensbidrag (refereegranskat)abstract
- To study the physical mechanisms of phenomena such as polar mesospheric summer echoes, the SCRAP (Scattering of Radar waves on Aerosols in Plasmas) experiment aimed to validate theories on density fluctuations in dusty plasmas. The SCRAP team developed two identical free falling units (FFUs) designed to create a cloud of copper particles once they eject from the REXUS17 sounding rocket 124 seconds after launch. By using the EISCAT incoherent scatter radar system to observe the cloud, the SCRAP experiment proposed to relate theoretical predictions to a controlled object. The SCRAP experiment was launched from ESRANGE on March the 17th 2015. The FFUs GPS signal was lost during launch and the units were therefore not found. Moreover, no backscattering from the copper cloud was observed by the radar.
|
|
