Development of detectors and calibration methods for spectral irradiance and radiometric temperature measurements

The research work, described in this thesis, has been carried out at the Metrology Research Institute of Helsinki University of Technology between 2000 and 2005. The research focused on the development of new detectors, calibration methods and their applications in optical radiometry. A new photodetector, which is based on three GaAsP Schottky-barrier photodiodes, has been introduced. The spectral properties of the GaAsP trap detector have been studied in the wavelength range between 200 nm and 600 nm. Spectral reflectance of a single windowless GaAsP photodiode, measured with high-accuracy gonioreflectometer, has been presented. Based on these measurements, the internal quantum efficiencies for both the single photodiode and the trap detector have been calculated. A novel scanning method for characterization of filter radiometers, which uses a wavelength tuneable Ti:Sapphire laser source, has been described. High accuracy calibration of filter radiometers at 900 nm has been conducted. The results have been compared to the spectral irradiance responsivities measured with the more conventional monochromator-based method. Both the laser-based method and the monochromator-based method have been used for characterization of the detectors for radiometric measurements of the thermodynamic temperatures of several blackbodies in irradiance mode. Four filter radiometers with central wavelengths between 600 nm and 900 nm have been used. The measured temperatures include the freezing temperature of silver and copper, which are defined by the International Temperature Scale of 1990.reviewe

Assessment of power characteristics of unmanned tractor for operations on peat fields

Received: June 1st, 2021 ; Accepted: January 3rd, 2022 ; Published: January 11th, 2022 ; Correspondence: [email protected] this article, power characteristics of a state-of-the-art unmanned ground vehicle (UGV) are characterised. It is demonstrated that in terms of power characteristics requirements, purposebuilt computer aided autonomous UGV systems are capable of replacing systems that utilise conventional tractors in peat field operations, with milled peat extraction operations as a case study. The authors demonstrate the viability of the UGV in achieving optimal mobility capabilities in operating on peatland surface. The UGV of interest was assessed for two operations of milled peat extraction: milling and harrowing. For both operations, the power consumption of the UGV and the drawbar pull of the implements (passive miller and harrower) were measured and analysed. The required drawbar pull values of the investigated implements remained in the range of 4–8 kN, which corresponded to the drawbar power of 14–36 kW. It was found that the UGV of interest is capable of carrying out milled peat operations in terms of traction capacity. However, it was found that the power supply capacity to be insufficient, thus requiring an improved solution

Electric solar wind sail applications overview

We analyse the potential of the electric solar wind sail for solar system space missions. Applications studied include fly-by missions to terrestrial planets (Venus, Mars and Phobos, Mercury) and asteroids, missions based on non-Keplerian orbits (orbits that can be maintained only by applying continuous propulsive force), one-way boosting to outer solar system, off-Lagrange point space weather forecasting and low-cost impactor probes for added science value to other missions. We also discuss the generic idea of data clippers (returning large volumes of high resolution scientific data from distant targets packed in memory chips) and possible exploitation of asteroid resources. Possible orbits were estimated by orbit calculations assuming circular and coplanar orbits for planets. Some particular challenge areas requiring further research work and related to some more ambitious mission scenarios are also identified and discussed.Comment: 18 pages, 3 figures, accepted for publication in ESTCube-1 special issue of Proceedings of the Estonian Academy of Science

Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1

This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with -1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.Peer reviewe

Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1

This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with - 1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.</p

Satelliidi alamsüsteemid ja nendevahelised liidesed

BeSt programmi toetusel valminud sisupakett annab ülevaate klassikalise väikesatelliidi alamsüsteemidest kasutades Eesti Tudengisatelliidi programmi käigus konstrueeritud ESTCube-1 näidet

Kokkuvõte

Kokkuvõte (Mart Noorma), Õigekeelsus (Ene Voolaid

Nanojuhtme rakendamine maalähedasel orbiidil

Sisupakett annab ülevaate nanojuhtme (Hoytether) tööpõhimõttest ja selle kasutamisest kosmoserakendustes maalähedasel orbiidil

Suodatinradiometrien karakterisointi aallonpituudeltaan säädettävällä laserilla

Suodatinradiometrien spektrinen irradianssiherkkyys karakterisoidaan perinteisesti monokromaattoreita käyttäen. Monokromaattorin kaistanleveydestä ja suodatin radiometrien paikkavasteen epätasaisuudesta johtuvat ongelmat voidaan välttää käyttämällä ns. xy-menetelmää. Tässä menetelmässä irradianssiherkkyys saadaan liikuttamalla suodatinradiometriä tasavälisesti suhteessa aallonpituudeltaan säädettävän laserin teho stabiloituun säteeseen. Mittaukset toistetaan useilla aallonpituuksilla, jotta saadaan suodatin radiometrin herkkyys koko kaistan päästöalueella. Laserin aallonpituutta monitoroidaan mittauksen aikana, mikä poistaa kokonaan aallonpituuden epävarmuuteen liittyvät ongelmat, joita esiintyy usein monokromaattorimittauksissa. Koherentilla laservalolla suodattimen pintojen välinen interferenssi voi aiheuttaa virheellisiä tuloksia mitatussa herkkyydessä. Kulmaan hiottuja suodattimia ja ilma-lasipintojen anti-heijastuspinnoitteita käytettiin vähentämään interferenssin vaikutusta. Työssä esitetään titaani-safiirilaserilla saadut suodatinradiometrin mittaustulokset aallonpituusalueella 800-900 nm. Epävarmuusanalyysi osoittaa, että käyttäen esitettyä xy-menetelmää suodatinradiometrejä pystytään karakterisoimaan 0.09 % standardiepävarmuudella. Tulokset ovat yhtäpitäviä monokromaattoripohjaisella menetelmällä mitattujen tulosten kanssa

Populaarteaduslik tekst

Arko Oles