Solar Sails for Planetary Defense and High-Energy Missions

20 years after the successful ground deployment test of a (20 m)² solar sail at DLR Cologne, and in the light of the upcoming U.S. NEAscout mission, we provide an overview of the progress made since in our mission and hardware design studies as well as the hardware built in the course of our solar sail technology development. We outline the most likely and most efficient routes to develop solar sails for useful missions in science and applications, based on our developed ‘now-term’ and near-term hardware as well as the many practical and managerial lessons learned from the DLR-ESTEC GOSSAMER Roadmap. Mission types directly applicable to planetary defense include single and Multiple NEA Rendezvous ((M)NR) for precursor, monitoring and follow-up scenarios as well as sail-propelled head-on retrograde kinetic impactors (RKI) for mitigation. Other mission types such as the Displaced L1 (DL1) space weather advance warning and monitoring or Solar Polar Orbiter (SPO) types demonstrate the capability of near-term solar sails to achieve asteroid rendezvous in any kind of orbit, from Earth-coorbital to extremely inclined and even retrograde orbits. Some of these mission types such as SPO, (M)NR and RKI include separable payloads. For one-way access to the asteroid surface, nanolanders like MASCOT are an ideal match for solar sails in micro-spacecraft format, i.e. in launch configurations compatible with ESPA and ASAP secondary payload platforms. Larger landers similar to the JAXA-DLR study of a Jupiter Trojan asteroid lander for the OKEANOS mission can shuttle from the sail to the asteroids visited and enable multiple NEA sample-return missions. The high impact velocities and re-try capability achieved by the RKI mission type on a final orbit identical to the target asteroid‘s but retrograde to its motion enables small spacecraft size impactors to carry sufficient kinetic energy for deflection

Artificial neural networks for multiple NEA rendezvous missions with continuous thrust

The interest for near-Earth asteroids for scientific studies and, in particular, for potentially hazardous asteroids requires the space community to perform multiple-asteroid missions with close-up observations. To this end, multiple near-Earth asteroid rendezvous missions can help reduce the cost of the mission. Given the enormous number of asteroids, this work proposes a method based on artificial neural networks (ANNs) to quickly estimate the transfer time and cost between asteroids using low-thrust propulsion. The neural network output is used in a sequence search algorithm based on a tree-search method to identify feasible sequences of asteroids to rendezvous. The rendezvous sequences are optimized by solving an optimal control problem for each leg to verify the feasibility of the transfer. The effectiveness of the presented methodology is assessed through sequences of asteroids of interest optimized using two low-thrust propulsion systems, namely solar electric propulsion and solar sailing. The results show that ANNs are able to estimate the duration and cost of low-thrust transfers with high accuracy in a modest computational time

Artificial Neural Network for Preliminary Multiple NEA Rendezvous Mission Using Low Thrust

No abstract available

Artificial neural networks for multi-target low-thrust missions

Multi-target missions are an attractive solution to visit multiple bodies in a single mission, increasing the scientific return and reducing the cost, compared to multiple missions to individual targets. Designing multi-target missions represents a challenging task since it requires multiple options to be estimated, given the large number of objects which can be considered as potential targets. Low-thrust propulsion systems are preferred to rendezvous multiple targets in a mission as they allow to utilise less propellant mass than high-thrust systems to perform the same trajectory. However, low-thrust trajectories are computationally expensive to compute. This PhD thesis proposes to use artificial neural networks (ANN), as a fast and accurate estimation method for optimal low-thrust transfers. An artificial neural network and a sequence search (SS) algorithm can be designed to find solutions to three kinds of multi-target global optimisation problems: (i) multiple active debris removal missions (MADR), (ii) multiple near-Earth asteroid rendezvous (MNR) missions, with the option of returning a sample to Earth, and (iii) multi-objective optimisation of low-thrust propulsion systems for multi-target missions. MADR missions allows for the disposal of inactive satellites and larger objects, preventing the build-up of space junk and allowing to replace ageing agents in a constellation. Similarly, MNR missions allow to reduce the cost of each NEA observation and increase the possibility of visiting multiple asteroids of interest in a single mission. The trained ANN is employed within a SS algorithm, based on a tree-search method and breadth-first criterion, to identify multiple rendezvous sequences and select those with lowest time of flight and/or required propellant mass. To compute the full trajectory and control history, the sequences are subsequently recalculated by using an optimal control solver based on a pseudospectral method. Also, to optimise the propulsion system for a given mission, a multi-objective optimisation using a genetic algorithm is performed, where ANNs are employed to quickly estimate the cost and duration of multi-target transfers. The results show that neural networks can estimate the duration and cost of low-thrust transfers with high accuracy, for all the three applications. Employing machine learning within a sequence search algorithm to preliminary design multitarget missions allows to significantly reduce the computational time required with respect to other most commonly used methods in the literature, while maintaining a high accuracy. Given the combinatorial nature of the problem, the benefits in terms of computational time introduced by the ANN increase exponentially with a linear increase of the number of bodies in the database

Nanosatelliide kasutamine demonstratsioon- ja teadusmissioonidel

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKosmost on vaadeldud ja uuritud aastatuhandeid, kuid kosmosemissioonid lubasid seda esimest korda kohapeale uurima minna alles 64 aastat tagasi. Satelliidid võimaldavad teha toiminguid, mis maapealsete uuringutega on võimatud, näiteks maanduda teistele taevakehadele, tuua Maale neilt võetud proove vaadelda lähedalt komeete, ja asteroide ning saada paremaid vaatlusandmeid galaktikate, päikesesüsteemide, eksoplaneetide ja muude objektide kohta.. Ajalooliselt korraldasid kosmosemissioone suured riiklikud kosmoseagentuurid, kuid viimase 20 aasta jooksul on valdkond avanenud ka väikeettevõtetele, ülikoolidele ja pea kõigile teistele, kes on satelliidi kosmosesse saatmisest huvitatud. See on saanud võimalikuks tänu kuupsatelliitide standardiseerimisele. Tavaliselt peame kuupsatelliitide all silmas 1–10 kg nanosatelliite. Selle väitekirja autor on aidanud kaasa planeedimissioonide ja -instrumentide miniaturiseerimisele, töötades välja missioone ja missioonikontseptsioone ning arendades selliseid koormused ja simulatsioonivahendeid, mis aitaksid kaasa pikaajalisele eesmärgile uurida kosmost nanosatelliitidega. Lõputöö esimene osa keskendub uuenduslikule kosmosereiside tehnoloogiale: Coulomb Drag Propulsionile. Seda saab kasutada, et madalalt Maa orbiidilt kosmoseprügi eemaldada (plasmapidur) või kosmoses liikuda, kandmata Maalt kaasa võetud raketikütust (elektriline päiksepuri). Kõnealune tõukejõutehnoloogia on paigaldatud satelliitidele ESTCube-2 ja FORESAIL-1, mis peagi kosmosesse lennutatakse. Samuti analüüsib doktoritöö ideed külastada elektrilise päiksepurje juhitava kuupsatelliidilaevastikuga sadu asteroide. Lõputöö teises osas antakse ülevaade jätkuvast protsessist eesmärgiga arendada kaamera Euroopa Kosmoseagentuuri (ESA) ja Jaapani Kosmoseuuringute Agentuuri (JAXA) ellu viidavale Komeedipüüduri (Comet Interceptor) missioonile. Missiooni sondid viib 2029. aastal kosmosesse rakett Ariane 6. Kaamera on varustatud periskoobiga, et kaitsta seda ohtliku keskkonna eest, mistõttu kannab see nime Optical Periscopic Imager for Comets või OPIC. Nimi viitab ühtlasi Eesti astronoomile Ernst Öpikule, kes pakkus esimesena välja, et Päikesesüsteemi ümber asub kauge komeedipilv, mida tänapäeval tuntakse Öpiku–Oorti pilvena. OPIC-u väljatöötamist toetab spetsiaalselt selleks arendatud simulatsioonitööriist SISPO, mida kirjeldatakse doktoritöö viimases osas.Humans have been observing and exploring the cosmos for millennia, yet space missions enabled in-situ examination only during the last 64 years. Artificial satellites enable opportunities unfeasible for ground-based studies, such as landing on other planetary bodies, sample return, close observations of comets and asteroids, and improved observations of galaxies, solar systems, exoplanets, etc. Historically, space missions were operated by large space agencies, but in the last twenty years, the field expanded to small enterprises, universities and practically anyone interested in launching a satellite. This was partially enabled by the standardisation of cubesats, typically 1–10 kg nanosatellites. The author of this dissertation has contributed to the miniaturisation of planetary missions and instruments by developing missions, mission concepts, payloads and simulation tools that commit to the long-term aims of cosmic exploration with nanospacecraft. The first part of the thesis focuses on innovative technology for space travel – Coulomb Drag Propulsion. It can be utilised to remove space debris from Low Earth Orbit (named plasma brake) or travel in space without carrying the propellant from the Earth (named E-sail). This propulsion is accommodated on the ESTCube-2 and FORESAIL-1 satellites, to be launched soon. The dissertation also analyses the concept of visiting hundreds of asteroids with a fleet of cubesats driven by E-sail. The second part of the thesis presents an ongoing camera development for the ESA-JAXA Comet Interceptor mission to be launched in 2029 by the Ariane 6 rocket. The camera is equipped with a periscope to protect it from a hazardous environment. It is therefore named Optical Periscopic Imager for Comets or OPIC shortly, also referring to the Estonian astronomer Ernst Öpik, who was the first to propose the existence of a distant comet cloud around the Solar System, known today as the Öpik–Oort cloud. The development of the OPIC instrument is supported by a custom-made open-source simulation tool called SISPO, described in the last part.  https://www.ester.ee/record=b547253

Target evaluation and low-thrust trajectory planning for near-Earth asteroid mining

Near-Earth Asteroids (NEAs) are abundant with minerals that would be undoubtedly beneficial for future space exploration, as the utilization of these in-space resources could enable otherwise unaffordable missions. This thesis aims to address several remaining issues in asteroid mining mission planning, including target selection and ranking, multi-return low thrust trajectory design, NEA mining season determination, asteroid mining campaign designs, and other considerations. This study starts with a comprehensive asteroid resource investigation and an impulsive roundtrip accessibility analysis for the known 29,266 NEAs and 46% of them are found accessible. By combining the two studies, a NEA resource map is created, providing key knowledge of resource locations, types, reserves, and minimum delta-V requirements to retrieve the resources. Mining missions are then preliminarily constructed using impulsive trajectories for 13,481 NEAs, and a series of Figures of Merit (FoMs) are proposed. In total, over 900 accessible and known targets for mining water, Platinum Group Metals (PGMs) and silicates are ranked. Low-thrust mining missions are then studied. New Deep Neural Network (DNN) based models are constructed as the surrogate of the conventional optimization process. The new method reduces by 99.94% the low-thrust trajectory design time. Typical Solar Electric Propulsion (SEP) spacecraft configurations are used to design trajectories for supply delivery and resource transportation. The transportation capabilities of different spacecraft configurations are quantified. An asteroid mining campaign design framework is proposed, which integrates all the developed models, algorithms, and asteroid data. An example mining campaign on Bennu is presented, and an economic analysis is performed. The sensitivity analysis shows the low thrust mining missions are more resistant to changing economic parameters. Campaigns are then numerically designed and optimized for 76 known water-bearing and 58 potential PGM-bearing targets, using both impulsive and low thrust trajectories. The “NEA mining season”, which was an abstract concept, is validated. The mining seasons are categorized into three major types based on their feasibility for mining. Two 35-year water mining and PGM mining plans are generated. It is found the current known targets can form a $21,000 billion PGM mining industry and a$13,000 billion water mining industry. It is found that low thrust-based mining is the key to a successful mining campaign, and that it may increase the profit by 2.8 ~ 8.7 times

Sailing at the brink - The no-limits of near-/now-term-technology solar sails and SEP spacecraft in (multiple) NEO rendezvous

Near-Earth object (NEO) in-situ exploration can provide invaluable information for science, possible future deflection actions and resource utilisation. This is only possible with space missions which approach the asteroid from its vicinity, i.e. rendezvous. This paper explores the use of solar sailing as means of propulsion for NEO rendezvous missions. Given the current state of sail technology, we search for multiple rendezvous missions of up to ten years and characteristic acceleration of up to 0.10 mm/s2. Using a tree-search technique and subsequent trajectory optimisation, we find numerous options of up to three NEO encounters in the launch window 2019-2027. In addition, we explore steerable and throttleable low-thrust (e.g. solar-electric) rendezvous to a particular group of NEOs, the Taurid swarm. We show that an acceleration of 0.23 mm/s2 would suffice for a rendezvous in approximately 2000 days, while shorter transfers are available as the acceleration increases. Finally, we show low-thrust options (0.3 mm/s2) to the fictitious asteroid 2019 PDC, as part of an asteroid deflection exercise