Browsing by Author "Sitepu, Elioenai"

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    Drop Your Thesis! 2018 results: 4.74 seconds of microgravity conditions to enable future cubesat landings on asteroids
    (Elsevier, 2020-06-04) Gautier, F.; Sitepu, Elioenai; Le Blay, C.; Kersey, G.; Sanchez Cuartielles, Joan Pau
    Space exploration has seen a growing number of asteroid missions being launched; mostly due to their scientific interest, but also on account of the potential impact threat and prospective valuable resources of their targets. Landing safely on the surface of an asteroid is one of the main technical challenges before obtaining in-situ observations and ground-truth data. Given the asteroid's extremely weak gravitational field, purely ballistic descent trajectories become a suitable option to reach its surface. However, this is still a very risky operation due to the limited knowledge of the object's physical characteristics. Hence, deploying a small lander is often a more conservative option than endangering the mothercraft itself, and thus a simple CubeSat may provide a low cost solution for asteroid exploration. However, for a CubeSat system to be able to safely land on the surface of an asteroid, a sufficient dissipation of energy must naturally occur at touchdown, or else the resultant bouncing may lead to high uncertainties on the final landing location, or even yield an escape trajectory. This paper describes the result of ESA Academy's Drop Your Thesis! 2018 (DYT2018) programme. DYT2018 carried out a microgravity experiment, led by Land3U team from the Astronautics and Space Engineering Course at Cranfield University, to provide additional data on the engineering constraints relevant to land a CubeSat on the surface of an asteroid. The experiment was performed in ZARM's Drop Tower, located in Bremen, during two Drop campaigns in November 2018 and February 2019. A total of 7 drops were completed, each providing 4.74 s of microgravity under vacuum environment. The experiment measured the coefficient of restitution of a 1U mock-up, equipped with a 4-kg mass, touching down on the simulated asteroid surface with an average velocity of 150 mm/s. Three successful drops measured a coefficient of restitution of 0.26 ± 0.03
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    Granular sample collection simulation via counter rotating wheels sampler for small-sized system at reduced gravity environment
    (Elsevier, 2023-09-13) Sitepu, Elioenai; Cullen, David C.
    The launching and planning of space missions for asteroid exploration have increased due to their scientific interest and potential resources for future use, such as composition analysis and In-Situ Resource Utilization (ISRU) demonstration. Furthermore, the design of sample acquisition systems has been limited to accommodate CubeSats or small-sized payloads, as the utilization of CubeSats for scientific missions is also on the rise. Therefore, sample collection is a critical step in preparing for these missions. The focus of this study is to analyse a conventional counter rotating wheels sample acquisition concept on a granular bed in microgravity conditions on an asteroid, as well as on the Moon and Mars with different gravitational forces. The study introduces a set of Archimedes screws into the wheels as a novel sample acquisition approach and utilizes Discrete Element Modelling (DEM) to analyse it. The simulation shows that the addition of an Archimedes screw sampler is more efficient in collecting samples in a short sampling time (<2 s) than a conventional counter rotating wheels. For implementation on planetary bodies with significant gravitational force, such as the Moon or Mars, a limitation is observed and redesigning the sample collection chamber might be necessary to capture the particles. Finally, the study highlights potential future work that could provide a more detailed and comprehensive understanding of the newly designed counter rotating wheels sampler.
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    Towards drop your thesis 2018: 4.7 seconds of microgravity conditions to enable future CubeSat landings on asteroids
    (International Astronautical Federation (IAF), 2018-10-05) Sanchez Cuartielles, Joan Pau; Sitepu, Elioenai; Le Blay, Carole; Kersey, George; Ogborne, Stuart; Durrani, Daniyal Ahmad; Zanotti Fragonara, Luca; Gautier, Florian; Kingston, Jennifer
    An increasing number of interplanetary missions are aiming at visiting asteroids and other small bodies, since these may provide clues to understand the formation and evolution of our Solar System. CubeSats allow a low-cost solution to land on these objects, as opposed to risking a much more expensive mothership. The weak gravitational field on these small bodies may also enable the possibility of simply dropping a CubeSat from afar (i.e. ballistic landing). However, ballistic landing of an unpowered spacecraft may be feasible solely within certain asteroid locations, and only if sufficient energy can be dissipated at touchdown. If such conditions are not met, the spacecraft will rebound off the surface. It is likely that the necessary energy dissipation may already occur naturally due to energy loss expected through the deformation of the regolith during touchdown. Indeed, previous low-velocity impact experiments in microgravity seem to indicate that this is exactly the case. However, data from past asteroid touchdowns, Hayabusa and Philae, indicate the contrary. This paper describes the development of an experiment which aims to bridge the aforementioned disagreement between mission data and microgravity experiment; to understand the behaviour of CubeSat landing on asteroids. The experiment will also test a novel damping system made by origami paper that should increase the dissipated energy at touchdown. The experiment will take place at the ZARM Drop Tower in Bremen in November 2018. With the constraint of 5 drops, the experiment will measure the coefficient of restitution during an available time window of 4.74 seconds of microgravity conditions. A 1UCubeSat mock-up will be used to represent a future asteroid lander. In order to mimic the landing of actual missions, the mock-up will have a mass of about 4 kg and it will be given a velocity of 15 cm/s with minimal rotation. This will be achieved by an automated spring-based release mechanism. An asteroid simulant, ESA03-A KM Bentonite Granules will be used to replicate an asteroid mechanical properties at the surface. This paper reviews the final design and the engineering challenges of the experiment.