The Lunar Ultraviolet Cosmic Imager (LUCI) is an innovative all-spherical mirrors telescope, proposed to fly as a scientific UV imaging payload on a lunar mission in collaboration with Indian Aerospace Company-TeamIndus, Axiom Research Labs Pvt. Ltd. Observations from the Moon provide a unique opportunity to observe the sky from a stable platform far above the Earths atmosphere. LUCI will observe at a fixed elevation angle and will detect stars in the near ultraviolet (200-320 nm) to a limiting magnitude of 12 AB, with a field of view of around 0.5 degrees. The primary science goal is to search for transient sources and flag them for further study. The instrument has been assembled in the class 1000 clean room at the M.G.K Menon Laboratory for Space Sciences. Here we will describe the optomechanical assembly procedures we have carried out during the optical alignment and integration of the payload. Opto-mechanical alignment of the instrument was carried out by using alignment telescope cum autocollimator (for coarse alignment) and ZYGO interferometer (fine alignment). We will also discuss the ground calibration tests performed on the assembled telescope. The results from the ground calibration activities will help in establishing the full calibration matrix of the instrument once operational.
We describe the development and implementation of a light-weight, fully autonomous 2-axis pointing and stabilization system designed for balloon-borne astronomical payloads. The system is developed using off-the-shelf components such as Arduino Uno controller, HMC 5883L magnetometer, MPU-9150 inertial measurement unit, and iWave GPS receiver unit. It is a compact and rugged system which can also be used to take images/video in a moving vehicle or in real photography. The system performance is evaluated from the ground, as well as in conditions simulated to imitate the actual flight by using a tethered launch.
The ultraviolet (UV) window has been largely unexplored through balloons for astronomy. We discuss here the development of a compact near-UV spectrograph with fiber optics input for balloon flights. It is a modified Czerny-Turner system built using off-the-shelf components. The system is portable and scalable to different telescopes. The use of reflecting optics reduces the transmission loss in the UV. It employs an image-intensified CMOS sensor, operating in photon counting mode, as the detector of choice. A lightweight pointing system developed for stable pointing to observe astronomical sources is also discussed, together with the methods to improve its accuracy, e.g. using the in-house build star sensor and others. Our primary scientific objectives include the observation of bright Solar System objects such as visible to eye comets, Moon and planets. Studies of planets can give us valuable information about the planetary aurorae, helping to model and compare atmospheres of other planets and the Earth. The other major objective is to look at the diffuse UV atmospheric emission features (airglow lines), and at column densities of trace gases. This UV window includes several lines important to atmospheric chemistry, e.g. SO2, O3, HCHO, BrO. The spectrograph enables simultaneous measurement of various trace gases, as well as provides better accuracy at higher altitudes compared to electromechanical trace gas measurement sondes. These lines contaminate most astronomical observations but are poorly characterized. Other objectives may include sprites in the atmosphere and meteor ashes from high altitude burn-outs. Our recent experiments and observations with high-altitude balloons are discussed.
The Segmented Mirror Telescopes (SMT) are built using small hexagonal mirror segments placed side by side to form a monolithic primary mirror of very large size. The effective figure of such a segmented primary mirror is maintained against external disturbances introduced by gravity, temperature, wind and vibration with the help of primary mirror active control system. This active control system consists of two levels of control – global and local level. At the global scale, three actuators per segment and two edge sensors per intersegment sides are used to maintain the shape of the primary mirror. At the local level, actuator control system executes the commands generated by the global control loop. Every mirror segment is controlled with the help of three actuators, where the major role of these actuators is to provide a tip, tilt, and piston to the mirror segments. In this paper, we describe the actuator developed for 1.5m diameter Prototype Segmented Mirror Telescope (PSMT). The actuator for this telescope is a soft actuator based on the voice coil mechanism. This actuator is designed for with the range of travel of ±1.5mm and the force range of 25N along with an offloading capability to reduce the power consumption. The prototype actuator is undergoing different tests at Indian Institute of Astrophysics (IIA), Bangalore. The tracking rate of 324nm/s is achieved with the tracking error of 22.5 nm RMS.
We describe the characterization and removal of noises present in the Inertial Measurement Unit (IMU) MPU- 6050, which was initially used in an attitude sensor, and later used in the development of a pointing system for small balloon-borne astronomical payloads. We found that the performance of the IMU degraded with time because of the accumulation of different errors. Using Allan variance analysis method, we identified the different components of noise present in the IMU, and verified the results by the power spectral density analysis (PSD). We tried to remove the high-frequency noise using smooth filters such as moving average filter and then Savitzky Golay (SG) filter. Even though we managed to filter some high-frequency noise, these filters performance wasn't satisfactory for our application. We found the distribution of the random noise present in IMU using probability density analysis and identified that the noise in our IMU was white Gaussian in nature. Hence, we used a Kalman filter to remove the noise and which gave us good performance real time.
We have designed and developed a compact ultraviolet imaging payload to y on a range of possible platforms such as high altitude balloon experiments, cubesats, space missions, etc. The primary science goals are to study the bright UV sources (mag < 10) and also to look for transients in the Near UV (200 - 300 nm) domain. Our first choice is to place this instrument on a spacecraft going to the Moon as part of the Indian entry into Google lunar X-Prize competition. The major constraints for the instrument are, it should be lightweight (< 2Kg), compact (length < 50cm) and cost effective. The instrument is an 80 mm diameter Cassegrain telescope with a field of view of around half a degree designated for UV imaging. In this paper we will discuss about the various science cases that can be performed by having observations with the instrument on different platforms. We will also describe the design, development and the current state of implementation of the instrument. This includes opto-mechanical and electrical design of the instrument. We have adopted an all spherical optical design which would make the system less complex to realize and a cost effective solution compared to other telescope configuration. The structural design has been chosen in such a way that it will ensure that the instrument could withstand all the launch load vibrations. An FPGA based electronics board is used for the data acquisition, processing and CCD control. We will also brie y discuss about the hardware implementation of the detector interface and algorithms for the detector readout and data processing.
We are developing a compact UV Imager using light weight components, that can be own on a small CubeSat or a balloon platform. The system has a lens-based optics that can provide an aberration-free image over a wide field of view. The backend instrument is a photon counting detector with off-the-shelf MCP, CMOS sensor and electronics. We are using a Z-stack MCP with a compact high voltage power supply and a phosphor screen anode, which is read out by a CMOS sensor and the associated electronics. The instrument can be used to observe solar system objects and detect bright transients from the upper atmosphere with the help of CubeSats or high altitude balloons. We have designed the imager to be capable of working in direct frame transfer mode as well in the photon-counting mode for single photon event detection. The identification and centroiding of each photon event are done using an FPGA-based data acquisition and real-time processing system.