Two-craft tether formation relative equilibria about circular orbits and libration points

The relative equilibria of a two spacecraft tether formation connected by line-of-sight elastic forces moving in the context of a restricted two-body system and a circularly restricted three-body system are investigated. For a two spacecraft formation moving in a central gravitational field, a common assumption is that the center of the circular orbit is located at the primary mass and the center of mass of the formation orbits around the primary in a great-circle orbit. The relative equilibrium is called great-circle if the center of mass of the formation moves on the plane with the center of the gravitational field residing on it; otherwise, it is called a nongreat-circle orbit. Previous research shows that nongreat-circle equilibria in low Earth orbits exhibit a deflection of about a degree from the great-circle equilibria when spacecraft with unequal masses are separated by 350 km. This paper studies these equilibria (radial, along-track and orbit-normal in circular Earth orbit and Earth–Moon Libration points) for a range of inter-craft distances and semi-major axes of the formation center of mass. In the context of a two-spacecraft Coulomb formation with separation distances on the order of dozens of meters, this paper shows that the equilibria deflections are negligible (less than 10^?6°) even for very heterogeneous mass distributions. Furthermore, the nongreat-circle equilibria conditions for a two spacecraft tether structure at the Lagrangian libration points are developed.     

Telemetry,telecommand and safety sub-systems for scientific ballooning from Hyderabad

Highly sophisticated balloon-borne scientific payloads have stringent requirement on the telemetry and command system. The development and fabrication of the on-board TT&C package for telemetry, tracking, command, safety and ranging for these experiments is done in-house at the National Balloon Facility (NBF) at Hyderabad. In the last few years, we have made major improvements both in the ground station and the on-board sub-systems, thereby improving the data quality, data handling speed and the general flight control along with aviation safety. The new system has telemetry data rate up to 1 Mbps. A reduction in weight, power and cost of the reengineered on-board integrated package has also lead to the ease of operation during field tests prior to launch and at remote recovery sites. In this paper, we describe the details of the new control package, its flight performance and our plans for portable S-band telemetry and telecommand system to cater to the balloon flights from Antarctic station and long duration balloon flights.     

Future of Space Astronomy: A global Road Map for the next decades

The use of space techniques continues to play a key role in the advance of astrophysics by providing access to the entire electromagnetic spectrum from radio to high energy γ rays. The increasing size, complexity and cost of large space observatories places a growing emphasis on international collaboration. Furthermore, combining existing and future datasets from space and “ground based” observatories is an emerging mode of powerful and relatively inexpensive research to address problems that can only be tackled by the application of large multi-wavelength observations. While the present set of astronomical facilities is impressive and covers the entire electromagnetic spectrum, with complementary space and “ground based” telescopes, the situation in the next 10–20 years is of critical concern. The James Webb Space Telescope (JWST), to be launched not earlier than 2018, is the only approved future major space astronomy mission. Other major highly recommended space astronomy missions, such as the Wide-field Infrared Survey Telescope (WFIRST), the International X-ray Observatory (IXO), Large Interferometer Space Antenna (LISA) and the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), have yet to be approved for development.     

Enhancement of primary education using EDUSAT: Rajiv Gandhi project for EDUSAT supported elementary education network (RGPEEE) overview

Providing education access to the children in the age group 6–14 years is a constitutional obligation and challenge for the union as well state governments, as the development of elementary education is a key factor for a nation's development. Due to the non-availability of required number of trained and expert teachers’ knowledge-divide exists between students population of urban and rural/remote areas. To bridge this gap Distance Learning or Tele-education is the best option. A dedicated satellite for the purpose (EDUSAT) was launched on 20th September 2004 to serve the nation in all the education activities. It was decided to provide a Tele-education network in and around the Sidhi district of Madhya Pradesh, with uplink and studio facility (Hub) at Jabalpur (MP) and around 700 receive only terminals (ROTs) in various schools. Since the medium of teaching used in this network is Hindi, it was later decided to extend the coverage to connect around 50 primary schools with ROTs in six surrounding states viz. Jharkhand, Bihar, Chhatisgarh, Uttar Pradesh, Rajasthan and Uttaranchal. The network is configured as a DTH network using state-of-art digital technology, in Ku-band with 3.8 m antenna and 16 W power amplifier at Hub. The ROTs are designed to operate on solar power for 2.5 h continuously, taking into consideration the non-availability of primary power in the rural areas. The teachers of the schools are trained for the proper operations of the ROTs. The teachers of these rural schools also contribute to the content generation, with local relevance, in coordination with Indira Gandhi National Open University (IGNOU). At present the network with around 1000 ROTs is being utilized for 2 h per day. The RGPEEE network is in the process of being augmented with 32 satellite interactive terminals (SITs), to be used for teachers training. The project is being managed by two tier management system. In order to oversee the project implementation and monitoring an Apex Core Group, consisting of Apex Committee and Standing Committee, has been constituted. The Apex Committee takes care of policy decisions where as, the Standing Committee takes care of day to day affair.     

Near infrared studies of the massive X-ray binary 2S 0114+65

We present near-infrared spectroscopy of the massive X-ray binary 2S 0114+650. These observations covering the spectral range 1.08–2.35 μm span the region where Paschen and Brackett series recombination lines of hydrogen are expected to be seen, namely, Paβ , Brγ and Br 10–17 lines. The absence of any of these lines in emission supports earlier inferences that the optical component in 2S 0114+650 is unlikely to be a Be star but rather a B type supergiant. Near-IR photometry gives J = 8.78, H = 8.53 and K = 7.96; these values show marginal variations from earlier reported measurements.     

Evolution of the periodicities in 2S 0114+650

We have analysed 9 years of data from the All Sky Monitor on the Rossi X-ray Timing Explorer for 2S 0114+650 to study the evolution of its spin, binary, and super-orbital periods. The spin history of the neutron star in this system exhibits torque reversals lasting 1 year. The newly discovered super-orbital period has remained stable over the 9-year span, making 2S 0114+650 the fourth known system to exhibit stable super-orbital modulation. We compare its super-orbital period evolution with those of the other three such systems.     

Periodic components in Cyg X-3

Hard X-ray observations of Cyg X-3 in the energy range 20–100 keV were made with a Balloon-borne telescope using two large area proportional counters. The source was seen with a total significance of 20.

A 121 s periodicity was seen during Fourier analysis of the data. The phenomenon can be interpreted as due to transient pulsation since no other peak was seen in our data. Quasi-periodic oscillation in the range 0.06–20 mHz have been observed from Cyg X-3 at lower energies. Interestingly, most of the reported periods are multiple of the present measurements. The observed pulsation at high energies indicate the occasional unstable behaviour of the inner parts of the accretion disk connected with the basic rotation period of the compact object.

The 4.8^h modulation, characteristic of the orbital period of the binary system was seen in the data, with a broad maximum between the phase 0.3 to 0.7.     

Automated design architectures for co-orbiting spacecraft swarms for planetary moon mapping

This work describes the design and optimization of spacecraft swarm missions to meet spatial and temporal visual mapping requirements of missions to planetary moons, using resonant co-orbits. The algorithms described here are a part of Integrated Design Engineering and Automation of Swarms (IDEAS), a spacecraft swarm mission design software that automates the design trajectories, swarm, and spacecraft behaviors in the mission. In the current work, we focus on the swarm design and optimization features of IDEAS, while showing the interaction between the different design modules. In the design segment, we consider the coverage requirements of two general planetary moon mapping missions: global surface mapping and region of interest observation. The configuration of the swarm co-orbits for the two missions is described, where the participating spacecraft have resonant encounters with the moon on their orbital apoapsis. We relate the swarm design to trajectory design through the orbit insertion maneuver performed on the interplanetary trajectory using aero-braking. We then present algorithms to model visual coverage, and collision avoidance in the swarm. To demonstrate the interaction between different design modules, we relate the trajectory and swarm to spacecraft design through fuel mass, and mission cost estimations using preliminary models. In the optimization segment, we formulate the trajectory and swarm design optimizations for the two missions as Mixed Integer Nonlinear Programming (MINLP) problems. In the current work, we use Genetic Algorithm as the primary optimization solver. However, we also use the Particle Swarm Optimizer to compare the optimizer performance. Finally, the algorithms described here are demonstrated through numerical case studies, where the two visual mapping missions are designed to explore the Martian moon Deimos.     

Characteristics and performance of thin LaBr3(Ce) crystal for hard X-ray astronomy

We have developed a new detector using thin lanthanum bromide crystal (32 × 3 mm) for use in X-ray astronomy. The instrument was launched in high altitude balloon flight on two different occasions, December 21, 2007, which reached a ceiling altitude of 4.3 mbs and April 25, 2008 reaching a ceiling altitude 2.8 mbs. The observed background counting rate at the ceiling altitude of 4 mbs was ∼4 × 10⁻³ ct cm⁻² s⁻¹ keV⁻¹ sr⁻¹. This paper describes the details of the experiment, the detector characteristics, and the background behaviour at the ceiling altitude.     

Recent studies of the optical counterpart of GX 1+4

The galactic X-ray source GX 1+4 has been undergoing remarkable changes since early 1991. The X-ray pulsar has shown fast spin down accompanied by an increase in the hard X-ray intensity. We have obtained 1.6Å resolution spectra of the optical counterpart extending the known spectrum to 8500Å. The Ca II (8498Å) line seen for the first time from this source is indicative of a nova burst scenario. Other lines detected for the first time are detailed and the significance of these features is discussed.