C J Jagdeesha, LV Muralikrishna Reddy & R.M.Vasagam

Conventional earth observation and remote sensing missions are extremely costly and also expensive to operate. Current airborne and space borne optical / synthetic aperture radars are playing an important role in remote sensing applications. However, even as good as they envisioned or employed, it is impossible for our limited non-geosynchronous earth orbit satellites to provide a staring presence on a time scale of days , weeks , or months over a selected target or area of interest. This gap in capability of persistent remote sensing observation and another gap where there is little number of sensors in the altitude between air and space need to be addressed. Consequently both aero and space industry started directing their attention to missions involving inexpensive satellites. Furthermore, many space programs focused on the development of micro-, nano-, and pico- satellites for educational purposes. Conventional large satellite is more than 1000 kg mass and costs more than 100 million pounds; whereas a conventional small satellites 500-1000 kg and 25-100 million pounds, a mini-satellite 100-500 kg and 7-25 million pounds, microsatellite 10-100 kg and 1-7million pounds, nano-satellite 1-10kg and 0.1 to 1Mpounds and pico-satellite less than a Kg and less than 0.1 million pounds.

The design considerations for small satellite constellations for environmental monitoring and early warning for few cases will be suggested in this paper. In main, the constellation of small satellites use is recommended for EWS than large satellites. The small satellites have much shorter development timelines, ranging from 18-24 months. Small satellites have shortened technology refresh cycle made possible by the lower costs. These small satellites often have less redundancy than their large counterparts which can mean shorter life on orbit. There will be hedging against design problems or component failures since replacement satellites can be launched much sooner. EO images are often limited by cloud cover, with roughly 66% of the earth’s surface covered by clouds throughout the year. Mixed constellations can operate in multiple environments such as in cloudy condition (SAR-synthetic aperture radars) and at night (IR/SAR-infrared) and can provide contextual information to images (HSI). The early warnings on water quality of lakes, water supply, power network stability, transportation network stability, crop failures, ecosystem vulnerability, environmental flows, eutrophication status of wetlands, biodiversity on thresholds etc., are going to be in need of these mixed satellite constellations.
The Indian experience from academic sector in building small satellites (pico and nano) will be highlighted. The systems thinking in building small satellites and business opportunities of small earth stations will also be presented in the context of varied natural resource management / monitoring needs .

There is one big commonality of small satellites called as CubeSats; commonality is that the use of almost exclusively commercial off-the-shelf (COTS) electronic components. This is done in order to keep the costs low, because space-qualified parts are extremely expensive. For the design of a satellite it is useful to build the satellite bus around the payload. This means that the payload and the mission objectives are the design drivers for the subsystems. Procurement programs with minimum development risks produce only flight models for cost reasons and because they can rely on the long experience of manufacturers. Qualification models or prototypes are usually not considered. However it is not unusual that even in flight models components or items are used which are not available as COTS products and which have to be specially developed for the program. A somewhat detailed look at the use of small satellites for sustainable satellite systems is being brought out in this paper. Small satellites constellations can be used for environment and disaster monitoring and forecasting. For example say two satellites having multispectral imager, hyper spectral imager and infrared imager, one satellite for SAR (Synthetic Aperture Radar) multi-look, single look, scan and strip modes. Such constellations are typically used for blizzard (snow storms) monitoring. Some small satellite constellations can be used for tracking and monitoring the illicit trafficking in weapons and sensitive technologies. These constellations will have three main functional systems (a) space-based information and communication system (SICS), (b) conventional information and surveillance system (CISS), and (c) illicit arms traffic surveillance integrated mission management. The architecture here comprises of optical constellation, SAR constellation, and communication and suitable bus constellation.

About 10 tonnes of space garbage clutter low earth orbits of up to 2000km.Russia is ringing alarm bells over the snowballing problem of space junk , after it lost one of its nano-satellites in collision with a piece of Chinese debris. Three years ago the probability of collision between a spaceship and debris larger than one centimeter was estimated at one case in every five years, while today it is likely to occur once in 18 to 24 months. The small satellites can be lost in collisions, but can be replaced soon at much less time and cost than large satellites. Then can we think of near-space remote sensing.
The new science, technology and innovation policy (STI policy) 2013 aims to focus simultaneously on the twin challenges of increasing the number of “people for science” and of combining “the benefits of excellence and relevance” to grow “science for people” .The policy seeks to direct the STI enterprise to achieve inclusive innovation; it suggests that India’s STI led developmental efforts will have to aim at faster, inclusive and sustainable growth. The STI policy perspective includes the following: a. facilitating private sector investment in R&D, b). treating multi-stakeholder participation in the Indian R&D system, c). treating R&D in the private sector at par with public institutions for availing public funds,d. benchmarking of R&D funding mechanisms and patterns globally, e). aligning venture capital and inclusion of innovation fund systems, f). modifying the intellectual property rights policy to provide for march-in rights for social good when supported by public funds and for co-sharing IPRs generated under public-private partnerships. g) exploring newer mechanisms for fostering incubators in technology businesses and science-led entrepreneurship, and h. providing incentives for commercialization of innovations with focus on “green manufacturing”. Green embedded systems and green electronics are to be encouraged while developing sustainable small satellite systems and sensor networks.

Near-space remote sensing is also a possibility which can compete with present day small satellite missions. In near-space, between 20km and 100km, there are no clouds, thunderstorms, or precipitation. In near-space there are no ionospheric scintillations that will significantly degrade microwave communication and navigation performance which explains why near-space has received much attention in recent years and why several types of near-space vehicles are being studied and developed, or employed. These near-space vehicles can be classified as three major categories: 1. free-floaters, 2. Steered Free-floaters, 3. Maneuvering vehicles. Near-space vehicles provide a potential to high-resolution and wide swath SAR imaging, which is a contradiction for conventional SARs . The potential configurations including multichannel in azimuth, multi aperture in elevation, and space-time coding MIMOSAR. It is anticipated that near space vehicle-borne multi-antenna SARs, especially MIMO SAR, enable SAR systems to be operated with high flexibility and reconfigurability, thus ensuring previously unprecedented remote sensing performance.

India experiences a number of disasters like floods, droughts, water supply, Tsunamis, air, water and land pollution, cyclones, earth quakes, land slides, crop failures, potential outbreak of diseases to humans and other livestocks, potential damage to flora and fauna etc., periodically. It is chronic in some part or the other parts. Early warning systems (EWS) are a part of environmental security systems to forecast these disasters. . Environmental security, for us here, means not only giving protection from physical threats, chemical threats, biological threats and cyber threats but also include a chain of several causal connections and people’s concerns, namely,: understanding and mapping the hazard, monitoring and forecasting events, processing and disseminating understandable warnings to political authorities and the population, and undertaking appropriate and timely actions in response to the warnings. Environmental security, generally for resource managers, means water security, ecosystem security, food security, energy security, habitat security etc. In our concept it is not merely a top down technocratic and administrative approach but an attempt to involve society, local communities and people in general by giving them access to information, scientific knowledge etc., and also engage them in the feedback process using modern communication systems.

Pilot less aerial vehicles, (PAVs) be it fixed wing or multirotor type, are now-a-days used for high precision mapping and surveying. Increased efficiency, on-site safety and cost reduction are the operational benefits, but hey even have environmental benefits like eco-friendly and very less noisy and quick to deploy and accessible for small businesses (agribusinesses, say). Whether these PAVs are characterized as helpful drones in a disaster or a killer drone will depend on policy, regulation and its legal issues.

The wireless sensor networks, small satellites, near-space remote sensing, micro air vehicles , UAVs technology based remote sensing to aid our understanding of sustainble use of these technologies for better natural resources monitoring and early warning systems will be discussed in this paper.