Satellites

A satellite is an object that orbits a larger object, most commonly a celestial body.

It can either be a natural satellite or an artificial satellite:

• Natural satellites are Objects that orbit a larger object in space naturally, such as the moon orbiting Earth or Earth orbiting the sun.
• Artificial satellites are Objects that are launched into space to orbit a celestial body, such as a planet or the moon.

Artificial satellites have many uses, including:

• Communication: Relaying communication
• Weather forecasting: Providing weather data
• Navigation: Providing GPS and other navigation services
• Broadcasting: Providing satellite television and radio
• Scientific research: Conducting scientific research
• Earth observation: Observing Earth
• Military: Providing reconnaissance, early warning, signals intelligence, and potentially weapon delivery.

Communication terms:

Frequency: L, S, Ku, Ka. Ku Band: 12-18 GHz Ka Band: 26.5-40 GHz; It is difficult to build hardware for Ka-band. They are faster. High-Throughput Satellite (HTS): [Throughput: amount of material passing through the system] It reuses satellite ‘beams’ several times over smaller areas(spot beams). They are primarily deployed to provide point-to-point broadband Internet access to regions unserved or underserved by terrestrial technologies where they can deliver services comparable to terrestrial services in terms of pricing and bandwidth. HTS can furthermore support point-to-multipoint applications and even broadcast services such as DTH distribution to relatively small geographic areas served by a single spot beam. HTSs have been game-changers in the West, providing Internet connectivity many times faster, smoother, easier and probably cheaper than now. HTSs provide at least twice the total throughput of a classic FSS(fixed satellite systems) satellite for the same amount of allocated orbital spectrum thus significantly reducing cost-per-bit.

History of Satellite launches launches

• First three experiments: These were launched free of cost, which is an example of India’s successful space cooperation policy.
  • Aryabhatta(1975): launched with the help of the Soviet Union.
  • Bhaskara (1 & 2): Earth observation satellites. Paved the way for future remote sensing satellites, in which today India is a world leader.
  • APPLE (1981): India’s first experimental communications satellite launched by European Ariane rocket.
• SITE & STEP: experiments designed to obtain hands-on experience on the utilization of satellites for television broadcasting and telecommunications.
• By the 1980s India developed its first satellite launch vehicle SLV-3, thrusting India into a league of six countries at that time. Later ASLV was developed.
• The first satellite launched by India’s Satellite Launch Vehicle (SLV) was the Rohini Satellite (RS-1), which was launched on July 18, 1980
• IRS-1A(1988): 1st Indian operational satellite which started imaging Earth from orbit(Polar orbit).
• INSAT-2 Series(1990s): a series of multipurpose satellites built in India indigenously.
• Today India has more than 300 transponders in space in C-band, Extended C-band, Ku-band, Ka/Ku band & S-band.

Satellites in India

India currently has 54 operational satellites, of which

• 22 are earth observation ones [EOS-04 is the last one operated]
• 21 are communication-based.
• Eight are navigation satellites,
• 3 are science satellites.

Communication Satellite (CMS-series):

CMS-01 latest.

Indian National Satellite System (INSAT)

The INSAT system was launched in 1983 multipurpose geostationary satellites launched by ISRO to satisfy telecommunications, broadcasting, meteorology, and search and rescue operations.

• It is the largest domestic communication system in the Asia PacificRegion.
• It is a joint venture of the DoS, DoT, IMD, AIRand Doordarshan.
• The overall coordination and management of the INSAT system rests with the Secretary-level INSAT Coordination Committee.
• INSAT satellites provide transpondersin various bands (C, S, Extended C and K_u) to serve the television and communication needs of India.

Geostationary Satellites (GSAT)

GSAT is a series of Geostationary Communication Satellites some of which are part of the INSAT series. GSAT 7: Navy; GSAT 7A: Air force(proposed). GSAT 29: For JK & North East to boost communication by GSLV Mk III D2. High Throughput Satellite: Operational payloads in Ka & Ku Band. Qu band communication payload. High-resolution geo Camera. GSAT 11: 5.7 Tonne: heaviest Indian satellite, launched from French Guiana. [Ariane V] Airane space: JV between Safran + Airbus. Also supports Ka. Also used for earth observation: For example, INSAT 3DR is used for Weather observations.

Remote sensing satellites:

Remote sensing satellites are used to study and monitor the Earth’s physical characteristics by measuring the radiation that is emitted and reflected from the Earth.

They are used for a wide range of applications, including:

• Environmental analysis: Satellites can be used to analyze the atmosphere, ocean, and land for environmental purposes.
• Agriculture: Satellites can be used to measure soil and crop water content, which helps with agricultural optimization.
• Disaster management: Satellites can be used to help with disaster response.
• Urban planning: Satellites can be used for urban planning.
• Mineral prospecting: Satellites can be used for mineral prospecting.
• Forestry: Satellites can be used for forestry.
• Ocean resources: Satellites can be used for ocean resources.

It may be split into:

• “active” remote sensing : when a signal is emitted by a satellite or aircraft and its reflection by the object is detected by the sensor.
• “passive” remote sensing : when the reflection of sunlight is detected by the sensor.

• Hyper spectral Imaging(HSI): uses continuous & contiguous ranges of wavelengths: [Eg: 400-1100 nm]. It can have hundreds or thousands of bands.
• Multi-spectral Imaging[MSI]: uses a subset of targeted wavelengths at chosen
• Hyper imaging satellite(HySIS): It has a critical chip called “optical imaging detector array” indigenously developed by ISRO.
  • Hyper-imaging: Combining the power of digital imaging + spectroscopy (across the spectrum).
    • Thus giving both spatial and spectral information.
    • We can check the physical as well as chemical properties of the target.
    • This technique was also used on Chandrayaan-I
  • Earth imaging.

New Nomenclature for Earth Observation Satellites:

In 2020, ISRO had moved to a new naming system for its earth observation satellites which till then had been named thematically, according to the purpose they were meant for.

The new series is named as the Earth Observation Satellite (EOS–series) – They would include: CARTOSAT, OceanSAT, INSAT series, ResourceSat, GISAT, ScatSAT.

• SCATSAT-1 is a satellite that provides weather forecasting, cyclone prediction,

Satellites after New Naming system – Earth Observation Satellites(EOS)

• Purposes: Land and forest mapping and monitoring, mapping of resources like water or minerals or fishes, weather and climate observations, soil assessment, and geospatial contour mapping are done through these satellites.
• Launches:

Name	Launch Date	Orbit	Purpose
EOS-01	Nov 07, 2020	LEO	Disaster Management System, Earth Observation
EOS-02	FY23-Q2		A micro-satellite(formerly known as Microsat 2A). Launched as a test payload for SSLV-D1 (Small Satellite Launch Vehicle)
EOS-03	Aug 12, 2021	GTO	Earth Observation – ended in a failure
EOS-04	14th Feb 2022	Sun-Synchronous orbit of 529 km	Radar-imaging satellite which would replace the RISAT-1 (2012) but has been non-functional for the last few years. It uses synthetic aperture radars. Radar imaging is unaffected by weather, cloud or fog, or the lack of sunlight. It can produce high-quality images in all conditions, making it suitable for surveillance. Applications: agriculture, forestry and plantations, flood mapping, soil moisture and hydrology. It will complement the data from Resourcesat, Cartosat and RISAT-2B.

Old Naming System

• Cartosat series of satellites were meant to provide data for land topography and mapping,
• Oceansat satellites were meant for observations over sea.
• RISAT  –  For Radar imaging
• Some INSAT-series, Resourcesat series, GISAT, Scatsat, Megha-Tropiques, and a few other earth observation satellites were named differently for the specific jobs they were assigned to do, or the different instruments that they.

CARTOSAT

It will replace the IRS series. It provides high-resolution scene specific spot imagery. It is useful for cartographic applications, urban & rural applications, coastal land use & regulations & utility management like road networking.

There are a total of 8 CARTOSATs have been launched.

• CARTOSAT 2: 2007: Remote Sensing Satellite dedicated for defence forces.
  • It is believed that surveillance by CARTOSAT-2 with a resolution of about 65cm was used to plan and execute military operations such as ‘surgical strikes’
• Other: 1 (2005), 2, 2A, 2B, 2C, 2D, 2E, 2F, 3.
• CARTOSAT-3: Very high resolution of 25cm.
  • Comparison: Best military grade satellites can provide a 10cm resolution. Best satellite images commercially available are 25-30cm resolution.
  • This can be used to monitor progress of road construction, coastal land-erosion, forest conservation, oceanic changes and infrastructure development.
    • BUT Indian regulators restrict access to satellite images sharper than one meter to the government.
  • BUT unless we have  a sophisticated technology available to analyse the generated images, it will forever be inferior, and less valued, than coarser images scanned by better processing software.

Draft Space Remote Sensing Policy – 2020′

SpaceRS Policy – 2020

• Aim: encouraging various stakeholders in the country to actively participate in space based remote sensing activities to enhance commercialization of space technology.
• Features:
  • Promote Indian Industries to carry out space based remote sensing activities within and outside India.
  • Enable easy access to space based remote sensing data.
  • Concentrate on realisation of space based remote sensing systems to cater to the country’s needs.
  • Provide a timely and responsive regulatory environment for the commercial Indian industry.
• Earlier Remote sensing data policy (RSDP) 2011 is said to be more restrictive and provides less opportunities to service providers.

Other Satellites

ASTROSAT

India’s first dedicated multi wavelength space observatory, for a more detailed understanding of our universe.

• Visible, Ultraviolet, low and high energy X-ray simultaneously with the help of its five payloads.
• Aims at understanding:
  • the high energy processes in binary star systems containing neutron stars and black holes,
  • to estimate magnetic fields of neutron stars,
  • to study star birth regions and
  • high energy processes in star systems lying beyond the Milky Way galaxy.
• Exclusive club of nations with space-based observatories. Only US, European Space Agency(EAS), Japan and Russia have such observatories in space.
• Design life ended in 2020.

Private Players in Satellite technologies

Role of Private players currently: Many of these companies want to launch their own satellites, of varying dimensions, and the experience with ISRO has not been smooth always.

ISRO has roped in a consortium of six companies to deliver the country’s first industry-built spacecraft by late 2017.

• Contract: ISRO recently signed an agreement with the consortium. The contract includes assembly, integration and testing (AIT) of two spare navigation satellites consecutively in around 18 months. The contract was signed between ISRO Satellite Centre (ISAC) and the consortium lead, Alpha Design Technologies P Ltd.
• Alpha is a defence manufacturing contractor while the others are small and medium-sized vendors that already supply components to ISRO.
• The others in the consortium are Newtech Solutions, Aidin Technologies and DCX Cables of Bengaluru, Vinyas Technologies of Mysuru and Avantel Systems of Hyderabad.
• The work will start around January and the first spacecraft will be brought out in around nine months.

100-Watt Radioisotope Thermoelectric Generator (RTG):

The UR Rao Satellite Centre (URSC) of ISRO invited proposals for the three-phase development of a 100-Watt Radioisotope Thermoelectric Generator (RTG).

• URSC is ISRO’s lead centre for design, development, fabrication, and testing of all Indian-made satellites.
• The centre envisions using RTG for power generation and thermal management of ISRO’s deep space missions.
• Advantages: RTGs are lightweight, compact spacecraft power systems that are extraordinarily reliable.
• Mechanism: They provide electric power using heat from the natural radioactive decay of plutonium-238, in the form of plutonium dioxide. The large difference in temperature between this hot fuel and the cold environment of space is applied across special solid-state metallic junctions called thermocouples, which generates an electric current using no moving parts.
  • Sometimes referred to as “nuclear batteries”, RTGs are not fission reactors, nor is plutonium the type that is used for nuclear weapons.
• Other agencies: : More than 2 dozen US space missions have used RTGs since the first one was launched in 1961 like Cassini, New Horizon and Curiosity etc.

Other satellites are being launched

• INSPIREsat-1 is a student satellite:
  • developed by the Thiruvananthapuram-based Indian Institute of Space Science and Technology in collaboration with the University of Colorado in the US where it was assembled and tested. Students from Nanyang Technological University in Singapore and National Central University of Taiwan have also contributed.
  • This satellite will study the dynamics of the upper atmosphere and carries an X-ray spectrometer for studying solar flares.
• INS-2TD,
  • It is a technology demonstrator for the first India-Bhutan joint satellite that is scheduled to be launched next month.
  • The two countries had signed a space agreement last year, and its first outcome would be the launch of BhutanSat, or INS-2B, on a PSLV rocket in March.
  • The INS-2TD that will fly on Monday has a thermal imaging camera meant for earth observation purposes, like assessment of land and water surface temperature, and identification of forest and tree cover.

Space Junk

Space debris, also called space junk, artificial material that is orbiting Earth but is no longer functional. Space junk or debris consists of spent rocket stages, dead satellites, fragments of space objects and debris resulting from ASAT.

Speeding at an average speed of 27,000 kmph in LEO, these objects pose a very real threat as collisions involving even centimetre-sized fragments can be lethal to satellites.

Present situation:

• For protecting its space assets, ISRO was forced to perform 19 collision avoidance manoeuvres (CAM) in 2021, of which 14 were in Low Earth Orbit (LEO) and five in the geostationary orbit, according to ISRO’s Space Situational Assessment for the year.
• ISRO officials say the volume of debris is likely to go up in the coming years with the increase in space missions globally. Globally, 2021 saw the highest space object-to-launch ratio. In other words, more space objects are placed in orbit per launch. In 2020, 522 objects were placed in space with 102 launches compared to 1,860 objects in 135 launches in 2021.

The Network for Space Objects Tracking and Analysis (NETRA) project

ISRO has launched NETRA project, which is a space debris tracking radar with a range of 1,500 km and an optical telescope will be inducted as part of establishing an effective surveillance and tracking network under NETRA.

• It have two such radars deployed 1,000 km apart for spatial diversity.
• The government has given the go-ahead for the deployment of the radar.
• It will be capable of detecting and tracking objects 10 cm and above in size.
• It will be indigenously designed and built.
• Radars and optical telescopes are vital ground-based facilities for keeping an eye on space objects, including orbital junk.
• At present, we have a Multi Object Tracking Radar at Sriharikota range, but it has a limited range. To protect our space assets, we need to augment our capabilities.
• ISRO’s efforts towards space situational awareness (SSA) is coordinated by the SSA Control Centre in Bengaluru and managed by the Directorate of Space Situational Awareness and Management at the ISRO headquarters.

Problem of space Debris:

• Digantara (eye in the sky) India’s first air and space surveillance company, has developed India’s first in-orbit Space debris monitoring and tracking system.
  • It’ll provide global real-time earth coverage by deploying a constellation of cost-efficient nano satellites in LEO and a space-based air surveillance payload for accurate tracking of both aircraft and space objects.
  • It will use LIDAR

NEO-01: China has launched a robot prototype in April 2021 that can scoop up debris left behind by other spacecraft with a big net. It  will use a net to capture debris and then burn it with its electric propulsion system.