Recently, the Indian Space Research Organisation (ISRO) chairman has mentioned the launch of an “SSLV-D1 Micro SAT in April 2022”.
About Small Satellite Launch Vehicle:
- The Small Satellite Launch Vehicle (or SSLV) is a small-lift launch vehicle being developed by the Indian Space Research Organisation (ISRO)
- Its payload capacity to deliver 600 kg (1,300 lb) to low Earth orbit (500 km (310 mi)) or 300 kg (660 lb) to Sun-synchronous orbit (500 km (310 mi)) for launching small satellites, with the capability to support multiple orbital drop-offs.
- The smallest vehicle weighing only 110-tonne. It will take only 72 hours to integrate, unlike the 70 days taken now for a launch vehicle.
- SSLV is a three-stage all solid vehicle
- It is perfectly suited for launching multiple microsatellites at a time and supports multiple orbital drop-offs.
- The key features of SSLV are low cost, with low turn-around time, flexibility in accommodating multiple satellites, launch on demand feasibility, minimal launch infrastructure requirements, etc.
- On 21 December 2018, the Vikram Sarabhai Space Centre (VSSC) at Thumba completed the design for the vehicle.
- The maiden flight is expected no earlier than December 2021, from the First Launch Pad, and in the future a dedicated launch pad in Sriharikota called Small Satellite Launch Complex (SSLC) will be set up.
- A new spaceport, under development, near Kulasekharapatnam in Tamil Nadu will handle SSLV launches when complete.
- After entering the operational phase, the vehicle’s production and launch operations will be done by a consortium of Indian firms along with New Space India Limited (NSIL).
- The Government has sanctioned a total cost of Rs. 169 Crores for the development project including the development & qualification of the vehicle systems and the flight demonstration through three development flights (SSLV-D1, SSLV-D2 & SSLV-D3).
- ISRO’s new chairman Dr Somanath is credited with designing and developing the SSLV during his tenure as director of the Vikram Sarabhai Space Centre in Thiruvananthapuram since 2018.
- The maiden flight of the SSLV was scheduled to launch in July 2019 but that has since been delayed due to setbacks from Covid-19 and other issues.
Why it need?
- Low earth orbit has emerged in recent years on account of the need for developing countries, private corporations, and universities for small satellites.
- Till now, the launch of small satellites has been dependent on ‘piggy-back’ rides with big satellite launches on ISRO’s work-horse – the Polar Satellite Launch Vehicle (PSLV).
Launch Vehicle of ISRO:
Launch Vehicles are used to carry spacecraft to space. India has two operational launchers:
- Satellite Launch Vehicle-3 (SLV-3) was India’s first experimental satellite launch vehicle, which was an all solid, four stage vehicle weighing 17 tonnes with a height of 22m and capable of placing 40 kg class payloads inLow Earth Orbit (LEO)
- The Augmented Satellite Launch Vehicle (ASLV) Programme was designed to augment the payload capacity to 150 kg, thrice that of SLV-3, for Low Earth Orbits (LEO). Under the ASLV programme four developmental flights were conducted. The first developmental flight took place on March 24, 1987 and the second on July 13, 1988.
- Polar Satellite Launch Vehicle (PSLV) is the third generation launch vehicle of India. It is the first Indian launch vehicle to be equipped with liquid stages. After its first successful launch in October 1994, PSLV emerged as the reliable and versatile workhorse launch vehicle of India with 39 consecutively successful missions by June 2017. During 1994-2017 period, the vehicle has launched 48 Indian satellites and 209 satellites for customers from abroad.
- Besides, the vehicle successfully launched two spacecraft – Chandrayaan-1 in 2008 and Mars Orbiter Spacecraft in 2013 – that later travelled to Moon and Mars respectively.
- Geosynchronous Satellite Launch Vehicle Mark II (GSLV Mk II) is the largest launch vehicle developed by India, which is currently in operation. This fourth generation launch vehicle is a three stage vehicle with four liquid strap-ons. The indigenously developed cryogenic Upper Stage (CUS), which is flight proven, forms the third stage of GSLV Mk II. From January 2014, the vehicle has achieved four consecutive successes.
Significance of SSLV:
- The development and manufacture of the SSLV are expected to create greater synergy between the space sector and private Indian industries – a key aim of the space ministry.
- Indian industry has a consortium for the production of PSLV and should come together to produce the SSLV as well once it is tested.
- One of the mandates of the newly-created ISRO commercial arm, New Space India Limited (NSIL) is to mass-produce and manufacture the SSLV and the more powerful PSLV in partnership with the private sector in India through technology transfers.
- Its aim is to use research and development carried out by ISRO over the years for commercial purposes through Indian industry partners.
- Small satellite launches have so far depended on ‘piggy-back’ rides with big satellite launches on the Polar Satellite Launch Vehicle (PSLV) — ISRO’s work-horse with more than 50 successful launches. As a result, small satellite launches have relied on ISRO finalising launch contracts for larger satellites.
Important Satellite Orbits
Low-earth orbits (LEO)
As implied by its name, Low Earth Orbit is relatively low in altitude ranging between 200 and 1200 km above the Earth’s surface. However, LEO is still very close to the Earth in relative terms. It is especially so when it is compared to other forms of satellite orbit including geostationary orbit.
Medium–earth orbits (MEO)
The medium earth orbits have medium range altitudes in the range of 5,000-10,000 km. They are generally used for navigation satellites. These orbits are also used for communication satellites that cover the North and South poles.
Highly elliptical orbits (HEO)
The satellites in such orbits are placed at a high altitude of more than 35790 km. It means the elliptical HEO orbits are higher when compared to both geostationary and geosynchronous orbits. Technically, circular orbits provide optimal solution for many satellites but elliptical orbits have their own advantages in certain applications. The elliptical orbit is often called the Highly Elliptical Orbit (HEO).
Geostationary satellite orbits
Such satellites orbit once a day and move in the same direction as the Earth. So, such satellites appear stationary above the same point on the earth’s surface. They can only be above the Equator and are placed at an altitude of 35,790 km. They are one of the most popular orbit formats. They have diverse applications ranging from direct broadcast to communications or relay systems.
As the height of a satellite increases, so the time for the satellite to orbit increases. At a height of 35790 km, it takes 24 hours for the satellite to orbit. This type of orbit is known as a geosynchronous orbit, i.e. it is synchronized with the Earth. One particular form of geosynchronous orbit is known as a geostationary orbit. In this type of orbit the satellite rotates in the same direction as the rotation of the Earth and has an approximate 24 hour period. This means that it revolves at the same angular velocity as the Earth and in the same direction. So, it always remains in the same position relative to the Earth. Geostationary orbit can only be over the equator. For a satellite to be stationary, it must be above the Equator.
The satellites in these orbits are placed at an altitude of 35790 km. There is a specific spot above the Earth where a satellite can match the same rotation of the Earth. This special position in high Earth orbit is known as a geosynchronous orbit.
A geosynchronous orbit synchronizes with the rotation of the Earth. More specifically, the time it takes for the Earth to rotate on its axis is 23 hours, 56 minutes and 4.09 seconds, which is the same as a satellite in a geosynchronous orbit. The geosynchronous satellites are particularly useful for telecommunications and other remote sensing applications.
While geosynchronous satellites can have any inclination, the key difference to geostationary orbit is the fact that they lie on the same plane as the equator. Geostationary orbits fall in the same category as geosynchronous orbits, but it’s parked over the equator. This one special quality makes it unique from geosynchronous orbits.
Global Positioning System (GPS) satellites are in another specific spot known as semi-synchronous orbits. While geosynchronous orbits match the rotation of Earth (24 hours), semi-synchronous orbits take 12 hours to complete an orbit. The semi-synchronous orbits are placed approximately 20,200 kilometres above the surface. This puts them in the medium Earth orbit range out of the three classes of orbits based on altitude. These orbits are nearly circular.
There are different types of satellites. Some satellites orbit the equator while others orbit from pole-to-pole. For example, Landsat, Worldview and Sentinel-2 satellites are in a polar orbit (or near-polar orbit). Almost all the satellites that are in a polar orbit are at lower altitudes. They are often used for applications such as monitoring crops, forests and even global security. Polar orbits are used for reconnaissance and Earth observation. Polar orbit satellites are also used for photography and mapping.
A polar orbit travels north-south over the poles and takes approximately an hour and a half for a full rotation. As the satellite is in orbit, the Earth is rotating beneath it. As a result, a satellite can observe the entire Earth’s surface in the time span of 24 hours. Higher altitude satellites orbit more slowly because the circumference of the circular orbit is larger. In addition, the pull of gravity is weaker at higher altitudes.
These are polar orbits which are synchronous with the Sun. A satellite in a sun synchronous orbit would usually be at an altitude of 600 to 800 km. Generally these orbits are used for Earth observation, solar study, weather forecasting and reconnaissance. This happens because the ground observation is improved if the surface is always illuminated by the Sun at the same angle when viewed from the satellite.
When a satellite has a sun-synchronous orbit, it means that it has a constant sun illumination through inclination and altitude. For sun-synchronous orbits, it passes over any given point on Earth’s surface at the same local solar time. Because of the consistent lighting in sun-synchronous orbits, scientists leverage this in various remote sensing applications.
Source: Indian Express