ISRO successfully launches 'spy satellite' RISAT-1

[Godless-Kafir]

i dont see the point in launching a spy satellite in polar sycronus orbit most of the countries are in the equatorial belt. This is only an radar imaging satellite? It would be an inefficient orbit for a spy satellite.

 

[Yusuf]

i dont see the point in launching a spy satellite in polar sycronus orbit most of the countries are in the equatorial belt. This is only an radar imaging satellite? It would be an inefficient orbit for a spy satellite.

Sir,
It has to lauched in polar axis as the earth rotates on that axis. That is how the satellite covers all of the globe.

To get a (close to) global coverage with such a relatively low orbit it has to be polar or at least close to polar. As such a rather low orbit will have an orbital period of roughly 100 minutes the Earth will rotate around its polar axis with about 25 deg between successive orbits with the result that the ground track is shifted towards west with these 25 deg in longitude.

 

[Dovah]

Well done ISRO.

 

[Ray]

Spy Satellites

Spysats and military communications satellites dominate space from 600 to 1,200 miles altitude. The spysats gather electronic intelligence (ELINT), signal intelligence (SIGINT) and radar intelligence (RADINT). Hamsats also operate there.

Science research satellites do much of their work at altitudes between 3,000 and 6,000 miles above Earth. Their findings are radioed to Earth as telemetry data.

From 6,000 to 12,000 miles altitude, navigation satellites operate. Best known are the U.S. global-positioning system (GPS) and Russia's equivalent GLONASS satellites.

As described above, the so-called Clarke Belt is the region of space 22,300 miles above Earth where satellites seem stationary above the rotating Earth. Best known occupants of the Clarke Belt are the many domestic and international TV broadcast, weather reporting and communications satellites.

Space Today Online - Answers To Your Questions

 

[Ray]

A polar orbit is an orbit in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Sun) on each revolution. It therefore has an inclination of (or very close to) 90 degrees to the equator. Except in the special case of a polar geosynchronous orbit, a satellite in a polar orbit will pass over the equator at a different longitude on each of its orbits.

Polar orbits are often used for earth-mapping, earth observation, and reconnaissance satellites, as well as for some weather satellites. The Iridium satellite constellation also uses a polar orbit to provide telecommunications services. The disadvantage to this orbit is that no one spot on the Earth's surface can be sensed continuously from a satellite in a polar orbit.

It is common for near-polar orbiting satellites to choose a sun-synchronous orbit: meaning that each successive orbital pass occurs at the same local time of day. This can be particularly important for applications such as remote sensing of the atmospheric temperature, where the most important thing to see may well be changes over time, which you do not want to see aliased onto changes in local time. To keep the same local time on a given pass, it is desirable for the orbit to be as short as possible, which is to say as low as possible. However, very low orbits of a few hundred kilometers would rapidly decay due to drag from the atmosphere. A commonly used altitude is approximately 1000 km; this produces an orbital period of about 100 minutes.[1] The half-orbit on the sun side then takes only 50 minutes, during which local time of day does not greatly vary.

To retain the sun-synchronous orbit as the Earth revolves around the sun during the year, the orbit of the satellite must precess at the same rate. Were the satellite to pass directly over the pole, this would not happen. But because of the Earth's equatorial bulge, an orbit inclined at a slight angle is subject to a torque which causes precession; it turns out that an angle of about 8 degrees from the pole produces the desired precession in a 100 minute orbit.

A satellite can hover over one polar area a large part of the time, albeit at a large distance, using a polar highly elliptical orbit with its apogee above that area. This is the principle behind a Molniya orbit.

Polar orbit - Wikipedia, the free encyclopedia

 

[Kesang]

We can rely on ISRO.

 

[utubekhiladi]

Not a spysat, but Risat can do surveillance: Isro

CHENNAI: India's space horse Polar Satellite Launch Vehicle (PSLV) proved its might for the 20th time in a row on Thursday, with PSLV- C19 injecting India's first indigenous microwave Risat into orbit nearly 18 minutes after blastoff from the Sriharikota launch pad. At 1858kg, Risat I is the heaviest payload carried by PSLV so far.

Prime Minister Manmohan Singh lauded the launch and the department of space. He had on Wednesday told Parliament that the C-band radar can "image various parts of the country, including border areas". To queries if India had launched a spy satellite, Isro chief Radhakrishnan said, "This is not a spy satellite." But he added that the satellite can "do day and night surveillance which optical sensing satellites cannot. Optical sensing satellites use illumination from the sun to take images of earth. So those satellites cannot be used at night or during bad weather."

Risat I is to be followed by a geoimaging satellite (Gisat) that will provide "near real-time pictures of large areas". Risat I will transmit pictures only during passage over India, while Gisat will deliver data on "areas of interest...sector wise imaging every five minutes and entire Indian land surface every 30 minutes at a 50 metre resolution".

"This is a grand success," said Isro chairman K Radhakrishnan. "The satellite reached an orbit of 470km-480km as targeted. In the next three days, it will be pushed to an altitude of 536km and will soon enter a polar sun-synchronous orbit," he said.

Soon after the satellite separated from the rocket, the solar panel was deployed and the 6m synthetic radar antenna panel weighing 230kg opened. "It is pointing to the earth," Radhakrishnan said. "It will start sending images from May 1."

Risat I will also be used for agriculture imaging and to study floods. "It will be useful because some parts of the country are perennially cloudy and flooded. The satellite can give an estimation of the area under cultivation and flood within one hour of the calamity. It can also provide details of soil moisture, forest biomass, coral reef and other geological aspects," said the Isro director. The satellite can cover the entire globe.

The satellite will supplement results of the Israel-made Risat II, which has been sending data since April 2009. Information from remote sensing satellites is used by different government agencies. Now, such information will be available to users within an hour of an image being taken while earlier, the data used to be available only 21 days later.

Isro rakes in Rs 45 crore per year through information-sharing with other government departments. More than 80,000 pages of data are downloaded by authorized users every year. Radhakrishnan said the satellite cost Rs 378 crore, while PSLV cost Rs 110 crore.


Not a spysat, but Risat can do surveillance: Isro - The Times of India

 

[pmaitra]

 

[Godless-Kafir]

Sir,
It has to lauched in polar axis as the earth rotates on that axis. That is how the satellite covers all of the globe.

To get a (close to) global coverage with such a relatively low orbit it has to be polar or at least close to polar. As such a rather low orbit will have an orbital period of roughly 100 minutes the Earth will rotate around its polar axis with about 25 deg between successive orbits with the result that the ground track is shifted towards west with these 25 deg in longitude.

The satellite will orbit from south pole to north pole covering areas like artic and antartic. We have no intrest in those areas. The orbit circleing the tropic of cancer is where most of the nations including usa,china,india,pakistan are.

 

[Yusuf]

The satellite will orbit from south pole to north pole covering areas like artic and antartic. We have no intrest in those areas. The orbit circleing the tropic of cancer is where most of the nations including usa,china,india,pakistan are.

Please understand that if you put it in the direction you are saying, it will cover only on strip of earth which is equator. The satellite does not zig zag in space. The poles that form a few minutes a day of the entire mission. Please read 100mins is the time to make one revolution around the earth.

The earth rotates like this. That is why satellite is place in polar orbit.

This gives it global coverage.

To have say coverage of just one area which would be a waste of a satellite, we will have to put a satellite in geostationary orbit 36,000km up

 

[pmaitra]

Both have their own advantages. Geo-Synchronous orbits allow a satellite to focus on one region, for example a military base, always, but are expensive to launch because they have to go much higher, and needs very powerful rockets. Polar orbits are much lowers, and are easy to launch with relatively weaker rockets, can survey the entire earth, but cannot focus on any place all the time. At lower orbits, the angular, and consequently, the orbital velocity can be increased, but then, the faster it travels, the less accurate the photographs and telemetry data become.

 

[nitesh]

cross post: in the final orbit

Welcome To ISRO :: Press Release :: April 28, 2012

 

[Son of Govinda]

Indian rocket successfully launches Risat-1 satellite

Indian rocket successfully launches Risat-1 satellite - Times Of India

SRIHARIKOTA : On an early Thursday morning, an Indian rocket successfully launched into orbit a microwave Radar Imaging Satellite (Risat-1) from the spaceport here in Andhra Pradesh, around 80 km from Chennai.

The indigenous Risat-1, with a life span of five years, would be used for disaster prediction and agriculture forestry and the high resolution pictures and microwave imaging could also be used for defence purposes as it can look through the clouds and fog.

At exactly 5.47 a.m., the rocket - Polar Satellite Launch Vehicle C19 (PSLV-C19) - standing 44.5 metres tall and weighing 321 tons and with a one-way ticket, hurtled towards the skies ferrying the 1,858 kg Risat-1 after unshackling itself from launch pad No.1.

With a rich orange flame at its tail and a plume of white smoke, the rocket ascended towards the blue sky amidst the resounding cheers of Isro scientists and media team assembled at the launch centre.

People perched atop nearby buildings too happily clapped as PSLV-C19 went up.

Space scientists at the new rocket mission control room of the Indian Space Research Organisation (Isro) were glued to their computer screens watching the rocket escaping the earth's gravitational pull.

The Isro-made Risat-1 is the heaviest luggage so far ferried by a PSLV since 1993.

At around 17 minutes into the flight, PSLV-C19 delivered Risat-1 into a polar circular orbit at an altitude of 480 km and an orbital inclination of 97.552 degrees.

Isro, with its network of ground stations, monitored its health.

"PSLV-C19 mission is a grand success. This is the 20th successive successful flight of PSLV. India's (indigenously built) first radar imaging satellite was injected precisely into orbit," Isro chairman K. Radhakrishnan said after the launch.

For Isro, this is the first launch this fiscal as well as in the calendar year.

Remote sensing satellites send back pictures and other data for use. India has the largest constellation of remote sensing satellites in the world providing imagery in a variety of spatial resolutions, from more than a metre ranging up to 500 metres, and is a major player in vending such data in the global market.

With 11 remote sensing/earth observation satellites orbiting in the space, India is a world leader in the remote sensing data market. The 11 satellites are TES, Resourcesat-1, Cartosat-1, 2, 2A and 2B, IMS-1, Risat-2, Oceansat-2, Resourcesat-2 and Megha-Tropiques.

Risat-1's synthetic aperture radar (SAR) can acquire data in C-band and would orbit the earth 14 times a day.

In 2009, Isro had launched 300 kg Risat-2 with an Israeli built SAR enabling earth observation in all weather, day and night conditions.

With Thursday's launch the PSLV rocket has launched successfully 53 satellites out of 54 it carried - majorly remote sensing/earth observation satellites both Indian and foreign - and has been a major revenue earner for Isro.

The one failure happened in 1993 when the satellite was not able reach the orbit.

The rocket that delivered Risat-1 in the space is Isro's four stage PSLV's upgraded variant called PSLV-XL.

The letters XL stand for extra large as the six strap-on motors hugging the rocket at the bottom can carry 12 tonnes of solid fuel as against the base version that has a fuel capacity of nine tonnes.