Indian Regional Navigation Satellite System: Analysis & Insights

September 18, 2013 1:24 pm

I am happy to write that India has initiated the implementation of its own Navigational Satellite System named Indian Regional Navigation Satellite System. This means that India will soon have its own positioning and tracking systems actively implemented in the military and civilian establishments in and around India.
Having sat through the orbital mechanics, attitude dynamics, space propulsion and spacecraft design classes at Mississippi State University, I am more than eager to analyze the IRNSS based on what I’ve learned and make an attempt to look into the possible opportunities that the IRNSS may provide along with the challenges it may face.

Given below is a figure which is my conception of how IRNSS would be (This is a Ground Track or 2D plot of Path traced by the satellites as per the information given above, simulated using STK):

IRNSS: Ground Track (Simulated in STK)

IRNSS Life Expectancy

Any constellation of satellites tends to have a definite life expectancy with respect to their primary mission objectives. Apart from the primary mission objectives, the satellites individually have a definite operational life depending on various factors. Now the life of a constellation is the minimum life of the constituting satellites, orbit wise or operation wise. In other words, the constellation is said to be alive as long as the satellites are alive and looking at where they are supposed to be looking at.

The reality of natural forces such as the earth not being a perfect sphere, the earth’s gravitational sphere of influence being non-uniform and constant movement of earth’s neighboring bodies( moon, planets and so on) tend to impart a condition on any satellite that is otherwise called orbital-decay.

Orbital Decay may result in the reduction in orbit altitude, satellites swaying away from their target locations or any other orbital transformation that may be beyond the scope of orbital corrections or station-keeping. Estimating such orbital decay would give us an approximate timeline of the viability of the satellites, with respect to their mission objectives.

I wanted to see how long the IRNSS would last mission-objective wise and used STK to estimate the orbital decay of IRNSS constellation.

The geostationary satellites oscillate (very minutely) in the north-south direction and the geosynchronous satellites make a longitudinal shift towards the left by approximately 40o that may otherwise be a distance of approximately 4500 km on the surface of the earth. This is a considerable shift that clearly indicates that at least 2 of the 4 geosynchronous satellites would go out of range from the target area. The leftward shift may not necessarily be a unidirectional shift as the simulation is based on orbit parameters that include my assumptions and the perturbation component is J4 which is quite discreet in its own way. More than the direction of the shift made by the ground-track, it the amplitude that seems interesting to note. If such a large variation is set to occur with very few disturbances included, the real time decay of the orbits may be much beyond what this simple simulation has captured.

To get a more realistic view of orbital decay, I decided to simulate the recently launched satellite IRNSS-1A alone using the TLE data available, so that we can have a look at a simulation based on the inputs from real time satellite tracking data.

This simulation’s significant feature is the “swaying” of the geosynchronous orbit, measuring little over 40o in longitude or a surface distance of 4500-5000km. This is quite similar to the “swaying” captured in the previous simulation shown in Video.1.

The “swaying” of the geosynchronous orbit of IRNSS-1A indicates that a steady station-keeping responsibility is to be shouldered in order to keep the tracking/positioning process with minimum error propagation. This really matters because the error propagation in the tracking/positioning process would directly impact the direction shown on a display device on earth (the GPS unit that we use). The more the error, the higher will the pointing errors in the device, ultimately confusing the user. The error correction does involve a considerable amount of signal processing from the ground-based segments of IRNSS but it is always better to avoid as much error as possible so as to keep the error-correction minimal and accurate.

My Choice of IRNSS Constellation Configuration

IRNSS Constellation Configuration

It has to be noted that, for two satellites to be above and below the equator at the same time looking over India, the two geosynchronous orbits need to be inclined to the equator such that one of them should be indicated with a negative angle for inclination (for the sake of symmetry) such as 29o and -29o. Now, negative inclination is just a mathematical indication of the downward inclination the orbit might have with respect to the equator. In real terms the inclinations of the orbits may be 29o and 151o. The launch costs may increase but if the cost of positioning service at the error-correction/ground-based processing stage is reduced with expensive launches (lift-off and delta-V burns), then I would consider that a valuable and sensible investment as the whole purpose of the program is to create an effective positioning service to be used by the military and civilian population of India and possibly by those in the surrounding regions. Also largely varying elevation and azimuth angles of satellites would mandate a strongly regulated ground-based tracking system that has the flexibility and economic frugality to accommodate the data coming in from far away directions at the same time. I would suggest deploying separate ground stations dedicated for the IRNSS so as to avoid over-use of available resources and also keep the positioning service devoid of complications that may arise out of sharing transceiver resources.

Anomalies Noticed So Far

I am not really sure about this but from what I know the official releases have claimed that IRNSS-1A has been launched into an inclined geosynchronous orbit with an inclination of 29o. I have been using publicly available internet resources to track IRNSS-1A and the data that I have collected do not corroborate the officially released data.

I downloaded the TLE data of IRNSS-1A, some of which is given below:

TLE downloaded sometime around the end of July, 2013:
1 39199U 13034A 13218.60084382 .00000094 00000-0 10000-3 0 244
2 39199 027.0423 140.5285 0019429 182.2365 263.8787 01.00275460 565

TLE Downloaded around middle of Aug, 2013:
1 39199U 13034A 13227.33681052 .00000000 00000-0 10000-3 0 327
2 39199 027.0503 140.3669 0019595 184.2844 175.6837 01.00274917 647

TLE Downloaded on 29th, Aug, 2013:
1 39199U 13034A 13240.13145032 .00000088 00000-0 10000-3 0 363
2 39199 027.0586 140.1274 0019230 182.8373 115.8814 01.00269935 774

The 9th to 16th characters in the second line of Two Line Element set, indicate the inclination of the satellite’s orbit and in the case of IRNSS-1A, whose TLE data is given above, shows that as of 29th August, 2013, IRNSS-1A is in an orbit that is inclined at 27o with the equator. This is 2 degrees lesser than that is officially released (29o). A difference of 2 degrees in inclination seems mathematically small but in space-terms, missing the target orbit by 2 degrees is colossal mission failure that would impact the entire constellation configuration and operational effectiveness of the IRNSS. There is always room for correction and optimization, but the failure to meet the planned targets would remain a reality.

Opportunities provided by IRNSS

A whole world of opportunities would be open to India with the IRNSS including, elementary terrestrial, aerial and marine navigation that may be used by the defense establishments. The civil applications mean more than anything in my view. With the help of a dedicated navigational system in place, the civilian population will get a viable access to what is popularly called as vehicle tracking and fleet management. The Indian fishermen along the coast of Tamilnadu and Kerala, who are currently left vulnerable to firing and arrests by the Sri Lankan Coast Guard for crossing maritime border will get an opportunity to track their location with respect to the border that they do not want to cross. Most importantly, they will get a concrete scientific method to prove their innocence with regards to their not crossing the borders. The implementation however requires the administration to issue the tracking devices that may be installed in all the fishing boats. The tracking data will be recorded on a timely basis and the administration will have an eye on all the fishermen who go out into the waters. Anyone who is nearing the borders can we warned about it and the data can be shared with neighboring countries so that both countries would know whose boat is located how far from their respective maritime borders. This way any case of arrests/firing may be dealt with the analysis of this tracking information recorded and be used to resolve conflicts. This will empower the fishermen to scientifically prove in cases where they encountered firing/arrests, without crossing the maritime borders. The administrations too cannot claim trespassing without any tracking data that may suggest fishing boats have crossed the maritime borders. One press of a button and the shore-station would get the distress call from the fisherman who is suspecting an attack or arrest from neighboring coast guard ships. One bright glow and loud alarm from the tracking device on the fishing boat can alert the fisherman if he is about to cross the maritime border. All the legitimate boats will have a designated tracking device and therefore identifying pirate vessels from harmless fishing vessels would become a reality. The solution to such sea-based border issues however require the strict implementation of such tracking information in the marine industries, especially fishing. With IRNSS in action, the administration need not view the cost of renting out other navigational systems as an administrative burden.

The average Indian would have access to finding routes within India and traveling by self would become more safe and comfortable. The defense establishments would have accurate tracking systems to help them during military operations along the disputed borders, more importantly without having to depend on international administrations.

Challenges for IRNSS

The configuration of IRNSS calls for reliable satellites since, this constellation operates on a minimum number of satellites from the navigational standpoint. For an accurate positioning on earth, at least 4 satellites are required. With 3 geostationary and 4 geosynchronous, the constellation cannot afford to have any satellite system/sub-system failure. Losing one satellite means losing precise tracking in one region of the IRNSS target area. The IRNSS constellation, from the systems engineering point of view, is yet to add the element of redundancy for reliability. This may be due to cost restrictions but having an expensive system so vulnerable actually makes the investment very risky. In future, I would like to see more satellites operating over regions already covered by these 7 satellites, such that, if one of the satellites fails, the system’s functionality does not get compromised. The back-up satellites are an additional cost but their presence means prolonged “system-survivability” and in case of no failures, added positioning accuracy. The additional satellites may be used for military operations unless there is a need for a civilian deployment in case of a failure.

One more area to look into while considering add-on satellites is constellation optimization methods that can help estimate and determine satellite positions in existing and new orbits so as to enable the reliability and extended lifetime of mission objectives.

The STK simulations show that the IRNSS-1A goes through a one-hour eclipse almost every day, with the eclipse timing ranging from 0.3 to 1.3 hours. The average is around 1 hour. Now the satellite is powered with a 90 ampere-hour lithium battery and solar panels that have a capacity of 1.6 kW. Regular discharge and recharging of batteries do impact the battery lifetimes and the satellite should not be rendered useless because of a failed battery given that apart from the payload, other sub-systems of the satellite depend on the battery power too. The chances may be rare but when electrically operated attitude-control maneuvers and payload activity clash during an eclipse time, the satellite goes into a peak demand state and a repetitive exposure to such peak-demand situations may impact the battery negatively. The subsystem with the shortest life-span would be the life-span of the entire satellite and it definitely should not be the power system i.e., the solar panels and battery-pack.

I had a great time looking into the details of IRNSS and its first satellite IRNSS-1A. While preparing for this post, I got an opportunity to work with Systems Took Kit (STK), previously known as Satellite Tool Kit (about 5 years back). I sincerely hope IRNSS becomes a success in terms of real-world applications in India, helping the military and civilian population alike. Thanks to whoever pitched the idea of Indian Regional Navigational Satellite System. I am sure there is so much to this system than what we have explored so far and I would look for more to learn about it as the system is realized in due course.

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