The Indian Space Research Organisation (ISRO) successfully launched the SSLV-D2 rocket on Friday morning. The rocket placed three satellites into the orbit shortly after it’s launch from Andhra Pradesh’s Sriharikota.

“Mission accomplished”, ISRO tweeted after the SSLV-D2 rocket whizzed through the sky from the launch pad at the Satish Dhawan Space Centre at exactly 9:18 am today morning. The rocket, during its 15 minute flight, carried one each of a mini, micro and a nano satellite, that it successfully placed into the 450 km circular orbit around the Earth.

After the successful launch, ISRO announced on twitter: “Mission is accomplished successfully. SSLV-D2 placed EOS-07, Janus-1, and AzaadiSAT-2 into their intended orbits.”

The three satellites placed into their respective orbits by the rocket are ISRO’s EOS-07, US-based firm Antaris’ Janus-1 and Chennai-based space start up SpaceKidz’s AzaadiSAT-2, an 8.7 kg satellite developed by 750 girl students from across India.

This was second developmental flight of Small Satellite Launch Vehicle (SSLV) by ISRO with the space agency carrying out the first test on August 9, last year which had partially failed. The first SSLV had failed to inject its satellite payload in their intended orbits.

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ISRO’s SSLV are intended to cater to the emerging small and microsatellite commercial market and launch up to 500 kg satellites to low earth orbits on ‘launch-on-demand’ basis.

The SSLV provides low-cost access to space, offers low turn-around time and flexibility in accommodating multiple satellites, and requires minimal launch infrastructure.

An investigation into the failure of SSLV-D1 by ISRO revealed that the mission failed after the upper stage of the launch vehicle injected the satellite into a highly elliptical unstable orbit due to a shortfall in velocity.

It also revealed that there was a vibration disturbance for a short duration on the Equipment Bay (EB) deck during the second stage separation.  The vibration affected the Inertial Navigation System (INS), resulting in declaring the sensors faulty by the logic in the Fault Detection & Isolation (FDI) software.

The failure detection logic identified a degraded accelerometer and isolated it for improved mission performance.

During the second stage separation, all six accelerometers experienced measurement saturation due to high vibration levels for a short duration.  This malfunction initiated a salvage mode with the purpose of saving the mission, but it could not inject the satellite into a safe orbit.

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~By Dinesh C Sharma

NavIC, India’s very own navigation satellite system, is projected to provide positioning and navigation services on the lines of US-owned Global Positioning System (GPS). However, a new study has warned that signals from NavIC satellites may interfere with WiFi signals in receivers.

The Indian navigation and positioning system consists of a constellation of seven satellites launched by the Indian Space Research Organisation (ISRO) between 2013 and 2018. The technology is likely to be available on smartphones and car navigation systems in future.

The NavIC satellites send signals in frequency bands of L5 (1176.45 MHz) and S-band (2492.08 MHz).  S-band is utilized by NavIC for navigation systems, but the same band is also shared by other communication systems like Long-Term Evolution (LTE), Bluetooth and Wireless Fidelity (Wi-Fi).

The study says that NavIC signals get affected by  out of band interference due to Wi-Fi signal as the two are located closely. It found that “NavIC reception on S-band frequency is severely affected by Wi-Fi transmission.”

“These interfering signals present a threat to the NavIC receiver performance. To equip both the facilities (WiFi and NavIC) in future cell phones, it will be a challenge to mitigate such kind of radio frequency interference,” says the study published in journal Current Science. The study was done by Dr Shweta N Shah of Electronics Engineering Department at Sardar Vallabhbhai National Institute of Technology, Surat, and Ph D scholar Darshna D Jagiwala. ISRO’s Ahmedabad-based Space Applications Centre (SAC) provided necessary equipment for the study.

Explaining the findings, Dr Shah told India Science Wire that “NavIC has S band signals and there are much stronger terrestrial S band signals that can pose problem for S band and dual frequency Standard Positioning Service (SPS) receivers of NavIC if not addressed properly.”

Currently, she said “Wi-Fi receivers are present in every cell phone. That’s why it was necessary to study Wi-Fi interference to verify the performance of NavIC signal reception in cellphones. This kind of interfering signal represents a threat to the performance of the NavIC receivers.”

In the experimental set up having both types of receivers, it was found that a part of the S-band of NavIC system overlaps the unlicensed band which is shared by other communication technologies like Bluetooth, Wi-Fi and Industrial Scientific Medical (ISM) bands. When the frequency channel of Wi-Fi was superimposed with the frequency of the S-band signal of the NavIC receiver, interference was observed in S-band signal of NavIC receiver due to the extremely low power level of the signal at the user’s receiver.

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Wireless experts feel radio frequency interference between NavIC and other bands may pose regulatory challenges, besides quality of services. In India, Wi-Fi signals are exempted from licensing in the frequency band 2400 – 2483.5 MHz. This means the usable part of any Wi-Fi system or channel India must be contained within 2483.5 MHz.

“Residual or unintended signals normally go beyond this limit due to the basic characteristic of digital emissions. The NavIC signal is centered at 2492.08 MHz with a bandwidth of ± 8.25 MHz. This means that the lower part of NavIC signal can get interference from residual / unintended signals of Wi-Fi systems. Also, the upper part of the NavIC signal goes beyond 2500 MHz and since the frequency band above 2500 MHz is used for other purposes, NavIC receivers can pick up signals (and receive interference) from such other systems operating above 2500 MHz,” explained Pawan Kumar Garg, former Wireless Advisor, Government of India, while speaking to India Science Wire.

“To reduce interference from Wi-Fi (below 2483.5 MHz) as well as systems operating above 2500 MHz, it is desirable that the NavIC receivers should use reduced bandwidth of ± 7.5 MHz, if possible, and with sharp cut off filters on both ends,” Garg added. (India Science Wire)

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Indian agency sends into orbit highest number of satellites ever launched in a single mission

Till date, the highest number of satellites launched in a single mission so far was 37, a record that Russia set in 2014. The US space agency, NASA, had launched 29. On February 15, the Indian space agency, ISRO, created history with its incomparable Polar Satellite Launch Vehicle setting into orbit 104 satellites at one go.

In its 39th flight from the space centre at Andhra Pradesh’s Sriharikota, it launched the 714 kg Cartosat-2 series satellite for earth observation at the end of a 28-hour countdown. The rocket also carried 103 co-passenger satellites, together weighing about 664 kg at lift-off.

“This day shall go down as a landmark in the history of our space programme,” president Pranab Mukherjee tweeted. “Congratulations to @isro for the successful launch of PSLV-C37 and CARTOSAT satellite together with 103 nano satellites!” prime minister Narendra Modi tweeted.

Within 20 minutes of the launch, the satellites settled into orbit. Of the 103 co-passenger satellites or nano-satellites, only two are Indian—ISRO’s INS-1A and INS-1B. 

The 101 international nano-satellites were launched as part of commercial arrangements between Antrix Corporation Limited, ISRO’s commercial arm, and the international customers. There was one satellite each from Israel, Kazakhstan, the Netherlands, Switzerland and United Arab Emirates and 96 from the USA.

“We are not looking at it as a record or anything like that; we are just trying to maximise our capability with each launch, in trying to utilise that launch for the ability it has got and getting the maximum return,” ISRO chairman AS Kiran Kumar said.

The Cartosat-2 series satellite, with a mission life of five years, will send images that would facilitate coastal land use and regulation, road network monitoring, distribution of water, creation of land use maps, etc.

Way to go, ISRO!

Compiled by Sucheta Dasgupta

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