(GIST OF SCIENCE REPORTER) ISRO’s Maiden SSLV Mission

[November-2022]

ISRO’s Maiden SSLV Mission

The Indian Space Research Organisation (ISRO) planned an inaugural flight of its new Small Satellite Launch Vehicle (SSLV), which ran into rough weather.

Small Satellite Launch Vehicle

Small Satellite Launch Vehicle (SSLV) is the new launch vehicle of ISRO. It has been developed to lift small satellites (mini, micro or nano satellites 10 to 500 kg) at low cost with quick turnaround time for commercial launch as compared to Polar Satellite Launch Vehicle (PSLV). It has a payload capacity of up to 500 kg at 45° inclination to a 500-km low Earth orbit or 300 kg to a 500-km altitude sun-synchronous polar orbit. The vehicle can carry different combinations of CubeSats, and micro or mini-satellites into orbit.
The vehicle is also capable of supporting multiple orbital drop-offs, launch-on-demand flexibility under minimal infrastructure requirements. The initial developmental cost of the vehicle was around ₹170 crore, and subsequently cost per launch is estimated about ₹30 crores. This is sharp contrast to the cost per launch of PSLV at about ₹200 crore.
SSLV is a three-stage solid propellant vehicle along with Velocity-Trimming Module (VTM). The satellite injection into precise orbit is achieved through terminal stage VTM. Some new features include: expandable bellow based circular separation system for second stage; super capacitors for powering pyro systems, O-give composite payload fairing with co-cured cork thermal protection system, and liquid propulsion based terminal stage VTM. In addition, SSLV has miniaturized low-cost avionics with commercial-off-the shelf (COTS) components, low cost NavIC integrated inertial navigation system, onboard checkout computer with minimum ground interfaces.
The first stage SS1 is the third largest solid booster of ISRO, containing 87 tons of solid fuel. The second stage, SS2 contains 7.7 tons of solid fuel. While the third stage, SS3, is a new composite upper stage solid motor containing 4.5 tons of solid fuel.
The VTM on top of the SSLV contains 0.05 tons of the hypergolic liquid fuel. VTM is equipped with 16 MMH/MON3 thrusters, each capable of producing 50 N of thrust. Eight 50 N thrusters are utilized for reaction control systems to change the stage’s orientation in space, while the other eight are used as axial thrusters for changing velocity that can alter the stage’s orbit. VTM provides roll control for the second and third stages and also has the ability to inject multiple payloads into different orbits.
The SSLV has been developed with the sole purpose of launching small satellites to meet the demand of the burgeoning space sector, while India’s workhorse Polar Satellite Launch Vehicle (PSLV) will be spared for bigger missions.
SSLV is a much simpler version of PSLV. It provides low-cost access to space ondemand basis. It is ready to transfer vehicles with modular and unified systems and standard interfaces for end-to-end industrial production. The SSLV rocket can be manufactured in about a week’s time, and it will take just 72 hours to set up, with a team of six people. By contrast, the PSLV requires a much larger team and over 60 days of lead time to be ready for a mission.
The SSLV program is scheduled to fly three development launches (D1, D2, D3) before ISRO’s commercial arm, NewSpace India Limited (NSIL), takes up the flights for customers. The second development launch is scheduled for late 2022 and the third launch in the second quarter of 2023. A dedicated Small Satellite Launch Complex (SSLC) will be set up at Sriharikota, and a new launch site is planned at Kulasekarapattinam in Tamilnadu for sun-synchronous polar launches. From this new launch site, SSLV will fly on a trajectory that avoids Sri Lanka and the need for a “dogleg” manoeuvre, which is required for launches from Sriharikota. The other contemporary launch vehicles to SSLV are Minotaur I (US), Start-1 (Russia) and Kuaizhou (Chinese).

The Payloads:

The primary payload for SSLV D-1 is EOS-02 and the copassenger was AzaadiSAT.
EOS-02: EOS-02 (formerly known as Microsat-2A) was a small experimental earth observing satellite developed by ISRO as a test payload for the maiden SSLV launch. The satellite carried two payloads: a mid-wavelength and a long-wavelength infrared (MWIR & LWIR) camera with a 6m ground resolution. EOS-02 was intended to meet the increasing user demands for cartographic applications, urban and rural management, coastal land use, utilities mapping, and various other GIS applications.
The EOS-02 was configured around a cuboid 552x600x600 mm, ISRO’s standard Small Satellite Bus-1 (SSB-1). The structural construction was of aluminium honeycomb with a total mass of 145 kg. All payload elements were accommodated on the top deck. The spacecraft carried two deployable solar panels generating 350 W power and batteries for power storage. The satellite had a 10-month design life. It was to be placed in a 356 km low earth circular orbit.

AzaadiSAT:

AzaadiSAT was an 8-Unit CubeSat structure weighing around 8 kg. It carried 75 different payloads each weighing around 50 g and conducting femto-experiments (experiments of small size). The payloads include a UHF-VHF transponder working in ham radio frequency to enable voice and data transfer for amateur radio operators, a solid-state PIN diode-based radiation counter to measure the ionizing radiation in its orbit. It also had a long-range communication transponder and a selfie camera to click pictures of its own solar panels. The ground station developed by ‘Space Kidz India’ was to be utilized for receiving the data from the spacecraft. The AzaadiSAT’s mission life was expected to last six months.
The significance of this project was to mark the 75th anniversary of Independence. The satellite was built by 750 girl students (predominantly class 8-12), 10 each from 75 rural schools across India. Space Kidz India (SKI) developed the basic and simple experiments that enabled students to learn
the fundamentals of spaceflight, and integrated the spacecraft parts with support of their teachers and SKI’s online coaching. This was a first of its kind ‘All women space mission’ as part of promotion of this year’s UN theme “Women in Space”.

What Went Wrong?

All events up to the velocity trimming module ignition, viz., SS1 ignition, SS2 ignition, SS1 separation, S2C separation, SPLF separation, SS2 separation, SS3 ignition, and SS3 separation went well as expected. The problem seems to be at the SSLV’s terminal stage VTM. As per the launch profile, the VTM was supposed to have burnt for about 20 seconds at 653 seconds after launch. However, it burnt for only 0.1 seconds, denying the rocket of the requisite altitude boost.
Both the satellites onboard SSLV D-1, the primary EOS- 2 and the secondary AzaadiSAT were separated from the vehicle with the VTM burn. The injected spacecraft, however, missed their intended orbital trajectories, and entered into a 356 kmx76 km elliptical orbit instead of 356 km circular orbit. The satellites were no longer stable at a much lower perigee of 76 km, and fell to the Earth due to atmospheric drag. At first sight, this deviation appears to be due to a sensor fiasco in the VTM phase and mission software logic failed to identify and correct it.
A committee would analyse it and recommend the appropriate corrective action. ISRO will come back soon with SSLV-D2 after implementation of the committee’s recommendations.