ISRO preps for re-entry experiment of decommissioned satellite on March 7
Bengaluru ( PTI): The Indian Space Research Organisation (ISRO) is preparing for a challenging experiment of controlled re-entry of a decommissioned low earth orbit satellite, Megha-Tropiques-1 (MT1), into the earth's atmosphere on March 7.
MT1 was launched on October 12, 2011, as a joint satellite venture of ISRO and French space agency CNES for tropical weather and climate studies.
Although the mission life of the satellite was originally three years, the satellite continued to provide valuable data services for more than a decade supporting regional and global climate models till 2021, the Bengaluru-headquartered space agency noted in a statement on Sunday.
UN/IADC (Inter-Agency Space Debris Coordination Committee) space debris mitigation guidelines recommend deorbiting a LEO (Low Earth Orbit) object at its end-of-life (EOL), preferably through controlled re-entry to a safe impact zone, or by bringing it to an orbit where the orbital lifetime is less than 25 years, according to ISRO.
It is also recommended to carry out "passivation" of on-board energy sources to minimise the risk of any post-mission accidental break-up.
The orbital lifetime of MT1, weighing about 1,000 kilograms, would have been more than 100 years in its 20 degree inclined operational orbit of 867 km altitude. About 125 kg on-board fuel remained unutilised at its end-of-mission that could pose risks for accidental break-up.
This leftover fuel was estimated to be sufficient to achieve a fully-controlled atmospheric re-entry to impact an uninhabited location in the Pacific Ocean.
Controlled re-entries involve deorbiting to very low altitudes to ensure impact occurs within a targeted safe zone.
Usually, large satellites/rocket bodies which are likely to survive aero-thermal fragmentation upon re-entry are made to undergo controlled re-entry to limit ground casualty risk. However, all such satellites are specifically designed to undergo controlled re-entry at EOL.
MT1 was not designed for EOL operations through controlled re-entry which made the entire exercise extremely challenging.
Furthermore, the on-board constraints of the aged satellite, where several systems had lost redundancy and showed degraded performance, and maintaining subsystems under harsher environmental conditions at much lower than originally designed orbital altitude added to the operational complexities.
Innovative workarounds were implemented by the operations team based on the study, deliberations, and exchanges among the mission, operations, flight dynamics, aerodynamics, propulsion, controls, navigation, thermal, and other subsystem design teams across the ISRO centres, which worked in synergy to surmount these challenges.
An uninhabited area in the Pacific Ocean between 5 degrees south to 14 degrees south latitude and 119 degrees west to 100 degrees west longitude was identified as the targeted re-entry zone for MT1.
Since August 2022, 18 orbit manoeuvres were performed to progressively lower the orbit. In between the de-orbiting, aero-braking studies at different solar panel orientations were also carried out to gain better insights into the physical process of atmospheric drag affecting the orbital decay of the satellite.
The final de-boost strategy has been designed after taking into consideration several constraints, including visibility of the re-entry trace over ground stations, ground impact within the targeted zone, and allowable operating conditions of subsystems, especially the maximum deliverable thrust and the maximum firing duration of the thrusters.
The final two de-boost burns followed by the ground impact are expected to take place between 16.30 hours to 19.30 hours on March 7.
Simulations show that no large fragments of the satellites are likely to survive the aerothermal heating during the re-entry.
"As a responsible space agency committed to safe and sustainable operations in outer space, ISRO proactively takes efforts for better compliance with the UN/IADC space debris mitigation guidelines on post-mission disposal of LEO objects," the statement said.
The re-entry experiment of MT1 has been undertaken as a part of the ongoing efforts as this satellite with sufficient leftover fuel presented a unique opportunity to test the relevant methodologies and understand the associated operational nuances of post mission disposal by direct re-entry into the Earth's atmosphere, it was stated.
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India is amazing from space, for sure going back to my father's home country: NASA astronaut Sunita
New York (PTI): India is amazing from space, NASA astronaut Sunita Williams said and voiced optimism that she will visit her “father's home country” and share experiences about space exploration with people there.
Williams was responding to a question on how India looked from space when she was in the International Space Station and on the possibility of her collaborating with the Indian Space Research Organisation (ISRO) on space exploration.
"India is amazing. Every time we went over the Himalayas, and I'll tell you, Butch got some incredible pictures of the Himalayas. Just amazing,” Williams said.
The 59-year-old NASA astronaut and fellow astronaut Butch Wilmore addressed reporters at their first joint press conference days after they returned to Earth as part of the SpaceX Crew-9 mission, having been stranded in space for over nine months.
"And you can see, like I've described it before, just like this ripple that happened, obviously when the plates collided, and then as it flows down into India. It's many, many colours," she said.
"I think, when you come from the east, going into like Gujarat and Mumbai, the fishing fleet that's off the coast there gives you a little bit of a beacon that here we come, and then all throughout India, I think the impression I had was it was just like this network of lights from the bigger cities going down through the smaller cities. Just incredible to look at at night as well as during the day, highlighted, of course, by the Himalayas, which is just incredible as a forefront going down into India,” she said.
William's remarks echoed the observation made 41 years back by Sqn Ldr Rakesh Sharma, who lifted off on a Soviet rocket to become the first Indian in outer space. Asked by then Prime Minister Indira Gandhi how India looked from there, Sharma said, "Sare jahan se achcha."
Williams added “I hope, and I think for sure, I'm gonna be going back to my father's home country and visiting with people and getting excited about the first, or not the first, but the Indian national who's going up on the Axiom Mission coming up, pretty awesome,” she said.
She made those remarks while referring to the Axiom Mission 4 (Ax-4) commercial astronaut mission to the International Space Station that will include Mission Pilot Shubhanshu Shukla of India.
Lucknow-born Shukla will be India’s second astronaut after former Indian Air Force officer Rakesh Sharma to go to space in 1984.
"They'll have a hometown hero there of their own who will be able to talk about how wonderful the International Space Station is from his perspective. But I hope I can meet up at some point in time. We can share our experiences with as many people in India as possible because it's a great country, another wonderful democracy that's trying to put its foot in space countries. We'd love to be part of that and help them along,” she said.
Williams's father Deepak Pandya hailed from Gujarat and came to the US in 1958 where he did his internship and residency training in Medicine in Cleveland, Ohio.
She was born in Ohio to Deepak and Ursuline Bonnie Pandya.
When Wilmore asked Williams if she planned to take her crew members on the trip to India with her, she replied with a laugh "Absolutely. You might stick out a little bit but that's okay. We'll get you all primed with some spicy food, will be good.”
NASA astronauts Williams, Nick Hague and Wilmore, and Roscosmos cosmonaut Aleksandr Gorbunov, returned to Earth on March 18 onboard SpaceX’s Dragon spacecraft, which splashed down in the sea off the coast of Tallahassee, Florida.
