International Space Station to fall from sky
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(Dr RK Chadha)
The National Aeronautics and Space Administration (NASA), USA has announced that its operations on the International Space Station (ISS) will end in 2030 after completing 3 decades in space science.
The 28 March 2023 issue of Smithsonian Magazine carried an article entitled, The ISS will fall from Sky after the end of the decade. What will replace it?
The decommissioning of ISS will mark the end of an era for a hallmark program that brought scientific research and international collaboration to its center. The space station has been continuously occupied since November 2000. An international crew of seven people live and work while traveling at a speed of about 8 km per second, orbiting Earth about every 90 minutes. Sometimes more are aboard the station during a crew handover. Space stations won’t last forever as stresses on the primary structure accumulate over some time with constant temperature changes during its orbital journey in and out of view of the sun leading to the development of cracks on its façade in addition to spaceborne debris hammering its exterior. Though it will be a sad moment to see the 420-ton ISS meet its watery grave in some remote corner of the Pacific Ocean, it will also be an occasion to celebrate its achievements and make room for new adventures with private players entering into the space business.
The ISS is constantly losing its altitude due to atmospheric drag and requires regular boosts to stay in the designated orbit, otherwise, it will eventually fall back to Earth on its own and that could be dangerous. People still remember the scare on 11 July 1979 when parts of Skylab, America’s first space station broke up in the atmosphere and showered its burning debris over the Indian Ocean and Australia; luckily no one was killed or injured.
To avoid such an eventuality NASA plans to deorbit the space station safely by the end of this decade by using a special module called the Progress spacecraft first developed by Russia as a cargo ship with the sole purpose of topping up food, water, and fuel supplies to the space station. This cargo ship will dock with the ISS and push it down with its engines aiming for a remote area in the Pacific Ocean, where the ISS will burn up and break apart during re-entry. There had been discussions to put the ISS into a higher Geosynchronous orbit or at Lagrange Point instead of crashing it into the Pacific Ocean.
A Lagrange point is a special location in space where the gravitational forces of two bodies, like the Earth and the Sun, balance out each other so that an object can stay there without much effort.
While technically it could be possible to put a spacecraft in higher orbits or at Lagrange point, it is not possible in the case of ISS because it is optimized for Low Earth Orbit (LEO) that is 400 km above Earth’s surface; to go to higher orbits, more powerful engines, more fuel, more shielding from radiation and micrometeoroids, and more cooling systems to deal with the higher temperatures are required. Besides, the ISS is too enormous with its 420-ton weight and 357-foot wingspan, and will require a lot of thrust and delta-v which is a change in velocity required to change a spacecraft orbit. To give an example, from LEO to Geostationary Orbit (GEO) that is 36,000 km above the equator, it would need 4 km/s of delta-v or to boost it to Lagrange L2 point on the opposite side of the Earth and Sun, it would need about 3.5 km/s delta-v.
There are other issues like ISS is not a single piece but is made up of several modules that are connected by bolts and wires. To move it as one piece all these connections need to withstand the stress and the vibrations of rockets for which it is not designed. It is becoming too expensive to maintain the aging space station which is taking up a few billion dollars every year to keep it operational. The bottom line is, though it is not technically impossible to move the ISS, it is impractical and will become a white elephant in space given constant maintenance and will add to junk in the already crowded space. In the final analysis, there will not be many benefits to maintaining ISS in space as it has already served its purpose where amazing science experiments have been conducted while exploring Earth from LEO. There are several other ways to continue that legacy in space and thus crashing the ISS in the Pacific Ocean is the right decision.
Sensing enormous business opportunities that the space industry will offer in the coming decade Prime Minister Narendra Modi has outlined a grand vision for ISRO scientists after the success of Chandrayan 3 mission to aim for India’s space station by 2035. At present, there are only two international space stations, ISS and China’s Tiangong. India’s Unique Selling point (USP) is the low-cost space missions that will have a greater advantage over other competitors, both in private or government-owned space missions. (The author is former Chief Scientists of NGRI, Hyderabad)