The agency plans to retire the ISS in 2031 due to the structural stresses that have been accumulating over its prolonged period of service.
In a novel approach, NASA is inviting companies to develop a “space-tug,” a potent vehicle with the capability to tow the ISS from its orbit and guide it towards Earth.
This specialized space tug, dubbed the US Deorbit Vehicle (USDV), is designed to maneuver the ISS from its position 175 miles above Earth to approximately 75 miles, marking the beginning of its ultimate descent into the Pacific Ocean.
Proposals for this innovative project are expected no later than November 17, and the phased retirement of the ISS is scheduled to commence in 2026, with NASA allowing the station to start decaying naturally.
“This has been done before, notably with the Mir space station. Many tons of material will hit the ocean relatively intact, and there will definitely be a warning to clear the airspace (we get about one of these a month for disposal of much smaller spacecraft like ISS cargo ships),” said Jonathan McDowell, an astrophysicist at Harvard University.
“Here’s what’s tricky. You can fly the ISS safely down to an altitude of about 250 km. After that, you need this special USDV ship to take over the steering – it’s like driving down a motorway with a lot of wind gusts – you need a lot of muscle power to stay on the road. If you ever lose control and the ISS starts tumbling, you’re in trouble because then you can’t reliably point the rocket engines in a particular direction.”
NASA’s initial step in this meticulous plan involves allowing the ISS to undergo natural decay, thereby reducing its orbit from around 250 miles to 200 miles above the Earth’s surface.
This gradual process will span a few years. In 2030, the residing crew of the ISS will embark on their final descent to Earth, securing any vital equipment.
The ISS will continue its approach towards the Earth, reaching the critical ‘point of no return’ at 175 miles above the surface.
At this point, the $1 billion space tug will exert a controlled force to nudge the ISS out of orbit. The ensuing re-entry will witness the external components of the station melting and the internal hardware vaporizing as the ISS traverses Earth’s atmosphere at a staggering 18,000 miles per hour.
The remnants that endure the re-entry will be directed towards Point Nemo, a designated region in the Pacific Ocean, which serves as a final resting place for over 260 spacecrafts.
“Another trick is that it will take about eight tons of propellant (fuel and oxidizer) to bring the station down from the lowest controllable height. But you can’t use a rocket engine that takes six hours to burn that much fuel because, in 30 minutes, you’ll be so low that you lose control and start tumbling,” McDowell explained.
“So you need a serious rocket engine that can burn through eight tons in only 15 minutes or so, doing the full deorbit burn in an amount of time shorter than the time taken to get too low to control. So the USDV has to be big (lots of propellant) and have a big engine (so big push in a short time), and none of the existing cargo ships have either of those. Hence the need to develop a new vehicle to dispose of the ISS safely.”
The inception of the ISS was announced by President Ronald Reagan during his State of the Union Address on January 25, 1984, with a commitment for NASA to complete it within a decade.
The first US component was launched into space on December 4, 1998, and the station became operational two years later. Since the arrival of the first crew in November 2000, the ISS has welcomed more than 250 visitors from 20 countries.
The ISS was initially slated for decommission after 15 years of service, a timeline that has been significantly surpassed. However, due to signs of wear and tear, this iconic structure will finally be decommissioned.
The responsibility for the safe deorbit of the station is a collective effort among five space agencies – NASA, CSA (Canadian Space Agency), ESA (European Space Agency), JAXA (Japan Aerospace Exploration Agency), and the State Space Corporation Roscosmos. Each agency holds accountability for the hardware they have contributed.
The ISS, designed for interdependency, relies on this collaborative partnership, with the US, Japan, Canada, and ESA countries committed to its operation through 2030, and Russia until at least 2028.
NASA evaluated several alternatives for the ISS’ decommissioning, including disassembly and return to Earth, elevation to a higher orbit, or allowing it to decay until it randomly descends to Earth.
However, these options were ruled out due to the structural design challenges, the need for re-boosting, and potential risks associated with uncontrolled descent.
In anticipation of the ISS’s retirement, NASA has already initiated a transition plan, inviting private companies to conceptualize a new space station. Companies like Axiom Space, Jeff Bezos’ Blue Origin, and Northrup Grumman have expressed interest in operating a commercial station.
“The International Space Station is entering its third and most productive decade as a groundbreaking scientific platform in microgravity. This third decade is one of the results, building on our successful global partnership to verify exploration and human research technologies to support deep space exploration, continue to return medical and environmental benefits to humanity, and lay the groundwork for a commercial future in low-Earth orbit,” concluded Robyn Gatens, the director of ISS.
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.