Introduction
NASA is planning to decommission the International Space Station (ISS) in 2030. The ISS has been in orbit for over 20 years and has been a key platform for research and exploration of our solar system. However, with the station now nearing the end of its operational life, NASA has begun to make plans for its eventual decommissioning.
The ISS is a collaboration between NASA and other space agencies around the world, including the Russian space agency Roscosmos, the European Space Agency (ESA), the Japanese Aerospace Exploration Agency (JAXA), and the Canadian Space Agency (CSA). Since its launch in 1998, the ISS has been visited by over 240 people from 18 different countries. It has been a key platform for conducting experiments in microgravity, studying the effects of space on the human body, and testing new technologies for future space missions.
Before the ISS is decommissioned, NASA plans to continue using it for a wide range of research and exploration activities. This will include studying the effects of long-term space travel on the human body, developing new technologies for deep space exploration, and conducting experiments in a variety of fields including biology, physics, and materials science.
While the end of the ISS is certainly a significant milestone in the history of space exploration, NASA is already looking ahead to the future. The agency is currently working on plans for a new space station, known as the Deep Space Gateway, which will be located in the vicinity of the Moon. This new station will serve as a stepping stone for human missions to deep space destinations such as Mars, and will be equipped with state-of-the-art technology and systems to support long-term human habitation in space.
NASA's plans to decommission the ISS in 2030 mark the end of an era for the space station, which has been a key platform for research and exploration for over two decades. While its decommissioning will mark a significant milestone, it will also pave the way for new and exciting opportunities for space exploration in the future.
Why is NASA planning for the end of the International Space Station?
The ISS has maintained a continuous human presence aboard the microgravity laboratory for more than 21 years with assembly missions starting in 1998. Throughout the years, NASA and its international partners have worked together to operate, maintain, and upgrade parts of station. The technical lifetime of the station is limited by the primary structure, which includes the modules, radiators, and truss structures. The lifetime of the primary structure is affected by dynamic loading (such as spacecraft dockings/undockings) and orbital thermal cycling.
NASA has committed to fully use and safely operate the space station through 2030, as the agency also works to enable and seamlessly transition to commercial owned and operated platforms in low-Earth orbit. This will allow NASA to buy the services it needs from commercial companies for microgravity research and technology demonstrations while the agency explores the Moon and Mars.
Why did NASA decide to deorbit the space station instead of alternative options?
NASA has examined several options for decommissioning of the ISS, including disassembly and return to Earth, boosting to a higher orbit, natural orbital decay with random re-entry, and controlled targeted re-entry to a remote ocean area.
Disassembly and Return to Earth: The ISS modules and truss structure were not designed to be easily disassembled in space. The space station covers an area about the size of a football field with initial assembly of the complex requiring 27 flights by NASA since retired space shuttle with its large cargo bay and multiple international partner missions over a span of 13 years. In addition, new hardware has recently been added to the space station, like the roll-out solar arrays and the Russian Nauka and Prichal modules. Any disassembly effort to safely return individual components would face significant logistical and financial challenges, requiring substantial work by astronauts and ground support personnel as well as a spacecraft with a capability similar to the space shuttle's large cargo bay.
Boost to Higher Orbit: The space station flies at an altitude where Earth's atmosphere still creates drag, which requires regular re-boosts to stay in orbit. The station operates in low-Earth orbit above 400 km in altitude and has a mass of more than 430,000 kg. Depending on solar activity, the station's orbital lifetime (the amount of time before the station would naturally re-enter from atmospheric drag alone) at this altitude is roughly one to two years without re-boosts. It is for this reason the station cannot remain in orbit indefinitely – it will naturally fall back to Earth. Decommissioning by boosting an object to a higher “graveyard” orbit to greatly extend the orbital lifetime is often done with smaller satellites operating near geostationary orbits (~36,000 km in altitude); however, this is not a realistic target for space station decommissioning because of the large mass of the space station and low operational altitude. Existing propulsive assets like the Russian Zvezda Module and Progress spacecraft do not have the capability to raise the space station's altitude to such a high target.
With current capability, it would only be possible to raise the station's altitude enough to slightly extend the orbital lifetime (a few decades at best), but not escape low-Earth orbit. This disposal method would carry a high risk to future operations in low-Earth orbit since the station could not be refueled for debris avoidance maneuvers. A debris strike on space station could render the station uncontrollable or create additional orbital debris that would present a risk to other missions. Alternative propulsive methods to escape Earth's gravitational pull have been explored, but these options would require new hardware, large amount of additional propellants, and would impose large additional cost burdens for the development, test, and deployment of these methods. Ultimately, this decommissioning strategy would only increase risk of station being struck by orbital debris and delay the uncontrolled re-entry of the space station to a later date.
Random v Controlled Re-entry: A natural orbital decay of the space station with a completely random re-entry would not ensure that the surviving debris lands in a remote, unpopulated area. The risks to the ground population associated with an uncontrolled re-entry for space station are not acceptable for NASA without mitigation. It is for this reason that a propulsive maneuver is required to mitigate this risk and ensure a controlled, targeted re-entry into a remote uninhabited area in the ocean.
How will NASA deorbit the International Space Station?
The primary objective during space station deorbit operations is the safe re-entry of the space station's structure into an unpopulated area in the ocean. The chosen approach for decommissioning is a combination of natural orbital decay and the execution of a re-entry maneuver for final targeting and to control the debris footprint. This final maneuver is expected to require a large percentage of the space station's propellant reserves.
Due to the high propellant cost of this final space station maneuver, the Earth's natural atmospheric drag will be used as much as possible to lower station's altitude while setting up deorbit. Eventually, once all crew have safely returned to Earth and after performing small maneuvers to line up the final target ground track and debris footprint over the South Pacific Oceanic Uninhabited Area (SPOUA -the area around Point Nemo), space station operators will perform a large re-entry burn, providing the final push to lower station as much as possible and ensure safe atmospheric entry into the target footprint.
The space station will accomplish the deorbit maneuvers by using the propulsive capabilities of the space station and its visiting spacecraft. NASA and its partners have evaluated varying quantities of Russian Progress spacecraft to support deorbit operations. Additionally, NASA is evaluating whether U.S. commercial spacecraft can be modified to provide capability to deorbit the space station.
What happens when the space station deorbits? Will parts of the space station burn up?
The space station is the largest single structure ever built in space, and represents physics and engineering challenges when it comes to re-entry modeling. Station is primarily made up of a combination of truss elements, modules, solar arrays, and radiators. The truss acts as the backbone of the station, providing physical support for the solar arrays, radiators, and modules. The various modules provide pressurized volume for the many microgravity experiments, a habitable area for crew, and ports for visiting spacecraft to dock and undock. The solar arrays and radiators provide power generation and thermal control for station hardware.
Based on behavior observed during the re-entry of other large structures such as Mir and Skylab, NASA engineers expect breakup to occur as a sequence of three events: solar array and radiator separation first, followed by breakup and separation of intact modules and the truss segment, and finally individual module fragmentation and loss of structural integrity of the truss.
As the debris continues to re-enter the atmosphere, the external skin of the modules is expected to melt away and expose internal hardware to rapid heating and melting. Most station hardware is expected to burn up or vaporize during the intense heating associated with atmospheric re-entry, whereas some denser or heat-resistant components like truss sections are expected to survive re-entry and splash down within the the South Pacific Oceanic Uninhabited Area (SPOUA -the area around Point Nemo). NASA engineers continue to refine estimates for the size of the re-entry maneuver necessary to control the size of these debris footprints and ensure debris falls within the desired target area.
Why did NASA choose to bring the space station down to Earth at Point Nemo?
Point Nemo is the location in the ocean that is farthest from land. This remote oceanic location is located at coordinates 48°52.6′S 123°23.6′W, about 2,688 kilometers from the nearest land. Because of its distance from populated areas, this location is traditionally used for spacecraft disposal and represents an excellent target for ensuring any hardware that survives the heat of re-entry does not land near populated areas on Earth. NASA continues to investigate alternate footprint targets and ground paths for station disposal to minimize risk the to Earth's population.
Why doesn't NASA plan to repurpose part of the space station for future commercial use or educational purposes such as displaying its modules or parts in a museum?
NASA will assess what internal components on the International Space Station can be used on commercial destinations or returned for display, including any science facilities, payloads, and other equipment.
There currently are no proposals from commercial providers to repurpose major structural parts of the International Space Station, and such plans would have to consider the cost and difficulty of reusing such pieces of station. NASA has entered into a contract for commercial modules to be attached to a space station docking port with plans to later detach, and awarded space act agreements for design of three free-flying commercial space stations.
In addition, much of the structural hardware on station was designed and built in the late 1990's and 2000's, whereas new commercial destinations will benefit from more recent technology advancements.
Source: NASA