NASA Safety Panel Issues Clarion Call for ISS Deorbit Tug

NASA’s Aerospace Safety Advisory Panel made it crystal clear today that building a tug to deorbit the International Space station is “not optional,” budget constraints notwithstanding. The panel has been urging NASA for years to provide a U.S. deorbit capability and NASA finally requested the first tranche of funding in FY2024, but ASAP worries it may fall victim to congressional cuts. That cannot be allowed to happen, they warned, or catastrophe could ensue.

At a briefing on the panel’s third quarter meeting, ASAP Chair Patricia Sanders exclaimed it would be “inconceivable” to allow the ISS to make an uncontrolled reentry and the government must provide funding to build a Deorbit Vehicle.

The 420 Metric Ton International Space Station is the largest space object ever built. Composed of modules from the United States, Russia, Europe and Japan with Canada’s Canadarm2 remote manipulator system, massive solar arrays and many scientific instruments and hardware on the exterior, it orbits the Earth every 90 minutes passing over the entire globe from 51.6º North to 51.6º South latitude, the most populated areas of the planet.

NASA and its international partners have known from the beginning they could not allow the ISS to make an uncontrolled reentry. NASA did that with its first space station, the comparatively small (76 MT) Skylab that reentered over Australia and the Indian Ocean in 1979, dropping debris in western Australia.

The Soviet Union/Russia operated seven space stations from 1971-2001, with the largest, Mir, from 1986-2001. They intentionally deorbited all but one into the Pacific Ocean where they caused no reported damage. The exception was Salyut 7 because they lost control of it on orbit. The 20-MT ton Salyut 7 was docked to another module (Kosmos 1686) about the same size and the combination made an uncontrolled reentry over Argentina in 1991.

Luckily no one was injured in either case, but Skylab and Salyut 7/Kosmos 1686 could have spread debris anywhere under their paths.

The risk of falling space debris is getting increased attention these days, especially with China’s uncontrolled reentries of three Long March 5B rockets that launched the modules for their Tiangong-3 space station, causing great consternation to NASA Administrators past and present.

The previous space stations and the Long March 5B stages are small compared to ISS.

Until Russia’s invasion of Ukraine, the plan was to use the engines on a trio of Russian Progress cargo spacecraft to deorbit ISS at the end of its lifetime. The United States, Japan, Canada and Europe have committed to ISS operations through 2030. Russia is committed only until 2028, but NASA insists that’s only because Russia makes its plans on a four-year cycle and the prior agreement was through 2024. They are confident Russia ultimately will agree to 2030.

ASAP doesn’t want to take any chances, not only as to whether Russia will still be a partner in 2030 and provide the Progress spacecraft, but whether ISS will be able to last that long. The first ISS modules were launched in 1998 and next week, on November 2, the facility will celebrate 23 years of permanent occupancy by international crews rotating on roughly 6-month shifts.

Today ASAP members praised the ground-based teams that keep ISS operating, but expressed continuing concern about air leaks on the Russian segment that date back several years. Some have been located and remedied, but others remain “elusive.” Basically ISS is old and getting older and although the partners want to keep it going until 2030, it’s not clear it will last that long.

NASA is asking for $180 million in FY2024 for the ISS Deorbit Vehicle, with a total estimated cost of $1 billion, as part of its $27.2 billion budget request.  A Request for Proposals is out and the plan is to award a contract next spring with the vehicle ready by 2029. But the Fiscal Responsibility Act deal cut by President Biden and then-Speaker Kevin McCarthy calls for nondefense discretionary spending, which includes NASA, to be held at FY2023 levels.

ASAP Chair Patricia Sanders minced no words. Noting NASA will have to make “difficult choices” if Congress cuts funding and the “can-do” agency must acknowledge it can’t do everything without needed resources, she emphasized the Deorbit Vehicle is one of the “few areas that are not discretionary.”

“The Deorbit Vehicle for the International Space Station is not optional. The day will inevitably come when the Station is at the end of its life — and we may not be able to dictate that day — it is inconceivable to allow the Station to deorbit in an uncontrolled manner. Station is simply too massive and would pose extreme hazard to populations over a broad area of Earth. This needs to be resourced and resourced now if we are to avert a catastrophe.”

ASAP was created by Congress after the 1967 Apollo fire that killed the first Apollo crew — Gus Grissom, Ed White and Roger Chafee.  It reports both to Congress and the NASA Administrator.

Sanders also stressed the importance of restoring communications antennas in Guam for NASA’s Tracking and Data Relay Satellite System (TDRSS) that were destroyed by Typhoon Mawar in May. Now there is a “blind spot over the Indian Ocean” that impacts the “safe operation of launches and missions” including the ISS, the James Webb Space Telescope, and the Artemis program.

She said funding for both the Deorbit Vehicle and the Guam antennas is included in the disaster relief supplemental and ASAP “strongly encourages” it be approved.

Furthermore, if there is a government shutdown, Sanders stresses “it is imperative” that work on the vehicles for Artemis II and Artemis III not be interrupted or there could be “impacts on vehicle configuration that could adversely affect safety and mission assurance.”