Reentry of International Space Station Batteries into Earth's Atmosphere
Observation & Tracking of Reentries
- Some users reported seeing large fireballs and asked how to identify them after the fact.
- Others suggested tools for:
- Satellite and debris tracking and replaying past orbits.
- Catalogs of recent reentries.
- Crowdsourced meteor / fireball reports and videos.
- Consensus: many bright events are meteors, but reentries move more slowly across the sky; both are common enough that specific identification can be non‑trivial.
Why Deorbit the ISS Batteries
- Main reasons cited:
- They can’t remain in low orbit safely without active station‑keeping.
- Uncontrolled long‑term debris is a collision risk.
- Letting the atmosphere burn them up is effectively “free” compared to propulsive disposal.
- The pallet was jettisoned unusually because an earlier Soyuz launch failure disrupted planned cargo craft disposal schedules.
“Why Not Boost Them to the Sun or Elsewhere?”
- Multiple comments stress that sending mass into the Sun is energetically very expensive:
- You must largely cancel Earth’s ~30 km/s solar orbital velocity.
- Delta‑v to hit the Sun from Earth orbit exceeds that needed to escape the Solar System.
- One participant argued lunar slingshots could make a solar impact “trivial,” but others countered that:
- Lunar gravity assists offer too little velocity change.
- Gravity assists are not “free” and still require significant delta‑v.
- No real missions use this to cheaply impact the Sun.
- Broad agreement: deorbiting into Earth’s atmosphere is vastly cheaper and safer for trash.
Recovery vs Destructive Reentry
- Returning ~2.6 tonnes via capsules is described as prohibitively expensive and capacity‑limited.
- Space Shuttle–style large downmass is gone; current vehicles mostly only return crew and small cargo.
- Controlled reentry via a cargo craft would localize the footprint over remote ocean; the pallet’s uncontrolled reentry had low but non‑zero risk, with some tracks passing near major European cities.
Environmental & Toxicity Concerns
- Some worry about nickel compounds from nickel–hydrogen batteries as toxic heavy‑metal pollutants.
- Others respond:
- The absolute mass is tiny compared to global nickel fluxes (e.g., from meteorites and oceans).
- Reentry distributes material over huge areas, strongly diluting it.
- Debate notes that “dilution” logic breaks down only at very large scales of space activity, which we are far from.
Risk, Prediction & Public Alerts
- Reentry time and location are hard to predict precisely due to variable atmospheric drag and solar activity.
- Users compare the coarse time windows (±0.4 days) and wide latitude bands to more deterministic missions like the Moon landings, noting the very different data and control situation.
- German national warning apps issued broad, low‑likelihood alerts; some users were surprised either by the scale or by not receiving notifications.
ISS Fate and Alternate Orbits
- Questions raised about “parking” ISS in a higher or lunar orbit instead of eventual controlled deorbit.
- Replies emphasize:
- Huge fuel requirements to raise ISS to high Earth or lunar orbit.
- Ongoing station‑keeping even in higher orbits.
- Aging hardware, radiation, thermal design, and logistics constraints.
- Risk of long‑term debris if an unmaintained hulk breaks up.
- Some note that a moderately higher LEO could lengthen orbital lifetime, but still poses long‑term debris concerns.
Battery Technology Discussion
- Thread links photos and specs: each old nickel–hydrogen battery is roughly 1×1×0.5 m and ~169 kg; the pallet carried several.
- Nickel–hydrogen batteries are praised for extremely long cycle life and high faradaic efficiency, despite lower energy density than lithium.
- Comments touch on:
- High‑pressure hydrogen storage in these cells (~1200 psi) and comparisons to other pressure vessels (fuel‑cell cars, CNG tanks, scuba, reactors).
- A brief primer on faradaic efficiency vs overall energy efficiency, with references to electrochemistry concepts.