NASA approved a safety waiver for this week's reentry of Van Allen Probe

Source: Ars Technica

Background

No one on the ground has ever been injured by falling space junk, but there are examples of space debris causing property damage Ars Technica.

Van Allen Probes

NASA’s two Van Allen Probes were launched into elliptical orbits ranging from a few hundred miles above Earth up to an apogee of nearly 20,000 miles. The orbits are inclined 10° to the equator, limiting the risk of injury or damage to a swath of the tropics. NASA ended the mission in 2019 when the satellites ran out of fuel.

At that time, engineers expected the spacecraft to re‑enter the atmosphere in 2034. Higher‑than‑anticipated solar activity caused the atmosphere to swell outward, increasing atmospheric drag on the satellites beyond initial estimates, according to NASA. Van Allen Probe B is now expected to re‑enter no earlier than 2030, with a similar risk to the public.

The two spacecraft were built by the Johns Hopkins University Applied Physics Lab. NASA said the mission made several major discoveries, including “the first data showing the existence of a transient third radiation belt, which can form during times of intense solar activity.”

Re‑entry Risk History

Several NASA satellites have re‑entered the atmosphere without complying with the government’s risk standard. One of them, the Rossi X‑ray Timing Explorer (RXTE), fell out of orbit in 2018 with a 1‑in‑1,000 chance of harming someone on the ground. No one was hurt. RXTE was launched in 1995, just four months before NASA issued its first standard on orbital debris mitigation and re‑entry risk management Spaceflight Now.

International Context

While NASA has exceeded its standards before, the U.S. government is not a top offender when it comes to unmitigated re‑entry risks. China launched four heavy‑lift Long March 5B rockets between 2020 and 2022 and left its massive core stages Ars Technica in orbit to fall back to Earth. The four abandoned rocket cores, each nearly 24 tons in mass, re‑entered the atmosphere uncontrolled. Two of them dropped wreckage on land—in the Ivory Coast and Borneo—but no injuries were reported.