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Space Weather Clears for the Flyby Window

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Region 4409, which fired 23 of 24 flares in a single day, went quiet on the one day it mattered most.

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ScienceDeveloping

Key takeaway

The sunspot region that threatened the flyby produced only minor flares on the day of maximum crew exposure.

NOAA's three-day forecast for 6 to 8 April showed a maximum Kp of 3.0, well below the G1 storm threshold.¹ SpaceWeather.com recorded only B9 and C2 class flares on 6 April, with a Kp index of 2.0 and all sunspot magnetic fields stable.² Solar wind speed sat at 539.4 km/sec with a northward Bz of 0.75 nT, conditions that reduce coupling to Earth's magnetic field.

The 20% daily X-class flare probability from Region 4409 that hung over the mission through update #4 did not materialise. The G3 geomagnetic storm that peaked at Kp=7 on Days 3 and 4 resolved four days ago. Two days ago Region 4409 produced an M7.5 , the strongest flare of the mission week. Today, with the crew at maximum distance and behind the Moon, it produced nothing above C2.

Region 4409 remains active; it previously fired 23 of 24 flares, or 96%, in a single day, including three M-class events.³ The same sunspot group that threatened the flyby went quiet on the one day it mattered most.

Deep Analysis

In plain English

The Sun is not constant. It has active regions, called sunspots, that can fire powerful bursts of radiation called solar flares. A strong enough flare, if it hits a spacecraft in deep space, can deliver a significant radiation dose to the crew. Region 4409 was a particularly active sunspot that had been firing flares throughout the mission. In the days before the flyby, forecasters gave it a 20% daily chance of firing an extreme X-class flare. On 4 April, it produced an M7.5 flare, one of the strongest during the mission week. On 6 April, the most important day of the mission, Region 4409 went quiet. Only minor B9 and C2 flares occurred. The space weather cleared exactly when it mattered most.

What could happen next?

Consequence
Quiet space weather on 6 April kept crew radiation dose within expected margins, though the exact figures remain undisclosed by NASA.

Mentions:NOAA →Space Weather Prediction Center →Region 4409 →Space weather →M7.5 →G3 geomagnetic storm →

First Reported In

Update #5 · Records fall while Orion goes silent

· 6 Apr 2026

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Causes and effects

Caused by

G3 storm hits crew in deep space

The G3 storm peaked on Days 3-4 from a different solar event; Region 4409's quiet on 6 April contrasted with the prior storm severity, with the sun going calm on the mission's highest-risk day.

Occurred 4 Apr 2026

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This Event

Space Weather Clears for the Flyby Window

The 20% daily X-class flare probability that hung over the mission through previous updates did not materialise, leaving Kp=2 quiet conditions for the flyby.

Different Perspectives

ESA

The European Service Module has operated without anomaly for five consecutive days, with the OMS-E engine's translunar injection precision directly responsible for eliminating both correction burns. ESA's hardware contribution is the mission's highest-performing subsystem.

NASA

NASA cancelled a second consecutive outbound correction burn and confirmed Orion in lunar gravitational dominance, while declining to publish any crew radiation dose data through a complete G3 storm cycle. Bipartisan congressional rejection of its $18.8 billion FY2027 budget proposal means the agency faces a political fight even as its spacecraft performs above expectations.

Dual-framework nations

Signing both the Artemis Accords and the ILRS framework is rational hedging, not defection; smaller nations maximise access without exclusive commitment. Lunar governance is genuinely multipolar, and the US coalition count of 61 overstates exclusivity.

Boeing / Northrop Grumman

SLS component production spans more than 40 US states, giving the industrial base strong political protection regardless of commercial alternatives. Congressional mandates guarantee contracts through FY2029, insulating the supply chain from technical programme changes.

NASA Office of Inspector General

The IRB heat shield findings should have been published before launch. The Starship HLS is two years behind schedule with a worsening manual control dispute. NASA has no crew rescue capability for lunar surface operations. The programme is proceeding with documented, unresolved risks.

US Congress

The One Big Beautiful Bill Act mandates $1.025 billion per year for SLS through FY2029 regardless of NASA's restructuring. Congress is preserving the employment base SLS components provide across more than 40 states, independent of whether the technical architecture requires the rocket beyond five missions.