My web research resulted in figuring out that launching Space Shuttles in rain, apart from lightning, wind and turbulence related problems, wasn't permitted due to:

  1. brittleness of the heat shield tiles (to prevent tiles fracturing due to high velocity impact with rain droplets)
  2. wet tiles and water soaked in the space between them would freeze in orbit causing potential damage.
  3. to not allow water inside frontal thrusters (located in the nose of the Shuttle)

But what about reentry and landing? I found few articles describing reentry/landing delays due to unfavourable weather.

For landing, freezing is no longer a problem, thrusters would be at the leeward side.

I guess there's two parts of the question:

  1. Was reentry velocity still high enough at the rain clouds altitude to be concerned about point 1 above?
  2. Were there any de-facto Shuttle landings through rain or rain clouds, or was it avoided by delaying reentry every single time there was bad weather?
  • $\begingroup$ But there could be rain during the Shuttle was on the launch pad. $\endgroup$ – Uwe Nov 22 '19 at 10:38
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    $\begingroup$ See the related question. $\endgroup$ – Uwe Nov 22 '19 at 10:42
  • $\begingroup$ @Uwe Funnily enough, they were drying the tiles with heat after the rain before launch, according to this article google.com/url?sa=t&source=web&rct=j&url=https://… $\endgroup$ – Sergiy Lenzion Nov 22 '19 at 11:02
  • $\begingroup$ From a NASA page : "After each flight, the orbiter thermal protection system is rewaterproofed. Dimethylethoxysilane is injected into each tile through an existing hole in the surface coating with a needleless gun, and the AFRSI blankets are injected with DMES from a needle gun." $\endgroup$ – Uwe Nov 22 '19 at 11:32
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    $\begingroup$ That article is about an orbiter that got soaked after landing. They were drying it out in the OPF horizontally. On the pad they didn't dry out the tiles. Remember the Rotating Service Structure was closed over the orbiter until "close" to launch. Some got wet on the pad by a late rain; I remember them going belly to sun to dry out the tiles in space. $\endgroup$ – Organic Marble Nov 22 '19 at 12:36

The orbiters were not allowed to fly through precipitation on landing for the following reasons:

The orbiter is not to encounter precipitation on any approach due to decreased visibility, damage to the TPS, and the potential for triggered lightning. Undesirable aspects of thunderstorms include rain (TPS, structure), hail (TPS, structure, control), severe wind shear (structure), turbulence (control, performance, structure), and natural or triggered lightning (structure, electronic/software systems). Environmental design requirements for the orbiter are based on no in-flight penetration of thunderstorms (ref. Appendix 10-10, Volume X, Space Shuttle Level II Program Specification). The participants in the Weather Rules Workshop held at JSC/MSFC in October 1987 developed the thunderstorm, lightning, and precipitation limits based on scientific knowledge, engineering judgment, and experience.

Space Shuttle Flight Rules, precipitation rule rationale, p. 2-26

The landing weather flight rules are well summarized here:

The weather criteria are as follows:

– Cloud coverage of 4/8 or less below 8,000 feet and a visibility of 5 miles or greater required.

– The peak crosswind cannot exceed 15 knots, 12 knots at night. If the mission duration is greater than 20 days, the limit is 12 knots, day and night.

– Headwind cannot exceed 25 knots.

– Tailwind cannot exceed 10 knots average, 15 knots peak.

No thunderstorm, lightning or precipitation activity is within 30 nautical miles of the landing site.

– At least two approach paths must be free from detached non-transparent thunderstorm anvils less than three-hours old within 30 nautical miles of the runway.

– Turbulence must be less than or equal to moderate intensity.

– Consideration may be given for landing with a “no-go” observation and a “go” forecast if, at decision time, analysis clearly indicates a continuing trend of improving weather conditions, and the forecast states that all weather criteria will be met at landing time.

(emphasis mine)

The intent was clearly to wave off the deorbit burn if the criteria would not be met at landing. If the forecast for Florida landings was bad for several days, a landing could be targeted for California. (Florida landings were highly desirable to avoid the cost of ferrying the orbiter across the country.)

There is at least one documented case where mistakes were made and the orbiter landed through flight-rule-exceeding clouds (maybe technically in-limits...). That was on STS-53. The story is well told at Wayne Hale's blog here and it is worth reading for a discussion of the decision process.

Bret Copeland mentioned in comments that a similar event happened on a mission late in the program, STS-133. The commander was quoted about it:

"We have flight rules that govern the weather for landing the space shuttle and one of the rules is the layer of clouds can't be less than 8,000 feet above the ground for landing. Unfortunately for our landing, we broke out at 3,500 feet above the ground. So we didn't see the runway until then," Lindsey recalled after the mission.

Source: https://spaceflightnow.com/shuttle/sts133/anniversary/

I am not aware of any case where the orbiter landed through precipitation.

Addressing this comment " I found few articles describing reentry/landing delays due to unfavourable weather" - there were many! Check the Space Shuttle Missions Summary and search for "flight duration changes/landing".

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