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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?
Fred
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Sergiy Lenzion
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  • But there could be rain during the Shuttle was on the launch pad. – Uwe Nov 22 '19 at 10:38
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    See the related question. – Uwe Nov 22 '19 at 10:42
  • @Uwe Funnily enough, they were drying the tiles with heat after the rain before launch, according to this article https://www.google.com/url?sa=t&source=web&rct=j&url=https://spaceflightnow.com/station/stage7a/010524delay/&ved=2ahUKEwjUkoGD1f3lAhWTA3IKHTeGBnEQFjAcegQIChAB&usg=AOvVaw1iVeTeC6wuXJwfM6f-31Rj – Sergiy Lenzion Nov 22 '19 at 11:02
  • 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." – Uwe Nov 22 '19 at 11:32
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    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. – Organic Marble Nov 22 '19 at 12:36
  • @OrganicMarble But there was a risk that the water would freeze while drying out in space. Does sun heat prevent the water to freeze in vacuum? The surface of the tiles were heated but conduction of heat to the core of the tiles was very small. – Uwe Nov 22 '19 at 13:12
  • @Uwe I can only state what was actually done. STS-4 "- During prelaunch rain storms, approximately 500 lbs water absorbed by tiles requiring bottom-to-sun for many hours to dry-out water (to prevent ice damage to tile)." From Space Shuttle Missions Summary – Organic Marble Nov 22 '19 at 13:30
  • @Uwe Water can't exist as a liquid in vacuum (look at the bottom of a phase diagram as in http://www1.lsbu.ac.uk/water/water_phase_diagram.html), so any that was left over in orbit would be ice which would sublimate directly to gas when heated. – llama Nov 22 '19 at 18:00

1 Answers1

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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".

Organic Marble
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    STS-133 had a similar experience - breaking out of clouds at about 3500 ft: https://www.youtube.com/watch?v=FKlGlRdgKLA Steve Lindsey was interviewed about it https://spaceflightnow.com/shuttle/sts133/anniversary/ (feel free to incorporate into your answer). – Bret Copeland Nov 22 '19 at 14:45
  • Thanks! I will when I return to a real PC. – Organic Marble Nov 22 '19 at 14:50
  • One downside of having the primary landing site in Florida... – Darrel Hoffman Nov 22 '19 at 19:09
  • @DarrelHoffman the most thunder-riffic state in the USA. – Organic Marble Nov 22 '19 at 19:17
  • "– 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."

    Why would the criteria change for longer duration missions?

     – paulmrest Nov 23 '19 at 01:25
  • Related: https://space.stackexchange.com/questions/40062/why-was-the-shuttle-landing-crosswind-limit-reduced-for-longer-missions – Organic Marble Nov 23 '19 at 01:53
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    I forgot about visibility factor (since the landing is essentially a manual procedure). They didn't have wipers on the front window, did they? :) – Sergiy Lenzion Nov 23 '19 at 04:15
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    Nope, no wipers. https://spaceflight.nasa.gov/gallery/images/shuttle/sts-135/hires/iss028e015098.jpg – Organic Marble Nov 23 '19 at 04:20
  • It is interesting to note that, had Columbia (on her final mission, STS-107) been able to land, the approach conditions would have been pretty dicey...unexpected low clouds rolled in shortly before the planned landing time, IIRC (however, situations like these were practiced for regularly during Shuttle Training Aircraft missions). It is also in interesting to note that, had the entry been waved off for one rev, Columbia's ground track would have crossed the greater Houston metro area - right about the time she broke up... – Digger Dec 23 '19 at 17:05
  • @Digger yeah, that last is haunting. Imagine the SSME powerheads crashing into the Control Center.... – Organic Marble Dec 23 '19 at 17:06
  • @OrganicMarble A slight correction to my last comment (above). It is more correct to state that a portion of the debris field would have been located near/in a portion of the greater Houston metro area. A bad day gone worse, for sure... – Digger Dec 23 '19 at 17:21