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A spacecraft which needs to both maneuver and enter the atmosphere needs both a reaction control system and a thermal protection system (aka heat shield). As the heat shield needs to be on the outer surface and the RCS needs to exhaust to outside the vehicle, this means that there need to be openings in the heat shield for the RCS exhaust. The shuttle orbiter and the Apollo command module are examples of spacecraft with RCS openings in the heat shield.

What measures are taken to prevent RCS openings from being a point of failure or allowing damage to the RCS engines during re-entry?

shuttle nose RCS

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The columbium jet nozzles themselves can take the heat, but "penetrations" of the spacecraft heat shield are a definite potential failure point, including penetrations for the Reaction Control System (RCS) jets. The design to preclude hot gas intrusion while preventing damage to the surrounding Thermal Protection System can be quite complex.

The forward RCS provides attitude control and small velocity increment translation from main engine cutoff during ascent until the entry interface. It includes 16 radiation-cooled thrusters (14 primary and 2 vernier), made predominantly from columbium (disilicide coated except for the injector plate), and fully exposed to aerodynamic heating. Surrounding HRSI tiles of the TPS have been partially replaced by other materials. Insulation-filled metallic plume shields are placed downstream of long scarf (primary -Z and -X and vernier) thrusters. High density (22pcf) RSI tiles form the TPS in narrow areas between the -Z, +Y, and -X thrusters. Thermal barriers serve to block gaps between nozzle exits and adjacent TPS from boundary layer gases. Other thermal barriers are required between the plume shields and surrounding tiles. Each thruster is housed within a cylindrical titanium container that seals the internal compartment from the exterior environment. The design is complex.There are approximately 20 maximum temperature limits to be observed, many with several variations associated with position, mission phase, or frequency of occurrence. The primary downfiring (-Z) thrusters experience the most severe entry heating. A section through the downstream edge of this installation is shown in figure 37.

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Source SHUTTLE TPS THERMAL PERFORMANCE AND ANALYSIS METHODOLOGY

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(image source, annotated)

Example thermal barriers:

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From here

Acronymology

HRSI - High-temperature Reusable Surface Insulation (aka black tile)

RSI - Reusable Surface Insulation

SIP - Strain Isolation Pad

TPS - Thermal Protection System

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An "RCS opening" is a rocket nozzle, which has to withstand massive heat loading from engine burns. Massive enough that the nozzle will also withstand the heat load on reentry.
You just have to make sure there's no gap between the nozzle and the heat shield around the nozzle.

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  • $\begingroup$ And the heat shield around the nozzle should not be damaged by a hot nozzle during an RCS burn. So long continous burns should be avoided, but a well designed RCS system should avoid long burns to save fuel anyway. $\endgroup$ – Uwe Aug 21 at 10:29
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    $\begingroup$ @Uwe shuttle dumped the forward RCS prior to entry, this could take a couple minutes. "It takes 90 seconds to dump 50 percent forward RCS with 4 jets (twice as long using a 2 jet dump)." (from the Shuttle Crew Operations Manual) Some ISS reboost burns using the jets were pretty long too. $\endgroup$ – Organic Marble Aug 21 at 13:12
  • $\begingroup$ @Uwe: Didn't you see the RCS powered Venus orbital insertion? $\endgroup$ – Joshua Aug 21 at 18:12

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