What effect (if any) would leaving the cargo bay doors open have had during a shuttle reentry?

Question

The cargo bay doors of the Space Shuttle were used on-orbit as radiators for thermal control. The cargo bay doors were closed before the reentry burn and descent to the surface, but could there have been a way to utilize the radiators for further active thermal control?

Reasons I believe they were not used this way:

1. The streamlines (streaklines?) going over the leading edge extensions look like they are going straight into where the doors would be, in their open position. This would likely either break them off or melt them.

2. The stagnation temperature behind the radiators is still higher than the temperature of the shuttle, so this would potentially have the opposite effect, at least according to this visualization.

3. Some unknown destabilizing effect on the elevons / vertical tail

Answer 1

The shuttle was not certified to enter with the payload bay doors open. In fact, it was not even certified to enter with more than one of the latches that held the doors closed failed open.

Space Shuttle Flight rule A10-23 states that with even a single latch gang failed open steps will be taken to minimize entry structural loads. For more than one failed open, an EVA would be performed to install latch tools to hold the doors closed. (sorry about all caps, that's the way they wrote the rules)

FOR FAILURE OF ANY TWO PLBD LATCH GANGS TO FULLY ENGAGE
(CENTERLINE OR BULKHEAD), AN EVA WILL BE PERFORMED TO INSTALL
MANUAL LATCH TOOLS ON AT LEAST ONE OF THE FAILED LATCH GANGS.

B. FOR FAILURE OF ANY SINGLE OR MULTIPLE PLBD LATCH GANGS TO
FULLY ENGAGE (CENTERLINE OR BULKHEAD), ENTRY LOADS WILL BE
MINIMIZED PER THE FOLLOWING:

1. ENTRY TEST MANEUVERS WILL NOT BE PERFORMED, AND ANY
PROGRAMMED TEST INPUTS (PTI’S) WILL BE INHIBITED.

2. CONSIDERATION WILL BE GIVEN TO TARGETING A RUNWAY/HAC
APPROACH AT THE PLS OR SLS TO MINIMIZE TAILWIND AT HAC
INITIATION AND TURBULENCE/SURFACE WINDS.

The rationale section is as follows:

There is no analysis which indicates that entry with multiple latch gang failures is an acceptable condition. Although the latch tools have not been proven to provide the same structural integrity as a nominal latch gang, performing an EVA to install these latch tools provides a workaround to recover at least some load-carrying capability. Two latch tools are required to secure a single failed latch gang; however, only two centerline and two bulkhead latch tools are flown. When two of the same type gangs have failed, only one gang can be secured, as both available tools are required to secure one of these latch gangs.

A 1991 Rockwell assessment (which refined analyses performed in 1981 and 1987/1988) for a PLBD single latch-out (centerline or bulkhead) certified a nominal entry trajectory in AUTO flight control by exhibiting structural, thermal, and aerodynamic margins above the required 1.4 safety factor. This analysis shows that steps and gaps may occur as a result of the payload bay-to-ambient delta pressure and latch disengagement. Temperature exceedances may occur at these steps and gaps, but the resulting thermal damage poses no flight safety concerns. The extent of the postflight repairs can be limited by minimizing side slip and steady pitch-up maneuvers, according to the 1991 analysis. (Reference Structural Assessment of Shuttle Payload Bay Doors for Entry with a Latch Gang Out, SSD91D0276, May 1991, and A/E FTP #96, 12/18/92.)

Although entry test maneuvers and PTI’s should not expose the vehicle to conditions outside of its certification limits, flying a nominal entry trajectory minimizes adverse mechanical, thermal, and aerodynamic loads. Vehicle accelerations, heating, and compartment-to-ambient pressure differentials can be limited by avoiding these maneuvers. Selecting a runway/HAC that minimizes HAC winds (most importantly, tailwind at HAC initiation) will help to minimize normal loads, and selecting a landing site with benign turbulence and surface wind conditions reduces the need for any abrupt directional control maneuvers.

Source: Generic Flight Rules

To sum up, analysis showed that with even one latch gang out, a safe landing could be performed, but there would be thermal damage to the doors. Since the shuttle was by nature reusable, damage to its structure was highly undesireable, so there was no need to perform further analysis about the effects of multiple latches open (or the doors open). One latch out was bad enough. So steps were taken to generate procedures that tried to ensure that a maximum of one latch would be out for entry.

Therefore, no exact analysis was ever done of the case you describe, but even the first steps of getting into that case were highly undesirable and to be avoided.

Answer 2

For numerous aircraft, certain doors become part of the airframe structure when closed. If these doors are not properly secured, the structure is compromised, affecting flight safety.

The Space Shuttle was built like an aircraft; aside from the thermal protection, it used conventional aircraft construction materials (aluminum alloy) arranged in structural elements (spars, stringers, ribs, bulkheads, etc.) just like a typical aircraft, and derives some portion of its strength and stiffness from the exterior skin (or the layer to which the TPS is applied). The dome-shaped cross-section of the body isn't that way purely for aerodynamic reasons. It's also for structural reasons, resisting various kinds of linear, bending, and twisting loads with a minimum of material. Some of these loads are transmitted through the doors. This requires that the doors are in their properly closed position with all of the latches secure (the latches are themselves load paths). If any of the latches is not secure, certain forces have to be carried by some other path, potentially over-stressing it, resulting in some level of damage.

To summarize: apart from thermal considerations, leaving the cargo bay doors open during re-entry would likely lead to catastrophic break-up at some point due to inability of the airframe to handle the normal loads encountered during re-entry and landing.