posted 08-22-2016 08:33 AM               

Does anyone know why the fabric was changed from silver to white?

posted 08-02-2019 10:44 PM            

So what was the purpose of the reflective coating on the cover garment then? If the reflective material was only useful if the astronaut was coming in contact with directed solar light/heat or another kind of directed heat (which was not expected), then the reflective material was useless and only for the look and style of the suit as a number of people have said.

There is a Life Magazine picture of X-15 test pilot Scott Crossfield wearing a silver material X-15 high altitude pressure suit and sitting in a chamber filled with heat lamps directed at him. The picture was meant to illustrate the effectiveness of the reflective fabric of the suit in radiating away the heat from Crossfield. Of course, this is a directed heat as opposed to something more like ambient heat being "given off" (as opposed to directed) from the avionics of the Mercury spacecraft.

So just as the reflective material on the Mercury suit sounds as if it was of superfluous value because the astronauts would not be coming in contact with a directed heat source aboard the spacecraft, the same might be said of the X-15 suit unless the X-15 suit makers were expecting the X-15 pilots to be coming in contact with direct solar heating through the X-15's window.

I would like to note though that one of the layers of fabric in the Apollo lunar suit was reflective mylar. But the mylar was buried between other layers. And I believe the mylar was added in expectation of direct solar radiation on the suit while being used on the lunar surface.

I'd be interested to hear everyone's perspective on this question — namely, did the reflective fabric coating on the Mercury suit (and while we're at the X-15 suit as well) have any real value?

posted 08-03-2019 09:50 PM               

The silver reflective coating of the Mercury spacesuit was designed to reflect radiant heat.

Mercury astronauts carried a small suit cooling system as they were transferred to the launch vehicle. This is different from the Apollo setup, which had breathing oxygen. Looking at the film of the Mercury launch for Alan Shepard, you can see his famous one last look at the launch vehicle as he exits the transfer vehicle. Shepard has his helmet visor open. The Apollo crews, who wore the bubble helmet, required oxygen as well as suit cooling.

The Mercury suit silver coating allowed a separation of the suit cooling and cabin cooling functions, reducing the workload on either system. The suit cooling system would not have to contend with the additional radiant heat from spacecraft systems. Of course, if the cabin temperature was hot, the astronaut would eventually get hot, just as if the cabin were cold, the astronaut would eventually feel cold. The silver suit finish acted in a similar way to the silver reflective finish found inside a thermos flask by reflecting radian heat (think of feeling the suns warm rays).

posted 08-06-2019 02:20 AM               

The Mercury program, as well as the high altitude aircraft programs, identified issues with the silver suit finish reflecting light, causing distractions and annoyances (think light reflecting off a mirror ball).

The white suit color achieved a similar reflection of heat energy, without the problems found with the silver finish. If no other conditions or material changed, other than the color, the results of Ed White's EVA would not change with a silver suit.

If there was a case whereby the suit temperature was to rise too high because the environmental control system could not cool the white-colored suit enough, then I believe NASA would address the ECS system performance rather than change the suit color.

From a physics perspective regarding color, with black being the total absorption of light energy, and white being the total reflection of light energy, then white is a better-suited color for thermal protection of heat energy, over the shade of grey that the silver suits represent.

From a material specification, the aluminized finish reflects light energy better than white nylon fabric weave, because the fabric has a 3-dimensional texture, with the aluminized finish acting more like a mirror than a white fabric surface.

The insulation properties of each material (excluding color) has not been considered in this discussion, nor has ease of manufacture, ease of handling, and ease of use. The silver finish also presented problems with flaking of the aluminized surface, which could contaminate the spacecraft environment.

posted 08-07-2019 06:54 PM            

With directed heat, I am assuming the reflective surface would deflect heat. But with dissipated, scattered heat, the reflective surface might not do anything more than act as an insulating layer against the heat (rather than as a reflective layer that redirects the heat, and in effect, bounces the heat off of the suit).

posted 08-08-2019 03:07 AM               

Convection transfers heat energy through gases and liquids, conduction transfers heat energy in solids, and radiation is a method of heat transfer that does not require particles to carry the heat energy. Instead, heat is transferred in infrared waves.

Avionics components produce heat as a byproduct of their operation, in the same way household electrical appliances get warm during continuous use. Where the avionics components make contact with the spacecraft structure, heat can transfer via conduction. Steps can be taken during construction to insulate the electrical components from the structure, using specialist insulators, but sometimes this is not possible. The heat transferring into the spacecraft structure can be used as a method of cooling the avionics component, by drawing heat energy away from the heated item, and engineers can use this design to their advantage.

Convection can be used to transfer heat energy by passing heat energy into a liquid or gas. This is how radiators and air conditioners work, and why a fan can be used to move air about for both cooling and heating. The avionics components can transfer heat energy into the air inside the spacecraft cabin, which in turn, can transfer the heat energy into the crew. The crew can also transfer their heat energy into the cabin air via the process of convection.

Thermal imaging cameras use the camera sensor to detect warm and cool items by measuring how much infrared energy is given off (or radiated) by the item. Infrared energy can transfer heat energy by radiation. Radiated heat can be reflected by the use of reflective surfaces, like the chrome reflector found on electric bar heaters. The silver aluminized spacesuit was designed to radiate the infrared heat energy. The silver surface has no impact on heat energy transferred via convection or conduction. If you sit on a hot surface wearing a silver suit, you will still feel the heat, unless the suit has some additional insulation within.

The Apollo lunar module and command module used reflective material to reflect thermal energy (heat energy).

In zero-g, heat does not rise, and cool air does not fall, warm air rises because it is less dense than cooler air, meaning warm air weighs less than cool air. Heat energy will still transfer within moving air, which is why the spacecraft uses both suit and cabin cooling air. Liquid cooling garments were used in later programs as a way of removing the crew body heat using both the process of conduction and convection.