Question Shuttle heating in LEO

[Coolhand]

I'm sure someone here knows the answer,

Is sunlight energy a big deal in earth orbit? remember Apollo 13 where the ship froze up after the systems were shut down... The shuttle needs radiators in LEO, how much of this is used to cool the systems (avionics, etc) and how much is used to dissapate the heat absorbed by sunlight.

Also, how hot or cold would the shadow side of a shuttle in orbit be?

thanks.

 

[Urwumpe]

Also, how hot or cold would the shadow side of a shuttle in orbit be?

Could cool down to about -120°C, if you keep attitude for long times. The thermal differences between shadow and light side of the shuttle are actually enough to prevent closing of the payload bay doors - the infamous banana effect.

But other than the LM, the shuttle has a full passive thermal control system around the cabin and the fuel cells always produce heat, if they also produce electricity - conditions like inside the Apollo 13 LM are impossible in the shuttle. If you have a full loss of electricity the Shuttle is practically dead - it has no batteries as backup.

 

[Coolhand]

hmm.. so really my question is, how is sunlight powerful enough to heat one side (how hot does it become?) and yet didn't cook the astronauts in an apollo capsule with no power? When it comes to keeping a shuttle cool, are we mostly concerned with the internal systems heating the ship, or sunlight?

 

[JamesG]

The Apollos rotated slowly to prevent heat gradients from forming on the hot and cold sides. Both the CM and LM were well insulated, so as in Apollo 13 without electrical heat, the interiors can get very cold. The Shuttles are also very well insulated, but have much more internal heat generation, both electrical and human, plus the residual heat from launch that has to be radiated away.

 

[tblaxland]

hmm.. so really my question is, how is sunlight powerful enough to heat one side (how hot does it become?) and yet didn't cook the astronauts in an apollo capsule with no power? When it comes to keeping a shuttle cool, are we mostly concerned with the internal systems heating the ship, or sunlight?

A spacecraft in the vicinity of Earth will receive insolation of approx 1366W/m^2. It will also receive significant radiation from Earth itself (which is one reason why the Apollo craft had to operate their flash evaporators near the Earth and the Moon).

Take a hypothetical cylindrical spacecraft, 6.4m long x 4.3m dia (about the size of the LM), black body properties, in cis-lunar space (so radiation from Earth/Moon is negligible). Using Stefan-Boltzmann's law we can calculate that this will reach equilibrium at an average skin temperature of about 275K if it is long side to the sun (just like Apollo "BBQ mode"). In the Apollo 13 case, there was little internal heat being generated so the internal temperature will slowly approach this temperature (the rate being determined by the amount of insulation). "Apollo by the numbers" tells me that the LM cabin temp got down to 49°F (9°C/282K), so I'm pretty comfortable with those numbers.

EDIT: A few more quick calcs show the spacecraft in LEO should have an equilibrium temperature of about 324K on the sunny side, and about 246K on the dark side.

 

[Coolhand]

Tells me everything i wanted to know, thanks for taking the time to explain.

 

[Moonwalker]

A spacecraft in the vicinity of Earth will receive insolation of approx 1366W/m^2. It will also receive significant radiation from Earth itself (which is one reason why the Apollo craft had to operate their water spray boilers near the Earth and the Moon).

Water spray boilers are used on the Space Shuttle to reject heat from the APU lubrication oil and hydraulic fluid whenever the APU's are running, regardless if the Shuttle is in space or on the ground.

The Apollo spacecraft had no water spray boilers. Nor did it have a hydraulic system. To gimbal the service propulsion engine, an electromechanical actuator design has been chosen.

I think you are referring to the the water-gylcol subsystem of the Apollo environmental control system.

 

[tblaxland]

Water spray boilers are used on the Space Shuttle to reject heat from the APU lubrication oil and hydraulic fluid whenever the APU's are running, regardless if the Shuttle is in space or on the ground.

The Apollo spacecraft had no water spray boilers. Nor did it have a hydraulic system. To gimbal the service propulsion engine, an electromechanical actuator design has been chosen.

I think you are referring to the the water-gylcol subsystem of the Apollo environmental control system.

You are right, I was getting confused between the water spray boilers and the flash evaporators. The shuttle has both, Apollo only had the latter. My confusion was because they both use the same principle of operation, ie, the phase change (liquid to vapour) extracts energy from the heat source, although the specifics of the implementation are different (importantly, the flash evaporators won't work on the ground).