Old School Spacecraft Thermal Insulation

Quote of the Day

Everything not forbidden is compulsory.

— T.H. White, The Book of Merlin. I have heard people make similar statements about quantum mechanics, particle physics, and cosmology.

Introduction

I saw this article about a solar probe called the Solar Orbiter that uses a form of insulation with a history that dates back to early man. The article makes the following statement.

At such a close distance, the spacecraft needs protection from the sun's powerful rays. The mission will endure 13 times the intensity of normal sunlight and temperatures as high as 520°C.

I will show where the factor of 13 comes from. Before I discuss the insulation, however, here is a brief video that describes the mission of this probe.

Background

The article describes the insulation as a pigment similar to that used to make cave paintings by ancient man.

The pigment is called 'Solar Black', a type of black calcium phosphate processed from burnt bone charcoal. It retains its properties under intense conditions, even over thousands of years.

The material was developed by the Irish company Enbio.

Analysis

The article states that the probe will come as close as 42 million kilometers to the Sun. Since radiation intensity follows an inverse-square law relationship with distance, we can compute the increase in solar intensity with distance shown in Figure 1.

Figure 1: Increase in Solar Intensity with Distance.

Conclusion

I was able to derive the stated 13x increase in solar radiation level using a simple square-law relationship.

I find the use of low-tech materials and techniques interesting in high technology projects. Other examples I have seen recently include:

• Cork is used to make space craft heatshields.
• Knots and ropes being used to rig cables on rovers.