Space blankets and How the TeamIndus spacecraft will survive in space

A look at multi-layer insulation and how we use it

Out there in the harsh environment of space, spacecraft must deal with extreme hot and cold temperatures. The spacecraft need not just survive the extreme temperatures but also function in such harsh environments throughout the mission.

Difficulties of managing heat in space

Spacecraft can experience temperatures in space that are either too hot or too cold. Solar radiation can heat the spacecraft to hundreds of degrees, posing a risk to their survival. On the other hand, being eclipsed from the Sun when behind a celestial body (say Earth) can be too cold for the spacecraft, sometime as cold as hundreds of degrees below 0° C.

Experiencing either too hot or too cold temperatures beyond the survival limits of the spacecraft can permanently damage it and its components can cease to function as intended. Depending on the environmental conditions, the spacecraft components need to be heated or cooled down. It is particularly difficult to do so efficiently because:

  • Electric power onboard the spacecraft is too limited to make use of heaters excessively.
  • The environmental conditions can drastically vary depending on the mission phase, making it difficult for one solution to adapt to all needs.

This is where a technique called multi-layer insulation (MLI) comes in.

Preserving heat using a multi-layer space blanket

Crucial parts of a spacecraft are usually covered with multiple layers of a highly insulating material called Kapton. Between each successive Kapton layer, another insulating material called Mylar is used.

A closeup of a multi-layer insulation material. Source: Wikipedia

Such multi-layer insulation (MLI) allows minimal heat to pass through either way, thereby maintaining the desired temperature on the spacecraft parts it is designed to protect. Materials used in MLI are also very stable at a wide range of temperatures and do not deform easily. They are thus useful in a wide variety of cases.

#1: Protection against excessive heat

Notably, NASA’s James Webb Space Telescope (JWST) to be launched in 2020 will use a MLI sunshield to protect its optics. The sensitive optics must function at extremely cold temperatures and will get deformed if exposed to excess heat.

Cross-section of JWST’s MLI sunshield that protects the sensitive optics from the Sun’s heat. Source: NASA JSWT

Interestingly, the insulating material used between the Kapton layers is no material at all, but vacuum. Vacuum itself is a poor conductor of heat and thus enables the MLI setup to preserve the optics, allowing us to explore the Universe.

#2: Protection against excessive cold

Alternately, missions sent to the outer solar system need to be warm enough to function. At such large distances from the Sun, the spacecraft quickly start losing heat to deep space. A lot of the electronic components can cease functioning at this point or the craft can also be permanently damaged.

NASA’s New Horizons spacecraft on a flyby mission to Pluto was thus fully covered with a gold-colored MLI to retain internal heat.

NASA’s New Horizons spacecraft fully covered with a gold-colored MLI (multi-layer insulation) to retain internal heat. Source: Wikipedia

#3: Why not just use a thick block shield instead?

Using one thick block will conduct heat from one end of the spacecraft to the other. A multi-layer insulation made up of different material means that each layer is hotter/cooler than the other and the heat dissipation is thus minimized. Additionally, a thick shield would increase the weight of the spacecraft which is not desired. MLI on the other hand is quite lightweight.

#4: Protection from impacts

Despite being thin, an MLI covering also provides protection to the spacecraft from micrometeorite impacts. If say, an outer facing layer is damaged, the rest of the layers still serve the purpose because redundant layers are used to enhance reliability.

Use of MLI on the TeamIndus spacecraft

MLI insulation is key to the functioning of a lot of key components throughout the mission. We thus use MLI extensively on our spacecraft. Here are some mission scenarios where we need the comfort of a space blanket.

#1: In lunar orbit

While orbiting the Moon in its nighttime, the spacecraft will face extreme cold temperatures. For example, in the S2 orbit shown in the diagram below, the spacecraft will experience nighttime temperatures colder than -50° C for more than an hour.

Orbits of the TeamIndus Z-01 spacecraft around the Moon

To ensure functioning of the components and to prevent damage to the spacecraft, all its crucial parts are covered in MLI as shown below.

TeamIndus spacecraft model showing MLI covered parts (yellow).

#2: Facing the heat during the lunar descent

Our spacecraft will begin the landing phase just after sunrise. The heat loads on the spacecraft will be maximum at this time due to combination of the heat from the Sun, the Moon and most notably the main engine firing throughout the landing. Parts of the main engine cross 1000° C and such intense heat can damage the spacecraft if it reaches the main deck above the engine. The titanium heat shield is thus connected to the main engine and it takes most of the heat load.

The titanium heat shield (yellow) takes the intense heat load from the main engine.

However, it needs to be ensured that the residual heat is not conducted to the rest of the spacecraft via the main deck. The 15-layer MLI protection is thus employed to protect the spacecraft by not letting the heat from the engine and heat shield reach the main deck.

MLI protection (yellow) between the main deck (purple line) and the heat shield (brown).

The propulsion tanks and the fuel lines onboard the spacecraft are also MLI protected.

#3: Communication equipment

The X-band transmitter used for sending data can touch close to -50° C during the nighttime lunar orbits, which is beyond its operational range. Similarly, the motors driving the antenna may become non-operational too at such low temperatures.

Both the motors in the antenna and the X-band transmitter are thus covered with MLI to prevent heat loss during such phases. Supplementary heating is also provided by the heaters onboard the spacecraft.

Antenna motors (center) wrapped in MLI at its bottom.

#4: MLI everywhere else

Other components onboard the spacecraft like the descent sensors (Laser Altimeters and Descent Cameras), the star sensor, the Inertial Measurement Unit (IMU), battery, etc. are all MLI protected to keep them within desired temperatures.

Star sensor model shown covered in MLI.

Conclusion

That was a sneak peek into a kind of thermal protection technology used in space missions and some scenarios where we use MLI for our spacecraft. MLI is employed in all space missions as an established method for maintaining the spacecraft heat against either of the extreme temperatures.