Why are satellites wrapped in golden coloured paper days before the launch?
Ranjitha, Chitradurga
Satellites in orbit are exposed to various types of space adversaries against which they have to be protected.
The golden paper or foil what we normally see is in reality is a multi layer insulation, known as MLI. It consists of lightweight reflective films assembled in many thin layers. These layers are typically made of polyimide and/or polyester films (according to design, could be from 5 to 30 layers) that are vapour deposited with 99.99 per cent aluminium, on one or both sides. Ideally the satellites are designed to work in a temperature range of -23 degrees celsius to + 40 degrees celsius.
Today's spacecrafts see a multitude of temperature fluctuations that can range from lows of -100 degrees celsius to highs of +150 degrees celsius, depending on the spacecraft's orbit.
This can be Low Earth Orbit (LEO), Geosynchronous Earth Orbit (GEO), Synchronous or Interplanetary Orbit. Basically, the MLI is thermal insulation primarily intended to reduce heat loss by thermal radiation. In its basic form, it does not appreciably insulate against other thermal losses such as heat conduction or convection. It is therefore commonly used on satellites and other applications in vacuum where conduction and convection are much less significant and radiation dominates. MLI gives many satellites and other space probes the appearance of being covered with gold foil.
The MLI also provides protection against fine space dust, for which the foil is kept a little distance away from the parts required to be protected.
S P S Jain, Greater Noida.; P K Jain, Deputy Director, Satellite Communication, ISRO, Bengaluru.
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Why does fresh milk get spoilt easily , unlike boiled milk?
Preethi Venkatachalam, Mettur, Tamilnadu.
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