In space technology Helium gas at very low temperatures was used to produce vacum conditions similar to those that exist in outer space. Simulation studies were carried out in high vacuum conditions and this helped in undertaking manned space flights. Helium was also used in a Russian Sputnik while testing the flight of the dog Laika in 1957. The first manned flight was successfully completed in 1961. Helium gradually became quite indispensable to space technology.
A rocket in space uses Helium in more than one way. In its three stages of launch, the first stage uses Helium to purge fuel gases comprising of Hydrogen mixed with Oxygen in the fuel vessel. It is pumped into a rocket fuel tank to create pressure, which is required for firing the rocket. Helium slowly increases pressure and can be used to control the flammability of Hydrogen. A Saturn booster, like the type used on the Apollo Lunar missions, required about 13 million cubic feet of Helium for firing and more for checkouts.
Helium is also used as a coolant in Hydrogen fuelled rockets. During operation of a satellite in space, cryogenic properties of Helium help in avoiding overheating of its components. Being an inert gas it does not react with the other chemicals present and can be safely used. Space borne Helium cryostats are designed to store super fluid Helium. They are compact and made light weight using aluminium alloys casings.
Helium cryostats are specially designed for space applications in many other optical equipment in the flight on board. The casings have multi-layer volume insulation that allows Helium to stay at low temperatures for several years in Space. High technology devices and porous plugs are designed to control the flow and avoid any probability of leakage. It is expected that not even one milligram of Helium would leak from the cryostat over the hundred years.
Astronomical bodies moving towards satellites are detected using infrared sensors. Normal cosmic radiation occurs at 3K and cooling of infrared detectors to 2K using liquid Helium is another useful application. Spacecraft also use Helium in specially designed magnetometers for space. The Helium Vector Magnetometer can sense the altitude of a satellite; help in detecting other satellites and also help in measuring magnetic fields of Earth, Moon, Sun and Planets. Helium ionized gas magnetometers have been used to detect radiation belts around the Earth.
In Space, Helium is present in minute quantities. Since sound can travel at five times the speed in Helium than in air, presence of Helium helps in detection of low flying cruise missiles. Helium is also used in heat-guided missiles. It is also expected that in future Helium can help in safe landing of a spacecraft or satellite after completion of its life span. This is because after completing its life, a spacecraft becomes a hazard to other orbiting satellites crossing its path. According to NASA as many as 50,000 pieces of broken satellites and other debris are already orbiting the Earth. Floating and travelling with high speed they run high risk of collision with existing satellites.
A collision, if it ever takes place, would be highly dangerous in destroying existing satellites, while creating huge loss and huge amount of junk in Space. On its own the debris would take to reach the atmosphere, where it will burn on re-entry and be destroyed.
To expedite the process of safe re-entry in the atmosphere, satellites can be provided with an extra engine to get back into the Earth’s atmosphere. This, however, would require extra fuel tank and result in an increase in the overall weight of the satellite. Alternatively, specially designed satellites such as ‘Clean Space’ are planned to be launched to take debris back into atmosphere and get rid of orbiting debris and space junk.
A satellite can carry a folded balloon, the balloon weight would be negligible to carry. After completion of the life of the satellite, the balloon can be filled with the available Helium on-board. This balloon would then help in creating a drag force to allow spent rocket parts to gravitate towards Earth’s.