On July 14, the Indian Space Research Organisation (ISRO) launched its Chandrayaan 3 mission. In roughly a month, the mission spacecraft has built up its momentum around earth, slingshot itself to the moon, and there, is currently preparing to descend over the lunar surface on August 23.
While Chandrayaan 3 has a complicated mission, a lot has gone into increasing the chances of its success, including how its instruments were built and tested. A journey through space – even as short as the one from earth to the moon – is an adventure in which the spacecraft’s own needs need to be balanced against the harsh demands of spaceflight.
The solar wind
A particularly frustrating problem is due to the sun. The scorching hot surface of the star, a very busy place, emits a stream of energetic charged particles, like protons and electrons, moving extremely fast, called the solar wind. Since they are charged and earth has a magnetic field, these particles are deflected and guided towards earth’s magnetic poles.
When they cross over into the planet’s upper atmosphere, the electrons and protons collide violently with atoms there, especially oxygen and nitrogen, which are its chief constituents. When the oxygen and nitrogen atoms absorb an electron, they acquire ‘excess’ energy that they release as photons, or light, of some frequencies. Oxygen is responsible for the shades of green and orange, whereas nitrogen contributes to the blues.
These interactions produce the radiant display known as the northern lights, spanning a spectrum of hues and intensities.
Earth’s magnetic field renders such beautiful skies as well as protects the life and objects it hosts from the wrath of the solar wind. But earth also has its own van Allen radiation belts – particles from the solar wind that are now trapped along the planet’s magnetic field.
Particles that sway polls
This said, unlike instruments on the ground, satellites, space stations, and moon-bound spacecraft like Chandrayaan 3 have no ‘natural’ protection, leaving them vulnerable to a variety of issues.
The equipment onboard these spacefaring vessels have to withstand the impact of the particles of the solar wind or face catastrophic failure. The potential problems range from laptops crashing to a complete malfunction of critical systems, as was the case with Canada’s Anik E2 satellite in 1982.
Generally, these effects are categorised as displacement damage and single-event transients. Displacement damage results when the impact of a charged particle in the solar wind is so strong that it displaces an atom in an electronic chip. Such damage, due to which the chip’s performance decays over time, is usually permanent.
Single-event transients cause signals being transmitted by the spacecraft to momentarily fluctuate, corrupting the intended message encoded in the transmission. In a famous example of such signal corruption, votes ended up being miscounted in an election in Belgium in 2003. A single-event transient flipped a bit in a voting machine from ‘0’ to ‘1’, resulting in one candidate receiving 4,096 votes more in the poll.
With all possible outcomes in mind, scientists and engineers use advanced engineering techniques to design and manufacture the corresponding electronics, and these are commonly called radiation-hardened electronics.
During chip design, manufacturing, and packaging, experts meticulously consider radiation levels and possible damage mechanisms, and incorporate multiple layers of protective measures in both software and hardware components. For instance, three copies of the same signal can be transmitted (triple modular redundancy). In the unwelcome event of bit corruption, the other two bits can ‘outvote’ the corrupted bit.
These safeguards also need to be mindful of those required to protect the instruments against other problems.
For example, just before they get to space, they need to be launched. On the launchpad, the rocket’s contents – including the spacecraft it is launching – will be subject to severe vibrations. So the instruments have to be built and tested to make sure they survive this experience.
A hairy environ
In space, the spacecraft could experience enormous temperature fluctuations. Chandrayaan 3 itself may have to work through both -200 degrees to 200 degrees Celsius, depending on the satellite’s position relative to the moon and the sun. Wires could break, solder could fail, and chips could crack. Support materials on the solar panel (required to power the spacecraft) made of copper could become more ‘active’ – like water at its boiling point – and seep through the solar cell, rendering it inefficient.
When some materials are placed in a vacuum, they release air molecules trapped in them. This outgassing can be a nuisance, particularly with temperature fluctuations. For example, outgassed air molecules can deposit themselves on a camera lens, and there’s no one on the moon to wipe the lens. The result: bad photos. Outgassed molecules lodged between electrical contacts can even burn the contacts and electrical switches.
Sometimes there are problems that experts don’t fully understand, but nonetheless need to deal with. For example, one explanation for why some metal coatings form whiskers – electrically conductive protrusions – is that they are expressions of built-up stress in the metal. Some metals ‘grow’ whiskers when in a vacuum, and the whiskers can short some circuit or other. Several satellites have failed completely as a result.
In response, experts need to carefully select the metal coating and optimise the way it is applied – an exercise both knowledge- and resource-intensive.
So far, so good
These are just a few of the profound challenges that any space mission must contend with. Vacuum, extreme temperatures, and radiation make for a brutal workplace in which to perform one’s job, so only the most resilient, sophisticated, and smart solutions survive.
Chandrayaan 3 has survived so far – and this is why, even before it attempts to land on the moon, it represents an important collective achievement, on the part of ISRO as much as the wider national community of people who acquired and synthesised the requisite knowledge, engineered and assembled the materials, planned for a host of eventualities, and eventually launched it to the moon.
Awanish Pandey is a senior fellow at CERN.