Spacewalks, no cakewalk

Spacewalk, wherein astronauts leave their spacecraft to carry out repairs or install devices, has been much in the news.

Hardly two months ago, NASA astronauts Christina Koch and Jessica Meir performed the first all-women spacewalk outside the International Space Station (ISS).

They spent seven hours outside the ISS replacing a failed power-control unit. Koch had already carried out four spacewalks, but it was the first such mission for Jessica who became the 15th woman to walk in space. They stepped outside on October 18 and made their way to a location called Port Truss structure to replace the battery charge-discharge unit.

They returned to the airlock with the damaged part, which subsequently is to be placed on the next SpaceX Dragon resupply ship for inspection on Earth.

Superlatives

The first woman to spacewalk was the Russian cosmonaut Svetlana Savitskaya, who went outside the Salyut 7 space station on July 25, 1984, for three-and-a-half hours. The first person to spacewalk was Alexei Leonov, who died recently at the age of 85. He achieved this feat on March 18, 1965.

Tethered to his spacecraft by a five-metre cable, the Russian floated above Earth for 12 minutes.

The first American astronaut to spacewalk was Ed White in June 1965, who also spent 20 minutes outside the craft. Some 570 people have been in space so far, about 70 of them women. There have been hundreds of spacewalks. There have been several memorable spacewalks.

The Hubble Space Telescope required a series of spacewalks to carry out both the initial repairs and repairing malfunctions to extend its lifetime. Thanks to these spacewalks, the Hubble Telescope still functions, after 30 years.

The long and short of it

The longest spacewalk, in March 2001, lasted nearly nine hours and took place during the STS-102 space mission, involving Susan Helm and Jim Wess. The McCandless spacewalk in 1984 used a jet pack called Manned Manoeuvring Unit (MMU). Bruce McCandless made the first untethered spacewalk during the American STS-41A space mission. He flew a hundred metres from the space shuttle. It was observed as a human being operating like an angel moving in transearth space. The shortest spacewalk, in September 2004, was only 14 minutes as astronaut Michael Fincke working at the ISS was forced to abort walk due to a pressurisation tank problem.

The spacewalk with most people was in 1992, for the mission STS-49 which involved the capture of an errant satellite, Intelsat VI, stuck in low Earth orbit instead of a geostationary orbit.

A July 1990 spacewalk to repair insulation on a Soyuz spacecraft turned out most dangerous as MIR space station hatch did not close.

The most recent spacewalks, now happening and continuing this month involves the sophisticated Alpha Magnetic Spectrometer (AMS) onboard the ISS. NASA astronaut Andrew Morgan and ESA astronaut Luca Parmitano would need to take at least four spacewalks (saga began on November 15 with a six-hour spacewalk) to repair the ailing Dark Matter (DM) experiment outside the ISS.

AMS records the number of particles passing through all of its detectors, (more than 200 billion to date) type of particles, mass, charge, velocity, the distance of travel, etc.

The recent November 2, 2019 launch carried the final supplies for the spacewalks and also the required tools for upgrading devices. Luca Parmitano and Drew Morgan will perform the last of their spacewalks to repair AMS.

These spacewalks will enable many more years of data collection by the special instruments by extending the lifetime of the two-billion-dollar telescope.

Fixing AMS is such a big job, that astronaut teams will need five spacewalks to finish the work, which started on November 22, 2019.

During the November 15 spacewalk, the astronauts removed a debris shield from the ailing AMS. It was too big to be inside, so it was jettisoned.

In this garbage-removal duty Morgan was anchored in place by two robot arms on November 22, once again ventured in the vacuum of space to repair AMS.

These are known as spacewalk surgeries to repair the instruments.

The procedures developed to perform these spacewalks would be crucial for future astronaut teams who will require different types of extravehicular activity in forthcoming manned missions to the Moon and Mars.

(The writer is with Indian Institute of Astrophysics, Bengaluru)