The past and future of lunar exploration

It is almost 50 years since man first landed on the lunar surface, when on July 20, 1969, Neil Armstrong took the first giant step for humankind. Apollo 11 was the spacecraft in which three astronauts embarked on the lunar voyage, with two of them landing on the moon. Apollo 10 made the first manned round trip around the moon.

In the next three years, till December 1972 when Apollo 17 made the final manned lunar trip, 12 astronauts walked on the lunar surface. Apollo 17 spent three days on the moon, collecting several kilograms of rock (earlier Apollo manned missions had already brought back 300 kg of lunar rock).

Apollo 15 also had a rover (for the first time) on the moon wherein the astronauts traversed some kilometres from their spacecraft. The Russian robotic vehicle, launched in 1973, traversed nearly 40 km on the moon (more than the distance traversed by all Apollo astronauts together). The unmanned Russian probes Luna 16, 20, and 24 also brought back several kilograms of lunar rock.

Since December 1972, no human being has been to the moon. With the recent death of Apollo 12 astronaut, Alan Bean, only four men who have actually landed on the moon are alive today. They are Charles Duke, David Scott, Edwin Aldrin and Harrison Schmitt. The successful manned landing on the moon by Apollo 17 was the culmination of John F Kennedy’s vision outlined in 1961, to land Americans on the moon by the end of the decade.

After the Apollo manned missions and the unmanned Russian Luna probes of the early 1970s, there has been a comparative lull in further exploration of the moon. The focus turned to planets like Mars and Venus and outer planets of the solar system as ably demonstrated in the success of the Pioneer 10 and 11 as well as the Voyager 1 and 2 missions.

The manned lunar landing technology of 50 years ago was quite advanced. While we appreciate our current Indian Geosynchronous Satellite Launch Vehicle (GSLV) trying to put five to six tonnes in orbit, the Apollo manned missions had 150 tonnes in orbit before embarking to the moon. The various space stations subsequently developed, like Skylab, Mir, etc, had around a hundred tonnes in orbit 50 years ago.

Following the Apollo and lunar missions, there was a gap of more than around 20 years before the Clementine probe to the moon was launched. The Asian missions, especially China’s, have been more active recently in exploring the moon, with a number of Chang’e missions. The Japanese Selene probe and the Indian Chandrayaan-I (2008) were the other unmanned trips to the moon.

Humans or robots?

In this connection, it is interesting that US President Donald Trump recently signed a directive to send astronauts to the moon, or rather send Americans back to the moon. Some experts feel it is perhaps best to send robots — and we already have illustrious examples in the Lunokhod and the Martian rovers — as lunar dust could prove hazardous to astronauts’ health (there is evidence for this from the experience of Apollo astronauts). The robotic missions, costing only a fraction of the manned missions could deliver instruments to the lunar surface for identifying water, hydrogen, etc and search for better understanding of the lunar environment. Perhaps, a moon valley outpost could be constructed by robots, followed by manned missions.

There are also proposals for Russia-US cooperation to use a lunar space station as a stepping stone to manned space flights to Mars. The reason being that the escape velocity from the moon (or around it) is only one-fifth of that of the Earth, and therefore, the energy required to fly from the moon to Mars is only 4% of that required to fly from Earth’s surface to Mars.

China recently launched a relay satellite, Queqiao, to prepare for a lunar rover mission later this year. It has settled into an orbit that will take it 60,000 km from the far side of the moon, where China will aim to land a rover called Chang’e 4. This would make it the first probe to soft-land a rover on the far side of the moon (about which little is known). Queqiao should be well-positioned to provide continuous communication with the robot rover on the far side of the moon.

Another Chang’e mission would explore the moon’s South Pole Aitken basin with a payload of instruments. China previously launched the Chang’e 3 rover on the moon five years ago and, in October 2014, carried out an unmanned round trip around the moon and back to earth.

India plans to launch Chandrayaan-2 in October which would also land a rover with many instruments on the lunar surface. The Japanese space agency, JAXA, is considering two future missions, a lunar pole mission to look for water and a sample return mission from the far side of the moon. The search for water on the moon has been spurred of late by new evidence of the mineral moganite in lunar meteorites by a Japanese team.

Recent missions have also found evidence of lunar water ice concentrations at the poles in several ‘cold trap’ pockets. This is considered as the first evidence of abundant water ice at mid and lower lunar latitudes. Water broken up into hydrogen and oxygen can be used as fuel to propel interplanetary spacecraft (to Mars and beyond) from the moon’s surface.

In short, space missions to our nearest celestial neighbour is likely to operate in full swing in the near future.

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