NASA’s new heavy-lift rocket, the Space Launch System, which is still in development, will enable the construction of DSG. It will be supplemented by Russia’s less-powerful Proton-M and Angara rockets. However, it is misleading to portray this as a purely Russia-US partnership, because the three other ISS partners (the European, Japanese and Canadian space agencies) are highly likely to be involved too.
Since Apollo 17 came back from the moon in 1972, no human has ventured further from home than “low-Earth orbit”, an altitude of only 400km in the case of the ISS.
The ISS began construction in 1998 and has been continuously occupied by (usually) six crew since November, 2000. Previously planned to last until 2020, the project has been extended until 2024 and could be eked out longer. However it is ageing – and many would argue that it should have already been replaced. It has cost somewhere in the region of $150bn. That isn’t cheap, but, to put it into context, it works out as about the same as what humanity has frittered away on buying lipstick over the same 20-year period.
“From the moon’s point of view, the DSG would…offer great opportunities for scientific measurements.”
We can expect a comparable or larger price tag for the DSG, which is due to begin to be assembled in the mid-2020s, assuming that NASA can get its heavy-lift Space Launch System ready in time despite a precarious funding situation.
Unlike the ISS, the DSG would not be continuously inhabited. Current plans call for one annual 42-day visit by a four-member crew, at first. When unoccupied, instruments on the DSG could continue to collect useful scientific data, especially when close to the moon. It won’t be placed into a low lunar orbit, but into special points in space such as where the gravitational attraction between the Earth and moon are balanced. This allows it to follow a “near rectilinear halo orbit” (see video below). From the moon’s point of view, the DSG would repeatedly sweep low over one pole, offering great opportunities for scientific measurements.
However, these orbits are only quasi-stable, so some adjustments would be necessary to maintain the DSG in these configurations without floating away elsewhere. The Canadian Space Agency has suggested the use of a solar sail to do most of the work, rather than using thruster fuel. I think that is a great idea, because solar sails, which get a push from radiation pressure, have not yet been trialled adequately to test their potential – so this is an opportunity to assess how to best work them. Apart from their use in manoeuvring around the solar system, solar sails may one day propel probes to the nearest stars.
The DSG is a ways from reality, it is a logical next step after the ISS – and any long-term multinational cooperative enterprise in space has to be a good thing, given the bickering between nations going on down here on Earth. It may not lead us very quickly to Mars though – government-funded projects are often cash-strapped, meaning the plans could lag behind private enterprise efforts from independent exploration companies.
Is a Lunar Orbiting Station and Base the Next Step For Space Exploration?
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This story was written by David Rothery. Some content may be edited for length.