Gateway to the Moon - and beyond!
Image credit: NASA, ESA
Nasa’s upcoming space station endeavour - a multi-purpose outpost orbiting the Moon - aims to support long-term human return to the lunar surface and serve as staging points for deep space exploration.
For over 22 years, humans have maintained a continuous presence in space, on board the International Space Station (ISS). It has now become almost routine, as astronauts and cosmonauts regularly blast off for stays in low-Earth orbit (LEO), with relatively little fanfare.
But all of this is about to change. Nasa currently expects the ISS to retire from active service in 2030, because a hot, new destination in the sky is about to re-open its doors: the Moon.
The successful launch of Artemis 1 in November 2022 was the first step on the journey, testing the rocket that will take four crew members, including the first woman, back to our natural satellite.
The plan now is to launch Artemis 2 in 2024, which will take four astronauts out of Earth’s orbit for the first time since Apollo and take them around the Moon. This will be followed by the Artemis 3 mission, currently scheduled for 2025 on the space agency’s wildly optimistic timeline, during which humans will touch down on the lunar surface once again and begin a new era of human space exploration.
Initially, the new missions may look like a high-definition remake of the original Moon landings, as flags are planted and astronauts in bulky space suits bounce across the Moon in low-gravity. But they are also very different to the Apollo missions of decades ago, as this time around Nasa is planning to stay.
After the first landing, Artemis 4, the Orion space capsule containing the astronauts, will be accompanied by the International Habitation Module (I-HAB). This will be docked with a propulsion module in orbit around the Moon, to form the backbone of a brand-new space station called the Lunar Gateway – humanity’s first to orbit a body other than the Earth.
Although most of the attention will, understandably, be on the astronauts down below, taking further small steps for mankind, it will be an important moment, as Gateway won’t just make it easier to get to the Moon, but it will also be our first concrete steps towards taking humans to Mars.
“What we really bring to the table is that centralised [Lunar Transit] Hub,” says Dan Hartman, programme manager for Gateway at Nasa and an ISS veteran. “We have the infrastructure for all these different vehicles – the human lander, the Orion vehicle – to aggregate there, to transfer to EVA suits [for space walks], to transfer the logistics, and then take two crew down to the surface in the lander.”
In other words, at its most basic level, Gateway is lunar ‘Park & Ride’ – a place where astronauts can transfer from one vehicle, such as an Orion capsule that launched atop Nasa’s Space Launch System rocket from Earth, into a lunar lander, like a specially modified version of SpaceX’s enormous new Starship rocket, which has won the contract to take the first astronauts down to the surface.
“Once we get those first two elements out there, the Power and Propulsion Element mated with what we call I-HAB, which is our habitation and logistics outpost, we are ready to receive crew from Orion,” says Hartman.
The rationale behind using Gateway as an interchange, instead of flying directly, is prudent from a logistical perspective, as it will essentially break the two trickiest parts of any mission to the Moon in two: getting to Lunar orbit, and travelling two and from the lunar surface. “If the lander had a development problem, we could carry on launches from Kennedy to the Gateway,” says Hartman.
Gateway then gives Nasa greater flexibility and a back-up plan if the extremely complex ballet of getting every part of the Artemis programme together goes awry. It means that if, for example, Starship doesn’t work out as the lander, substituting it out will be easier as it won’t require redesigning the entire programme. And similarly, if other viable launch vehicles emerge, swapping them in is more straightforward.
Having Gateway in orbit around the Moon has other advantages, too. “We offer almost 100 per cent communication coverage with the Gateway flying in a rectilinear ‘halo’ orbit around the Moon, so it [provides] almost constant access to what we’re doing,” says Hartman.
And with the propulsion module, Gateway will be able to move into different orbits to potentially float above wherever on the lunar surface is the most interesting.
“Whereas Apollo was down around the equatorial, we can go anywhere we need to, to hit different items of interest that the scientists want to see on the Moon,” says Hartman.
When it comes to building a new space station, Nasa of course isn’t starting from scratch, and nor is Hartman, who joined the ISS programme in 1994 and was responsible for the design of several major sections of the station, before he transferred to the Gateway programme. “We’ve been able to infuse a lot of the technology from the ISS,” says Hartman.
One clear example of this is how Gateway will be powered. In 2017, Nasa launched an experimental mission to test a new type of solar array called iROSA: instead of needing to launch panels fully formed, Nasa launched it folded up and unfurled it in space, saving both weight and volume in the cargo bay. Because of this successful in-space experimentation, Gateway will be using the same system from day one.
“We’re using the same company and the same technology,” says Hartman. In fact, because the technology is proven, Gateway will be taking the technology even further, using iROSA panels that are even more energy dense, with even greater power-generating capacity.
And much of the technology in the I-HAB on the new station will be carrying over, too.
“I applied lessons learned all over the place,” says Hartman, “If it’s an exercise device, or a carbon dioxide scrubber or fluid contamination in our pumps, that’s all [things] we have learned from the ISS.”
However, there are also significant differences to ISS – which Gateway designers need to plan for. “It’s just a completely different radiation environment and different thermal environment around the Moon, than we have here at LEO,” says Hartman.
The difference with ISS is not just technical. ISS was designed for 24/7 usage as an orbiting science lab, but while it will still support scientific research, Gateway is designed for shorter stays as astronauts’ transit to and from the Moon, and it will remain empty for extended periods. So the economics of Gateway are very different, which has led to certain design choices.
For example, while the ISS has spent the last 20 years recycling astronaut urine back into clean drinking water, this is one technology Gateway won’t be making use of.
“It’s easier and less expensive to just carry your water and your oxygen in tanks and in bags with you for a 30-day mission,” says Hartman. “It’s pretty expensive and pretty heavy, [but] you’re better off from an economic trade-off. If we stayed longer, we would put a regen system on Gateway.”
Resupply missions to the Gateway will also be more expensive than to the ISS. Nasa recently contracted SpaceX to use its Falcon Heavy rocket to fly several resupply missions – which is physically like three of the Falcon 9 rockets it uses to fly to the ISS strapped together. That means that Gateway trips will require more hardware and more fuel.
“There’s a lot of vehicles coming and going to the ISS, maybe 10 to 12 a year, be it crew or cargo,” says Hartman, “You can do it to the Moon, but it’s really, really, really expensive. And so what we have done across the board is try to shave mass out of everything. And one of the principal ways you can shave mass is you get into a redundancy discussion.”
Nasa is trying to be smarter about how it manages resources on the Gateway. “On the ISS, let’s say they have three computers that run everything. We’re going to try to get [more] reliable computers and we’re going to go with two,” says Hartman. “We’re trying to really reduce our reliance on other pieces of equipment.”
Getting back to the Moon is obviously an exciting prospect, but this isn’t the full extent of Nasa’s ambitions. The Artemis programme falls under the agency’s ‘Moon to Mars’ strategy, the idea being that technologies pioneered by Artemis will one day be used to reach the Red Planet. Gateway is a key part of the plan.
“You could effectively put pieces of your Mars transfer vehicle at the Gateway,” says Hartman, who points to how life support, environmental control systems – and everything else that is going to be needed for a 21-month Mars mission – will need to be thoroughly tested before astronauts are blasted off into deep space. “Before you say, ‘OK, let’s hit the go button and go to Mars’, you really want to wring out that system,” says Hartman.
It is this consideration that has informed how Hartman and his team have iterated beyond the ISS design. “As you connect all the modules together, there’s a lot of places on the ISS where you’re dead-ended, you can’t expand,” says Hartman. “So every one of our modules that we’re flying, we have added docking ports. three to each one. Then if we have a vehicle that we’re going to put in one of those docking ports, we’re making sure the other end of that vehicle also maintains a docking port.”
This means that though the Lunar Gateway will only initially be one-sixth of the size of the ISS, there is much more scope for expansion by adding new modules or reconfiguring the existing layout. And this could prove particularly useful when testing cutting-edge modules for a Mars mission, such as one usual proposal to inflate modules like a balloon.
“Inflatables are a big thing right now,” says Hartman. “You can blow them up, that gives the crew tremendously more volume. And fundamentally they could be lighter.”
Perhaps eventually Gateway will gain its own recycling system to test how astronauts can remain hydrated during the long journey to Mars. Mars is driving other Gateway design decisions, too. “We’re building a lot of autonomy into our systems that really don’t need interaction,” says Hartman. “They can self-heal, self-diagnose and make system changes on the Gateway without any of our onboard crew members or ground controllers participating.”
The reason for autonomy isn’t just to ease the burden on staff – there’s a very practical reason too: latency. “We just don’t know how to operate very well, in a far-off region, with crew on it, where we don’t have constant communications with us,” says Hartman.
As the Moon is 384,400km away from Earth, voice communication can lag between 10 and 15 seconds. On Mars, depending on where in the orbit the two planets are, messages to and from Earth could be delayed anywhere between 5 and 20 minutes. Gateway will act as a proving ground for some of the autonomous systems that will be necessary on a deep space mission, where radioing in “Houston, we have a problem” won’t be an option.
Ultimately, then, whatever vehicle eventually takes humans to Mars could end up looking something like the Lunar Gateway. It will be a sad day when, some time in the 2030s, the ISS is shuttered and sent into a controlled burn in Earth’s upper atmosphere. But it will be leaving a technological legacy that will have got humans back to the Moon.
Thanks to Gateway, the next 'Giant Leap' won’t just be more steps on the Moon – it could be the first small steps towards getting humans to Mars, too.
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