Escape from it all: go above and beyond in your quest for relaxation. Space hotels promise to capitalise on the ultimate dream. But there’s an elephant in orbit, and nobody’s talking about it.
“We’ve seen a lot of great concept designs for orbital hotels lately,” says Dr Iwan Cornelius. “But none of them seem worried about radiation.”
Cornelius is the managing director of Amentum Scientific, an Australian predictive scientific modelling company that quantifies the risks of radiation exposure for the aviation, transport, mining and space industries.
“I’m guessing being sick in space is not good,” the former radiation worker quips. “It’s a long way to your local GP – and the emergency department.”
Radiation exposure has bothered NASA since the earliest days of its space programs. It’s why the International Space Station (ISS) has a tiny bunker surrounded by water and equipment where astronauts can hunker down.
“One thing you’ll notice with all these concept diagrams for space hotels is there’s not a lot of information about a radiation refuge,” Cornelius notes.
Space weather forecasting is in its infancy: think solar storms, the cosmic radiation background, and relativistic electron precipitation events.
A sentinel probe is sitting halfway between the Earth and the Sun. When it senses charged particles flashing by, it sounds an alarm. The notice it gives ranges from days to hours – even minutes.
“If we’re talking about a packed hotel in space, where will they go?” Cornelius asks. “How long will it take to get there? Does everyone get access to a shelter – including staff? I don’t know if this is being thought through”.
And solar events aren’t the only space radiation source.
“We really don’t know much about it,” Cornelius says. “So we need to crunch the numbers to understand the risks.”
Amentum Scientific provides radiation exposure risk models for military and commercial pilots. It’s a surprisingly unregulated space.
“So in Europe, it’s a regulatory requirement that they monitor exposures of pilots and crew to radiation,” Cornelius says. “Once outside of the EU, it’s magically not an issue. Nobody wants to know about it.”
Pilots and cabin crew take a greater background radiation dose than nuclear fuel workers and hospital equipment operators. But, as Cornelius points out, the likelihood is very low that aircrew might be accidentally exposed to high-level radiation.
Very little space weather makes it through to our atmosphere. But it’s enough to make a difference.
“There are a couple of clinical studies showing slightly elevated cancer incidence in pilots,” Cornelius says, “but they are weird ones, such as melanomas in body regions you wouldn’t expect based on sun exposure. This indicates it’s an X-ray or something else able to penetrate the aircraft’s skin and clothing.”
Even protected by Earth’s magnetosphere, astronauts in low-Earth orbit face an even greater risk. Some have even reported “seeing” flashes of light. Researchers assume this could be cosmic rays hitting optic nerves or triggering the visual cortex.
Anyone travelling to the Moon or Mars will be completely unprotected – save whatever protection they carry with them. And that means damaged DNA and cognitive impairment are almost a certainty.
“There’s research going on into active shielding – usually creating a synthetic magnetosphere,” Cornelius says. “But I think we’ll be using wormholes before they arrive. It’s very, very early days”.
Come rain or shine…
Radiation is a deceptively banal word. It encompasses a whole spectrum – from the gently warming infrared through to cell-splitting gamma rays.
“Yes, the magnetosphere will deflect a lot of the lower energy stuff, but then the higher stuff just punches through and is still there where the space station is,” says Cornelius.
Space hotel guests will not likely face an exceptionally high risk. Especially if they only visit for a few days every few years.
Read also: What will happen when humans colonise space?
“As for short-term missions into space, I wouldn’t be worried going up there for that – so long as there’s a good solar forecast,” says Cornelius.
It’s a different matter for the concierge. Hotel staff with similar levels of protection to Space Shuttle astronauts could absorb about 10 millisievert (mSv) over a six-month shift. And that’s not including events such as solar flares.
The current safe annual limit for the general public is just one mSv. For medical professionals, it’s about three mSv. Providing protection is costly: only mass can absorb radiation.
The alternative is evacuation. That, however, may not always be possible – especially at short notice. The ebb and flow of the general galactic cosmic radiation background can be forecast up to three months in advance, Cornelius says. But nothing can yet predict a solar event.
“A lot of researchers are working on it,” he says. “I’m sure they’ll get there eventually.”
But science is only just beginning to grasp the complexities of space weather. The same Van Allen Belts that deflect solar radiation now appear to generate their own storms.
“There’s a precipitation of electrons,” Cornelius says. “Based on what the magnetic fields are doing, these electrons can funnel down towards the Earth. And that radiation causes a reaction that produces different types of radiation. In the end, you get gamma rays and x-rays in a beam – a kind of space lightning.”
And just like ‘regular’ lightning of the sort we see in a thunderstorm, it’s not something you want to get struck by.
“We have the technology,” Cornelius says. “We build the modelling tools to predict it. We’ve got the hardware to detect it.”
Space tourism is already taking off. The first tourist was California millionaire Dennis Tito, who flew to the ISS in 2001 for a reported US$20 million.
Since then, a slew of ideas for space hotels have been cast about. Among the latest is Orbital Assembly’s Voyager Station. This is touted to accommodate 400 guests by 2027 in a rotating artificial-gravity wheel. A smaller Pioneer Station, for 28 people, is slated for 2025.
Then there’s Orbital Reef. This commercial space station has attracted big names such as Amazon, Boeing and Arizona State University. Its first stage – due for launch in the late 2020s – will encapsulate some 830 cubic metres and accommodate up to 10 people.
On all these craft, lead-lined safe rooms won’t be the answer. “It’s counter-intuitive, but the density of lead means it can produce more radiation than what’s coming in,” says Cornelius.
A high-velocity charged particle is highly likely to hit the closely packed lead atoms. Cornelius says that these collisions produce a lot of neutrons: “And the heavier something is, the more impacts occur.”
That’s why water is – for the moment – the best shielding. “Water is very good at slowing neutrons down,” says Cornelius. “So, in addition to not being as dense – and therefore not generating as many secondary particles – it also slows them down. It occupies a good middle ground.”
But being less dense means a lot more of it is needed. And water also tends to be consumed.
“Effluent also has a lot of water in it – so I guess you could use that as shielding as well,” Cornelius says. In low-Earth orbit, aluminium sheets are an option. “Most activity here is lower-energy electrons,” Cornelius says. “You can knock them down with a bit of aluminium a few millimetres thick”.