For the first time in history, two civilian astronauts will perform a spacewalk from a commercial spacecraft.
SpaceX's Polaris Dawn is a 'first-of-its-kind' mission that will carry four private astronauts further into space than mankind has traveled since the Apollo missions of the 1960s and 1970s.
On day three of the mission, two of the crewmembers will venture out into the vacuum of space, marking the first time a commercial spaceflight company has ever attempted a spacewalk.
But spaceflight safety experts have warned the crew faces potentially deadly risks of radiation exposure and rapid changes in pressure that can cause life-threatening sickness.
Even more, the capsule doesn't have an airlock and the team is set to wear spacesuits that have never been tested in space.
Polaris Dawn lifted off around 5:30am ET from Cape Canaveral, Florida on Tuesday, carrying four US engineers and pilots – Jared Isaacman, who funded the trip, Scott Poteet, Sarah Gillis and Anna Menon – aboard SpaceX's Crew Dragon capsule for a five-day orbit.
Isaacman, the founder of the electronic payment company Shift4, bankrolled the mission and selected his personal friend, Poteet, as his mission pilot.
He has declined to say how much he has spent, but it is estimated to be more than $100 million.
After launch, Crew Dragon will ascend to an initial orbit of 745 miles above Earth before firing its thrusters to reach a height of 870 miles - further than any crewed spacecraft has traveled since the moon landings.
The two-hour spacewalk will take place after the spacecraft has descended back to an altitude of roughly 430 miles. This will be on the third day of the mission, which will be Thursday.
When an astronaut performs a spacewalk on the International Space Station (ISS), they put on their suits and then enter a sealed room where air is sucked out before the hatch opens.
This allows the astronaut to safely transition from the pressurized environment inside the ISS to the vacuum of space, and prevents the rest of the space station from being exposed to that vacuum.
But the Polaris Dawn spacewalk will be very different.
Even though Isaacman and Gillis will be participating in the spacewalk, the other two crew members - Menon and Poteet - will have to suit up too.
That's because without an airlock, the entire interior of Crew Dragon will be exposed to the vacuum of space.
To do this safely, they will have to depressurize the entire spacecraft first, and then bring it back to normal internal pressure after the spacewalk is complete.
'They are evacuating the entire Dragon,' independent space industry consultant Laura Forczyk told DailyMail.com.
'This is the first time that has ever been done on purpose.'
'So this is risky in that sense, but they have so many different precautions and redundancies that even though it is risky, it is not overly risky,' she added.
After the spacewalk, Crew Dragon will need to be filled back up with air and re-pressurized.
'If that system and the backup system does not work, then they would need to be returning with their spacesuits on, and that is something that has not been done before,' Forczyk said.
But it's highly unlikely that both those systems will fail, so the risk of the Dragon crew being forced to remain in their spacesuits until they return to Earth is low.
In the event of this kind of emergency, however, the crew has protocols in place that would allow them to return to Earth with Crew Dragon's cabin evacuated, Forczyk said.
Navigating all these fluctuations in pressure, however, will come with its own risks, spaceflight safety expert Tommaso Sgobba told DailyMail.com.
After the astronauts complete the spacewalk, they will need to gradually transition from the five pounds of pressure inside their suits back up to normal 14.6 psi cabin pressure.
There is a chance that this could give them decompression sickness, also known as 'the bends,' he said.
This acute medical condition is caused by a rapid decrease in pressure inside the body, which creates nitrogen bubbles in the blood stream. In some cases, it can be fatal.
To prevent decompression sickness, flight controllers will perform a 45-hour-long 'pre-breathe' protocol prior to the spacewalk.
This will boost oxygen levels in the cabin while slowly decreasing air pressure to help remove nitrogen from the crew's bloodstreams.
And that's not the only sickness that the crew will have to worry about.
During spaceflight, some astronauts experience motion sickness that may result in vomiting, Sgobba said.
Unless a person has been to space before, it's very difficult to predict whether they will be one of these unlucky members of the crew, he added.
That's important to note because aside from Isaacman, none of the Polaris Dawn crewmembers have ever traveled to space before.
'Now, if you vomit while you are inside the spacesuit, that is the end of your story - your life story. You get suffocated,' Sgobba.
So Isaacman - and especially Gillis, as this will be her first spaceflight - will have to make sure that they are not experiencing any stomach issues before they don their suits and exit Crew Dragon.
But in general, the fact that the Polaris Dawn crew are civilians should not have a significant impact on mission safety, Forczyk said.
'It's not a concern. They have been trained so well by SpaceX,' she said.
The spacewalk will take about two hours from the opening of the hatch to closing it and re-pressurizing the spacecraft.
But Isaacman and Gillis will only spend about 15 minutes each outside of the spacecraft. They will do so while tethered to their spacecraft by 12-foot-long, oxygen-supplying cord called an umbilical.
In the vacuum of space, they will rely entirely on their spacesuits for life support. The fact that these suits have never been used in space before poses another level of danger and risk, Forczyk said.
'Any new spacesuit that goes up that has not been in action - that is something that they want to make sure works appropriately before they even evacuate the Dragon,' she said.
The main difference between these suits and the ones used by NASA astronauts is the form of life support.
NASA astronauts wear their life-support systems on their backs, while the SpaceX suits provide life support through the umbilical that is attached to the space capsule.
The suits have undergone extensive testing on the ground, so much so that it actually delayed the Polaris Dawn launch by two years, Forczyk said.
'The spacesuit was the number one reason why Polaris Dawn has been delayed for so long,' she said. Initially, the mission was expected to launch in November 2022.
Sgobba does not think that the new suit design will pose any added risk to the astronauts' safety.
'This technology they are using is the simplest technology they can use, and being the simplest is also the safest,' he said.
The spacewalk will arguably be the most dangerous part of the Polaris Dawn mission. But the astronauts will encounter risks as early as day one.
Achieving the mission's historic altitude means that Crew Dragon will have to pass through Earth's hazardous Van Allen Radiation Belt.
Entering the Van Allen Belt means the four-person crew 'will receive a hefty dose of space radiation, getting as much in a few hours as they would in 20 years on the Earth by one estimate.
NASA has noted that it is crucial 'to fly through this region quickly to limit exposure to radiation,' but the Polaris crew is set to spend hours in the lethal radiation.
High doses of space radiation can increase astronauts' long term risk of cancer by damaging cellular DNA.
Cells will attempt to repair these damages, and sometimes they succeed. But when the DNA is repaired incorrectly it can result in genetic mutations that can lead to cancer over time.
Radiation can also alter the cardiovascular system by damaging the heart, hardening and narrowing the arteries, and eliminating cells in the linings of blood vessels. These damages can ultimately lead to cardiovascular disease.
It impacts the brain too. Exposure can hinder neurogenesis, which is the process of generating new brain cells. This could lead to cognitive impairment and memory deficits.
NASA will use this mission to study the impact that high levels of space radiation have on human health. But any impact that this mission has on the Polaris Dawn crew's bodies will likely take years to emerge.
Despite all the risks, if the Polaris Dawn crew safely pulls of this mission, it will be a big step forward for SpaceX that further secures their position as a frontrunner in the commercial space race.
