A lack of hard data on the effects of radiation on astronauts — and how to mitigate the health threat — could set back NASA's plans to send people to Mars in the 2030s, experts tell Axios.

Why it matters: Radiation, particularly in the form of high-energy galactic cosmic rays, can increase an astronaut's risk of developing cancer, cardiovascular issues and even cognitive deficits.

• At the moment, NASA places a strict limit on the amount of radiation astronauts can be exposed to in their lifetimes, but a trip to Mars could require that limit to be exceeded.

The big question: Even though researchers have been studying the effects of radiation in lab experiments for years, they still don't know how radiation exposure on a months-long trip to Mars might impact astronauts.

What's new: In a study this week in the journal eNeuro, researchers exposed mice to a chronic, low dose of radiation over about 6 months, attempting to mimic the amount of radiation astronauts might experience during a flight to the red planet.

• They found the radiation exposure could cause anxiety, memory issues and difficulty with decision-making.

But, but, but: Some researchers say there are broader limitations to characterizing the threat posed by radiation in space.

• The type of radiation used for the new study isn't the same as cosmic rays, and the overall amount of radiation in the study is higher than what people would experience during a trip to Mars, Francis Cucinotta, a radiation researcher at the University of Nevada, Las Vegas told Axios in an interview.
• Mice and rats in general also aren't perfect analogues for astronauts, and there isn't a sure-fire way of mimicking the exact radiation a person experiences in space on Earth.
• It's not just about radiation on its own. Scientists are worried about a number of health concerns — including nutrition, sleep deprivation and muscle loss — that, in combination with radiation, could present serious health issues that astronauts will need to deal with millions of miles from Earth.

"We may never know until we send people, and they are going to be guinea pigs. These people are going to take a chance."

What to watch: NASA has looked into countermeasures like medication that could protect astronauts from the damage caused by radiation during a trip to Mars. However, Donoviel says that the agency needs to invest more heavily in those efforts to ensure the missions have the best chance of success.

The bottom line: The health threat posed by radiation is a serious one, and NASA may need to move more quickly to find effective ways to mitigate it if it wants to send humans to Mars in the coming years.

For those willing to risk their lives in myriad ways to go to space, radiation may be a secondary concern at best, even if it's a deal-breaker for NASA, former astronaut Michael Lopez-Alegria tells Axios.

• “You’re taking a lot more immediate, and much more visible, kinds of risks by launching to space that I think that radiation — at least for me — didn’t enter into the equation very prominently," Lopez-Alegria said in an interview.

The big picture: Astronauts aren't the only professionals with this kind of drive to continue doing their jobs at all costs. Elite athletes, for example, push past pain and injury in order to continue competing.

• Lopez-Alegria — who has spent more than 250 days in space — explained that because the risks posed by radiation are more likely to affect someone later in life, it isn't something astronauts tend to worry about.

Details: Overall, NASA won't allow astronauts to receive a lifetime radiation dose that would raise their risk of contracting a fatal cancer by more than 3%, but the total acceptable dose differs depending on who you are.

• Female astronauts, for example, have a lower threshold than men due to the way NASA calculates risk, leading some to say the agency's limits are discriminatory because it restricts the amount women can fly.

SpaceX is offering up its Falcon 9 rockets for regular rideshares to orbit for small payloads, the company announced Monday.

Why it matters: Usually small satellites are forced to hitch rides on a Falcon 9 with a larger payload bound for orbit, but these rideshares won't need to wait on a primary mission for launch.

Details: SpaceX is charging per mission, with multiple small satellites able to fly in each rideshare without the need for a primary payload and without having to wait on delayed co-passengers, SpaceX said.

• SpaceX is offering a flight to sun-synchronous orbit from California for a mission weighing 150 kilograms, about 330 pounds, or less for as low as $2.25 million.
• The company will also allow operators that run into delays to slot their flight into a later rideshare and apply the money already paid to SpaceX for that flight instead, preventing delays for other missions.
• SpaceX's first SmallSat Rideshare Program flight is expected to launch between November 2020 and March 2021 with another expected in 2022 and one more scheduled for 2023.

The big picture: A number of launch providers coming online in the coming years and flying today — like Virgin Orbit, Rocket Lab and Vector — are dedicated to sending small satellites to orbit. But SpaceX's new rideshare program could help operators get their wares to orbit on the (relative) cheap if they can wait for the launch window.

Yes, but: It's still unclear how much of a market there will be for small, commercial satellite launches in the future. The demand may not be able to support all those rocket companies, leading to eventual consolidation, experts have told Axios.

Go deeper: Houston, we have a rocket bubble

The month of August is usually lauded as one of the best times of year for skywatching, but this year the Moon will blot out our view of the Perseid meteor shower — typically one of the best.

Details: During the Perseids' peak from Aug. 12 to 13, the bright Moon will drown out all but the brightest meteors even for those in areas relatively free of light pollution.

• Under usual circumstances, people should expect to see about 60 meteors per hour during the peak of the August shower, but this year, it will be more like 20 per hour, if that, according to NASA skywatching expert Bill Cooke.

"To put it colloquially, this year's Perseids are going to suck."

The big picture: It's not just the Perseids that the Moon will foil this year. It will also be bright and nearly full during the Orionid meteor shower in October, the Leonids in November and the Geminids in December, Cooke said.

But, but, but: If you're still interested in heading out to check out a meteor shower or two this year, prioritize the fireball rich Perseids and Geminids, and be sure to find a dark area and allow your eyes to adjust for at least 30 minutes; that means no phones, Cooke said.

The U.S. is developing a sentient, artificial brain for satellite data (Sarah Scoles, The Verge)

A crashed Israeli lunar lander spilled tardigrades on the Moon (Daniel Oberhaus, Wired)

Blocked from Hawaii, telescope seeks Spain permit (Joseph Wilson and Caleb Jones, AP)

Super-Earth 31 light-years away found in habitable zone (Rebecca Falconer, Axios)

The Milky Way mapped in 3D (Axios)

The solar system's most famous storm — Jupiter's Great Red Spot — glows in this newly released image taken by NASA's Juno spacecraft.

• At the time the photo was taken, Juno was flying about 26,697 miles above Jupiter's clouds during the mission's 21st close flyby, according to NASA.

Background: The Great Red Spot has been observed since at least 1831, but it may have been raging for years longer than that.

• At one point, the storm could fit as many as 3 Earths side by side within it, but today, the storm is now about the size of 1 Earth.