What’s Rad in the Suborbital Spaceflight Business?

When I see an article title such as “Radiation From Sudden Solar Flares Are A Danger To Airline Passengers And Now Space Tourists, Say Scientists,” I cringe a little bit because the title is so obviously clickbait. It preys on a human’s fears about radiation, airline travel, and now the suborbital space tourism business to generate the desired clicks. I blame the editor for this type of title. I also blame myself because I did end up reading the article. But it’s because I’ve researched this topic and was curious (pinky-swear).

And with that confession made, I must also state that I am not a scientist. But I am a researcher. And I just so happened to write a paper about this particular topic about the efforts of Blue Origin, SpaceX, and Virgin Galactic. My previous efforts mean I have ready access to data from trustworthy sources to bring meaning to this. Continuing on...

Airline Passengers Radiation Exposure

The contents of the Forbes article provide are more down-to-Earth than the title indicates. The author reports on a new study, which notes that radiation from solar flares may expose aircraft passengers to “double the annual exposure limit.” He makes the logical extension that solar flares and galactic cosmic rays (GCR) could also impact people taking rides on Virgin Galactic’s and Blue Origin’s suborbital vehicles.

Unfortunately for the author, that “annual exposure limit” can reference many different exposure levels. For example, airline passengers’ recommended maximum allowable annual radiation exposure level is 1 millisievert (mSv). However, the average annual radiation dose a person receives from living on Earth is estimated at 6.2 mSv, with most of it coming from natural background sources.

I am guessing that the author is referencing the former exposure level, which means that according to that study (which appears to be unavailable), airline passengers during a routine flight would be exposed to 2 mSv’s of radiation from a solar flare. This number is also brought up later in the article in reference to annual exposure. That dose is well below the annual radiation dose a person receives annually. Even with that understanding, some more clarification is in order.

First, a U.S. cross-country flight averages about six hours. During those six hours, a passenger would be exposed to ~.035 mSv--meaning a passenger would have to fly more than 28 times across the U.S. to exceed the recommended annual maximum exposure. But I’ve been on 10+-hour flights, which implies my and my co-passengers exposure was likely a little higher. Where an airline flies can also increase or decrease a passenger’s radiation exposure. Flying towards the north or south poles increases that exposure, while flying closer to the equator (with one exception) can decrease it.

Suborbital Passenger Radiation Exposures--As High as Astronauts in LEO?

But what about the “risks” of radiation exposures during a Blue Origin or Virgin Galactic suborbital flight? Referencing some NASA-established limits, it turns out that radiation exposure limits of astronauts are somewhat higher--as high as 6 sieverts in some cases. Space shuttle astronauts during an 8-day mission had received a dose of ~5.59 mSv, while after six months, ISS astronauts had received a dose of ~160 mSv. This data verifies that astronauts are exposed to more radiation in Earth’s orbit than that of the average person on the ground. Does this mean that the suborbital passengers will get higher doses of radiation during their fun-rides? Based on data, the answer appears to be no.

There are a couple of things to remember about the spaceflight profiles of Blue Origin’s New Shepard and Virgin Galactic’s SpaceShipTwo. First, they both are very short in duration (the airplane ride up for SpaceShipTwo is significantly longer than the rocket flight). And both travel to ~100 kilometers in altitude--significantly lower than the orbit of the space shuttle or ISS. Radiation exposure is impacted by time and altitude. This is why the dose received from suborbital fun-ride passengers will be much, much less than what a passenger receives during a cross-country flight.

The table above uses data from NASA and a study published in “Aviation, Space, and Environmental Medicine.” Within the introduction of that study, the authors noted that:

Radiation doses from suborbital flight altitudes and durations are anticipated to be less than those experienced during an average round-trip, cross-country airline flight and are unlikely to result in significant detriment, though longer, orbital flights may expose SFPs to doses potentially harmful to IMD function.

They indicate that an orbital flight would raise space flight participants’ (SFP) radiation exposures significantly. But a person could ride up and down on either of these suborbital attractions thirteen times before they get exposed to the equivalent cross-country flight dose. Of course, this doesn’t mean that maybe these suborbital rides shouldn’t pause as large flares toss their energy the Earth’s way. It’s not clear if the authors of that ASE study included suborbital flight dose estimates received during an event like that. But with those suborbital vehicles available, it would make an excellent experiment to implement when the appropriate time comes around the corner. In the meantime, it should be reasonably easy to pause operations during flare-ups.

And that leaves us at the end of the Forbes article. The study the article references nearly provides a shrug as a conclusion. Its writers first note that the exposure risks presented by solar flares and GCRs during airline flights are likely not high enough to justify adjusting or canceling flights. The data I gathered supports that part of the conclusion.

As for the suborbital businesses--the writers note they need to gather more data to characterize the dose risks for those businesses’ passengers. Based on other studies, it may very well be the radiation exposure risk of the same events during those rides, especially since they are so low and short, is also nothing to worry about. This is good news for a business that is dealing with other very basic challenges, such as having a market. But more experiments on this would be helpful and provide customers with a bit more confidence in the services they are using.

G-forces, on the other hand--oy! But that’s another story.

C'Mon, Ride The (Commercial Space) Train

Two events occurred in two countries that seem to be very similar. The first is India, which generally has a decent space program with one very reliable launch vehicle--the Polar Satellite Launch Vehicle (PSLV)--and one that isn’t so reliable, the Geosynchronous Satellite Launch Vehicle (GSLV). The Indian government is contracting the building of five of its PSLVs out to the commercial sector. While it isn’t clear that the Indian Space Research Organisation will continue building PSLVs, I’d be shocked if it didn’t. The PSLV is India’s most reliable rocket, and not having access to it could cripple some of its space plans. If both government and commercial organizations build the PSLV, it will be interesting to see what transpires. Maybe they could help the GSLV become more reliable?

The other country, South Korea, is also transferring its rocket-building efforts and technologies to commercial South Korean companies. The thing is, South Korea’s space launch efforts have been less...prolific..than India’s. While India might launch seven rockets in a good year, South Korea might launch a single rocket every three years (or longer). According to the article, the rocket tech transferred is related to the Korean Satellite Launch Vehicle-2 (KSLV). It would be interesting if this resulted in a Hyundai of launch vehicle manufacturers.

While the actions of these two nations don’t necessarily equate to a trend, it’s interesting to see that the space agencies in both are working with their commercial counterparts. It may indicate that each nation has internal requirements relying on robust launch systems (maybe) operated commercially. If both work out, they will apply pressure on the plans of other commercial operators. Who knows, a magic launch number may yet appear because competition can create grudging honesty. India’s and South Korea’s commercial operators may benefit from their governments’ backing, especially if smallsats aren’t quite as profitable as many seem to think (yet).