Calculating the Risk

Recently I have been involved in discussions about public risk resulting from commercial space flight.  It is interesting to think back to the shuttle days and how those calculations were made.

If you ever were invited to a shuttle launch and got a car pass to park on the causeway – seven miles from the launch pad – you might not have noticed the fine print at the bottom of the windshield placard – noting that you were accepting the risk to you and your family from launch hazards.  I’m betting you didn’t read that.  By the rules of the Range Safety organization, you should not have been there.  But the KSC center director had ‘accepted’ the responsibility for allowing you to be present when the risk calculations exceeded the standard that the Range set for the general public.

The limit for public risk was 30 chances in a million that one person could be seriously injured or killed from an event.  Don’t ask how they came up with that number.

The LCC building at KSC was constructed a full 3 statute miles from the Apollo launch pads because somebody did a calculation about the maximum explosion hazard from a Saturn V.  Three miles was far enough to be safe, or so they thought in the 1960s.

We still used that LCC building for the Space Shuttle launches and I was present in the firing room for several of them.  Every time before the clock counted down to zero, I would remember the hazard calculation for that room.

Follow this logic:  If, exactly at the moment of liftoff, the Orbiter blew up and took out not only itself and the astronauts but the External Tank as well so that the Solid Rocket Motors would be free flying, then if the hydraulic systems on the SRBs – now without any computer brain to command them – steered randomly but in just the right direction, and if the Flight Safety Officer took the maximum seven seconds to recognize the problem and send the destruct command, and then if the aft segment of the SRB – which did not have the linear shaped charge but was generally thought to peel apart when the rest of the booster destructed, rather stayed intact and burning – Then there was a non-zero probability that the flaming solid rocket aft segment could land on the LCC building with catastrophic results.

That is a lot of ‘ifs.’  And for several ‘ifs’ there was no way to calculate the probability, it is just assumed that they occur.  Given that all of those things happened, the only variable was the exact direction that the errant flaming segment might travel. Assuming an equal probability for each degree of heading, the ‘calculated’ hazard for the LCC exceeded the maximum allowed by the range rules, even for essential personnel.  But the firing room crew is essential to the launch so the KSC director again ‘accepted’ responsibility.

Those big louvers on the windows facing the launch pad were merely for shade, not for blast protection.  If something big hit them, they would probably just add to the shrapnel.

But even more, the KSC director ‘accepted’ responsibility for the hazard to workers in the Orbiter Processing facilities and the VAB who were not essential to the ongoing launch but were critical for maintaining schedule to the next shuttle launch.  And the KSC director also ‘accepted’ responsibility for the VIPs gathered on the balcony of the office building across the street from the LCC, and for the media at the Press site, and for other VIPs at the Banana Creek viewing stands.

That is a lot of ‘acceptance’ which let the Range organization off the hook, so to speak. Many of the guests and workers were not aware that they were in a hazard area.  It wasn’t a secret, it was quietly announced or in the fine print; never dwelt on.

That is for hazard areas as the Range calculated them.  Probably 1 chance in a ten thousand that you could be harmed.  Would you have still wanted to go?

As we go forward with ‘commercial’ launches, the FAA is responsible and has adopted virtually unchanged the calculations performed by the USAF Eastern Range.  But here is the catch; the KSC director is not allowed to ‘accept’ risk for commercial launches; its not in his/her area of responsibility.

Hopefully those smaller rockets will have a smaller hazard area than the shuttle.  But maybe not for some of the proposed super heavy boosters.

It will be interesting to see how all this plays out.  Public safety – what is your personal risk acceptance?  What probability would make you stay home and watch on TV rather than come see it live?  1 in a million, one in a hundred thousand, one in ten thousand, what?

And I wonder about the relatively unsophisticated calculation about the hazard from the Saturn V back in the 1960s.  I am guessing that most of the folks who came out to watch those launches would have accepted some risk, probably more than people would today.

They were willing to take more risks for a worthwhile cause in those days.

About waynehale

Wayne Hale is retired from NASA after 32 years. In his career he was the Space Shuttle Program Manager or Deputy for 5 years, a Space Shuttle Flight Director for 40 missions, and is currently a consultant and full time grandpa. He is available for speaking engagements through Special Aerospace Services.
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11 Responses to Calculating the Risk

  1. Fred Mushel says:

    I saw the maiden launch of Endeavour on May 7, 1992 on the NASA Causeway from launch pad 39B. It was a spectacular sight. The color and deep neon yellow of the solid rocket booster flames cannot be captured by any film or video or “data” image sensor. The flames appear on film, video or data captured media as washed out yellow or white. Only the human eye could see the actual color and intensity of the SRB flames; an experience I will never forget. I was also fortunate to see the launch of Columbia in February 1994. Again, I was in awe of the sight of the SRB flames.
    I wasn’t aware of the risks you mention, but I am probably in greater danger commuting to and working in midtown Manhattan near Times Square than at a Shuttle or Apollo launch with all the vehicle/bicycle traffic on every street, all day and night, as well as the aging infratsucture of NYC transit, bridges, tunnels and roads.

  2. Charley says:

    Yep, worse odds driving your car. I would certainly accept the risk. But, I would live in Boca Chica.

  3. lion says:

    Went to fireworks shows where the hazard was a lot higher than an errant shuttle booster. Ashes fell down where we were standing. It wasn’t government funded & July 4 was important, so the risk tolerance was higher.

    The battle between SpaceX & the FAA over the last month showed quite a difference in opinion between the 2. The FAA only approved a flight after they lowered the altitude & expanded the no fly zone. It begs the question of what they will ever use the launchpad for. When they bought it 5 years ago, the neighbors were easy to buy out. Now the last neighbors are staying to be near the space program.

  4. Thanks Mr. Hale–another thoughtful post. I did read the fine print the first time I got tickets to the Causeway–the bus drivers and announcements about getting back to the bus should there be an “anomaly” reinforced that. Of course, when the opportunity to view STS-130 from Banana River/Saturn V came up, I accepted without pause. I hope to view Artemis 1 from Banana River as well…
    This in no way minimizes your point, and I take it very seriously–you know what you’re talking about. As noted, I face more risk commuting by bicycle (and part of the reason I’m retiring “early”. Keep up the good work!

  5. Spacebrat1 says:

    no matter what the risk, probably safer to watch a launch live than the drive up I-95 from South Brevard? hmmmm

  6. rangerdon says:

    The three shuttle launches we saw — one a night launch in the VIP area — were a life highlight. For my brilliant engineer father, no longer with us, they were epiphanies. The risk was worthwhile. As the saying goes, “risk is our business.” And that goes for life – if we never take a risk, even as spectators, we don’t fully live.

  7. Dan Adamo says:

    Thanks for those stats, Wayne. I’m sure you’re still familiar with similar risk levels my colleagues in Shuttle Trajectory Operations dealt with regarding orbit debris collisions. A collision probability (Pc) less than 1-in-100,000 would be tolerated without mandatory action. Between that threshold and Pc less than 1-in-10,000, an evasive maneuver would be considered. At Pc greater than 1-in-10,000 an evasive maneuver was considered mandatory and critical to flight safety, even if high-priority mission events like a payload deploy or EVA had to be cancelled.

    In managing risk, it’s certainly important we have stats like Pc to consider, but equally important is the “worthwhile cause” you mention in your closing sentence. Only then can we trade the statistics against a “payoff” to justify (or reject as irresponsible) what’s to be done. This trade-off is what I call a “calculated” risk. Sending humans to Mars with our current technology and knowledge of hazards like radiation exposure and one-third gravity adaptation is what I call a “blind” risk and one not worth taking until our ignorance of the hazards is dispelled to some extent. What troubles me is neither SpaceX nor NASA has a plan to quantify these risks closer to home before sending humans on a multi-year journey to Mars.

    Equally troubling are human space flight justifications like “fighting complacency” in achieving a return to the Moon before 2025. I don’t think there’s political capital backing such a stunt to justify loss of life in the process. If anyone disagrees, I’d like to read their contemplated statement to Congress or an accident investigation board on behalf of Artemis risk-taking. The risk/gain trade equation was far different during the Apollo Program 50 years ago.

  8. CJones says:

    The insurance industry has a very long history being in the risk assessment business calculating risk(s) and consequently what to charge for covering the assessed risk(s). Certainly on the commercial side of the space business the insurance industry will have a say on how launch sites are managed. I reference the commercial satellites that were lost due to launch mishaps where insurance partially covered the loss.

    A very interesting topic – in my business where new and/or first time technology deployment is involved, we defer to the risk experts. “If it can afford to be insured – we can invest in it”.

  9. Charles F. Bolden Jr. says:

    Great food for thought, Wayne. I’m of the belief that today’s generation of space enthusiasts are much more like the military aviators with whom I served and share an “It’ll never happen to me…” attitude that will allow the beaches and causeways around the Cape as well as every authorized viewing site aboard KSC and CCAFS to be filled for the first launches of the CST-100, Crew Dragon, Falcon Heavy, New Glenn, New Shepard, etc.

    Charlie B.

  10. Crash Davis says:

    “Equally troubling are human space flight justifications like “fighting complacency” in achieving a return to the Moon before 2025. I don’t think there’s political capital backing such a stunt to justify loss of life in the process.”

    So you are of the mind-set that humans should not explore and continue another 47 years shackled to LEO? That is a pretty lame attitude and actually tragic. Humans are naturally destined to expand their boundaries. And yes that will entail some risk. The risk is worth it as has been demonstrated in the past with the United States space program.

  11. Crash Davis says:

    “Equally troubling are human space flight justifications like “fighting complacency” in achieving a return to the Moon before 2025. I don’t think there’s political capital backing such a stunt to justify loss of life in the process.”

    So you would rather humanity be shackled to LEO for the next 48 years? That is representative of a lot of America’s Can’t Do attitude and actually really tragic. Mankind is destined to explore and expand his presence in the Cosmos. The past US Space Program demonstrated the significant benefits of Exploration, planned and unplanned. Yes, there will be risks. But all great endeavors entail risk.

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