How safe is safe enough for point-to-point suborbital?

Business travelers are unlikely to fly on point-to-point suborbital flights unless their employers approve. (credit: SpaceX)



With the 737 MAX in the news for being risky, it is timely to remember that airline travel in general is astonishingly safe. As of 2018, the overall risk of death was one fatal accident per three million flights. It will take many decades, at the earliest, for suborbital travel to reach this safety milestone. Regular Mars service may be able to match the safety rate per kilometer traveled (one death per 80 billion passenger-kilometers) with less than 1,500 non-fatal trips in a row given the minimum Earth-Mars distance of 54.6 million kilometers.

If the risk of death per suborbital trip is high, it is unlikely that businesses will permit key individuals to travel via point-to-point suborbital spaceflight. One possible standard for the risk being low is to compare the risk of point-to-point suborbital spaceflight to other risky, but legal, forms of transportation. An 800-kilometer trip by motorcycle takes about as long to complete, door-to-door, as a trip via airplane. At 109 deaths per billion kilometers, there is a 1 in 11,500 chance of dying on an 800-kilometer motorcycle trip, which means a decrease in life expectancy of one day per 31.5 years of life expectancy. That is about the same as the life expectancy of an executive who is 52 years old. The average age of a “C-suite” executive (CEO, CFO, CIO, etc.) is 54 years old.

Depending on how productive an executive is while in transit, a company might be willing to let an executive trade a day of life expectancy for an extra day not in transit. If point-to-point suborbital travel can meet this 1-in-11,500 trip standard and the transit time is reduced by 24 hours, that might be safe enough. (And motorcycle travel might be unsafe enough to have travel policy not reimburse mileage for business motorcycle trips.)

If there are 11,500 suborbital point-to-point representative spaceflights, in a row, that are successful, that might retire enough risk for businesses to consider approving this form of transportation. Representative flights would need to be of sufficient reentry velocity to reflect the likely reentry velocity in a long-distance suborbital flight. Almost all of the risk is likely to be during launch and reentry, so sufficiently high reentry velocity flights that merely go up and down may suffice as being representative.

The best representative flight would be to match a potential suborbital travel route. Regular suborbital package delivery at human-survivable acceleration and deceleration levels might defray the cost of risk retirement.

An orbital launch and reentry is likely riskier than a suborbital launch and reentry. A total of 11,500 successful orbital flights in a row with no fatalities might also demonstrate that a rocket is safe enough for point-to-point suborbital travel. Travelers to orbit, the Moon, and Mars are likely to accept Soyuz and Space Shuttle levels of risk—approximately one fatal accident per 81 launches—at least at first. Retiring risk via orbital trips could permit commercial orbital service to enable continued improvement in safety levels until suborbital point-to-point travel is demonstrated to be safe enough.

Even at prices of $1 million per orbital launch, versus $62 million today, 11,500 launches would cost $11.5 billion, and would take 31.5 years at the rate of one launch per day. This is likely the most obvious obstacle demonstrating why suborbital point-to-point passenger travel will be unlikely to be a $20 billion per year industry by 2030 (see “Could suborbital point-to-point really be worth $20 billion a year in 2030?”, The Space Review, March 25, 2019). There are other reasons that are less obvious but may still delay the offering of sub-orbital point-to-point passenger service even longer than proving this level of safety.


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