Saturday, April 8, 2023

SuperHeavy+Starship have the thermal energy of the Hiroshima bomb, Page 2: shattered windows and flying shrapnel.

 Copyright 2023 Robert Clark

 In the blog post, "SuperHeavy+Starship have the thermal energy of the Hiroshima bomb", I noted the SuperHeavy/Starship launch potentially can be damaging to people and property if it explodes. 

 I was using an exclusion radius though of only 2 miles, 3.2 km based on this hazard notice: 

 However,  this FAA report on page 22 puts the exclusion zone around the launch pad at about 5 mile radius:

 This is about about how far away Starship launch watchers are on South Padre Island when watching the launch from outside. It’s also the distance where space launch reporters such as Tim Dodd the “Everyday Astronaut” and others report on the Starship launches from hotel rooms on South Padre Island:

SpaceX Starship: Slo-mo SN9 flight video shows explosion in stunning detail SpaceX's Starship tackled its latest "hop test" — and it didn't end well.
FEB. 3, 2021. Ryan Chylinski, co-founder of Cosmic Perspective, tells Inverse he and his team were on a hotel balcony on South Padre Island during the launch — around five miles away. “We could certainly feel the rumble of the Raptors [the craft's engines] at this distance," he says. "And that explosion shockwave, wow!” he adds.

 It's also uncomfortably close to the distance to Port Isabel, TX at 6 to 7 miles away, a town of about 5 thousand people. 

 However, even 5 miles is likely to still not be a safe distance based on other large explosions at the kiloton level such as the Texas City disaster:

April 16, 1947: Ship Explosion Ignites 3-Day Rain of Fire and Death.
…It shattered all the windows in Texas City and half of those in Galveston, 10 miles away. Some debris reached an altitude of nearly 3 miles before falling back to earth. Two airplanes circling overhead were blown apart by the heavy shrapnel. A one-ton piece of the ship's propeller shaft landed 2½ miles away. Other pieces sailed 5 miles.

 The Texas City explosion was at the approx. 3 kilotons of TNT level. The N-1 Soviet rocket explosion was at about the 1.2 kiloton level. Since SuperHeavy/Starship is about 2.5 times larger than N-1 we can estimate that if it were to explode it might result in an explosion at about the 3 kiloton level, comparable to the Texas City disaster.

 Then outside launch spectators on South Padre Island would be at risk of being hit by flying shrapnel even at the 5 mile distance.

Shattered Windows.

 This page gives a summary of the kinds of damage that can result in explosions at the kilotons of TNT level:,5,1&rem=&therm=_1st-50,_noharm-100,35&cloud=1&zm=13

 It estimates the area of shattered windows by how far away a 1 psi overpressure would reach. However, the page actually underestimates the extent of the shattered windows: while 1 psi is a nice round number to work with, even at some fraction of a psi some proportion of windows would still be shattered.

 Half the windows in the Texas City disaster for instance shattered in Galveston at 10 miles away, a distance farther away than would be predicted by the 1 psi overpressure criterion.

 Note also that large plate glass windows such as those common in store fronts, commercial buildings, and hotel rooms are easier to shatter than the small windows seen in homes. Then launch watchers in hotel rooms on South Padre Island would be at risk of being injured by shattered windows if SH/SS were to explode.

 A greater distance of shattered windows than expected also happened for example in the Soviet N-1 rocket explosion:

 The aftermath

As the shockwave and the rain of metal debris subsided, Menshikov and his colleagues all emerged out of their shelter stunned but unhurt. Flames were still raging at the launch pad to the northeast under a starry night. The power was shut off around the entire center but five minutes later most facilities started getting their lights back on. (704)

Top officials were allowed to leave their launch control bunker around 3.5 kilometers from the pad only half an hour after the explosion. When they came up to the surface, a drizzle of unburned kerosene droplets was still coming down to the ground. As was later estimated, as much as 85 percent of the propellant onboard the rocket did not detonate, reducing the force of the blast from a potential 400 tons to just 4.5 - 5 tons. (233) Also fortunately, evacuation measures proved to be effective, as all reports from various sites included "no fatalities." (685) However due to paranoid secrecy, security services apparently intentionally disconnected still operational phone lines between technical facilities and the residential area, leaving numerous family members agonizing for hours over the fate of their loved ones.

In the meantime, test officers and engineers were streaming back from their shelters to their regular work places. Menshikov and his colleagues found their fueling station in total disarray. Doors and windows were blown off, main gates crooked, equipment thrown all over the floor. Most buildings at Site 113 and surrounding facilities were in similar shape. As dawn came, they were terrified to see numerous dead birds and small animals littering the steppe.

The heaviest damage was obviously at the epicenter of the explosion. The "Right" pad of the N1 rocket at Site 110 was completely wrecked. One of the 180-meter lightning towers collapsed and was twisted into a spiral. (705) Some pieces from the rocket were found as far as 10 kilometers away and a 400-kilogram gas reservoir landed on the roof of the assembly building at Site 112, four kilometers from the pad.

Windows were blown off in buildings at Site 2, located six kilometers from the launch pad and as far as 40 kilometers away. A main display window at the Luna cafe in the main residential area at Site 10, some 35 kilometers from the epicenter, was shattered.

  The terrible force of the explosion can be better appreciated by watching a video of it though:
The Largest Rocket Explosion Ever - The Soviet N1 Moon Rocket Failure.

 Now keep in mind the Superheavy/Starship would have  times or more the force of this explosion if it did explode. 

 Then when estimating the distance to which shattered windows are to be expected a statistical evaluation must be given for the proportion of shattered windows by distance. This defense department report provides the numbers for a 50% chance of shattering:


 The numbers in the report given in terms of kilopascals, kPa, where 1 kPa = 0.145 psi., show that depending on the size of the window it can shatter at overpressures down to 0.6 kPa, ~0.1 psi, well less 1 psi:

Flying Shrapnel.

 As with shattered windows the distance shrapnel can be propelled has to be given statistically rather than as single set number. This article discusses the range of distance shrapnel can travel depending on energy content of the explosion:

April 2019
Engineering Case Histories: Case 106: Delayed fireball type explosions.
When a vessel containing a flammable liquid under pressure (such as those in an LNG road tanker truck) ruptures and ignites, a vapor fireball explosion can occur.

Sofronas, A., Consulting Engineer

How far away is a safe distance? Flying fragments from pressure effects may not have a reasonable safe distance. Some sources2 mention that 80% of the debris lands within 4 × Rmax and, in rare instances, up to 30 × Rmax (where Rmax is the calculated fireball’s maximum radius). 


Consider that an LNG tanker truck with a load of M = 19,000 kg (10,000 gal) of propane overturns, a fire erupts and the tanker explodes into a fireball after 10 min of being engulfed in a fire. The heat of combustion (Hc) for propane is 50,000 kJ/kg.

From experimental data, the fireball duration, t, can be approximately calculated as shown in Eq. 1:

t = 0.45 × (M)1/3 = 12 sec                                                                                                 (1)

At the end of the fireball growth period, t, it achieves its maximum radius (Eq. 2):

Rmax = 2.9 × (M)1/3 = 2.9 × (19,000 kg)1/3 = 77.4 m                                                   (2)

 Using the equation (2), for a 1,000,000 kg total methane fuel load for SuperHeavy/Starship, that would be a fireball radius of 290 m. Then if some proportion of the fragments can be sent 30 times the fireball radius, for SH/SS that would be 8,700 m, 8.7 km away.

 That would be for relatively small proportion of the fragments though. A statistical examination has to be done to see the proportion of the fragments that could reach say 5 km. 

 Even if the proportion of fragments that can reach beyond the 5 km exclusion zone is small, it must be kept in mind many residents and visitors in Port Isabel and South Padre Island will be outside to watch the launch, increasing the chance someone could be hit by the fragments.

 Note also, the Mexican border is inside the 5 km exclusion zone. Then Mexican citizens on the other side of the border also run the risk of being hit by flying shrapnel if there is an explosion. In such a case, SpaceX would run the risk of causing an international incident.

 Alternative Proposals.

 SpaceX does not have to launch Superheavy/Starship from the Boca Chica launch site. Note that the original proposal by SpaceX for passenger flights was from a platform 20 miles off shore because of noise levels from a launch. This can still be done. The launch tower would have to be made mobile. This is doable of course as the Saturn V, Space Shuttle, and SLS mobile launch towers showed. The Starship launch tower would have to  be carried to the coast, lifted onto a barge, then transported to a location sufficiently distant off-shore.

Another possibility would not to use a Superheavy at all. SpaceX could take a clue from the Falcon Heavy development which actually costs 1/4th to 1/6th that of entire new rocket built from scratch. SpaceX would first build a smaller two-stage with the Starship now as the first stage and a smaller mini-Starship, if you will, as the upper stage. Such a rocket could get ca. 100 tons to LEO. After many successful launches of this vehicle, Space would then proceed to a triple-core version, a la the Falcon Heavy. Such a triple-core vehicle would be able to match the 300 tons to LEO of the SuperHeavy/Starship. Note that, prior to the Falcon Heavy launch, SpaceX had launched over 1,000 Merlin engines on actual orbital flights. Such an approach would similarly result in high reliability of the Raptor engine before extending to a triple-core version. But as it is now SpaceX proposes to build the biggest rocket ever made with engines that have made zero actual flights to space.

 Note that this smaller two-stage vehicle could do both manned lunar and Mars missions in a single launch, rather  than 8 to 16 refueling flights needed for the SuperHeavy/Starship approach. When SpaceX wanted the high cargo triple-core version that then would be launched off-shore. It will almost certainly be the case the single core Starship would launch far more times than the triple-core version, just like is the case with the Falcon 9 compared to the Falcon Heavy.

 See discussion here:

The Missed Lesson of the Falcon Heavy.

  Robert Clark

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