behind the scenes

Brian left a comment:

I am reminded that RAH and Virginia, for short story, used a roll of butcher paper and two days of time to work out the calculations for an orbit. For a line that read (IIRC) ‘And he took off and departed Lunar orbit’.

Nobody saw the time and butcher paper, but it got baked into the story. And it felt right.

Probably one of the many reasons people still read Heinlein, but not many of his peers from that era.

Wikipedia and spreadsheets make it a lot easier.

…but, yes, there’s still some work.

I’ve got one scene in the novel where kinetic energy weapons (2 TEU cargo containers full of gravel, with phenolic resin ablative shields over steel nosecones, which small steering vanes and simple PID loop controllers) strike targets on a Caribbean island.

Here’s some of the text:

As the gravel boats – spaced out in a rough circle – entered the thermosphere the first few molecules of air started to impact the nosecones, but the density was so low that it would have taken specialized sensors to even detect it. Sensors that the boats did not have.

After a 400 kilometer fall through the thermosphere the boats entered the mesosphere, still punching downwards towards the rapidly growing Carribean ocean at almost Mach 30, dropping over 10 kilometers in height every second.

The air was still sparse enough that a human without a space suit would pass out immediately and die almost as quickly as on the surface of the moon, but there was just barely enough air that the maneuvering vanes at the rear of the boats began to click-click-click as they moved to fine tune their paths.

Ten seconds from ground.

The air around the boats thickened rapidly. Now 0.001 atmospheres, now 0.01, now 0.1 atmospheres.

The hypersonic impact of the falling ships against the air was so powerful that molecules themselves began breaking apart. Ozone, molecular oxygen, water vapor, even triple bonded molecular nitrogen all shattered, throwing off a cascade of atoms, ions, and raw electrons.

Subtle luminous hints in front of each gravel boat soon grew and brightened, turning into fiery disks just millimeters in front of each nosecone. Inside each boat the software noted that the rate of successful radio packet transmissions had fallen from “six nines” to fifty percent, and then below a key threshold. The ionization blackout caused different subroutines to be loaded and executed. Each boat switched from GPS to inertial navigation. Ring laser gyros that had been designed fifty years previously, open sourced a quarter century ago, found in archives two weeks ago, and fabbed, tested, and installed a week previously now directed the gravel boats.

Seven seconds from ground.

The boats crossed the boundary between the meosphere and the stratosphere and the density of the atmosphere kept climbing – now up to 0.3 atmospheres.

On gravel boat number three – the one aimed for the southern-most guardhouse – a wrinkle in the hastily applied heat shield resulted in an uneven flow of superheated air over the nosecone. The uneven force force tugged on irregularity harder and harder and then in a millisecond tore a fingers-width of ablative panel away from the underlying metal.

With the carbon laminate gone the underlayment burned through nearly instantly. Once the underlayment was gone a pencil thin jet of 6,000 degree Kelvin ionized air began burning through the steel nosecone, quickly vaporizing the metal and contributing traces of lunar iron and to the emission lines of the blazing glow.

Six seconds from ground.

Here’s some of the math:

Note how I start with things like

  • initial velocity of an item falling from lunar orbit (11 km/s)
  • the dimensions of a standard cargo container
  • the density of granite gravel

and end up with things like

  • terminal velocity at impact
  • energy of one boat hitting, as measure on the nuclear kiloton scale
  • seconds elapsed from top of mesosphere to earth impact

It may not matter to anyone else, but it matters to me.

And, I’m happy to say, to Brian.

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6 Responses to behind the scenes

  1. eddie says:

    When I read this yesterday, I thought about xkcd What If. He does this kind of homework too, but for a weekly funny-strip instead of a novel.

    Then today’s xkcd What If is about things falling from orbit, atmospheric friction, and heat shields.

    Go figure.

  2. Brian Dunbar says:

    “And, I’m happy to say, to Brian.”

    Love that movie. Not the least because .. hey, cocky Marines who have no idea what they’re stepping into: I could relate.

  3. ElamBend says:

    I’m embarrassed to admit that I had to check to see that Mesopause was a real term/concept.

    As for Aliens, that part is the Paxton’s greatest work.

    • Brian Dunbar says:

      > that part is the Paxton’s greatest work.

      I think the HBO series Big Love is _actually_ his greatest work. He’s so good in it I completely forgot the same guy was Hudson the Wonder Private.

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