My good friend Jeff Mann, the true Yard Ramp Guy, has asked me to revisit some of my original contributions. And so: my From the Archives series. This week I'm under siege. By medieval ramp monsters.

Feels Like I Just Arrived in the 21st Century

I know I've kinda built up the idea about myself that I don't care about medieval warfare, that I consider it an absurd waste of thought. And, well, generally speaking, you'd be right. I think it's a distraction from the things that actually matter, like actual historical construction methods. I'm interested in how they put things together, not how they broke them.

That being said, some slightly interesting uses were found for ramps in war, specifically for the purposes of siegecraft.

The first use was actually pre-medieval, though it was used on occasion in medieval times. Siege ramps are huge earthen ramps built right up a castle or city wall, a cliff face, or other positions of strength. They're about as absurd as you'd think: the builders are going to come under constant attack by the people above, resulting in a wasteful loss of life. It was really only used when the besiegers grossly outnumbered the besieged, were otherwise unable to break through the enemy defenses, and had little care for loss of life on their side. The Romans used it a few times, as did a few of the smaller empires before them, and a few of the smaller kingdoms they conquered.

Me, Looking Forward

The other use was in siege towers. These, at least, were constructed with a bit more safety in mind for the troops on your side: not that sending them over an enemy castle wall is, particularly, a safer idea. Siege towers, depending on the whim of the builder, were generally a bizarre hybrid of ramp, staircase, ladder, and watchtower, all built out of wood and canvas and stuck on wheels to roll right up to the castle walls, where troops could exit the tower directly onto those walls.

They also usually had sheltered positions for archers to fire from. Still absurdly dangerous, of course, but you at least had some shelter from enemy arrows, at least until you got onto the wall. They still were vulnerable to fire, which medieval people loved to use on each other.

All in all: I prefer my ramps for actual construction purposes.

Space Junk

In 2013, director Alfonso Cuarón came out with Gravity, a movie about junk. Specifically, it's a movie about space junk.

In the film, a missile strike on a satellite results in a runaway chain reaction of collisions between space junk and satellites. This brings down space stations, satellites, and spacecraft left and right, rendering Earth's orbit useless to manned travel. 

Gravity is an excellent movie, and we’ll forgive a few scientific inaccuracies, since they're all in service of the plot. (Neil Degrasse Tyson, despite his multiple criticisms of the science, is a fan of the film.)

The threat in Gravity is a very real one. It's a scenario known as Kessler Syndrome, where space debris collides with space debris, generating more space debris, which collides with yet more space debris, until that specific orbit around Earth is so filled with debris that it is rendered nearly useless for human purposes. (Low Earth orbit is the most likely orbit to be lost to this process, though geosynchronous orbit is another possible victim.)

It's not astonishing that this is a serious concern for NASA and other space scientists. There are more than 2,000 satellites in orbit, about 1,500 of which are operational, along with nearly 18,000 trackable artificial objects.

Smaller objects are even more common—at least 29,000 chunks of debris in orbit that are more than 10cm in size, nearly 700,000 between 1-10cm in size, and 170 million chunks of debris below 1 cm in size.

Even with how spacious Earth's orbit is, there's a very high chance of impact, and at least one satellite is destroyed by debris every year. Space junk is a serious threat even if it doesn't trigger Kessler Syndrome.

Steps are being taken to combat the risk. We're tracking debris much more carefully than ever right now. The International Space Station and other spacecraft have special protective layers known as Whipple shield: instead of building hulls out of thicker material, engineers add an extra thin layer some distance over the regular hull. The layer isn't meant to stop the debris but to break it into smaller chunks. In essence, Whipple shield turns debris from a bullet into birdshot. It even makes the needed thickness for the inner hull much smaller, so overall spacecraft mass is actually reduced.

And this: we’re developing a technology known as a laser broom. Targeting a laser on debris will heat up one side of the debris. The resulting heat emissions will then alter and destabilize the debris' orbit, causing it to burn up in the atmosphere.

Like me, trying to make pizza.