Melting rock using a Fresnel lens - GIF

**Altair** · Nov 24, 2021, 10:27 AM

Melting rock using a large Fresnel lens.

Previously:

Melting a wrench with electricity - GIF
Melting a machine gun barrel by firing 700 rounds through it - GIF
Melting a padlock - GIF

**nova_robotics** · Nov 24, 2021, 08:41 PM

I was doing this! I bought a few different Moon simulants, and Mars simulant, and we started melting regolith simulant into structural shapes. We also made fibreglass, which turned out surprisingly easy to make. The objective was to go after a contract with the CSA (Canadian Space Agency). CSA said the idea was stupid and they'd rather truck concrete to Mars and the Moon, seriously.

Melting rock using a Fresnel lens - GIF-img_20181118_132625.jpg

Melting rock using a Fresnel lens - GIF-img_20181014_142629.jpg

**Gadgeteer** · Nov 24, 2021, 11:04 PM

To quote Paris Hilton, "That's hot!."

**hemmjo** · Nov 25, 2021, 04:20 AM

Inspired by the Solar Challenger in the early 80's, I had the 8th grade students in my class build a parabolic reflector. It was an 4' diameter dish. Made of fiberglass and epoxy resin over a plaster form. It was made in 8 segments bolted together. Covered with Chrome Mylar donated by one of the dads who worked at Dupont. We had to make a few extra as the first few attempts were not very good. But the last few were awesome.

After it was completed, we took it outside. We had to instantly stop testing as the brightness of the focal point was way too intense. After borrowing a class set of welding goggles from other schools, we went back out another day. The first test was piece of black construction paper. We never even saw flames, it just disappeared. A common 2 x 4 would instantly burst into flames. It would heat a piece of 1/4" steel to bright red in a very short time. We never tried to melt rock.

One of my goals as a teacher was always to make kids impressed with the things that could actually do, if they wanted to.

We did the math on the reflector, not taking into account the surface imperfections. Four foot diameter is about 12.5 square feet. 3 inch diameter target is about 0.05 square feet. That is a magnification of about 250 times. Once again not taking into consideration the surface defects of the "homemade" reflector.

I regret I have no photos of the project.

I wish I still had the dish, but I gave it to a science teacher when I retired.

**odd one** · Nov 25, 2021, 06:56 PM

That's the kind of teaching and experimenting that I remember most fondly in school and had the most impact on me. I was very fortunate to have several of those teachers, Safety standards were much more relaxed back then....thank god. Fire, explosions and huge electrical arcs tend to grab the attention of impressionable minds. Sure you made a lasting impact on several of those kids as well.