# Cooking in Space

Someone in the Worldbuilding SE asked How to Build a BBQ for the ISS.

My first through was: Why not just stick it in a sealed container out in direct sunlight for a bit? It'll get plenty cooked without insulation.

This gave me a mental image of a couple of astronauts in EVA suits sitting in an airlock with hotdogs on sticks soaking up the sun.

So, my question is: Could they cook the hotdog before it desiccates?

• The hotdog may be freeze dryed by the vacuum. – Uwe Apr 21 '18 at 8:22
• I don't understand, are you asking about the sealed container scenario, or food directly exposed to space? – uhoh Apr 22 '18 at 3:48
• @uhoh, directly exposed: hotdog on a stick. – ShadoCat Apr 24 '18 at 16:55
• @Uwe, If the hotdog was in the shade, I think that it would free dry but in direct sun, I think that it will gain more heat than it radiates. – ShadoCat Apr 24 '18 at 16:56

You will have to build a solar cooker to cook your hot dogs in space at 1 AU from the Sun. I can't vouch for all aspects of the physical behavior of the hot dog, but I think this can be done.

In this answer I explain the equation for an estimate of the equilibrium temperature of a blackbody heated by visible light, and radiating in infrared light.

$$T \sim \left( \frac{(1-a_{vis})}{e_{ir}} \frac{I_{Sun}}{4 \sigma} \right)^{1/4}$$

where $a_{vis}$ is the visible light albedo, $e_{ir}$ is the infrared emissivity (both should really be weighted averages over the appropriate wavelength ranges), $\sigma$ is the Stefan–Boltzmann constant (about 5.67E-08 W m^-2 K^-4), and I is the intensity of sunlight, and for 1AU is the solar constant and about 1360 W/m^2.

Most things have high infrared emissivity, let's assume the hot dog's emissivity is 0.9. Hot dogs come in different colors, and they can change color as they cook, but let's give this one albedo of 0.5. In space, all by itself, in sunlight at 1 AU, the hot dog will equilibrate at only 240K, which is -33C. It will quickly freeze, then more slowly freeze-dry.

Google sez (click for full size, or just google "how hot to cook hot-dogs") that hot dogs will cook in an oven at about 350F, which is 177C which is 450K.

Since the equilibrium temperature scales as the fourth-root of the intensity of sunlight $I$, you need to increase it by a factor of (450/240)^4 or about 12.3. Google also sez a hot dog is a 2cm diameter cylinder, so you will need a parabolic cylinder a little longer than the hot dog and 25 cm wide, and mess with keeping your hot dog in focus and rotate it.

However, this may quickly burn your hot dog to a cinder, depending on its heat transfer properties. You will have to experiment with speed of rotation, ramping the intensity of the sunlight etc. before you can make the perfect hot dog in orbit.

When finished, you'll have to find a way to get it into your suit quickly so that you can eat it while hot. I've seen this done on TV, but in reality, hmm...

Good luck, and Bon Appetit!

• So, it would radiate faster than it would gain heat (assuming it wasn't deep frozen to begin with). – ShadoCat Apr 25 '18 at 17:15
• @ShadoCat It gains heat from the Sun independent of its temperature, but it radiates heat proportional to the fourth power of the temperature ($T^4$). So if it starts at room temperature the radiation looses heat faster than the Sun warms it. The reason that the Earth is warmer than 240K is that it has an atmosphere filled with greenhouse gases that let most of the warmth from visible light in, but trap some of the infrared radiation trying to go out. – uhoh Apr 25 '18 at 17:26