How Do You Weigh Things in Space?

Astronauts need to know their mass while in orbit, but a normal scale would be free-falling around the Earth with them. So how do they measure their mass without gravity?

Hosted by: Michael Aranda
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[BEP]

I'm using "spriginess" instead of spring constant from now on.

[garypalmer]

I like how you correctly mentioned the astronauts are not floating but are actually in free fall. So many people even scientist get that fact wrong from time to tome. Good on yah 👍

[OdysseyWorks]

The title should have said. How to measure mass in space.

[Master_Therion]

Astronaut 1: How much do I weigh? I feel fat :(
Astronaut 2: No weigh! You matter.

[ExtraAmpersand]

Thanks, Patreon patron Peter, for patronizing the Patreon. I too patronize the Patreon, becoming a Patreon patron, pledging a pittance compared to Peter the Patreon patron, so Patreon patron Peter takes priority for proposed ponderings!

I spent way too long working this out… :D

[OneUpdateataTime]

Space never ceases to be cool the more you learn about it

[TheStackeddeck]

Cool I just learned a real-world application for the calculus subject I just finished. It was exactly what yall are talking about

[electronicsNmore]

You'd think over time that spring would change in height due to compression and decompression, just like a spring on your vehicle's suspension.

[milky_wayan]

learned about this in physics class, awesome

[JiveDadson]

Note to self: Apply to NASA for acronym thinker-upper job. Spring Loaded Universal Reciprocating Mass Equivalence Decider, or "SLURMED". First draft. Needs work.

[danielbudney]

While they both register the same thing (oscillation frequency), if the U.S. solution uses a high-speed camera, it's not very elegant. All you need is an optical switch attached to a timer: when the beam is uninterrupted (because the plunger leaves on its out-bound path), the timer starts. When the beam is interrupted again (because the plunger returns from a full oscillation), it switches the timer off ... "precisely" measuring one oscillation without any human human error. I don't know how many oscillations the Russians measure, but attaching this kind of "on/off" measurement to a computer would let you record any number of oscillations without need for anything so sophisticated as a high-speed camera (or any need for human interpretation of the images). It would also be much easier to get micro-second accuracy than using a high-speed camera would.

[YourBuddyDinec]

Cmon and SLAMMD, and welcome to the JAMMD!

[adlockhungry]

What about how scientists determine the mass and density of planets and other large bodies in space?

[minutegameplays]

Interesting, never thought about it, it is a smart way of doing it. Makes sense...

F=ma, F is the spring force, m is the mass of the astronaut, a is the acceleration of said mass.
F is an elastic force, so F=kx, where k is a known spring constant and x is the displacement of the end point of the spring to its equilibrium position, where F is 0.

plugging the second into the first equation:
kx = ma

k is known, x and a can be measured. In the end:
m = kx/a.

it is not that simple since they also have to subtract the friction force, but including it and some statistical mumbo jumbo later to get the average of the measurements over many oscillations and include errors, we get the m result! :)

[PumatSol]

So instead of measuring the astronauts’ gravitational mass, it measures their inertial mass. Einstein saves the day again!

[zupmeoff]

Well since space isn’t real, I guess we’ll never know.

[EvilKimau]

Fun Fact: The SLAMM algorithm that NASA developed for markerless tracking is the basis of most modern camera Augmented Reality systems like ARCore & ARKit

[mixiekins]

But wait, do they need to keep a duplicate spring as a metrology standard for calibration? The one they use should eventually stray in accuracy as the metal fatigues from repeated use, right?

[GOD-help-us-all]

This sounds like the algebra I learned in school. useless to me. But a great presentation that I could fully understand.

[SkyChady]

I still want to know what space smells like.