When you eat a sandwich in space flight, does your craft lose mass?

OK just a fun little and actually technical question since extended manned space flight seems to be a topic floating around. I'd like to hear the views and reasoning behind some answers. Not because I am some kind of last word I just thought it may be fun to multiply the simple question to weeks or months long space flight and how you intend to deal with waste without disrupting the life support systems or unnecessarily taxing the energy of an 'open chute' into space. For instance, would the water you consume actually decrease the mass of your life support (in the short term) meaning you don't have to regenerate new water for your trip. Tis may be a biological question or pure physics. What do you think?

I am no expert but I am sure mass cannot be destroyed only compressed and converted.

I don't think the mass of the craft would have changed, because nothing has really changed.
It's more like a transfer. take sandwich out of lunch box , eat sandwich.
All the weight/mass is still part of the craft.

Sort of a silly question.
The mass remains the same. Where would it go?

Regarding waste management:
www.spaceref.com...

Regarding recycling.
science.nasa.gov...

lol, that's a funny question..

But the answer is NO..

It will however alter when they jettison the umm, end result.

lol I wonder if it ever happens like this:

From Joe Dirt:

Meteor Bert: Well, it ain't a meteor.
Joe Dirt: Yeah, it is. It came out of the sky.
Meteor Bert: Well I'm sure it did but it ain't no meteor. It's a big ol' frozen chunk o' sh##.
Joe Dirt: What?
Meteor Bert: Oh yeah, see them airplanes they dump their toilets 36,000 feet. The stuff freezes and falls to earth. We call 'em Boeing bombs.
[chomps teeth]
Joe Dirt: No, that can't be. That's not what it is.
Meteor Bert: Oh, afraid so. See that peanut? Dead giveaway.
Joe Dirt: Uhhh, no, that's a space peanut.
Meteor Bert: No, afraid not. That just a big ol' frozen chunk of poopy.
Studio manager: Dude, you were eating off it!

don't be silly, the drink tang

Actually a small amount of mass will be lost. Because part of the sandwich will be turned into energy after it is eaten and then the person would burn the energy off.

reply to post by buster2010


burning calories is just an expression, the nutrients absorbed by the body remain, and the waste is eliminated, but no mass is lost.

When I eat a 2-pound dinner I don't weight two pounds more an hour later, so how much does 'energy' weigh?

reply to post by Illustronic


Are you sure?
The next time you eat a large amount of food, weigh the food and then weigh yourself before and after you eat it. Then, continue to weigh yourself every hour for 24 hours (or until you use the bathroom).
I'd actually be interested to see the results.
Hmm...I might try that myself....

Consider an unmanned craft like New Horizons running off of plutonium decay, expending heat into cold space, which is lost energy and E=Mc2. then consider that Jr. High School experiment with a match lit and burnt in a contained vessel on a scale, the weight doesn't change but there is no biological life form in that vessel to consume mass/energy. A life form consumes mass, and doesn't discharge all of that mass into waste, it eats it for energy.

reply to post by Illustronic

The energy "consumed" when food is eaten is chemical energy, not nuclear energy. It is the same as the match. There isn't any loss of mass involved.

If you take a one pound rock out of your cars trunk and put it in the glove box does your car lose mass?

No, You just moved the mass around.

my opinion is that if the craft is completely sealed then no the mass would be the same always but that would be next to impossible so i believe the craft would lose a small amount of mass because you would eat the sandwich you body would convert it to nutrients and energy as the body uses the energy it will be converted to heat and as long as the craft is not perfectly insulated some heat will be lost and the mass will be decreased. Thats my 2 pence worth but it is late and i might had a different view in the morning.

reply to post by CLPrime


I would have to calculate the consumption of beer along the way, and I'm no math wizard, just an observer of stimulus/response. So when you move to get to the scale how are the calories used to move you effect your weight? Is energy consumption measurable in mass turned to energy and does energy weigh anything? (I suppose I would also have to collect the lost skin particles to get precise measurements, most of the dust in my house is from me and my wife).

In a spacecraft everything is contained, until you open a door to the outside. Then you will lose more mass than the weight of your waste, simply have to.

reply to post by Illustronic


Even food mass converted to chemical energy for our benefit is still contained in us. If we want the consumption of food to cause any reduction at all in the mass of the spacecraft, then I suppose we could have a release for gas, allowing such bodily function to escape into space. This would be akin to the release of "heat" (actually radiation by-products of the plutonium decay) into space. But even that would only allow a negligible amount of mass to escape. And, if we did that, we'd have a lot of explaining to do to all of the alien worlds who happen to encounter our gas clouds.

OK, this simple thread is getting ridiculous. I believe the mass doesn't change due to the sandwich consumption. I have always wondered about how life support systems and their effect on minute mass loss but alas, a contained vessel can not lose mass that way. But the inside heats the outside that loses heat and that's why there is thermal protection, so heat/energy is not mass?

reply to post by Illustronic


I wish I had a scale sensitive enough to weigh individual skin cells. For my bathroom scale, I think such considerations can be ignored. The nearest half-pound should do.
And, the "energy" "expended" by walking to the scale is inconsequential. As has already been pointed out, this energy doesn't actually go anywhere. It's in the form of nutrients and oxygen, and, over the course of respiration and regular cell functions, both bringing "energy" in and taking "energy" out, these processes cancel themselves out.

I understand that mass is not lost, but a simple question here.

Say a person is starving, and they loose 20lbs while they are starving. Where does that mass go? If someone hasn't eaten anything for 2 weeks they can't be pooping out 20lbs of waste? Where is all that fat and muscle going if it's not being consumed and turned into heat/energy?