What is payload?

[cantab]

How's this for a simple and practical definition: The payload is the bit you can easily swap out. In the case of a rocket launcher that's simple. In the case of a spaceplane or shuttle the contents of the cargo bay are payload and the crew are payload; I'd list the real Shuttle as having a payload of 24.4 tonnes plus seven crewmembers. The orbiter or spaceplane itself though are not payload because you can't easily replace them with something else, at least not without it being reasonably considered a whole new launch system.

And yes, a destination needs to be specified. The "default" is Low Kerbin Orbit though.

[The_Rocketeer]

From Oxford Dictionaries (my underline):

Definition of payload in English:

noun

1 The part of a vehicle’s load, especially an aircraft’s, from which revenue is derived; passengers and cargo.

1.1 Equipment, personnel, or satellites carried by a spacecraft.

1.2 Computing The actual information or message in transmitted data, as opposed to automatically generated metadata.

2 An explosive warhead carried by a missile.

2.1 Computing The effects of a virus on a computer system.

So, following the first definition, payload is the part of the rocket vehicle, equipment, cargo and/or crew that must reach the ultimate goal (which could include returning), thereby making the mission successful. This seems solid to me. (EDIT: it's also relevant to speak of the payload for each stage, as each stage has it's own particular end goal, e.g. ascent stage is orbit, transfer stage is encounter with next planet/moon, etc. This is what I was getting at in my first post in this thread)

I think mathematically people use payload as a shorthand when they mean payload mass or payload mass fraction. That's really just the mass of the above, or that mass as a fraction of the whole rocket. When talking about the payload mass fraction a rocket possesses, they're talking about the most payload mass it can carry and still reach its goal, e.g. LKO.

Edited September 17, 2015 by The_Rocketeer

[nothingSpecial]

Some of responses are really insightful.

So far vast majority points out that payload can be swapped/removed/modified, and lifter is essential into getting to the orbit.

But now I have something come to mind.

If my rocket lifter has no control block, and is controlled by probe core inside it's payload fairing, it won't fly without

payload.

So... The probe core is necessary for liftoff so it cannot be considered payload. Right?

[The_Rocketeer]

Some of responses are really insightful.

So far vast majority points out that payload can be swapped/removed/modified, and lifter is essential into getting to the orbit.

But now I have something come to mind.

If my rocket lifter has no control block, and is controlled by probe core inside it's payload fairing, it won't fly without

payload.

So... The probe core is necessary for liftoff so it cannot be considered payload. Right?

No, I think this is a false definition for payload. Your mission won't work at any stage without a control centre (pod or probe), so that element is always payload (unless you have more than 1 for some strange reason).

[cantab]

If my rocket lifter has no control block, and is controlled by probe core inside it's payload fairing, it won't fly without

payload.

So... The probe core is necessary for liftoff so it cannot be considered payload. Right?

I think that's just being overpedantic. My understanding is that real rockets have their own control and guidance systems anyway, it's a bit of a KSP oddity being able to let one box of electronics control the whole mission. In fact KSP's 2.5m "reaction wheel" is clearly based on the Saturn V Instrument Unit that sat just above the third stage fuel tanks.

[Joonatan1998]

I think payload is the part of the rocket that could be replaced with full fuel tanks and still reach orbit without using fuel from them.

Probe core is often included in payload, but it really is too light to matter much.

[AbacusWizard]

A more utilitarian approach:

What do you actually want to do once you're at your destination?

That's your payload.

[MalfunctionM1Ke]

I Keep it a little simpler.

A "Pay"-load is everything that pays for the launch. I.e. a satelite or a Command Module with a Lander attached.

Everything I bring back and can sell for scrap is a Bonus.

Also there is an interesting XKCD about it:

http://imgs.xkcd.com/comics/payloads_large.png

Edited September 18, 2015 by MalfunctionM1Ke

[LN400]

It's my understanding (right or wrong) that to see what the payload is, you need to define the mission first, or the end result you want, if you like.

Let's say I want to know what the surface of Minmus is like and I want to know the temperature at Minmus' surface. For this I would need either a probe that can survey the surface or a crew, and a thermometer. For the crew, I would need all the things needed to keep them alive and get them back.

Count up all the things I need to put together there, and that's the payload.

Then it's a question of how to get all of that to Minmus. None of the parts needed for that is payload.

An analogy: Let's say I want to watch a youtube video and let's say we're now at the stage where YT starts sending data my way. The data is what I want, the data is the reason I went to youtube in the first place. The data is the payload. To send it to me, the data is wrapped in a packet with all sorts of labels and instructions just to get it to my computer and to the right application on that computer. None of that is payload. Only the data, the reason I went to YT, is.

[Superfluous J]

A more utilitarian approach:

What do you actually want to do once you're at your destination?

That's your payload.

I'm in this boat as well, with a nod to "each stage has a payload" as well.

For contests, the payload is defined by the contest. For your own personal missions, it's defined by you. For the Space Shuttle, the contents of the Cargo bay are the payload. For the SRBs and that big orange tank, the shuttle and its contents are the payload. If you're lifting a bunch of fuel tanks to orbit and you fill them, just to drain that fuel into the lifter engines, then you're being clever and smart but it doesn't change the fact that the empty tanks that once held fuel are a payload. If they have any leftover fuel at the end, that's also payload.

So it's simple, really

[Val]

I'm in this boat as well, with a nod to "each stage has a payload" as well.

For contests, the payload is defined by the contest. For your own personal missions, it's defined by you. For the Space Shuttle, the contents of the Cargo bay are the payload. For the SRBs and that big orange tank, the shuttle and its contents are the payload. If you're lifting a bunch of fuel tanks to orbit and you fill them, just to drain that fuel into the lifter engines, then you're being clever and smart but it doesn't change the fact that the empty tanks that once held fuel are a payload. If they have any leftover fuel at the end, that's also payload.

So it's simple, really

I can very much agree with this.

[Warzouz]

My definition of payload is quite simpe : useful part you deliver at target.

- Lifting stage target is LKO

- Interplanetary stage target is low body orbit