What is payload?

[nothingSpecial]

I have recently read several threads that are concerned by payload fraction, and now I want to ask: what exactly is considered payload?

Just to keep things straight:

1. The question is in ambiguity what is exactly being compared.

2. The compared designs in question are a) multi-stage non recoverable rocket lifter and SSTO reusable spaceplanes. Other designs will be questioned later.

3. Spaceplanes usually bring crew to the orbit too.

4. If rocket launched craft is being returned to Kerbin, what is considered to be payload?

5. If spaceplane performs orbital maneuvers, isn't it become a payload as a whole?

So.

Fig. 1 shows what I can easy understand - something that is put in orbit is payload, everything else is launcher.

Fig. 2 is what brings me the initial confusion. As I understand from reading KSP forum, usually people suppose "what comes into cargo bay and then put into orbit" (2a). But if my spaceplane's mission is to add module to station and bring crew to the same station, or maybe not the same, aren't crew quarters become payload (2b)? What about probe that has it's own RCS or LFO engine or ion engine? Does propulsion of this probe counts as a part of payload? If so, isn't the whole spaceplane becomes payload if the mission contains making orbital maneuvers (2c)? What about single stage to Mun or, why the hell not, single stage to Laythe?

Fig. 3 is even more confusing. What is considered payload for the manned vehicles? Crew capsule that safely returns home with all the sciency equipment (3a)? The spacecraft as whole (3b)? Doesn't it mean that spaceplane as a whole should be considered payload?!

And then STS-like stacks come into consideration and I am completely lost.

Please help me someone!

Edited September 15, 2015 by nothingSpecial

[Pipcard]

When people talk about the real-life Space Shuttle's payload, they usually consider only what is in the cargo bay (2a). This is because the Shuttle orbiter (the spaceplane part) and its engines are considered part of the launch system and not the payload. But with the prematurely canceled Soviet "Buran" spaceplane and "Energia" booster, you can treat the payload as what was in the cargo bay (up to ~30 tonnes), or the entire spaceplane+payload (up to ~72 tonnes, but Energia could launch up to ~100 tonnes), because the spaceplane wasn't an integral part of the launch system.

With Fig 3, people would consider the entire mass of a Soyuz (orbital + re-entry + service module) or Apollo (command + service + lunar module) as the payload.

Edited September 15, 2015 by Pipcard

[peteletroll]

"Payload" by itself has actually little meaning. "Payload to low Kerbin orbit" may be more explicit.

[RizzoTheRat]

A mix of the above IMO. To my mind the payload is the mission equipment that needs to be put in to an LKO. If I'm launching a new lander to send to Minimus then both the lander and it's booster are payload, and that sits nicely in 3b. If I'm using a spaceplane to bring a crew to orbit then the crew and their module is payload, as it could be flown by a single pilot, and I usually carry excess fuel on those missions to top up the station.

[Starhawk]

I think of it like this:

The capsule is the payload of the return stage.

The return stage is the payload of the lander. (If it's a single craft mission with a staged lander)

The lander is the payload of the transfer stage.

The transfer stage is the payload of the lifter.

Happy landings!

[nothingSpecial]

When people talk about the real-life Space Shuttle's payload, they usually consider only what is in the cargo bay (2a).

With Fig 3, people would consider the entire mass of a Soyuz (orbital + re-entry + service module) or Apollo (command + service + lunar module) as the payload.

Well that what I thought.

But... Why?! Soyuz or Apollo, once in orbit, preform all the same things the Shuttle makes. Especially if we talk about Apollo: it has LEM that stays into space (as in Shuttle cargo), command module that brings crew back to Earth (as Shuttle cockpit) and service module that circulizes around Moon and then brings CSM with astronauts home (as Shuttle OMS). Isn't it... a little bit inconsistent?

"Payload" by itself has actually little meaning. "Payload to low Kerbin orbit" may be more explicit.

A mix of the above IMO. To my mind the payload is the mission equipment that needs to be put in to an LKO. If I'm launching a new lander to send to Minimus then both the lander and it's booster are payload, and that sits nicely in 3b. If I'm using a spaceplane to bring a crew to orbit then the crew and their module is payload, as it could be flown by a single pilot, and I usually carry excess fuel on those missions to top up the station.

Well than the whole Shuttle or whole CSM, LEM and TLI stage are payload to low Earth orbit, so the whole SSTO spaceplane should be payload to LKO orbit, isn't it?

I think of it like this:

The capsule is the payload of the return stage.

The return stage is the payload of the lander. (If it's a single craft mission with a staged lander)

The lander is the payload of the transfer stage.

The transfer stage is the payload of the lifter.

Happy landings!

Well this is interesting and not confusing. But I don't suppose it is useful if we try to compare different approaches...

[Starhawk]

Well this is interesting and not confusing. But I don't suppose it is useful if we try to compare different approaches...

I suppose you're right. In the end, if you want to do comparisons I think you have to define the term payload quite carefully.

Happy landings!

[nothingSpecial]

I suppose you're right. In the end, if you want to do comparisons I think you have to define the term payload quite carefully.

Happy landings!

Yeah, that what I try to do here. Because if I try to think about it harder than just usual cached "STS was way too expensive", I realize that the single STS launch should be compared with couple of Soyuzes and a Proton.

[The_Rocketeer]

Short version:

Payload = mass of whole vehicle - mass of shed stages - mass of current stage propulsion components.

It's stage-dependent. The first stage of a Saturn V has a massive payload (everything above it), but the ascent stage of the LM is carrying the smallest fraction of the total mission payload (2/3 of the crew complement plus moon rocks).

See this post.

Edited September 17, 2015 by The_Rocketeer

[Pipcard]

The Kankoh-maru space tourism SSTO concept was described as having a 4-tonne payload. I can only assume that this is the mass of the 50 passengers (with an average mass of 80 kg)

[nothingSpecial]

The Kankoh-maru space tourism SSTO concept was described as having a 4-tonne payload. I can only assume that this is the mass of the 50 passengers (with an average mass of 80 kg)

I just realized that if you put a person under fairing, then one-way trip wouldn't be more difficult than Sputnik-1.

[Guest]

I'm pretty sure I can get this nailed down for you, but it might take me a bit, so be patient.

I have recently read several threads that are concerned by payload fraction, and now I want to ask: what exactly is considered payload?

The vehicles "payload" is the sum total of stuff launched into orbit by your rocket, STS, or Space-plane.

1. The question is in ambiguity what is exactly being compared.

The weight of the payload, divided by the weight of the non-payload part of the rocket, is your payload fraction.

If a 50ton rocket can somehow put a 50ton payload into orbit, then that rocket has a payload fraction of 50%.

4. If rocket launched craft is being returned to Kerbin, what is considered to be payload?

An object being de-orbited (hopefully on purpose) is usually what remains of the original payload of the rocket.

For example, a crew capsule returning to Kerbin is the last bit of the spacecraft that was the original payload.

5. If spaceplane performs orbital maneuvers, isn't it become a payload as a whole?

The space-plane is the lifter, the object being carried by the space-plane is the payload.

For example, a space-plane going onto orbit to deliver a satellite is the lifter, the satellite is the actual payload.

Fig. 1 shows what I can easy understand - something that is put in orbit is payload, everything else is launcher.

Yes.

As I understand from reading KSP forum, usually people suppose "what comes into cargo bay and then put into orbit" (2a).

Also, yes.

But if my spaceplane's mission is to add module to station and bring crew to the same station, or maybe not the same, aren't crew quarters become payload (2b)?

No. Crew is crew, not payload. The station module you're delivering is your payload.

What about probe that has it's own RCS or LFO engine or ion engine? Does propulsion of this probe counts as a part of payload?

The probe itself, along with it's own integrated propulsion systems, is your payload.

If so, isn't the whole spaceplane becomes payload if the mission contains making orbital maneuvers (2c)?

No, the space-plane is the lifter, not the payload.

What about single stage to Mun or, why the hell not, single stage to Laythe?

Given the fact you're not delivering anything, the vehicle is the vehicle, not a payload.

Fig. 3 is even more confusing. What is considered payload for the manned vehicles? Crew capsule that safely returns home with all the sciency equipment (3a)?

The crew capsule is only a portion of the original payload. That which is sent into orbit is the payload.

The spacecraft as whole (3b)?

Yes, in this case, the spacecraft itself is your payload.

Doesn't it mean that spaceplane as a whole should be considered payload?!

No. The Space-plane is the lifter, not the payload.

And then STS-like stacks come into consideration and I am completely lost.

That which is contained in the cargo bay of the STS is it's payload, regardless of whether or not it's left in orbit.

The best description of payload that I can think of is this: Your payload is the part of the Rocket/STS/Space-plane, that is not involved with getting the vehicle into orbit.

So when your Rocket gets into orbit, the combined weight of everything left on it is the payload. Typically this is the spacecraft detached into orbit.

When the STS gets into orbit, because the vehicle is designed to be reusable, and must be recovered, only the non-reusable object in the cargo bay is payload.

For Space-planes the same rule as STS applies, only that which is in the cargo bay is payload.

I hope this helps.

[RCgothic]

A payload is whatever is being transported to accomplish a mission. The craft doing the transporting is not the payload, but may have been the payload of an earlier stage.

It's a little fuzzy whether you count crew as payload, but passengers definitely are.

To go through your examples:

1) Cargo is plainly payload. It's going to be used for a purpose that wasn't simply getting into space.

2) The shuttle by itself is not payload, it is the transfer vehicle. It may never have been payload (spaceplane SSTO or STS), or it may have piggybacked as a rocket's payload previously (Buran). Cargo is again plainly payload, whether being taken up or brought down. The forward command section is not payload unless it later detaches for some purpose, but the Kerbals inside may be if they're being taken somewhere for a purpose.

3) The Apollo CM is the payload of the CSM and Saturn, The CSM is also part of the Saturn's payload. The LM is another part of it.

[nothingSpecial]

The best description of payload that I can think of is this: Your payload is the part of the Rocket/STS/Space-plane, that is not involved with getting the vehicle into orbit.

A-ha!

So. The STS orbiter is not a payload, but for example, Buran is payload for Energia lifter? And if I put one spaceplane on the back of another, piggyback style, into orbit, the first one will be payload if it's engines weren't used?

2) The shuttle by itself is not payload, it is the transfer vehicle. It may never have been payload (spaceplane SSTO or STS), or it may have piggybacked as a rocket's payload previously (Buran). Cargo is again plainly payload, whether being taken up or brought down. The forward command section is not payload unless it later detaches for some purpose, but the Kerbals inside may be if they're being taken somewhere for a purpose.

So passenger rocketship SSTO with no cargo holds will have only passengers as it's payload, right? Like several dozens of kilograms at best. Edited September 15, 2015 by nothingSpecial

[RCgothic]

A-ha!

So. The STS orbiter is not a payload, but for example, Buran is payload for Energia lifter? And if I put one spaceplane on the back of another, piggyback style, into orbit, the first one will be payload if it's engines weren't used?

I think you've got it now.

[Guest]

And if I put one spaceplane on the back of another, piggyback style, into orbit, the first one will be payload if it's engines weren't used?

Yes. By George I think he's got it!

[KerikBalm]

Payload is stuff that played no role in getting the vehicle to orbit.

You can't count an entire SSTO as payload, because you can't delete the entire SSTO and get to orbit.

I can delete everything inside a mk3 cargobay, and still reach orbit.

I can delete everything inside a fairing, and still reach orbit.

If it can't fly without it, it is not payload.

[nothingSpecial]

Okay.

So when I had such design...

...the spaceplane was a payload!

...I don't think this is a cheap design but it should be more efficient than STS in terms of payload fraction... and more expensive also because of separated orbital insertion engines costs.

If it can't fly without it, it is not payload.

Also I realized that if craft has no probe core, the pilot cannot be considered payload, only passengers. So my smallest spaceplanes have zero payload fraction... Edited September 15, 2015 by nothingSpecial

[mhoram]

In order to make this a bit more complicated, i once created a family of lifters based on the schema below.

Usually the payload contained fuel for the engines of the engine deck which stayed in orbit.

However the mass of the engine deck did not count in my interpretation as part of the payload.

[nothingSpecial]

...Usually the payload contained fuel for the engines of the engine deck which stayed in orbit

But that means payload participated in liftoff so it wasn't really a payload?

[The_Rocketeer]

But that means payload participated in liftoff so it wasn't really a payload?

Grey area. The payload could be the structure of the 'payload' stage, not counting the fuel it contained on the pad.

[mhoram]

@nothingSpecial: the payload fuel was only used for orbital maneuvers after reaching a stable orbit and deorbiting the launch-propellant and engines. Sorry for the ambiguity.

[nothingSpecial]

Grey area. The payload could be the structure of the 'payload' stage, not counting the fuel it contained on the pad.

I once thought about using this as a clever way to carry less fuel overall until I realize that that means pushing extra tank mass in upper stage.

@nothingSpecial: the payload fuel was only used for orbital maneuvers after reaching a stable orbit and deorbiting the launch-propellant and engines. Sorry for the ambiguity.

Ah, I see.

[Champ]

The weight of the payload, divided by the weight of the non-payload part of the rocket, is your payload fraction.

If a 50ton rocket can somehow put a 50ton payload into orbit, then that rocket has a payload fraction of 50%.

Weight of the payload divided by the weight of the whole craft.

Your definition, applied to your exemple, gives a payload fraction of 100%.

[nothingSpecial]

Weight of the payload divided by the weight of the whole craft.

Your definition, applied to your exemple, gives a payload fraction of 100%.

No it's not in fact.

Mass of payload: Mp = 50 t.

Mass of rocket (mass of lifter): Ml = 50 t.

Whole mass: M = Mp + Ml = 100 t.

50 t / 100 t = .5 = 50%

Payload fraction of 100% means you have no lifter and still get your payload in orbit, possibly with Hyperedit.