# RequestSingle Person Spacecraft

#### gattispilot

OK. But the gauge should show volume or pressure? or do we need a pressure gauge and volume. Not sure if the volume changes due to RCS

#### Urwumpe

##### Not funny anymore
Donator
No, the volume is the volume of the tank, that never changes. A gas tries to fill all the volume available, contrary to a liquid.

#### gattispilot

oK. thanks. So the gauge should read pressure, correct?

Donator

#### gattispilot

Thanks. So the center gauge reads tank pressure. MAx 5000 psi, correct?
Not sure what value to get to set the animation?

Along the same line would be air for breathing correct?

#### Urwumpe

##### Not funny anymore
Donator
Not sure what value to get to set the animation?

What about a linear scale from zero to 3E7 (Pa), with zero being zero and 3E7 (Pa) being 1.0

#### gattispilot

Sure So pascals and not PSi? Either way I make a linear scale and not round. But what value should I be getting to tell the needle to move?

I am thinking tank pressure.

We have it defined already here:

private: inline double GetTankPressure() const { return TANK_CONSTANT * GetPropellantMass(tank) * TEMPERATURE; }

#### Urwumpe

##### Not funny anymore
Donator
Orbiter uses SI units internally, so its easier to do the internal model calculations in SI units. For displaying data, you can always convert it into any unit you like - [0.0 ... 1.0] for animation of the dial, or [0.0 ... 5000] for numeric indicators in a MFD or generic cockpit HUD, etc...

#### gattispilot

Thanks. In the past. I had the needle move as the fuel changed. Not sure if that is still the case?

//fuellevel = GetPropellantMass(tank)/10.4;
//SetAnimationArm(anim_fuel2, fuellevel);

#### Urwumpe

##### Not funny anymore
Donator
Thanks. In the past. I had the needle move as the fuel changed. Not sure if that is still the case?

//fuellevel = GetPropellantMass(tank)/10.4;
//SetAnimationArm(anim_fuel2, fuellevel);

If you look at the formula, then yes: At constant temperature until reaching the minimum operating pressure of the regulator, the pressure will drop linear with gas mass consumption.

If the propellant gas slowly warms or cools in operation (As usual), the pressure will vary a lot. 27K more temperature ~ 10% higher pressure.

Also, higher temperature means lower mass flow to the thrusters at the same thrust.

#### gattispilot

OK. I know we have where the tank pressure is affected by temperature. Where Temperature doesn't change. Not sure if we can get Temperature?

But if a constant then get GetPropellantMass(tank)/10.4 and move the needle by that amount? I guess I could not a digital gauge? Where the value is displayed?

#### Arvil

##### Well-known member
I would expect a simple bourdon tube pressure gauge, and wouldn’t even have to be calibrated to psi, Pa, kg/cm3, it could be just 0 to 100% with maybe 0, 25, 50, 75, 100% marks, and maybe a green mark at the 100% point for filling, and red arc at 0 to 25 % at ‘bingo fuel’ time to head home. I don’t how easy it would be to animate that. Something like SCBA gauges. And maybe a red light goes on at 25% to warn the operator of bingo fuel.
Hope that helps.

#### gattispilot

Yes, Thanks. Animating would not be hard. I just not sure what value I need to be getting to tell the pointer to move?

#### Urwumpe

##### Not funny anymore
Donator
I would say, a variable propellant temperature would be something better suited for version 2.0. Since the SPS is supposed to operate in LEO, the difference between orbital night and day could really have alot of impact on the temperature there, also the two tanks are not inside the pressurized volume of the spacecraft, but behind the micrometeoroid protection.

#### gattispilot

Thanks. But what value do I get to make the gauge change?

#### Urwumpe

##### Not funny anymore
Donator
Thanks. But what value do I get to make the gauge change?

As usual in orbiter animations, the range is 0.0 to 1.0. So, you just look at the texture for the dial and measure the rotation range of the pointer and then make sure that 0.0 is at 0 and 1.0 at the maximum of the scale.

#### gattispilot

Yes. I know the range. BUt do I use GetPropellantMass(tank)/10.4 then apply that to the animation or something else?

#### gattispilot

On the gauge something like this?

The one on the right shows the animation range 0-1. When the tank is full the needle will be at 100% and tank empty at 0% . But do I just use
GetPropellantMass(tank)/10.4 for the animation state?

#### Attachments

• fuelpercentsps.jpg
44.1 KB · Views: 6

#### Arvil

##### Well-known member
@Urwumpe can speak to the math, he knows it better than I, besides it’s his request. But visual looks great! If a gauge like this is what he likes, a couple suggestions:
Looks like you got this from an image of a glycerin-filled gauge, might whiteout the bubble. In space the bubble floating around the face might get annoying, don’t know if there’s glycerin in those things in space.
Might try to calculate the max dV you might need to return to dock and expand the red to the equivalent %. SCBA air gauges are typically 20 to 25%.
Consider printing % N<sub>2</sub> in the upper face or whatever the fuel is.
If you want a little fun, print ‘gattispilot’ on the lower face, after all you are the manufacturer.
Keep up the good work.

#### Arvil

##### Well-known member
Another suggestion. In the case of a standard gauge like this in the cabin, if the gauge fails/leaks, there would be a shutoff valve immediately accessible to shutoff the flow of fuel into the cabin. Might wish to install an image of a quarter-turn valve handle or knob somewhere close.

Replies
7
Views
807
Replies
1
Views
572
Replies
6
Views
435
Replies
16
Views
1K