Method and apparatus for measuring the amount of fuel aboard a spacecraft
A method and apparatus for measuring the amount of fuel aboard a spacecraft under weightless conditions utilize at least one orifice, at least one flow latch valve for the selection of an orifice to be used, and at least one control valve for releasing a stream of a pressurizing gas from at least one high-pressure tank in order to restore pressure in a fuel tank following a pressure reduction due to withdrawal of fuel. The amount of fuel remaining in the fuel tank is determined based on the time required to restore fuel tank pressure by a flow of gas from the high pressure tank to the fuel tank, via the orifice.
1. Apparatus for measuring the amount of fuel aboard a spacecraft under weightless conditions, said apparatus comprising:
at least one orifice;
at least one flow latch valve for selecting an orifice;
at least one control valve for releasing a stream of a pressurizing gas from at least one high-pressure tank to supply pressure to at least one fuel tank that contains said fuel, via said orifice that is selected; and
measurement and calculation means for determining an amount of fuel of the at least one fuel tank based on
a measured first pressure, a measured first temperature, and a measured first vapor pressure of the at least one fuel tank prior to releasing the stream of pressuring gas from the at least one high-pressure tank,
a measured time period of the supply of pressurizing gas from the at least one high-pressure tank to the at least one fuel tank,
a measured second pressure, a measured second temperature, and a measured second vapor pressure of the at least one fuel tank after completion of the supply of pressurizing gas from the at least one high-pressure tank to the at least one fuel tank,
a measured third averaged pressure, a measured third averaged temperature, and a fuel tank volume as a function of the internal pressure of the high-pressure tank, and
a temperature-dependent fuel density, an orifice coefficient and a parameter that takes into account the dependence of the critical flow on the supply pressure.
2. The apparatus according to claim 1 , wherein the apparatus further comprises at least one check/latch valve for selecting the at least one fuel tank.
3. The apparatus according to claim 1 , wherein the at least one control valve is closed when a desired pressure has been reached in at least one fuel tank to be pressurized.
4. The apparatus according to claim 3 , wherein the at least one control valve is closed by telecommand.
5. The apparatus claim 1 , wherein the at least one orifice, the at least one latch valve and the at least one control valve are configured in a redundant fashion.
6. The apparatus according to claim 1 , wherein the amount of fuel is determined by means of the formulas
mProp
:=
p
1
-
pVI
T
1
·
VT
(
p
1
)
-
p
2
-
pV
2
)
T
2
·
VT
(
p
2
)
+
delta_mHe
·
R
p
1
-
pV
1
T
1
·
rho
(
T
1
)
-
p
2
-
pV
2
T
2
·
rho
(
T
2
)
with
delta_mHe
:=
dt
·
K
·
pHe
c
·
[
1
R
·
THe
·
[
(
a
THe
-
b
)
+
1
pHe
]
]
1
2
and
VT
(
p
)
:=
V
0
+
aV
·
p
and
rho
(
T
)
:=
rho
20
·
[
1
+
α
Prop
·
(
T
-
293
)
]
.
7. A method of measuring the amount of fuel aboard a spacecraft under weightless conditions, said method comprising:
opening at least one latch valve for selecting an orifice;
releasing a stream of a pressurizing gas via the selected orifice, from at least one high-pressure tank having at least one control valve; and
determining an amount of fuel of the at least one fuel tank based on
a measured first pressure, a measured first temperature, and a measured first vapor pressure of the at least one fuel tank prior to releasing the stream of pressuring gas from the at least one high-pressure tank,
a measured time period of the supply of pressurizing gas from the at least one high-pressure tank to the at least one fuel tank,
a measured second pressure, a measured second temperature, and a measured second vapor pressure of the at least one fuel tank after completion of the supply of pressurizing gas from the at least one high-pressure tank to the at least one fuel tank,
a measured third averaged pressure, a measured third averaged temperature, and a fuel tank volume as a function of the internal pressure of the high-pressure tank, and
a temperature-dependent fuel density, an orifice coefficient and a parameter that takes into account the dependence of the critical flow on the supply pressure.
8. The method according to claim 7 , further comprising:
opening at least one check/latch valve for selecting at least one fuel tank to be pressurized.
9. The method according to claim 7 , further comprising:
releasing a stream of a pressurizing gas from at least one high-pressure tank having at least one control valve.
10. The method according to claim 7 , further comprising closing the at least one control valve when a desired pressure has been reached in at least one fuel tank.
11. The method according to claim 7 , wherein the amount of fuel is determined by means of the formulas
mProp
:=
p
1
-
pVI
T
1
·
VT
(
p
1
)
-
p
2
-
pV
2
)
T
2
·
VT
(
p
2
)
+
delta_mHe
·
R
p
1
-
pV
1
T
1
·
rho
(
T
1
)
-
p
2
-
pV
2
T
2
·
rho
(
T
2
)
with
delta_mHe
:=
dt
·
K
·
pHe
c
·
[
1
R
·
THe
·
[
(
a
THe
-
b
)
+
1
pHe
]
]
1
2
and
VT
(
p
)
:=
V
0
+
aV
·
p
and
rho
(
T
)
:=
rho
20
·
[
1
+
α
Prop
·
(
T
-
293
)
]
.