Fuel tank rules of thumb

Does anyone have formulae or rules of thumb for the mass of a fuel tank to
hold a certain weight or volume of fuel such as LH2, LOX, or Kerosene - eg
if I said 75 tonnes of LH2 at 3g what would the tank weigh?

thanks...
Roger

I use 15 percent
of the enclosed LH2,2 percent of the enclosed LOX, and
2.5 percent of the enclosed kerosene BRBR


Does that vary depending on the tank material (aluminum, composite, etc?)

Thanks,


Matt Bille
)
OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR

(MattWriter) wrote in message ...
I use 15 percent
of the enclosed LH2,2 percent of the enclosed LOX, and
2.5 percent of the enclosed kerosene BRBR


Does that vary depending on the tank material (aluminum, composite, etc?)

Thanks,

Generally, I stick with aluminum or other metals.
However, I am not predisposed to any one material
or approach. What works and bears up under analysis
is what is important.

Incidentally, my rule of thumb numbers do not apply
to pressure-feds, quite obviously. I have not found
pressure-feds to have any practical application except
for quite low delta-vee requirements.

Best regards,
Len (Cormier)
PanAero, Inc. and Third Millennium Aerospace, Inc.
( http://www.tour2space.com )


Matt Bille
)
OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR

Does anyone have formulae or rules of thumb for the mass of a fuel tank to
hold a certain weight or volume of fuel such as LH2, LOX, or Kerosene - eg
if I said 75 tonnes of LH2 at 3g what would the tank weigh?

Mass /kg = a x V^b

LOx LH2 JP4

a 27.0 32.3 30.5

b 0.843 0.794 0.824

found at

S. S. Pietrobon,... nsto.pdf (156,748 bytes), 49th Int. Astronautical
Congress, IAF-98-V.3.07, Melbourne, Australia, Sep.-Oct. 1998.
IAF98pap.pdf (123,896 bytes)

http://www.sworld.com.au/steven/pub/nsto.pdf

quoting NASA TM X-3554

(David Shannon) wrote in message . com...
Does anyone have formulae or rules of thumb for the mass of a fuel tank to
hold a certain weight or volume of fuel such as LH2, LOX, or Kerosene - eg
if I said 75 tonnes of LH2 at 3g what would the tank weigh?

Mass /kg = a x V^b

LOx LH2 JP4

a 27.0 32.3 30.5

b 0.843 0.794 0.824

found at

S. S. Pietrobon,... nsto.pdf (156,748 bytes), 49th Int. Astronautical
Congress, IAF-98-V.3.07, Melbourne, Australia, Sep.-Oct. 1998.
IAF98pap.pdf (123,896 bytes)

http://www.sworld.com.au/steven/pub/nsto.pdf

quoting NASA TM X-3554

Thanks for the post and intersting reference.

A lot depends upon insulation concept, tank shape, etc.,
of course, but, IMO, the referenced formual seems to be
optimistic for mass of LOX tanks and pessimistic for the
mass of LH2 tanks.

BTW, V refers to the volume i kL or m^2.

Best regards,
Len (Cormier)
PanAero, Inc.
( http://www.tour2space.com )

Len I have not found pressure-feds to have any practical
Len application except for quite low delta-vee requirements.

Really? Once you've achieved low earth orbit, if you wanted
significant delta-V from there, say, to get to an outer planet,
wouldn't you use a small, low pressure engine with a huge
expansion ratio, pressure-fed from tanks?

After all, it doesn't much matter how long your burn takes
once you're in orbit. Small engines improve your mass ratio,
and low-pressure engines presumably weigh less also.

I would guess the lower limit on engine size is set by Isp
scaling issues: at some point the drag and even radiative
losses to the chamber walls and whatnot probably overcome the
mass ratio advantage.

(Iain McClatchie) writes:

Len I have not found pressure-feds to have any practical
Len application except for quite low delta-vee requirements.

Really? Once you've achieved low earth orbit, if you wanted
significant delta-V from there, say, to get to an outer planet,
wouldn't you use a small, low pressure engine with a huge
expansion ratio, pressure-fed from tanks?

After all, it doesn't much matter how long your burn takes
once you're in orbit. Small engines improve your mass ratio,
and low-pressure engines presumably weigh less also.

....OTOH, long burns lead to high gravity losses, and you lose some of the
benefits of the "Oberth Effect"...


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

(Iain McClatchie) wrote in message . com...
Len I have not found pressure-feds to have any practical
Len application except for quite low delta-vee requirements.

Really? Once you've achieved low earth orbit, if you wanted
significant delta-V from there, say, to get to an outer planet,
wouldn't you use a small, low pressure engine with a huge
expansion ratio, pressure-fed from tanks?

After all, it doesn't much matter how long your burn takes
once you're in orbit. Small engines improve your mass ratio,
and low-pressure engines presumably weigh less also.

I would guess the lower limit on engine size is set by Isp
scaling issues: at some point the drag and even radiative
losses to the chamber walls and whatnot probably overcome the
mass ratio advantage.

OK. The rules for deep space are different from those for Earth
to LEO, where I tend to focus. I agree that low-pressure,
pressure-feds deserve a look--once in space.

Other things change too. For example, my rather extreme preference
for reusable hardware versus expendable perhaps doesn't make too
much sense for tankage for lunar missions--where one needs a large
delta vee for recovery.

Best regards,
Len (Cormier)
PanAero, Inc.
( http://www.tour2space.com )

Gordon D. Pusch wrote:

...OTOH, long burns lead to high gravity losses, and you lose some of the
benefits of the "Oberth Effect"...


Use perigee kicks. Minimizes gravity losses from low thrust systems.

--
Scott Lowther, Engineer
Remove the obvious (capitalized) anti-spam
gibberish from the reply-to e-mail address

Scott Lowther writes:

Gordon D. Pusch wrote:

...OTOH, long burns lead to high gravity losses, and you lose some of the
benefits of the "Oberth Effect"...

Use perigee kicks. Minimizes gravity losses from low thrust systems.

....At the price of having to make a large number of restarts, any one of which
may fail (perhaps catastrophically), plus multiple passages through the van Allens...


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'