ULA Innovation: Integrated Vehicle Fluids (IVF)

[Robotbeat]

Much better to just stretch the upper stage and use it as a tanker.

[Kabloona]

IVF works beautifully in concert with fuel cells and solar electric systems.  You let those systems handle long-duration low-level power demands and turn IVF on when you need to do heavy lifting. This enables them to be compact and light since they don't have to handle peak loads.  You can even eliminate dedicated controllers and power processing units which are major elements in the cost of those systems. The mission transition time is dependent on tank thermo, power level and other stuff but its usually after many days. 

I didn't understand this bit about "mission transition time." What exactly happens "after many days?"

Thanks!

Sounds like maybe transition to solar power only, after the cryos have boiled off.

[jongoff]

IVF works beautifully in concert with fuel cells and solar electric systems.  You let those systems handle long-duration low-level power demands and turn IVF on when you need to do heavy lifting. This enables them to be compact and light since they don't have to handle peak loads.  You can even eliminate dedicated controllers and power processing units which are major elements in the cost of those systems. The mission transition time is dependent on tank thermo, power level and other stuff but its usually after many days. 

I didn't understand this bit about "mission transition time." What exactly happens "after many days?"

Thanks!

Sounds like maybe transition to solar power only, after the cryos have boiled off.

My guess is that he's saying that solar arrays only start being a net win after "many days", and that before that threshold it's lighter and cheaper to just use the boiled off propellant. This might change for missions in deep space where the natural boiloff rate is a lot lower.

~Jon

[sdsds]

What exactly happens "after many days?"

Sounds like maybe transition to solar power only, after the cryos have boiled off.

My guess is that he's saying that solar arrays only start being a net win after "many days"

Thanks, these both seem like reasonable interpretations. (I favor the second principally because I don't understand how a stage with absolutely no propellant helps a mission at all, even if it has electric power.)

This might change for missions in deep space where the natural boiloff rate is a lot lower.

Indeed! I'm wondering if they envision being able to retain propellant long enough that the IVF thrusters could provide propulsion for missions with trajectories like that of LADEE? How about GRAIL?

[TrevorMonty]

ULA long term plans are for a ACES upper stage with better insulation and fuel life measured in weeks and maybe months in some versions. A IVF Centuar is a means of testing the technology and reducing costs, improving stages life from hours to weeks is just a bonus.

[Port]

okay, this might be obvious but not for me so:

why use a piston engine (+generator i'd assume?) instead of an fuel-cell?
i'd see no problem designing a system of multiple cells, churning out amps from excess Hydrogen/Oxygen for a much lower weight and no moving parts
(much less failure modes, there's a reason gemini/apollo didn't use piston engines for power)

[kevin-rf]

... I don't understand how a stage with absolutely no propellant helps a mission at all, even if it has electric power.

Me too. And, that there's no existing requirement for that "capability".

Cough,.... Historically, that was how Agena was used... So it will finally transitioned to LH/LOX!

[Damon Hill]

okay, this might be obvious but not for me so:

why use a piston engine (+generator i'd assume?) instead of an fuel-cell?
i'd see no problem designing a system of multiple cells, churning out amps from excess Hydrogen/Oxygen for a much lower weight and no moving parts
(much less failure modes, there's a reason gemini/apollo didn't use piston engines for power)

This question has been repeatedly asked and explained in this thread.  Go back to the start and begin reading.

Hint: in the right context, seemingly wasted heat is very useful.

--Damon

[TrevorMonty]

The patent link at #36 was most informative.

[Norm38]

okay, this might be obvious but not for me so:

why use a piston engine (+generator i'd assume?) instead of an fuel-cell?
i'd see no problem designing a system of multiple cells, churning out amps from excess Hydrogen/Oxygen for a much lower weight and no moving parts
(much less failure modes, there's a reason gemini/apollo didn't use piston engines for power)

I could see why a fuel cell was a poor choice, but wasn't seeing the problem with a gas turbine, so I read the docs.
http://tinyurl.com/ula-ivf2012

Similarly a fuel cell could be used to drive IVF with the advantage of no high speed machinery and an extensive history of spaceflight. Proton Exchange Membrane (PEM) cells have shown a tremendous amount of promise in recent years. However, 20kW is a relatively large fuel cell for flight applications and because all power is produced as electricity (as compared to perhaps 10% for the IC engine) it must be converted via motors to shaft power with their attendant switching systems and losses. This grows the fuel cell to address conversion efficiencies. Reactants are only consumed at a mixture ratio of 8 – which is generally insufficient for regenerative cooling so unless a bulky and costly radiator system is employed a larger flow of hydrogen must be brought to the fuel cell to maintain thermal stasis. From a consumables standpoint the fuel cell loses its advantage over the IC engine. The PEM cell efficiency is founded on low operating temperature which produces condensed liquid water which must be disposed of without providing any benefit for vehicle settling. In general, the use of a fuel cell system would be most advantageous for cryewed vehicles where the water produced has a strong positive influence on vehicle mass. For cryogenic propulsive stages the cost differential between IC engines and fuel cells likely favors the former.

So unless there's crew to drink the water, fuel cells are out.  Also correct, 20kW is a LOT of electrical power.  A 20kW electric motor and drive set is not that small or lightweight.  In vacuum, the aluminum heat sink for the power electronics may have the same mass as the ICE engine block.  And for many similar reasons, it's why production automotive hybrid vehicles are parallel hybrids instead of series.  It's more efficient to have the ICE crankshaft mechanically coupled to the wheels than convert all shaft power to electricity and only use an electric motor.

As for turbines:

A turbine could be used for such an application but it would be exquisitely small with extremely high rotating speeds to produce only 20kW with low density hydrogen as the working fluid. Provisions for heat and shaft power extraction could be made but the overall developmental complexity of cooling, lubrication, ignition, control and power take off at this very low power level seemed daunting compared to the IC engine. The use of such small turbines on ground based installations is virtually unheard of. Virtually a whole new technology would have to be developed at substantial cost and risk.

So the turbine would be smaller. But too small, too high RPM, hard to get the heat out, and not off the shelf technology.
But note that if IVF were used on a methane launcher, 20kW natural gas micro-turbines are commercially available, so that may be an option. (But of course those turbines burn 80% nitrogen, not pure O2)
For hydrogen, the ICE came out ahead.

Yes the docs are a very good read.

[gin455res]

okay, this might be obvious but not for me so:

why use a piston engine (+generator i'd assume?) instead of an fuel-cell?
i'd see no problem designing a system of multiple cells, churning out amps from excess Hydrogen/Oxygen for a much lower weight and no moving parts
(much less failure modes, there's a reason gemini/apollo didn't use piston engines for power)

I could see why a fuel cell was a poor choice, but wasn't seeing the problem with a gas turbine, so I read the docs.
http://tinyurl.com/ula-ivf2012

Similarly a fuel cell could be used to drive IVF with the advantage of no high speed machinery and an extensive history of spaceflight. Proton Exchange Membrane (PEM) cells have shown a tremendous amount of promise in recent years. However, 20kW is a relatively large fuel cell for flight applications and because all power is produced as electricity (as compared to perhaps 10% for the IC engine) it must be converted via motors to shaft power with their attendant switching systems and losses. This grows the fuel cell to address conversion efficiencies. Reactants are only consumed at a mixture ratio of 8 – which is generally insufficient for regenerative cooling so unless a bulky and costly radiator system is employed a larger flow of hydrogen must be brought to the fuel cell to maintain thermal stasis. From a consumables standpoint the fuel cell loses its advantage over the IC engine. The PEM cell efficiency is founded on low operating temperature which produces condensed liquid water which must be disposed of without providing any benefit for vehicle settling. In general, the use of a fuel cell system would be most advantageous for cryewed vehicles where the water produced has a strong positive influence on vehicle mass. For cryogenic propulsive stages the cost differential between IC engines and fuel cells likely favors the former.

So unless there's crew to drink the water, fuel cells are out.  Also correct, 20kW is a LOT of electrical power.  A 20kW electric motor and drive set is not that small or lightweight.  In vacuum, the aluminum heat sink for the power electronics may have the same mass as the ICE engine block.  And for many similar reasons, it's why production automotive hybrid vehicles are parallel hybrids instead of series.  It's more efficient to have the ICE crankshaft mechanically coupled to the wheels than convert all shaft power to electricity and only use an electric motor.

As for turbines:

A turbine could be used for such an application but it would be exquisitely small with extremely high rotating speeds to produce only 20kW with low density hydrogen as the working fluid. Provisions for heat and shaft power extraction could be made but the overall developmental complexity of cooling, lubrication, ignition, control and power take off at this very low power level seemed daunting compared to the IC engine. The use of such small turbines on ground based installations is virtually unheard of. Virtually a whole new technology would have to be developed at substantial cost and risk.

So the turbine would be smaller. But too small, too high RPM, hard to get the heat out, and not off the shelf technology.
But note that if IVF were used on a methane launcher, 20kW natural gas micro-turbines are commercially available, so that may be an option. (But of course those turbines burn 80% nitrogen, not pure O2)
For hydrogen, the ICE came out ahead.

Yes the docs are a very good read.

There is a type of gas-turbine that is described here:
http://www.agileturbine.com/publications/Small%20Scale%20Combined%20Heat%20and%20Power.pdf
that uses a sub-atmospheric cycle -- combustion, expansion, cooling and then compression.

In the link above it is suggested as the engine in residential scale Combined Heat and Power unit. In this application it is claimed to have some advantages; a) the combustion is at slightly subatmospheric pressure and this eliminates the need for a natural gas fuel pump; and 2) although having lower power density than a conventional (compressor, combustion, expansion) turbine, it scales to small powers better.

In the outlined (IVF) flat head piston engine the enthalpy comes indirectly through the cooling system. Perhaps a sub-atmospheric turbine would supply the enthalpy (heat output)  more directly (/simply) , much as in the above CHP application.

(makes one wonder if a sub-atmospheric staged combustion rocket engine is feasible and possibly simpler - no feed pump, lower pressures, and better scalability - though using the propellant as a heat sink before burning it upstream sends logical circularity warning Klaxons in my head - though I think it works?)

[gin455res]

okay, this might be obvious but not for me so:

why use a piston engine (+generator i'd assume?) instead of an fuel-cell?
i'd see no problem designing a system of multiple cells, churning out amps from excess Hydrogen/Oxygen for a much lower weight and no moving parts
(much less failure modes, there's a reason gemini/apollo didn't use piston engines for power)

I could see why a fuel cell was a poor choice, but wasn't seeing the problem with a gas turbine, so I read the docs.
http://tinyurl.com/ula-ivf2012

Similarly a fuel cell could be used to drive IVF with the advantage of no high speed machinery and an extensive history of spaceflight. Proton Exchange Membrane (PEM) cells have shown a tremendous amount of promise in recent years. However, 20kW is a relatively large fuel cell for flight applications and because all power is produced as electricity (as compared to perhaps 10% for the IC engine) it must be converted via motors to shaft power with their attendant switching systems and losses. This grows the fuel cell to address conversion efficiencies. Reactants are only consumed at a mixture ratio of 8 – which is generally insufficient for regenerative cooling so unless a bulky and costly radiator system is employed a larger flow of hydrogen must be brought to the fuel cell to maintain thermal stasis. From a consumables standpoint the fuel cell loses its advantage over the IC engine. The PEM cell efficiency is founded on low operating temperature which produces condensed liquid water which must be disposed of without providing any benefit for vehicle settling. In general, the use of a fuel cell system would be most advantageous for cryewed vehicles where the water produced has a strong positive influence on vehicle mass. For cryogenic propulsive stages the cost differential between IC engines and fuel cells likely favors the former.

So unless there's crew to drink the water, fuel cells are out.  Also correct, 20kW is a LOT of electrical power.  A 20kW electric motor and drive set is not that small or lightweight.  In vacuum, the aluminum heat sink for the power electronics may have the same mass as the ICE engine block.  And for many similar reasons, it's why production automotive hybrid vehicles are parallel hybrids instead of series.  It's more efficient to have the ICE crankshaft mechanically coupled to the wheels than convert all shaft power to electricity and only use an electric motor.

As for turbines:

A turbine could be used for such an application but it would be exquisitely small with extremely high rotating speeds to produce only 20kW with low density hydrogen as the working fluid. Provisions for heat and shaft power extraction could be made but the overall developmental complexity of cooling, lubrication, ignition, control and power take off at this very low power level seemed daunting compared to the IC engine. The use of such small turbines on ground based installations is virtually unheard of. Virtually a whole new technology would have to be developed at substantial cost and risk.

So the turbine would be smaller. But too small, too high RPM, hard to get the heat out, and not off the shelf technology.
But note that if IVF were used on a methane launcher, 20kW natural gas micro-turbines are commercially available, so that may be an option. (But of course those turbines burn 80% nitrogen, not pure O2)
For hydrogen, the ICE came out ahead.

Yes the docs are a very good read.

There is a type of gas-turbine that is described here:
http://www.agileturbine.com/publications/Small%20Scale%20Combined%20Heat%20and%20Power.pdf
that uses a sub-atmospheric cycle -- combustion, expansion, cooling and then compression.

In the link above it is suggested as the engine in residential scale Combined Heat and Power unit. In this application it is claimed to have some advantages; a) the combustion is at slightly subatmospheric pressure and this eliminates the need for a natural gas fuel pump; and 2) although having lower power density than a conventional (compressor, combustion, expansion) turbine, it scales to small powers better.

In the outlined (IVF) flat head piston engine the enthalpy comes indirectly through the cooling system. Perhaps a sub-atmospheric turbine would supply the enthalpy (heat output)  more directly (/simply) , much as in the above CHP application.

(makes one wonder if a sub-atmospheric staged combustion rocket engine is feasible and possibly simpler - no feed pump, lower pressures, and better scalability - though using the propellant as a heat sink before burning it upstream sends logical circularity warning Klaxons in my head - though I think it works?)

Perhaps sub-atmospheric is a misnomer in this context. In the link to the CHP application description, the combustion is sub-atmospheric because the fuel is burning in a mixture of air and mildly pressurised (and probably choked?)  natural gas ahead of an expander. In the rocket context the engine will be working sub-(the pressure of the propellant tanks).

[Port]

Thanks for the reply, the paper was very interesting.

Actually i thought of something more SOFC-like for several reasons, but i can see why the ICE was chosen.
The Turbine is very interesting (especially for BFR/MCT etc reasons imo), especially since mr. musk has some serious issues with "fool-cells"

[sdsds]

Similarly a fuel cell could be used to drive IVF with the advantage of no high speed machinery and an extensive history of spaceflight. Proton Exchange Membrane (PEM) cells have shown a tremendous amount of promise in recent years. However, 20kW is a relatively large fuel cell for flight applications and because all power is produced as electricity (as compared to perhaps 10% for the IC engine) it must be converted via motors to shaft power with their attendant switching systems and losses. This grows the fuel cell

20kW is a LOT of electrical power.  A 20kW electric motor and drive set is not that small or lightweight.

Is the 20 kW requirement determined by what's needed to restart the main (RL10) engine?

As I understand the first flight of the additional thruster(s), all RL10 starts (indeed all aspects of the main mission) will be handled exactly as they have been historically. The new thruster will be started only for the deorbit burn. For that mission how much smaller will the fuel cell they use be?

Then, if you had a deep space mission that only needed two RL10 starts (for the ascent and Earth-departure burns), could you then perform e.g. the GRAIL mission profile, possibly through LOI, all with the Centaur thruster, and then separate the spacecraft once in lunar orbit?

As a spacecraft customer, I might be willing to pay a considerable premium for "delivery in lunar orbit."

[Damon Hill]

The RL10 pretty much starts itself by bootstrapping.  I think actuators are electrical, but power requirements couldn't be remotely that great.  No fuel cells used at any time.  IVF supports the entire stage, not just the engine(s).  This includes post-mission operations.

[sdsds]

Hmm, perhaps it's a matter of semantics, but something on Centaur apparently requires mechanical shaft power that would take a 20 kW electric motor. I'm thinking that requirement is pumps, and those pumps are used to meet the RL10 startup propellant inlet pressure requirements. Is that wrong?

[Damon Hill]

The IVF engine mechanically drives pumps that pressurize the main propellant tanks; the tanks operate at different pressure levels including a higher pressure for RL10 operations when a higher pressurization gas flow rate is required--that's when the IVF engine heat is very useful, to warm up the very cold boiloff gasses.  Optionally, IVF can power pumps for a high power thruster independently of the RL10 engine.

The RL10 engine remains essentially unchanged running on its own expander cycle turbopump.  The higher tank pressure should meet the RL10's input head pressurization needs, which in turn was used to eliminate boost pumps some time ago.  That's what all the high pressure helium was for, which IVF will eliminate.

IVF is a hybrid system that both generates average electrical power needs and charges a battery, which can support peak power demands and IVF engine start/stop conditions.

I'm not clear exactly how the IVF platform demonstrator flight is supposed to operate in parallel with legacy Centaur systems; might get a little tricky.  I think they want to verify that the internal combustion engine operates correctly in microgravity and that engine cooling and pressurization do the right things at the right time.  I think in this mission the goal of IVF is to support post-mission disposal and some cruise time.

Additionally, the IVF engine can 'supercharge' itself to double output power, from about 26hp to 50hp, should such peak power levels be required.  There's a lot of headroom built into the design for future growth.  IVF is really flexible, and I have to keep re-reading the documentation to appreciate the many details.

[TrevorMonty]

Here is an interesting extract from one of the papers.
 
I think this the approach that XCOR are using ie using a ICE to drive cryogenic pumps for Lynx and also a RL10 replacement. This maybe part of reason ULA are using XCOR for engine development.
A 1200lbf engine is not large but could be used for missions where high thrust is not critical, ie gravity losses are not an issue.The engine should be low cost as the expensive fuel pump is all ready supplied.

"IVF can be used to directly drive cryogenic pumps for a small scale rocket engine without requiring power extraction from engine nozzles.
A single IVF module could readily drive a 5300N (1200 lbf) thrust hydrogen engine while simultaneously
doing tank pressurization and thruster operations."

[Damon Hill]

I've never understood precisely how XCOR's system really works; somehow I got the impression the piston pumps were to directly pump propellant; perhaps it's a very similar system to IVF's internal combustion engine?  I was a little skeptical but I didn't have much information to go on.

[TrevorMonty]

XCOR say piston pumps but not engine that drives them. A ICE would make sense as they expect dozens of flights out the Lynx engines.