The Case for The Case for Orbital Propellant DepotsOrbital Propellant Depots

Jonathan GoffJonathan Goff

Rand SimbergRand Simberg

Dallas BienhoffDallas Bienhoff

Frank ZeglerFrank Zegler

Space Access 2008Space Access 2008

Castles and FoundationsCastles and Foundations ““If you have built castles in the air, your work need not be lost; that is where If you have built castles in the air, your work need not be lost; that is where

they should be. Now put the foundations under them.”they should be. Now put the foundations under them.”

– – Henry David ThoreauHenry David Thoreau

““If we are serious about this, then our objective must be more than a If we are serious about this, then our objective must be more than a disconnected series of missions, each conducted at huge expense and risk, disconnected series of missions, each conducted at huge expense and risk, and none and none building a lasting infrastructure to reduce the expense and building a lasting infrastructure to reduce the expense and

risk of future operationsrisk of future operations. If we are serious, we will build capability, not just . If we are serious, we will build capability, not just on the ground but in space. And our objective must be to make the use of on the ground but in space. And our objective must be to make the use of

space for human purposes a routine function.” –John Marburgerspace for human purposes a routine function.” –John Marburger

Famous Heinlein quote: “Once you're in orbit, you're halfway to anywhere.”Famous Heinlein quote: “Once you're in orbit, you're halfway to anywhere.” Corollary: As hard as getting to orbit is, it’s only half the challenge of getting Corollary: As hard as getting to orbit is, it’s only half the challenge of getting

anywhere else.anywhere else.

What are Propellant DepotsWhat are Propellant Depots Facilities in space that can Facilities in space that can

receive, store, and transfer receive, store, and transfer propellants and other fluids propellants and other fluids to visiting vehicles.to visiting vehicles. Can be located in LEO, at Can be located in LEO, at

Lagrange Points, or at any Lagrange Points, or at any other point of interestother point of interest

Can be supplied from Can be supplied from earth, off-world sources, earth, off-world sources, and maybe even from and maybe even from planetary atmospheresplanetary atmospheres

Contemporary Analogy: Contemporary Analogy: Gas StationsGas Stations

Historical Analogy:

Naval Coaling Stations in the 19th/20th century

Why Propellant Depots Now?Why Propellant Depots Now? The “Bahn Principle”The “Bahn Principle”

The best time to discuss an important new idea is The best time to discuss an important new idea is when it is when it is almostalmost ready for primetime. ready for primetime.

Corollary: The “Greason Principle”Corollary: The “Greason Principle” The best time to enter a new business field is when The best time to enter a new business field is when

the business case actually closes, but nobody else the business case actually closes, but nobody else realizes it does.realizes it does.

Many of the main emerging entrepreneurial space Many of the main emerging entrepreneurial space companies started before SpaceShipOne killed the companies started before SpaceShipOne killed the giggle factor for suborbital space.giggle factor for suborbital space.

However, being too far ahead of the curve also However, being too far ahead of the curve also carries its own risks.carries its own risks.

Key Benefits of Propellant DepotsKey Benefits of Propellant Depots No need for HLVs for trips No need for HLVs for trips

beyond LEObeyond LEO Allows for reusable in-space Allows for reusable in-space

transportation systemstransportation systems Enables safer, more Enables safer, more

affordable, more flexible affordable, more flexible operations beyond LEOoperations beyond LEO

Disaggregates earth-to-LEO Disaggregates earth-to-LEO and deep-space and deep-space transportation.transportation.

A key enabler for private A key enabler for private lunar expeditions, lunar expeditions, commercial development, commercial development, and eventually settlement.and eventually settlement.

Provides a high flight-rate, Provides a high flight-rate, low-hassle market for future low-hassle market for future earth-to-orbit transportation earth-to-orbit transportation systemssystems

Provides infrastructure that Provides infrastructure that both takes advantage of both takes advantage of and promotes advances in and promotes advances in lower-cost transportationlower-cost transportation

Is one of the technologies Is one of the technologies we we mustmust master if we ever master if we ever want to become a truly want to become a truly spacefaring civilization.spacefaring civilization.

Key Technological ChallengesKey Technological Challenges While microgravity handling and transfer of storable While microgravity handling and transfer of storable

propellants is a proven technology, there remain propellants is a proven technology, there remain some challenges and technical risk for orbital some challenges and technical risk for orbital cryogenic storage and transfer.cryogenic storage and transfer.

Microgravity Cryogenic Fluid Management IssuesMicrogravity Cryogenic Fluid Management Issues Propellant orientation not constrained as in a 1G fieldPropellant orientation not constrained as in a 1G field

Boil-off venting problems: you don’t want to vent liquidBoil-off venting problems: you don’t want to vent liquid Engine feed/propellant transfer problems: you want to avoid Engine feed/propellant transfer problems: you want to avoid

accidentally ingesting gas in your feedlinesaccidentally ingesting gas in your feedlines Mass gauging: how do you tell how much you have left if you Mass gauging: how do you tell how much you have left if you

don’t know what the orientation is?don’t know what the orientation is? Boil-off: Cryogens like to be cold, sunlight is hot, vacuum is a Boil-off: Cryogens like to be cold, sunlight is hot, vacuum is a

lousy heat sink, and boiling cryogens build pressure in your lousy heat sink, and boiling cryogens build pressure in your tanks. Also vented propellant boil-off is mass you have to tanks. Also vented propellant boil-off is mass you have to ship at great cost out of a gravity well that is wasted.ship at great cost out of a gravity well that is wasted.

Propellant Settling: A Key Enabler to Microgravity Propellant Settling: A Key Enabler to Microgravity Cryogenic Fluid ManagementCryogenic Fluid Management

If you can provide a sufficient force to the fluid to force it to If you can provide a sufficient force to the fluid to force it to take an orientation of your choosing, many of these problems take an orientation of your choosing, many of these problems become much easier. become much easier.

This is called “propellant settling”This is called “propellant settling” Methods of propellant settlingMethods of propellant settling

Propulsive Settling (Apollo, Centaur, and others)Propulsive Settling (Apollo, Centaur, and others) Diaphragms (common with storable propellants but some work has Diaphragms (common with storable propellants but some work has

been done for cryo propellants)been done for cryo propellants) Rotational MotionRotational Motion Tethers and Gravity GradientsTethers and Gravity Gradients Surface Tension DevicesSurface Tension Devices Magnetic Propellant PositioningMagnetic Propellant Positioning

If you can settle the propellant, propellant transfer and storage If you can settle the propellant, propellant transfer and storage become very similar to terrestrial cryogenic handling.become very similar to terrestrial cryogenic handling.

Long-Term Cryo StorageLong-Term Cryo Storage Low Boil-off and Zero Boil-Off Low Boil-off and Zero Boil-Off

(ZBO) Technologies:(ZBO) Technologies: Multi-layer MLIMulti-layer MLI SunshieldsSunshields Thermodynamic VentsThermodynamic Vents Vapor-cooled WallsVapor-cooled Walls Magnetic Propellant Magnetic Propellant

PositioningPositioning CryocoolersCryocoolers

Lots of prior art and current Lots of prior art and current research, but still some work to research, but still some work to go.go.

While LOX is definitely easier, While LOX is definitely easier, even LH2 may be long-term even LH2 may be long-term storable without too much storable without too much more hassle.more hassle.

Microgravity Cryogen Transfer and Prox-Ops IssuesMicrogravity Cryogen Transfer and Prox-Ops Issues

Settled propellant transfer is much Settled propellant transfer is much easier than pure microgravity easier than pure microgravity transfertransfer No two-phase flowNo two-phase flow Very similar to transferring Very similar to transferring

cryogens on earthcryogens on earth Every time a cryogenic upper Every time a cryogenic upper

stage relights on orbit, it is stage relights on orbit, it is performing cryogenic propellant performing cryogenic propellant transfertransfer

Proximity operations and Proximity operations and automated fluid coupling automated fluid coupling interfaces are also becoming more interfaces are also becoming more technologically maturetechnologically mature Orbital Express demonstrated Orbital Express demonstrated

Autonomous Rendezvous and Autonomous Rendezvous and Docking, as well as storable Docking, as well as storable propellant transfer.propellant transfer.

Off-loading most of the “smarts” to Off-loading most of the “smarts” to a robotic tug may allow for much a robotic tug may allow for much simpler tanker/customer-side simpler tanker/customer-side mechanical and fluid interfaces.mechanical and fluid interfaces.

NASA Ain’t Gonna Do It: NASA Ain’t Gonna Do It: The Importance of a The Importance of a CommercialCommercial Propellant Depot Propellant Depot

NASA has no intention of funding a propellant depot NASA has no intention of funding a propellant depot development project.development project. It competes too much with existing parochial interests (the It competes too much with existing parochial interests (the

Shuttle workforce)Shuttle workforce) A NASA-operated depot would have many drawbacksA NASA-operated depot would have many drawbacks

A NASA-operated depot can’t buy propellant from the cheapest A NASA-operated depot can’t buy propellant from the cheapest source, if they happen to be “dern furiners”source, if they happen to be “dern furiners”

NASA gets money by meeting parochial interests (jobs), not by NASA gets money by meeting parochial interests (jobs), not by providing goods or services in an economic mannerproviding goods or services in an economic manner

NASA is always at the whim of Congress for fundingNASA is always at the whim of Congress for funding We’re only likely to see a propellant depot in our lifetimes We’re only likely to see a propellant depot in our lifetimes

if someone can find a way to close the business case.if someone can find a way to close the business case.

Chickens and EggsChickens and Eggs Propellant Depots face a classical “chicken Propellant Depots face a classical “chicken

and egg” problem (much like orbital RLVs)and egg” problem (much like orbital RLVs)Most enabled markets won’t exist until Most enabled markets won’t exist until

propellant depots are already operationalpropellant depots are already operationalThere’s a time lag between when a new There’s a time lag between when a new

technology hits the market and when the technology hits the market and when the market adapts to and incorporates the new market adapts to and incorporates the new capability.capability.

Government could prime the pump, but that Government could prime the pump, but that probably can’t and shouldn’t be counted on.probably can’t and shouldn’t be counted on.

Fried Chicken?Fried Chicken? There may be ways around There may be ways around

chicken and egg problemschicken and egg problems Suborbital and Orbital RLV Suborbital and Orbital RLV

projects give some hints at how to projects give some hints at how to proceedproceed Incremental developmentIncremental development Get others to pay for some or all Get others to pay for some or all

of your R&D (XCOR)of your R&D (XCOR) Suborbital RLVs also help reduce Suborbital RLVs also help reduce

technology development cost by technology development cost by providing a low-cost, quick-providing a low-cost, quick-turnaround turnaround g environment.g environment.

Leveraging commercial orbital Leveraging commercial orbital projects (Bigelow stations, COTS projects (Bigelow stations, COTS vehicles, etc.) can reduce up-front vehicles, etc.) can reduce up-front development cost somewhatdevelopment cost somewhat

Introducing The PanelistsIntroducing The Panelists Rand Simberg (Wyoming Space and Information Systems)Rand Simberg (Wyoming Space and Information Systems)

““Recovering” aerospace veteran/blogger at Transterrestrial MusingsRecovering” aerospace veteran/blogger at Transterrestrial Musings Long-time proponent of orbital propellant depots (including a recent Long-time proponent of orbital propellant depots (including a recent

Popular MechanicsPopular Mechanics article) article) Will discuss business and market aspects of propellant depotsWill discuss business and market aspects of propellant depots

Dallas Bienhoff (Boeing)Dallas Bienhoff (Boeing) ““Mr Propellant Depot”Mr Propellant Depot” Has led many projects for Boeing related to propellant depots and Has led many projects for Boeing related to propellant depots and

cryogenic upper stages (including many AIAA and STAIF papers).cryogenic upper stages (including many AIAA and STAIF papers). Will be discuss Boeing’s work on propellant depotsWill be discuss Boeing’s work on propellant depots

Frank Zegler (ULA)Frank Zegler (ULA) Member of the Atlas V Centaur teamMember of the Atlas V Centaur team Has participated in many projects related to settled propellant transfer, Has participated in many projects related to settled propellant transfer,

cryo storage, propellant depots, etc. (lots of AIAA papers and patents)cryo storage, propellant depots, etc. (lots of AIAA papers and patents) Will discuss some of ULA’s propellant depot related workWill discuss some of ULA’s propellant depot related work