Sa08 Prop Depot Panel Jon Goff

The Case for Orbital Propellant Depots Jonathan Goff Rand Simberg Dallas Bienhoff Frank Zegler Space Access 2008

Castles and Foundations
“ 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.”
– Henry David Thoreau
“ 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, and none building a lasting infrastructure to reduce the expense and risk of future operations . 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 space for human purposes a routine function.” –John Marburger
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 anywhere else.

What are Propellant Depots
Facilities in space that can receive, store, and transfer propellants and other fluids to visiting vehicles.
Can be located in LEO, at Lagrange Points, or at any other point of interest
Can be supplied from earth, off-world sources, and maybe even from planetary atmospheres
Contemporary Analogy: Gas Stations
Historical Analogy: Naval Coaling Stations in the 19 th /20 th century

Why Propellant Depots Now?
The “Bahn Principle”
The best time to discuss an important new idea is when it is almost ready for primetime.
Corollary: The “Greason Principle”
The best time to enter a new business field is when the business case actually closes, but nobody else realizes it does.
Many of the main emerging entrepreneurial space companies started before SpaceShipOne killed the giggle factor for suborbital space.
However, being too far ahead of the curve also carries its own risks.

Key Benefits of Propellant Depots
No need for HLVs for trips beyond LEO
Allows for reusable in-space transportation systems
Enables safer, more affordable, more flexible operations beyond LEO
Disaggregates earth-to-LEO and deep-space transportation.
A key enabler for private lunar expeditions, commercial development, and eventually settlement.
Provides a high flight-rate, low-hassle market for future earth-to-orbit transportation systems
Provides infrastructure that both takes advantage of and promotes advances in lower-cost transportation
Is one of the technologies we must master if we ever want to become a truly spacefaring civilization.

Key Technological Challenges
While microgravity handling and transfer of storable propellants is a proven technology, there remain some challenges and technical risk for orbital cryogenic storage and transfer.
Microgravity Cryogenic Fluid Management Issues
Propellant orientation not constrained as in a 1G field
Boil-off venting problems: you don’t want to vent liquid
Engine feed/propellant transfer problems: you want to avoid accidentally ingesting gas in your feedlines
Mass gauging: how do you tell how much you have left if you don’t know what the orientation is?
Boil-off: Cryogens like to be cold, sunlight is hot, vacuum is a lousy heat sink, and boiling cryogens build pressure in your tanks. Also vented propellant boil-off is mass you have to ship at great cost out of a gravity well that is wasted.

Propellant Settling: A Key Enabler to Microgravity Cryogenic Fluid Management
If you can provide a sufficient force to the fluid to force it to take an orientation of your choosing, many of these problems become much easier.
This is called “propellant settling”
Methods of propellant settling
Propulsive Settling (Apollo, Centaur, and others)
Diaphragms (common with storable propellants but some work has been done for cryo propellants)
Rotational Motion
Tethers and Gravity Gradients
Surface Tension Devices
Magnetic Propellant Positioning
If you can settle the propellant, propellant transfer and storage become very similar to terrestrial cryogenic handling.

Long-Term Cryo Storage
Low Boil-off and Zero Boil-Off (ZBO) Technologies:
Multi-layer MLI
Sunshields
Thermodynamic Vents
Vapor-cooled Walls
Magnetic Propellant Positioning
Cryocoolers
Lots of prior art and current research, but still some work to go.
While LOX is definitely easier, even LH2 may be long-term storable without too much more hassle.

Microgravity Cryogen Transfer and Prox-Ops Issues
Settled propellant transfer is much easier than pure microgravity transfer
No two-phase flow
Very similar to transferring cryogens on earth
Every time a cryogenic upper stage relights on orbit, it is performing cryogenic propellant transfer
Proximity operations and automated fluid coupling interfaces are also becoming more technologically mature
Orbital Express demonstrated Autonomous Rendezvous and Docking, as well as storable propellant transfer.
Off-loading most of the “smarts” to a robotic tug may allow for much simpler tanker/customer-side mechanical and fluid interfaces.

NASA Ain’t Gonna Do It: The Importance of a Commercial Propellant Depot
NASA has no intention of funding a propellant depot development project.
It competes too much with existing parochial interests (the Shuttle workforce)
A NASA-operated depot would have many drawbacks
A NASA-operated depot can’t buy propellant from the cheapest source, if they happen to be “dern furiners”
NASA gets money by meeting parochial interests (jobs), not by providing goods or services in an economic manner
NASA is always at the whim of Congress for funding
We’re only likely to see a propellant depot in our lifetimes if someone can find a way to close the business case.

Chickens and Eggs
Propellant Depots face a classical “chicken and egg” problem (much like orbital RLVs)
Most enabled markets won’t exist until propellant depots are already operational
There’s a time lag between when a new technology hits the market and when the market adapts to and incorporates the new capability.
Government could prime the pump, but that probably can’t and shouldn’t be counted on.

Fried Chicken?
There may be ways around chicken and egg problems
Suborbital and Orbital RLV projects give some hints at how to proceed
Incremental development
Get others to pay for some or all of your R&D (XCOR)
Suborbital RLVs also help reduce technology development cost by providing a low-cost, quick-turnaround  g environment.
Leveraging commercial orbital projects (Bigelow stations, COTS vehicles, etc.) can reduce up-front development cost somewhat

Introducing The Panelists
Rand Simberg (Wyoming Space and Information Systems)
“ Recovering” aerospace veteran/blogger at Transterrestrial Musings
Long-time proponent of orbital propellant depots (including a recent Popular Mechanics article)
Will discuss business and market aspects of propellant depots
Dallas Bienhoff (Boeing)
“ Mr Propellant Depot”
Has led many projects for Boeing related to propellant depots and cryogenic upper stages (including many AIAA and STAIF papers).
Will be discuss Boeing’s work on propellant depots
Frank Zegler (ULA)
Member of the Atlas V Centaur team
Has participated in many projects related to settled propellant transfer, cryo storage, propellant depots, etc. (lots of AIAA papers and patents)
Will discuss some of ULA’s propellant depot related work

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Sa08 Prop Depot Panel Jon Goff

by jongoff on Mar 31, 2008

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Sa08 Prop Depot Panel Jon Goff Presentation Transcript