NearTerm Propellant Depots: Implementation of a Critical Spacefaring Technology

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Near-Term Propellant Depots Implementation of a
Critical Spacefaring Technology

• Jonathan Goff, Masten Space Systems
• Bernard Kutter and Frank Zegler, ULA
• Dallas Bienhoff and Frank Chandler, Boeing
• Jeffrey Marchetta, University of Memphis
• Presented by Jonathan Goff at AIAA SPACE 2009
• Pasadena, CA September 17, 2009

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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, around
  other planetary bodies or at any other points of
  interest
• Can be supplied from earth, offworld sources, and
  maybe even from planetary atmospheres
• Can handle different sorts of fluids ranging from
  LOX/LH2 cryogenics to space storables to
  hypergols
• Can range in size from a Falcon-1 launched
  single-use fuel tank with a docking adapter to
  massive, ISS-sized transportation nodes.

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Historical Solutions to the Propellant Logistics
Problem

• Rocket-powered spaceflight isnt the only
  historical example of logistically challenging
  transportation.
• Similar Historical Analogies
• Antarctic Exploration
• Food/Fuel Caches
• Steam-powered Navies
• Naval Coaling Stations and Colliers
• Steam-powered railroads
• Coaling and watering stations
• Long-range jet powered military planes and
  helicopters
• Mid-air refuelling
• The historical solution to this problem has
  always been to cache propellants along the way.
• Early visionaries of the Space Age, including von
  Braun, recognized this reality as well.

Propellant Depots are the Solution to Space
Transportation Logistics Challenges Most In-line
with Historical Precedent
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Propellant Depot Questions

• Key Questions about Propellant Depots
• Are they technologically feasible at this time?
• How would you go about doing depots?
• Whats the best way to use them in a space
  transportation architecture?
• What sort of missions/capabilities to depots
  enable?
• How do they compare economically versus other
  options?
• How do you handle the logistics of running a
  depot?

This Paper
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Overview

• Prop Depot Technologies
• m-gravity Cryo Fluid Management
• Thermal Control
• Rendezvous and Propellant Transfer
• Depot Concepts
• Depot Technology Maturation Tools
• Conclusions/Future Work

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Propellant Depot Technologies m-gravity Cryo
Fluid Management

• While mg fluid handling is feasible, and
  sometimes desirable, settled handling is much
  higher TRL
• There are many settling options, including
  inertial (propulsive), tether-based, and
  electromagnetic
• Inertial settling is highest TRL, with decades of
  operational experience (Saturn SIV-B, Centaur,
  DIV-US, Ariane-V, etc)
• Fluid handling options interact with other depot
  design decisions
• ED-tether based systems can use tether for
  reboost and settling.
• Inertially settled depots can use boiloff from
  passive thermal control systems for settling and
  stationkeeping.

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Propellant Depot Technologies Thermal Control

• Passive versus Active, Zero Boiloff (ZBO) Thermal
  Control
• ZBO propellant storage is technologically
  feasible, and greatly simplified by settling
  propellants
• With settled propellants, active cooling is a lot
  closer to terrestrial experience than in mg
  conditions.
• Passive systems can tend to be a lot simpler and
  more reliable than active cooling systems
• Good passive thermal control is important even if
  active cooling is used
• Lowers the amount of heat that has to be actively
  rejected
• Acts as a backup in case of problems with active
  cooling
• Interesting Observation 1 Boiled propellants
  can be reused for stationkeeping propulsive
  purposes, meaning that for LEO depots, ZBO might
  not be necessary.
• Interesting Observation 2 Many of the features
  that make LH2 a headache for long-term storage
  make it useful in multi-fluid depotsLH2 is a
  wonderful heat sponge
• Interesting Observation 3 Due to stationkeeping
  demands and the challenging thermal environment
  LEO depots push you towards a use it or lose
  it, high throughput mode of operations.
• Interesting Observation 3a Depots at L-points
  are more suited for long-term storage and less
  frequent use.

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Propellant Depot TechnologiesRendezvous and
Transfer

• Recent research into orbital servicing (such as
  Orbital Express, XSS-11, FREND, etc) has
  significantly advanced the TRL of needed
  propellant transfer technologies
• Efficient and safe depot operations require
  extremely reliable prox-ops and transfer
• Need to minimize possibility of damage to depot
  or tanker from rendezvous/transfer operations
• Berthing using robotic arms or Boom Rendezvous
  may be preferable to traditional docking
• Many options for how to handle propellant
  delivery
• Progress/ATV/COTS-like tanker spacecraft
• Integrated-stage tanker spacecraft
• Dumb tankers plus tugs
• Personal Preference Tugs for prox-ops plus dumb
  tankers (based on or integrated with the delivery
  stage) with standardized docking/propellant
  transfer interfaces
• The most expensive bits get reused multiple times
• They dont have to be launched every time
• Minimizes the amount of engineering an particular
  launch provider needs to provide propellant
  delivery services
• Maximizes competition in propellant launch

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Near-Term Depot Concepts

• Single-Use Pre-Depot
• Simple, typically 2-launch architecture
• Enables unmanned and limited manned exploration
  missions using existing and near-term EELVs
• Single-Launch Single-Fluid Simple Depot
• Typically LOX-only, simpler than multi-fluid
  depots
• Much larger depot capacity than the single-use
  pre-depot
• Single-Launch Dual-Fluid Depot
• LH2 tank is built integral to LV fairing, upper
  stage LH2 tank is converted to depot LOX tank
  after deployment
• Can be based on existing or stretched versions of
  existing upper stages, or can be based on future
  upper stages like ACES or Raptor.
• Doesnt require orbital assembly to provide large
  propellant capacity (75-115mT of LOX/LH2)
• Sufficient capacity to enable manned exploration
  without requiring HLVs
• Self-deployable throughout the inner solar system
• With a depot at L1/L2 as well as LEO, manned
  ESAS-class exploration feasible with existing
  upper stages (with mission kits)
• Multi-Launch Modular Depots
• Largest propellant capacity (200 mT feasible)
• Integral robotic arm for easier berthing
• Can be combined with the above Dual-Fluid concept
  to reach 450 mT capacities
• Can be built up modularly

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Depot Technology Maturation Tools

• Low-cost, iterative technology maturation and
  demonstration testbeds reduce the cost and risk
  of reducing depots to practice
• They enable demonstrating the few
  first-generation depot technologies that still
  need demonstration
• They allow other promising options to be
  evaluated
• CRYOTE (CRYogenic Orbital TEstbed) allows
  long-duration experiments in the space
  environment
• Integrated with the ESPA ring for use with EELVs
• Large experiment volume makes results easier to
  scale than previous CFM experiments
• Relatively frequent flight opportunities as a
  secondary payload
• Suborbital testbeds (CRYOSOTE) flown on reusable
  suborbital vehicles enable short duration, but
  very low-cost experiments
• 2 - 5 min mg time per flight
• Flight costs lt50k
• Rapid reflight capabilities
• Large payload fairing compared to sounding
  rockets (60in diameter)
• Proof-of-concept experiments for various
  subsystems
• Pre-fly orbital experiments for debugging before
  committing to expensive orbital missions

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Conclusions/Future Work

• There are several approaches to depots that are
  both useful for manned space transportation
  beyond LEO, while also being near-term feasible.
• Recent development work on autonomous rendezvous
  and docking, orbital servicing and propellant
  transfer, orbital CFM testbeds, and suborbital
  RLVs lower the technological hurdles for
  implementing depots
• Avenues for Future Investigation
• A lot of these recent concepts drastically change
  the picture for how depots would be used in space
  transportation, which suggests further research
  into how best to integrate these concepts
• More investigation is needed to evaluate which
  approaches to tanker design and prox-ops are
  best, and how the economics of a multi-launch
  depot-centric architecture compares with
  alternatives