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Lunar L1 Gateway & SEP Design Briefing. Gateway Element Lead: Frank Lin Lead Systems Engineer: Jim Geffre JSC Gateway Design Team SEP NASA GRC SEP Team 11/2/01. Briefing Objectives. Review work done to date by JSC Advanced Design Team on Gateway architecture

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Lunar l1 gateway sep design briefing l.jpg

Lunar L1 Gateway & SEP Design Briefing


Element Lead: Frank Lin

Lead Systems Engineer: Jim Geffre

JSC Gateway Design Team




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Briefing Objectives

  • Review work done to date by JSC Advanced Design Team on Gateway architecture

    • Focus on design of Gateway Element

  • Review work done to date by NASA GRC on Gateway architecture

    • Focus on design of Solar Electric Propulsion (SEP) system

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Briefing Outline

  • Gateway Architecture Overview

  • Gateway Mission Overview

  • Requirement Development

    • Mission Requirements and Constraints

    • Functional Allocation Matrix (FAM), N2 Charts, Sub-system Requirements

  • Gateway Sub-Systems Descriptions

  • Preliminary Hazard and Reliability Analysis

  • Future Technology Investments

  • Open Issues/Forward Work

  • Solar Electric Propulsion

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Gateway Architecture

“Earth’s Neighborhood”

GPS Constellation

Crew departs from and returns to ISS

L1 Gateway

Lunar Habitat

Lunar Lander

Crew Transfer Vehicle

  • L1 Gateway

  • “Gateway” to the Lunar surface

  • Outpost for staging missions to Moon, Mars and telescope construction

  • Crew safe haven

  • Lunar Lander

  • Transports crew between Gateway and Lunar Surface

  • 9 day mission (3 days on Lunar surface)

  • Lunar Habitat

  • 30-day surface habitat placed at Lunar South Pole

  • Enables extended-duration surface exploration and ops studies

  • Crew Transfer Vehicle

  • Transports crew between ISS and Gateway

  • Nominal aerocapture to ISS, or direct Earth return contingency capability

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Gateway Mission Profile

Launch Gateway on DELTA IV-H

Activate Critical Systems, Inflate & Checkout Gateway

LEO Operations

Launch Shuttle with Gateway Outfitting Crew

Shuttle Rendezvous and Docking with Gateway

Outfit & Checkout


SEP Autonomously Dock with Gateway

Launch SEP on DELTA IV-H

Autonomously Deploy SEP Solar Arrays

Gateway and SEP spiral to LL1 (unmanned)

Up to 15 days*

Lunar Surface Mission

Crew Arrives at Gateway in CTV

Crew Returns to Earth in CTV

30 days

LL1 Operations

Telescope Mission

Deliver Lunar Lander to Gateway (unmanned)

30 days

Gateway Logistics Resupply / Cargo Delivery (unmanned)

Science Mission

*Reflects crew time spent in Gateway

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Go/No go for TLI?

Repair successful?

Gateway go/no go for SEP launch? TLI?

Dock successful?

Stack go for TLI ?

Gateway Mission Flow Chart

Send replacement/repair mission on Shuttle



Delta IV




Inflate, activate,

and checkout

in LEO

All systems go?





All systems go?

Shuttle outfitting

in LEO, final


(detailed list TBD)








SEP Rndz/

dock with


at LEO

Fully deploy SEP arrays

Partial SEP array deploy

Launch SEP stage

Shuttle returns




Attempt repair on later Shuttle mission if possible


Stabilize Gateway and SEP



Lunar lander

Lunar mission


Gateway uses chem

prop system

for separation

and L1 insertion

Config Gateway for

stable L1 ops


Transit from

LEO to LL1

SEP stage

undocks for return

Telescope arrives

Telescope mission


* Refer to Lunar L1 Architecture Operational Events Flow Chart

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Requirements and Constraints

Top Level Requirements

  • Stage telescope construction and lunar surface missions from Gateway

    • Two telescope construction missions per year

    • Two lunar surface excursions per year

  • Support crew of four

  • Design lifetime of 15 years

  • Simultaneously support three docked vehicles (CTV, Lunar Lander, Logistics Module)

  • Provide EVA capability for nominal operations

  • Maintain position at lunar L1 Lagrange point

  • Autonomous transfer from low-Earth orbit to lunar L1

    Design Goals and Constraints

  • Incorporate inflatable technology

  • Delivery to lunar L1 via solar electric propulsion

  • Crew safety is highest priority

  • Maximum system technology demonstration capability

  • Maximize use of technologies viable for future human space exploration

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Gateway Requirement Development Process


N2 Chart

  • Defines System interface connectivity for Gateway by mission phase

  • Defines type and disposition of system interfaces

  • Defines Gateway functions for each mission phase

  • Identifies Gateway Sub-systems for each mission phase

Sub-system Requirements

  • Defines required systems for each mission phase

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Gateway Element Summary

Inflatable Airlock (4)

Radiators (3)

  • Element Design Lifetime: 15 yrs

  • Element Mass:

    • Launch: 22,827 kg

    • Outfitting: 588 kg

    • Post-outfitting: 23,415 kg

    • Resupply mass/Volume:

      • 6-months: 805 kg / 3.878 m3

      • 24-months: 2,824 kg / 7.587 m3

  • Element Volume:

    • Launch: 145 m3

    • Operational: 275 m3

  • Power provided:

    • PV Array: 12 kW Nom/14.4 kW Peak

    • Energy Storage:

      • Batteries 71 kW-h

      • Flywheel 20 kW-h

  • Support Missions:

    • Outfitting at LEO: One mission/architecture

    • HF&H consumables: Two missions/year

    • ECLSS/Prop: One mission/two years

  • Estimate Element Cost: XX M

  • System Reliability: 72%



RCS jets

Prop & ECLS tanks

EVA Work Platform/ Telescope Assembly Site

P/V Arrays (2)


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Gateway Configurations

Launch Configuration

LEO, Transit, L1 Stand-by Configuration

Lunar Operations Configuration

Telescope Operations Configuration

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Gateway Systems

  • Attitude Control System (ACS)

  • Avionics


  • EVA

  • Human Factors & Habitability (HF&H)

  • Power

  • Propulsion

  • Robotics

  • Structures

  • Thermal Control

  • Mission Operations

  • Mission Success

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Attitude Control System Design Summary

  • System Requirements:

    • Maintain Solar Inertial Attitude for Gateway in low-Earth orbit and at Lunar L1

    • Provide 1,000 N-m-s of Momentum Storage

    • Provide 20,000 W-hr of Energy Storage

  • Assumptions Made:

    • Momentum storage requirements are equivalent to NGST

    • Flywheel system axis must be aligned with one of the Gateway’s body axes

  • Concept Trades Considered:

    • Flywheels

    • Control Moment Gyros

    • Chemical RCS

  • Selected Technologies:

    • Integrated Power and Attitude Control System (IPACS) Flywheels

      • Rationale: The flywheel system offers the potential for a coupled energy storage and attitude control capability, and is the least mass alternative. A CMG system would require a larger lithium-ion battery system to accommodate the extra 20 kW-hr of energy storage. Chemical RCS requires a large propellant load to handle the attitude control needs for 15 years.

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Attitude Control System Design Summary

System Specification:

  • Physical dimensions: Mass: 318 kg Volume: 0.288 m3

  • Provide 70 kWe peak power to user

  • TRL 3

    Issues and Concerns

  • None

    Forward Work

  • Determine flywheel system reliability & lifetime

IPACS Flywheel


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Avionics System Design Summary

  • System Requirement

    • Provide guidance, navigation, control, communications, and health monitoring of Gateway

  • Assumptions Made

    • Communications would follow proposed Ka-band upgrade and operate in the 32ghz range

    • UHF would be used for space-to-space communication between vehicles

    • Flight Computer System would be a quad-redundant system based on the X-38 Fault

    • Tolerant Processor model

    • The flight computer, itself, would be based on the Universal Mini-Controller (UMC)

    • Flight Computers would be distributed so that they could also collect data from subsystems

    • near their respective locations

    • Wiring would include a combination of fiber optics, wireless, and parasitic use of the power

    • buses where applicable, optimally selected to minimize mass and maximize reliability

  • Concept Trades Considered

    • NA

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Avionics System Design Summary

  • System Specification

    • Mass is 251kg

    • Total Volume Required: 1.0 m3

    • Overall Sub-system TRL Level: 6

  • Issues and Concerns

    • None

  • Forward Work

    • None

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Data Acquisition

& Control

Avionics System Design Summary



Gateway Avionics Architecture











Digital Voice




Data Buses






Flight computers


Crew Interface

- Hand


- Switches




Sensor Data

HDR and LDR Data

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ECLSS System Design Summary

  • System Requirement

    • Control cabin temperature, humidity (NASA-STD-3000), and pressure (select at 9 psia)

    • Provide crew consumables (O2, N2, H2O) for cabin, airlock and EVA

    • Provide closed air, water recovery and waste management systems to minimize re-supply

  • Assumptions Made

    • Two-year re-supply period

    • Crew daily O2 consumption rate - 0.84 kg/person/day

    • Crew drinking and food preparation – 2.8 kg/person/day, hygiene, 6.8 kg/person/day

    • No dishwasher, no laundry, no salad machine

  • Concept Trades Considered

    • High pressure vs. cryogenic N2 and O2 storage

    • CO2 removal technology: 4 x BMS vs. solid amine

    • Biological water recovery technology (BWR) vs. Vapor Phase Catalytic Ammonia Removal technology (VPCAR)

  • Selected Technologies

    • Cryogenic w/ High pressure for Rationale: Cryogenic system has less mass. High inflation pressure tanks for initial Gateway inflation for shorter inflation time.

    • 4 x BMS CO2 removal system Rationale: relative mature close CO2 removal system

    • VPCAR Rationale: Mass, volume and power benefits. Shorter

      • turn-around time. Restart ability.

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ECLSS System Design Summary

  • System Specification

    • ECLSS System Mass: 2851 kg

      • Dry Mass: 2174 kg

      • Fluid Mass: 677 kg

    • ECLSS System Volume: 15.9 m3

    • TRL Level:

      • CO2 removal 9

      • Oxygen generation system 6

      • CO2 reduction system 6

      • CO2 compressor 3

      • Trace contaminant control 4

  • Issues and Concerns

    • NASA-STD-3000 set long-term mission spacecraft pressure at 14.5 – 14.9 psia.

  • Forward Work

    • Report

  • Fire detection and suppression 9

  • Vapor Phase Catalytic Ammonia Removal (VPCAR) 4

  • Water recovery from brines (air evaporation system) 6

  • WRS product water post processor (ion-exchange beds) 6

  • Solid Waste Processing (Lyophlilization water recovery) 3

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Air Evaporation


System (AES)

ECLSS System Design Summary

ECLSS Water RecoverySystem Block Diagram

Respiration, condensate




Urine + flush water


Hygiene wastewater

Food preparation

45 kg/day



Cond HX



Sabatier CO2 reduction subsystem


ECLSS Air Revitalization System Block Diagram







O2 Gen. subsystem

Waste Processing System

Cabin at 9.0 psia

O2 30%

N2 70%

Air leaks





O2 from propulsion cryogenic storage

Water from water recovery system



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EVA System Design Summary

  • System Requirement

    • Store 4 Space Suits from CTV

    • Support Four six month mission phases prior to resupply

      • 10 EVAs (8 hr) for Telescope mission for four missions

      • Gateway maintenance at one EVA per six month mission

      • Total of 84 4 hr EVAs prior to resupply

  • Assumptions Made

    • 10 EVAs for Telescope mission

    • 1 EVA for Gateway maintenance per six month mission

    • Two tool boxes for Telescope assembly

  • Concept Trades Considered

    • Recharge system to recharge 3000 psi PLSS Oxygen tanks from low pressure cryo tanks

      • Chose thermal compression to 850 psi, mechanical compression from 850 psi to 3000 psi, (ORCA), ECLSS emergency repress tank used as accumulator for rapid refill then recharged using compressor.

  • System Specification Dry Mass Volume Minimum TRL

    • Space Suits 636 kg 3.62 m3 TRL 2

    • Vehicle Support for EVA 212 kg 0.34 m3 TRL 3

    • EVA Translation Aids 123 kg 3.36 m3 TRL 9

    • EVA Tools 132 kg 0.2 m3 TRL 9

    • Airlock 433 kg 8.18 m3 TRL 3

Eva system design summary l.jpg


Trim cooler




Swing Bed CO2 &

Humidity Remover






C & W


H2O Evaporator

Lunar Space Suit Schematics

EVA System Design Summary

Issues and Concerns

  • Lack of Technology Development Funds to raise low TRL items within schedule needs

    Forward Work

  • Light weight PLSS

  • Recharge system to recharge 3000 psi PLSS tanks from 150 psi lox supply

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Pressure O2






800 to 3000 psi

850 psi

Relief Valve





Q = 90 BTU/lb

LOX at sub critical pressures


Gateway Space Suit Oxygen Recharger Schematic ECLSS top off configuration

Gateway EVA System Block Diagram

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Habitability and Human Factors (HF&H) System Design Summary

  • System Requirement

    • Provide consumables for 60 days

    • Provide a minimum habitable volume of 60 m3 (15 m3/person)

    • Comply with MSIS/NASA-STD-3000

  • Assumptions Made

    • Maximum contingency duration of Gateway use is 60 days, with a 25-day crewed maximum nominal mission phase.

    • Gateway station provides an “oasis” in terms of living environment

  • Concept Trades Considered

    • Crew Quarters: Dorm Style v. Private Quarters

    • Waste Collection Facility: Plumbed v. self-contained facility v. bags only

    • Hygiene Facility: Partial-body cleansing v. Full-body cleansing

    • Medical Equipment: Med kit only v. nominal mission life support v. contingency scenario life support

    • Exercise Capability: No exercise v. limited resistive v. cardio only v. resistive and cardio training

    • Food System: Shuttle food system (pure-ambient) v. Conditioned food

    • Clothing: Clothing as consumable v. washer/dryer

    • Acoustics: Acoustic abatement throughout module v. Acoustic abatement at CQ and equipment room hatch only

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Habitability and Human Factors (HF&H) System Design Summary

  • System Specification

    • Mass: 2507.48 kg

    • Volume:

      • HF&H equipment: 15.04 m3

      • Habitable volume: 200 m3

    • TRL Level: 8

  • Issues and Concerns

    • Conditioned food: This is a nutritional need for the health of the crew, but is currently not considered feasible because of infrequent resupply missions to the Gateway/radiation issues

    • Windows: Additional viewing windows (for scientific observation and recreation) are preferable in the Gateway

    • Resupply: Logistics of resupply of crew-preference and crew-specific items (e.g. clothing, food, hygiene consumables) needs to be more well-defined with consideration for radiation exposure

  • Forward Work

    • Research possible HW mass losses between now (current Station hardware) and fly date

    • Double check depressurization compatibility of HW and supplies

    • Continue modifying detailed layout

    • Research exercise technologies

    • Research food technologies

    • Investigate lighting effects and simulated windows

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Habitability and Human Factors (HF&H) Cabin Layout




Exercise Facility









CQ = Crew Quarters

HF = Hygiene Facility

WCF = Waste Collection Facility

SMF = Space Medical Facility

HDTV = High Definition TV


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EPS System Design Summary

  • System Requirements

    • Provide 1kW (Peak) during ascent, orbit injection and deployment for Gateway survival and initial on-board operations.

    • Provide 2KW during LEO operations (90 min. orbit with 45 min. eclipse time) prior to rendezvous with SEP.

    • Provide continuous 12 KW while at LL1 with an energy storage capability to compensate during the 13 hr maximum eclipse time every 6 weeks for the entire Gateway life cycle of 15 years.

  • Assumptions Made:

    • Power generation and storage sized to include 30% contingency and 20% additional mass for secondary support structure.

    • It assumed that the overall EPS system is about 70% efficient (user power/power generated)

    • Arrays 1 fault tolerant, but rest of H/W 2 fault tolerant (ring bus architecture assumed).

      • High voltage DC to be provided by array and batteries and distributed within the Primary Distribution System.

      • Secondary Distribution System is 115 Vac, 3Ø, 400 Hz

      • Two Tertiary Distribution Systems included: 28 Vdc and 110Vac, 1Ø, 60Hz.

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EPS System Design Summary

Concept Trades Considered:

  • Ultraflex vs. Inflatable PV Array

  • Thin-film vs. Fiber Li-Ion Battery

  • 28 Vdc vs. 115 Vac, 3Ø, 400Hz

    Selected Technologies:

  • Ultraflex, Fiber Li-Ion integrated into structure, 115AC, 3Ø, 400Hz

    Rationale: Lower mass and design simplicity

    System Specification:

  • Physical dimensions: Mass: 1,335 kg Volume: 27 m3

  • Provide 12 kW nominal with 14.4 kW Peak to user

  • Arrays capable of 20.7 kWe

  • TRL

    • PV Arrays 7

    • Deployment Truss 6

    • Battery 2

    • Wiring Harness 9

    • PMAD 6

      Issues and Concerns

  • Development of 400 Hz RPC Box

  • Development of Fiber Li-Ion Battery System

    Forward Work

  • Full assessment of the Fiber Li-Ion battery capability and integration into vehicle structure.

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EPS System Architecture

Charge / Discharge Unit #1

Fiber Li-Ion Fabric Section

Charge / Discharge Unit #1

Representation of a Single String of the “Inner Loop” Power Distribution System

Fiber Li-Ion Fabric Section

UltraFlex Array Unit #1

UltraFlex Array Unit #2

Bus B

Bus C

Bus A


155 Vdc








115 Vac, 3Ø, 400 Hz



Secondary Distribution System





Fiber Li-Ion Fabric Section

Fiber Li-Ion Fabric Section

Charge / Discharge Unit #2

Charge / Discharge Unit #3

Power Bus #3

Power Bus #2

Tertiary Distribution System

Power Bus #1

Charge / Discharge Unit #2

Charge / Discharge Unit #3

110 Vac, 1Ø, 400 to 60 Hz Frequency Converter

115 Vac, 3Ø,

400 Hz to 28 Vdc Converter

EPS System Block Diagram

Primary Distribution System

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Propulsion System Design Summary

  • System Requirement:

    • Provide Gateway vehicle with approx. 50 m/s delta V per year for station keeping

  • Assumptions Made:

    • Propellant resupplied once every two years

    • Vehicle lifetime 15 years

    • Propulsion system for station keeping only, no ACS

    • Book-keep ECLSS and EVA O2 (491 kg)

  • Concept Trades Considered:

    • Propellant selection -Tridyne, Hydrazine, NTO/MMH, LOx/CH4

    • System size vs. regularity of resupply

  • Concept(s) Selected:

    • 12 x 110 N LOx/CH4 engines Rationale: Mass/volume savings, non corrosive exhaust products

  • System Specification:

    • Mass: 176 (dry) kg. 1,444 (total) kg.

    • Dimensions/Volume: Approx. 1.23 m3 tank

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Propulsion Preliminary Design Summary

  • Issues and Concerns:

    • Thruster placement due to the nature of the inflatable structure design and plume impingement on solar arrays

  • TRL:

    • Engines 4

    • Cryocoolers 4

  • Forward Work:

    • None

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Propulsion Preliminary Design Summary

Integrated LO2/LCH4 Gateway Propulsion Schematic

110 N

RCS Engines

322 s Isp

3.8 MR


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Robotics System Design Summary

  • System Requirement

    • Support EVA activities and maintenance, inspection and mobility of both intra- and extra- vehicular systems

  • Assumptions Made

    • Large arm needed for gross payload manipulation

    • Dexterous robot needed for human-equivalent manipulation

    • Will use automated “smart systems” where appropriate

  • Concept Trades Considered

    • No tasks or requirements were identified that required a trade study

  • System Specification

    • Robotic Manipulator System

      • Mass: 543 kg

      • Dimensions/Volume: Arm- 15.2 m x Æ.33 m

      • RWS Stowed- ISPR 1.01 m x 1.07 m x 1.98 m

      • TRL Level: Arm- 9

      • RWS- 8

    • Robonaut

      • Mass: 136 kg

      • Dimensions/Volume: .71 m³

      • TRL Level: 5

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Robotics System Design Summary

  • Issues and Concerns

    • Current work reflects generic robotic requirements defined as:

      • Gross payload manipulation

      • Human-equivalent manipulation

  • Forward Work

    • Continue development of Robonaut to increase autonomy and functionality

    • Define and identify the robotic requirements associated with telescope construction

    • Size RMS based on telescope construction requirements

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Robotics System Design Summary

Available Solutions

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Structures System Design Summary

  • Structural Requirements

    • Interface to Delta IV Heavy

    • Support crew of 4 for 25 days

    • Provide docking mechanisms for CTV and Lunar Lander

    • Provide worksites for constructing/assembling telescope

    • Provide structure to mount other systems within primary structure

  • Assumptions Made

    • 6 g axial and 2.5 g radial launch loads

    • 9 psi nominal internal pressure

  • Concept Trades Considered

    • Hardshell vs. Inflatable vs. Hybrid Gateway Structure

      • Hybrid structure encouraged by architecture team for future applicability to future exploration missions

  • System Specification

    • Gateway total Mass: 7354 kg

    • Overall length: 9.3 m

    • Hard shell Dia.: 4 m

    • Inflatable Dia: 9 m

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Structures System Design Summary

  • Issues and Concerns

    • Radiation protection not incorporated into design due to unavailable design support from SF2

    • Material properties for the mission at L1 are assumed to be acceptable at EOL for the mission duration.

    • Procedure for replacing MM/OD shielding on inflatable not identified

  • Forward Work

    • Incorporating radiation protection

    • More detailed design and analysis of primary structure

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TCS System Design Summary

  • System Requirement

    • Collect, Transport, and Reject 15.6 kW to space

    • Provide heaters to maintain low temperature limits of the Gateway shell

  • Assumptions Made

    • Radiators are freeze tolerant

    • All radiator panels see deep space environment

    • Air distribution over the internal inflatable wall prevents condensation (no heaters on fabric)

  • Concept Trades Considered

    • Single Loop vs. Dual Loops

    • TCS working fluid types

    • Flow Through Radiators vs. Heat Pipe Radiators

    • Number of Radiator panels

  • Concepts Selected

    • Single loop Rationale: Less hardware, no toxic fluid needed

    • 60% propylene glycol/40 % water Rationale: Freeze tolerance, safer working fluid

    • Flow through radiators Rationale: Lower mass

    • Three radiator panels Rationale: Redundancy

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TCS System Design Summary

  • System Specification

    • 663 kg Total Mass

      • 115.4 kg Fluid mass, 547.6 kg Dry mass

    • 3.39 m3 Total Volume

      • 0.84 m3 ETCS & Radiators, 2.56 m3 Multi-layer Insulation

    • TRL levels

      • Flow through, flexible, freeze tolerant radiators: 4-5

      • All other TCS components: 9

  • Issues and Concerns

    • Working fluid concerns regarding freeze tolerance

    • Will single loop architecture function in the environment

    • Inflatable inner wall air flow

    • Exposure of equipment in inflatable section to space vacuum

    • Equipment operation at 9.0 psia operating pressure

  • Forward Work

    • More detailed analysis to characterize the thermal environment

    • Evaluate test data for flexible radiators and heat pipes

    • Investigate attachment methods for flexible radiator to inflatable shell

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Gateway Thermal Control System Schematic



Radiator bypass







TCS System Block Diagram

Redundant Pumps

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Mission Operations Assessment

  • Gateway checkout in LEO

    • Critical Gateway systems to be checked out prior to Shuttle outfitting mission

      • Pressure vessel integrity

      • Life support system

      • Electrical power system

      • GNC/attitude control system

      • Data processing

      • Communication system

      • Thermal control system

    • Remaining systems will be checked out during Shuttle outfitting mission and prior to transfer to Lunar L1

      • Robotics

      • Waste collection system

      • HF&H

      • Inflatable airlocks

  • LEO Outfitting Mission

    • Pressurized cargo carriers considered:

      • MPLM, SpaceHab module

    • Recommendation

      • Modify double SpaceHab with IBDM

        • Zero Shuttle modification required

      • Launch Gateway SRMS on sill longeron and relocated using SRMS

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Mission Operations Assessment

  • Gateway Resupply strategy

    • Immediate resupply

      • CTV to carry immediate crew resupply items

        • Limited volume and mass items

      • CTV to leave contingency food on Gateway

      • CTV to swap out shelf life sensitive items that are common on CTV and Gateway

        • Medical supplies, food, etc.

    • Short term resupply

      • Once every six months

      • Use Lunar Lander habitable volume for stowing resupply items

      • Resupply items include: Food, clothing, medical supplies (items that are less time and radiation sensitive), misc. crew supplies, etc.

    • Long term resupply

      • Once every two years

      • Require a module capable of carrying pressurized and unpressurized cargo

        • Identified as a new element to the Gateway architecture.

      • Resupply items include: Station keeping propellant, ECLSS system consumables, large ORUs and tools, experiments, etc.

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Safety and Mission Assurance Strategies for HumanExploration – Gateway II PHA Summary

  • Open Work from Hazard Analysis

    • An analysis of the radiation protection of the vehicle's final configuration should be done. This will affect the hazard controls for two conditions identified concerning excessive radiation in the crew habitable environment.

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  • System Reliability & Sparing

    • Reliability Block Diagram Analysis predicted a Gateway reliability with no repair of approximately 72%. This reliability is associated with mission success modeling of all the supporting subsystems which includes EVA suits for telescope construction.

    • Sparing requirements for one re-supply cycle (10,225 hours) of the Gateway will be significant given the reliabilities of the modeled subsystems.

  • Crew Safety

    • The PHA has documented the subsystem design mitigations controlling the hazards identified.

    • All subsystems will meet fail-op/fail-safe requirements as specified in the Human Ratings Requirements with the option of the LTV ticket back to LEO. This however only applies to crew safety and not mission success.

    • Open Work: Analysis to evaluate the inherent radiation protection of the Gateway design

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Gateway Mass Summary

Mass Limit: 35,400 kg (Delta IV Heavy Capability)

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All masses and volumes are entered in metric units

Cost estimates are shown in 2001 dollars

Cost includes hardware development and manufacturing

Assume three prototype for each system 2 prototype / flight unit

Year of technology (YRTECH)value is 2005

Development start date(DSTART)=1/02

Completion date of first prototype (DFPRO)=4/07

Completion date of last proto/flight unit (DLPRO)=4/09

Twenty percent program reserve added to PRICE-H cost figures

Does not include recurring or operations costs

Gateway Cost Summary


$ 979.1 M


$ 453.8 M


$ 31.3


$ 50.8


$ 5.1


$ 59.1 M


$ 87.9 M

To Be Updated


Integration &

Test $ 59.2 M

Thermal Control

$ 62.2 M

Human Factors

& Habitability

$ 0.45 M


$ 130.2 M


$ 104 M

PRICE –H Cost Analysis Assumptions

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Future Technology Investments

  • ACS

    • Flywheel technology


    • Vapor Phase Catalytic Ammonia Removal (VPCAR)

    • Lyophilization Water Recovery

  • EVA

    • Inflatable Airlock

    • Next Generation Space Suit

  • EPS

    • Fiber Li-Ion Batteries

  • Propulsion

    • Cryo Cooler

  • Structures

    • Radiation Protection Materials and Methods

    • MMOD Protection Materials and Methods

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Open Issues / Forward Work

  • No radiation protection analysis

  • Unknown long-duration material degradation in Lunar L1 environment

  • Unknown effects of multiple spirals through Van Allen radiation belts

  • Need a detailed orbit propagation to determine exact station-keeping requirements

  • Resupply vehicle design unknown

  • Gateway trash disposal

  • Need better definition of telescope mission requirements to complete design of Gateway systems

  • Examine rigid structure design for comparison to current inflatable concept

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Lunar L1 Gateway Mission ArchitectureSolar Electric Propulsion (SEP) Stage Preliminary Configuration Summary of Oct. 12, 2001 Presentation

NASA Glenn

Tim Sarver-Verhey

Tom Kerslake

Len Dudzinski

Leon Gefert

Janice Romanin

Robert Sefcik

Dave Hoffman

October 25, 2001

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Gateway Solar Electric Propulsion (SEP) Stage

  • System Requirements

  • Launch on a Delta IV Heavy or Shuttle to 400 km 28.5° LEO[1]

    • “Exploration Class” Delta IV Heavy presumed - 35 MT to LEO

  • 30 MT payloads [2]

    • Lander & Habitat mass

  • 35 MT Total SEP Stage Mass Limit

    • Derived from requirements #1

  • Maximum 6-month LEO-to-Lunar L1 trip time [2]

    • A 30 MT Lander must be delivered to Lunar L1 every 6 months

  • TRL 6 by 2005 for all systems technologies[1]

  • Assumptions Made

  • Structural & electrical interfaces with SEP stage payloads

    • 5 kW power transfer from SEP stage to Gateway Habitat payload

    • 12 m maximum Gateway Habitat payload diameter x 10 m length

  • SEP stage housekeeping power 1% of total power required

  • 20% SEP stage dry mass margin


    [1]“Lunar L1 Gateway Introduction Package”, J. Geffre, 7/9/01

    [2]“Lunar L1 Architecture Timeline”, email from J. Geffre, 7/27/01

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Gateway Solar Electric Propulsion (SEP) Stage

  • Primary Issues/Trades Considered

  • What is the power required vs. trip time?

    • To deliver 30 MT to L1 in 180 days, a 584 kW SEP stage with 15.0 MT dry mass and 20.0 MT of xenon propellant is required - assuming 2,700 s (Isp).

  • What is the cost?

    • ~$1B Total SEP Stage Cost ($521.5M DDT&E + $435.1M Flight Unit) (FY01 $).

  • Should the SEP stage remain attached to the Gateway Habitat?

    • No – better to re-use the stage since its excess power is not needed & its large deployed array area would impact Gateway Habitat field-of-view and work areas.

  • How many times can/should an SEP stage be reused?

    • At least 2 roundtrip transfers per SEP stage are feasible by oversizing the solar arrays and assuming LEO replacement of the electric thruster and xenon and A/C system fuels pallets is possible.

  • Should solar array pointing be solar inertial or articulating?

    • Inertial solar arrays have significant vehicle operations & mass advantages: reduces array area & mass, reduces structural dynamic impacts associated with articulation, allows constant power Hall Thruster operation, thruster boom provides isolation needed to mitigate thruster plume impingement.

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Gateway Solar Electric Propulsion (SEP) Stage

System Specification

Initial conceptual design sizing highlights…subject to further revision!


  • 180-day trip time, 400 km 28.5° LEO to Lunar L1

  • 46-day return, Lunar L1 to 400 km 28.5° LEO

  • 584 kW SEP Stage Power (supports 2 round trips)

  • 7,300 m2 High-Voltage Thin-Film Solar Array (2 wings)

  • 12 Direct-Drive Hall Effect 50 kW Engines (incl. 1 spare)

    Mass Characteristics

  • 15.0 MT SEP Stage Dry Mass (incl. 20% margin)

  • 20.0 MT Xenon propellant

  • 30.0 MT Payload

  • 65.0 MT Vehicle Initial Mass LEO

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Gateway Solar Electric Propulsion (SEP) Stage

Issues & Concerns/Forward Work

  • Attitude control subsystem refinement

    • Impacts of thruster boom movements

    • Impacts of large deployed area in LEO

    • Momentum wheel & ACS thruster & propellant sizing

    • Rendezvous & docking with payloads

  • Other subsystem sizing/refinement

    • GN&C

    • C&DH

  • LEO refurbishment

    • Remote/robotics or crew-tended?

    • Thruster pallet replacement

    • Xenon tank pallet replacement

    • ACS propellant replacement/refill

  • Large area array packaging & deployment

    • Dynamic analysis

    • Stiffness requirements

  • Type of thruster boom

    • Deployable (SRTM) vs. rigid (ISS) or combination

    • Stowage & deployment of fluid & power lines

    • Dynamic analysis

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SEP “Main Body”

Xenon Tank Pallet

Deployable Boom

Solar Arrays not shown (see below)

Thruster Pallet with Hall Effect Engines

Radiator (x4)

Gateway Solar Electric Propulsion (SEP) Stage

  • Thrusters (TRL 3/4):12 Direct Drive 50 kW Hall Effect Thrusters (HET)

    • Xenon, 2500 - 2700 s Isp, 2.6 N thrust per engine

    • ~8500 hrs life

    • 11 HETs required + 1 spare

    • HET mounted on replaceable 4m diam. thruster pallet

  • Deployable Thruster Boom (TRL 7):

    • 35m articulated boom for thrust vectoring (18.5 m deployable boom + 8m inner & outer rigid booms)

  • Replaceable Xenon Tank Pallet (TRL 7)

    • 4m diam x 4m cylinder (3 internal tanks)

  • Photovoltaic Arrays (TRL 3/4): Two 3,750m2 AEC-Able SquareRigger style wings

    • Thin-film cells (12% AM0 eff., 2006 target)

  • SEP main body (4.5m diam x 1.5m) contains:

    • Array mechanisms

    • Energy storage (Li-ion) & power processing

    • Attitude & reaction control systems

    • GN&C and C&DH systems

    • Docking interfaces

Rigid Booms (at both ends of deployable boom)

Gateway Habitat Payload

Xenon Pallet

SEP Main Body

Thruster Boom

HET Pallet