ORBITAL FLUID SERVICING AND RESUPPLY OPERATIONS* 

R. N. Eberhardt** and W. J. Bailey' 

Martin Marietta Denver Aerospace 

Denver, Colorado 

ABSTRACT 

The capability to reservice spacecraft and 

satellites with expendable fluids will provide 

significant increases in the usability, 

operational efficiency and cost-effectiveness of 

in-space systems. Initial resupply will be 

accomplished from the Orbiter cargo bay starting 

with monopropellant servicing which will 

eventually be extended to servicing of 

bipropellants and pressurants. Other fluids, 

such as freon, ammonia, methanol, superfluid 

helium and liquid/gaseous nitrogen may also need 

to be resupplied once a space station becomes a 

reality. These fluiddgases are required for 

subsystem working fluid replacement and 

payload/experiment fluid replenishment. A 

logistics module operating on a 90-day 
I .v serGicing. Resupplying hundreds of thousands of 

pounds of cryogenic propellants and reactants 

(e.g., liquid hydrogen, liquid oxygen, liquid 

nitrogen trifluoride) for users such as the 

Orbital Transfer Vehicle (OTV) and DoD also 

represents future logistics challenges, 

Implementation of on-orbit fluid transfer 

requires solving many problems including fluid 

management in the low-g environment, 

*Data and information presented in this 

paper was obtained from work performed 

under Martin Marietta contract NAS9-17585, 

Orbital Spacecraft Consumables Resupply 

System (OSCRS) study, with the NASAJohnson Space Center, and from work 

performed under Martin Marietta IRAD 

Tasks D-72s and D-46s. 

**Manager, Fluid Systems (OSCRS), Member AIAA 

OSCRS Fluid System Lead Engineer, Member AIAA + 
system docking and interface mating, 

configuration of "user friendly" avionics to 

monitor and control the entire servicing 

operation, and minimized maintenance and 

enhanced reliability. Candidate fluid transfer 

methods and possible gas transfer methods are 

discussed, and preliminary storable 

monopropellant and bipropellant tanker designs 

are summarized. 

I. INTRODUCTION 

The life of many spacecraft can be 

significantly extended if they are resupplied on 

orbit with propellants and pressurant gases, and . 

the life of many scientific payloads increased 

if their consumable working fluids are 

replenished. The capability to reservice 

spacecraft and satellites with expendable fluids 

will provide significant increases in the 

usability, operational efficiency and 

cost-effectiveness of in-space systems. Initial 

resupply will take place from the Shuttle 

Orbiter cargo bay starting with monopropellant 

servicing and proceeding to bipropellants and 

pressurant gases. A recent phase B study, 
"> . ' 

4 VIUICCIA. U~UCCCIUL~ UUII~LUAIUUAC.~ L\ebUyyAy 3CUUJ 

(OSCRS), was completed addressing preliminary 

designs for storable tankers for these 

propellants and gases (Ref. 1 and 2). This 

first generation of servicing will utilize 

astronaut control from the Aft Flight Deck (AFD) 

and EVA for umbilical mate/demate. 

Future propellant transfer will involve 

cryogenic propellants, and superfluid helium for 

scientific payloads. The trend will be to 

automatic, remotely operated servicer systems 

which can be used in conjunction with the OW 

and space station to extend satellite life in 

orbit beyond the current range of the Orbiter. 

Resupplying superfluid helium to space 

observatories such as the Space Infrared 

Telescope Facility (SIRTF) offers significant 

cost savings by extending the orbital life 

without the need to return to the ground to 

replenish the liquid helium. The use of the OMV 

operating out of the space station to retrieve 

the SIRTR and bring it to the station for 

resupplying the helium is currently being 
4 

... 

investigated as a means of economically 

achieving a ten-year on-orbit operational life 

goal (Ref. 3). The technology for superfluid 

helium on-orbit fluid management is not as 

mature as for the storable propellant and is 

currently the focus of studies being carried on 

at both NASA-Ames and NASA-GSFC (Ref. 4 and 5). 

The resupply of cryogenic fluids such as 

liquid hydrogen, liquid oxygen and liquid 

nitrogen have applications to space-based 

Orbital Transfer Vehicles (OTV), space station 

life support and laboratory facilities, 

scientific and applications satellites and 

space-based military systems. The technology 

base for orbital fluid management of these 

fluids, including resupply approaches and 

techniques is not as mature as for the storables 

or superfluid helium (Ref. 6). A cryogenic 

fluid management test facility has been in the 

planning stages for the past 10 years. It is a 

shuttle-based test bed configured to obtain the 

desired technology data base to permit the 

design of efficient cryogenic storage and 

resupply systems (Ref. 7). Orbital test data of 

the type to be obtained with this facility is 
Three elements are involved in orbital fluid 

resupply of any of the fluids mentioned above. 

These are the resupply tanker, a space depot and 

the user system to be resupplied. Shuttle-based 

tanker designs are strongly influenced by 

maximum diameter in the cargo bay and minimum 

length since these are parameters in the 

transportation costing algorithm. The high 

transportation costs likewise drive the tanker 

designs to derived requirements for redundancy 

and fail-safe/fail-operational features for all 

mechanisms. Logistics issues associated with 

the tanker include centralization of storage, 

maintenance, checkout and integration facilities 

to support ground operations and the degree of 

space-basing elements to provide quick-reaction 

capability for spacecraft servicing. 

Logistics issues associated with the depot 

include the relative degree of extra vehicular 

activity (EVA) versus automated or 

intravehicular activity (IVA), which is a major 

driver in design complexities as well as 
.. 

timelines for mating and demating between the 

depot and user being serviced. Logistics 

considerations involving ancilliary facilities 

at the depot such as thermal enclosures become 

particularly important when considering the 

cryogenic fluids. Timelines for servicing 

cryogenics are sensitive to the thermal 

environment in a servicing bay; low emissivity 

interior surfaces are required to minimize 

chilldown losses and boil-off associated with 

the resupply sequence. 

The diversity of the on-orbit consumables 

resupply task outlined above in terms of types 

of fluids, current status of technology, degree 

of autonomy, and ground vs space-basing of 

elements manifests itself in a wide range of 

logistics options which strongly influence the 

degree of cost advantage available from on-orbit 

fluid servicing. 

will thus try to outline for the decision makers 

and designers more definitive data regarding 

requirements and technology readiness, operation 

concepts and options and a summary of how these 

translate into specific preliminary designs for 

storable monopropellant and bipropellant tankers. 

The remainder of this paper 
. . ... 11. REQUIREMENTS AND TECHNOLOGY READINESS 

Current and future space programs will 

require resupply of depleted fluids for a number 

of different subsystem applications, including 

propellants, power reactants, coolants, life 

support, and experiment or process consumables. 

Many of these applications will make use of 

fluid storage systems in space and will require 

orbital transfer for resupply of spent systems. 

Initial loading of these systems in space may 

also be required. 

User Requirements 

The potential for on-orbit resupply is 

extensive and is summarized by representative 

categories in Table 11-1. The most likely early 

applications will be the resupply of satellites 

from the Orbiter cargo bay. Satellites in 

higher orbits can be reached by using an 

automatic refueling/fluid resupply system 

attached to an OW, or spacecraft on-board 

propulsion can be used to lower the spacecraft 
Table 11-1 Candidate Spacecraft for Fluid Resupply 

__ ~~ 

FLUID RESUPPLY PRESSURANT I I 

I\ v I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

Gamma Ray 

Observatory 

Space Station 

Spartan Platform 

Multi-Mission 

Modular S/C 

Mark I1 Propulsion 

Geopotential 

Research Mission 

Cosmic Ray 

Experiment 

Eureca 

2500 lb N2H4 

(1136 kg) 

800 lb N2H4 

(364 kg) 

2000 lb N2H4 

(909 kg) 

5000 lb N2H4 

(2273 kg) 

3000 lb N2H4 

(1364 kg) 

550 lb N2H4 

(250 kg) 

1700 lb N2H4 

(773 kg) 

2 YR 

1-3 MO 

1-2 YR 

2-4 YR 40 lb GN2 

(18 kg) 

6 MO 

2 YR 

9 MO 

I 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 
*I 

I X-Ray Timing 

I Explorer 

I 

I 

I 

I 

I 

I 

I 

I 

I Mobile SAT-B 

I GEO Platform 

I Mobile SAT-C 

Approx. 

500 lb N2H4 

(227 kg) 

3 YR 

1100 lb N2H4 Resupply Approx. 10 lb GN2 

(500 kg) at SS for (4.5 kg) 

GEO 

2100 lb N2H4 2 YR 

(995 kg) 

2200 lb N2H4 2 YR 

(1000 kg) 

~~ 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 I 
Table 11-1 Candidate Spacecraft for Fluid Resupply (continued) 

I FLUID RESUPPLY PRESSURANT I 

I IrnITY INTER VAL I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

DoD 1 

DoD 2 

EOS Platforms 

Platform System 

Techno logy 

7000 lb MMH & NTO 

(3182 kg) 

6000 lb MMH & NTO 

(2727 kg) 

5000 lb MMH & NTO 

(2273 kg) 

2-3 YR 

3-5 YR 

2 YR 

3 MO 

SI RTF 

AXAF 

1100 lb LHe 

(500 kg) 

130 lb LHe 

(59 kg) 

LDR 1900 lb LHe 

2 YR 

1.6 YR 

2 YR 
I 

I 

I GP-B 

LOU* W5J 

440 lb LHe 2 YR 

I Dark Sky 550 LHe 3 YR 

I 

I Material Technology 500 lb (227 kg) LN2 

I Laboratory 700 lb (318 kg) LO2 

I 

I 

I 

180 lb (82 kg) H20 

238 lb (108 kg) LAr 

45 lb (20 kg) LH2 

I 

I Orbital Transfer 28000 lb (12727 kg) LH2 

I Vehicle 168000 lb (76364 kg) LO2 _. 

.. 

.. 

... 

.. 
to orbits accessible by the shuttle. The advent 

of space station and platforms in polar orbit 

will significantly improve resupply operations 

and provide substantial economic benefits by 

enhancing spacecraft maneuverability/ 

survivability, and improving mission performance 

capability. Additional specifics concerning 

storable consumable resupply requirements can be 

found in Ref. 2. 

Interface Requirements 

Three interface areas which drive the design 

of tanker subsystems include carrier, ground, 

and crew interface requirements. Basic tanker 

designs will initially be compatible with 

Orbiter interface provisions. An orderly 

transition to interface with other carriers is 

envisioned; however, this definition of 

requirements (for OW, Space Station, OTV) has 

not been finalized and presently can be assessed 

in only generic terms. Possible tanker 

compatibility with expendable launch vehicles is 

an area of interest which will be addressed in 

the future. Most likely these interfaces will 

be very similar to the Orbiter's; typical 
.. 

AIALLALOLtlb dLT. 3uIlYAlULAL.T.U 111 AUUIL IL-6 LUL 

different carrier applications for an Orbital 

Spacecraft Consumables Resupply System (OSCRS). 

On-orbit operation of an OSCRS-type tanker 

to accomplish a spacecraft resupply mission 

includes interfaces with the crew for both 

EVA-operated mechanical and electrical umbilical 

connections and release, as well as tanker 

control and monitoring from a control station 

located on the Aft Flight Deck (AFD). 

machine/human factors requirements of the AFD 

control station were derived from preliminary 

operational scenario analysis which resulted in 

the following: 

The man 

a) Provide a control station concept for the 

AFD which minimizes OSCRS impact on other 

payloads. 

b) Optimize the man-machine interface for data 

display to the crew and OSCRS commanding. 

.. .. .. 
:I.. 

, -. 

.. .... 

.. 

I-.. 

.. :. 

i' 

c) Meet all redundancy/safety related 

requirements. 

d) Provide manual safing and securing options 

for the OSCRS. 

e) Include any optional interface with the 

Orbiter GPC. 

Requirements for resupply tanker ground 

processing indicate the need for a completely 

flexible concept for ground checkout, servicing, 

launch support and mission turnaround, including 

refurbishment operations. The tanker requires a 

wide variety of ground support equipment (GSE) 

to accomplish these operations as well as 

transportation, handling, and processing GSE to 

provide the necessary capability to integrate 

the tanker into the Orbiter. The desire not to 

impact Orbiter processing by tanker's use of 

existing Orbiter facilities or Orbiter GSE is an 

important part of the development of the ground 

processing approach. General ground processing 

capabilities and facility requirements are 

listed in Table 11-3. .. 
a) Receiving inspection and checkout area to 

perform off-line verifications and testing. 

b) Bonded storage area for tanker equipment and 

spares. 

c) Pressurant servicing of gaseous helium and 

gaseous nitrogen up to storage pressure of 

5000 psig (34,475 kPa). 

d) Servicing of N H , MMH, and N 0 , 24 24 

cryogens and other resupply fluids. 

e) Tanker/Orbiter interface simulation and 

integrated interface testing. 

f) Interfacility tanker handling. 

g) Intrafacility tanker transportation and 

processing. 

h) Standard Orbiter installation/removal. 
.. 

.. 

Table 11-3 Ground Processing Requirements 

(cont . ) 

i) Contingency fluid and pressurant deservicing 

during launch preparation and post-mission. 

j) Contingency fluid decontamination during 

launch processing. 

k) Areas for tanker associated EGSE to support 

ground processing, launch operations and 

mission turnaround activities. 

.. 

1) Ordnance storage, handling and installation. 

m) Other standard payload processing needs as 

identified in the Launch Site Accommodations 

Handbook for STS Payload (K-STSM-14.1), and 

agreed to in the Payload Integration Plan 

(PIP) and Annex 8, Launch Site Support Plan. 

n) Emergency pressurant/propellant/fluid 

deservicing. 

0) Turnaround area for off-line 

reconfiguration, component changeout, and 
p) Provisions for software reconfiguration and 

retest for the next mission. 

Svstem Requirements 

.. 

.. 

The key system requirements that drive the 

design of on-orbit resupply servicers, and the 

rationale for their selection, are shown in 

Table 11-4. Many impact the overall servicer 

configuration while others affect only specific 

subsystems. It is important to note, however, 

that they collectively reflect the complexities 

associated with different designs regardless of 

the fluid being resupplied. On-orbit resupply 

covers a broad range of servicing scenarios, 

first from within the Orbiter cargo bay and 

eventually from and around the Space Station, 

which involves the use of orbital maneuvering 

and orbital transfer vehicles. Propellants 

(N2H4, MMH, and N204) will be the first 

fluids to be resupplied, followed by pressurants 

(GN2 and GHe) and other fluids (H20, etc.). 

Liquid helium (LHe) will most likely be the 

first cryogen to be resupplied followed by 

LN2, LH2, LO2, LAr and LCH4. 
.. 

Table 11-4 Requirements That Drive Resupply Tanker Design And Rationale 

Requirements Rat iona 1 e 

I 

I Monopropellant tanker sized for 3000 lb. 

I Bipropellant OSCRS sized for 7000 lb (3182 kg) 

I which is typical of larger bipropellant spaceI craft. Other fluid capacity sizing is yet to be 

I determined. 

I 

I Permit interconnection of two separate tankers 

I (or a tanker supplemental fluid module) 

I 

I 

I 

I Standard orbiter interface provisions 

I 

I 

I 

I 

I Operational after one failure 

I 

I 

I Safe after two failures 

I 

I Design for useful life of 80 flights 

I 

I Optimize mass fraction 

I 

I 

I I 

I I 

I I 

I Convenience in servicing I 

1 satellites that require 1 

1 more fluid than the I 

I nominal tanker capability1 

I 

I Minimum cost and risk; 

I operational flexibility 

I 

I Optimize life and 

I minimize cost 

I 

I Mission success 

I probability 

I 

I 

I Acceptable safety 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 
... ill .. 

I I'ldllUUA LUIUI~CLAUIL 1111LAUAAy WILL1 CaydUAALLy LV 

I evolve to automatic 

I 

I 

I EVA friendly 

I Capable of relocation in the cargo bay during 

I orbital operations 

I 

I 

I 

I Capable of removal from the cargo bay without 

I draining or venting 

I 

I Provide for emergency separation of satellite 

I from Orbiter without EVA. 

I 

~~ 

1 L1IIILIIIUII1 LUbL UllU 

I development risk 

I 

I 

I Minimize EVA problems 

I Maximum location 

I flexibility for launch, 

I on-orbit and landing 

I operations 

I 

I Flexibility in ground 

I operations 

I 

I Safety 

I 

I 

I Modifiable for attachment to OW, Space Station, 

I or orbiting platforms 

1 Maximize commonality, 

I minimize overall costs 

I I 

I Provide thermal control independent of Orbiter 

I attitude 

I Minimize operational 

I constraints on Orbiter 

I I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I Provide capability of venting fluids and/or gas I Flexibility in servicing I 

I from tanker and satellite I different types of I 

I I satellite propulsion I 

I I systems I 

.. 
.. 

.. 

Table 11-4 Requirements That Drive Resupply Tanker Design And Rationale (cont) 

Requirements Rat ionale 

I .I I 

I I different types of I 

I I satellites I 

I I I 

I Modifiable to supply high-pressure gas I Flexibility in servicing I 

I Permit resupply to satellite with various I Capability to resupply I 

I propellant orientation/acquisition systems I all types of satellites 1 

I I storable fluid systems I 

I I I 

1 Provide capability for short lead-time hardware/ I Minimize ground I 

I software changes and minimize ground processing I turnaround time I 

I I I 

I Provide avionics growth capability to I Commonality; Minimize I 

I accommodate resupply systems for other fluids I cost of overall resupply I 

I 1 systems I 

.. 

. .. 
I. 

.. 

.. 

.. 

A summary of the major technology issues 

associated with on-orbit fluid management and 

fluid resupply for the range of future systems 

application is presented in Table 11-5. The 

applicability of the various types of 

servicer/tankers is indicated with the storable 

tanker having the greatest level of technology 

maturity at this time. Other major issues are 

also indicated such as long-term on-orbit 

operations, fluid conditioning and quantity 

gaging, which is just one specific example of a 

broader category called instrumentation/ 

diagnostics. Instrumentation diagnostics which 

are operable in zero gravity are key to the 

control and monitoring of orbital fluid 

systems. Special design considerations, such as 

control of fluid motion in the low-g 

environment, may be significant for systems 

requiring a stringent degree of pointing 

accuracy or minimized residual impulse imparted 

from the moving fluids. 

Table 11-6 Fluids Systems Technology 

Applicability 
.. 

111. DESIGN/OPERATIONAL CONCEPTS 

AND FEATURES 

The fluid transfer technique selected to 

resupply spacecraft tankage is highly dependent 

on the configuration of the tankage. Spacecraft 

propellant management for tankage generally can 

be classified into two different types - 

diaphragm and surface tension. Diaphragm-type 

tankage utilizes elastomeric membranes to 

separate the propellant from the pressurant 

(except for minimal migration/ 

permeation of both propellant and pressurant 

across the diaphragm). Such systems predominate 

in hydrazine tankage design. Tankage using 

surface tension propellant management devices 

(PMD), such as woven screens, perforated sheets 

and vanes, operates by preferentially 

positioning the propellant in the tank to meet 

specific user requirements. These systems are 

most common in bipropellant (and to a lesser 

extent in hydrazine) systems where tighter 

propellant management requirements prevail. 

Current bipropellant incompatibilities with 

elastomeric materials (especially N204) also 
drive these systems to surface tension-type 

concepts which co-mingle pressurant and 

propellant within the tank. Surface tension 

forces are then used to effectively dominate the 

gravitational and flow forces, and position 

vapor-free liquid for delivery to the tank 

outlet. Expulsion efficiencies greater than 99% 

can be achieved by such systems. 

Fluid Transfer Techniques 

Four candidate transfer methods have been 

defined for accomplishing resupply. These 

techniques are most applicable to specific 

spacecraft user tankage configurations and 

include : 

a) Adiabatic Ullage Compression - applicable 

exclusively to blowdown tankage systems 

utilizing either diaphragm or surface 

tension PMD's, and currently limited to 

use only on monopropellant systems. 
b) Ullage Exchange - applicable to pressureregulated surface tension tankage and 

currently limited to use only on 

bipropellant systems or non-diaphragm 

monopropellant tankage where a closed 

circulation loop can be established. 

.. . .. 

c) Vent/Fill/Repressurize - applicable to 

pressure-r egula t ed surf ace tens ion 

tankage with in-tank liquid/vapor 

separation. No spacecraft are currently 

designed to use this technique. Also, 

any type of diaphragm tankage can use 

this technique. 

d) Drain/Vent/Fill/Repressurize - applicable 

to surface tension tankage with simple or 

complex PMD's for either monopropellant 

or bipropellants. 

Detailed discussions of each of these 

approaches can be found in Ref. 1. 

... .... 

A summary of fluid transfer system 

applicability is presented in Table 111-1. 

Monopropellant and bipropellant systems are 
... 

.. 

addressed, including both blowdown and pressureregulated cases. Surface tension and diaphragm 

tankage options are included. The selection of 

the appropriate resupply method depends on the 

set of spacecraft design features. It is 

desirable for the servicer not to drive the 

design of the spacecraft to accomplish the 

resupply. 

Selected fluid transfer approaches using the 

adiabatic ullage compression method for 

monopropellant and the drain/vent/fill/ 

repressurize method for bipropellants are shown 

schematically in Figures 111-1 and 111-2, 

respectively. They represent optimized 

configurations for resupply of these propellants 

and are not constrained by the need to 

demonstrate open technology or unproven concepts. 

Figure 111-3 illustrates a simplified 

schematic of a cryogenic transfer/resupply 

system showing both the supply and user systems. 
Modular vs Dedicated Desipn 

.. 

Modular versus dedicated design approaches 

were examined for both monopropellant and 

bipropellant applications. In both cases, 

modular was found to be the most cost-effective 

approach considering the relatively significant 

cost for each pound to orbit. The study 

assessment for hydrazine illustrates the 

approaches used to select the preferred modular 

design. 

Since the basic derived requirement for 

propellant load was approximately 3000 lb (1364 

kg), the initial cost is minimized by minimizing 

the size (and number of tanks) that can meet the 

requirement; this results in the three tank 

configuration for monopropellant hydrazine. 

Minimum life cycle cost will be obtained by 

minimizing transportation cost which is achieved 

by using the system with the best mass 

fraction. Figure 111-1 shows the mass fraction 

for various configurations considered in the 

trade study as a function of propellant load. 

The best mass fraction for the basic design load 

of 2910 lb (1323 kg) is achieved by using a 
.. 

.. 

three tank configuration. As shown, this 

configuration can be designed (and qualified) to 

a series of configurations from two tanks to 

five tanks, with a maximum delivered capacity of 

4850 lb (2204 kg). 

The total recurring cost for 80 flights of a 

representative propellant load distribution is 

shown in Figure 111-2 for a 3000 lb (1364 kg) 

non-modular design, a 5000 lb (2250 kg) 

non-modular design, and a modular design. If a 

modular basic OSCRS is used over the propellant 

load range (i.e., 2, 3, 4 or 5 tanks are used 

for a given mission, as appropriate), the cost 

savings shown in Figure 111-2 indicate that the 

modular approach is better than either three 

tank or five tank non-modular (fixed) OSCRS 

supplying the 80 mission propellant load 

distribution by $20 M and $49 M, respectively. 

... 

. ... 

For scenarios requiring more propellant than 

the maximum capability of a single 

tanker/servicer, an approach to interconnect two 

servicers has been baselined and incorporated as 

a growth provision into the preliminary design. 

.!t:. :.I.. 

... 
High Pressure Gas ReSUpplV Techniques 

4i 

Pressurant resupply to a user system will 

evolve from low, to medium, to high pressure 

resupply for varying quantities of GHe and GN 

gas supplied in conjunction with monopropellant 

and bipropellant applications. The following 

three transfer methods have been baselined and 

represent an evolution of technology needs as 

delivered pressure level requirements to a user 

increase : 

2 

a) Pressurant delivered at 50 - 500 psia (345 - 

3450 kPa - Resupply in this pressure range 

will be accomplished by using variable 

set-point regulator control of pressurant 

stored in 1 to 3 storage bottles. Redundant 

control legs provide fail-operational 

capability. 

b) Pressurant delivered at 500 - 3000 psia 

i3450 - 20.700 kPa - Resupply in this 

pressure range will be accomplished by using 

variable set-point regulator control of 

pressurant stored in 3 to 6 isolatable 

storage bottles using a cascaded resupply 
... mode. One bottle at a time will be used in 

this approach. When spacecraft and bottle 

pressures equalize, the bottle will be 

closed and the next (higher pressure) bottle 

will be brought on line. 

continues until proper mass/pressure is 

delivered. 

The process 

c) Pressurant delivered at 3000 - 5000 psia 

120.700 - 34.500 kPa - This pressure range 

is accommodated by installing gas single 

stage compressors (with an outlet/inlet 

ratio of 3:l) into the regulated/cascaded 

system defined above. 

(up to 7 plumbed in parallel) is depleted 

individually and when the 3:l ratio of 

Each storage bottle 

outlet-to-inlet 'pressure is reached the next 

bottle is brought on line. 

For the above defined transfer methods the 

GN /GHe can be stored at pressure as high as 

4500 psia (31,050 kPa) in 4.7 ft (0.13 m ) 

pressurant bottles. Each bottle holds 13 lb (6 

kg) of GHe or 90 lb (41 kg) GNg. 

either be plumbed together without isolation or 

2 

3 3 

Bottles can 
:.: 

each bottle can be selected by a separate 

electrically operated valve. The pressurant 

requirements for each mission will be optimized 

so that the proper number of bottles will be 

included. Resupply of spacecraft pressurants 

will occur first, then residuals left in the 

bottles (which are significant when a cascaded 

mode is used) will be used to expel tanker 

propellants for user propellant reservice. 

The most significant factor controlling the 

pressurant resupply process is the dissipation 

of the heat of compression in spacecraft tanks 

in the low-g vacuum environment. As the maximum 

temperature in these tanks is approached the 

amount of pressurant being introduced will have 

to be decreased, resulting in an increased 

resupply timeline. These tanks will have to be 

close-coupled with other spacecraft elements 

(propellant tanks) so that heat can be 

dissipated. Insulated pressurant tanks (even 

partially insulated) will be almost impossible 

to resupply using the methods previously defined. 

IV. ~ 

Two categories of technology (shown in Table 
.. 

.. 

IV-1) have been identified for on orbit fluid 

resupply, technology enhancements and open 

technology issues. Technology enhancements can 

improve the performance and reduce risks, but 

are not prerequisites to accomplishing fluid 

transfer. The refueling of a hydrazine 

satellite with a diaphragm tank and a blowdown 

pressurization system does not require 

resolution of any open technology issues. 

However, the same is not true for fluid resupply 

of surface tension tankage where more complex 

fluid management issues come into play and 

include high pressure pressurant reservicing 

operations. 

addressed prior to design commitment of resupply 

systems having required fluid transfer 

f 1 exib i li ty . 

Open technology issues must be 
Table IV-1 Fluid Reservicing Technology Issues 

Technology Enhancement 

T echo logy 

o Hardware 

a) Variable set-point regulators and 

relief valves 

b) Monopropellant catalytic vent life 

with long burn times and high 

concentrations of non-condensible 

gases and pulsed operations 

o Processes 

a) Pressurant solubility effects during 

fill 

b) Contamination control during venting 

c) Adiabatic compression heating in 

surface tension tankage 

Open Technology Issue 

Techno lonv 
a) Automatic fluid coupling 

b) Resupply mechanism to make and brake 

the fluid coupling 

c) High pressure gas compressor is not 

state-of-the-art 

d) Tank quantity gaging system 

e) Oxidizer burner and fuel burner that 

can accept high concentrations of 

non-condensible gases, and pulsed 

operation. A burner that could handle 

both simultaneously or separately is 

desired 

o Processes 

a) Separation of gadvapor from liquid 

during venting (required for ullage 

exchange and vent/fill/repressurize 

transfer methods to be effective) 

b) Total filling of complex PMD's 

c) No-vent fill 
.. .. 

Recommendations 

o Hardware 

a) Design, build and test an electronics 

variable set-point regulator to 

minimize risk 

b) Test existing design over complete 

range of expected conditions 

o Processes 

a) Minimize the time the liquid is / 

exposed to high pressure. Run tests .. 

to understand process for contingency 

operations 

b) Study required to better quantify 

requirements 

c) Refine computer programs using ORS 

data and extrapolate to PMD tanks 

o Hardware 

a) & b) Design, build and test these 

devices together to minimize risk 
c) Design, build and test to assure 

reliable long life 

d) Continue JSC contract work 

e) Design, build and test over complete 

range of expected operating conditions 

o Processes 

a) Studies followed by drop tower and 

Storable Fluid Management 

Demonstration (SF'MD) testing 

b) & c) Conduct tests and analysis of 

storable fluid in ground tests 

and determine if zero-g tests are 

r equ i red 
, 

.. .. 

Total filling of complex Propellant 

Management Devices (PMDs) requires venting the 

tank after the liquid has been drained back to 

servicer catch tanks; this is followed by a 

no-vent fill. Evolution of dissolved gas and/or 

heating of vapor during the fill may prevent 

complete filling. Our present knowledge of 

adiabatic heating is adequate. However, we may 

be able to significantly shorten the fill time 

with a better understanding of the process. 

dissolved gas comes,out of solution during 

transfer it could slow down the transfer and 

interfere with complete filling. This can be 

minimized by reducing the time the tanks are 

pressurized. 

process would maximize the efficiency of the 

filling operation. 

of fluid reservicing technology issues can be 

found in Ref. 1 and 2. 

If 

A better understanding of the 

A more detailed discussion 

The resupply of cryogens on-orbit has many 

unresolved technology issues associated with 

thermal control and low-g fluid management. The 

Cryogenic Fluid Management Facility (CFMF) 

Program (Ref. 7) addresses these issues and 

provides an approach for investigating the 
d 

I. . E. .. .. 

behavior of LH in a low-g environment with 

the object of performing on-orbit experiments to 

resolve open cryogenic storage and transfer 

issues. The uniqueness of liquid helium places 

this cryogen in a class by itself. LHe resupply 

is being addressed by the Astronomic/ 

Astrophysics science communities which require 

on-orbit instruments/sensors which operate at 

LHe temperatures (Ref. 4 and 5). 

2 

.. .. 
V. SYSTEM DESIGNS 

Preliminary designs of both storable 

monopropellant and bipropellant resupply systems 

have recently been completed on the Orbital 

Spacecraft Consumables Resupply System (OSCRS) 

contract with NASA-JSC (Ref. 2). Provisions for 

resupplying relatively large quantities (on the 

order of 20 kg gaseous helium and 140 kg gaseous 

nitrogen) of high pressure (3000-5000 psig; 

20,700-34,500 kPa) gas were also incorporated 

into the propellant tanker designs. 

Monopropellant Design 

The basic monopropellant design is shown in 

Figure V-1. It consists of three TDRS-type 

hydrazine storage tanks with diaphragms, a 

bolted aluminum structure, a triple redundant 

avionics subsystem for data handling and 

control, and a multilayer insulation blanket in 

combination with tank heaters for thermal 

control. The configuration shown has a capacity 

of 2910 lb (1323 kg), with an estimated mass 

fraction of 0.60. Each tank can be loaded 97 

percent full, and operate at a maximum expected 
1 

operating pressure (MEOP) of 500 psia 

(3,450 kPa). Two additional tanks can be added 

to this basic structure to provide a total 

capacity of 4850 lb (2205 kg), resulting in a 

mass fraction of 0.66. 

.. 

In order to minimize tank changeout, two 

monopropellant OSCRS units are recommended; one 

containing three TDRS propellant tanks providing 

a maximum resupply capacity of 2910 lb (1323 kg) 

while the other is configured with two TDRS 

propellant tanks providing a maximum resupply 

capacity of 1940 lb (882 kg). An estimate of 

more than 75% of the resupply potential can be 

accommodated without reconfiguration of either 

of the units. A modular building block approach 

was adopted so that the servicer could be 

customized to meet user-specific needs for the 

remaining 25% of the reservicing missions. 

Features of the basic fluid system design 

and its associated designed-in growth options 

are shown in Figure V-2. Provisions are 
.. .. 

.. 

.. 

.. 

included for two added propellant tanks in an 

add-on propellant module, added pressurant tanks 

for propellant expulsion and an add-on module 

for pressurant resupply. The propellant tank 

are plumbed so that they can be depleted 

individually or in combinations up to all tanks 

simultaneously. Flowmeters are provided in the 

transfer line to determine propellant 

transfer red. 

A major design driver influencing the level 

of redundancy shown was the requirement to be 

fail-operational, and to meet all the redundancy 

requirements for safety with the 

fail-operational system after one failure has 

occurred. Dual fluid disconnects for both 

propellants and pressurants, dual catalytic 

vents and quad valve packages are all part of 

the fail-operational and safe design features. 

Special operational features, such as the 

separate vent line at the gas diSCOMeCt, for 

venting of the gas side of spacecraft 

diaphragm tankage, if required, are provided. 

Fluid resupply lines to the spacecraft user 

incorporate emergency disconnect provisions. 

The design also includes provisions through 
.. 

:. , 

appropriate fluid control orifices and variable 

driving pressure levels to minimize the 

potential for hydrazine decomposition and 

adiabatic detonation. 

The detonation of hydrazine vapor at 

elevated temperatures depends on the local 

temperature and the quantity of vapor present. 

This detonation process is strongly affected by 

the catalytic action of materials in contact 

with the fuel. NASA-JSC, through STS Payload 

Safety Review panel interpretations, has 

established acceptable criteria and certification approaches for adiabatic compression 

detonation (Ref. 8). Typically, if the vapor 

never exceeds 160°F, then detonation can be 

avoided by controlling the material 

compatibility requirements. If the temperature 

never exceeds 200"F, then qualification of 

materials to 200°F is necessary to verify that 

detonation will not occur. If the temperature 

does not exceed 250"F, then qualification 

testing can be used to verify that detonation 

does not occur. Temperatures above 250°F are 

not allowed. 
8 

Bipropellant DesiRn 

A bipropellant OSCRS tanker for resupplying 

monomethyl hydrazine (MMH) and nitrogen 

tetroxide ("TO) is shown in Figure V-3, with the 

major subsystems and subsystem elements 

identified. The same simple pressure-fed 

approach adopted for the monopropellant tanker 

to expel propellants into user tankage was also 

selected for the baseline bipropellant design. 

Six L-SAT type propellant tanks with screen-type 

propellant management devices, and six 

pressurant bottles, make up the basic fluids 

capability. The oxidizer and fuel tanks are 

identical. Two of the tanks (one each oxidizer 

and fuel) are used as receiver "catch" tanks. 

They are used to dump the residual propellant 

remaining in the receiver tanks so they can be 

vented with a minimum of liquid in the vented 

gas. This configuration provides 7540 lb 

(3428 kg) of usable bipropellants. Propellant 

storage tanks can be loaded to 98 percent full 

and have a maximum expected operating pressure 

(MEOP) of 150 psia (1035 kPa). This basic 

propellant configuration achieves a mass 

fraction of 0.70. 
.. 

The basic bipropellant OSCRS configuration 

can be reconfigured with only four L-SAT tanks 

to meet lower propellant requirements and 

increase the mass fraction. Also, the basic 

design may have all six tanks loaded with 

propellant if no catch tanks are required for 

resupply operations. The basic bipropellant 

structural configuration has been designed to 

allow for the increased propellant load, and all 

associated subsystem changes are incorporated to 

permit higher and lower propellant capacities. 

The full capacity six-loaded-tank option can 

provide a resupply quantity of 11,400 lb 

(5182 kg) with a mass fraction of 0.76. With 

tank changeout a bipropellant configuration with 

two loaded tanks achieves a mass fraction of 

0.55. 

Features of the basic bipropellant fluid 

subsystem design are shown schematically in 

Figure V-4. The bipropellant tanks are plumbed 

so that they can be depleted individually, in 

combinations up to all three at the same time or 
in a series arrangement. Dual fluid disconnects 

for all propellants and pressurants meet the 

fail-operational design requirement. Pressurant 

purge and overboard vent capability is provided 

for the propellant transfer line. All potential 

propellant-contaminated vent products exhaust 

through a bipropellant burner system (which is 

redundant) to reduce propellant to less 

hazardous and objectionable combustion 

products. Fluid resupply lines to the 

spacecraft user incorporate emergency disconnect 

provisions to allow quick jettison of the 

spacecraft should Orbiter operations require 

immediate cargo bay door closure and STS 

return. The disconnect provisions also provide 

a means of separating the spacecraft to permit 

cargo bay door closure should the servicing 

disconnect hang-up in the disconnect operation 

following servicing. 

The bipropellant OSCRS can accommodate 

future growth, particularly with regard to the 

supply of high pressure pressurant gases. Gas 

compressors (not shown in Figure V-4) can be 

added to supply spacecraft users with up to 270 

lb (123 kg) of gaseous nitrogen at up to 
4500psia (31 mPa). Variable set-point 

regulators provide pressurant control in the 

3000 psia (20.7 mPa) and below range. 

relief valves and variable set-point relief 

valves plumbed in parallel provide overpressure 

protection against regulator failure for both 

the OSCRS and a user spacecraft. 

Pressure 

Avionics Desipn 

The avionics subsystem is made up of 

equipment installed on the OSCRS structure and 

located in the cargo bay, and equipment located 

at the Aft Flight Deck. The OSCRS avionics 

design to perform these functions is shown in a 

schematic block diagram in Figure V-5. 

equipment installed on the OSCRS structure 

includes sensors, microcomputers and valve 

drivers for monitoring and controlling the fluid 

transfer operation and other functions 

associated with berthing and separation. The 

equipment installed at the Aft Flight Deck 

provides the man-machine interface for crew 

The 
..--, I.. 

.. 

monitoring and control of the fluid transfer 

operation. The Aft Flight Deck avionics also 

provides on-board data downlink, and an optional 

interface to the Orbiter General Purpose 

Computers (GPC) via the multiplexerdemultiplexer (MDM). 

.. 

The avionics system is triply redundant and 

provides two-fault-tolerance for commanding 

valves and monitoring the propellant transfer 

operation. Valve commands are fed through a 

majority vote box that is designed to prevent 

valve actuation in the event of two failures. 

If two of the three OSCRS microcomputers fail, 

switches and a safety sequencer provide the 

capability to by-pass the microcomputers and 

shut down and safe the system. Also, even if 

two of the three OSCRS microcomputers fail, the 

third microcomputer continues to provide the 

capability to monitor the system. 

VI. SUMMARY 

The design of efficient and cost effective 

resupply tankers is strongly driven by the 

degree of flexibility and modularity 
.. .. ... .. .. 

.. 

.. 

incorporated into the configuration to 

accommodate the requirements and design 

preferences of the user community. Although it 

is a reasonable design goal to produce a tanker 

which will resupply every user no matter what 

his fluid quantities, tanker types, pressure 

levels, and thermal conditioning requirements, a 

severe design penalty may result when one set of 

requirements drives the design but that space 

system only represents one percent of the total 

mission model. In this case, from a total 

system standpoint considering both the tankers 

and the overall logistics scenario, it is more 

cost effective to either bring the system to the 

ground and resupply, or configure and launch a 

dedicated tanker. 

For spacecraft designers, by judicially 

configuring the spacecraft to accommodate 

resupply rather than optimizing the propulsion 

of fluid systems independent of this 

interaction, significant overall cost savings 

for the logistics operations and the total 
program may result. For example, limiting 

gaseous system pressures to 3000 psia (20.7 mPa) 

will permit resupply of the gas in a cascade 

approach rather than requiring a compressor 

which is not state-of-the-art, have increased 

power requirements and lengthens transfer 

times. Selecting one concept of propellant 

management device over another is also a strong 

influence on the overall transfer operations and 

resultant cost. Appropriate tanker designs, 

however, need to incorporate as many provisions 

as possible to service the diversity of 

spacecraft configurations without adversely 

penalizing the design with features (and 

resultant configuration cost) not needed by the 

majority of users. 

VI1 . REFERENCES 

1. Orbital Spacecraft Consumables Resupply 

System (OSCRS) Study, Final Report (Draft), 

Volume I, Executive Summary, MCR-86-1351, 

Martin Marietta Denver Aerospace, Denver, 

Colorado, October 1986. 

2. Orbital Spacecraft Consumables Resupply 
System (OSCRS) Study, Requirements 

Definition Document, MCR-86-1323, Martin 

Marietta Denver Aerospace, Denver, Colorado, 

March 1986. 

3. Wiltsee, C. B. and Manning, L. A.: 

Servicing Operations for the SIRTF 

Observatory at the Space Station, AIAA Paper 

87-0504, AIM 25th Aerospace Sciences 

Meeting, Reno, Nevada, January 12-15, 1987. 

4. Kittel, Peter: Orbital Resupply of Liquid 

Helium, AIM Paper 85-0959, AIAA 20th 

Thermophysics Conference, Williamsburg, 

Virginia, June 19-21, 1985. 

5. DiPirro, M. J., et al: On-orbit Transfer of 

Superfluid Helium Using the Thermomechanical 

Effect, AIAA Paper 85-0964, AIAA 20th 

Thermophysics Conference, Williamsburg, 

Virginia, June 19-21, 1985. 
6. Eberhardt, R. N. and Fester, D. A.: Orbital 

Fluid Management, AIAA Paper 85-1234, 

AIAA/SAE/ASME/ASEE 21st Joint Propulsion 

Conference, Montery, California, 

July 8-10, 1985. 

7. Eberhardt, R. N. and Bailey, W. J.: 

Cryogenic Fluid Management Facility, in: 

"Advances in Cryogenic Engineering," 

Vol. 31, Plenum Press, New York (1986), 

pp. 905-914. 

8. Latch Valve Overheating in Hydrazine 

Systems, Memorandum NS2/85-L274, from 

Manager, National Space Transportation 

System, Lyndon B. Johnson Space Center, 

January 13, 1986. 
! 

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ORE1MAL PCZGE I$ 

OF POOR QUALITY 

Tableg Fluid Transfcr Metbod Applicability 

Ullage Exchange 

Vent/Fill /Repressurize 

Drain/Vent/Fill/Repressurize 0 e.. 

Diap. - Diaphragm lank 

S.T. - Surface Tension Tank 

*Not applicable to complex surface tension device 
mmrm PAGE IS 

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Tab& 9 Fluid Rmervkiwg Trcbnology Iss-wr 

Technology Enhancement 

Techno 1 ogy 

o Hardware 

a) Variable set-point regulators and 

re1 ief valves 

b) Monopropellant catalytic vent life 

with long burn times and high 

concentrations of non-condensi bl e 

gases and pulsed operatlons 

o Processes 

a) Pressurant solubility effects during 

b) Contamlnation control during venting 

c) Adiabatic compression heating in 

fill 

surface tension tankage 

Open Technology Issue 

Technology 

o Hardware 

Automatic fluid coupling 

Resupply mechanism to make and brake 

the fluid coupling 

High pressure gas compressor is not 

state-of-the-art 

Tank quantity gaging system 

Oxidizer burner and fuel burner that 

can accept high concentrations of 

non-condensible gases, and pulsed 

operation. A burner that could handle 

both simultaneously or separately is 

desired 

o Processes 

a 1 Separation of gashapor from 1 iquid 

during venting (required for ullage 

exchange and vent/fil l/repressurire 

transfer methods to be effect1 ve) 

b) Total filling of complex PMD's 

c) No-vent fill 

Recomnendatlons 

o Hardware 

a) Design, build and test an electronics 

varlable set-point regulator to 

minimlze rtsk 

b) Test exlstlng design qver complete 

ran4e of expected conditions 

o Processes 

a) Mlnimlze the time the liquid is 

exposed to high pressure. Run tests 

to understand process for contingency 

operations 

b) Study required to better quantify 

requi rements 

c) Refine computer programs using ORS 

data and extrapolate to PMD tanks 

Recommendations 

o Hardware 

6 b) Design, build and test these 

Design. build and test to assure 

reliable long life 

Continue JSC contract work 

Deslgn. build and test over complete 

range of expected operating conditions - 

devices together to minimize risk 

o Processes 

a) Studies followed by drop tower and 

Storable Fluid Management 

Demonstration (SFMD 1 testing 

b) 6 c) Conduct tests and analysis of 

storable fluid in ground tests 

and determine if zero-g tests are 

required 

C;I&IMAC PJiGE IS 

OF POOR QUALITY 

10 
Figure 111-X Monopropellant Design Comparison Mass Fraction vs 4 Propel 1 ant Load 

80 FLIGHTS 

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LEGEND 

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: I :1w: 

: um- : ius1 : 

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m: mm: 

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Figure 111-% OSCRS Recurring Cost Comparison 

5 

111-3 
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Figure f.?T OSCRS Basic Monopropellant Configuration 

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LONGERON TRUNNIONS 

.. ' TV CAFERAS 

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Figure fl Basic Bipropellant OSCRS 

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