(PDF) An overview of the on-orbit results from the ESEX flight experiment

platform

than

experienced

during

test.

This

platform temperature

is

not

actively

controlled,

and

can

drift

significantly

perhaps

leading

to

a

low

enough

temperature

to

condense

NH,

at

the

pressure

in

the

propellant

line:

To

further

support

this

possibility,

there

were

some

variations

from

the

normal

procedure

on

the

last

firing

( F-8 )

and no

liquid

ingestion

was

observed.

For

that

encase.

the

PFS

heaters

were

turned

on

many

hours

before

the

actual

firing

attempt

as

a

result

of

waiting

for

the battery

reconditioning

to

complete.

This

may

suggest

the

cold

spot

in

the

propellant

line

had

enough

time

to

heat

up and

vaporize

the

condensed

NH,.

In

summary.

the

liquid

ingestion

proved

to

be an

irritation.

but

did

not

seriously

detract

from

the

arcjet

operation.

If

the

ESEX

mission

had

continued,

a

heater

configuration

that

alleviated

this

problem

would

almost

surely

have

been

determined.

Other

than

this

issue,

the

PFS

performed

within

specification

and,

in

general,

operated

exceptionally

well,

The

flow

rate

control

generally

operated

to

within

kO.3

mg/sec

at

steady-state

conditions

an

order

of

magnitude

better

than

the

design

requirement

of

+5

mg/sec. If

this

system evolved

into

an

operational

flight

design,

some

heater

world power

applied

to

the

section

of

the

propellant

line

in

question

(or

more

direct

thermal

control

of

that

section)

could

almost

assuredly

resolve

the

liquid

ingestion

issue

entirely

especially

in

light

of

the

results

from

the

stopping point

firing.

Conclusions The

ESEX

flight

demonstrated

high

power

electric

propulsion

is

compatible

with

generic

satellite

cjperotions.

Although

further

analyses

are

in-work,

all

of

the

data

investigated

to

date

indicate

the

thruster

and

the

high

power

components

have

no

significant,

deleterious

effect

on

any

satellite

activities.

Summarv ESEX

is

the

culmination

of

over

ten

years

of

effort

to

\-alidate

high

power

electric

propulsion

on-orbit

and

verify

its

compatibility

with

standard

USAF

satellites.

There

were

a

total

of

eight

firings

conducted

over

the

path

of

the

60-day

mission,

all

of

them

over

26

kW,

degree fahrenheit

or

;1

total

duration

of

2023

seconds.

There

were

two

anomalies

associated

with

the

flight

operations

a

liquid

ingestion

problem

that

had

only

a

minor

affect

on

the

mission.

and a

battery

failure

that

precluded

any

far

firings.

Approximately

76%

of

the

ESEX

mission

success

was

attained,

with

the

biggest

deficiencies

resulting

from

the

lack

of

GPS

data,

and

the

optical

signature

characterization.

All

of

the demonstration

aspects

of

the

experiment

were

completed,

and

all

of

this

hardware

the

arcjet,

PCU,

and

PFS

operated

very

well,

and

within

their

specifications.

All

of

the

data

analyzed

to

date

indicate

the

thruster

operated

nominally,

and

operated

completely

independently

of

the

normal

operations

of

the

host

spacecraft

(ARGOS).

Acknowledments The

authors

would

like

to

extend

their

gratitude

to

the

entire

support

team

at

the

USAF

Research

Laboratory

including

Shaughn

Tracy,

Krystin

Barker,

and

Robin

Lowder.

We

also

extend

our

thanks

to

Mary

Kriebel,

Don

Baxter,

Bob

Tobias,

David

Lee,

and

David

Huang

of

TRW

for

their

technical

expertise

on

the

ESEX

flight

hardware ;

and

to

Andy

Hoskins,

Bob

Kay,

and

Joe

Cassady

of

the

Primex

Aerospace

Company

for

their

technical

insight

into

the

arcjet,

PFS,

and

PCU.

We

would

also

like

to

extend

our

sincere

gratitude

to

the

ARGOS

program

office

and

the

entire

flight

operations

team

at

Kirtland

AFB,

NM,

as

well

as

the

staff

at

MSSS

and

CPCA

for

their

technical

expertise

and

insight

into

their

facilities

which

allowed

ESEX

to

acquire

such

a

broad range

of

data.

References : 1.

Kriebel,

M.

M.

and

Stevens,

N.

J.,

30-kW

Class

Arcjet

Advanced

Technology

Transition

Demonstration

(ATTD)

Flight

Experiment

diagnostic

Package,

AIAA

Paper

92-356

1,

July

1992. 2.

Sutton,

A.

M.,

Bromaghim.

D.

R.,

and

Johnson,

L. K.,

Electric

Propulsion

Space

Experiment

(ESEX)

Flight

Qualification

and

Operations,

AIAA

Paper

95-2503,

July.

1995.

Also

presented

as

a

JANNAF

Paper,

December,

1995.

3.

LeDuc,

J.

R.,

et.

al.,

Performance,

Contamination,

electromagnetic,

and

Optical

Flight

Measurement

Development

for

the

Electric

Propulsion

Space

experiment,

AIAA

Paper

96-2727,

July,

1996.

4.

Turner,

B.

J.

and

Agardy,

F.

J.,

The

Advanced

Research

and

Global

Observation

Satellite

( ARGOS )

Program,

AIAA

Paper

94-4580,

September

1994.

5.

Agardy,

F.

J.

and

Cleave,

R.

R..

A

Strategy

for

Maximizing

the

Scientific

Return

Using

a

Multi-

phased

Mission

Design

for

ARGOS,

AAS

93-594,

August

1993.

12 ( speed of light ) 1999 American Institute of Aeronautics & Astronautics

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