T y G C J r ali e t f aP tSe I n tsun a n l de P T L ... · A p p l i c a t i o n s o f C l o c k s...
20
Applications of Clocks to Space Navigation & “Planetary GPS” April 20, 2004 Stephen M. Lichten Jet Propulsion Laboratory Manager, Tracking Systems and Applications Section *This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology https://ntrs.nasa.gov/search.jsp?R=20060014041 2020-07-08T07:08:38+00:00Z
Transcript of T y G C J r ali e t f aP tSe I n tsun a n l de P T L ... · A p p l i c a t i o n s o f C l o c k s...
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
Apr
il 20
, 200
4
Ste
phen
M. L
icht
enJe
t Pro
puls
ion
Labo
rato
ryM
anag
er, T
rack
ing
Sys
tem
s an
d A
pplic
atio
ns S
ectio
n *
This
rese
arch
was
car
ried
out a
t the
Jet
Pro
puls
ion
Labo
rato
ry, C
alifo
rnia
Inst
itute
of T
echn
olog
y, u
nder
a
con
tract
with
the
Nat
iona
l Aer
onau
tics
and
Spa
ce A
dmin
istra
tion
Jet P
ropu
lsio
n La
bora
tory
Cal
iforn
ia In
stitu
te o
f Tec
hnol
ogy
https://ntrs.nasa.gov/search.jsp?R=20060014041 2020-07-08T07:08:38+00:00Z
Lich
ten
- 2
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
•H
ow G
PS
“wor
ks” f
or tr
acki
ng a
nd n
avig
atio
n at
Ear
th
•Im
porta
nce
of c
lock
s fo
r GP
S
•D
eep
Spa
ce T
rack
ing
•C
once
pts
for c
omm
unic
atio
ns/n
avig
atio
n sy
stem
s at
oth
er p
lane
tary
bod
ies
•S
pars
e G
PS
-like
pla
neta
ry s
yste
ms
and
track
ing/
navi
gatio
n
Out
line
of P
rese
ntat
ion
Lich
ten
- 3
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”H
ow G
PS
Wor
ks
•G
PS
det
erm
ines
use
r pos
ition
via
“tria
ngul
atio
n” to
thre
e G
PS
sat
ellit
es
•Th
e us
er’s
GP
S re
ceiv
er c
ompa
res
each
sat
ellit
e’s
uniq
ue p
seud
oran
dom
code
to m
odel
s st
ored
in th
e re
ceiv
er to
mea
sure
the
time
dela
y, a
nd h
ence
dist
ance
, to
each
GP
S s
atel
lite
–R
equi
res
that
all
GP
S s
atel
lites
be
“syn
chro
nize
d” to
“sam
e” ti
me
–U
ser d
oes
not n
eed
a go
od c
lock
: afo
urth
GP
S m
easu
rem
ent d
eter
min
esth
e us
er ti
me
offs
et fr
om “G
PS
tim
e”
•E
ach
GP
S s
atel
lite
cont
inuo
usly
broa
dcas
ts it
s ep
hem
eris
and
offs
etfro
m “G
PS
tim
e,” w
hich
is d
efin
edpr
ecis
ely
rela
tive
to h
ighl
y st
able
grou
nd c
lock
s. W
ith th
ese
data
, a G
PS
user
rece
iver
can
in re
al-ti
me
uniq
uely
dete
rmin
e its
loca
tion
(and
tim
e of
fset
from
“GP
S ti
me”
) by
track
ing
four
GP
Ssa
telli
tes
Eac
h G
PS
sat
ellit
etra
nsm
its a
uni
que
pseu
dora
ndom
cod
e
Lich
ten
- 4
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”H
ow G
PS
Wor
ks (c
ont.)
•O
pera
tiona
l C
ontr
ol S
egm
ent (
OC
S). T
he U
SA
FO
CS
con
sist
s of
one
Mas
ter C
ontro
l Sta
tion
(MC
S) a
tS
chrie
ver
AFB
in C
olor
ado
Spr
ings
, plu
s m
onito
rst
atio
ns a
t the
MC
S, H
awai
i, K
waj
alei
n, D
iego
Gar
cia
and
Asc
ensi
on Is
land
. The
sta
tions
pas
sive
ly tr
ack
rang
ing
data
from
all
GP
S in
vie
w. T
he M
CS
estim
ates
and
pre
dict
s ea
ch s
atel
lite’
s e
phem
eris
and
cloc
k pa
ram
eter
s an
d pe
riodi
cally
upl
oads
them
to e
ach
GP
S fo
r re-
trans
mis
sion
in it
s na
viga
tion
mes
sage
.
•G
PS
eph
emer
is/c
lock
upl
oads
are
upd
ated
eve
ryse
vera
l hou
rs. D
urin
g th
at ti
me
perio
d, th
e br
oadc
ast
ephe
mer
is d
egra
des
only
mod
erat
ely
beca
use
…–
GP
S a
re in
rela
tivel
y hi
gh-a
ltitu
de, w
ell-b
ehav
ed o
rbits
–G
PS
all
carr
y pr
ecis
e (a
tom
ic) c
lock
s
–K
now
ledg
e of
GP
S ti
me
is m
aint
aine
d th
roug
h th
e ve
ry s
tabl
e gr
ound
cloc
ks a
t the
gro
und
track
ing
site
s
GP
S M
CS
Lich
ten
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Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”H
ow G
PS
Wor
ks (c
ont.)
•Th
e D
esig
n Tr
ade
for G
PS. T
he G
PS
des
igne
rsin
corp
orat
ed …
–Ac
cura
te (a
tom
ic) c
lock
s at
ope
ratio
nal g
roun
d tra
ckin
g si
tes
and
onbo
ard
the
GPS
sat
ellit
es
–A
24/7
glo
bal t
rack
ing
netw
ork
to a
ccur
atel
y an
d co
ntin
uous
lyde
term
ine
and
upda
te G
PS o
rbits
and
clo
cks
–In
con
trast
: the
GP
S u
ser t
ypic
ally
car
ries
rela
tivel
y si
mpl
eeq
uipm
ent a
nd d
oes
not r
equi
re a
goo
d cl
ock
•Th
e U
.S. g
over
nmen
t ele
cted
to in
vest
in ro
bust
and
relia
ble
GP
S s
pace
and
gro
und/
cont
rol s
egm
ents
(infra
stru
ctur
e), t
hus
enab
ling
the
user
seg
men
t(m
illio
ns o
f use
rs) t
o ca
rry
rela
tivel
y si
mpl
e an
dch
eap
user
equ
ipm
ent
•R
ough
ly $
12B
to d
evel
op G
PS
(in
1980
s)
GP
S M
CS
Lich
ten
- 6
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”G
PS
Per
form
ance
Tod
ay
•S
tand
alon
e co
mm
erci
al re
ceiv
er (h
andh
eld,
aut
os, b
oats
etc
.)–
10 m
eter
s re
al-ti
me
posi
tioni
ng.
•P
erfo
rman
ce is
lim
ited
by G
PS
clo
ck &
orb
it m
odel
ing.
•C
omm
erci
al re
ceiv
er w
ith d
iffer
entia
l ser
vice
s–
2 m
eter
s re
al-ti
me
posi
tioni
ng. R
equi
res
loca
l/reg
iona
l diff
eren
tial
serv
ice
subs
crip
tion.
•P
erfo
rman
ce is
lim
ited
by G
PS
clo
ck &
orb
it m
odel
ing.
•JP
L pr
ecis
ion
glob
al d
iffer
entia
l GP
S (G
DG
PS
) sys
tem
–10
cm
real
-tim
e po
sitio
ning
acc
urac
y. R
equi
res
glob
al d
iffer
entia
lse
rvic
e fro
m c
omm
erci
al p
artn
er.
•N
etw
ork
proc
essi
ng im
prov
es o
rbits
and
elim
inat
es d
epen
denc
e on
clo
cks.
•N
on-r
eal-t
ime
(min
utes
to d
ays)
geo
detic
pos
ition
ing
–Be
tter t
han
1-cm
non
-real
-tim
e po
sitio
ning
acc
urac
y. R
equi
res
glob
alne
twor
k da
ta +
spe
cial
sof
twar
e.•
Net
wor
k pr
oces
sing
impr
oves
orb
its a
nd e
limin
ates
dep
ende
nce
on c
lock
s.
Lich
ten
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Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”S
pace
craf
t Nav
igat
ion
with
JP
L B
lack
jack
GP
S R
ecei
vers
SR
TM
C
HA
MP
SA
C-C
J
AS
ON
-1
G
RA
CE
Feb
2000
Jul 2
000
N
ov 2
000
D
ec 2
001
M
ar 2
002
FedS
at
I
CE
Sat
C
OS
MIC
O
STM
Dec
200
2
Dec
200
2
S
ept 2
005
2
008
Mis
sion
s In
Dev
elop
men
t
>12
year
sof
on-
orbi
tpe
rform
ance
45-c
m a
ccur
acy
4-cm
acc
urac
y4-
cm a
ccur
acy
Sub-
met
er re
al-ti
me
dem
o1-
cm a
ccur
acy
1-cm
acc
urac
y
5-cm
acc
urac
y
Of a
ll th
ese,
onl
y th
e G
RA
CE
GP
S re
ceiv
ers
carr
ied
high
-qua
lity
cloc
ks (U
SO
s).
Lich
ten
- 8
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”D
eep
Spa
ce T
rack
ing
•C
halle
nges
of d
eep
spac
e tra
ckin
g fro
m E
arth
–W
eak
sign
als
•N
AS
A D
eep
Spa
ce N
etw
ork
uses
70-
m a
nd 3
4-m
ant
enna
s–
Geo
met
ry a
nd v
isib
ility
–Li
ght t
rave
l tim
e fro
m E
arth
•5
to 2
5 m
inut
es to
Mar
s•
~ 1.
3 se
c to
Moo
n–
Ref
eren
ce fr
ame
issu
es
•Ty
pica
l dat
a ty
pes
–Tw
o-w
ay D
oppl
er, 0
.03
mm
/s–
Two-
way
rang
e, 2
met
ers
–D
elta
-Diff
eren
tial o
ne-w
ay ra
nge,
VLB
I•
2 nr
ad =
0.0
6 ns
ec =
1.2
cm
del
ay–
Opt
ical
nav
igat
ion
Lich
ten
- 9
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
•Th
e M
ER m
issi
on d
ram
atic
ally
pro
ved
the
high
val
ue o
f hav
ing
navi
gatio
n &
tele
com
“in
fras
truc
ture
” du
ring
chal
leng
ing
surf
ace
oper
atio
ns o
not
her p
lane
tary
bod
ies
•W
hat i
s th
e be
st a
ppro
ach
for M
ars?
For t
he M
oon?
•Lig
ht tr
avel
tim
e to
Mar
s is
tens
of m
in, b
uton
ly a
bout
1 s
ec to
the
Moo
n•
Impo
rtan
ce o
f aut
onom
y
•Som
e Ea
rth-
orbi
ting
GPS
can
be
usef
ully
trac
ked
at M
oon
“In S
itu” T
rack
ing
at O
ther
Pla
neta
ry B
odie
s
Lich
ten
- 10
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
MA
RS
Orb
iter
Oth
erM
ars
Orb
iter
•Su
rfac
e or
low
Mar
s or
bit v
ehic
le c
an b
etr
acke
d w
ith 1
-way
Dop
pler
•Per
form
ance
dep
ends
on
user
’s c
lock
•10-
8 clo
cks,
1 o
rbite
r onl
y: 3
km
in 2
4 hr
s•1
0-9 c
lock
s, 1
orb
iter o
nly:
300
m in
24
hrs
•By
trac
king
two
orbi
ters
sim
ulta
neou
sly,
depe
nden
ce o
n us
er’s
clo
ck is
redu
ced
or e
limin
ated
•IM
U a
nd a
ngle
-sen
sing
may
impr
ove
perf
orm
ance
or r
obus
tnes
s•C
an b
e ch
alle
ngin
g if
targ
et v
ehic
le is
man
euve
ring
Act
ive
IMU
onbo
ard1-
way
1-w
ay
Trac
king
a V
ehic
le a
t Mar
s W
ith 1
or 2
Nav
/Com
Orb
iters
as
Infra
stru
ctur
e
Lich
ten
- 11
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
Trac
king
a V
ehic
le a
t Mar
s W
ith 1
or 2
Nav
/Com
Orb
iters
as
Infra
stru
ctur
e
MA
RS
Orb
iter(
s)
•Su
rfac
e or
low
Mar
s or
bit v
ehic
le c
an b
etr
acke
d w
ith 2
-way
dat
a ty
pes
•Use
r doe
s no
t nee
d ex
trem
ely
good
clo
ck•<
100
m p
ositi
on a
ccur
acy
in 2
4 hr
s w
ithju
st 1
trac
ker (
orbi
ter)
•Com
bina
tion
of 3
trac
kers
(orb
iters
and/
or g
roun
d) c
an p
rovi
de re
al-ti
me
know
ledg
e <
100
m•I
ncor
pora
ting
angl
e-se
nsin
g an
d/or
IMU
data
can
redu
ce n
umbe
r of t
rack
ers
•Can
be
chal
leng
ing
if ta
rget
veh
icle
ism
aneu
verin
g
Act
ive
IMU
onbo
ard
2-way
rang
e or D
oppl
er
Lich
ten
- 12
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”M
ER
Tra
ckin
g vi
a O
dyss
ey a
nd M
GS
•Tw
o-w
ay D
oppl
er tr
acki
ng w
as s
ucce
ssfu
lbe
twee
n th
e la
nded
MER
and
Ody
ssey
. Apo
sitio
n w
as e
vent
ually
det
erm
ined
(day
sla
ter)
acc
urat
e to
tens
of m
eter
s.
•O
ne-w
ay D
oppl
er tr
acki
ng w
assu
cces
sful
bet
wee
n M
ER a
nd M
GS
durin
g an
d af
ter t
he c
ritic
alEn
try/
Des
cent
/Lan
ding
.
Lich
ten
- 13
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
•Th
ree
key
appr
oach
es to
nav
igat
ion/
tele
com
infra
stru
ctur
e as
sets
in L
unar
or
Mar
tian
regi
mes
1.R
ely
on s
impl
er d
ata
type
s su
ch a
s 2-
way
or 1
-way
Dop
pler
with
“orb
iters
of o
ppor
tuni
ty,”
i.e.
, exi
stin
g or
bitin
g ve
hicl
es (a
s w
as d
one
with
MER
)
2.D
eplo
y a
spar
ser v
ersi
on o
f a G
PS-li
ke c
onst
ella
tion.
Pro
vide
Nav
igat
ion
serv
ices
sim
ilar t
o ho
w G
PS d
oes
at E
arth
. Sam
e sp
ace
vehi
cles
can
als
o pr
ovid
e Te
leco
mm
unic
atio
ns s
ervi
ces.
3.D
eplo
y co
nste
llatio
n ut
ilizi
ng d
ual o
ne-w
ay tr
acki
ng b
etw
een
infr
astr
uctu
re a
sset
s an
d us
ers,
whi
ch m
ust b
e eq
uipp
ed w
ithco
mpa
tible
nav
igat
ion/
tele
com
tran
scei
vers
.
Lich
ten
- 14
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
•Th
ree
key
appr
oach
es to
nav
igat
ion/
tele
com
infra
stru
ctur
e as
sets
in L
unar
or
Mar
tian
regi
mes
(con
t.)
1.R
ely
on s
impl
er d
ata
type
s su
ch a
s 2-
way
or 1
-way
Dop
pler
with
“orb
iters
of o
ppor
tuni
ty,”
i.e.
, exi
stin
g or
bitin
g ve
hicl
es (a
s w
as d
one
with
MER
)
•Ad
vant
ages
–N
o ne
w te
chno
logy
; use
s w
hate
ver o
rbite
rs a
re th
ere
(low
ers
cost
)
–G
ood
user
spa
ce c
lock
s no
t nee
ded
(low
ers
cost
).
•Ty
pica
lly, l
ong-
term
orb
iters
car
ry U
SO
s.
•D
isad
vant
ages
–P
oore
r per
form
ance
(ten
s of
met
ers
to k
ilom
eter
s af
ter ~
day
s)
–R
eal-t
ime
is n
ot e
asily
don
e w
ith D
oppl
er, s
ince
tim
e hi
stor
y is
nee
ded
to in
fer d
ynam
ics.
Can
not e
asily
trac
k irr
egul
arly
man
euve
ring
vehi
cles
.
–U
ses
wha
teve
r orb
iters
are
ther
e --
not
ava
ilabl
e on
dem
and.
Won
’t be
imm
edia
tely
avai
labl
e fo
r em
erge
ncie
s.
Lich
ten
- 15
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
•Th
ree
key
appr
oach
es to
nav
igat
ion/
tele
com
infra
stru
ctur
e as
sets
in L
unar
or M
artia
nre
gim
es (c
ont.)
2.D
eplo
y a
spar
ser v
ersi
on o
f a G
PS-li
ke c
onst
ella
tion.
Pro
vide
Nav
igat
ion
serv
ices
sim
ilar t
o ho
w G
PS d
oes
at E
arth
. Sam
e sp
ace
vehi
cles
can
als
opr
ovid
e Te
leco
mm
unic
atio
ns s
ervi
ces.
–A
dvan
tage
s–
Hig
h pe
rform
ance
pos
sibl
e, d
epen
ding
on
cove
rage
/vis
ibili
ty a
nd c
lock
qua
lity
–R
eal-t
ime
emer
genc
y se
rvic
es p
ossi
ble
–D
isad
vant
ages
–H
ighe
r cos
t for
ope
ratin
g in
frast
ruct
ure
asse
ts (d
edic
ated
con
stel
latio
n) a
t Moo
n or
Mar
s
–H
ighe
r cos
t and
com
plex
ity fo
r util
izin
g hi
gh q
ualit
y sp
ace
cloc
ks (a
s w
ith G
PS
)
–Te
chno
logy
cha
lleng
es …
•A
vaila
bilit
y/co
vera
ge d
eter
min
ed b
y sp
arse
ness
of c
onst
ella
tion
–S
mal
l, ch
eap
very
sta
ble
spac
e cl
ocks
to d
eplo
y on
infra
stru
ctur
e an
d us
ers
–C
ombi
natio
n of
bet
ter c
lock
s +
IMU
can
com
pens
ate
for c
over
age
“gap
s”
–D
evel
op a
cos
t effe
ctiv
e co
ncep
t of o
pera
tions
.–
Key
trad
e: s
houl
d gr
ound
trac
king
term
inal
s be
rem
otel
y de
ploy
ed (a
s ar
e us
ed fo
r GP
S o
pera
tions
)?If
so, s
houl
d th
ey b
e eq
uipp
ed w
ith h
ighl
y st
able
clo
cks?
How
long
can
/will
suc
h gr
ound
aut
omat
edgr
ound
term
inal
s fu
nctio
n in
a h
ostil
e en
viro
nmen
t? C
an th
e sy
stem
be
mai
ntai
ned
sole
ly v
ia E
arth
track
ing?
How
wou
ld th
e re
fere
nce
fram
e tie
be
mai
ntai
ned?
Lich
ten
- 16
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
•R
esul
ts o
f asi
mul
atio
npe
rform
ed to
eval
uate
trac
king
cove
rage
for a
Mar
s ne
twor
k of
low
-alti
tude
orbi
ters
Lich
ten
- 17
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
•Th
ree
key
appr
oach
es to
nav
igat
ion/
tele
com
infra
stru
ctur
e as
sets
in L
unar
or
Mar
tian
regi
mes
(con
t.)
3.D
eplo
y co
nste
llatio
n ut
ilizi
ng d
ual o
ne-w
ay tr
acki
ng b
etw
een
infr
astr
uctu
re a
sset
s an
d us
ers,
whi
ch m
ust b
e eq
uipp
ed w
ithco
mpa
tible
nav
igat
ion/
tele
com
tran
scei
vers
.–
Adv
anta
ges
•R
eal-t
ime
high
(sub
-met
er) a
ccur
acy
(if c
over
age
is a
dequ
ate)
•S
mal
ler n
umbe
r of g
ood
spac
e cl
ocks
nee
ded
beca
use
syst
emre
lies
on d
ual-o
ne-w
ay tr
acki
ng d
ata
(inse
nsiti
ve to
clo
cks)
–D
isad
vant
ages
•S
elf-j
amm
ing
(tran
scei
vers
tran
smitt
ing
and
rece
ivin
gsi
mul
tane
ousl
y)•
Sys
tem
com
plex
ity fo
r sca
labi
lity
to m
any
sim
ulta
neou
sve
hicl
es/u
sers
•U
sers
mus
t car
ry c
ompa
tible
tran
scei
vers
–R
ole
of c
lock
s•
Goo
d cl
ocks
not
requ
ired
for p
reci
se ra
ngin
g be
twee
n sp
acec
raft,
but a
t lea
st o
ne to
sev
eral
long
-term
sta
ble
and
prec
ise
spac
ecl
ocks
are
requ
ired
to m
aint
ain
syst
em ti
min
g an
d re
fere
nce
fram
ere
gist
ratio
n (e
quiv
alen
t to
know
ledg
e of
UT1
-UTC
at E
arth
).•
With
out t
hese
sta
ble
cloc
ks, s
yste
m a
uton
omy
will
not
be
poss
ible
and
syst
em o
pera
tion
will
be
mor
e co
mpl
ex a
nd c
ostli
er
Adv
ance
d G
PS
fligh
t rec
eive
rs fo
rE
arth
,at
mos
pher
ic, a
ndoc
ean
scie
nce
and
for
prec
ise
navi
gatio
n.
Aut
onom
ous
Form
atio
n Fl
yer
(AFF
) and
Sof
twar
eR
econ
figur
able
Rad
io/T
rans
ceiv
ers
for i
nteg
rate
d de
ep-
spac
ena
viga
tion/
tele
com
and
form
atio
n fly
ing.
GR
AC
E c
ombi
nes
spac
e G
PS
plu
sul
tra-p
reci
se (1
-m
icro
n de
lta-ra
nge)
inte
r-spa
cecr
aft
trans
ceiv
ers
Lich
ten
- 18
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
•Th
e ab
ility
to fl
y at
omic
clo
cks
on G
PS
sat
ellit
es h
as p
rofo
undl
y de
fined
the
capa
bilit
ies
and
limita
tions
of G
PS
in n
ear-
Ear
th a
pplic
atio
ns
•It
is li
kely
that
futu
re in
frast
ruct
ure
for L
unar
and
Mar
s ap
plic
atio
ns w
ill b
eco
nstra
ined
by
finan
cial
fact
ors
•Th
e de
velo
pmen
t of a
low
cos
t, sm
all,
high
per
form
ance
spa
ce c
lock
-- o
r ultr
a-hi
gh p
erfo
rman
ce s
pace
clo
cks
-- c
ould
revo
lutio
nize
and
driv
e th
e en
tire
appr
oach
to G
PS
-like
sys
tem
s at
the
Moo
n (o
r Mar
s), a
nd p
ossi
bly
even
chan
ge th
e fu
ture
of G
PS
at E
arth
•M
any
syst
em tr
ade
stud
ies
are
requ
ired.
The
per
form
ance
of f
utur
e G
PS
-like
track
ing
syst
ems
at th
e M
oon
or M
ars
will
dep
end
criti
cally
on
cloc
kpe
rform
ance
, ava
ilabi
lity
of in
ertia
l sen
sors
, and
con
stel
latio
n co
vera
ge.
–Ex
ampl
e: p
rese
nt-d
ay G
PS c
arry
10-1
3 clo
cks
and
requ
ire s
ever
al u
pdat
es p
er d
ay.
With
10-1
5 clo
cks,
a c
onst
ella
tion
at M
ars
coul
d op
erat
e au
tono
mou
sly
with
upd
ates
just
onc
e pe
r mon
th.
•U
se o
f GP
S tr
acki
ng a
t the
Moo
n sh
ould
be
eval
uate
d in
a te
chni
cal s
tudy
.
Sum
mar
y
Lich
ten
- 19
Jet P
ropu
lsio
n La
bora
tory
C
alifo
rnia
Inst
itute
of T
echn
olog
y
App
licat
ions
of C
lock
s to
Spa
ce N
avig
atio
n &
“Pl
anet
ary
GPS
”
•N
ext s
teps
: Dev
elop
a p
rogr
am to
per
form
sim
ulat
ions
and
exp
erim
ents
to e
valu
ate
and
com
pare
cap
abilit
ies
and
cost
s fo
r the
diff
eren
t nav
igat
ion/
tele
com
sce
nario
s fo
rM
oon
and
Mar
s in
frast
ruct
ure
Sum
mar
y (c
ont.)
•D
eter
min
e ho
w p
reci
se/s
tabl
e fli
ght c
lock
san
d IM
U s
enso
rs c
an “f
ill in
” cov
erag
e ga
psfo
r spa
rser
ver
sion
s of
GPS
–G
oal i
s to
det
erm
ine
how
GP
S-li
ke c
apab
ilitie
sca
n be
ena
bled
with
few
er th
an 4
“GP
S” i
n vi
ew•
How
long
and
how
acc
urat
ely
can
posi
tioni
ng b
esu
stai
ned
with
3, 2
, 1 o
r eve
n 0
orbi
ters
in v
iew
?
–U
se c
urre
nt G
PS
terr
estri
al a
nd s
pace
dat
a to
perfo
rm te
sts
and
expe
rimen
ts. E
xcel
lent
dat
ase
ts a
nd te
st fa
cilit
ies
are
avai
labl
e.•
Eva
luat
e cl
ocks
and
IMU
sen
sors
ove
r a w
ide
rang
e of
per
form
ance
–E
valu
ate
diffe
rent
con
cept
s of
ope
ratio
ns•
Wha
t is
the
valu
e of
an
extre
mel
y ac
cura
te g
roun
dcl
ock
at M
ars
or M
oon?
How
sur
viva
ble
is a
grou
nd c
lock
, ver
sus
a sp
ace
cloc
k in
an
orbi
ter?
Doe
s th
e gr
ound
clo
ck e
nabl
e si
mpl
ifica
tion
ofth
e or
bitin
g pa
yloa
ds?
Is th
e tra
de w
orth
whi
le?
•E
valu
ate
GP
S tr
acki
ng a
t the
Moo
n an
d ho
wco
vera
ge m
ight
be
exte
nded
to th
e fa
r sid
e
Mar
s
EML 2
EML 1
Moo
n
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