NEW HORIZONS MISSION TO PLUTO/CHARON: REDUCING COSTS OF A LONG-DURATION MISSION
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IAC-04-A.8.01
NEW HORIZONS MISSION TO PLUTO/CHARON:
REDUCING COSTS OF A LONG-DURATION MISSION
Alice F. Bowman
Johns Hopkins University Applied Physics Laboratory, Laurel, MD (USA)
Alice.Bowman@jhuapl.edu
Albert A. Chacos, Christopher C. DeBoy, R. Michael Furrow,
Karl E. Whittenburg
Johns Hopkins University Applied Physics Laboratory, Laurel, MD (USA)
Al.Chacos@jhuapl.edu, Chris.DeBoy@jhuapl.edu, Mike.Furrow@jhuapl.edu,
Karl.Whittenburg@jhuapl.edu
ABSTRACT
The long-duration and long light-time delay of NASA’s planned New Horizons mission to Pluto, its
moon Charon, and the extended mission to one or more Kuiper Belt Objects poses unique chal-
lenges to mission operations, especially in this time of limited space exploration budgets. A num-
ber of courses of action can be followed to reduce wear on Observatory hardware, reduce opera-
tions staffing costs, and reduce Deep Space Network usage and costs without sacrificing the
health and safety of the Observatory or risking the successful completion of the primary mission.
Major components in this system are an autonomy subsystem that can react quickly enough to
safe the Observatory when it is out of contact with the ground station; the use of a beacon to indi-
cate the health of the Observatory during the dormant phases of the mission; command loading
and verification strategies to accommodate the long light-time delays; and the combining of op-
erations personnel to take advantage of similarities of Observatories, supporting ground station
setup, and procedures. When planned early in the mission development phase, these compo-
nents are easily integrated into the operations concept and Observatory hardware to form a co-
hesive plan to mitigate cost and risk. Cost reduction measures for long-duration missions, such
as those planned for New Horizons, enable funding for a greater number of equally important
space exploration missions from a limited space exploration budget.
1. BACKGROUND design, development, and mission opera-
tions are delegated to the Johns Hopkins
University/Applied Physics Laboratory
The New Horizons (NH) mission is part of
(JHU/APL) in Laurel, MD, USA. The Tom-
NASA’s New Frontiers Program. It was
baugh Science Operations Center (TSOC),
awarded in the fall of 2001, with a start date
named for the discoverer of Pluto, would
of January 2002 at a cost of less than
serve as the center of scientific research
$600M. Dr. S. Alan Stern of Southwest Re-
and data repository for this mission.
search Institute (SwRI) in Boulder, CO,
Throughout this paper, the term “Observa-
USA, is the mission’s Principal Investigator
tory” is defined as the integrated spacecraft
(PI) and is responsible for the overall NH
and science instrument payloads.
mission. Responsibilities of Observatory
1The primary mission would be to conduct a MISSION
TIMEFRAME
detailed first reconnaissance flyby of the (nominal- OBJECTIVE
PHASE
planned)
Pluto/Charon system, with observations KBO 1 80 days pre and Science Observa-
planned to begin 150 days prior to and 60 (extended 90 days post KBO tion Final Rehears-
days after closest approach (C/A). The ex- mission) 1 C/A als, Navigation &
tended mission would be to conduct a flyby Targeting, Science
Collection, Data
of one or more Kuiper Belt Objects (KBOs). Return
The NASA decision to fund the extended Cruise 4 91 days post KBO Beacon-Hibernation,
mission would be made sometime after (extended 1 C/A to 81 days Annual Checkouts,
launch of the NH Observatory. Table 1 gives mission) pre KBO 2 Precession Maneu-
vers, Navigation &
an overview of the currently planned NH Targeting
mission phases. KBO 2 80 days pre and Science Observa-
(extended 90 days post KBO tion Final Rehears-
The NH Observatory primary launch window mission) 2 C/A als, Navigation &
Targeting, Science
would span 35 days from January 11 to Feb- Collection, Data
ruary 14, 2006, giving C/A arrivals from July Return
2015 to July 2020. If launched in the first 23
days of the launch window, a Jupiter Gravity
Assist (JGA) would be used to reduce flight
time to Pluto/Charon by as much as 5 years;
if launched in the last 12 days, the trajectory
Fwd LGA (+Y)
would be a direct flight to Pluto/Charon.
Launch would be from Cape Canaveral, FL, MGA (+Y)
2.1m HGA
USA, using an Atlas 551 with a Star 48B
PEPSSI
upper stage. Figure 1 depicts the current F-8 RTG
configuration of the NH Observatory. SWAP
Table 1 NH Mission Phase Overview Thrusters
TIMEFRAME Sun Sensors
MISSION
(nominal- OBJECTIVE
PHASE Heat Shield
planned)
Launch & Launch + 60 days Observatory (Obs.) Thrusters
Early Opera- (Jan–Mar 2006) Checkout, Naviga- LORRI
tions (LEOps) tion & Targeting
SDC
Cruise 1 Cruise following Instrument Commis- PERSI/Alice
LEOps to 61 days sioning, Flight Tests, Star Trackers
PERSI/Ralph
before Jupiter C/A Navigation & Target-
(Mar–Dec 2006) ing, etc. Figure 1 NH Observatory Current Con-
Jupiter 60 days pre to 40 JGA, Navigation & figuration
days post JGA Targeting, Jupiter
(Jan–Apr 2007) Science
Cruise 2 41 days post JGA Beacon-Hibernation,
to 201 days pre Annual Checkouts,
Pluto/Charon C/A Precession Maneu-
(Apr 2007–Jan vers, Navigation &
2015) Targeting, Re-
hearsal 2. INTRODUCTION
Pluto/Charon 200 days pre to Science Observa-
14 days post tion Final Rehears-
Pluto/Charon C/A als, Navigation &
The NH mission operations team (MOps) is
(Jan–Jul 2015) Targeting, Science expected to face a number of unique opera-
Collection, First- tional challenges as a result of the long-
Look Data Return duration and light-time delay of this mission.
Pluto/Charon 15 days to 270 Return of
Data Retrieval days post Pluto/ Pluto/Charon Sci-
Recognition and mitigation of these chal-
Charon C/A (Aug ence Data, Naviga- lenges began from the onset. To help ad-
2015–Apr 2016) tion & Targeting dress the long duration and the subsequent
Cruise 3 271 days post Beacon-Hibernation, Deep Space Network (DSN) usage and
(extended Pluto/Charon C/A Annual Checkouts,
costs, a beacon-hibernation phase would be
mission) to 81 days pre Precession maneu-
KBO 1 C/A vers, Navigation & implemented for the cruise between JGA
Targeting and Pluto/Charon C/A denoted as Cruise 2.
2To address the long light-time delay that will gency telemetry. Dormant periods would be
reach approximately 4.5 hours one way at when the Observatory is in a passive spin-
Pluto/Charon, an autonomy safing strategy hibernation (PS-H) state with no active G&C
and a modification to nominal command control. The majority of time during Cruise 2
load and verification would be implemented. would be spent in PS-H with the operations
Both of these mitigations would result in team relying upon the beacon tone to indi-
changes to the standard staffing concept of cate the health of the Observatory. In the
the mission operations team and would be current concept, the Observatory could be
done with minimal risk to the primary mis- placed in PS-H for up to 11 months at a
sion objectives occurring, at the earliest, 9.5 time. Cruise 2 would last approximately 7.5
years after launch. years, assuming a 2015 Pluto/Charon arri-
val.
3. MISSION DURATION
3.1.1 Active Periods
Because of the long duration of this mission
and the resulting relative cost of DSN sup- Active periods would comprise about 2
port as compared with the total mission cost, months of each year. Planned periods of
as well as the number of spacecraft compet- Observatory activity would include preces-
ing for the DSN stations, it was decided dur- sion maneuvers, TCMs, and annual check-
ing the concept study phase that DSN costs outs. Precession maneuvers would be con-
and usage would be minimized in order for ducted to maintain MGA pointing to Earth for
the proposal to be considered by NASA. beacon tone transmission/reception and
One way of reducing costs is to reduce the emergency commanding at 7.8 bps. The
number of required DSN passes by placing high gain antenna (HGA), MGA, and forward
the Observatory into a beacon-hibernation low gain antenna (LGA) would be co-aligned
mode. Deep Space 1 first demonstrated the (Figure 1). Another precess to the edge of
feasibility of using a set of beacon tones to the MGA would be conducted before the
indicate a spacecraft’s health.1 During the pointing drifts outside of the HGA deadband,
Deep Space 1 technical demonstration, one (Figure 2). These maneuvers would require
of four beacon tones was transmitted for the DSN 70-m antenna support of one 8-hour
short periods between telemetry contacts. pass per day for a week, for a total of ap-
Based on these results, a beacon- proximately 504 hours of 70-m antenna
hibernation concept was developed for the time. Preliminary analysis indicates that ap-
NH mission, utilizing eight beacon tones proximately nine precession maneuvers
(four each on two carriers), with one “green” would be required outside of the annual
and seven “red” tones, each indicating a checkout periods. While TCMs require DSN
specific Observatory state of health. support of one 8-hour pass per day for a
week, all needed TCMs would be planned to
3.1 Cruise 2 occur during the annual checkout periods.
The mission operational concept for Cruise
2 (the phase between Jupiter and
Pluto/Charon) is to have “active periods” and
“dormant periods”. Active periods would be ac on Precess
when the Observatory is in either an active Be
spin or a three-axis stabilized state, meaning M GA Angle
that Guidance and Control (G&C) is control-
ling the Observatory attitude. (See the
Appendix for a discussion of NH Observa-
HGA C m
tory modes and states.) The active periods d
would include planned precession maneu-
vers to orient the medium gain antenna
(MGA) to Earth, trajectory correction ma-
neuvers (TCMs), annual checkouts, and Figure 2 NH Precession Angles
response to “red” beacon tones or emer-
3The annual checkout period would be de- requiring attention, the autonomy rule facility
voted to accessing the NH Observatory sub- (ARF) would initiate one of seven “red” bea-
system and instrument states of health, ob- con tones, disable the preloaded weekly
taining navigation data to support any “green” tone, and broadcast the “red” tone
needed TCMs and the next period of PS-H, continuously. In certain cases, the ARF
and performing routine maintenance on des- would command the Observatory to go the
ignated subsystems and instruments. The Active Spin-Earth Acquisition (AS-EA) safe
first annual checkout period would occur state, in which case telemetry would be
within 6 months after the end of the Jupiter broadcast at the emergency rate (10 bps)
phase. Each of the eight planned checkouts instead of a “red” beacon tone, and a 14-day
spans 50 days. DSN contacts would vary “demote to Active Spin–Sun Acquisition (AS-
from two to three 8-hour passes per week SA) state” timer would be initiated. Dormant
except for the one annual checkout that in- periods will comprise on average approxi-
cludes the Pluto/Charon rehearsal. At the mately 10 months each year and require
end of the checkout period, the MGA-to- 281 hours of 34-m and 182 hours of 70-m
Earth pointing would be precessed to the DSN beacon support over the 7.5-year pe-
edge of the pointing deadband. The mission riod of Cruise 2.
operations team would load the time tag
commands to broadcast the weekly “green” 4. LONG LIGHT-TIME DELAY
beacon tone corresponding to the already
scheduled weekly DSN beacon contacts and
The NH mission end of life would be realized
the time tag commands to “wake up” the
at a solar distance of 50 AU. Analysis early
Observatory for precession maneuvers,
in the concept study phase determined that
TCMs, and annual checkout periods. Each
probability was high that two KBOs with di-
nominal annual checkout period would util-
ameters greater than 50 km could be
ize approximately sixteen 8-hour 70-m DSN
encountered within 50 AU.2 As a result, the
passes (or 128 hours), while the one annual
MGA is being sized to provide emergency
checkout period that contains the first
commanding out to 50 AU. Primary mission
Pluto/Charon rehearsal is currently esti-
objectives would occur at approximately 32
mated to require 392 hours of 70-m DSN
AU, with the extended mission objectives
support time. This gives a total of 1288
(first KBO encounter) predicted at 40 AU.
hours of 70-m support over Cruise 2 to sup-
One Way Light Time (OWLT) delays would
port all annual checkouts.
be 4.3 hours and 5.3 hours respectively.
Due to these long OWLT, Observatory saf-
3.1.2 Dormant Periods ing and command loading and verification
concepts would be modified from missions
During the beacon-hibernation phase of with shorter OWLTs.
Cruise 2, the Observatory would be placed
in PS-H with the “green” beacon tone broad- 4.1 Observatory Safing
cast weekly for a 24-hour period centered
around the planned DSN contact. Each
During all cruise phases of this mission ex-
weekly DSN beacon contact would be
cept for the cruise from Earth to Jupiter
scheduled for 1.5 hours, although it is ex-
(Cruise 1), the Observatory would be placed
pected to take much less time for the DSN
in a PS-H state for long periods, relying
to receive and analyze the tone (less than
upon the ARF to determine the state of
45 minutes). These measures would be
health and report this state to the NH mis-
taken to cover any DSN or operations con-
sion operations center (MOC) via a beacon
tingency that might arise. For distances of
or telemetry. The ARF would report in three
less than 25 AU, the 34-m stations would be
different ways, “green” beacon tone, “red”
used to support beacon contacts. At dis-
beacon tone, or emergency telemetry by
tances of 25 AU and beyond, use of the 70-
commanding the Observatory to AS-EA.
m stations would be necessary to detect the
Many components would be turned off dur-
beacon tone. The “green” tone will not be
ing this phase, partly to reduce wear and
broadcast continuously to maximize the life-
partly to reduce risk.
time of the traveling wave tube’s cathode
filament. In the case of an onboard failure
4Within the ARF, conditions would be defined Consultative Committee for Space Data
that merit a “red” beacon tone. Definition of Systems (CCSDS) Command Operations
the conditions triggering a “red” beacon tone Procedure 1 (COP 1) protocol for TCTF up-
will be chosen carefully to maximize safety link verification. The Observatory Command
and minimize false or non-mission threaten- and Data Handling subsystem (C&DH) will
ing conditions that do not require operations accept the TCTF and its command contents
intervention. Because there are seven “red” after performing validity checks that include
beacon tones, if a “red” tone were received, a check of the TCTF sequence number. The
the mission operations team would have a entire TCTF would be rejected if any
good indication of the type of onboard frame/command check fails or the sequence
anomaly just from the particular tone re- number is not the one expected. The failure
ceived. of one telemetry frame would cause a re-
transmit request to be sent to the ground
Because DSN telemetry contacts would not and all subsequent telemetry frames to fail
be scheduled during the dormant periods of until the expected sequence number is re-
the cruise phases, it will be imperative that ceived. To mitigate this potential failure and
the ARF request for a telemetry contact be to increase the chances that the first attempt
done only when needed to avoid impacting to transmit the TCTFs to the NH Observa-
the DSN schedule. The seven “red” tones tory is successful, the ground station soft-
would be divided into priority categories, ware would be modified to include the ability
with not all “red” tones requiring immediate to send each TCTF up to “n” times. The NH
ground intervention. When ARF places the Observatory C&DH would accept only the
Observatory in AS-EA, ground intervention first valid expected TCTF and would ignore
must occur within 14 days or the ARF would other TCTFs with the same sequence num-
command the Observatory to AS-SA and ber. When OWLTs are short, TCTFs will
broadcast the highest priority “red” tones. routinely be sent one time. As the OWLTs
increase, the mission operations team would
4.2 Command Loading and have the ability to increase the number of
times the TCTFs are sent. It is expected that
Verification
no more than n = 3 will be used operation-
ally. Early in the mission, tests would be per-
The nominal uplink rate for the NH Observa-
formed to verify the sending and receipt of
tory will be 500 bps, with the capability of a
TCTFs at n > 1.
2000-bps rate when needed. It is expected
that at 2000 bps, the longest command load
Command load verification will be accom-
would take 15 minutes to radiate. 70-m
plished by loading the command and time
downlink rates for the Observatory would be
tag macros in a disabled state, commanding
variable, ranging from about 37 kbps at Jupi-
a dump of the onboard memory containing
ter to about 1000 bps at Pluto/Charon. While
the load and verifying the dump against the
these downlink rates limit telemetry data
expected image on the ground. After ground
return, especially at Pluto/Charon and be-
verification, commands would be sent to
yond, the largest telemetry delay would be
enable the macros and to enable the load
due to the OWLT. For this reason, ways to
transition autonomy rule, which would allow
decrease the number of OWLTs required for
activation of the new load when the current
loading commands on the Observatory were
load completes. This process requires a de-
explored.
lay of three OWLTs plus an OWLT to verify
the “command load enable” status. When
Nominally, the operations center ground
OWLTs reach a pre-determined duration,
station would send each telecommand
the command loading and verification strat-
transfer frame (TCTF) once to the DSN for
egy would be modified so that the command
upload to the Observatory. Each TCTF
load, verification, and enabling time is de-
would contain command or time tag macros.
creased to one OWLT plus an OWLT to ver-
Command macros contain individual com-
ify the “command load enable” status, and
mands; time tag macros contain the execu-
optimally would not span more than one 8-
tion time for each command macro. NH
hour DSN pass.
would implement a modified version of the
5With the modified strategy, the command pending on the current staffing need and
and time tag macros would be loaded with a Observatory events. In some cases this is
ground-calculated checksum. As part of the problematic and results in the requirement
C&DH acceptance of the command macro, that staff be experts in more than a few dis-
an onboard checksum would be performed ciplines in order to minimize staffing cost.
and compared to the ground-calculated
checksum uploaded with command macro. 6. DSN USAGE AND COST
Only if the checksums match would the
command macro be enabled. Furthermore, SAVINGS
the load transition autonomy rule would
allow activation of the new load only if all Both the 34-m and the 70-m DSN antenna
macros in the loaded range were reporting resources are heavily subscribed, and any
“enabled” (i.e., they have all passed the reduction in use would help ease this strain.
checksum compare.) At the end of the DSN This is especially true of the 70-m antenna
pass or the beginning of the next pass, the resources. Unfortunately, the distances of
command load “enabled” status is verified this mission require heavy reliance on the
via telemetry. The mission operations team 70-m resources to get the downlink rates to
also would have the ability to delay the support telemetry and data retrieval in a
dump of the on-board memory containing timely manner. After Jupiter, all DSN teleme-
the command load so that it corresponds to try passes would be run with the 70-m an-
the next scheduled DSN pass. When this tennas. By incorporating a beacon, the mis-
strategy is followed, the dump would be sion operations team would not have to rely
compared with the expected ground image, upon a DSN telemetry pass to ascertain the
and the command to enable the transitional health of the Observatory; the receipt of a
autonomy rule would be sent during this beacon tone via a DSN beacon pass would
second pass. This would result in the mis- give this information. Also, these DSN bea-
sion operations team having three strategies con passes would make use of the 34-m
to perform a command load and verification antennas out to 25 AU, thereby reducing this
choosing the strategy that best fits the mission’s 70-m antenna requirements. Cou-
OWLT delay and mission phase. ple these 70-m resource savings with the
fact that a DSN beacon pass would take
much less time (conservatively estimated at
5. MISSION OPERATIONS 1.5 hours) than scheduling one or more
CENTER STAFFING weekly 8-hour DSN telemetry pass, and the
DSN 70-m antenna usage would be de-
The lengthy periods spent with the Observa- creased by approximately 2274 hours.
tory in PS-H during Cruise 2 would allow for
a reduction in mission operations center 7. SUMMARY
staffing. An average of 5 operations center
staff per month would be needed to support
As currently planned, the NH mission would
operations for the first 2 years after Jupiter
be a long-duration mission with long
and then would decrease to 3.5 operations
OWLTs, both of which pose challenges to
center staff per month to support the remain-
the project budget and mission operations
ing years of Cruise 2 before the
team. Developing a concept of operations
Pluto/Charon phase begins. This translates
that meets these challenges early in the life
into significant savings compared with an
of the project would allow hardware and
average of about 9.5 operations center staff
software to be developed to support these
per month needed to support a more tradi-
concepts from the very beginning, saving
tional mission concept.
cost. Use of a beacon-hibernation mode
supported by an autonomy system with em-
Additionally, a staffing concept would be
phasis on simplicity and safing the Observa-
developed to allow sharing of staff among
tory for long periods of time would save in
Observatories with common onboard hard-
DSN usage, cost, and staffing. Co-locating
ware and ground systems. This allows a
mission operations centers for Observato-
pool of staff equally well versed in opera-
ries with common onboard hardware and
tions to move between Observatories de-
6common ground systems would allow staff 3A-N mode/state would be the typical con-
sharing between missions, decreasing costs figuration of the Observatory when in 3A
for both projects. Developing a strategy for mode. It would be used for instrument com-
command load verification that minimizes missioning and calibration, selected encoun-
OWLTs would decrease DSN usage and ter science observations, and optical naviga-
time devoted to command loading. In addi- tion.
tion, the ability of the ground station to send
telemetry frames more than once and the 3A-TCM mode/state would be entered via
Observatory to accept the first valid frame MOps ground command for G&C controlled
and wait for the next expected frame would TCMs and would be maintained only long
add additional robustness to Observatory enough to complete the TCM.
command loads.
AS-N mode/state would be the typical state
Many of the cost reductions would also add of the Observatory when in AS mode. Ex-
robustness and lessen risk to the mission. amples of its planned use are science ob-
Incorporating the beacon to support the servations not requiring 3A mode, checkout
beacon-hibernation concept and the ARF to activities not requiring 3A mode, and pre-
trigger the appropriate beacon tone when in cessions to maintain the HGA to Earth.
PS-H would reduce DSN usage and opera-
tions center staff. It also would reduce risk AS-TCM mode/state would be entered via
to the mission, as it would not be possible to MOps ground command for G&C controlled
maintain real-time contact with the Observa- TCMs and would be maintained only long
tory given the long light-time delays. Using enough to complete the TCM.
shared staff between common Observato-
ries and ground stations also would lessen AS-EA mode/state would be entered after
risk, as it would allow a larger pool of staff the occurrence of Observatory faults such
during inactive periods on both Observato- as low voltage sensing (LVS) or a loss of
ries, increasing team depth more than would communications. After 14 days, if no contact
normally be possible. has been made with the Observatory or if
internal reference is lost for 24 hours, the
8. APPENDIX autonomy rule facility (ARF) would time out
and would command the Observatory to AS-
A brief description of the NH Observatory SA mode/state.
modes and states is provided for clarifica-
tion. AS-SA mode/state would be entered only
when the Observatory cannot point to Earth
The NH Observatory would have three (loss of inertial reference capability) or after
modes of operation (three axis [3A], active an extended loss of communications (14 day
spin [AS], and passive spin [PS]) and six in AS-EA mode).
states (trajectory correction maneuver
[TCM], normal [N], hibernation [H], encoun- PS-N mode/state would be the typical state
ter [E], Earth acquisition [EA], and Sun of the Observatory while in PS mode. This
acquisition [SA]). There would be a total of mode/state would be used to transition the
ten mode/state combinations, since not all Observatory out of PS-H and verify that the
states are allowed in every mode, as shown Observatory subsystems are nominal before
in Table 2. transitioning to PS-TCM or an AS mode. In
PS-N, G&C would be on and operating in a
3A-E mode/state would be used for instru- passive state, i.e., not actively controlling the
ment pointing and scanning for science ob- spin axis. It also would be used during non-
servations. Autonomous exiting of this state active periods in Cruise 1 to save propellant.
is allowed only with the expiration of a long-
term backup timer (currently envisioned to PS-TCM mode/state would be entered via
be 14 days). Due to the propellant required MOps ground command and would be used
to maintain this state, it is used only when for MOps initiated and controlled TCMs,
required. spin-ups, and spin-downs. This mode/state
7would be maintained only long enough for 9. ACKNOWLEDGMENTS
the completion of these activities.
The authors gratefully acknowledge the
PS-H mode/state would be the mode/state support and dedication of all the scientists
used for journeys from Jupiter to Pluto (if on and engineers on the New Horizons team
a JGA trajectory) or from Launch + 1 year to whose efforts result in the realization of this
Pluto (if on the Pluto-direct trajectory), from concept of operation. Special mention is
Pluto to KBO 1, and from KBO 1 to KBO 2. made of the Deep Space Mission System
Most subsystems would be powered off (in- (DSMS) personnel supporting the New Hori-
cluding the G&C subsystem), and the pro- zons program at NASA’s Jet Propulsion
pulsion system latch valves would be Laboratory. Furthermore, we acknowledged
closed. The Observatory would remain in that it is due to the unyielding dedication and
PS-H mode/state except during the annual support of the Mission Principal Investigator,
checkout periods and for those precession Dr. S. Alan Stern, that this mission is well on
maneuvers occurring outside of the annual its way to becoming the first mission to
checkout period. Pluto/Charon despite various impediments
along the way.
Table 2 NH Observatory Modes and States
State Mode 10. REFERENCES
Active Passive
3-Axis
Spin Spin
TCM 3A- AS-TCM PS-TCM 1. DeCoste et al., “Deep Space 1 Technol-
TCM ogy Validation Report – Beacon Monitor
Normal 3A-N AS-N PS-N Operations Experiment,” Jet Propulsion
Hibernation Not Not PS-H
allowed allowed
Laboratory, California Institute of Technol-
Encounter 3A-E Not Not ogy. February 2000.
allowed allowed
Earth Not AS-EA Not
2. J. Spencer, M. Buie, L. Young, Y. Guo,
Acquisition allowed allowed
Sun Not AS-SA Not and A. Stern 2003. “Finding KBO Flyby Tar-
Acquisition allowed allowed gets for New Horizons,” Earth, Moon and
Planets 92, 483-491.
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