American Institute of Aeronautics and Astronautics

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Automated Spacecraft Conjunction Assessment at Mars and 

the Moon

David S. Berry1, Joseph R. Guinn2, Zahi B. Tarzi3, and Stuart W. Demcak4

California Institute of Technology, Jet Propulsion Laboratory, Pasadena, California, USA, 91109

Conjunction assessment and the related activity of collision avoidance are areas of 

current high interest in organizations that conduct space operations. Most current 

conjunction assessment activity focuses on the Earth orbital environment (spacecraft plus 

debris), however, Earth is not the only orbital domain in which there is interest in avoiding 

collisions in space. Several of the world's space agencies have satellites in orbit at Mars and 

the Moon, and additional future missions are planned. A question that has arisen at some 

recent mission reviews is the potential for collisions along the planned and/or current

spacecraft trajectory. While the intuitive probability of collisions in these sparsely populated 

environments is very low, the consequences of a collision are catastrophically high. Intuitive 

notions may also be faulty due to factors including (a) many orbits of scientific interest have 

similar characteristics, and (b) surface spacecraft using relay services require periodic 

flyovers that may be shared among several orbiters. Analytic approaches can provide much 

more certain assessments of the probability of collisions than can intuitive approaches. This

paper will describe the techniques used at the Jet Propulsion Laboratory to perform

conjunction assessment at Mars and the Moon. In brief, the method involves automatically 

initiating analysis scripts, automatically downloading ephemerides from the Deep Space 

Network portal, adding supplementary ephemerides for planned and/or non-operational 

missions, performing pairwise comparisons of various user selectable conjunction attributes, 

preparing reports, and communicating the results to interested parties. For each orbital 

environment, a unique set of process parameters is maintained. The techniques discussed are 

not unique to any specific orbital environment, so they could be utilized for any orbital 

environment where multiple spacecraft operations may be contemplated. The paper will also 

discuss future work (e.g., adding an option to produce output in Consultative Committee for 

Space Data Systems Conjunction Data Message format).

Nomenclature

OBJ = combined object radius

x = distance along major axis

xm = x component of projected miss distance

y = distance along minor axis 

ym = y component of projected miss distance

σx = major axis standard deviation for combined covariance

σy = minor axis standard deviation for combined covariance

I. Introduction

ONJUNCTION assessment and the related activity of collision avoidance are areas of current high interest in 

organizations that conduct space operations. Most current conjunction assessment activity focuses on the Earth 

orbital environment (spacecraft plus debris), however, Earth is not the only orbital domain in which there is 

 1 Program Area Manager, Mission Design & Navigation Section, M/S 301-121, AIAA Senior Member. 2 Deputy Section Manager, Mission Design & Navigation Section, M/S 301-121, AIAA Senior Member. 3 Engineering Graduate Student, Mechanisms & Mobility Section, M/S 303-422, AIAA Student Member. 4 Navigation Engineer, Mission Design & Navigation Section, M/S 264-282.

C
American Institute of Aeronautics and Astronautics

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interest in avoiding collisions in space. Specifically, several of the world's space agencies have satellites in orbit at 

Mars and the Moon, and additional future missions are planned for these orbital environments. This paper will 

examine the process of conjunction assessment that has been implemented at the Jet Propulsion Laboratory (JPL) for

these two principal non-Earth orbital environments as of 2012. A question that has arisen at some recent mission 

reviews is the potential for collisions along the planned and/or actual spacecraft trajectory, even though the number 

of spacecraft currently operating in or planning operations in these orbital environments is relatively small.

II. Non-Earth Orbital Environments With Potential for Spacecraft Collisions

A. Conjunction Assessment at Mars

The first non-Earth environment for which there was interest in conjunction assessment and collision avoidance 

is Mars, where the United States National Aeronautics and Space Administration (NASA) and the European Space 

Agency (ESA) have spacecraft in orbit and/or on approach. NASA operates the Mars Odyssey and Mars 

Reconnaissance Orbiter (MRO) missions at Mars, with the Mars Science Laboratory (MSL) on approach as this 

paper is being written. ESA operates the Mars Express (MEX) spacecraft. Since mid-2002, when the Mars Odyssey 

spacecraft joined the Mars Global Surveyor (MGS) in orbit at Mars, ad hoc collision avoidance studies have been

conducted on an occasional basis for the Mars environment. The frequency of collision avoidance studies increased 

when MEX arrived on scene in late 2003, however, the analyses continued to be run manually on an ad hoc basis.

The MRO aerobraking campaign in 2006 was also a major driver in conjunction assessment studies at Mars. During 

the aerobraking process, it was possible that MRO would cross the orbital paths of the three other operational 

spacecraft then at Mars or the two Martian moons, so a detailed collision avoidance strategy involving frequent 

conjunction assessments was developed.

1 Several agencies have recently announced interest in launching Mars 

missions (e.g., the Indian Space Research Organization (ISRO), Roscosmos, and the China National Space 

Administration (CNSA)), expanding the need for conjunction analysis in the future. The tracking data sources for 

Mars are presently the Deep Space Network (DSN) and the ESA Tracking Station Network (ESTRACK). Radar is 

not in use for tracking spacecraft at Mars.

B. Conjunction Assessment at the Moon

The second non-Earth environment for which there is major interest in conjunction assessment and collision 

avoidance is the Moon, where NASA has several spacecraft in orbit: the Lunar Reconnaissance Orbiter (LRO), 

GRAIL-A, GRAIL-B, ARTEMIS-P1, and ARTEMIS-P2. In addition, ISRO and the Japan Aerospace Exploration 

Administration (JAXA) have spacecraft in orbit at the Moon that are no longer actively being tracked (ISRO's

Chandrayaan-1 spacecraft, which failed in 2009, and the Ouna spacecraft, which was a sub-satellite of JAXA's

SELENE mission). The tracking data source for the Moon is presently the DSN. As at Mars, radar is not in use for 

tracking spacecraft at the Moon.

III. "MADCAP"

A process named "MADCAP" (MArs Deepspace Collision Avoidance Process) was developed at JPL to 

automatically and systematically examine various aspects of multiple spacecraft in orbit about Mars. MADCAP

originated in the scripts that were run on an ad hoc basis for the purpose of occasionally calculating close 

approaches at Mars, first between two NASA spacecraft (MGS, Odyssey), and subsequently between one ESA and 

two to three NASA spacecraft (MEX, MGS, MRO, Odyssey). When an analysis was desired, an ephemeris was 

requested from ESA for the MEX spacecraft, and the analysis program was run manually. However, given that it is 

planned that the Mars-orbiting spacecraft remain in operations for a number of years, this ad hoc analysis was

insufficient to properly understand the risk of potential collisions. Although the spacecraft are in relatively stable

science orbits, they are modified periodically, e.g., in order to adjust orbit phasing for relay operations. The 

spacecraft are also subject to the standard environmental perturbations (e.g., atmospheric drag, gravity, solar 

radiation pressure). Due diligence suggested that JPL navigators always be prepared to answer the "how close are 

the orbits?" question whenever asked rather than having to arrange an ad hoc analysis on short notice. Hence 

MADCAP, which was created by wrapping an automation and reporting framework around the scripting that had

been run manually in the past.

IV. Methodology

This section will discuss the principal aspects of the MADCAP method. MADCAP consists of a set of python 

and perl scripts that utilize JPL's MONTE next generation navigation software for infrastructure and essential 
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computation. The multi-script architecture is not critical to describing the high-level process so for simplicity the 

discussion here will treat MADCAP as it were a single script. Input parameters for the lower level scripts are created 

automatically by the top layer script, so effectively there is only a single parameterization accessible to the user. 

After initialization, the script autonomously accesses the DSN Service Preparation Subsystem (SPS) portal and 

downloads the latest ephemerides for the spacecraft specified in a parameter file. Using these ephemeris files, and 

optionally adding some supplementary ephemerides for planned and/or non-operational missions, various user 

selectable attributes of the orbits of the spacecraft are pairwise analyzed. Output tables containing collision metrics

for each spacecraft pair are created. If the value of a given attribute for a pair of spacecraft is less than a user 

specified minimum threshold (e.g., the minimum close approach distance) then a notification email is sent to a list of 

addresses specified in a parameter file. A summary file of the results of all closest approach distance analyses is also 

produced. Plots of a few conjunction attributes can also be generated.

The next several sections discuss the key aspects of the MADCAP methodology in greater detail.

A. Parameterization

Although its roots are at Mars, as noted above MADCAP is also used to analyze conjunctions at the Moon. The 

principal features that allow MADCAP to be used for conjunction assessment in orbital environments other than 

Mars are (a) the general purpose nature of the MONTE software, and (b) the use of a parameter file containing 

inputs to be used by the script. The main parameters that establish the orbital environment are the specification of 

the central body and a list of at least two spacecraft (or other bodies including natural satellites or debris). For each 

orbital environment, a unique set of process parameters is maintained depending on the preferences of the mission 

management and the navigation teams involved at that environment. Several parameters are provided that allow 

detailed specification of the ephemeris files that should be used in the analysis (see "Ephemeris Files" below).

In a given parameter file, the user must specify the conjunction attribute upon which the analysis will be 

performed (e.g., the relative distance and speed at closest approach), along with the threshold that will trigger the 

user notification process. Other key parameters specify a list of data items that should be analyzed and 

printed/plotted and several parameters for use in calculating the probability of collision (coordinate system, the radii 

of the objects in kilometers (km), constant covariance sigmas (in km) and the covariance reference frame). The 

covariance sigmas are constant in the initial version of MADCAP because the true covariance data is not contained 

in the Spacecraft Planetary Kernel (SPK) ephemeris files available on the DSN Portal.

There are also several parameters used to specify directories to which ephemeris files should be downloaded, 

where to find a second file for a given spacecraft if it is desired to perform the analysis on more than one trajectory

for the same spacecraft, and a directory where the output reports will be archived. Finally, there is a parameter that 

allows one or more email addresses to be specified for delivery of MADCAP reports.

B. Analysis Scripts/Automated Initiation

MADCAP is activated by a Linux cron job on a schedule that is based on the ephemeris update frequency of the 

spacecraft operating in the environments under study. It is currently scheduled to run automatically twice weekly in 

the case of Mars, and daily in the case of the Moon. The script can also be initiated manually from the Linux 

command line by executing the script and passing it the required parameter file if an analysis is desired outside the 

automation framework.

C. Ephemeris Files

Ephemeris files for the spacecraft in the parameter list are automatically downloaded from the DSN's SPS Portal, 

which is the source of the ephemeris files used in predicts generation for all DSN tracking. Automated access to the 

ephemeris repository is desirable because the multiple teams involved in navigating the various spacecraft upload 

their updated ephemeris files on a schedule that makes sense for their spacecraft, with no coordination required

among the teams. MADCAP receives a listing from SPS that itemizes the available ephemeris files for each 

spacecraft specified in the parameter file, parses the list to select the ephemeris for each spacecraft that was most 

recently submitted by each of the navigation teams, then downloads and stores it in the location defined by the user 

in the input file. The most recent ephemeris file for each spacecraft is selected based on the largest SPS file ID,

which monotonically increases with time. 

However, not every ephemeris file that is desirable for conjunction analysis is uploaded to the DSN SPS. 

MADCAP also provides a means in the parameter file to indicate that an ephemeris should not be downloaded from 

SPS for special cases; if the spacecraft is not currently being tracked by the DSN, there may not be an ephemeris on 

SPS. For example, ephemeris files for ISRO's Chandrayaan-1, JAXA's Ouna, and NASA's Viking and MGS orbiters

are not currently uploaded to the SPS. These spacecraft are no longer operational, but they are still in orbit and can 
American Institute of Aeronautics and Astronautics

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be used in analyses if an appropriate ephemeris is available. Ephemeris files for non-operational spacecraft can be 

added by specifying an ephemeris file location in one of the MADCAP parameters. Though the uncertainty of the 

states in such ephemerides is greater than that of current solutions, these long term predictions are better than 

nothing. The trajectory being used for Chandrayaan-1 is based on the best quality reconstruction created by JPL 

Navigation using data primarily from the DSN and from the Johns Hopkins University Applied Physics Laboratory 

(APL) tracking station. The trajectory being used for Ouna was propagated at JPL using the Mean Elements Long 

Term Propagator functionality within JPL's MONTE navigation software based on orbital elements provided by 

JAXA. The Viking and MGS trajectories are not included in present analyses, but preparations to add them to the 

Mars environment parameters in the near future are underway.

In addition, sometimes navigation teams wish to include both a current solution and a longer term reference 

trajectory in the analysis. MADCAP also allows a user to optionally specify one supplementary file per spacecraft 

that will be used in addition to the most recent trajectory file downloaded from the SPS.

Note that natural body ephemerides (e.g., a natural planetary satellite) may also be specified for analysis. For 

example, at Mars, close approaches of spacecraft to the natural satellites Phobos and/or Deimos may be of interest.

D. Orbit Comparisons

MADCAP performs pairwise comparisons for all combinations of two spacecraft [ !

! = !!

(!!!)!!!

], where "n" is 

the number of spacecraft listed in the parameter file. Comparisons occur over the duration of the overlapping time 

period of the two ephemeris files analyzed. A variety of conjunction attributes may be selected for analysis, as listed 

in Table 1.

Table 1. MADCAP Orbit Conjunction Attribute Options

Conjunction Attribute Description

closap_times Times of closest approaches of the two bodies

closap_distance Relative distance and speed at closest approach

closap_angles Angles between velocity vectors and orbit planes with respect to central body

closap_state_diff State of spacecraft 2 relative to spacecraft 1

closap_states States of both spacecraft with respect to central body and coordinate system

xing_distance Distance between orbits at orbit crossings

xing_distance_min Smaller of orbit crossing distances

xing_times Times of orbit crossings

xing_times_min Times of minimum orbit crossing

xing_traj Radius and true anomaly at orbit crossings

xing_traj_min Radius and true anomaly at minimum orbit crossing

mod_distance Minimum orbit distances (useful for nearly coplanar orbits)

mod_distance_min Smaller of two minimum orbit distances 

mod_times Times of minimum orbit distances

mod_times_min Times of smaller of two minimum orbit distances 

mod_traj Radial distance and true anomaly at minimum orbit distances

mod_traj_min Radial distance and true anomaly at smaller of two minimum orbit distances 

col_prob Collision probability for specified covariance

The threshold values for the conjunction attribute of interest can be set differently for each spacecraft in the 

analysis by use of the threshold parameters. If the thresholds for two spacecraft being compared are different, then 

the maximum value of the two thresholds is used in the analysis, giving more conservative results.
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E. Output Reports

MADCAP prepares various reports, which are written to file. Three types of reports are produced: detail, 

summary, and plots.

A detailed output table is created for each pair of spacecraft analyzed. The output tables contain the results of 

analysis of the conjunction attributes specified by the user, and are sorted by the conjunction attribute desired by the 

user. Each line in the output table will contain the information on the conjunction attributes requested in the 

parameter file. Depending on the amount of overlap between the two ephemeris files in the comparison, these 

detailed reports can be quite long. A sample detailed report is shown in Appendix B, Figure 1.

The summary report focuses on the "close approach distance" attribute, and categorizes the close approaches as 

green, yellow, or red depending on the magnitude of the close approach. The thresholds for these categorizations are 

established by the navigation team chiefs for the missions operating in the Mars and Lunar orbital environments. 

Those conjunction events categorized as red have two sections in the summary report. In one section appear all the

red conjunctions predicted for a user selectable future time period (e.g. 14 days), and in a separate section 

immediately following the first appears the first red conjunction (if any) for each spacecraft pair throughout the 

overlap period between the two ephemerides. Conjunctions rated as green are generally not printed in the summary 

report. A sample summary report is shown in Appendix B, Figure 2.

MADCAP will also generate plots of several of the conjunction attributes if requested by the user, specifically, 

relative distance at closest approach, minimum orbit crossing distances, and/or minimum orbit distances. Included in 

the MADCAP parameter list are optional x-axis and y-axis limits for plots generated by MADCAP. A sample plot is 

shown in Appendix B, Figure 3.

F. Communicating Results

The MADCAP parameter file contains a list of email addresses to which the output reports will be sent; these are 

nominally fixed group email addresses that can be modified independently without having to change MADCAP 

parameters. Accommodations are made for normal engineering reporting and for management escalation reporting.

G. Decision Process

Current spacecraft in the Mars and Moon environments normally maintain a safe separation. However, 

occasional close approaches with low miss distance have warranted some escalation of communication and 

discussion as to whether any action was in fact necessary. At present no official decision-making process has been 

established for handling these events, but future work plans include the development of procedures and standards.

V. Collision Probability

Based on an argument from intuition, the probability of collisions in the sparsely populated Mars and Moon

orbital environments is very low (effectively zero). However, the consequences of collision are catastrophically 

high: millions to billions of dollars/euros/yen/etc. in lost tax revenue investment, irreparable loss of science data, and 

the creation of a debris environment in otherwise pristine orbital environments are three obvious consequences. The 

international repercussions of spacecraft from two different nations/agencies colliding would also very likely be 

undesirable. Given world economy, spacecraft collisions and the resultant waste of tax revenue can potentially lead 

to reduced popular support for the world's space agencies, the many benefits of space exploration notwithstanding. 

Intuitive notions regarding collision probability may also be faulty due to other factors. For example, many 

orbits of scientific interest have similar characteristics (e.g., equatorial orbits, polar orbits, sun-synchronous orbits, 

body-synchronous orbits, etc.). Also, particularly at Mars since 2004, surface spacecraft such as the Mars 

Exploration Rovers or the Mars Science Laboratory use relay services that require periodic flyovers in order to 

transmit science and engineering data. These flyovers may be shared among several orbiters such as MRO, Mars 

Odyssey, and MEX. Analytic approaches can provide much more certain assessments of the probability of collisions 

than can intuitive approaches. The problem of analyzing collision probability has been studied extensively in the 

Earth environment (see, for example, References 2 through 8), and similar analytic approaches can be utilized in 

other orbital environments where the potential for spacecraft collisions exists. After considering several different 

approaches to calculating the collision probability, an advisory group selected for MADCAP a technique based upon 

equation (1) of Reference 2:

P = 1

2 !! !" x !" y

! "OBJ

OBJ

# exp " OBJ2"y

2

OBJ2"y

2

# {("1

2 )![(x + xm" x

)

2

+(y + ym

" y

)

2

]}dxdy

 (1)
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"At the time of closest approach, a projection is done onto the plane perpendicular to the relative velocity (often 

called the collision plane), thereby reducing the dimensional complexity from three to two. For convenience, the 

axes of the collision plane can be aligned to correspond with the major and minor axes of the projected, combined, 

error ellipse."2

Assessing the probability of collision requires at minimum the trajectories of the spacecraft under study, 

estimates of the uncertainty in those trajectories, a common reference frame, and a model of the spacecraft. 

Trajectory uncertainties are generally provided via a covariance matrix; MADCAP has parameters that express 

constant covariance sigmas (in km) given that the actual covariance information is not available in the SPK 

ephemeris files. MADCAP accommodates two reference frames ("RTN" for the spacecraft radial-transverse-normal 

frame, and "XYZ" for the Cartesian frame). If the trajectories of the two spacecraft are not in the same reference 

frame, then the states in one of the trajectories need to be rotated into the frame of the other. The model of the 

spacecraft is assumed to be spherical so as to not require attitude information; the actual radius of the sphere (in km)

may perhaps be enlarged by a "keep-out zone".

VI. Future Work

The development of MADCAP has been conducted using portions of several small budgets applicable to 

multimission software and operations, and it has grown in a "semi-organic" manner. While already useful, it has not 

yet reached its full potential. MADCAP has a number of areas where future work would be beneficial. Future work 

is anticipated in several areas as follows:

1) Determining the response when close approaches are "too close" has not yet been formalized. At the NASA 

Goddard Space Flight Center (GSFC), there is a well defined Collision Avoidance Risk Assessment 

(CARA)9 process that is followed in the event that a close conjunction is predicted in the Earth orbital 

environment. Such measures are not presently formalized at JPL, but are executed on a case-by-case basis. 

Development of a standard response is desirable.

2) True covariance information needs to be added to improve the collision probability computation. As noted 

above, the covariance matrix data is not available in the SPK file structure, and "default" covariances are 

presently used; these are established based on the experience of the navigation team for the particular 

spacecraft. Incorporating "true" covariance information will require future work and will make the 

probability calculation more accurate. A change in the collision probability formulation may also be 

necessary.

3) Collaboration with GSFC, which is chartered by NASA with the conjunction assessment function for Earth 

orbiting satellites10, would be desirable. Such a collaboration might focus on comparing techniques, process 

improvements based on technical interchange, cost-sharing, and formal division of labor (e.g., allocating 

the responsibility for conjunction assessment to JPL if the DSN is used to track the objects, or GSFC if

Space Network/Near Earth Network and/or the United States Strategic Command (USSTRATCOM) is 

used to track the objects). Collaboration with ESA's Space Situational Awareness program11 may also be a 

possiblity.

4) More sophisticated automation features than Linux "cron" are under consideration. Event driven 

automation may be feasible given that the SPS provides an email message when a new ephemeris file is 

accepted into its repository. MADCAP could subscribe to the messages from SPS and kickoff an analysis 

run any time an ephemeris for one of the specified spacecraft is uploaded by a navigation team. Also 

possible is incorporating MADCAP into a more general purpose automated ground navigation system that 

is currently being prototyped at JPL, in which case a process of polling SPS for the most current 

ephemerides would likely be implemented.

5) There are other current shared orbital environments of potential (though lesser) interest, specifically, the 

Sun-Earth Lagrange Points L1 and L2. At L1, NASA's Advanced Composition Explorer (ACE) and WIND 

spacecraft orbit, as does ESA's Solar and Heliospheric Observatory (SOHO) mission. At L2, NASA's 

defunct Wilkinson Microwave Anisotropy Probe (WMAP) spacecraft, CNSA's Chang'e 2, and ESA's 

Herschel and Planck satellites orbit. L2 is also the destination of NASA's future James Webb Space 

Telescope (JWST). The L1 and L2 environments are quasi-stable and objects in these environments use 

halo or Lissajous orbits about the Lagrange point; because of the instability there is a need for orbit 

maintenance on a regular basis. An offset from L1 is also necessitated by the fact that the radio telescopes 

pointed directly at L1 also point directly at the Sun, so the radio interference would be prohibitive for 

tracking. Currently analysis of spacecraft orbits at Sun-Earth L1/L2 are not automated, though they could 
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easily be (for the Sun-Earth L1 environment, an experimental parameter file setup by one co-author took 

less than an hour). In the future, Earth-Moon L1/L2 may also become orbital environments of interest for 

conjunction assessment given current discussions regarding their use as destinations for human missions 

and/or far-side relay.

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6) In the not too distant future, it is anticipated that an international standard now in development by the 

Consultative Committee on Space Data Systems (CCSDS) will be available for communicating information 

about predicted conjunctions, specifically, the CCSDS Conjunction Data Message (CDM)13. This new 

message builds on the CCSDS Orbit Data Message standard already in use among many satellite operators.

The CDM is an evolution of USSTRATCOM's recent efforts to share conjunction data; to meet the need of 

commercial and non-US satellite operators for actionable satellite conjunction geometry data, 

USSTRATCOM began sharing a Conjunction Summary Message (CSM) in July 2010. In October 2010, a 

collaboration with the CCSDS on an international standard message format was initiated. The goal of this 

collaboration is the CDM, which is targeted to eventually replace the CSM. Since its inception in October 

2010, the CCSDS CDM draft standard has matured rapidly. Coordination to date of this international 

standard has involved achieving consensus by the international community on the content and format of the 

information deemed necessary for mitigating the consequences of satellite conjunctions. As of April 2012, 

the CDM is in the final stages of the CCSDS Standards Development Process14 (at the time of this writing 

it is a "Red Book", which means that it has been made available for international review and comment).

The CDM is primarily targeted towards implementation in the densely populated Earth orbital 

environment, however, provision is made within the standard to report conjunctions detected in orbital 

regimes other than Earth. It is anticipated that as part of the prototyping effort required by the CCSDS 

Standards Development Process, the option to select a CDM as a MADCAP output format will be made 

available. Once the CDM is completed, agencies and industry alike can use a common international 

standard to understand the nature of the geometry of a pending conjunction and decide on an optimal 

maneuver plan, if necessary. In the future, any organization that can detect a conjunction could send a 

CCSDS CDM to warn a satellite operator. That operator could receive multiple warnings from multiple 

detectors, but the format of the warnings would be standardized, thus simplifying their integration and the 

necessary decision-making process.

VII. Conclusion

The techniques used at JPL for automated conjunction assessment at Mars and the Moon using MADCAP have 

been presented. The processes that have been implemented are not unique to any specific orbital environment, so 

they could be utilized for any orbital environment where operations of at least two spacecraft may be contemplated.

MADCAP is currently in daily operation, and because of this current users are generating a number of ideas to 

improve it. Potential future work to enhance the current baseline operation has been outlined. The relatively near

future likely holds the prospect of additional spacecraft at Mars, the Moon, Earth-Sun-L1/L2, and Earth-MoonL1/L2. MADCAP can be used in all of these multi-spacecraft environments to ensure a safer orbital environment for 

all.
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Appendix A

Acronym List

ACE Advanced Composition Explorer

APL Johns Hopkins University Applied Physics Laboratory

CARA Collision Avoidance Risk Assessment

CCSDS Consultative Committee for Space Data Systems

CDM CCSDS Conjunction Data Message

CNSA China National Space Administration

COLA collision avoidance

CSM Conjunction Summary Message (United States Strategic Command)

DSN Deep Space Network

ESA European Space Agency

ESTRACK ESA Tracking Station Network

GSFC Goddard Space Flight Center (NASA)

ID file identifier (SPS)

ISRO Indian Space Research Organization

JAXA Japan Aerospace Exploration Agency

JPL Jet Propulsion Laboratory

JWST James Webb Space Telescope

km kilometers

Ln Lagrange Point "n" (n ∈ {1,2,3,4,5})

LRO Lunar Reconnaissance Orbiter

MADCAP MArs Deepspace Collision Avoidance Process

MEX Mars Express

MGS Mars Global Surveyor

MRO Mars Reconnaissance Orbiter

MSL Mars Science Laboratory

NASA National Aeronautics and Space Administration

RTN Radial-Transverse-Normal

SOHO Solar and Heliospheric Observatory

SPK Spacecraft Planetary Kernel

SPS Service Preparation Subsystem (DSN)

URL Uniform Resource Locator

USAF United States Air Force

USSTRATCOM United States Strategic Command

WMAP Wilkinson Microwave Anisotropy Probe
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Appendix B

Sample MADCAP Reports

# Table of closest approach events for 'SC01' and 'SC02'

# Begin Time: 27-APR-2012 00:55:27.0000 TAI

# End Time: 10-MAY-2012 00:01:06.1840 ET

# Central Body: Moon

# Coordinate System: IAU Moon Pole

# Output Time System: UTC (UTC-ET = -66.1855 sec [at begin time])

# Ephemeris files supplied by user:

# /home/common/scripts/inputs/ephemerides/de421.boa

# /home/moon/scripts/inputs/ephemerides/de421_Lunar.boa

# /home/moon/scripts/inputs/ephemerides/spk_sc1_120424_120510_120425_od123v1.bsp

# /home/moon/scripts/inputs/ephemerides/spk_sc2_120423_120510_120425_od234v1.bsp

# /home/moon/scripts/inputs/ephemerides/spk_sc2_14day_20120426_01.bsp

#

# Calendar Julian R E L A T I V E Collision

# Date Date (days) Distance (km) Speed (km/s) Probability

06-MAY-2012 11:31:03.547 2456053.97990 14.05064 2.89753 0.00587

01-MAY-2012 10:23:40.970 2456048.93311 28.22475 2.90483 0.00229

03-MAY-2012 02:07:21.064 2456050.58844 55.77511 2.89525 0.00007

08-MAY-2012 03:14:48.459 2456055.63528 98.52263 2.89337 0.00000

04-MAY-2012 19:47:24.982 2456052.32459 101.18978 2.89296 0.00000

09-MAY-2012 20:54:47.876 2456057.37139 106.70121 2.89202 0.00000

04-MAY-2012 18:48:55.329 2456052.28397 117.16007 2.78184 0.00000

09-MAY-2012 19:55:59.805 2456057.33055 123.63937 2.77510 0.00000

06-MAY-2012 10:32:28.335 2456053.93922 156.52384 2.78277 0.00000

08-MAY-2012 04:12:23.166 2456055.67527 157.77379 2.77459 0.00000

01-MAY-2012 09:25:18.583 2456048.89258 161.40894 2.78341 0.00000

03-MAY-2012 03:05:11.955 2456050.62861 162.27488 2.78455 0.00000

09-MAY-2012 18:58:25.709 2456057.29058 178.92676 2.89047 0.00000

04-MAY-2012 17:51:02.803 2456052.24378 178.94706 2.89263 0.00000

08-MAY-2012 05:11:11.591 2456055.71611 184.02384 2.90152 0.00000

08-MAY-2012 02:16:15.138 2456055.59462 208.21421 2.78206 0.00000

03-MAY-2012 01:09:04.252 2456050.54797 209.51074 2.78897 0.00000

06-MAY-2012 12:28:35.422 2456054.01985 209.66565 2.78080 0.00000

01-MAY-2012 11:21:24.605 2456048.97320 211.00835 2.78628 0.00000

03-MAY-2012 04:03:45.035 2456050.66927 225.18690 2.90283 0.00000

01-MAY-2012 08:27:18.702 2456048.85230 254.57115 2.91349 0.00000

06-MAY-2012 13:27:26.398 2456054.06072 267.06229 2.91237 0.00000

Figure 1. Sample MADCAP Detail Report (sort by Relative Distance, Ascending)
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Collision Analysis was performed between SC01, SC02, SC03, SC04, SC05, and SC06 using 

the following ephemerides:

SC01.SHORT.oem.bsp_V0.634 28-FEB-2012 00:00:00 UTC - 17-MAR-2012 00:00:00 UTC

SC01.LONG.oem.bsp_V0.19 (Ref) 18-FEB-2012 00:00:00 UTC - 12-FEB-2013 00:00:00 UTC

SC02.SHORT.oem.bsp_V0.637 28-FEB-2012 00:00:00 UTC - 17-MAR-2012 00:00:00 UTC

SC02.LONG.oem.bsp_V0.17 (Ref) 18-FEB-2012 00:00:00 UTC - 01-AUG-2012 00:00:00 UTC

spk_SC03_jpl-nam-tpm.bsp 31-MAY-2010 23:58:53 UTC - 31-DEC-2013 23:58:53 UTC

spk_SC04_noburn.bsp 21-FEB-2012 08:00:00 UTC - 29-FEB-2012 23:59:59 UTC

spk_SC05_reference_traj.bsp (Ref) 24-FEB-2012 17:15:00 UTC - 05-JUN-2012 07:11:50 UTC

spk_SC05_od108v1.bsp 26-FEB-2012 13:00:00 UTC - 07-MAR-2012 23:59:59 UTC

spk_SC05_reference_traj.bsp (Ref) 24-FEB-2012 17:30:00 UTC - 05-JUN-2012 07:11:11 UTC

SC06-short_01.bsp 28-FEB-2012 00:00:00 UTC - 13-MAR-2012 00:00:00 UTC

SC06-long.bsp_V0.1 (Ref) 18-FEB-2012 00:00:00 UTC - 20-OCT-2012 00:00:01 UTC

The following body pairs have a status RED close approach event in less than 14 days:

SC04-SC05 (SC04 Ref) 19.76 km 01-MAR-2012 00:49:18 UTC

SC04-SC05 (SC04 Ref) 10.26 km 01-MAR-2012 02:43:52 UTC

SC04-SC05 (SC04 Ref) 0.80 km 01-MAR-2012 04:40:43 UTC

SC04-SC05 (SC04 Ref) 1.27 km 01-MAR-2012 05:20:46 UTC

SC04-SC05 (SC04 Ref) 8.42 km 01-MAR-2012 06:56:27 UTC

SC04-SC05 (SC04 Ref) 18.13 km 01-MAR-2012 08:46:52 UTC

SC04-SC06 (SC04 Ref) 11.63 km 03-MAR-2012 14:37:48 UTC

SC04-SC06 (Both Ref) 11.82 km 03-MAR-2012 14:37:48 UTC

SC05-SC06 (SC05 Ref) 11.83 km 10-MAR-2012 07:27:40 UTC

SC05-SC06 (Both Ref) 12.39 km 10-MAR-2012 07:27:40 UTC

The following body pairs are status RED (closap_distance <= 20 km):

SC04-SC05 (SC04 Ref) 0.80 km 01-MAR-2012 04:40:43 UTC

SC04-SC06 (SC04 Ref) 11.63 km 03-MAR-2012 14:37:48 UTC

SC04-SC06 (Both Ref) 11.82 km 03-MAR-2012 14:37:48 UTC

SC05-SC06 (SC05 Ref) 11.83 km 10-MAR-2012 07:27:40 UTC

SC05-SC06 (Both Ref) 10.13 km 26-MAY-2012 23:31:33 UTC

The following body pairs are status YELLOW (20 km < closap_distance <= 200 km):

SC04-SC06 137.29 km 29-FEB-2012 07:10:33 UTC

SC04-SC06 (SC06 Ref) 136.78 km 29-FEB-2012 07:10:33 UTC

SC03-SC06 39.24 km 29-FEB-2012 10:10:08 UTC

SC03-SC06 (SC06 Ref) 39.45 km 29-FEB-2012 10:10:08 UTC

SC04-SC05 28.57 km 29-FEB-2012 22:55:07 UTC

SC05-SC06 23.99 km 01-MAR-2012 22:54:45 UTC

SC05-SC06 (SC06 Ref) 23.98 km 01-MAR-2012 22:54:45 UTC

SC03-SC05 129.79 km 04-MAR-2012 11:32:00 UTC

SC01-SC05 (Both Ref) 175.00 km 26-MAR-2012 03:21:24 UTC

SC01-SC06 (Both Ref) 186.87 km 11-APR-2012 02:26:47 UTC

SC01-SC02 (Both Ref) 190.13 km 23-APR-2012 18:04:30 UTC

SC03-SC05 (SC05 Ref) 118.59 km 24-APR-2012 19:25:44 UTC

SC01-SC04 (Both Ref) 157.92 km 18-MAY-2012 20:09:11 UTC

SC03-SC04 (SC04 Ref) 116.37 km 22-MAY-2012 23:03:05 UTC

SC04-SC05 (SC05 Ref) 45.17 km 05-JUN-2012 06:18:10 UTC

SC04-SC05 (Both Ref 45.17 km 05-JUN-2012 06:18:10 UTC

SC01-SC03 (SC01 Re) 68.86 km 27-JUN-2012 20:06:28 UTC

The collision metric tables and plots have been archived in: /COLA/MADCAP/Moon/archive

Figure 2. Sample MADCAP Summary Report (Sort by Close Approach Date)
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Figure 3. Sample Mars Collision Metrics Plot.

 SC01 SC02 

SC02

SC02
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Acknowledgments

The authors thank members of JPL's Mission Design and Navigation Section who contributed to the 

requirements development and incremental improvement of the MADCAP, particularly those involved in the 

ongoing navigation operations of the Mars Odyssey, Mars Reconnaissance Orbiter, and GRAIL spacecraft.

This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, 

California, under contract to the National Aeronautics and Space Administration. Clearance number CL#12-1952.

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