The Deep Space Catalog - Catalog Description

Jonathan C. McDowell

Aug 2020: Rev 1.0.8

The Catalog

I have compiled a catalog of over 1000 artificial objects in `deep space'. Version 1.0 of this catalog has been released online at

By deep space, I mean broadly space beyond the region where the US satellite catalog provides coverage. Note that the term has been used with a variety of definitions. In the context of the SGP4 orbit model [3], `deep space' refers to orbital periods above 225 minutes, corresponding to altitudes of about 5900 km, a region normally thought of as `medium Earth orbit' these days. For our purposes a boundary somewhere beyond 50,000 km seems needed. It also appears desirable to exclude communications satellites on supersynchronous transfer orbits which have apogees typically in the 60,000 to 100,000 km range.

For definiteness I adopt a boundary I call [14] EL1:4, the Earth-lunar 1 to 4 orbit resonance in which a satellite in a circular orbit will complete four revolutions of the Earth for every one that the Moon does. EL1:4 is at 152066 km from Earth's center. The choice is motivated by the idea that satellites well within this distance can to first order ignore the Moon and be regarded as being in simple Keplerian orbits on short timescales (clearly, even much closer in at GEO, lunisolar perturbations are important on longer timescales). Satellites at this distance or beyond are more strongly affected by lunar perturbations and should be considered as part of a three-body system. This distinction is obviously not a sharp one and is somewhat arbitrary but it seems as good as any. It also echoes the Sun-Jupiter 1 to 4 resonance which approximately marks the inner edge of the asteroid belt and which serves as a good candidate for a boundary between the inner and outer solar system.

The main catalog table (Table I)

The core of the catalog is a table of artificial objects (the `object table') which have at some time been further from the Earth than the EL1:4 distance. For each object, I provide the launch date, one or more names, the international designation of the launch, a deep space catalog ID, and a standard catalog ID.

The standard catalog ID requires more explanation. For some objects, a US Satellite Catalog number exists. In this case, the standard catalog ID is that number, prefixed by the letter S. However, a significant number of known artifical space objects, both near-Earth and deep space, don't appear in the US Satellite Catalog. To provide a systematic way of referring to these I have created an `auxiliary catalog' with standard IDs prefixed by the letter A. This auxiliary catalog is also in preparation for publication.

As an example: Deep space catalog entry D00967 is the Lisa Pathfinder spacecraft. Its standard catalog ID is S41043, reflecting its catalog number in the official US catalog. Deep space catalog entry D00968 is the Lisa Pathfinder Propulsion module. Its standard catalog ID is A08465, reflecting its entry in the auxilary catalog since it was never added to the US catalog. Note that the A catalog numbering is entirely separate from the S catalog, so A08465 has no connection to US catalog entry S08465, a debris object from a 1975 Soviet satellite.

The D catalog numbers are in order of assignment, with a few exceptions due to backfilling deleted entries. In particular, the numbers are often in chronological order but NOT always, so you should not depend on this.

The columns in the object table are shown in Table D.I, Object Table Description, below. In the catalog, countries and owner organizations are identified using a standard set of alpanumeric codes whose meaning is given in a separate Organizations table, maintained on the author's website [15].

Table D.I Object Table Description
Column NameDescription
DeepID Sequence - D0001 onwards
StdID Entry in US catalog or in auxilary catalog
IntDes COSPAR international designation of launch
LDate UTC launch date
Name Name used by owner agency
AltName Alternate name for object
Owner Code for owner organization
State Code of owner country
Mass Launch mass of object, kg
DryMass Dry mass of object, kg
Length Longest dimension of main body of object, m
Diam Shortest dimension of main body of object, m
Span Longest dimension of object including antennas, etc., m

The Hill Sphere

The remainder of the catalog treats the time history of each object as a series of mission phases. In this context, a phase is a time interval when either (1) the object may be considered as moving under the gravitational influence of a given astronomical body or (2) the object is on the surface of such a body. Here we introduce the concept of the Hill gravitational sphere of influence [16]. Consider a spacecraft moving in the joint gravitational field of the Earth and the Sun. Close enough to the Earth, we may neglect the Sun's gravity and treat it as being in Earth orbit. Far enough from Earth, and we can ignore our home world and treat the spacecraft as being in solar orbit. The Hill sphere is the boundary at which it becomes better to pick one case over the other. In general for small body B of mass m(B) orbiting big body A with mass m(A) at an orbital radius R, and a spacecraft feeling the gravity of both of them, it is a better approximation to calculate a B-centered orbit rather than an A-centered orbit if its distance r to B satisfies

r < (m(B)/ 3m(A))1/3 R

There's another popular definition of the sphere of influence, the Laplace sphere, which is useful when considering points at rest with respect to the body B. The Hill sphere is more appropriate for objects moving in orbit, the case we are considering here. The well-known L1 and L2 Lagrange points lie on the Hill sphere. Note that in this discussion by `orbit' I include unbound (hyperbolic) as well as bound (elliptical) orbits.

The mission phase table (Table II)

The mission phase table contains entries for each contiguous period for which an object is in orbit around a particular body.

Table D.II Mission Phase Table Description
Column NameDescription
DeepID Sequence - D0001 onwards
Name Name, repeated from Table I
Phase Sequential phase number for object
Body Central body
PStart UTC Start time of phase
PEnd UTC End time of phase
Dest Status at end of phase
Epoch Epoch of orbital data
Orbit Representative orbital data for phase

The PEnd column is in general the PStart of the next phase, if any. A phase can start by crossing a Hill sphere boundary so that the object is in orbit around a new body, or it can start when the object separates from a parent object to which it was previosly attached (e.g. the separation of a lander from an orbiter). A new phase is also started at periapsis of a hyperbolic encounter (flyby), a planetary orbit insertion or an orbit escape burn.

As a simple example in Example I we consider the Mars Insight spacecraft, listing only the key data. The probe passes the EL1:4 boundary on May 5, leaves the Earth's Hill sphere on May 10, remains in solar orbit until arriving in Mars' Hill sphere on Nov 22, and lands on Mars Nov 26. Each of these phases requires a different form of trajectory data (relative to a different central body, or a surface position).

Example I - Mars Insight
D00997 Mars InSight Lander 0 Earth 2018 May 5 1105 Launch from VS SLC3E by Atlas V 401
D00997 Mars InSight Lander 1 Earth 2018 May 5 1105 2018 May 5 1238 Separated from launch vehicle
D00997 Mars InSight Lander 2 Earth 2018 May 5 1238 2018 May 5 2153 Entered deep space 2018 May 5 115 x -110126 x 63.54
D00997 Mars InSight Lander 3 Earth 2018 May 5 2153 2018 May 10 2355 Entered solar orbit 2018 May 5 111 x -110094 x 63.57
D00997 Mars InSight Lander 4 Sun 2018 May 10 2355 2018 Nov 22 1639 Entered Mars sphere 2018 May 31 1.008 x 1.434 AU x 2.24
D00997 Mars InSight Lander 5 Mars 2018 Nov 22 1639 2018 Nov 26 1944 Landed on Mars 2018 Nov 26 7 x -16942 x 13.50
D00997 Mars InSight Lander 6 Mars 2018 Nov 26 1944 - Operating on surface 2018 Nov 26 - x - x -

The object table and the mission phase table are also available as tab-separated-value files which may be useful for import into software packages.

Orbital Data

For each entry in the mission phase tables, estimates of basic orbital parameters are provided. In the initial release of the catalog, these are periapsis, apoapsis and inclination. For solar orbiting phases, the distances are radii in AU from the Sun's center (note: and not the barycenter) and the inclination is relative to the ecliptic. For other central bodies, distances are heights in km above a sphere corresponding to the body's nominal equatorial radius, and inclination is relative to the body IAU equator of date. The intent is to supplement these orbital parameters with full Keplerian osculating elements at a specific epoch in a subsequent data release.

Unfortunately, the orbital data are approximate in many cases, and sometimes mere guesses. The author began collecting deep space trajectory data in 1993 and the catalog will include a number of previously unpublished orbits. Sources which provided, or which were raided for, data that is being incorporated into the catalo$ include:

Archival research can occasion bring useful surprises. The only source I have found for the heliocentric transfer trajectory of the Pioneer Venus Orbiter mission is a state vector scribbled in pencil on a telegram in the history archives at NASA-Ames! I would be remiss if I did not thank the engineers and scientists who kindly have provided trajectory data over the years, including F. Bernardini, D. Collins, J. Insprucker, T. Kawamure, D. Lauretta, R. Mitchell, M. Rayman, R. Roads and W. Thompson. Trajectory information on launch vehicle final stages is impossible to find other than by personal contacts. Detailed citations are provided in the catalog.