You can freely make and distribute your own code which calls the SGP4 libraries, but you may not distribute those libraries themselves. Everyone who wants to use whatever you create will need to make their own (free) account on space-track.org, and will have to download their own individual copy of the US Government libraries. The full license is included as a text file in the zip distribution, in several different places. It reads:
AIR FORCE SPACE COMMAND (AFSPC) OPEN SOURCE AGREEMENT for SGP4 -
(Simplified General Perturbations #4)
THIS OPEN SOURCE AGREEMENT ("AGREEMENT") DEFINES THE RIGHTS OF USE,
REPRODUCTION, DISTRIBUTION, MODIFICATION AND REDISTRIBUTION OF CERTAIN
COMPUTER SOFTWARE ORIGINALLY RELEASED BY THE UNITED STATES GOVERNMENT
AS REPRESENTED BY THE GOVERNMENT AGENCY LISTED BELOW ("GOVERNMENT
AGENCY"). THE UNITED STATES GOVERNMENT, AS REPRESENTED BY GOVERNMENT
AGENCY, IS AN INTENDED THIRD-PARTY BENEFICIARY OF ALL SUBSEQUENT
DISTRIBUTIONS OR REDISTRIBUTIONS OF THE SUBJECT SOFTWARE. ANYONE WHO
USES, REPRODUCES, DISTRIBUTES, MODIFIES OR REDISTRIBUTES THE SUBJECT
SOFTWARE, AS DEFINED HEREIN, OR ANY PART THEREOF, IS, BY THAT ACTION,
ACCEPTING IN FULL THE RESPONSIBILITIES AND OBLIGATIONS CONTAINED IN
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
The intended purpose of the SGP4 propagator is to properly propagate
an object's Two Line Element Set (TLE) supplied by the USSTRATCOM'S
Joint Functional Component Command for SPACE Joint Space Operations
Center (JSpOC) such that the positions calculated for that object
agree with those calculated by the JSpOC. SGP4 propagator is to be
used solely for the purpose of propagating JSpOC created TLEs. TLEs
created and supplied by the JSpOC are created in such a way as to be
compatible with the SGP4 propagator. In this way,
compatibility/interoperability issues between the JSpOC and the user
of JSpOC SGP4 TLEs are addressed. Examples of what SGP4 should not be
used for, included but are not limited to, propagating JSpOC created
state vectors which come from any of the various other messages the
JSpOC creates, such as Vector Covariance Messages, Orbital Conjunction
Messages, Conjunction Data Messages, etc.
Government Agency: Air Force Space Command Government Agency Original
Software Designation and Software Title: SGP4
User Registration Requested. Please Visit: Government Agency Point of
Contact for Original Software:
A. "Contributor" means Government Agency, as the developer of the
Original Software, and any entity that makes a Modification.
B. "Covered Patents" mean patent claims licensable by a Contributor
that are necessarily infringed by the use or sale of its Modification
alone or when combined with the Subject Software.
C. "Display" means the showing of a copy of the Subject Software,
either directly or by means of an image, or any other device.
D. "Distribution" means conveyance or transfer of the Subject
Software, regardless of means, to another.
E. "Larger Work" means computer software that combines Subject
Software, or portions thereof, with software separate from the Subject
Software that is not governed by the terms of this Agreement.
F. "Original Software" means any or all of the computer software
first released under this Agreement by Government Agency with
Government Agency designation SGP4, with title identified herein,
including object code and accompanying documentation, if any.
G. "Recipient" means anyone who acquires the Subject Software under
this Agreement, including all Contributors.
H. "Redistribution" means Distribution of the Subject Software to
I. "Reproduction" means the making of a counterpart, image or copy of
the Subject Software.
J. "Sale" means the exchange of the Subject Software for money or
K. "Subject Software" means the Original Software, or any respective
L. "Use" means the application or employment of the Subject Software
for any purpose.
- GRANT OF RIGHTS
A. Under Non-Patent Rights: Subject to the terms and conditions of
this Agreement, each Contributor, with respect to its own contribution
to the Subject Software, hereby grants to each Recipient a
non-exclusive, world-wide, royalty-free license to engage in the
following activities pertaining to the Subject Software:
B. Under Patent Rights: Subject to the terms and conditions of this
Agreement, each Contributor, with respect to its own contribution to
the Subject Software, hereby grants to each Recipient under Covered
Patents a non-exclusive, world-wide, royalty-free license to engage in
the following activities pertaining to the Subject Software:
- Offer for Sale
C. Redistribution and use of binary forms,are permitted provided that
the following conditions are met:
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
Neither the name of the Air Force Space Command nor the names of its contributors may be used to endorse or promote products derived
from this software without specific prior written permission.
D. The rights granted in Paragraphs A. and B. allow the Recipient to
sublicense those same rights. Such sublicense must be under the same
terms and conditions of this Agreement.
- OBLIGATIONS OF RECIPIENT
A. Distribution or Redistribution of the Subject Software must be
made under this Agreement except for additions covered under paragraph
- Whenever a Recipient distributes or redistributes the Subject Software, a copy of this Agreement must be included with each copy of
the Subject Software; and
B. Each Recipient must ensure that the following copyright notice
appears prominently in the Subject Software:
Copyright 2015 United States Government as represented by the
Administrator of Air Force Space Command. All Rights Reserved.
C. A Contributor may add its own copyright notice to the Subject
Software. Once a copyright notice has been added to the Subject
Software, a Recipient may not remove it without the express permission
of the Contributor who added the notice.
D. A Recipient may not make any representation in the Subject
Software or in any promotional, advertising or other material that may
be construed as an endorsement by Government Agency or by any prior
Recipient of any product or service provided by Recipient, or that may
seek to obtain commercial advantage by the fact of Government Agency's
or a prior Recipient's participation in this Agreement.
E. In an effort to track usage and maintain accurate records of the
Subject Software, each Recipient, upon receipt of the Subject
Software, is requested but not obligated to register with Government
Agency by visiting the following website: astrodynamicStandards.org.
Recipient's name and personal information shall be used for
statistical purposes only.
F. A Recipient may choose to offer, and to charge a fee for,
warranty, support, indemnity and/or liability obligations to one or
more other Recipients of the Subject Software. A Recipient may do so,
however, only on its own behalf and not on behalf of Government Agency
or any other Recipient. Such a Recipient must make it absolutely
clear that any such warranty, support, indemnity and/or liability
obligation is offered by that Recipient alone. Further, such
Recipient agrees to indemnify Government Agency and every other
Recipient for any liability incurred by them as a result of warranty,
support, indemnity and/or liability offered by such Recipient.
G. A Recipient may create a Larger Work by combining Subject Software
with separate software not governed by the terms of this agreement and
distribute the Larger Work as a single product. In such case, the
Recipient must make sure Subject Software, or portions thereof,
included in the Larger Work is subject to this Agreement.
H. Notwithstanding any provisions contained herein, Recipient is
hereby put on notice that export of any goods or technical data from
the United States may require some form of export license from the
U.S. Government. Failure to obtain necessary export licenses may
result in criminal liability under U.S. laws. Government Agency
neither represents that a license shall not be required nor that, if
required, it shall be issued. Nothing granted herein provides any
such export license.