TanSat – Space Traffic Management

by Marissa Herron

Increased access to space has created a congested environment that impacts satellite operators both domestically and internationally. In response, Space Policy Directive – 3[1] directed the development of a Space Traffic Management (STM) capability[2]. The Department of Commerce is leading this effort[3]. The 18th Space Control Squadron currently provides collision avoidance notifications to satellite operators to facilitate the responsible use of space. The 18th SCS services are provided free to U.S. satellite operators[4] as well as international satellite operators. The current expectation is that the Department of Commerce will take the place of the 18th SCS in providing a free basic service, thereby allowing the 18th SCS to focus on its primary mission serving national security needs. 

How can a STM capability help? One reason is to facilitate international communication and coordination amongst satellite operators. An example that could have benefited from a STM organization is China’s TanSat satellite[5]. This satellite was designed with the intent of utilizing a highly desirable scientific orbit where NASA’s A-train constellation resides[6]. NASA’s A-train operators and Earth Science Division Director unexpectedly learned of TanSat’s plans through a science conference. The planned close proximity of TanSat to the A-train constellation necessitated some level of communication and coordination between NASA and China. 

[1] https://trumpwhitehouse.archives.gov/presidential-actions/space-policy-directive-3-national-space-traffic-management-policy

[2] Similar terms also include Space Situational Awareness (SSA) and the more recent Space Domain Awareness (SDA). 

[3] https://www.space.commerce.gov/category/ssa-stm

[4] Also known as “Owner/Operator” or O/O

[5] https://ceos.org/document_management/Virtual_Constellations/ACC/Meetings/AC-VC-12/Day%202/5.%20YiLiu%20-%20TanSat.pdf

[6] https://atrain.nasa.gov/

Image source: eoportal[7]

Congressional legislation, known as the Wolf Amendment, prohibits NASA from engaging in bilateral efforts with China[8]. With an exception, NASA’s Earth Science Division Director, Michael Freilich, met with the TanSat project. They discussed the TanSat’s mission similarities to NASA’s Orbiting Carbon Observatory-2 (OCO-2), science data exchanges, and the potential for TanSat to join the A-train constellation[9].

[7] https://directory.eoportal.org/web/eoportal/satellite-missions/t/tansat

[8] https://www.forbes.com/sites/williampentland/2011/05/07/congress-bans-scientific-collaboration-with-china-cites-high-espionage-risks/?sh=134b78544562, https://en.wikipedia.org/wiki/Wolf_Amendment

[9] https://directory.eoportal.org/web/eoportal/satellite-missions/t/tansathttps://spacenews.com/earth-science-discussion-latest-sign-of-nasa-china-ties/, https://ceos.org/document_management/Virtual_Constellations/ACC/Meetings/AC-VC-12/Day%202/5.%20YiLiu%20-%20TanSat.pdf

Image source: CEOS, TanSat Mission Status, 2016[1]

[1] https://ceos.org/document_management/Virtual_Constellations/ACC/Meetings/AC-VC-12/Day%202/5.%20YiLiu%20-%20TanSat.pdf

Image credit: IAP/CAS[11]

Satellites flying in a constellation formation require constant communication and coordination. These neighboring satellites must maintain a science “box” to facilitate consistent science measurements and also maintain the satellite’s appropriate location behind and in front of neighboring satellites. Since these satellites are in Low Earth Orbit (LEO), they experience some atmospheric drag and require periodic reboosts to maintain their positions. They also may experience close approach warnings with orbital debris and need to mitigate the risk by maneuvering the satellite. Anytime a satellite in the constellation maneuvers, they need to communicate and coordinate with their neighbors to prevent collisions and to ensure minimal impact to the science mission of their neighbors. TanSat eventually decided not to pursue the operational complexities of joining a constellation[12]. The discussions between NASA and TanSat occurred in 2015 and 2016, which was very close to TanSat’s 2016 launch date[13]. This is very late in the development of a satellite to re-consider the fuel budget, propulsion capabilities, and operational impacts to joining a constellation. Furthermore, participation in the A-train constellation would have necessitated a partnership with NASA and regular communications between NASA and China; which the Wolf Amendment prohibits.

[11] https://directory.eoportal.org/web/eoportal/satellite-missions/t/tansat

[12] https://directory.eoportal.org/web/eoportal/satellite-missions/t/tansat, https://spacenews.com/earth-science-discussion-latest-sign-of-nasa-china-ties/

[13] https://ceos.org/document_management/Virtual_Constellations/ACC/Meetings/AC-VC-12/Day%202/5.%20YiLiu%20-%20TanSat.pdf, https://directory.eoportal.org/web/eoportal/satellite-missions/t/tansat

Although China did not launch into the A-train constellation, they did launch into an orbit lower than the A-train orbit. Although an improved posture, this still presented a risk to the A-train constellation. Security concerns with sharing data related to the launch and insertion orbit uncertainties prevented further communications. NASA was left hoping that its potentially vulnerable international joint mission constellation was in the right place at the right time during TanSat’s insertion. Fortunately, both the A-train constellation and TanSat remained unharmed during the launch and insertion of TanSat. 

Since a successful launch of TanSat, the A-train constellation has learned to operate with the occasional close approach of TanSat. Communications, when necessary, are routed through the State Department. The ideal and minimal risk approach is for the satellite operators to communicate directly with one another. This reduces any potential confusion or misinterpretation that can occur when passing an urgent message through multiple parties[14]. However, the restrictions on communications with China resulted in NASA adapting to the use of the State Department for communications and sending messages with the expectation of not receiving a timely response. Depending upon the technical details of the close approach, this can mean sending a message that says “Stay put. I’ll move.” One benefit of the A-train satellite choosing to move is knowing the expected propulsion performance and outcome of the maneuver of your own satellite’s systems. Despite the cost of fuel, this single, proactive maneuver can facilitate greater certainty and knowledge of the resultant orbital state (and fewer unnecessary maneuvers).

[14] Keep in mind that operational messages have a time-critical urgency and, thus, need the most efficient path of communication possible.

Image created using celestrak.com’s Orbit Visualization

An STM organization needs to include an emphasis on the development of international relationships with an encouragement for communications regarding planned orbits as well as operational impacts. International entities are not required to communicate their launch and orbit plans, but the TanSat example clearly demonstrates the benefit that TanSat and the A-train could have received had the communications occurred early in the design life and with the assistance of a STM organization[15]

A STM organization that can enable the development of international relationships could have facilitated communications on this topic and redirected any potential issues down a cooperative path. Looking at the Venn diagram, the International operator could communicate their design phase information (A) to a civil STM organization. This organization could then identify potential neighbors to the planned international satellite and then connect the international operator with the relevant domestic operator (B). Making these connections between operators is valuable and enables both operators to communicate and coordinate technical details as needed (C). If needed, the STM organization could help facilitate initial communications and logistics (D)[16] that enables the relationship.

[15] The Registration Convention does require parties to report objects launched, but this is not a timely tool. Objects are often reported well after launch and may contain errors or incomplete reporting. The Registration Convention simply serves a registry or database of space objects and is not intended for satellite design and operations as discussed above. https://www.spacelegalissues.com/the-1976-registration-convention/https://www.unoosa.org/oosa/en/ourwork/spacelaw/treaties/registration-convention.html, https://www.faa.gov/about/office_org/headquarters_offices/ast/media/Conv_Regi_Objects_Launched.pdf

[16] The STM organization will need to be careful to not interfere with time-critical communications that will eventually occur once satellite operations begin. 

This process is effectively what occurred for the TanSat – A-train situation. The differences are that a conference served as the connecting mechanism for the operators (B) and NASA required approval to communicate with TanSat (C).

Although requirements can only be imposed domestically, future international satellite operators should be encouraged to communicate their plans to this STM organization. Through international involvement and acceptance, standards can eventually be implemented that encourage the responsible use of space and benefit to all.

Many of these standards will be set domestically and proven over time. Cooperation with the international community can lead to the early acceptance of mutually beneficial standards. NASA has engaged with international partners on topics such as thresholds for maneuvering, risk calculations, and operational best practices. Additionally, the Orbital Debris Mitigation Standard Practices informed the  2010 United Nations Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space (UN COPUOS)[17]

International collaboration and partnerships bring new ways of thinking, broadens and deepens expertise, and strengthens international relations. For these reasons, it is vitally important that the international community be included in the STM framework and encouraged to participate by facilitating unimpeded cooperation. The implementation of an STM organization to facilitate these relationships is a key enabler to success.

[17] Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space,

A/RES/62/217, 2007, available at


Share your thoughts