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Ephemeris sharing gives operators predicted orbit data to screen for close approaches; autonomous collision avoidance can use that assessment to plan or execute a maneuver with less delay. They are complementary, not competing, approaches. A safe workflow still depends on timely, trustworthy trajectory and uncertainty data, clear responsibility for maneuver decisions, and coordination between operators.
What is the difference?
An ephemeris describes a spacecraft’s predicted orbit over time. When operators share ephemerides, a screening service or another operator can compare predicted trajectories, identify possible close approaches, and assess uncertainty. Sharing makes assessment possible; it does not, by itself, decide whether a maneuver is needed or who should make one.
Autonomous collision avoidance uses onboard or automated systems to help plan or execute a maneuver in response to a conjunction assessment. Depending on the system, people may retain the decision to maneuver even if the spacecraft can carry out the maneuver autonomously.
How do the two approaches compare?
| Question | Ephemeris sharing | Autonomous collision avoidance |
|---|---|---|
| What does it do? | Provides predicted orbit data for conjunction screening and risk assessment. | Can help plan or execute a maneuver in response to a close approach. |
| What must be available? | Usable, timely trajectory data and, where needed, covariance describing uncertainty. | A conjunction assessment, a capable and validated control system, and a defined mitigation process. |
| Who coordinates? | Operators and screening services exchange data and resolve maneuver responsibility. | Ground teams may set the decision and coordination process even when maneuver planning or execution is automated. |
| Does it replace the other approach? | No. It supplies information that can support either ground-led or automated responses. | No. Automation still relies on dependable trajectory information and safety procedures. |
| Comparative safety outcome | The cited NASA and ESA sources do not provide a statistic directly comparing safety outcomes for the two approaches. | |
What makes ephemeris sharing useful?
Frequency and latency matter
NASA’s Spacecraft Conjunction Assessment and Collision Avoidance Best Practices Handbook (2023 revision) recommends submitting at least one ephemeris per day for screening. For spacecraft in lower-drag low Earth orbit with a perigee below 500 km, it recommends three per day. These are handbook recommendations for the stated conditions, not universal requirements for every orbit or operator. Low-latency exchange helps ensure that screenings use useful, current predictions.
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Standard formats and reachable contacts support coordination
NASA recommends standard CCSDS formats for ephemerides, conjunction data messages (CDMs), and maneuver notifications. It also recommends operations contacts who can be reached at any time. These practices help operators exchange and interpret information and coordinate when a close approach requires a response. Sharing agreements may also provide access to more types of space situational awareness products than default access.
What does autonomy change—and what does it not?
Automation can reduce delays in processing conjunction information and planning or carrying out a maneuver. It does not make ground safety processes unnecessary. NASA policy requires projects using autonomous maneuvering to implement a conjunction assessment and mitigation process. That process typically includes emulating the autonomous control system to generate predicted ephemerides with covariance, and reporting anomalies that affect the spacecraft’s mitigation capability. Under the described process, the project manager decides whether to mitigate after considering screening and recommendations.
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This division matters: an autonomous system may act quickly, but its action still needs to be assessed within a mission’s safety and coordination framework. In a multi-operator environment, the operators also need a clear arrangement for who is responsible for maneuvering.
What has been demonstrated or deployed?
NASA’s Starling 1.5 demonstration
NASA’s Starling 1.5 experiment combined cross-operator trajectory screening with an explicit maneuver-responsibility arrangement. In the reported close approach with a Starlink satellite, Starling accepted responsibility and autonomously planned and executed the maneuver that resolved the conjunction. This demonstrates one coordinated workflow; it does not establish that the same setup is suitable for every spacecraft or operator.
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NASA’s CARA page reports that on-orbit conjunction assessment is driven by screenings from the U.S. Space Force’s 18th Space Defense Squadron, conducted three times daily. That is a reported screening cadence, not a measure of collision risk or proof that one approach is more effective than another.
ESA’s CREAM and CREAMPET projects
As of ESA’s account dated August 12, 2025, CREAM was a ground-based prototype generating actionable maneuver plans for implementation by ground teams. ESA described expanded pilot use and in-orbit demonstrations as steps being prepared. The cited account does not establish whether those planned demonstrations had occurred by October 7, 2026.
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ESA’s CREAMPET project explores privacy-protected exchange of sensitive data, including state vectors, covariance, and object characteristics. The project states a goal of reducing dedicated flight-dynamics engineer time by 20–30%; that is a target, not a measured operational result. ESA also notes that protecting privacy can limit functionality.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should operators weigh when designing a workflow?
- Data quality: Are the predicted trajectories and uncertainty data current and fit for screening?
- Exchange speed and compatibility: Can the parties share and interpret ephemerides, CDMs, and maneuver notifications in a timely, standard format?
- Decision authority: Is it clear who assesses risk, decides to maneuver, and carries out or supervises the maneuver?
- Cross-operator coordination: Can responsible operations teams be reached and agree how to avoid conflicting actions?
- Auditability and safeguards: Can autonomous behavior be emulated for assessment, and can anomalies affecting mitigation capability be reported?
- Privacy: Does the value of protecting exchanged data outweigh any reduction in what the screening or coordination process can do?
The available primary-source accounts describe guidance, a specific demonstration, and projects at different development stages; they do not establish a universally superior approach or quantify comparative collision-prevention results. The practical choice is therefore a mission-specific workflow that combines reliable data exchange, screening, clear responsibility, and automation only where its behavior can be assessed and governed.
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