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NPR 8079.1
Effective Date: June 27, 2023
Expiration Date: June 27, 2028
Printable Format (PDF)

Subject: NASA Spacecraft Conjunction Analysis and Collision Avoidance for Space Environment Protection

Responsible Office: Office of the Chief Engineer

| TOC | Preface | Chapter1 | Chapter2 | Chapter3 | Chapter4 | Chapter5 | AppendixA | AppendixB | AppendixC | AppendixD | AppendixE | AppendixF | ALL |

Chapter 5. Technical Requirements

This chapter captures the baseline technical requirements that the project manager meets. An approved CAOIA is sufficient to document deviations from this baseline.

Note: The requirements in this chapter may be captured in a NASA technical standard; when it becomes available the NPR may be adjusted accordingly.

5.1 Ephemeris Sharing

5.1.1 The specifications shown in Table 5-1 apply to ephemeris production as documented in the CAOIA. (Additional ephemeris quality context is provided in the CA2 Handbook, Section 6.1.)

Table 5-1 Ephemeris Specifications

Parameter Low-Earth Orbit Other Earth Orbits Non-Earth Orbits
Predictive duration 7 days (or full spacecraft lifetime if less than 7 days) 14 days The conjunction assessment screening interval for the mission's orbit regime. Typically, 14-21 days.
Delivery frequency Daily Twice weekly At least weekly
Ephemeris point spacing ~ 1/100th of an orbit in either time or true anomaly.1
Covariance at each ephemeris point The covariance consists of at least the six spacecraft state parameters. This covariance should be at least as statistically representative of the spacecraft's state position error histories as the DOD precision catalog covariances are for well-tracked objects in similar orbits.2
Maneuvers All known maneuvers within the ephemeris file span including maneuver execution error in the appropriate ephemeris covariances.
Format CCSDS standard OEM Format3 CCSDS standard OEM Format3 CCSDS standard OEM Format3 or SPK Type 134
1Spacecraft with extremely long period orbits and/or highly eccentric orbits may require more specialized approaches.
2Covariance realism software exists as open-source code on the CARA software repository.
3The definition for the standard on the Orbit Ephemeris Message (OEM) is in the Consultative Committee for Space Data Systems (CCSDS) standard CCSDS 502.0-B-2, "Orbit Data Messages," Section 5. https://public.ccsds.org/Pubs/502x0b2c1e2.pdf
4The Spacecraft and Planet Kernel (SPK) file format types are described in the JPL SPICE Toolkit at https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/spk.html#Supported%20Data%20Types

5.2 Maneuverable Spacecraft

5.2.1 The project manager shall coordinate all maneuver efforts with CARA or JSC FOD. This typically includes the following:

a. Providing maneuver notifications to CARA or JSC FOD in the CCSDS Orbit Parameter Message (OPM) format. (See CA2 Handbook, Section 6.1 and CCSDS standard 502.0-B-2, Section 3, at https://public.ccsds.org/Pubs/502x0b2c1e2.pdf.)

b. Submitting proposed maneuver plans in the form of ephemerides with covariance to CARA or JSC FOD at least 24 hours in advance of intended execution to allow for conjunction assessment screening. Conformity with this timeline may require out-of-cycle ephemeris production and submission. CARA and JSC FOD will screen the proposed maneuver ephemerides against other objects and notify the project of the results.

c. Contacting CARA or JSC FOD and negotiating a contingency approach for emergency situations that do not allow notification 24 hours in advance.

d. Taking responsibility for all mitigating actions required for close approaches with existing on-orbit active spacecraft during project transit to and from the final on-orbit location (transiting spacecraft yield right-of-way to on-station objects). (See the CA2 Handbook, Section 4.3.)

5.2.2 For maneuverable spacecraft, the project manager shall promptly inform CARA or JSC FOD of all anomalies that either affect the ability to perform conjunction mitigation or compromise agreements documented in the CAOIA. This typically includes reporting anomalies that affect a non-HSF mission's ability to maneuver to mitigate conjunctions (e.g., spacecraft in safe hold mode, thruster anomalies). JSC FOD will maintain knowledge of an HSF-related mission's ability to maneuver in accordance with JSC FOD's standard reporting protocols.

5.3 Conjunction Mitigation

5.3.1 Conjunction mitigation maneuvers follow a basic process:

a. CARA informs the project of high-risk conjunctions for which mitigation planning is appropriate. (See sections 4.3 and 4.4.) Typical mitigation scenarios and associated spacecraft capabilities are documented in the CAOIA. Low-risk conjunctions require no further action.

b. When the project manager generates a plan for conjunction mitigation, the project manager ensures that ephemerides with covariance, both with and without maneuvers, are provided to CARA for screening and risk assessment. The CAOIA documents the specific information and schedule exchanges between CARA and the project manager.

c. Based on the screening, CARA makes recommendations on the need to mitigate from a space environment safety perspective.

d. The project manager makes the conjunction mitigation decision.

5.3.2 For making decisions about mitigating conjunctions in Earth orbit, the project manager considers the following elements:

a. The baseline decision threshold (i.e., the mitigation threshold) for close-approach events is, at the mitigation commitment point, either a probability of collision (Pc) value in excess of 1E-04 (1 in 10,000) or a Euclidean miss distance less than the conjunction's combined hard-body radius (HBR).

b. The conjunction mitigation action reduces the Pc by at least 1.5 orders of magnitude below the mitigation threshold (e.g., 3E-06 for a mitigation threshold of 1E-04). (See the CA2 Handbook, Section 6.4.)

c. Deliberately engineered spacecraft close approaches require mission-specific safety-of-flight procedures resulting from intra-mission coordination and planning. Examples include proximity operations, on-orbit servicing activities, rendezvous, or operations of multiple spacecraft managed by one flight operations team that controls their relative positions.

5.3.3 For making decisions about mitigating conjunctions for non-Earth-orbiting spacecraft, the project manager considers the following elements:

a. Uncertainties with the spacecraft-specific orbit determination processes.

b. Defined thresholds for orbit crossing distance and timing.

c. Time required for planning and execution of mitigation maneuvers.

5.4 Post-Launch Deployments

Project managers of spacecraft deploying or jettisoning objects provide predicted ephemerides with covariance for the trajectory of the deployed objects 24 hours or as early as possible prior to the deployment time. This allows for screening the ephemerides and performing risk assessment to determine the safety of the trajectories of the deployed objects.

5.5 Advanced Capabilities

5.5.1 For spacecraft using non-instantaneous propulsion (e.g., hydro, electric, solar sail), differential drag, or novel propulsion capabilities, project managers should coordinate with CARA or JSC FOD to allow time to determine how to support these spacecraft-specific capabilities.

5.5.2 For spacecraft using autonomous maneuvering, the project manager implements a conjunction assessment and mitigation process as documented in the CAOIA. This process typically includes the following:

a. Using an emulation capability that reasonably predicts the behavior of the autonomous control system to generate predicted ephemerides with covariance according to the requirements of Section 5.1 of this NPR.

b. Complying with Section 5.2.2 for all autonomously planned maneuvers.

c. Having and, if required, using a capability to halt expected autonomously planned maneuvers for safety-of-flight reasons.

d. Notifying CARA or JSC FOD of all maneuvers initiated autonomously. (See the CA2 Handbook, Section 6.5.)

| TOC | Preface | Chapter1 | Chapter2 | Chapter3 | Chapter4 | Chapter5 | AppendixA | AppendixB | AppendixC | AppendixD | AppendixE | AppendixF | ALL |
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