External features consider a wide range of activities and identifies classes of action that satellite operators can take to make their mission more amenable to receive External Services (ES) or to increase the probability of successful external services such as fixing, improving, and reviving satellites and refers to any work to refuel, repair, replace, or augment a satellite in space.
They also consider design features that ensure or improve the detectability, trackability and identifiability of satellites in non-cooperative situations such as a low-power beacon or reflector. On-orbit servicing of satellites takes into consideration life-extension and upgradability as technology evolves, as well as the employment of external end-of-life disposal strategy.
abbreviated terms
| ADR | Active Debris Removal |
| ES | External Services |
| NASA | National Aeronautics and Space Administration |
| OOS | On Orbit Servicing |
| SSR | Space Sustainability Rating |
External Services rationale
The SSR does not assume that all operators will invest in External Services, and in some cases such as low altitude orbits or small satellites, external services are not deemed necessary. As such, the External Services module aims at providing bonus rating for missions where the investment in external services capabilities are appropriate. The tier score of the applicant is not impacted if ES are not used.
Three categories of actions by operators are presented below:
1. Actions during the design and pre-launch phase to make it easier for operators to have their mission serviced in the future
ES technology is evolving in ‘real-time’ often after missions are launched. A significant number of contemporary ES cases are satellites that were not designed to be serviced (non-cooperative satellites). It is expected that this will likely continue for the next one to two years. Given the relatively low level of quality of knowledge on these different ES features, the first iteration of the SSR will weight all ES features equally. The credit given to ES will be low and entirely bonus in the first version of the SSR, with scope for re-evaluation in later versions as verification, validation and successful demonstration of ES capabilities are proven.
Third-party organisations/companies such as NASA’s Satellite Servicing Projects Division (SSPD) and ESA’s Clean Space Office have begun independent assessment, verification and validation of ES features through their own testing, particularly design choices, e.g. grapple fixtures. Taking advantage of these verification tools or providing evidence of self-validation and verification is necessary for SSR credit to be applied.
2 . Commitment to use or demonstration of use of On Orbit Servicing (OOS)
The utilisation of OOS, either through the operator’s actions or payment of an external service will allow the operator to gain SSR credit, pending the mission complies with current regulatory standards.
As ES is a fairly new technology, the risks of failure are higher and non-trivial until consistent successful demonstration of these capabilities are proven. It is envisioned that future iterations of the SSR will account for technological demonstration of these services.
3. Utilising ES in line with current standards
In addition to external service market maturity and technology adoption, legislative and policy drivers will also impact market adoption and should be monitored closely. The SSR will assess if the operating team are complying with standards developed and proposed by international groups e.g. Consortium for Execution of Rendezvous and Servicing Operations (CONFERS).
Table 3: Evaluating of the External Services approach for Bonus score
| On-orbit (OOS) feature | Operators can take actions during the design and pre-launch phase to make it easier to have their mission serviced in the future. This does not imply that they will definitely use it | Installing of OOS features in preparation to create a fail-safe option. Examples include visual fiducials, grapple fixtures, mechanical features, grasp features, and items to make it easier to track the object in case of radio failures such as beacons | 1 |
| Standardised interfaces | Utilising OOS in line with current standards | Employment of OOS capabilities that include standardised interfaces | 1 |
| Life extension services | Commitment to use or demonstration of use of On Orbit Servicing |
External end-of-life removal service Included in quantitative model, including risk of failure |
1 |
| Use of external ADR (beyond compliance) | Commitment to use or demonstration of use of On Orbit Servicing | Use of external ADR but still complies with 25 year deorbit rule | 1 |