The Logic of Multiple Mitigations
Most complex space systems are confronted with a wide range of threats requiring a similarly large number of mitigations. For any given threat there may be multiple available mitigations to choose from, each with a certain associated resilience. To achieve the required resilience (and thus performance in the contested environment) several mitigations may be used in combination to achieve the desired effects. However, some mitigations may be combined to achieve the required resilience, while others are an exclusionary choice: one mitigation can be chosen, or another, but not both. It is important for the system operators to understand the logical constraints in the decision tree to ensure that optimal responses to the threats are identified and activated.
As an example, consider a radio frequency (RF) jamming threat to a satellite uplink, denying service to a group of users. The satellite communications (SATCOM) system has several available mitigations to lessen or eliminate the effects of the jammer. The first action might be to activate an adaptive nulling algorithm driving a phased-array antenna to null the jammer. This will provide a certain value of relief, perhaps 20 dB, which may be sufficient to restore acceptable operational performance. If not, the users may be able to switch to an advance anti-jam waveform, using some type of spread spectrum technique. This action may result in an additional 10 dB, in addition to the original 20 dB improvement. These two mitigations are thus complementary, with their beneficial effects being additive, also resulting in increased resilience. In this decision tree the response level may be incrementally increased as required.
In contrast, some threats, such as kinetic threats, may result in irreversible effects, requiring users to be migrated to another satellite or system. There may be any number of different user migration strategies, each with its own resilience, but they are all mutually exclusive: the operator must choose one among many. A migration may move all users from one beam, satellite, and/or system to one or more destinations, but the exact destination user configuration will be unique. If the forecast resilience is not achieved due to reduced recovered capacity, for example, then another migration may be chosen. However, this will take additional time and thus the impact to the users will be extended, even though the migration mitigation is technically reversible. Here the migration may be executed in incremental steps to continually optimized, but with continued (though limited) disruptions to the user population.
One additional scenario is one in which the combined effects of multiple mitigations is conditional. Consider a SATCOM satellite subjected to RF jamming, but no on-board mitigations are available on the satellite being jammed. If the users are migrated to a second satellite that does include anti-jam features such as adaptive nulling then there is a combined benefit due to the migration itself as well as that of adaptive nulling if there is a likelihood that the second satellite will also be jammed. The first mitigation enables the availability and selection of the second migration.
These simple examples illustrate the importance of understanding not only the range of available mitigations, but also the coupling and logical relationships between them. Some are both independent and reinforcing, some are independent and exclusionary, and some are conditionally related. Once understood, these relationships can be used to document system constraints as well as preferred courses of action (CoA) and guidelines for automated algorithms as well as human system operators.
