The authors state that the Advanced Ranging Instrument (ARI) can improve ranging accuracy by an order of magnitude by using multi-frequency links (X-up/X-down, X-up/Ka-down, Ka-up/Ka-down) to “remove the solar plasma noise in its entirety.” This claim is scientifically overstated and technically implausible, because:
1. Solar plasma is a dispersive medium that affects radio signals proportionally to 1/f21/f2, where ff is the frequency. While dual- or multi-frequency links can reduce plasma-induced noise by exploiting this frequency dependence, they cannot eliminate it entirely due to:
– Temporal and spatial variability of the solar wind and coronal plasma.
– Non-linear effects at low Sun-Earth-Probe angles (SEPA) where plasma density gradients are steep and unpredictable.
– Instrumental limitations in synchronizing multi-frequency signals and calibrating path delays with perfect accuracy.
2. Table 1 (Page 4) shows solar plasma errors for dual X/Ka-band systems at 20° SEPA as “<1 m” total line-of-sight error and “<5 cm” drift over 8 hours. These values are optimistic and assume ideal conditions. In practice, during solar maximum or extreme space weather events, residual errors can be significantly larger.
3. The authors cite Paik et al. (2018) and Border et al. (2020) as evidence of ARI’s success. However, these reports demonstrate improved performance under controlled conditions, not complete elimination of plasma noise. The claim of “removing solar plasma noise in its entirety” is not supported by the referenced literature or fundamental radio science principles.
Overstating the capability of ARI could mislead mission planners and radio scientists into underestimating navigation errors during critical mission phases (e.g., solar conjunctions, low-SEPA operations), potentially compromising mission safety and scientific accuracy.