Global geodetic parameter determination using GPS–SLR space ties onboard LEO satellites

Global geodetic parameters, such as Geocenter Coordinates (GCCs) and Earth Rotation Parameters (ERPs), are critical for the definition of the International Terrestrial Reference Frame (ITRF) and geophysical studies. Traditional ITRF realization relies heavily on ground-based local ties to combine multiple space geodetic techniques, but these ties suffer from spatial unevenness, high maintenance costs, and infrequent updates. Low Earth Orbit (LEO) satellites equipped with multi-geodetic payloads have emerged as a transformative solution, offering “space ties” that enable inter-technique linkage independent of ground surveys. This study explores the potential of GPS–SLR space ties onboard Swarm LEO satellites for precise parameter determination via observation-level combination. Using ground-based GPS, Swarm-borne GPS, and SLR-to-Swarm observations, three solutions (GPS-only, GPS + LEO, GPS + LEO + SLR) were analyzed and compared. Attributed to geocenter sensitivity of LEO satellites, Swarm-borne GPS observations significantly reduce GCC formal errors by 36.7–48.4%, and reduce the standard deviation (STD) of GCC time series by 20.4–39.1%. Meanwhile, ERP formal errors decrease by 31.5–40.2% due to enhanced observational geometry, and the Y-pole offset with respect to the IERS-20-C04 product decreases by 29.5%. SLR-to-Swarm observations further mitigate the β-angle dependence of GCC formal errors in the X/Y components and improves the consistency with external SLR solutions. The annual difference between GPS + LEO + SLR and SLR-60 day solutions was 0.6 mm in amplitude and 15° in phase for the GCC Z component. Due to SLR’s insensitivity to Earth rotation and its sparse temporal sampling, the contribution of SLR-to-Swarm observations to ERPs is marginal. This study confirms the value of LEO-based GPS–SLR space ties in advancing global geodetic parameter estimation.