## 1 Introduction  
In the modern era of space exploration, numerous spacecraft are launched with a limited communication system. These spacecraft may possess only an omnidirectional antenna and lack an onboard Tracking and Data Relay Satellite (TDRS) transponder capable of coherently transmitting a carrier signal through TDRS. Due to these limitations, alternative methods of tracking must be explored and utilized to accurately locate and communicate with the spacecraft.  
One such alternative method is Differenced One-Way Doppler (DOWD) tracking, which has proven to be a valuable tool in overcoming the challenges presented by unstable onboard oscillators when using strictly One-Way Doppler (OWD) data. DOWD tracking measurement requires simultaneous OWD tracking from two non-collocated TDRSs. The process of differencing two OWD measurements results in a DOWD measurement, which offers precise information about the spacecraft's position and velocity, and it can be used to estimate a spacecraft's trajectory when other data types are not available. The effectiveness of DOWD measurements is largely dependent on the availability and performance of satellite communication networks such as the National Aeronautics and Space Administration(NASA) Space Relay (SR) [1]. The SR is a network of communication satellites that provides a continuous link between ground stations and user satellites, enabling real-time data transfer and control.  
A DOWD-based user spacecraft trajectory, however, is also dependent on the accuracy of the TDRS orbits used to transmit and receive radio signals. TDRS is a critical component of the DOWD technique as it provides a stable and reliable link for transmitting and receiving the radio signals necessary for the measurement. Any errors in the orbit of the TDRS satellites could result in changes to the radio signal path and cause inaccuracies in the DOWD measurements, which in turn affect the accuracy of the user satellite orbits.  
Errors in the orbit of the TDRS satellites can occur due to a variety of factors, including perturbations from other celestial bodies, gravitational potential anomalies, inaccurate modeling of the non-gravitational forces, inaccuracies in the satellite's onboard instruments, and measurement errors. These errors can accumulate over time and lead to significant deviations from the satellite's predicted orbit.  
To correct these errors, the Bilateration Ranging Transponder System (BRTS) and Telemetry, Tracking, and Command (TT&C) measurements [1; 2] are used to precisely track TDRS position and velocity as it orbits the Earth. By analyzing these sets of measurements, the TDRS orbit can be determined within 40 m of accuracy [3]. In contrast, reduced tracking, for instance, range-only (TT&C) could severely impact the accuracy of the TDRS satellites.  
This paper analyzes OWD tracking data from several spacecraft received by the Flight Dynamics Facility (FDF) at NASA Goddard Space Flight Center (GSFC). An analysis of TDRS orbit error impact on DOWD-based satellite orbits was conducted when the TDRS satellite orbits were determined using TT&C-only measurements. The study additionally investigated the impact of a TT&C-only TDRS orbit on the precision of the Local Oscillator Frequency offset determination by analyzing the one-way Doppler tracking data from the user spacecraft.