Title: A First-in-Flight Demonstration of the Deep Space Network's Multiple Uplinks Per Antenna Capability
Authors: 
    Douglas S. Abraham (1)
    Brandon J. Burgett (1)
    Matthew D. Chase (1)
    Jesse C. Fusco (2)
    Dennis M. Heher (2)
    Ethel Grace C. Monte De Ramos (3)
    Shantanu Malhotra (1)
    David D. Morabito (1)
    Robert H. Nakamura (2)
    Matthew C. Napoli (2)
    James A. O’Dea (1)
    Steven M. Olson (3)
    Emily R. Pascua (1)
    Marc Sanchez-Net (1)
    Mazen M. Shihabi (1)
    Dong K. Shin (1)
    Dana Sorensen (4)
    Zaid J. Towfic (1)

(1) Jet Propulsion Laboratory, California Institute of Technology
(2) NASA Ames Research Center
(3) NASA Deep Space Network
(4) Space Dynamics Laboratory, Utah State University

In order to mitigate the effects of ever increasing demand for NASA’s Deep Space Network (DSN) support, NASA has been developing antenna sharing techniques. These techniques include (Opportunistic) Multiple Spacecraft Per Aperture (MSPA) on the downlink, and the newly developed Multiple Uplinks Per Antenna (MUPA) technique on the uplink. These techniques rely on the fact that multiple spacecraft are in the same beam of a single DSN antenna. In the case of MUPA, the DSN's MUPA system multiplexes Forward Communications Link Transmission Units (FCLTUs) to all the spacecraft that are within the antenna beam onto a single frequency. Each spacecraft identifies its intended transfer frames based on its uplink Spacecraft ID (SCID). This paper discusses the first in-flight test of MUPA features as conducted with the Biosentinel spacecraft, operated by NASA Ames Research Center, carrying the JPL Iris transponder. The successful test of these MUPA features demonstrates the path to enable NASA and the DSN to cope with increased small-sat deployments and the emergence of multi-element lunar exploration missions. 

The Biosentinel spacecraft launched onboard Artemis-1 on Nov. 16, 2022 to study the impact of deep space radiation on DNA repair over a long time span spent beyond low Earth orbit. The spacecraft is a 6U CubeSat that hosts the JPL Iris software-defined-radio transponder. The Biosentinel Iris transponder supports features added specifically to aid in MUPA objectives, including: (1) SCID filtering, (2) the ability to change the turn-around-ratio, and (3) the ability for the Iris transponder to perform an onboard sweep to lock on to an uplink carrier that is not Doppler-compensated for the particular spacecraft. At the time of the demonstration, the spacecraft was approximately 0.3AU away from Earth. The demonstration aimed to demonstrate each of the above three Iris MUPA features as well as the heart of MUPA: the DSN-side FCLTU multiplexing capability implemented as the FMUX subsystem at the DSN station. 

Two passes were scheduled to support the demonstration, and both passes were fully utilized. The end result yielded a successful result for all success criteria, including the Iris transponder's ability to perform CLTU filtering based on the SCID and dynamic modification of the turn-around ratio. A partial success of the Iris' ability to perform carrier sweep was achieved, complicated by a configuration issue on the DSN transmit side. All of these aspects of the Iris transponder capability shall be discussed in detail in the paper. Finally, complete success was achieved on the DSN CLTU multiplexing capability through FMUX, with two separate clients transmitted CLTUs through FMUX to the spacecraft (with two different SCIDs). The CLTUs were received by the spacecraft and either were ignored (as intended due to having a different SCID than expected by the transponder) or executed (as intended due to a SCID match at the transponder).

This effort and the underlying system engineering are paving the way for the next critical step in implementing MUPA: preparations for a multiplexer demonstration with the SunRISE and EscaPADE projects, which are already in progress.