Session
Weekday Session 2: Beyond LEO
Location
Utah State University, Logan, UT
Abstract
An increased Cislunar traffic is expected by the end of this decade stemming from NASA’s Artermis program. Given the prioritization limitations of the Deep-Space Network (DSN) for ranging and tracking of increased deep- space assets, a more viable, and cost effective, independent navigation capability is needed. NASA’s 2015 Navigator Global Positioning System (GPS) deployed on the Magnetospheric Multi-Scale (MMS) spacecraft has validated the feasibility of acquiring weak GPS signals at distances up to 25 Earth Radii (~150,000km) or about 40% of the Cislunar trajectory. NASA plans to upgrade the flight proven MSS Navigator GPS for the future Lunar Gateway. Concurrently, the European Space Agency has confirmed the feasibility of an interoperable GPS and Galileo receiver at Lunar altitudes for a low acquisition and tracking threshold “Weak HEO” receiver for a Cubesat platform. This engineering analysis sets out to explore: (1) the smallest Global Navigation Satellite Systems (GNSS) receiver antenna that can ensure a positive carrier and code link for a Lunar bound Cubesat; (2) the position dilution of precision (PDOP) profile of this Lunar bound space vehicle; and (3) the expected improvement of the PDOP during the Moon Transfer Orbit (MTO) for an interoperable GNSS receiver, specifically Beidou. For the designed carrier-to-noise acquisition and tracking threshold of 15 dBHz, the Eb/N0 link was assured for a helix antenna with a minimum diameter of 130 mm and length of 200 mm for the GPS L1 frequency at a data rate of 50 bps. The Galileo E5a, E5b would require a larger diameter antenna at 760 mm at 448 bps data rate while Beidou requires a 350 mm diameter antenna for a 100 bps data rate to close their respectively. Utilizing the 130 mm diameter, 200 mm length helix antenna on a Lunar MTO, the preliminary assessment indicated that the GNSS PDOP calculated from valid carrier links increases from 20 when the vehicle is within the GNSS service volume to several 100th or 1000th at 60.3 Earth Radii. Due to their similar constellation altitude geometry, the Galileo E5b PDOP growth profile is similar to that of the GPS L1. The Beidou system however has a much lower PDOP growth. This difference is attributed to the set of Beidou Geosynchronous space vehicles (SV)s that have greater angular separation to the SV- receiver line-of-sight (LoS). For an interoperable GNSS receiver that can track the GPS, Galileo, and Beidou lower bound and upper bound frequencies simultaneously, the increased number of valid signals reduces the PDOP growth below 200. This engineering analysis re-affirms the potential of utilizing existing GNSS infrastructure for onboard navigation in Cislunar space, in particular, a helical antenna that can be accommodated on a Cubesat form factor.
Global Navigation Satellite System Performance in Cislunar Space for Cubesat Form Factors
Utah State University, Logan, UT
An increased Cislunar traffic is expected by the end of this decade stemming from NASA’s Artermis program. Given the prioritization limitations of the Deep-Space Network (DSN) for ranging and tracking of increased deep- space assets, a more viable, and cost effective, independent navigation capability is needed. NASA’s 2015 Navigator Global Positioning System (GPS) deployed on the Magnetospheric Multi-Scale (MMS) spacecraft has validated the feasibility of acquiring weak GPS signals at distances up to 25 Earth Radii (~150,000km) or about 40% of the Cislunar trajectory. NASA plans to upgrade the flight proven MSS Navigator GPS for the future Lunar Gateway. Concurrently, the European Space Agency has confirmed the feasibility of an interoperable GPS and Galileo receiver at Lunar altitudes for a low acquisition and tracking threshold “Weak HEO” receiver for a Cubesat platform. This engineering analysis sets out to explore: (1) the smallest Global Navigation Satellite Systems (GNSS) receiver antenna that can ensure a positive carrier and code link for a Lunar bound Cubesat; (2) the position dilution of precision (PDOP) profile of this Lunar bound space vehicle; and (3) the expected improvement of the PDOP during the Moon Transfer Orbit (MTO) for an interoperable GNSS receiver, specifically Beidou. For the designed carrier-to-noise acquisition and tracking threshold of 15 dBHz, the Eb/N0 link was assured for a helix antenna with a minimum diameter of 130 mm and length of 200 mm for the GPS L1 frequency at a data rate of 50 bps. The Galileo E5a, E5b would require a larger diameter antenna at 760 mm at 448 bps data rate while Beidou requires a 350 mm diameter antenna for a 100 bps data rate to close their respectively. Utilizing the 130 mm diameter, 200 mm length helix antenna on a Lunar MTO, the preliminary assessment indicated that the GNSS PDOP calculated from valid carrier links increases from 20 when the vehicle is within the GNSS service volume to several 100th or 1000th at 60.3 Earth Radii. Due to their similar constellation altitude geometry, the Galileo E5b PDOP growth profile is similar to that of the GPS L1. The Beidou system however has a much lower PDOP growth. This difference is attributed to the set of Beidou Geosynchronous space vehicles (SV)s that have greater angular separation to the SV- receiver line-of-sight (LoS). For an interoperable GNSS receiver that can track the GPS, Galileo, and Beidou lower bound and upper bound frequencies simultaneously, the increased number of valid signals reduces the PDOP growth below 200. This engineering analysis re-affirms the potential of utilizing existing GNSS infrastructure for onboard navigation in Cislunar space, in particular, a helical antenna that can be accommodated on a Cubesat form factor.
