Simulation Evaluation of Moon Transfer Orbit Navigation Using GPS Carrier Phases

NASA aims to bring astronauts to the moon by 2024. According to their lunar exploration program called the Artemis, the spacecraft Orion will be launched by the Space Launch System (SLS) and the Orion will bring astronauts to the moon. Then, they will land on the moon by using the human landing systems (HLS) docked to the Orion or by using the HLS docked to the lunar gateway orbiting around the moon whose components will be launched in 2023. The Japan Aerospace Exploration Agency (JAXA) is one of the international cooperation partners for this magnificent program. Although there are many technical challenges that should be addressed for accomplishing the lunar exploration mission, one of the key issues is the navigation of the Orion and of the supply spacecrafts to the gateway. Since the Orion will fly far beyond the GPS satellites, it will only receive signals coming from those GPS satellites located at the opposite side of the earth and the number of the available GPS satellites will become small. Moreover, the weaker GPS signals will enhance the measurements noises that corrupt the quality of the pseudo range and carrier phase. Following this background, this paper investigates the achievable navigation accuracy using the GPS carrier phases for the moon transfer orbit (MTO) through a series of simulation using actual ephemerides of the GPS satellites, moon, and sun. Starting from the altitude of about 180 kilometers, direct MTO, GPS pseudo ranges, and carrier phases are simulated. Then, the MTO navigation accuracy using the pseudo ranges or the carrier phases was evaluated. According to our simulation results, the navigation using the carrier phases was significantly more accurate than that using the pseudo ranges. The confirmed position estimation errors were below 100 meters until the altitude of about 200, 000 kilometers and below 180 until the moon altitude. The velocity estimation errors were about 1 cm/s until the altitude of about 200, 000 kilometers and became 5 mm/s after about 280, 000 kilometers.