Most satellite landers and orbiters today use either a dish or a single fixed antenna. This article will examine the benefits of using different antenna designs in the lunar environment. Specifically, the article will focus on a lunar orbit on the far side of the moon, where Vulcan Wireless has contributed to the development of advanced lunar communication devices for upcoming missions. Using a typical lunar orbit, the article examines the link performance for a particular operating scenario. The operational scenario that will be considered has three devices on the lunar surface, where all three devices are in a band and trying to exfiltrate sensor data back to Earth.
Landing and surviving on the moon require careful attention to both radio and antenna design. As an example, environmental conditions include extreme temperature changes ranging from -410°F (-246°C) to 250°F (121°C) on the lunar surface. Several upcoming missions will be utilizing both Vulcan Wireless’s software-defined radio (SDR) and cryogenic antenna for S-Band. This article compares the performance of this system with a Vulcan Wireless phased array antenna that is currently in development and available for future deployments. The basic metric that will be utilized for link performance is the data exfiltration rate. This is the amount of data, typically sensor data, that the lander or rover can transmit back to Earth on an average Earth day. The article will describe ways to maximize this data.
Vulcan Wireless is producing multiple SDRs for lunar operations within NASA Commercial Lunar Payload Services (CLPS) programs. Shown in Figure 1 are past and upcoming CLPS missions. Specifically, Vulcan Wireless has SDRs in Firefly’s Blue Ghost Mission 1, Firefly’s Blue Ghost Mission 2 and Firefly’s Lunar Orbiter. These missions are depicted in Figure 1 as item numbers 3 and 4.
Figure 1 Lunar landers and lunar orbiters in the NASA CLPS program.
Note that some near-side lunar missions can communicate directly with the Earth without the use of a lunar orbiter. However, far-side missions require an orbiter for communication. To communicate to a far-side lunar lander/rover, a basic approach involves the use of a directional satellite dish on the orbiter. This article will examine the communication performance in this extreme lunar environment. The key communication performance metric that is used is the number of data bits that the lunar lander can exfiltrate per Earth day. A larger number of exfiltrated bits means more sensor data and more images can be captured and analyzed back on Earth. The communication performance in the presence of interference will be discussed. The article will show how Vulcan Wireless’s phased array antenna can be used to combat interference and significantly increase the exfiltration rate.
For the communications protocol, a number of different communication waveform protocols can be used. The Vulcan SDR, shown in Figure 2, supports many different Consultative Committee for Space Data Systems (CCSDS) protocols that are used in space and lunar applications. Specifically, it supports CCSDS telecommand (TC), CCSDS telemetry (TM), CCSDS proximity and CCSDS DVB-S2, which are critical for ensuring reliable and standardized data transmission. The SDR has been used for uplinks, downlinks and crosslinks. The SDR also has support for precision navigation and timing. Software configurations allow the radio to be used for both time transfer and ranging applications. The SDR exceeds expectations in radiation testing at the NASA Goddard facility and it is also available with military-grade top secret and below encryption.
Figure 2 Vulcan Wireless SDR.
Figure 3 Vulcan Wireless cryogenic antenna.
The simulations use the antenna profile of the Vulcan Wireless cryogenic S-Band antenna shown in Figure 3. NASA has approved this antenna to withstand the lunar night, which can reach -410°F (-246°C). The lunar surface is particularly challenging due to the temperature extremes accompanying the change between lunar day and lunar night. A lunar day and lunar night are equal to one Earth month, which is 30 Earth days.
SINGLE ANTENNA POINTING AT THE LUNAR LANDER
To understand data exfiltration on the moon, a lunar orbit derived from the expected ephemeris of upcoming launches is used as an example. The tracks are shown in Figure 4. The upper image in Figure 4 shows the track for one Earth day and there are three distinct tracks. These are three passes that would occur during a 24-hour Earth day. The lower picture has many tracks, which correspond to all the passes within a 30-day Earth month. The yellow markings on both images in Figure 4 indicate the locations used in the simulation analysis.