Pre-mission, we need to ensure that several upgrades are made to bring the mission to technical sufficiency pre-launch.
Within a spacecraft, astronauts communicate with each other using an internal communication system, often referred to as the "intercom." This system allows astronauts to speak with each other within different parts of the spacecraft without needing to raise their voices or move to a different location.
Communicating from space involves more than pointing a spacecraft’s antenna at the Earth. NASA has an extensive network of antennas around the globe — over all seven continents — to receive transmissions from spacecraft. Network engineers carefully plan communications between ground stations and missions, ensuring that antennas are ready to receive data as spacecraft pass overhead.
Ground station antennas range from the small very high frequency antennas that provide backup communications to the space station to a massive, 230-foot antenna that can communicate with far-off missions like the Voyager spacecraft, over 11 billion miles away.
We encode data on various bands of electromagnetic frequencies. These bandwidths — ranges of frequencies — have different capabilities. Higher bandwidths can carry more data per second, allowing spacecraft to downlink data more quickly.
NASA’s Laser Communications Relay Demonstration (LCRD) will showcase the benefits of optical communications. The mission will relay data between ground stations in California and Hawaii over optical links, testing their capabilities. NASA will also furnish the space station with an optical terminal that can relay data to the ground via LCRD.
Higher bandwidths can mean higher data rates for missions. Apollo radios sent grainy black and white video from the Moon. An upcoming optical terminal on the Artemis II mission will send 4K, ultra-high definition video from lunar orbit.
Bandwidth isn’t the only constraint on data rates. Other factors that can affect data rates include the distance between the transmitter and receiver, the size of the antennas or optical terminals they use, and the power available on either end. NASA communications engineers must balance these variables in order to maximize data rates.
We also need to consider latency. Communications don’t occur instantaneously. They’re bound by a universal speed limit: the speed of light, about 186,000 miles per second. For spacecraft close to Earth, this time delay — or communications latency — is almost negligible.
However, farther from Earth, latency can become a challenge. At Mars’ closest approach — about 35 million miles away — the delay is about four minutes. When the planets are at their greatest distance — about 250 million miles away — the delay is around 24 minutes. This means that astronauts would need to wait between four and 24 minutes for their messages to reach mission control, and another four to 24 minutes to receive a response. The considerations for Saturn will be 7 times worse than this, and we need to prioritize low latency signals.
Lastly, we need to take into account interference due to other signals in the atmosphere. As communications transmissions travel over long distances or through the atmosphere, the quality of their data can deteriorate, garbling the message. Radiation from other missions, the Sun, or other celestial bodies can also interfere with the quality of transmissions.