A little while ago, NASA’s CAPSTONE satellite was launched atop a Rocket Lab Electron rocket from the base in New Zealand. For about six days, the rocket’s upper Photon stage will carry CAPSTONE toward the Moon and then separate and let it travel for more than four months. Eventually, this CubeSat-class satellite will enter a so-called near-rectilinear halo orbit (NRHO) to study its dynamics for at least six months. This is the orbit into which NASA’s Lunar Gateway, a crucial element of the Artemis program, is scheduled to be placed, so there’s the need to check for unexpected problems, which includes communications.
The Artemis Moon program is very ambitious, as it involves not only the return of astronauts to the Moon but also the construction of the Gateway, a space station orbiting the Moon. This is an unprecedented project, so it’s not possible to rely on simulations alone to ensure the stability of the Gateway in its orbit and the ease of communication. For this reason, NASA built the CAPSTONE (Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment) satellite to verify the correctness of the simulations.
In recent years, CubeSat-class nanosatellites, based on cubic units of 10 centimeters per side, have become very common. CAPSTONE consists of 12 units, so it’s not so small but it’s still possible to launch it with a small rocket such as the Electron made by Rocket Lab, a company that has been managing launches of small satellites for some years, in this case on behalf of NASA.
The CAPSTONE satellite is equipped with navigation and communication systems specially designed for the orbit in which it will perform its tests. NASA developed CAPS (Cislunar Autonomous Positioning System) technology precisely to allow the Gateway and other stations and spacecraft to navigate in the cislunar orbit without having to rely on Earth stations or satellites. CAPSTONE will be used to demonstrate this technology as well and will communicate with the Lunar Reconnaissance Orbiter (LRO) space probe as well.
The near-rectilinear halo orbit around the Moon that the CAPSTONE satellite will reach in November will take it up to about 1,500 kilometers of altitude in its closest approach and up to about 70,000 kilometers of altitude at the point of maximum distance from the Moon. One orbit of the Moon will be completed in about seven days during which it will be under the influence of Earth’s gravity for most of the time. The journey to reach that orbit is long because, for this mission, the cost is an important factor but the launch was a success.