Last time I talked about all planned missions to the Moon. This time, let us take a closer look at one of them – the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE). Let’s find out how a slam satellite can get to the Moon.
The rocket
We’ll start with the rocket bound to take the spacecraft to the Moon. The Capstone mission will utilize the Electron rocket to get into orbit. Electron is a small launch vehicle. It’s developed, build and launched by Rocket Lab. It will launch from LC-1A on the Māhia Peninsula in New Zealand. Originally, the plan was to launch from LC-2 in the Mid-Atlantic Regional Spaceport on Wallops Island in Virginia, United States. As this launch pad currently isn’t able to support the launch, Capstone will launch from New Zealand.
Electron is an 18 m height, two-stage rocket. It can be equipped with an additional kick-stage. For the Capstone mission, it will use a new Lunar Photon upper stage as kick-stage and more. After reaching orbit, Photon will detach from the second-stage and put itself and the Capstone spacecraft in a circular orbit at 250 km altitude. It will fire its engine multiple times to increase the orbit and prepare for trans lunar injection. A final engine burn will increase the speed to 11 km/s sending Photon and Capstone to the Moon.
Capstone will separate from Photon on the way to the Moon. While Photon will make one more burn to send it past the Moon into interplanetary space, Capstone will use its propulsion to enter into a near rectilinear halo orbit around the Moon.
The mission
More on the orbit later. For now, let us focus on the goals of the mission. In fact, one of the goals is the orbit. To be more precise, the goal is to verify, that a cis-lunar near rectilinear halo orbit can be used as predicted. No spacecraft has ever used such an orbit so far. Capstone will be the first. Therefore, it’ll test that the calculations are correct and that the orbit is usable as intended. By doing so, it’ll also test the required navigation technologies. In addition, it’ll also test new spacecraft-to-spacecraft navigation technologies. More on that, when we talk about the spacecraft.
The mission will last at least six months to get enough data about the orbit. In this time, it will not only collect data about the orbit, but also about the power and propulsion requirements to maintain it.
The orbit
As the orbit is one of the main goals of the mission, let’s take a closer look. What is a cis-lunar near rectilinear halo orbit? It’s nothing entirely new, as it is also known as a near rectilinear halo orbit (NRHO). It’s a unique, elliptical obit, which in this case has the Moon as its center point. In this case, the orbit will bring Capstone as close as 1,600 km to the North Pole and up to 70,000 km above the South Pole of the Moon. One orbit will take seven days.
So, why will Capstone and later Gateway use this orbit? Because it offers stability for long-term missions, while at the same time only requiring a minimal amount of energy to maintain it. Therefore, it is a great orbit for a space station at the Moon. Because resupplying a space station in lunar orbit is way more expensive than, for example, resupplying the Internation Space Station. But the orbit has more advantages, like an unobstructed view of Earth, which means unobstructed communication with ground stations on Earth.
The spacecraft
The Capstone spacecraft is a CubeSat about the size of a microwave oven. More precisely, it measures 12U, which is a standardized size for CubeSats. It’s owned and operated by Advanced Space, a commercial company contracted by NASA.
For demonstrating relative spacecraft navigation, without relaying on ground station, it will directly communicate with NASA’s Lunar Reconnaissance Orbiter (LRO). Therefore, it has a second flight computer and radio. The flight computer on Capstone will use data from this communication to measure it distance from LRO, as well as how fast the distance changes. From this, it will calculate the position of Capstone. The system doing this is called Cislunar Autonomous Positioning System (CAPS).
Credit for image at the top: NASA (NASA ID: ACD22-0003-001)
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