Though NASA's CAPSTONE spacecraft is small, it is not insignificant.
On June 28th, 2022 a small satellite was launched on a small rocket from Mahia Peninsula in New Zealand and began its long journey to the Moon. The spacecraft is the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE). It is a small technology demonstrator paid for by NASA that is expected to become the first spacecraft to enter a near-rectilinear halo orbit (NRHO) and serve as a pathfinder for a future manned space station known as the Lunar Gateway. It will also demonstrate new propulsion and navigation technologies.
The small rocket it launched on is called Electron, and it is operated by Rocket Lab, a space startup that was founded in New Zealand but is now headquartered in the US. The Electron rocket isn't large enough to send CAPSTONE directly towards the Moon, so it was launched attached to Lunar Photon, a kick stage that will use its thrusters to take CAPSTONE from Low Earth Orbit (LEO) and send it towards the Moon. Even then, CAPSTONE doesn't have enough fuel to take a direct route to the Moon, so it will spend a few months taking low-energy trajectory and arrive at its target NRHO on November 13th.
This spacecraft is really small by spacecraft standards, but I think its really important. Why? CAPSTONE is a simple mission that is doing multiple firsts, and more importantly, demonstrating what small satellites, small budgets, and small rockets can do.
Two-Fold Mission
CAPSTONE has two key goals. To practice using a near-rectilinear halo orbit (NRHO) and to demonstrate Cislunar Autonomous Positioning System (CAPS).
A Novel Orbit
As a key part of the Artemis program NASA is working with its international partners to build a manned space station known as the Lunar Gateway. The Lunar Gateway will serve as an outpost and place to prepare for lunar landings, and to perform pioneering deep space science. NASA selected a unique orbit for the space station that has never been used before, a near-rectilinear halo orbit (NRHO). A NRHO is a stable orbit that takes about a week to complete. A NRHO comes within about 1,600 km (1,000 mi) of the Moon's north pole before swooping way down to about 70,000 km (43,500 mi) beneath the south pole.
This orbit allows for easy access to the entire surface of the moon, and never goes behind the Moon. So, it can always communicate with mission control. It also requires relatively little rocket fuel to enter and leave this orbit.
The first components of the Lunar Gateway, which has already cost $1.8 billion*, are scheduled to launch in 2024. Before that NASA wants to practice entering, exiting, and maintaining a NRHO. NASA also wants to practice communicating with the Deep Space Network (DSN) from a NRHO. So, this is what CAPSTONE will do, after arriving in its target orbit its primary mission will last 6 months.
A New Way to Navigate
Cislunar Autonomous Positioning System (CAPS) is a new technique that allows a spacecraft to determine its precise location by communicating only with other spacecraft, and not with Earth. CAPSTONE will demonstrate CAPS by communicating with NASA's Lunar Reconnaissance Orbiter (LRO), which has been orbiting the Moon since 2009. LRO orbits the moon in a polar orbit much lower than a NRHO. Since the satellites are in different orbits, CAPSTONE can determine its precise location by communicating with LRO. If it finds that it is slightly off course, it can then correct itself without assistance from Earth.
In the future, a fleet of miscellaneous spacecraft in different orbits can all communicate with each other to determine their locations. They can then correct their orbits without assistance from people on Earth.
A Small Spacecraft
To fulfill this mission, a small, low-cost spacecraft was built. The CAPSTONE spacecraft is a 12U CubeSat built by Tyvak Nanosatellite Systems. The main structure of the spacecraft is 34 by 34 by 61 cm (13 x 13 x 24 in), which makes it about the size of a microwave. It has two antennas, one for communicating with LRO, and one to return data to Earth. Power is provided by two solar arrays. It is equipped with a small color camera that will take images of Moon and Earth.
Unique Propulsion
CAPSTONE is also pioneering a new propulsion system that was developed by Stellar Exploration in collaboration with Malin Space Science Systems. Many spacecraft use propulsion systems that keep hypergolic propellants at high pressures. By keeping the propellants at high pressures a pump is not needed to move the fuel to the engine. This requires little equipment and is reliable and long lasting. Stellar Exploration used NASA funding to create a unique propulsion system that does the opposite. It stores hydrazine in low pressure tanks and uses an electric pump to pressurize it before it is burned as fuel. This unique design makes the propulsion system extremely powerful for its small size. This system has 8 small thrusters and uses hydrazine and nitrogen tetroxide.
Built Different
Something else that makes CAPSTONE special is that it is not operated by NASA, but by a company. Typically, one of NASA's centers, such as JPL or Goddard, is put in charge of managing each mission. For CAPSTONE, NASA outsourced the development and construction work. They payed Advanced Space to design the spacecraft, who in turn contracted Tyvak Nano-Satellite Systems to manufacture the spacecraft and Stellar Exploration to build the propulsion system. Advanced Space will also operate and send commands, which is typically done by NASA
This is consistent with the NASA trend. Instead of designing or building it themselves, they hire a company to do it. Though this might sound like a bad idea, it is usually a good idea. In many cases companies do a job better and cheaper. They are incentivized to minimize spending and in doing so they often come up with clever solutions.
This idea is validated by the extremely low cost of CAPSTONE, which cost less than $30 million, including the launch vehicle. By comparison NASA's LADEE mission, which launched in 2013 to study the Moon, was considered low-cost at the time and cost $280 million. Though this isn't a fair comparison since LADEE was much larger and more complicated than CAPSTONE, it shows how insanely cheap CAPSTONE is.
Key Moment for Rocket Lab
This mission is also key for Rocket Lab. It is probably their highest-profile mission in their 16-year history. Rocket Lab is a company that is quickly growing and becoming a key player in the space industry.
They focus on launching dedicated smallsat missions using their small two-stage Electron rocket. Rocket Lab wants to reuse Electron's first stage and have fitted their rocket with parachutes and recently attempted to use a helicopter to snag the rocket's parachute. Electron typically launches payloads that weigh less than 200 kg (441 lbs). The Lunar Photon and CAPSTONE combo weigh 300 kg (661 lbs), which is Rocket Lab's heaviest payload yet. In order to allow for Electron to launch this payload Rocket Lab had to remove all unnecessary items, including cameras and recovery equipment. Rocket Lab also makes a lot of money by selling spacecraft components, including reaction wheels and star trackers.
The Lunar Photon spacecraft, is based on Rocket Lab's Photon spacecraft bus. Some Electron customers also purchase a Photon to act as a kick stage or to use it to deploy multiple satellites in one rocket launch. Rocket Lab's modifications to the Lunar Photon include making it capable of surviving in deep space and giving it a more powerful main engine. After deploying its payload, Rocket Lab will use Lunar Photon for testing, then will attempt a flyby of the Moon.
Conclusion
The CAPSTONE spacecraft is really small for a deep space mission. It is doing three important things that have never been done before, entering a new orbit, testing a new navigation system, and demonstrating a new propulsion system. And this is what makes CAPSTONE a misnomer.
A capstone concludes and finalizes something, but this spacecraft is more like a cornerstone. Instead of concluding something, it is beginning something. It is showing us that small satellites can be very useful, that outsourcing NASA projects really does save money, and that small rockets can be pushed to the limits to launch satellites much larger than they were designed for. It is demonstrating technologies that can be used on future Artemis missions, both manned and robotic. It is paving the way for the Lunar Gateway. It is setting a precedent: that small budgets, short timelines, and small satellites can do amazing things.
CAPSTONE is among the first of what soon may become a large group of small satellites that go beyond Earth orbit. Small satellites scheduled to launch on Artemis-1 and SIMPLEx missions will soon follow. And then many more.
Many more missions that will build on the cornerstone that is CAPSTONE.
Sources and Notes:
*This is the combined cost of contracts that have already been awarded for the design, construction, and launch of PPE and HALO, the first two Gateway modules.
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