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CAPSTONE (Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment)

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In 2019, NASA awarded a $13.7 million contract to Advanced Space of Boulder, Colorado, to develop and operate a CubeSat mission to the same lunar orbit targeted for Gateway – an orbiting outpost astronauts will visit before descending to the surface of the Moon in a landing system as part of NASA’s Artemis program. 1)

The Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) is expected to be the first spacecraft to operate in a near rectilinear halo orbit around the Moon. In this unique orbit, the CubeSat will rotate together with the Moon as it orbits Earth and will pass as close as 1,000 miles and as far as 43,500 miles (1000 x 70,000 km) from the lunar surface.

Figure 1: Highly elliptical, a near rectilinear halo orbit (NRHO) around the Moon takes advantage of a precise balance point in the gravities of Earth and the Moon and creates a stability that is ideal for long-term missions like Gateway (image credits: Advanced Space)

The pathfinder mission represents a rapid lunar flight demonstration and could launch as early as December 2020. CAPSTONE will demonstrate how to enter into and operate in this orbit as well as test a new navigation capability. This information will help reduce logistical uncertainty for Gateway, as NASA and international partners work to ensure astronauts have safe access to the Moon’s surface. It will also provide a platform for science and technology demonstrations.

“This is an exciting opportunity for NASA to aggressively push forward towards the Moon in partnership with several American small businesses as a vanguard to Artemis and sustained human presence beyond low-Earth orbit,” said Jim Reuter, associate administrator for NASA’s Space Technology Mission Directorate. “This mission is highly ambitious in both cost and schedule – and taking that deliberate risk is part of the objective of this mission – alongside the rapid technological advancement in cislunar navigation and the opportunity to verify orbital trajectory assumptions and retire unknowns for future missions.”

The 12U CubeSat is about the size of a small microwave oven. Onboard is a communications system capable of determining how far CAPSTONE is from NASA’s LRO (Lunar Reconnaissance Orbiter) and how fast the distance between the two spacecraft is changing. The inter-spacecraft information will be used to demonstrate software for autonomous navigation, allowing future missions to determine their location without having to rely exclusively on tracking from Earth.

CAPSTONE will provide NASA and its partners with important insights to support exploration of the Moon and Mars, including:

- Demonstration of spacecraft-to-spacecraft navigation services

- Verification of near rectilinear halo orbit characteristics for future spacecraft

- Experience entering this orbit with a highly efficient lunar transfer

- Experience with rideshare or small dedicated launches to the Moon

- Commercial experience providing mission planning and operations support services for CubeSats beyond Earth

- Rapid commercial delivery of a CubeSat mission beyond Earth orbit.

“CAPSTONE offers a lot in a small package,” said Advanced Space CEO Bradley Cheetham. “Not only will it serve as a pathfinder for Artemis, but it will also demonstrate key exploration-enabling commercial capabilities. Our team will be pioneering state-of-the-art tools for mission planning and operations to enable growth in the number of future missions to the Moon, Mars, and throughout the solar system.”

A number of launch options are possible for the mission, including being the primary payload on a small spacecraft launch vehicle. After launch, CAPSTONE will take approximately three months to enter its target orbit and begin a six-month primary demonstration phase to understand operations in this unique regime.

The award to Advanced Space is through a Phase III Small Business Innovation Research (SBIR) contract, a follow-on to earlier SBIR awards that developed CAPSTONE’s autonomous positioning and navigation system experiment.

The CAPSTONE team includes Advanced Space and Tyvak Nano-Satellite Systems, Inc. of Irvine, California. The project is managed by NASA’s Small Spacecraft Technology (SST) program within the agency’s Space Technology Mission Directorate. Based at NASA's Ames Research Center in California’s Silicon Valley, SST expands U.S. capability to execute unique missions through rapid development and demonstration of capabilities for small spacecraft applicable to exploration, science and the commercial space sector. Advanced Exploration Systems (AES) within NASA’s Human Exploration and Operations Mission Directorate will fund the launch and support mission operations. AES engages in activities focused on advanced design, development, and demonstration of exploration capabilities to reduce risk, lower life cycle cost and validate operational concepts for future human missions.

NASA’s Artemis lunar exploration program includes sending a suite of new science instruments and technology demonstrations to study the Moon, landing the first woman and next man on the lunar surface by 2024, and establishing a sustained presence by 2028. The agency will leverage its Artemis experience and technologies to prepare for the next giant leap – sending astronauts to Mars.



CAPSTONE CubeSat mission

The CAPSTONE mission is a pathfinder for NRHO operations that will be vital for future Lunar Gateway activities. Awarded in mid-2019 to Advanced Space LLC, the mission has since completed its key development and implementation milestones and is in final system assembly and test in preparation. This mission represents a new way of commercially partnering with NASA to enable rapid and cost-efficient technology demonstrations for highly condensed returns in experience to inform near-term operational needs. 2)

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Figure 2: The CAPSTONE spacecraft in a deployed (top) and stowed (bottom) configuration (image credit: Tyvak)

The CAPSTONE spacecraft is a 12U CubeSat that has been designed and is being built by Tyvak Nanosatellite Systems based on their exiting, commercial 12U satellite bus. In addition to the CAPS (Cislunar Autonomous Positioning System) payload flight board, CAPSTONE also includes a color commercial CMOS imager for generating images of the Earth and Moon, two communication systems (X-band and S-band) as well a CSAC for generating additional 1-way navigation data. The X-band system will be used for two-way communicate with the ground as well as part of the 1-way ranging experiment, while the S-band system will perform radiometric measurements with LRO to gather data for the CAPS payload using a S-band patch array antenna. The X -band system will be used to communicate with the ground, while the S-band system will perform radiometric measurements with LRO to gather data for the CAPS payload.

The spacecraft hosts a monopropellant hydrazine propulsion system, called CAPS, delivered by Stellar Exploration, Inc., providing over 200 m/s of total delta-V with eight 0.25-Newton thrusters. Four will be used for translational maneuvers and attitude control, and four will be used for attitude control and momentum desaturation.

CAPS is a unique innovation that operationalizes, and leverages investments made in algorithms, flight computers, and radios over the past decade. At its foundation, CAPS starts with the algorithms and logic of automated navigation layered on top of an innovative approach to absolute orbit determination that requires only relative radiometric ranging and Doppler measurements. In its most streamlined implementation, CAPS will be a software innovation that can be incorporated on any future spacecraft.

SBIR development: From 2017 to 2020 the CAPS development was supported via NASA SBIR contract through Goddard Space Flight Center. In this time the software was developed and tested in a lab environment that readied it for further integration and ultimately flight testing. With the Phase II concluded in mid-2020, the CAPS research and development was funded for continuation through a Phase II-e and Phase III SBIR awards. The intent for these awards is the ongoing development and support of the software as it approaches demonstration on the CAPSTONE mission. Part of these funding extensions is also to expand the data types ingestible by CAPS, thereby widening its navigation capabilities in the cislunar environment.

Crosslink: To demonstrate and accelerate the infusion of CAPS (Cislunar Autonomous Positioning System), CAPSTONE will perform numerous crosslink communication passes with LRO (Lunar Reconnaissance Orbiter) using its S-band telecommunication system. The tracking passes will occur when CAPSTONE is nearer to periapse, as LRO is in a polar, low lunar orbit. The availability of these passes will depend on a number of factors, including each spacecraft's power, their relative distances, lunar occultations, pointing constraints, and LRO ongoing science operational priorities. These tracking passes will provide two-way, coherent range and Doppler measurements to the CAPS flight software onboard CAPSTONE. The flight software will demonstrate CAPS in flight, while also downlinking the CAPSTONE-LRO crosslink data to the ground for further refinement, validation, and further development. The objective for CAPSTONE is to accelerate the infusion of autonomous spacecraft navigation, where such crosslink tracking may support the navigation needs of both spacecraft in the link. Eventually, during the enhanced mission phase, the goal is for the CAPS SW to provide full autonomous navigation onboard the CAPSTONE spacecraft thus demonstrating this capability for future cislunar mission applications.

Vision of a CAPS-enabled future: As cislunar space is poised for significant increases in mission activity, missions large and small are inherently constrained by the current limitations of ground tracking systems such as DSN (Deep Space Network) and the Near-Earth Network (NEN). The increasing the complexity of this problem is the ambiguity with which schedule and mission scope can be accurately projected. Many of these missions will be operating in orbital regimes that require frequent tracking and station keeping, which drives the demand for navigation even higher. NASA’s Artemis Program of lunar exploration will return US astronauts to the Moon and lay a foundation for development of lunar resources. The Artemis lunar architecture now in development includes major elements such as the Orion space capsule, the Lunar Gateway, a lunar lander, and the Space Launch System (SLS). Gateway will serve as a departure point for human excursions to the surface of the Moon. Many of these projects, and others from around the world, are now in development and can benefit from the CAPS capabilities for their operational navigation requirements.

Advanced Space foresees a future of increasing scientific and exploration activity within cislunar space. Future missions operated by NASA, commercial entities, and international agencies will face increasing congestion due to limited communication and navigation infrastructure.

The CAPSTONE 12U CubeSat, with a total mass of ~25 kg and a size of 34 x 34 x 64 cm, will serve as the first spacecraft to test a unique, elliptical lunar orbit as part of the CAPSTONE mission. As a precursor for Gateway, a Moon-orbiting outpost that is part of NASA’s Artemis program, CAPSTONE will help reduce risk for future spacecraft by validating innovative navigation technologies and verifying the dynamics of this halo-shaped orbit. 3)



Development status

• April 6, 2022: The pathfinder for NASA’s lunar outpost will launch in May to test an orbit around the Moon that has never been flown before. The CAPSTONE (Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment) is undergoing final construction – and with solar panel installation and vibration testing now complete, the small satellite will soon be shipped to its launch location in New Zealand. 4)

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Figure 3: Rebecca Rogers, systems engineer, takes dimension measurements of the CAPSTONE spacecraft at Tyvak Nano-Satellite Systems, Inc. in Irvine, California (image credit: NASA/Dominic Hart)

- CAPSTONE – operated by Advanced Space – will help pave the way for NASA’s future exploration of the solar system, testing out this significantly elongated and halo-shaped orbit before arrival of Gateway, a next-generation space station that will provide access to the Moon and potentially beyond. Like Gateway, CAPSTONE continues the tradition of commercial partnerships, with five companies, including American small businesses, making contributions. The spacecraft was built and tested by Tyvak Nano-Satellite Systems, Inc., a Terran Orbital Corporation in Irvine, California, and will be launched by Rocket Lab of Long Beach, California.

- Some of those partners are joining members of the CAPSTONE team at this year’s Space Symposium, sharing the project’s work and celebrating the induction of small satellite technologies into the Space Technology Hall of Fame. Small satellites, including CubeSats like CAPSTONE, can make meaningful contributions to science and exploration at a lower cost and faster cadence.

- The CAPSTONE mission sends a CubeSat – about the size of a microwave oven – to study this orbit for at least six months, launching via a trajectory known as a ballistic lunar transfer. This highly efficient trajectory uses very little fuel, making use of the Sun’s gravity to reach this unique orbit around the Moon.

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Figure 4: A member of CAPSTONE team inspects the installation of solar arrays on the mission’s CubeSat (image credit: NASA/Dominic Hart)

- By taking advantage of the precise points between the Earth and Moon where the gravity from both is balanced out, spacecraft traveling along this orbital path can save energy to maintain the orbit. It also takes less fuel to enter the orbit because of its elongated shape, only 1,000 miles away from the North Pole at its nearest pass to Earth every six and a half days.

- During its journey along this path, CAPSTONE will test out spacecraft-to-spacecraft navigation and communications systems with NASA’s Lunar Reconnaissance Orbiter (LRO), another spacecraft in orbit around the Moon. By demonstrating that two orbiting spacecraft can communicate and track their positions independent of Earth, NASA is showing how future missions could pinpoint their place in space as they reach for more distant destinations.

- Now that testing is completed, CAPSTONE is on track to launch next month and begin testing the path that NASA’s Gateway will follow in the years to come.

- CAPSTONE is commercially owned and operated by Advanced Space in Westminster, Colorado. It represents an innovative collaboration between NASA and industry to provide rapid results and feedback to inform future exploration and science missions.

- NASA’s Small Spacecraft Technology program within the agency’s Space Technology Mission Directorate (STMD) funds the demonstration mission. The program is based at NASA’s Ames Research Center in California’s Silicon Valley. The development of CAPSTONE’s navigation technology is supported by NASA’s Small Business Innovation Research and Small Business Technology Transfer (SBIR/STTR) program, also within STMD. Advanced Exploration Systems within NASA’s Exploration Systems Development Mission Directorate funds the launch and supports mission operations. The Launch Services Program at NASA’s Kennedy Space Center in Florida manages the launch.

• September 23, 2021: Practice makes perfect. As a Moon-bound CubeSat prepares for launch, the CAPSTONE team at Advanced Space’s operations center in Westminster, Colorado, conducted a series of mission simulations. The simulations virtually put the CubeSat through its orbital dynamics paces. 5)

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Figure 5: The team at Advanced Space, NASA's partner, performs the third operations readiness test at its CAPSTONE mission operations center in Westminster, Colorado. The team conducted simulated spacecraft trajectory and correction maneuvers necessary to perform spacecraft insertion into its final lunar orbit (image credit: Advanced Space)

- CAPSTONE, a technology demonstration mission, will test a unique lunar orbit that is intended for Gateway, the Moon-orbiting outpost for NASA’s Artemis program. CAPSTONE will demonstrate the ability of its spacecraft – a microwave-oven sized CubeSat – to enter into and maintain this special lunar orbit for approximately six months. The dynamics of this orbit, formally called a lunar near rectilinear halo orbit, or NRHO, have not been tested in spaceflight before. The NRHO takes advantage of a precise balance point in the gravity fields of Earth and the Moon. Spacecraft in this orbit will have a continuous, unobstructed view of Earth that will allow constant communications with mission controllers on Earth.

- For the test, the team processed simulated CAPSTONE spacecraft tracking data provided by NASA’s Deep Space Network, to create an accurate prediction of the spacecraft’s location and future trajectory. The mission simulation tests included the team performing the precise, time-critical orbit insertion maneuver into the NRHO. This critical maneuver reduces the spacecraft’s energy so it is captured by lunar gravity. Following the NRHO insertion maneuver, the team executed insertion correction maneuvers, which clean up errors and allows the team to transition to the next expected operations at the Moon. The test also allowed the team to practice responses to potential anomalies during simulated flight to ensure the spacecraft stays on course.

• March 23, 2021: NASA's CAPSTONE journey to the Moon will take about three months, starting with its launch to low-Earth orbit on a Rocket Lab Electron. Rocket Lab’s Photon spacecraft will take over next and conduct a series of orbit-raising maneuvers to prepare the CubeSat for its transfer path to the Moon. After separating from Photon, CAPSTONE will utilize an energy-efficient ballistic lunar transfer using its onboard propulsion system and enter into a near rectilinear halo orbit in the vicinity of and around the Moon. There, it will maintain the orbit to inform future spacecraft and demonstrate new technologies. 6)

- CAPSTONE’s propulsion system is designed and built by Stellar Exploration Inc. of San Luis Obispo, California. Initially funded by NASA’s Small Business Innovation Research program, the system is approximately 8-inches square by 4-inches deep. The system’s eight thrusters are fed hydrazine propellant from an unpressurized tank. CAPSTONE’s super small, high-performance thrusters integrate proven NASA technology with state-of-the-art industry fabrication techniques.

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Figure 6: CAPSTONE’s propulsion system undergoes environmental testing. Environmental testing ensures that spacecraft systems can operate after being launched into space and in the space environment (image credit: Stellar Exploration Inc.)


Launch: The CAPSTONE spacecraft will be launched in May 2022 on a three-stage Electron, a launch vehicle developed by Rocket Lab. After launching into a low Earth orbit from the Rocket Lab LC-1 (Launch Complex) on Mahia Peninsula, NZ at a latitude of approximately -39º, the Lunar Photon third stage will perform a series of apogee raising maneuvers to achieve the trans-lunar injection (TLI) characteristic energy, C3, of approximately -0.6 km2/s2 to put the spacecraft on its deep-space BLT trajectory. A true ballistic BLT (no deterministic maneuvers) requires instantaneous Sun- Earth-Moon geometry, however a deterministic apogee maneuver may be introduced in order to build a TLI period, as well as target a specific NRHO (Near Rectilinear Halo Orbit).

BLT Maneuver

Ballistic Lunar Transfers (BLTs) are a type of low-energy transfer in which a spacecraft travels to an apogee of 1-1.5 million km to utilize the Sun’s gravity to modify the spacecraft’s orbital perigee and inclination.
For CAPSTONE, this effect is used to decrease the inclination from a launch latitude of ~39° to an inclination in line with the Moon’s orbital plane, as well as raise the spacecraft’s perigee to the radius of the Moon. This reduces the deterministic spacecraft ΔV to approximately 20-60 m/s, compared to the 350-550 m/s required for a direct transfer to an NRHO. This reduction in spacecraft ΔV enables the mission to be achieved with a 12U-class CubeSat. The TLI C3 of approximately -0.6 km2/s2 is higher than -2.0 km2/s2, the value needed for a direct transfer. The BLT also requires three to four months of time to traverse, which is substantially longer than a direct transfer. This extended transfer duration provides for advantages from an operational perspective. First, there is ample time to characterize and navigate the spacecraft performance and then perform well-timed trajectory correction maneuvers that allow for a consistent entry time into the NRHO. When the spacecraft reaches perigee, it encounters the Moon and inserts into the NRHO.

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Figure 7: TCM Placement in the Earth-Centered EME2000 Frame (image credit: CAPSTONE Team, Ref. 2)

• In May 2022 Rocket Lab will launch a CubeSat to the Moon. This historic pathfinding mission supports NASA’s Artemis program which will land the first woman and first person of color on the Moon. 7)

- Using our Electron rocket and new Lunar Photon upper stage, Rocket Lab will inject the CAPSTONE CubeSat to a highly efficient transfer orbit to the Moon. CAPSTONE is owned and operated by Advanced Space in Westminster, Colorado, for NASA.

- CAPSTONE’s primary objective is to test and verify the calculated orbital stability of a Near Rectilinear Halo Orbit around the Moon, the same orbit planned for Gateway. NASA’s Gateway is a small space station that will orbit around the Moon to provide astronauts with access to the lunar surface. It will feature living quarters for astronauts, a lab for science and research and ports for visiting spacecraft. CAPSTONE will also test a navigation system developed by Advanced Space that will measure its absolute position in cislunar space using interaction with NASA's Lunar Reconnaissance Orbiter without relying on ground stations for navigation support.

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Figure 8: How we're getting there (image credit: Rocket Lab)

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Figure 9: The Electron launch vehicle is CAPSTONE’s ride to space. Once Electron reaches low Earth orbit, our Lunar Photon upper stage takes the reigns to deliver the CAPSTONE spacecraft onto its highly efficient ballistic transfer orbit to the Moon. Lunar Photon, with Advanced Space’s CAPSTONE attached, will orbit the Earth in elliptical phasing orbits over nine days to build up velocity for a Trans Lunar Injection (TLI) to deploy CAPSTONE into the deep space, low energy transfer orbit to the vicinity of the Moon (image credit: Rocket Lab)



1) ”NASA Funds CubeSat Pathfinder Mission to Unique Lunar Orbit,” NASA Press Release 19-073, 13 September 2019, URL: https://www.nasa.gov/press-release/nasa-funds-cubesat-pathfinder-mission-to-unique-lunar-orbit

2) Thomas Gardner, Brad Cheetham, Alec Forsman, Cameron Meek, Ethan Kayser, Jeff Parker, Michael Thompson, Tristan Latchu, Rebecca Rogers, Brennan Bryant, Tomas Svitek, ”CAPSTONE: A CubeSat Pathfinder for the Lunar Gateway Ecosystem,” Proceedings of the 35th Annual AIAA/USU Virtual Conference on Small Satellites, August 7-12, 2021, Logan, UT, USA, SSC21-II-06, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=5016&context=smallsat

3) ”What is CAPSTONE?,” NASA, 31 July 2020, URL: https://www.nasa.gov/directorates/spacetech/small_spacecraft/capstone

4) Frank Tavares, ”NASA’s CAPSTONE Prepares to Enter Unique Orbit,” NASA Ames Feature, 6 April 2022, URL: https://www.nasa.gov/image-feature/ames/CAPSTONE

5) ”CAPSTONE Team Keeps CubeSat on Track During Simulated Flight,” NASA Feature Ames, 23 September 2021: https://www.nasa.gov/feature/ames/capstone-team-keeps-cubesat-on-track-during-simulated-flight

6) ”Innovative Propulsion System Gets Ready to Help Study Moon Orbit for Artemis,” NASA Feature Ames, 23 March 2021, URL: https://www.nasa.gov/feature/ames/innovative-propulsion-system-gets-ready-to-help-study-moon-orbit-for-artemis

7) ”Mission To The Moon,” Rocket Lab, 2022, URL: https://www.rocketlabusa.com/missions/lunar/


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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