Rocket Lab’s now well-known for their Electron Rockets, and one of them is about to carry NASA and Advanced Space’s Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) mission on the first leg of its trip to the Moon.
It’s Rocket Lab’s new Photon vehicle and its HyperCurie engine that will bring CAPSTONE the rest of the way, though, and Photon’s maiden voyage into cislunar space might well become an unexpected highlight of the mission.
From kick stage to Spacecraft
Rocket Lab announced its first Photon in April 2019 at the 35th Space Symposium. In a short promotional video made in July, they elaborate on the Photon. They explained that it was a natural evolution of the Rocket Lab kick stage that circularizes the orbit after the second stage boost brings them to apogee, and then reorients itself to deploy satellites into independent circular orbits.
Photon keeps the Curie Engine, the kick stage’s in-space propulsion system, and adds power generation, attitude control and thermal management (among other capabilities) to turn Photon into a dual-function spacecraft that can launch clients’ satellites and then transition into hosting other companies’ payloads as a satellite bus.
Several test flights of the Photon platform have already passed: aside from an early test off a modified kick stage in June of 2020, their first test was the Photon Pathfinder satellite in August 2020 aboard the “I Can’t Believe It’s Not Optical” Electron mission, and the second was the Photon Pathstone aboard the “They Go Up So Fast” Electron mission in March of 2021. Rocket Lab has even published pictures on Twitter of the “briefcase”, the box that’s attached to the kick stage to turn it into an LEO Photon.
The Lunar CAPSTONE mission will be Photon’s first operational mission.
CAPSTONE’s halo around the Moon
The NASA-funded CAPSTONE mission—built by Terran Orbital based on designs by CAPSTONE owner and mission project manager Advanced Space—is one of the first steps in the American return to the Moon.
It’s a groundbreaking mission in several ways. Its size is one. The CAPSTONE satellite is comparatively tiny; it’s a 12U CubeSat that weighs just 55 pounds and is around the size of a microwave. While satellites that size are common in LEO, having one of them going all the way to the Moon outside of a rideshare program is unprecedented.
Its particular Lunar orbit is also unprecedented. It will be circling the Moon using a near rectilinear halo orbit (NRHO), a highly elliptical orbit that will take 7 days to circle the Moon and uses the gravitational forces of both the Moon and the Earth to remain stable with minimal fuel expenditures. This orbit is the same one that NASA is planning to use for their Lunar Gateway—an orbit which will allow it to have constant line-of-site with the Earth for communications, constant solar exposure for power, and regular periods of close access to the Lunar surface. CAPSTONE will be the first satellite using this orbit, and will track the distance between itself and the Lunar Reconnaissance Orbiter, sending the data to NASA to prepare for the Lunar Gateway.
Notably, CAPSTONE is also a nearly completely commercially-driven mission. While NASA provided funding, all of the organizations directly involved (Rocket Lab, Terran Orbital and Advanced Space) are commercial companies.
Photon slingshotting the CAPSTONE
Getting all this done with a small rocket like an Electron might seem unfeasible considering the distances involved. Rocket Lab is resolving this problem by creating a new kind of Photon, and having it use a new type of engine, that will allow Rocket Lab and Advanced Space to bring CAPSTONE to the Moon.
The Lunar Photon’s HyperCurie engines use electric pumps, instead of the pressure-fed Curie, which, according to Rocket Lab CEO Peter Beck on Twitter, lets you “use solar to charge up the batteries in between burns.” The HyperCurie eliminates the need for an ignition system by using “hypergolic” propellants, ones that spontaneously ignite on contact Rocket Lab hasn’t shared details on the propellant, but Beck also said on Twitter that it is a “green hypergolic,” which eliminates many traditional hypergolic propellants as they’re highly toxic. It also has expanded fuel tanks and solar panels.
(Rocket Lab posted video of a test firing of the HyperCurie in late April)
After the Electron and its nine Rutherford engines carry the Photon and CAPSTONE into an initial low Earth orbit, Advanced Space will command the Photon to begin a series of maneuvers called Ballistic Lunar Transfers that carries them into increasingly elliptical orbits around the Earth, moving farther and farther away, until it’s distant enough that the Sun’s gravity is able to change Photon and CAPSTONE’s orbit, bringing it back to cislunar space in just the right speed and direction to be captured by the Moon’s gravity.
Once CAPSTONE is on its final trajectory that will eventually bring it to the Moon, Photon will release the microwave-sized CubeSat, which will use its own propulsion systems to reach its halo orbit and begin operations.
This will be a complex and difficult mission, especially for the still-new Photon platform. While Advanced Space will be the ones managing these maneuvers, as they devised the idea in the first place, it still reveals tremendous faith in Rocket Lab’s technology. Proving the feasibility of using small inexpensive rockets like the Electron to send things to the Moon could ignite interest in a lot of companies that never would have considered it before.
Photon after CAPSTONE separation
What happens to Photon after CAPSTONE disconnects from it, though? Rocket Lab’s press materials say nothing about it. An article in The Verge in 2020 said that Photon would be doing a “lunar flyby,” and that Rocket Lab’s Moon program manager Amanda Stiles said at the time that “Rocket Lab is considering an extended mission with the vehicle,”,including sending it out into interplanetary space.
In an interview with Total Space though, Richard French (Rocket Lab’s Director, Business Development and Strategy, Space Systems) pointed to a slightly different fate for the Lunar Photon. He said they will “try to do a Lunar flyby and shake out the deep space capabilities…and then come back to Earth and dispose of it in the Earth’s atmosphere.” French didn’t elaborate however on what the shakeout will involve. It’s also unclear why Rocket Lab changed their mind regarding the ultimate fate of Photon between 2020 and 2022.
In an exchange with SpaceQ, Rocket Lab Communications Manager Murielle Baker confirmed French’s statement, saying that Photon will “conduct a flyby of the Moon at approximately 58 days after launch, followed by a return to Earth’s atmosphere that would cause Photon to be burnt up and destroyed.” No mention was made of any secondary mission, nor of any sensor equipment that might be used during the flyby.
Still, even if this Photon mission is just a flyby, Rocket Lab has made it clear that Photon will be going to Venus next year, carrying a probe that will descend into the Venusian atmosphere. So even if this flyby is just a flyby, Photon will be doing its own science very soon.
The CAPSTONE mission launched on Tuesday, June 28 at 5:55 am EDT.
Update – We edited the last sentence to reflect the launch earlier today.