CubeSat testing is already being planned this year for NASA’s planned Gateway space station near the Moon, according to conference presentations at the virtual Small Satellite Conference this week.
Thomas Gardner, director of engineering and mission systems lead of Advanced Space Systems LLC in Boulder, Colorado, spoke about the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) in two presentations – a short technical talk uploaded Saturday (Aug. 7) and a question-and-answer session Monday (Aug. 9).
CAPSTONE is meant to be a test for the planned Gateway space station that NASA and its partners plan to deploy in cislunar orbit later in the 2020s, to support Moon operations on the surface – including human missions under Artemis.
Before discussing CAPSTONE in more detail, the Canadian context is that our country will be contributing to Gateway; in exchange, NASA offered a Canadian Space Agency (CSA) astronaut – who has yet to be named – a seat on the Artemis II Moon-orbiting mission.
A Canadian robotic arm will be the headline contribution. In June, MDA received a $35 million design contract for Gateway external robotics interfaces. The company is also working on a $22.8 million Phase A Canadarm3 robotic arm contract it received from the Canadian Space Agency in December 2020. Canadarm3 will be a successor to the long-running Canadarm space shuttle arms (1981-2011) and Canadarm2 International Space Station arm (2001 to present) also managed by MDA. The new arm is expected to include a measure of artificial intelligence to perform autonomous survey and repairs in between astronaut occupations of Gateway.
Canada’s Moon contributions also include support for companies under the Lunar Exploration Accelerator Program (LEAP) that aims to put Canadian technology and science payloads on the Moon. There are numerous LEAP projects underway, but one of the more publicized ones is a lunar rover, for which the CSA released a Phase A tender in June.
CAPSTONE mission summary
CAPSTONE is planned to launch NET (no earlier than) Oct. 20, 2021 aboard a Rocket Lab Electron rocket from New Zealand, according to Gardner’s slides. Among notable mission milestones, the spacecraft is in its final assembly, launch site preparation for fueling is underway, and all regulatory and launch approvals are either complete or almost complete – putting the spacecraft on track for launch thus far, Gardner said.
The 12U CubeSat will take roughly 3 months to arrive at its target destination and then orbit the Moon for up to 18 months, to “understand the characteristics of the orbit and perform technology demonstrations,” according to Gardner.
One of the challenges of operating near the Moon, for example, is mass concentrations or “mascons” – whose stronger gravity can affect the orbit of objects passing above. This phenomenon was studied during the Apollo crewed missions of the 1960s and 1970s and NASA still uses modern-day spacecraft to study mascons. With CAPSTONE orbiting in approximately the same pathway as Gateway, the CubeSat will therefore allow the Artemis alliance to map any effects on its orbit ahead of deploying the larger space station.
Adding to the orbital path uncertainty, CAPSTONE will operate in what is called a “near-rectilinear halo orbit” (NHRO), which is the baseline plan for NASA’s Gateway and a newer orbital operation path for engineers. The European Space Agency describes NHRO as an “angelic halo” orbit, as the orbit appears from Earth to look like a lunar halo. At its closest, Gateway is planned to pass 3,000 km from the lunar surface and at its furthest, 70,000 km.
NHRO has several advantages, Gardner said: it is stable enough to minimize propellant use, it offers a continuous view of Earth (simplifying communications with NASA’s Deep Space Network, for example), and avoids or minimizes eclipses (allowing for more steady sunlight upon any solar panels for energy generation.) The orbit also provides coverage of the lunar north and south poles; notably, NASA wants to base its Artemis crewed operations near the south pole of the Moon, which has likely water sources.
CAPSTONE’s mission objectives are these, Gardner said:
- Validating and demonstrating operations near the Moon, which is challenging due to the “three-body problem” of having gravitational influences from the sun, Earth and Moon that may tug upon Gateway during its orbit, which as mentioned earlier is a newer one in terms of operations.
- Informing future lunar exploration requirements, including those of Gateway. NASA always is looking to lower the degree of risk and increase certainty for its larger missions, especially those involving humans; a CubeSat is thus an ideal platform for performing that function for Gateway.
- Demonstrating a Cislunar Autonomous Positioning System (CAPS). With no GPS-like capabilities at the Moon yet, Advanced System LLC’s CAPS will demonstrate inter-spacecraft ranging between Capstone and NASA’s long-running Lunar Reconnaissance Orbiter spacecraft to assist with tracking capabilities, and to enhance the technology readiness of the CAPS software ahead of future mission use. CAPS, Gardner said in his slides, will “perform peer-to-peer measurements between CAPSTONE and the LRO spacecraft to generate absolute estimates of spacecraft position and velocity.” (It should be noted that Sherbrooke, Quebec’s NGC Aerospace is also developing “GPS-like” technology and has received CSA LEAP funding for this purpose.)
Mission challenges
In his follow-up live presentation on Monday, Gardner alluded to some open questions that the mission will seek to answer. One of them is fuel usage in the new orbit. “We expect to be in a NRHO for basically about 12 months or so, [but it] depends on … fuel,” he said. “We have a pretty good, healthy fuel margin for the spacecraft, but you know the nuances of actual flying missions … we’ll see.”
Another design challenge will be radiation. ” We did several radiation analysis iterations on the spacecraft, making sure that you can handle what they call the total ionizing dose and the potential for single-event upsets,” Gardner said, referring to times when radiation can cause a circuit to trip aboard a spacecraft.
Happily, there is only one “critical path” maneuver in the mission, which is the lunar orbital insertion, so he said there are few cases where a single-event upset could cause a problem. One dangerous moment of the mission will be as the controllers raise the apogee of CAPSTONE’s Earth orbit en route to the Moon, as it will pass through several Van Allen radiation belts high above our planet, Gardner noted.
Gardner elaborated further on the potential of CAPS, saying that eventually it could lessen the load on NASA’s Deep Space Network that tracks spacecraft across the solar system. “We’re trying to evolve CAPS into a product that is sort of like GPS at the Moon, where we can play multiple spacecraft and have them talking to each other,” he said, “and eventually de-emphasize the need for ground navigation and the overhead that causes on multiple systems on the ground like the DSN … The objective here is to do the operations from all the activities we plan on doing, and then providing a series of ‘lessons learned’ discussions with NASA – especially to the Gateway folks.”
In terms of public engagement, he added, CAPSTONE will take advantage of its unique perch to photograph the Moon. “Of course we will bring a camera along so we can snap some good pictures,” he said. “People might be interested in seeing like the Moon. Although most of the Moon has been photographed so well [already], we’ll have pictures.”