CAPSTONE: The Story So Far

After decades of delays and false starts, NASA is finally returning to the Moon. The world is eagerly awaiting the launch of Artemis I, the first demonstration flight of both the Space Launch System and Orion Multi-Purpose Crew Vehicle, which combined will send humans out of low Earth orbit for the first time since 1972. But it’s delayed.

While the first official Artemis mission is naturally getting all the attention, the space agency plans to do more than put a new set of boots on the surface — their long-term goals include the “Lunar Gateway” space station that will be the rallying point for the sustained exploration of our nearest celestial neighbor.

But before launching humanity’s first deep-space station, NASA wants to make sure that the unique near-rectilinear halo orbit (NRHO) it will operate in is as stable as computer modeling has predicted. Enter the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment, or CAPSTONE.

CAPSTONE in the clean room prior to launch.

Launched aboard an Electron rocket in June, the large CubeSat will hopefully become the first spacecraft to ever enter into a NRHO. By positioning itself in such a way that the gravity from Earth and the Moon influence it equally, maintaining its orbit should require only periodic position corrections. This would not only lower the maintenance burden of adjusting the Lunar Gateway’s orbit, but reduce the station’s propellant requirement.

CAPSTONE is also set to test out an experimental navigation system that uses the Lunar Reconnaissance Orbiter (LRO) as a reference point instead of ground-based stations. In a future where spacecraft are regularly buzzing around the Moon, it will be important to establish a navigation system that doesn’t rely on Earthly input to operate.

So despite costing a relatively meager $30 million and only being about as large as a microwave oven, CAPSTONE is a very important mission for NASA’s grand lunar aspirations. Unfortunately, things haven’t gone quite to plan so far. Trouble started just days after liftoff, and as of this writing, the outcome of the mission is still very much in jeopardy.

Off to a Rocky Start

Rocket Lab’s Electron rocket performed perfectly during the June 28th launch, after which the booster’s third “kick” stage began a series of engine burns to gradually raise its orbit. After firing the engine six times in as many days, the kick stage performed the final trans-lunar injection (TLI) burn before releasing CAPSTONE on July 4th. This put the craft on a low-energy ballistic trajectory towards the Moon, which would be refined with a series of small course correction maneuvers over the course of the four month journey.

After entering the free-flying phase of the mission, CAPSTONE extended its solar arrays to start charging its batteries and stabilized itself in preparation for the first course correction burn which was scheduled for the following day. But shortly after communicating with NASA’s Deep Space Network (DSN) ground station in Madrid, contact with CAPSTONE was lost.

Communications were reestablished some 24 hours later, and analysis eventually determined that a malformed command from operators on the ground had put the spacecraft’s radio in an unexpected state, which in turn triggered the onboard fault-detection routines. The vehicle automatically reset itself and cleared the fault condition, as well as autonomously performed necessary maneuvers to keep itself on the intended flight path.

While CAPSTONE came away from this first anomaly unscathed, and ground controllers felt they could prevent the issue from reoccurring, the window for the first course correction maneuver had long since past. This meant a new maneuver had to be planned given the craft’s updated position and velocity, a delicate process which took additional time.

On July 7th CAPSTONE successfully performed the revised course correction burn (officially referred to as TCM-1), and placed itself on a trajectory within 0.75% of the calculated course.

A Troubling Tumble

After the initial communications difficulties were resolved, the mission continued without issue. A small course correction was made on July 12th, and the larger TCM-2 maneuver was performed on July 25th without incident. On August 26th, CAPSTONE reached an apogee of 1,531,949 kilometers (951,909 miles), the farthest away from Earth that its ballistic course would take it.

But on September 8th, just as the planned TCM-3 maneuver was about to end, the spacecraft’s attitude started to deviate. For reasons as of yet unknown, CAPSTONE’s reaction wheels were unable to counter the oscillation, and the vehicle entered into an uncontrolled tumble. With its antenna no longer pointed at Earth, communications were once again lost.

That evening mission controllers declared an operational emergency, which gave them access to additional capabilities of the DSN. Through this they were able to eventually receive a weak telemetry signal from CAPSTONE the following day, but the data looked grim. Due to its spinning, the craft’s solar arrays weren’t producing enough energy to charge the batteries, which was causing the spacecraft to reset frequently from lack of power. Worse, without energy to run the onboard heaters, the thrusters that would ultimately be needed to stop the tumble were now frozen solid.

But it wasn’t all bad news. It was determined that the TCM-3 burn had progressed far enough along that CAPSTONE was on the intended orbital trajectory — so while the spacecraft might be technically out of control, it was still heading to the Moon.

An Evolving Situation

Currently, the last update we have from the CAPSTONE team was made on September 15th. The big news is that, even though the craft is still spinning, the solar panels are getting enough light that the batteries are charging. There’s even been enough energy in the budget to run the heaters, though they are apparently operating on a reduced duty cycle. Even still, it’s enough to take the chill off, and its hoped that the propulsion system will soon reach a high enough temperature that its functionality can be evaluated. Assuming they can be brought back online, firing the thrusters against the direction of rotation should get CAPSTONE back under control.

Several more maneuvers need to be made before CAPSTONE reaches the Moon.

But we aren’t quite there yet. The update makes it clear that mission controllers are still analyzing the data to determine why CAPSTONE went out of control in the first place, and how to prevent it from happening again. The original mission timeline shows that a number of additional burns were planned to place the spacecraft in its intended orbit, and even then, that was just the beginning of it’s mission.

Luckily CAPSTONE shouldn’t need to make another course correction for a couple of weeks still, which will give engineers on the ground more time to assess the situation. Still, the fact that two out of the three major maneuvers have caused the vehicle to become unresponsive is troubling, especially when several more engine burns are still on the schedule.

26 thoughts on “CAPSTONE: The Story So Far

    1. Yeah, because sending all those rovers to mars and the James Webb telescope in space proved they are extremely incompetent. I mean, is child play to fly an helicopter for the first time in another planet. But a probe to the moon, tricky as hell.

      1. It’s also worth noting CAPSTONE’s a *dirt cheap* probe too, less than $25M for both the probe and the launch. There were, in fact, concerns that a probe that’s pretty important to Artemis overall probably shouldn’t be being handled via such a low-cost (and thus from NASA’s point of view, higher risk) process.

    2. This program is funded by NASA and is sharing some hardware with RocketLab such as the DSN, but this is primarily RocketLab’s show. Launched on their rocket, using a lunar transit stage they developed, which will inject their cubesat into lunar orbit, all flying their software. NASA has had a few rough spots, but you can’t deny that the Webb Telescope is one of their more astounding achievements. The science that that NASA project is doing is already making us rethink our understanding of the big bang and the early universe. This is primarily a commercial company using some NASA assistance.

      1. There are future Photon missions where the Photon will act as the spacecraft bus (e.g. EXCAPADE), but CAPSTONE is not one of them. CAPSTONE is a free-flyer, it separated from Lunar Photon prior to the first TCM. Both are now flying as independent spacecraft on different trajectories (Lunar Photon recently performed an Earth flyby and is likely going to act as a demonstrator mission for deep space / interplanetary operations).

    1. That’s what we get for scheduling content more than 24 hours out I suppose. But doesn’t look like anything has fundamentally changed since the 15th — still waiting for temperature to come up before attempting to de-spin.

  1. I feel sorry for the engineers working on this project. Imagine trying to get a good night’s sleep knowing that your creation is spinning helplessly out of control in a frozen vacuum 1,000,000 miles from home. Daytime you are the butt of everybody’s jokes: “Hey, Frank, how’s the spinning satellite today?”

  2. “After decades of delays and false starts, NASA is finally returning to the Moon.”

    Manned spaceflight is -SO- 1960s and a horrendous waste of limited funds compared with the cost versus science returns from robotic exploration. Only 3/4 of the projected cost of just one SLS launch OR the $3 billion annual ISS support costs for NASA would fully fund another Perseverance class Mars rover and long-term support for it. OR either of those would fund SIX of the smaller $500 million missions.

    1. I agree short term, the return on investment is absolutely lousy, but long term if you eventually end up moving some of your eggs into three or more baskets around the solar system – That would be an astronomical achievement. There would be some level of redundancy to our species, that is something that, a robotic explorer can not provide. Yes 99.9999% of the resources needed to survive would come from earth for multiple decades living off planet. But the level of learning to change that will be amazing. No one has written the manual on “So you are on the Moon^H^H^H^H^H^H^H^HMars, now what ? Don’t panic, and start to read this book: Simple guild to bootstrapping your species on a different planet Book 1 Volume 1” (also available as an audio book).

      Long term I can see robots helping by setting up the final destinations before humans arrive, but autonomous robotics is not there yet. And we do not even know, what we would need to know, to fully achieve the end goal before we start which is always the path to new knowledge.

      1. Oh and one thing that never happened back when NASA landed on the moon was to stay there for one full moon day (~29.53 earth days). Every mission was planned to be there under ideal sunlight conditions (To minimise the resources needed to keep astronauts alive). The longest mission was the Apollo 17 which spent 3 earth days 2 hours and 59 minutes (~75 hours) on the surface of the moon (lunar surface extravehicular activities total duration 22 hours 4 minutes). And the total mission duration was 12 days, 13 hours, 51 minutes, 59 seconds.

        If you add up all the EVA time of all the mission to the moon people were walking on the surface of the moon for a total of 3 earth days 9 hours 5 minutes 33 seconds, all the lunar modules spent in total 12 earth days 11 hours 28 minutes on the surface of the moon. So over all the lunar landing missions (Apollo 11,12,14,15,16,17) were close to 42% of a full moon day on the moon, and EVA was close to 11% of one moon day.

        We have not learned how to live there, unless we can spend much much much longer on the surface. And everything that we learn will be applicable to an eventual Mars landing. And if anything goes wrong the Moon is only 3 days away from earth (6 days to go there and back) where as Mars is longer, much much longer ( ) so in reality if something major goes wrong people are dead on Mars. The currently planned lunar missions are to debug what has been happening on earth for decades (simulated missions on the moon and mars).

        1. “We have not learned how to live there, unless we can spend much much much longer on the surface.”

          I mean… there’s nothing magic about the Moon’s surface. It’s space with gravity and rocks. I agree that it’s harder because the thermal environment changes are big and slow (as opposed to big and fast, which we’re perfectly fine with), but it’s really just thermal that’s the issue, and that’s not that hard to simulate, model, and test.

          1. Living there independently of earth, mining and refining minerals, manufacturing Oxygen (lots of oxygen in the moons Regolith, about 43% Oxygen by mass, that can be recovered with the right processing) and metals. Hydrogen is a real problem for long term independent life on the Moon, the temptation would be to use all the hydrogen in the water at the poles to make rocket fuel. But the real show stoppers to permanent independent life on the moon are Carbon (82 ppm) and Nitrogen (5 ppm) in Regolith. To live there could involve direct recycling of Everything high in carbon and fixed nitrogen to grow food (which most earth based religions may not be happy about). There is only so much that you can learn from simulation. Granted to have the same level of protection, from radiation and cosmic particles that earth enjoys, living under 5+ meters of Regolith most of your life would not be appealing to most (similar measures would be required for permanent life on Mars). Most of the things that would need to work have not even been thought of yet. Will chemical processes that work well in Earth gravity (9.807 m/s²) work the same at 1.62 m/s² (Moon) or 3.721 m/s² (Mars). Can that be simulated ? A chemical process that take an hour on earth may fail to occur at 16.5% or 38% gravity levels because chemical intermediaries that separated into layers failed to form fast enough. Maybe some processes will require centrifuges, maybe other chemical processes will be more efficient due to lower gravity.

            And finally living there for long enough and there is no coming back home to earth ever.

          2. “Living there independently of earth”

            Woah, woah, that’s entirely different than surviving a lunar day. Living off the Moon’s a pain in the neck. Much harder than Mars, for exactly the reasons you’re mentioning. Mars at least has reasonable carbon and nitrogen in the soil and atmosphere. It’d still suck to do it, but it wouldn’t be a goddamn disaster like the Moon. Trying to literally form a closed-cycle system on the Moon is waaay beyond what we’re capable of now. It’d be easier just to truck up (or drag from other bodies in space!) huge amounts of raw materials.

            I mean, we can’t even really do closed-cycle systems on Earth yet. If you get to the point of being able to support self-sustaining colonies on the Moon, you’re probably not far off from interstellar colony ship travel at that point.

          3. Solar radiation. Even as done it was a gamble. Nobody is staying on the moon for a full moon day until they build a radiation shelter on the surface. Perhaps at the bottom of a crater on one of the poles.

          4. @Pat
            I see the return to the Moon as a debugging zone for long term ideas and technology that will eventually be needed for Mars, NASA have plans for super conducting cables to transferring DC power from a RTG ( Radioisotope Thermoelectric Generator ) to their moon base. On Mars if things go wrong, best case it takes 4 months to get home, worst case 18 months depending on the launch window, but with the moon if everything goes wrong you can be back home on earth in 3 days (everybody dies vs everybody lives ?). But like I said initially everything will be shipped in from Earth, but that will eventually need to change. Unless there is a challenge, new technologies do not happen. Granted most of the “new technology” that what will be required are ancient technology on earth. But on earth we typically used gravity, large volumes of water, acid and power to purify elements. On the moon (and Mars) we will need to leverage the advantages of their atmospheres and lower gravity to help separate minerals and eventually extract individual elements. Geologists, and chemists I’m sure have been thinking about this for decades.

            Space 1.3e-10 Pascal 1.3e-15 atm 1.9e-14 psi 1.3e-15 bar
            Moon (ground level) 3e-9 Pascal 3e-14 atm 4.4e-13 psi 3e-14bar
            Mars (ground level) 651.8 Pascal 0.00643 atm 0.0945 psi 0.006518 bar
            Earth (sea level) 101353 Pascal 1.00000 atm 14.7 psi 1.01353 bar

            > Solar radiation
            Maybe you missed it, but I did say “Granted to have the same level of protection, from radiation and cosmic particles that earth enjoys, living under 5+ meters (~16 feet) of Regolith most of your life would not be appealing to most (similar measures would be required for permanent life on Mars).”

    2. “Manned spaceflight is -SO- 1960s and a horrendous waste of limited funds”

      Not really. One of the huge benefits of large amounts of flights – both manned and unmanned – to the moon is that since the Gateway orbit is a Lagrange orbit, you get *tons* of free CubeSat launches that can make it basically to Jupiter with very little propellant.

      And one of the problems with the idea of “let’s just fling tons of rovers out there because they’re cheap!” is that the ground support costs in terms of personnel and demands on infrastructure would be very high. It’s a little different with CubeSats because you’re not building them to last like 10+ years.

      Plus the idea that Perseverance only costs $3B is a bit silly, that’s assuming only the nominal ~2-ish years (which no one would’ve really considered a success). Curiosity’s total ground support costs are up to ~20% of the total mission cost at this point, and that’s still a bit fudgy given the way NASA budgets things: if you try to run 10x Curiosity missions simultaneously, the operations cost won’t just scale up by 10x.

      Infrastructure buildup in deep space is also helpful because it starts driving private companies, which further drives costs down.

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