How to Recycle a Spacecraft: Interview with Daniel Cosgrove, Space Sciences Lab, UC Berkeley
What is your role in the THEMIS-ARTEMIS missions?
My title is the Mission Operation Navigation Lead. What that means is that I’m responsible for coordinating all the navigation activities for THEMIS-ARTEMIS mission. Our group is called the Flight Dynamics Group. We figure out how to move spacecraft. Then the flight operators or controllers take those directions and command the spacecraft to do what we need it to do.
How would you describe the THEMIS mission to a high school student?
THEMIS mission is a group of five individual spacecraft but they are all replicas of each other; same design, same propulsion systems to move them around in their orbits and same instrument packages. The goal of the mission was to study the Earth’s magnetosphere environment. We are particularly interested in the interaction of the Sun’s energy with the Earth system. Some people refer to that as space weather.
What’s the “killer shadow”?
THEMIS had three spacecraft in orbit in a 24-hour period (the closest set of spacecraft to Earth), one in a 48-hour orbital period and one in a 72-hour period. After the original goal of the mission was successfully completed, the two spacecraft that were farther away (the 48-hour and 72-hour orbital period spacecraft) were in orbits that passed through what we call the “killer shadow.” The orientation of their orbits was such that the spacecraft would pass behind the Earth and hang behind it for quite a long time at their apogees. The amount of time that they hid in the Earth’s shadow would prevent the solar panels from providing power, drain the batteries, freeze the fuel, and the systems causing irreparable damage to the spacecraft.
Were the killer shadows known and anticipated before launch?
We always knew the killer shadows were going to be there. The original thought was that we would de-orbit the spacecraft before they were killed by these shadows. Often when you launch spacecraft to do missions you say it is going to require x amount of fuel and then add on extra fuel margins so you can handle any kind of problems that are thrown at you. But THEMIS went perfectly and we used less fuel than we expected. We had 50% of the fuel tanks left.
So we said, we’ve got to do something with these spacecraft instead of burning them up into atmosphere. That would be a better use of taxpayer money and our resources than destroying the spacecraft like we had planned. So the ARTEMIS mission was envisioned. ARTEMIS got the two spacecraft out of the shadows and allows them to continue to do science in some very interesting regions. At the same time the three other THEMIS spacecraft are still collecting data.
Where did the ARTEMIS spacecraft go?
The Moon. Through assistance from lunar gravity and doing multiple lunar flybys and Earth flybys, we shot those spacecraft into deep space. At one point, they were over a million kilometers away. We sent the spacecraft through gravity assists to deep space to do science out there to study the solar wind.
Then the spacecraft eventually came back and we occupied the Earth-Moon L1 (libration point 1) which is the point directly between the Earth and the Moon. We also spent about three or four months in the Earth-Moon L2 point, which is the point directly opposite the Moon.
What that means is that the spacecraft were kept in a region of space where the gravitational pull from the Earth and the Moon are equal; they are equally pulled towards the Moon and the Earth. The spacecraft will orbit that point in space instead of either planetary or moon body.
What’s so special about the Earth-Moon libration orbits?
Humans have operated spacecraft in libration style orbits but they have always been Earth-Sun libration orbits. ARTEMIS is the first mission ever to operate a spacecraft in an Earth-Moon libration orbit.
Every month the Moon moves around the Earth and passes through the Earth’s magnetotail so we could do similar data collection that we did with THEMIS. But we also spend quite a bit of time in the pristine solar wind and also in the lunar wake through the solar wind. Essentially because the Moon lacks magnetic field of its own, it acts very much like a boat would cutting through water through the solar wind. We spent time studying those interactions in space from the vantage point of these libration points.
Why did ARTEMIS leave the Earth-Moon libration points?
Eventually we had to put the spacecraft in lunar orbit so that we could be in more stable orbits. These libration points require a lot of operations, maneuvers, station-keeping events that we were doing every seven days. It is very difficult on a team to keep that rolling. Most people are tied to the rising and setting of the Sun and I’m not so lucky – that doesn’t mean anything as far as the spacecraft are concerned. The maneuvers occurred any hour of the night, not to mention that the spacecraft don’t pay any attention to weekends and holidays. We did that for about seven months per spacecraft. Eventually we dropped them into lunar orbit.
Describe a challenge that you faced in your work, and how you overcame it.
[Listen to Dan’s answer here]
From your perspective, what do you find most interesting about the mission?
I find that subject [of libration orbits] extremely fascinating. So far, my favorite part of the missions was doing the station-keeping in those orbits. We were the first people there, and so there was a lot of the exploration aspect. We got to plant a flag, essentially, for THEMIS, ARTEMIS and NASA by being the first people in that region or maintaining station-keeping in that region.
I think there is a lot that we will see in the future about missions going to that region. There is a lot of interest in the community for using libration style orbits to explore the Moon again with manned spaceflight, possibly positioning a space station there or a refueling station that would allow manned missions to Mars or to Near Earth Asteroids. People are very interested in these libration orbits because once you get to them, it is very easy to get out of them and go to the Earth or go to the Moon or leave the Earth-Moon system. They are a very, very good waypoint, from a navigational perspective, for doing many different things.
What advice would you give to a high school student who is interested in a career in science, technology, engineering or math?
Get involved. Get into internships or volunteer work. Get into projects where you can start working with people who are already doing things similar to what you are interested in. If you are in school and you are doing assignments that you are interested in, talk to your teacher to figure out how you might do an extra project that goes along with your interest. Find out if there are any local schools, universities or businesses that might have volunteer or internship opportunities. I learned a lot through those kinds of programs and experiences.
One thing I think you might lose in this age of electronic communication is face to face communication. You would be surprised at how many doors you can open if you actually go and find an engineer and talk to them directly. Science, engineering, technology and math folks love to talk about what they do. Seek them out and seek out those kinds of opportunities.
How has this advice helped you in your own life?
I have a Bachelor of Science in physics, but in science and engineering most people have a Masters degree, if not something higher. The way I got into this work was through seeking out these opportunities. When I was going to UC Santa Cruz and studying applied physics there, in my junior year I was lucky enough to get a student position at the Santa Cruz Institute for Particle Physics. I ended up working there for several years as a student and sought out every opportunity I had to gain responsibility and gain more knowledge. I was able to get in there and do the work without having a degree that people would normally need. If you can demonstrate your worth and your knowledge, what paper degree you have becomes secondary.
Another piece of advice would be to think about education not as a discrete step of units or goals. You need discrete goals such as graduating from high school, meeting entrance requirements for university, and getting a Bachelors degree. Those are all great goals but you should look at your education as a continuum. What are you really learning at these stages, and where do you really want to go? Then you can figure out how to affect that road. People can have a lot more influence on that road when they think about it in those terms.
What do you like to do when you are not working?
I like running a lot. I have completed several half-marathons and one marathon, and I’m getting ready to do my second marathon this next year. I like cycling, camping and outdoor activities. I focus on that when I’m out of work because so much of my work is in front of a desk. I also love technology and I’ve been very interested in the maker movement, the idea of do-it-yourself mentality to engineering and electronics.
I’m also a very avid board game player. Right now my favorite board game is Settlers of Catan. It’s not too complicated and doesn’t take too long but there is some interesting strategy to it when you are playing with good players. You have to have a good understanding of probability to do well at it. And I’ve loved playing chess for years.
