Ground-Based Research, Page 6

Steve Larson, on comets Bennett and Halley

Laurel Wilkening came in with Mike Drake, at the same time, not long after grad school. She went on to become quite an administrator. She was on the International Halley Watch oversight committee. She knew that I was interested in comets, and she encouraged me to propose to participate.

One of my problems, if you will, is that I never got a PhD. I started taking classes in the department, and after taking six units a semester while still working full-time, I didn’t get great grades and I was basically told I didn’t have a future in planetary astronomy.

But I was carrying out this cometary physical characterization program, and so I took her advice and I sent in a proposal. I had done work also on comet Bennett. It showed some fantastic structure at the head of the comet, which I had seen in drawings before. I thought they were figments of someone’s imagination. There were spirals and all kinds of fantastic features, and the comets I had seen up to that point were just fuzzy things. But comet Bennett came along, and by God, there were these spirals. That just absolutely blew me away, and I said, “I’ve got to learn more about these.”

We had a conference on comets, and published a paper on the determining the rotation of the nucleus. It’s like a lawn sprinkler effect; you’re putting stuff out, but because you’re rotating it, it looks like a spiral. I thought that was pretty cool. I had been looking out for other comets that had those kinds of features, so I proposed to be involved in the so-called Near Nuclear Studies Network, which was one of the many subdivisions of the International Halley Watch that specialized in different techniques.

I won an award to be part of that. I was a deputy discipline specialist, is what they called it. That turned out to be another fantastic experience, because I met people from all over the world, did a lot of traveling, and set up this network where we were observing the comet constantly at different longitudes.

Because the work on modeling these jet features on Bennett, I was invited to be a guest investigator on the Soviet Vega spacecraft mission to comet Halley. That made me a member of the Inter-Agency Consultative Group which had been set up to coordinate all the investigations. Those were interesting times, as well. I’ll never forget going down to South Africa. I was able to obtain my very own CCD camera for the first time, to make observations of comet Halley. We had built it so it was portable, so we shipped it down to South Africa, because the comet was more visible down there, and at its brightest during the time of the spacecraft encounters.

I went down with a guy I had hired to actually do the observations, to set things up and start observing, but I had to fly to Moscow for the encounter. I had just sent a telegram to the guy saying, “I’ll be up there at such-and-such a time,” but I never got anything back. I had no idea where to go, who to contact. But they had arranged to have somebody meet me, so it was okay. I went back to Mission Control and observed the data coming back from that encounter, and then that was followed a few days later by going to Darmstadt in Germany where the European Giotto spacecraft flew by.

Lyle Broadfoot, on airglow experiments

About 1986 my group started to get involved with the U.S. Air Force. That’s when we started to build experiments for the shuttle. We did ground-based experiments as well at the AMOS [Air Force Maui Optical Station].

We didn’t do much ground-based other than this work we did with the Air Force. But it was still flight data—flight-based—because what we were doing was observing the shuttle as it flew over the optical station. With their instrumentation—and we had our instrumentation tied to theirs—we would observe the airglow emissions.

Airglow means that something is active in the atmosphere, like the aurora. The aurora occurs because electrons, protons, are trapped in the magnetic field, and they come into the atmosphere and they excite the upper atmosphere. The emission changes as a function of altitude, and by observing the optical emissions we can say something about the density of the atmosphere at that moment.

What we were doing with the shuttle was they were firing their thrusters, and they were turning their thrusters to the ram direction to point their thrusters forward and fire them, and we were observing them to see what the interaction of the thrusters with the atmosphere was. So this is airglow. We had the shuttle do different configurations and fire jets in different directions, and we looked to see if we could see a signature that would be useful.

Of course, this was all before the Berlin Wall came down. Once the Cold War was over, that program started to slow down. At that time what we were trying to do is get signatures that would allow us to identify types of rockets and stuff that might fly over from some unknown location in the Soviet Union. So that work kind of slowed down. But we continued to do airglow.

The advantage to us working with them was that the experiments we did working for the Air Force only took two or three days—or probably just one day, because there’s not too much going on. The rest of the time—because we were usually up for seven to ten days—we used our instruments to look at different airglows in different directions; watch the airglow as the sun sets, and see what we could see in the night sky, and that type of thing. We worked on trying to tie that in to atmospheric models, trying to figure out how different things move around in the atmosphere.