Their words: Cassini’s Hunter Waite and the quest to look beyond
PASADENA, Calif. — Peering through the atmospheres of other worlds to determine what they are made of is difficult enough, but to do so reliably for 13 years is an astonishing accomplishment. Hunter Waite, the Ion and Neutral Mass Spectrometer (INMS) team leader at Southwest Research Institute (SwRI), spoke with SpaceFlight Insider about the mission in the lead-up to Cassini’s “final bow”.
Hunter Waite is the Principal Investigator for the MASPEX on NASA’s Europa investigation, which is the mass spectrometer element of the mission that is slated to be launched in 2023.
SFI: Hi Hunter, thanks for chatting with us about Cassini.
Waite: “Sure, no problem.”
SFI: So Cassini is going to be coming in at what, 76,000 miles an hour?
SFI: You have very, very sensitive instruments for detecting what’s in the atmosphere, is there any risk of saturating it or damaging it?
Waite: “Well, there are two sensors. Fortunately, the instrument was built to have a large dynamic range. And so it actually has two independent detectors, and one of them is about, let’s say is about 3,000 times less sensitive than the other. So if one saturates, and it has happened on these close flybys, then the other one takes over. And so we’ve been able to – we did this – we repeatedly used this technique at Titan, and we’re using it again here, so we’re pretty sure that up to the time probably that we lose the signal, which is the first thing that is going to happen, we will be able to disentangle the data.”
SFI: That’s—that’s very impressive from an engineering perspective. And how deep does—how deep do you think you’ll get data in the Saturn atmosphere versus how deep you were in the Titan?
Waite: “Well, it’ll be about the same dynamic pressure, because we’ve gone to the point where we pushed the thrusters to 70 percent of duty cycle at Titan, but not recently. But that’s pretty close to the edge, and, of course, we’ll get 100 percent and over in this particular case, so the dynamic pressure will be quite the same, but the dynamic pressure is dependent upon the velocity, and so it’ll be at a slightly lower density where that dynamic pressure reaches a point where it rotates the spacecraft around than it was at Titan.
SFI: It’s very impressive that you’re taking a space-based spacecraft that far into the atmosphere.
Waite: “It was built to go through Titan, so that’s the good thing. And it’s not very different in this particular case.”
SFI: And then, the ring rain was particularly interesting. Can you tell me more about the surprises you found?
Waite: “I can’t – for a couple of reasons. First of all, you know, if we publish this data, we have people from Science or Nature that don’t want it to have it reported previously.”
SFI: We understand.
Waite: “The other thing, which, in this case, is just as important, is that we’ve been getting this data near real time. You know, we’ve been getting it like a fire hose for the last month, right? And so we’ve got to make sure that this data that we understand it before we release it. We don’t want to perpetuate fake news, right?”
SFI: Make sure everything is calibrated, and everything is…
Waite: “Well, I think even more importantly [there are] things about fragmentation, the molecules, contamination—[there are] all kinds of issues that are unique to this particular high-velocity flyby that we have to understand and verify before we can be comfortable in releasing the information.”
SFI: Okay. Awesome. Is there anything else you want the public to know about the instruments you worked on, on or that you loved about the mission?
Waite: “I guess the—it’s been amazing that in almost every situation that we’ve been put – Titan and Enceladus and Saturn – having a mass spectrometer on board has been important to understanding the composition, we just could not ever imagine not previous experience the chemical complexity of these systems without having that information. So it’s been a real honor to be able to report that. Enceladus was great. We were able to see the H2, determine that there was food for the microbes in the interior. And the ring rain story will probably be equally as interesting.”
SFI: Oh, no doubt. That’s just a very very cool concept. Did you have to change the instrument in any way to get…
Waite: “We changed the—we have a way that we control how we scan the mass of the instrument – basically mass tables – with steps from one mass to another. We, of course, modified that real time to maximize on the things we were seeing, to get the best signal. So we’ve been—the spacecraft people allowed us to modify things, even after the last sequence upload, with real-time commands to upload our tables and modify it to optimize our measurements, and that was really nice.”
SFI: That’s really good.
Waite: “That was really nice of the spacecraft people because, you know, it’s not easy.”
SFI: No, it’s not. Frankly, I’m surprised they let you go 70 percent duty cycle at Titan.
Waite: “Yeah, I don’t think they really planned that.” (Laughs) “I think that one went in a little bit by surprise.”
SFI: Mind if I ask you one or two other questions for my editor? Since you’ve been looking at Enceladus’ geysers, do you know how long they might have been erupting? Or how young or old?
Waite: “Well, I mean, they’ve been around quite a while we think, so probably a – since it’s such an extensive ocean – it’s global. It would take millions of years to freeze, and how long it’s been in the process of thawing – maybe the life of the Solar System – we just don’t know. But it’s been a—things are not going to change quickly there, and they probably didn’t happen overnight, either.”
SFI: Maybe I’m misremembering, but aren’t there indications that there are other places on the planet that may have been active in the past?
Waite: “There [have] been some suggestions that there are other regions that were active, but that’s not too surprising in that if it’s a global ocean – maybe there was. The debate right now is that to get the ocean, you have to have tidal dissipation, and tidal dissipation is generally thought to be in the ice melting. But now that people are trying to take a look at [it] – since we think [there are] hydrothermal systems on it – trying to take a look at whether there is tidal dissipation going on deeper down in the rock as well. And that would potentially modify the model for how the heat flow occurs throughout the body – where the dissipation occurs. So, I think, stay tuned for that one. That is work that’s in progress.”
SFI: Something that we don’t know, which is, and we know it’s not your instrument, but if there is a molten core moving around and creating geothermal heat, is there any magnetic field on Enceladus?
Waite: “No. The magnetic field is being draped around it from Saturn. And that’s because there’s material that’s been ionized there, and it’s moving with Enceladus, so it’s dusty, it’s heavy, and it slows down the magnetic field and effectively bends it back.”
SFI: Much as what occurs with the solar wind…
Waite: “Yes, similar to that.”
SFI: And then based on the fly-throughs of the plumes, did it help you understand the mass of the E ring?
Waite: “Well, certainly the CDA people have looked at that, and yes, they have studied that. That is a source of the E ring, and they have a pretty good idea.”
SFI: Thanks so much for chatting with us!
Matthew Kuhns is an aerospace engineer living in California and enjoys capturing the beauty of the aerospace world with his camera. As an engineer he specializes in fuel & propulsion systems and as a photographer his internationally award-winning images are published in magazines and books. Kuhns was introduced to the founder of SpaceFlight Insider during the pre launch activities for SpaceX’s CRS-4 mission and was promptly brought on to the team as SFI’s California photographer.