Friday, September 15, 2017
I managed to fall asleep sometime after 9 p.m. Pacific Time Thursday evening. I awoke just before my alarm was set to go off at 2 a.m. Friday. I again felt grateful to the wise people in JPL media relations for making us go home Thursday afternoon so we didn’t have to stay “on Lab” overnight! When we left the hotel at 2:30, my colleague Stephen van Vuuren had already written his social media post to go live at 5 a.m. accompanied by a mosaic of Cassini’s final portrait of Saturn compiled by Jason Major, who has done much of the image processing for In Saturn’s Rings.
The drive from our hotel in Arcadia was very smooth until we got near Flintridge. Caltrans had blocked off all three exits from the westbound 110 to the JPL area for road construction! Fortunately, we were able to get off at the next exit and double back. Thank goodness for GPS and Google Maps navigation. That was not the kind of surprise we needed at 2:45 a.m.
The news media were setting up a bunch of TV cameras all along the platform at the back of the auditorium when we came in. (Stephen and I had a running joke about the way the BBC crew had been staking out and fiercely protecting their territory all week.) Several of the on-air talent women were adjusting their makeup in the mirror in the hallway outside the women’s restroom. We were cheered by the miraculous news that the Starbucks tent in the JPL courtyard was open for business.
The three rows of chairs at the front right of the room were reserved for Cassini team members. There were boxes of tissues on some of the seats. I snapped a quick photo and posted it on Facebook, and it went viral later that day.
JPL had provided us with a list of staff who would be in the auditorium that morning and potentially available for interviews. However, as team members started trickling in, the rest of us sensed that that this was their moment to be together and commemorate the occasion. I didn’t see anyone attempt to interview them. We heard that more than 3,000 other Cassini team members were gathered on the grounds at the Caltech campus.
The mood was not exactly joyful, but neither was it somber or morose. Someone labeled the event a “vigil,” but I felt that word carries more solemnity or gravity with it (no pun intended) than was evident. There was absolutely no tension in the room. There were no commands left to issue, nothing that could go wrong at this point—only watching and waiting for the inevitable to occur.
Everyone we had talked to over the previous several days told us that people had been preparing themselves for this moment since last November, when the “F-ring orbit” phase of the mission began, which would eventually lead to the Titan flyby that put Cassini into the final 22 orbits of the Grand Finale beginning in mid-April. Team members had a series of meetings and events the week before the public and media arrived. Any grieving appeared to have taking place long before this session. Consequently, the mood was more akin to a wake or a celebration of life than a funeral.
I said hi to Robert Pearlman from collectSPACE and author Rod Pyle. We took our seats a few minutes before the NASA-TV feed from JPL’s Charles Elachi Mission Control Center went live at 4 a.m. Throughout the program, the audience occasionally cheered when friends appeared in the prerecorded video clips or in live interviews from the mission control room.
Three graphics made repeated appearances during the telecast. The most important was a dual view of the X-band and S-band signals from Cassini. X-band is a high-energy microwave radio beam that normally transmits Cassini’s telemetry. S-band is a lower-energy frequency that is used for radio science only. The two sets of telemetry signals from Cassini showed up as sharp spikes in the center of plateaus representing the carrier waves in the graphs. When the spikes disappeared, all that would be left would be background noise, and then we would know that Cassini had lost radio contact with Earth.
Another interesting graphic showed the path of Cassini’s telemetry across the solar system from Saturn to Earth. By the time the telecast began, Cassini was actually already gone. But Saturn’s distance of 960 million miles (1.5 billion km) from Earth meant that it would take more than 83 minutes for that information to reach us and confirm the end of the mission. So the graphic showed where in the solar system the end of Cassini’s data signal was currently located. At about 4:15, the TV host announced that the end of the signal had crossed Jupiter’s orbit.
The other recurring graphic was a simulated view looking over Cassini’s shoulder as it approached Saturn. Supplementing the view were readouts of the spacecraft’s rapidly-increasing speed and rapidly-diminishing distance from Saturn’s cloud tops. NASA expected that contact with Cassini would be lost once it was about 1,000 miles above the clouds and traveling in excess of 77,000 mph.
In the final five “toe dip” orbits that Cassini made in late August and early September, mission planners sent Cassini deeper into Saturn’s atmosphere than had originally been planned. They did this because previous dips into the atmosphere had given them confidence that they could control the spacecraft at a lower altitude than the initial conservative projections. Deeper dips provided richer data, but they also slightly changed the spacecraft’s final orbits, so that loss of signal was now expected to be as much as a minute or so off from the original estimate.
TV cameramen had been taking position seated along the edge of the raised platform at the front of the room, with their cameras pointed at the Cassini team members for reaction shots. That row became more crowded as the expected loss of signal approached. Everyone’s eyes were glued on the projection screen and the scene in the mission management room.
The time of expected loss of signal came and went, to everyone’s surprise. Cassini exceeded expectations one final time! Then finally, the X-band signal disappeared for a second, and people pointed at the screen and shouted, “Oh!” The signal popped back weakly for a fraction of a second and then was gone. A few seconds later, the S-band signal also disappeared. A woman in the auditorium said, “Goodbye!” People in the audience wondered, “When are they going to call it?” Finally, in the control room, someone confirmed to the Flight Director, “We have loss of signal.” The Cassini team in the auditorium applauded for about ten seconds. There was silence on the net for another ten or fifteen seconds, and someone on the Cassini team in the auditorium said, “Now what?”
More long seconds of silence passed before Julie Webster, Flight Director, got on the net to Earl Maize, Project Manager:
Flight Director: Project Manager, Flight Director.
Project Manager: Go ahead.
Flight Director: OK, we call loss of signal, loss of X-band, at…[long pause]…call loss of signal at 11:55:46 [UTC] for the S-band. So that would be the end of the spacecraft.
Project Manager: Copy that. Project Manager on FSO COORD: There may be a trickle of telemetry left, but as you just heard, the signal from the spacecraft is gone, and within the next forty-five seconds, so will be the spacecraft. I hope you’re all deeply proud of this amazing accomplishment. Congratulations to you all. This has been an incredible mission, an incredible spacecraft, and you’re all an incredible team. I’m going to call this the end of mission. Project Manager off the net.
There was a standing ovation in the auditorium followed by lots of hugs and handshakes.
Here is the video I shot in the auditorium of the final several minutes of the mission.
I didn’t feel particularly sad at this moment. I was more numb than anything else. It was difficult at the time—and is still a challenge—for me to process what an overwhelming experience it was to be a spectator in that room and share the completion of the Cassini mission with members of the team. I am grateful to them and JPL for allowing us to crash their party.
Stephen and I decided not to stick around for the press conference at 6:30 a.m. We would be able to pick up anything we needed for the film from the video feed on NASA-TV. We stopped off at Denny’s for a quick breakfast. Then it was back to the hotel to watch the press conference, upload some social media posts, and try to catch a few hours of sleep.
A Pasadena Planetary Party
The next event on our calendar was a 4 p.m. Friday get-together for the Cassini science team at the Pasadena home of Andy Ingersoll, the legendary Caltech planetary scientist.
To say that the setting was amazing is a vast understatement. Dr. Ingersoll’s 5,600 sq. ft. house was built in 1911, and its original look-and-feel has been remarkably preserved. The house overlooks an impeccably manicured front lawn about two miles southwest of the Caltech campus. Working models of a trebuchet and a catapult (with golf balls for payload) were tucked into the corners of the front porch.
Although Stephen and I noted that we had a deficit of several college degrees and many IQ points relative to the party’s other guests, everyone welcomed us warmly. It was nice to chat with some of the Cassini scientists now that the mission was over and the mood was relaxed. Most folks seemed drained after a busy week, little or no sleep Thursday night, and then the emotional let-down after the end of the mission.
We introduced ourselves to Dr. Ingersoll, thanked him for inviting us, and talked to him a little about the movie. We chatted with Linda Spilker and her husband Thomas. When he heard about Stephen’s movie, he told us about a project he envisioned for an ion-powered spacecraft to hover just above Saturn’s ring plane. Can you imagine what kind of photographs that spacecraft would produce?
One scientist was passing around a graph of data captured by Cassini’s Ion and Neutral Mass Spectrometer (INMS) during the final plunge into the atmosphere. (Stephen remarked that you know you’re at a party of hard-core scientists when people are excitedly looking at a graph while they’re outside drinking beer.) Out of respect for the science team, I won’t discuss the graph other than to say that it showed INMS was still providing data up until the very end, when Cassini was about 850 miles in altitude.
Mike Malaska introduced us to two of his associates. We heard about the amazing geophysical map of Titan that they are compiling with the radar and Visual and Infrared Mapping Spectrometer (VIMS) data generated by Cassini. It’s an incredibly complex challenge. Since Titan’s atmosphere is essentially opaque to light in the visible spectrum, scientists have to use infrared light and radar to penetrate the thick smog. The resulting data produces blurry and often conflicted interpretations of what’s on the ground. The prevalent “river channels” seen by the Huygens lander during its descent don’t show up in the radar data from the Cassini flybys. Surface features that appear to be one type of topography from one angle may look like different types of terrain when scanned from a different angle on another pass. Computed positions of features relative to the mapping grid system might be a few kilometers off from one pass to another. Add to that difficulty the fact that Titan’s surface chemistry and features are unlike anything we experience on Earth, and you begin to appreciate the immensity of the task.
It’s easy to see why most Cassini scientists aren’t too heartbroken about the end of the mission. They have enough data to keep themselves busy for decades.
Many of the scientists we talked to (and almost all of the engineers) are moving onto the Europa Clipper mission as their next project, at least part time. It’s the only other outer solar system mission in the detailed planning phase. That’s a scary thought. (More about that in the final installment of this blog post.)
We said our goodbyes at about 7:30, our brains ready to explode. What an incredible group of really nice people who did some really incredible stuff. And once again, Stephen and I were convinced that JPL people have just about the coolest jobs on the planet. As we are both “physics dropouts,” we had a chance to see what might have been, had we made different decisions in our late teens.
Next: Part 3—When will we be back again?