OPAG, Day 1: Cassini and Juno status
Posted by Emily Lakdawalla
05-05-2006 18:15 CDT
The Outer Planets Assessment Group opened with the status of two of the three actual outer planets missions, Cassini and Juno. (There was no New Horizons status presentation for some reason.) Dennis Matson gave the Cassini update; most of what he presented was stuff I'd just seen at the Lunar and Planetary Science Conference in March. One new thing was a graph showing the data from a recent radio science Titan occultation, where they probed Titan's atmosphere by broadcasting radio signals at Earth as Cassini crossed behind Titan. "It turns out that the Ka-band gets absorbed at a higher altitude than these others," he said. (Ka-band has shorter wavelength/higher frequency than the X- and S-band radio signals that Cassini can also produce.) He didn't comment on what that actually meant, he just said the radio scientists were excited about the detail in the plots.
Next up was Scott Bolton, who reported on the status of Juno. Juno is currently in Phase B, which means they are working out the spacecraft and mission design but aren't building the spacecraft yet. Bolton spent the first half of his presentation explaining why their launch was recently delayed from 2009 to 2011. It doesn't have to do with any problem with the spacecraft design or mission plan. "We were originally proposing to a 2009 launch date; but upon selection, NASA informed us they didn't have the budget profile that was in the Announcement of Opportunity; they had a different one. Not only did they not have enough money, but it was kind of a flat profile. There was no bump. Typically a mission needs a big bump a couple of years before launch." That's when they need to establish contracts and start building the spacecraft and buy their launch vehicle and stuff.
Bolton went on to say that NASA had told them strongly that they did not want the Juno project to "descope" or reduce their instruments or other capability in order to solve the budget problem. The best way to fix the budget problem was to take a delay to a later launch date. Launch dates in either 2010 or 2011 would have no negative impact on the science. In the end, he said, the budget profile in 2010 looked too risky, so they took the delay to August, 2011. (One thing that might have made the 2010 launch date possible was the cancellation of Dawn. However, Bolton was very careful to say, the budget overrun of Dawn is NOT what caused the delay to 2011. It was just an overall budget problem at NASA.)
Of course, delaying a mission unavoidably increases the cost of the mission, Bolton said. "Unavoidable cost increases due to delay have to do with inflation; everything moved one year adds up to 4% of the total budget. Launch vehicle costs also went up by $36 million as soon as we were selected. Launch vehicle costs are going up across the board. All of the missions we have to launch are all going up in cost, just due to these increases in launch costs. Part of the reason is there aren't enough of them going." When there are fewer launches happening -- and it's not just NASA launches, it's the Air Force too -- then the fixed costs have to be spread over fewer missions, and everybody takes a hit.
"What we have with that delay is a longer phase B. There are advantages to this; we'll retire more risk. The disadvantage is, every time you wait, you have inflation, you have the team dragged out, you have the potential for launch vehicles to go up again." Juno's status is currently "green" for all the things that NASA watches them for -- meeting their technical, schedule, and programmatic promises, which, Bolton said, is unusual. "By this point, many missions have realized they have to descope, or costs go up. We have yet to see any problems with our design. We are set up to work as a well-oiled machine."
Clearly, the cost increases were weighing on Bolton's mind, perhaps because of the recent fracas over Dawn (though he did not say so). "All of the Announcements of Opportunity have the wrong numbers for the cost of the launch vehicle. Even if you don't ding the principal investigator for that, it all comes out of one pot. The general rule of thumb is that there are certain cost increases that projects may get because of something NASA imposes on them, such as a delay. NASA doesn't necessarily penalize you for that, but at some point they might say, we don't have the money, what are you going to do about it? We were directed not to take any descopes. Nevertheless it all comes out of all of our future. When Juno gets delayed, the Announcement of Opportunity for the next New Frontiers mission moves out, and everything gets smaller for our community." It's a problem, but nobody immediately had any solutions to suggest, and I guess there's really no solution; increasing costs are just a fact of life.
So, so much for the budget situation. Bolton gave a quick overview of the plan for Juno. "We have a 5-year cruise, assuming an Earth gravity assist. The baseline mission is 32 orbits of Jupiter. The orbit is designed for a minimum of high radiation doses." They do this by having a highly elliptical, polar orbit that goes within 5,000 kilometers of the cloud tops at perijove and then swings up and out and around the worst of Jupiter's radiation belts. Over time, the orbit gets a little more dangerous. "Each orbit is about 11 days. The orbit evolves downward, so perijoves go northward; the trajectories go through redder zones of radiation belts at the end of the mission. We can accomplish almost all of our science objectives in the first half of the mission."
Juno will be the first to be sent to Jupiter under solar power, with three huge solar arrays 11.5 meters long; and it's spin-stabilized. One thing I found interesting about the Juno instrument suite was that since it is designed primarily to study Jupiter's interior structure, composition, dynamics, and magnetosphere, a camera is really not a particularly important instrument. However, they will carry a camera, "which is mainly an education and public outreach tool," Bolton said. It would certainly be poor for public relations to go to such a pretty planet as Jupiter and not send back snapshots! The instruments that will actually be doing the heavy work include radio science, a magnetometer, a microwave radiometer, an energetic particle detector ("which has recently changed its name to JEDI," Bolton remarked), an auroral dust experiment, a radio and plasma wave science experiment, and an ultraviolet spectrometer.
The coolest-looking instrument is the microwave radiometer, which by broadcasting radio signals into Jupiter at a broad range of wavelengths can detect its structure many kilometers down. This will help in part to answer a fundamental question about Jupiter: is it rotating as a solid body, or as concentric cylinders? "Grade school kids are amazed that we don't know the answer to this question," he commented.