RIME (Radar for Icy Moons Exploration) is the first instrument ever deployed to the outer Solar System that can make direct measurements of conditions below the surface of an object. That makes it precisely tailored for Europa as well as Ganymede and Callisto, two other Galilean moons that also seem to have an internal ocean. Consider it a radar ‘sounder’ that can penetrate up to 9 kilometers below surface ice. RIME is a major part of why JUICE is going to the moons of Jupiter.
Consider it problematic as well, at least for the moment, while controllers working the JUICE mission try to solve an unexpected deployment issue. The 16-meter long antenna shows movement, but continues to have trouble in becoming released from its mounting bracket. The antenna is currently about a third of its full intended length, according to ESA, partially extended but still stowed away.
Image: Shortly after launch on 14 April, ESA’s Jupiter Icy Moons Explorer, JUICE, captured this image with its JUICE monitoring camera 2 (JMC2). JMC2 is located on the top of the spacecraft and is placed to monitor the multi-stage deployment of the 16 m-long Radar for Icy Moons Exploration (RIME) antenna. RIME is an ice-penetrating radar that will be used to remotely probe the subsurface structure of the large moons of Jupiter. In this image, RIME is seen in stowed configuration. The image was taken at 14:19 CEST. JMC images provide 1024 x 1024 pixel snapshots. Credit: ESA.
Given that two months of commissioning remain for the spacecraft, the agency is saying that there is abundant time to work the problem out, which may involve something as simple as a stuck pin, potentially sprung by warming the radar mount by rotating the spacecraft and turning the assembly into direct sunlight.
The memory of the Galileo probe to Jupiter hovers over the mission at least momentarily. Controllers never did free up Galileo’s high-gain antenna, though they were able to return outstanding data through ingenious use of its low-gain counterpart. Needless to say, the hope here is that RIME follows a different path and soon springs free.
In-flight adjustment and occasional repair are no strangers to deep space missions. We’re reminded of this also by the plan to save precious energy and keep Voyager 2 (and potentially Voyager 1) operational for a few years longer than previously thought possible. Both craft rely on RTGs (radioisotope thermoelectric generators) converting heat from plutonium into electricity, so that plutonium decay produces less power each year. Hence the need to turn off unneeded heaters and other systems to reserve power.
The new method: Use power heretofore reserved for a voltage regulator that triggers a backup circuit in the event of a serious fluctuation in voltage. Power is set aside in the spacecraft’s RTG for that purpose, but can be redirected to keeping the craft’s five science instruments operating until 2026. That gives up a certain safety measure, but even after 45 years in flight, the electrical systems on Voyagers 1 and 2 remain stable, so it seems a good gamble to produce further interstellar science. If the approach works for Voyager 2, it may be tried on Voyager 1 in the near future.
Suzanne Dodd is Voyager project manager at the Jet Propulsion Laboratory:
“Variable voltages pose a risk to the instruments, but we’ve determined that it’s a small risk, and the alternative offers a big reward of being able to keep the science instruments turned on longer. We’ve been monitoring the spacecraft for a few weeks, and it seems like this new approach is working.”
Image: Each of NASA’s Voyager probes are equipped with three radioisotope thermoelectric generators (RTGs), including the one shown here. The RTGs provide power for the spacecraft by converting the heat generated by the decay of plutonium-238 into electricity. Credit: NASA/JPL-Caltech.
Anything we can do to keep these priceless assets functioning is to the good. They are our only operational craft outside the heliosphere, a striking thought given their projected mission duration of a scant four years. Operating without one of its science instruments, which failed much earlier in the mission, Voyager 1’s power issues are slightly less pressing than its twin, but decisions about shutting down another instrument still loom, so the new RTG power draw may again come into play.