In the wee hours of the morning today, Cassini made its 127th and final close flyby of Saturn’s giant moon Titan, the second largest satellite in the solar system. There were many targeted observations planned on this final encounter, including radar studies of the “magic island”, a landform that has appeared and disappeared in Ligeia Mare, one of Titan shallow methane seas. It’s presumed this disappearing trick is the work of changing levels in the sea, but more data is needed.
But there’s more to this flyby than just some great science. Cassini has relied heavily on Titan’s mass to adjust its trajectory for very little fuel expenditure, and today was no exception. Today, Cassini used Titan’s gravity to lower its orbit significantly, bringing the periapsis (the low point) within the rings, and shortening the entire orbit to just about a week. Cassini will make twenty two dives into the area within Saturn’s rings, low enough to begin to directly sample some of Saturn’s tenuous upper atmosphere, gradually sinking on each closest approach until finally, next September, its predicted to impact the giant planet’s cloud decks and burn up.
It’s bittersweet, to be sure. Cassini has functioned like a champ, long past its original design life. But all things must come to and end, and Cassini will go out with a bang.
So as we prepare to say farewell in a few months, here’s a parting shot from Cassini: the last photograph it will be able to take of the Earth and Moon. This was taken on April 12, taking advantage of a viewing geometry that will not occur again on the mission, where Earth peeked through the gap between the A ring and the F ring:
This is pretty cool. 😉
On October 22, 2008, India joined the elite group of nations which have successfully sent spacecraft to orbit the Moon. The mission was successful, conducting joint operations with NASA’s Lunar Reconnaissance Orbiter and LCROSS impactor, deploying an impactor of its own to help search for lunar ice (and making India only the fourth country to place its flag upon the Moon), and providing the first definitive proof of water ice in the lunar soil. The mission was cut short, however, when the spacecraft abruptly stopped responding to ground commands on August 29, 2009. The cause of the failure was never determined, but it had been experiencing issues in several systems, including the star tracker that keeps its antenna aligned with Earth.
Like other deep space spacecraft, the moment it stopped transmitting it became impossible to track from Earth — the Moon is much too far away to track such small objects (in Chandrayaan-1’s case, about 1.5 meters by 1.5 meters) by radar.
Or is it?
As international governmental and private space programs grow at an astonishing rate, it has become clear that space traffic will increasingly become a problem not just in Low Earth Orbit (LEO) and in the immensely valuable Geostationary Earth Orbit (GEO, the province of most communications satellites) but in deep space as well. The recent move of the MAVEN spacecraft to dodge Mars’ innermost moon, Phobos, also underscores the hazards. So JPL conducted a study to see whether lunar spacecraft actually could be tracked from Earth. And guess what — they can!
JPL’s first target was LRO, because it’s an active spacecraft and therefore its real position is known with exquisite precision. Having located it with ground-based radar, the team moved on to something trickier: the Chandrayaan-1 spacecraft. Lunar spacecraft are difficult, because the Moon is so lumpy that a) dead spacecraft don’t stay long unless their orbits are fairly high, and b) orbits can be difficult to predict over long timescales. Nevertheless, they found it. Chandrayaan-1 is dead, but not gone, and certainly not forgotten.
Yes, you heard that right. They have yet to launch their crewed spacecraft as far as the ISS, but this week they announced that two undisclosed wealthy individuals have approached them about riding a Dragon capsule, boosted by their soon-to-fly Falcon Heavy, in a trip around the Moon. (I’m betting they’re talking a lunar swingby mission, not an orbital mission.) They plan on conducting this mission by the end of 2018.
For perspective, there are only two flights of Falcon Heavy currently on the manifest (the demo launch and a USAF experimental mission, one this year and one the next), and the crewed Dragon isn’t set to fly to the ISS until the fourth quarter of 2018 as it is. (And the GAO recently expressed serious doubt about that even happening.) So this is pretty ambitious. Exciting, and very very cool, but certainly a stretch goal.
Who are the two individuals? SpaceX isn’t saying. They did, however, say they’d be happy to give NASA dibs on flying to the Moon aboard Dragon first — an announcement which came as a great shock to NASA, since they found out about all of this the same time the rest of us did.
This is sure to shake things up, and I’d not put odds on whether or not they’ll manage this. I do have to wonder whether they’re overextending themselves. They have put a lot of very ambitious challenges in front of themselves. From a program risk perspective, this doesn’t seem like a good idea. But if they pull it off . . . hoo boy. There’s quite a payoff in terms of bragging rights, and it’s definitely a strong step towards their ultimate goal: Mars.
I have a particular fondness for pictures of the Earth and Moon together. NOAA’s latest weather satellite, the ground-breaking GOES-16, produced this particularly stunning example. It’s currently in its commissioning phase, so it isn’t yet contributing to weather forecasting. But it will, and when it does, it will be spectacular. This image was taken from geosynchronous orbit — 22,000 miles away. Earth and Moon are natural color, and this is not a composite — this is the image it actually took. It can be surprising to see the Moon look so dark; we’re used to seeing it so bright in our night sky. But it’s really because the Earth is so much brighter. The Moon is of course not a usual target for a GOES satellite; but it still will take pictures of the Moon every now and again for calibration purposes, since unlike the Earth, the Moon looks very much the same from one orbit to the next. For now, though, this image exists mostly to be beautiful. Enjoy it!
Here’s the latest view of our blue marble from Mars, courtesy of Mars Reconnaissance Orbiter:
It’s a composite image, merging images taken through different filters to produce color (although not “true” color, since MRO can see in infrared — vegetation shines very brightly in infrared, which makes Earth redder than it would be to the human eye), and processing Earth and Moon separately so that Moon can be bright enough to see without making the Earth just a big white smear. The Earth is one of the brightest objects in the solar system, and while the Moon looks really bright from here, it’s actually much darker than the Earth.
Believe it or not, the Moon was the real target of this image. MRO isn’t really equipped to take this kind of picture, since it has what’s called a “pushbroom” camera (great for mapping, terrible for portraiture or landscapes), but once every now and again it does — for calibration purposes. When this image was taken, the Moon was almost directly opposite the Earth from Mars’ perspective. That means it’s the Earth-facing side of the Moon that we can see — the same side of the Moon we’ve all grown up seeing. The lunar nearside is the best-known celestial object, and therefore a perfect calibration target. 😉 They know precisely how bright it should be.
Pretty neat, huh?
“Yutu”, the Jade Rabbit rover, delivered to the Moon by the Chang’e 3 lander, the first lunar lander sent by any nation other than the USA or the USSR and the first sent by anyone at all since 1976, has now officially ended its mission. The little rover survived a harrowing failure early on, but recovered (albeit without the ability to move anymore) and endured repeated long lunar nights (lasting almost half a month). But now, after an incredible 31 months, the rover can no longer survive. It’s well past its primary mission, which was only slated for three months. I haven’t been able to find out whether Jade Rabbit is succumbing to the environment or to a lack of funding — ten times past the original mission length, it’s often hard for any space agency to justify continued funding — but either way, it’s dang impressive. The mission team signed off by posting one final message on behalf of Jade Rabbit to Weibo: “I’m a rabbit that has seen the most stars!”
After the cancellation of Apollos 18-20, it looked unlikely that NASA would be allowed to return to the Moon. The attitude in the legislature was one of “been there, done that”. Human spaceflight had been re-aimed at low Earth orbit space stations and spaceplanes, while robotic missions were going ever further into the deepest recesses of the solar system. In 1977, the final death-knell for American lunar exploration seemed to have been struck when the funding to monitor the Apollo Lunar Surface Experiment Packages (ALSEPs) ran out, and the perfectly good autonomous stations were deactivated.
Perhaps this is why the first return to the Moon since Apollo was not exclusively a NASA project. In 1994, on January 25, the Clementine spacecraft blasted off from Vandenberg Air Force Base aboard a Titan II rocket (military surplus; the rocket had previously lived in a missile silo). All of the refurbished ICBM Titan II launches were for one customer: the United States Air Force. The USAF realistically had no particular interest in the Moon, but their Ballistic Missile Defense Organization had a number of crucial new technologies that it wanted to develop, and somewhere along the way, someone came up with the bright idea of testing them out in a spacecraft that would also orbit the Moon. This allowed them to get NASA on board, and also the French agency CNES, significantly reducing the amount each agency would need to spend. On February 19, the spacecraft arrived in lunar orbit, and on May 3, it became the first spacecraft to do something else remarkable: it departed lunar orbit to leave the Earth-Moon system altogether. The only spacecraft to have left lunar orbit previously were all sending capsules back to Earth. After leaving lunar orbit, the spacecraft then left Earth orbit, conducting a burn designed to put it on course to rendezvous with the asteroid 1620 Geographos; unfortnately, a thruster malfunction ruined that plan, and they ended up putting the spacecraft into a heliocentric orbit designed to take it one more time through the Earth’s Van Allen Belts for further study. Contact was lost in June of 1994.
Clementine was a short-lived probe, and one which, like the girl in the song, is now lost and gone forever. But it did something important in the meantime: it proved there was still a reason to go to the Moon.