R.I.P. LADEE: Probe smashes into lunar surface at 3,600mph
Swan dive signs off successful science mission
Pics NASA has confirmed that the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft, which has spent the last 100 days orbiting the Moon, has shuffled off its mortal coil in a spectacular swan dive into the lunar regolith between 9:30pm and 10:22pm PDT on Thursday.
LADEE, the little probe that could
"At the time of impact, LADEE was traveling at a speed of 3,600 miles per hour – about three times the speed of a high-powered rifle bullet," said Rick Elphic, LADEE project scientist at Ames.
"There's nothing gentle about impact at these speeds," Elphic told The Reg. "It’s just a question of whether LADEE made a localized craterlet on a hillside or scattered debris across a flat area. It will be interesting to see what kind of feature LADEE has created."
LADEE was launched last September (incinerating a local amphibian on the way) and was in position orbiting the Moon six weeks later. While in orbit, its mission was two-fold: it measured the level of dust particles suspended in the tenuous lunar atmosphere and tested out NASA's latest space broadband system: the Lunar Laser Communication Demonstration (LLCD).
Both missions are now considered a success, Elphic and LADEE project manager Butler Hine told The Reg, but – as is so often the way with scientific endeavor – the mission has raised a fascinating mystery.
On the basic question of dust in the Moon's atmosphere, the LADEE mission sampled particles 250km above the lunar surface, and the density of strikes increased the closer the probe came to the surface. Based on the evidence, these appear to be caused when small particles slam into the Moon's surface and throw up ejecta – some flying fast enough to reach high up, the majority staying close to the surface.
But it had been hoped that the LADEE probe could solve another enduring mystery. During the last Moon landing by Apollo 17, astronaut Gene Cernan saw a mysterious glow on the lunar surface just before sunrise and sketched out images of what this looked like. But based on LADEE's data, the glow shouldn't be visible.
Sketches of lunar dust clouds made by the Apollo 17 lander crew
"What they saw could not be explained by the very low dust levels that have been seen; it wouldn't create any signature that the human eye could see at all," said Hine. "We have since also tried to take images using our star trackers of the pre-sunrise glow about the lunar surface. So far we've seen nothing at all that resembles what he saw."
Broadband to shame terrestrial ISPs
Another mission for the LADEE probe was to test out NASA's LLCD space communications system, which uses lasers to communicate rather than low-bandwidth radio. The LLCD passed with flying colors, the team reports.
The system fires data from a 0.5-watt infrared laser mounted on the side of the probe to a network of three receiving stations in California, New Mexico, and Spain, consisting of clusters of eight telescopes, each on a gimbal, that can track the signals from space and upload new data.
In testing, the LLCD managed to send back 622Mbps of pure data, and achieved 20Mbps upload speeds from Earth. Initially, the team used engineering test data that can be easily checked for faults or breaks, but after that was completed NASA switched to beaming old science fiction movies to the Moon and back to test out the system.
El Reg hopes 2001 was included – Arthur C. Clarke would have approved. We just hope the Motion Picture Ass. of America doesn't start an outer-space lawsuit.
The LADEE test showed that the system worked as specified, but the data also showed that the connection would also work for communicating with Earth's Lagrange points and even all the way to Mars. Connection speeds might suffer from the distance with the current system, but a more powerful laser and larger receiving telescope would bring them back up, Hine explained.
Having that kind of bandwidth is going to be vital for future missions, not just for sending back data on the fly but also to protect the integrity of on-board systems. Data needs to be constantly backed up when in the harsh environment of space where radiation can fry circuits, and the new system will allow multiple backups to be taken and used to restore lost data in flight.
LADEE will make future missions cheaper
LADEE was the first spacecraft built using a new modular design system that will dramatically reduce the cost of future space probes.
The spacecraft was built using modules that can be slotted together easily. While each mission will take up different scientific instrumentation, the basic design won't change, which lowers the overall build cost.
Building the next generation of spacecraft for less
The total cost for the LADEE mission was $275m, slightly less than two F-35 fighter aircraft. Of that, the probe itself cost around $125m, with the launch vehicle setting NASA back $75m and the rest going on ground control systems and paying the wages of the staff to run them.
"LADEE proved the concept very nicely," Hine said. "The modular design is just a concept until you fly it once, so the first flight is very important, and proves out that these spacecraft can actually fly."
The first test flight wasn't a cakewalk either. LADEE was flying low over the lunar landscape and required constant updates to its flight path to do its job. It was also exposed to great temperature changes, passing from light to dark every other hour as LADEE orbited the Moon – but the probe performed superlatively.
The last lunar eclipse provided a much greater test of the probe as well. As the Earth cast its shadow over the Moon LADEE was left in the dark for four hours, crippling its solar panels and leaving the probe running on battery power which deteriorated quickly in the cold conditions.
Elphic said that the team was able to watch as LADEE chilled down and began to reach the limits of its power capabilities, but once the eclipse was over the spacecraft came back to life with almost no faults, with the exception of a couple of pressure transducers that died, and the probe was able to send back six more days-worth of data before impacting.
Now that the design has been proven it can be used on other probes, and Hine estimated that the costs to build each craft will fall dramatically. The next modular probe could be put together for between $80m and $100m (at least a 20 per cent saving) and the costs would fall to between $60m and $80m for the subsequent probe.
Furthermore, given the shakedown tests LADEE underwent, the probe is now considered proven to operate not just on lunar missions, but all the way out to Mars. This means the design could save huge amounts of money surveying the Red Planet and could help in NASA's plans to capture an asteroid and safely bring it back to our locale for study.
The final countdown
With LADEE's fuel exhausted, the decision was made to bring it down onto the lunar surface for a crash landing, rather than have it clogging up orbital tracks around the Moon.
NASA directed the craft to crash on the far side of the Moon. This has the disadvantage of making the strike not visible from Earth, but the decision was necessary because the agency wanted to avoid any risk of disturbing historical sites on the near side where mankind and its machinery have visited our satellite before.
The agency also held a small competition among members of the public to guestimate where exactly LADEE's final resting place would be. Over 5,900 people sent in their best guesses, and the telemetry for the flight should be turn up an answer sometime in the next day or two.
A NASA spokeswoman said that it was looking like over 500 people got the answer roughly right and, once the final answer has been obtained, certificates will be mailed out to the winners.
That's not to say the mission is totally over. LADEE's science team now has a wealth of data to go over, and it will take at least a year before it has been properly sorted, assimilated, and analyzed. There are also other modular probes for which to plan missions.
Considering the low cost of the LADEE mission, this has to rank as one more NASA success story. The data on dust will be important for understanding the Moon's ecology and the ability for man and machinery to function on the lunar surface, while the LLCD is going to prove vital for future off-world communications.
El Reg wouldn't be surprised if there have been a few bottles of beer sunk to LADEE's success. Certainly the team has earned it.