The NASA has launched its latest mission to the Moon. The unmanned LADEE probe lifted off from the Wallops rocket facility on the US east coast on schedule at 23:27 local time (03:27 GMT on Saturday). Its $280m (£180m) mission is to investigate the very tenuous atmosphere that surrounds the lunar body. It will also try to get some insights on the strange behaviour of moondust, which appears on occasions to levitate high above the surface. In addition, LADEE will test a new laser communications system that NASA hopes at some point to put on future planetary missions. Lasers have the capacity to transmit data at rates that dwarf conventional radio connections.
LADEE stands for Lunar Atmosphere and Dust Environment Explorer. Its programme scientist, Sarah Noble, says the mission is likely to surprise a lot of people who have been brought up to believe the Moon has no atmosphere. “It does; it’s just it's really, really thin,” she said. “It’s so thin that the individual molecules are so few and far between that they don't interact with each other; they never collide. It’s something we call an exosphere. The Earth has an exosphere as well, but you have to get out past where the International Space Station orbits before you get to this condition that we can consider an exosphere. At the Moon, it happens right at the surface.”
The Lunar Atmosphere and Dust Environment Explorer will operate for a total of about six months. Scientists are interested in understanding such wispy shrouds because they are actually the most common type of atmosphere in the Solar System. Mercury has one, as do a lot of the moons of the giant planets. Even some big asteroids are likely to have one, too. The dust phenomenon has puzzled researchers for decades. Apollo astronauts reported seeing a diffuse glow above the lunar horizon just before sunrise. The speculation has been that this glow was caused by electrically charged dust particles being lifted from the Moon's surface by ultraviolet light from the Sun. LADEE’s remote-sensing and sampling instrumentation will test this idea.
What it learns about the dust is also likely to inform engineers who are developing the systems to take humans back to the Moon and to other destinations where dust could be an issue, such as on asteroids. This fine particulate material, which comprises remnant rock shattered through eons of meteorite impacts, is considered a major hazard. “It’s not like terrestrial dust,” observed Butler Hine, LADEE project manager. “Terrestrial dust is like talcum powder. On the Moon, it’s very rough. It’s kinda evil. It follows electric field lines; it works its way into equipment. One of the questions about dust on the Moon is an engineering question: how do you design things so that they can survive the dust environment.”
Apollo astronauts found the chaffing moondust would stick to everything. There are concerns that if such material were breathed in, it could lead to respiratory problems. Having been launched by its Minotaur V rocket, LADEE will be sent on a long spiral out to the Moon. This will take about a month. A further month will then be needed to commission the spacecraft before its altitude is taken down to as low as 20km above the surface for a 100-day phase of science observations. LADEE will end its mission by crashing into the Moon. As well as its three science instruments, LADEE carries a demonstration laser telecommunications payload.
This system promises a big jump in data transmission rates. Engineers are hoping the test terminal on LADEE will achieve download rates in the region of 600 megabits per second. A number of receiving stations on Earth will be used, including the European Space Agency’s (Esa) optical ground station on Tenerife. Esa is keen to participate in the LADEE comms project because it too has ambitions in this area. Today, Europe and the US will often download data from each other's probes, and there will need to be some cooperation if the new technology is to be used the same way in the future.
Dust was a major nuisance for the Apollo astronauts. "We need some common standards, especially in optics," said Zoran Sodnik, the manager for Esa's Lunar Optical Communication Link project. "There are a lot of ground stations that operate in radio frequencies, and Esa and NASA have a long-lasting cross-support agreement. But in optical comms, there are very few ground stations. And if you don't try to agree on some standards, you will not be able to support the other agency's activities, and you would not be able to download the amounts of data that you would be able to download otherwise," he said.
John Grunsfeld, the head of science at NASA, said he had no doubts that optical communications was the way of the future. “Our Mars 2020 mission, we've already been having discussions about whether you could do laser comms on a rover on the surface of Mars. I think there is no question that as we send humans further out into the Solar System, certainly to Mars, if we want to have high-def, 3D video, we're going to have laser comms sending that information back.”
Lunar atmosphere thought to be only 1/100,000th the density of Earth's atmosphere
Earth's atmosphere contains some 100 billion air molecules per cubic cm at sea level
May be only about 100,000 to 10 million molecules per cubic cm at the Moon's surface
Very little known about this atmosphere's precise atomic and molecular composition
Spacecraft is 2.4m high and 1.8m wide, and weighs 383 kg fully fuelled
Based on a new low-cost modular chassis for use on other planetary missions
Mission will last six months in total with 100-day science observation phase
LADEE will be crashed into the lunar surface when its fuel supply has run out