The lure and mystery of moondust

Friday evening, September 6, 2013, the Lunar Atmosphere and Dust Environment Explorer (LADEE) was launched aboard a Minotaur rocket from Wallops Island, VA, on the mid-Atlantic seaboard.  This mission is proving interesting in a lot of ways — some to do with the Moon, and some to do with how space missions are now executed.

LADEE-event-ames

The LADEE spacecraft was developed at NASA Ames Research Center, in Silicon Valley and sitting right on the edge of the San Francisco Bay. Ames is home to the NASA Lunar Science Institute. So it was fitting that Ames hosted a “science night” for thousands of enthusiasts, with the LADEE launch as the highlight.

Now, for my friends who were expecting to see me at the Ames event, I apologize.  I had a major case of fatigue very early in the day, and did not think I would be able to drive home after the event.  So I left work after the last meeting of the day, into a big traffic jam (sigh), and connected my laptop to the biggest screen in the house so that I could watch it.

In recent years, our understanding of the Moon has been rapidly evolving. After decades of neglect following the Apollo missions in the late 1960s-early 1970s, we were suddenly on the hunt for water. As a result of Apollo, we believed that the Moon is an exceedingly dry, barren place with no hope of supporting humans without a continual lifeline of supplies from Earth.  So we stopped going.  Even the first pictures from the surface of Mars, from Viking in the 1970s, showed a dry, barren place with hardly any atmosphere.  A lot of people were probably wondering why governments were spending money on space at all.  In fact, the reason was international prestige; with that in hand, further scientific understanding was hard to justify to government budget and oversight committees.

It turns out we were wrong.  We now know water ice has been accumulating on the Moon, and Mars was once a very wet place.  We suspect that Jupiter’s moon Europa has icy oceans below its surface. And comets, coming from the far reaches of the solar system, are an amalgamation of rock, dust, water ice, and frozen “gases” like carbon dioxide, methane, ammonia, etc.  (At least, the latter would be gases at room temperature and pressure on Earth.)

The rocks from the Apollo missions did indeed contain faint traces of moisture, but it was felt these were probably contaminants brought from Earth.  Indeed, the samples are pretty dry.  Similarly sized samples of the Earth’s driest deserts have more water content.

In a nutshell, it now appears that water is virtually everywhere in the solar system.  With some ingenuity, human settlements can be sustained as far from the Sun as the water goes.  The Moon is the first step in figuring out how to do this.

The Moon’s exosphere

Like the Earth, the Moon is bombarded by a steady stream of atomic and subatomic particles from the Sun as well as meteorites from asteroids or other debris orbiting the Sun.  With no atmosphere like the Earth to slow or disintegrate small objects before they hit, the Moon is littered with small impact fragments that retain their sharp edges for millennia.  There is no erosion from abrasion against other fragments to round off the edges.  There is extreme heat and cold which would drive out moisture, and perhaps produce cracks.

The molecules and gases driven out would follow ballistic trajectories, hardly ever hitting another molecule before hitting the Moon’s surface, and perhaps bouncing again until it ran out of energy. Protons from the Sun might ultimately combine with atomic oxygen, also from the Sun, first forming hydroxyl (one hydrogen, one oxygen), and later water (two hydrogens, one oxygen).  [The Sun is about 78% hydrogen, 20% helium, and 0.86% oxygen, 0.4% carbon, etc..]  Furthermore, the surface is bathed in ultraviolet, knocking electrons off some atoms, leaving positively charged dust on the Moon that also has sharp edges.

Apollo_17_twilight_ray_sketch

A funny thing happened on the Moon during the Apollo 17 mission.  Astronaut Gene Cernan was set to observe the coronal and zodiacal light (CZL) of the Sun when it was hidden by the Moon. Indeed, he did see it, but there was more. There should have been just a small hump of light over the horizon, but in fact there were additional columns of light across the horizon as the Sun prepared to rise. It turned out there were similar sightings during Apollo 8, 10, and 15 during CZL observations. In fact, there was a lunar horizon glow (LHG) during the Surveyor missions preceding Apollo. The problem is, it wasn’t consistently seen; it was highly variable.

The LHG seen by Surveyor was from the surface of the Moon. To an extent, this can be explained by electrostatic charge on lunar dust. Ultraviolet radiation kicks electrons off the dust, leaving them positively charged, pushing away from each other, and rising off the Moon’s surface. This is expected a few meters up. But what the Apollo astronauts saw was at much higher altitudes.

Low-level lunar horizon glow (LHG) seen by Surveyor 7.  Credit: NASA

Low-level lunar horizon glow (LHG) seen by Surveyor 7. Credit: NASA

It is possible that the electrostatic charge is propelling smaller particles faster, onto trajectories high above the lunar surface. It could also be from sodium atoms in the Moon’s exosphere.

Part of what LADEE will do is gather more information on the composition of this tenuous lunar atmosphere and dust environment.  (Hence, the name.)  What is learned here will undoubtedly shed light on what is happening on other small bodies elsewhere in the solar system.  One has to imagine the moons of Mars, or for that matter, the moons of Pluto.  (Pluto itself seems to have a very very faint atmosphere; New Horizons will be visiting soon and find out more.)

Modularity

LADEE is built on a “modular common spacecraft bus” (MCSB); that is, a basic spacecraft framework (structure, propulsion, electrical buses).  It is intended to be utilized for a variety of missions, thus reducing the overall cost of spacecraft and mission development.

In fact, the MCSB is being utilized by Moon Express, a team competing for the Google Lunar X Prize.

Modularity and commonality are not new concepts in the spacecraft business. Commercial satellites are often built on a common bus, with small incremental improvements from one  spacecraft bus to the next.  Exploratory spacecraft are often developed with pairs of hardware — one for the spacecraft to be launched, and a spare set for testing and backup.  The spare set is often later used for a cheaper spacecraft.  Venus Radar Mapper, aka Magellan, utilized spare components from Galileo.  If the Galileo spacecraft was lost during launch or early in the mission, the spare set would have been appropriated to create the backup spacecraft, and there would have been no Magellan.  (At least, that was the plan. Check the launch dates; you’ll see something else happened.)

In the emerging industry of asteroid mining, one can see the glimmer of a spacecraft production line, where perhaps hundreds of spacecraft will ultimately be manufactured for various stages of asteroid resource exploration.  These are, so far, much smaller than the MCSB that LADEE uses.  (Although once resource extraction begins, it seems impossible for the spacecraft to retain a small size.)

Having done the prototyping of the bus and adapting it to LADEE, it is hoped that other missions will see fit to utilize it.  LADEE itself is a lunar orbiter.  Moon Express is building a lander.  A variety of other lander and rendezvous missions are possible using MCSB components.

Spaceports for small spacecraft

Wallops Island has been a flight facility for NASA or NACA, dating back to 1945. Sounding rockets have been launched from Wallops to study the upper atmosphere.  A variety of aircraft and scientific balloon missions have originated from there as well.

However, it is emerging as a launch facility for orbital and lunar missions.  This means payload integration, tracking range, etc.  While larger payloads are launched from Cape Canaveral to destinations like the International Space Station, Wallops is focused on small payloads in the range of 4-400 pounds (1.8 to 180 kilograms).

Rather than hitching a ride as a secondary payload on a larger rocket, it gives the opportunity for small payloads to be primaries, thus giving mission teams more control and flexibility in what they can do.

This particular launch involved an Orbital Sciences Minotaur V rocket.  A few months earlier, on April 21, Orbital launched an Antares rocket, carrying a few small payloads, including three copies of PhoneSat-1, developed at NASA Ames.

These are unmanned launches.  There is also a trend toward utilizing hardware for manned suborbital launches for unmanned orbital as well.

XCOR Aerospace is building its Lynx rocketplane to take-off and land on a runway.  As the vehicle matures, a version is planned to have a dorsal pod that extends from the fuselage.  The pod will be able to hold a rocket stage that could put a small payload into orbit.  (This would be a nanosatellite such as a CubeSat.)

Virgin Galactic, which is building SpaceShipTwo for tourists, is also building LauncherOne for small payloads.  Both will utilize the WhiteKnightTwo aircraft as their launch platform.  Currently, Virgin Galactic is planning commercial flights at New Mexico’s “Spaceport America.”

Thus, the options for payloads ranging from small to very small are gaining. Wallops and the state of Virginia undoubtedly hope to be a leading flight facility for launches of small payloads into orbit and beyond.

Putting it all together…

LADEE is a research and exploration mission built using a modular spacecraft design.  It is intended to answer questions about the nature of the tenuous lunar atmosphere/exosphere.  The lessons learned may be extrapolated to other small planetoids beyond Earth in the solar system. The launch from Wallops is part of an emerging trend to provide better options for smaller spacecraft.

Additional info

[Updates: around 2013-09-08 around 0820 PDT – a few additional words about Galileo and Magellan.]

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