DARTs in Space

Lockheed Martin; March 26, 2001; Press Release: "Space Telescope Using Light-Weight Membranes Studied"

DART outside the ISS. NASA/JPL

A novel light-weight method of constructing large space telescopes is being studied under contract by Lockheed Martin Space Systems Company for NASA's New Millennium Program.  The Dual Anamorphic Reflector Telescope (DART) consists of two trough-shaped reflectors in space.  Light bounces from the simple parabolic curve of one reflector to the other and focuses to a point. 

The key to the system is the simplicity of the reflectors.  The parabolic curve along the length of the mirror can be formed by light-weight reflective material that is tensioned over a correctly shaped frame.  This setup greatly reduces the mass of the telescope.  A 15-25-meter telescope could weigh 100 times less than the 2.4-meter Hubble Space Telescope.  Lower mass translates into lower deployment costs into space.  In fact with the DART system the ratio of structure to reflector mass decreases as the telescope aperture increases.  

Proposed space missions that may benefit from this technology include the Single Aperture Far Infrared (SAFIR) facility, Life Finder, and Planet Imager telescopes.  If the DART team can develop the concept to a sufficient point they may score a flight test in 2003/4 when NASA will test-fly five New Millennium Program projects into space for further evolution. 

Mystery of the Martian Gullies: No April Fools Joke

University of Arizona; March 30, 2001; Press Release: "Exotic CO2 Process May Have Carved Martian Gullies, UA Scientists Say"

Mars gully. NASA/MSSS

Last year images from the Mars Global Surveyor (MGS) discovered gullies on the sides of cliff and crater walls on the Red planet.  A theory was floated that water ice underneath the surface could become heated by sunlight during the warm part of the Martian year and suddenly melt and flow.  Gullies were formed where this water flow spilled through the sides of cliffs and craters.  

Now a team at the University of Arizona Lunar and Planetary Laboratory have published a new hypothesis in the April 1 issue of Geophysical Research Letters.  They believe that CO2 at times gushes out of the ground and forms a slurry of solid/gas CO2 and rocks.  This mixture flows down and digs the gullies spotted by the MGS.

This theory is bolstered by the fact that the atmosphere of Mars is mostly CO2.  The researchers propose that this gas condenses onto the planet's surface.  This surface is a very porous gravel created by impacts from space.  This process fills up the pore spaces between the gravel.  Winter temperatures causes the gas along the cliff surfaces to solidify.  The change of season causes the ice to expand when warmed.  With nowhere to expand the pressure of the CO2 builds with the temperature.  It turns into liquid -- which takes up more room than the solid -- and bursts through to the surface.

Mars: The British Are Coming

Space.com; March 27, 2001; Missions: "Mars Rock Return Mission Planned by British" 

NASA's plan for the 2005 launch of a $1-billion Mars sample return mission was scrapped after the failure of two Mars missions -- the latest being the Mars Polar Lander.  This may open the door for a British idea to return a pristine piece of another planet to Earth earlier and cheaper than NASA.

Beagle 2 on Mars.  ESA

The European Space Agency is planning to land the 30-kg "Beagle 2" craft on Mars in 2003 to carry out soil and weather analysis.  Using this mission as a hardware baseline, British scientists at the Royal Society in London are proposing to drop a similar lander that will dig up and return a bit of Mars to Earth.  

The key cost reduction in the British plan is based on the belief that a random location on Mars is composed of material from many regions.  This is due to the effects of fluid flows, blowing wind, and impact events.  Therefore any landing site will have an interesting mix of material for study.  This is in contrast to the NASA mission philosophy which was to employ costly rovers to gather rocks and soil from specific locations.

The British proposal is to obtain a 200-g core sample taken a meter below the random landing site.  The lander would rocket back into orbit for rendezvous with a waiting orbiter.  Within two years, when planetary alignments are suitable, the orbiter would leave Mars and return to Earth.  The simplicity of the mission saves hundreds of millions of dollars over the NASA version.  If given the go ahead by ESA the probe could be launch in 2009.

Recruiting More Eyes 

SpaceDaily.com; March 27, 2001; Spaceguard News: "Detecting Planet Killers as a Sideline"

What do the European Space Agency (ESA) GAIA astrometry satellite and the BepiColombo Mercury missions have in common?  Ostensibly not much.  GAIA is the follow-on to the ESA Hipparcos mission that measured the position of stars to unprecedented accuracy.  GAIA will be able to detect 1-billion objects down to magnitude 20 and determine their position with exceptional accuracy.  BepiColombo will place two orbiters around the planet Mercury and send down a lander. 

What they have in common derives from the increasing sophistication of sensors and computer technology to piggy-back secondary goals on an existing science mission.  In this case the two yet-to-be-launched missions will assist in detecting Near Earth Asteriods (NEA).  The goal is to add to the database of NEA and ferret out any potentially hazardous asteroids (PHA) that can threaten life on Earth.  Currently 291 of these PHA are known.

"The precision optics on GAIA will also give a colossal improvement in orbital measurements, allowing astronomers to make very precise, long-term orbit determinations.  This will allow them to work out whether asteroids measured by GAIA will eventually collide with Earth."
-- GIAA Project Scientist Michael Perryman

"In the case of near-Earth asteroids, we should find objects as small as 500 metres in diameter," states GIAA Project Scientist Michael Perryman. "The precision optics on GAIA will also give a colossal improvement in orbital measurements, allowing astronomers to make very precise, long-term orbit determinations.  This will allow them to work out whether asteroids measured by GAIA will eventually collide with Earth."

A class of asteroids called "Atens" that circle the Sun inside of Earth's orbit are of particular interest.   GAIA will have the ability to observe "fairly close" to the Sun, and catalog many of these possibly dangerious objects. 

BepiColombo concept.  ESA

From Earth orbit GAIA can not monitor the entire population Earth-crossers that hide in the glare of the Sun.  That's where the Mercury orbiting BepiColombo mission will help fill the gap.  From its location closer to the Sun it will be able to look out and detect asteroids that would be lost in the Solar glare from Earth. 

The polar orbiter will have a camera that can image the sky in a 6° x 360° strip.  According to Mission Scientist Rejean Grard: "By detecting asteroids that cross this field of view and comparing measurements made at different times, we could determine their orbits. Preliminary evaluations indicate that there could be up to 100 objects in the selected strip of sky at any one time."

While the number of 1-km diameter NEA may range in the hundreds to just over a thousand, there are millions of smaller objects that can pose a threat to Earth.  For instance It is estimated that the object that exploded over Siberia in 1908 was a mere 50-m in diameter.  An object that size hitting the Earth could wipe out a city.  Sub 1-km sized objects capable of doing much damage hit the Earth every few thousand years.