Robotic Missions in Sun-Earth Space - Nasa's Discovery Program

The Discovery program was initiated in 1989 to develop missions that could be accomplished using small spacecraft at a low cost in a relatively short time to address focused scientific goals. The emphasis is on projects that can be managed by academic and/or research organizations.

The program allows scientists to conduct small space investigations that complement NASA's larger and more expensive interplanetary missions. Each Discovery mission must have a fast development time (less than thirty-six months) and relatively low cost (less than $299 million). NASA calls it the "faster, better, cheaper" approach to space science. Mission of Opportunity projects are also allowed, but cannot exceed a cost to NASA of $35 million. The Discovery program focuses on specific research objectives related to planets, moons, comets, and asteroids.

Approximately every two years NASA publishes an Announcement of Opportunity (AO) in which it invites organizations to submit proposals for a future Discovery mission. The organizations can be educational institutions, commercial enterprises, nonprofit organizations, NASA Centers (or the JPL), or other government agencies. The most recent AO was released in January 2006.

TABLE 6.1 Explorers Program: operational missions as of February 2006 Adapted from "Current Missions," in Explorers Program, National Aeronautics and Space Administration, Goddard Space Flight Center, 2005, http://explorers.gsfc.nasa.gov/missions.html (accessed December 28, 2005)

TABLE 6.1
Explorers Program: operational missions as of February 2006
Name	Long title	Launch date	Orbit location	Mission
SOURCE: Adapted from "Current Missions," in Explorers Program, National Aeronautics and Space Administration, Goddard Space Flight Center, 2005, http://explorers.gsfc.nasa.gov/missions.html (accessed December 28, 2005)
ACE	Advanced Composition Explorer	08/25/1997	L1	Samples low-energy particles of solar origin and high-energy galactic particles
IMP-8	Interplanetary Monitoring Platform	10/26/1973	35 Earth radii	Measures magnetic fields, plasmas, and energetic charged particles
RXTE	Rossi X-ray Timing Explorer	12/30/1995	LEO	Observes black holes, neutron stars, X-ray pulsars and bursts of X-rays
Medium-Class Explorers (MIDEX)
Swift	(Named after a small nimble bird)	11/20/2004	LEO	Multi-wavelength observatory dedicated to the study of gamma-ray burst
WMAP	Wilkinson Microwave Anisotropy Probe	06/30/2001	L2	Measures cosmic microwave background radiation over the full sky
FUSE	Far Ultraviolet Spectroscopic Explorer	06/24/1999	LEO	Uses high-resolution spectroscopy in the far-ultraviolet spectral region
IMAGE	Imager for Magnetopause-to-Aurora Global Exploration	03/25/2000	7.2 Earth radii	Images Earth's magnetosphere
Small Explorers (SMEX)
FAST	Fast Auroral Snapshot Explorer	08/21/1996	215-2,500 miles	Investigates the plasma physics of the auroral phenomena at Earth's poles
SAMPEX	Solar Anomalous and Magnetospheric Particle Explorer	07/03/1992	LEO	Measures the composition of solar energetic particles and cosmic rays
SWAS	Submillimeter Wave Astronomy Satellite	12/05/1998	LEO	Surveys emissions of water, O2, C, and CO in galactic star forming regions
TRACE	Transition Region and Coronal Explorer	04/02/1998	LEO	Images the solar corona and transition region
RHESSI	Reuven Ramaty High Energy Solar Spectroscopic Imager	02/05/2002	LEO	Explore basic physics of solar flares
GALEX	Galaxy Evolution Explorer	04/28/2003	LEO	Space telescope that observes galaxies in ultraviolet light
University-Class Explorers (UNEX)/Student Explorer Demonstration Initiative program (STEDI)
SNOE	Student Nitric Oxide Explorer	02/26/1998	LEO	Measues effects of energy on nitric oxide in the Earth's upper atmosphere
CHIPS	Cosmic Hot Interstellar Plasma Spectrometer	01/12/2003	LEO	Conducts all-sky spectroscopy of the diffuse background
Missions of Opportunity (MO)
HETE-2	High-Energy Transient Explorer	10/09/2000	LEO	Detects and localizes gamma-ray bursts
Suzaku	(Formerly called Astro-E2, Suzaku is a vermillion bird)	07/10/2005	LEO	Studies X-rays emitted by stars, galaxies, and black holes
Integral	International Gamma Ray Laboratory	10/17/2002	1.4-23.5 Earth radii	Gamma-ray observatory

As of 2006 there were eleven missions listed under the Discovery program, as shown in Figure 6.1. Four of the missions (NEAR, Lunar Prospector, CONTOUR, and NetLander) ended during the late 1990s or early 2000s.

NEAR (Near Earth Asteroid Rendezvous) was the first mission launched under the Discovery program. On February 17, 1996, NEAR was launched into space to meet up with the asteroid 433 Eros. Asteroids are small celestial bodies that orbit larger ones. Most of the asteroids in the solar system are found in a massive asteroid belt that circles around the Sun between the orbits of Mars and Jupiter. 433 Eros is twenty-one miles long and has an elliptical orbit that carries it outside the Martian orbit and then in close to Earth orbit. On February 12, 2001, the NEAR spacecraft softly touched down on the asteroid. It was the first time in history that a spacecraft had landed on an asteroid. When it happened, 433 Eros was 196 million miles from Earth.

NEAR orbited 433 Eros for nearly a year before landing and returned dozens of high-resolution photographs of the asteroid. The spacecraft was built by the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, which also managed the mission for NASA. Before it landed, the spacecraft was renamed NEAR Shoemaker in honor of the late geologist Dr. Eugene M. Shoemaker (1928–97). The first Discovery mission was considered an overwhelming success.

Lunar Prospector launched on January 6, 1998, and assumed an orbit around Earth's moon to collect scientific data. In July 1999 the ship was purposely crashed into the lunar surface. CONTOUR launched on July 3, 2002 and was intended to encounter two comets in solar orbit. However, the spaceship was lost six weeks after launch. NetLander was a mission of opportunity in which NASA instruments were to fly aboard a French spaceship to Mars. However, the French mission was cancelled during the development phase.

Operational Discovery missions as of February 2006 were as follows:

• Stardust
• Genesis
• ASPERA-3
• Deep Impact
• MESSENGER

FIGURE 6.1 Discovery program master schedule "Discovery Program Master Schedule," in Discovery Program: Program Description, National Aeronautics and Space Administration, April 2, 2004, http://discovery.nasa.gov/images/missionschedule.gif (accessed January 31, 2006)

Stardust

Stardust was designed to collect particle samples from comet Wild 2 and return them safely to Earth. Comet Wild 2 is named after Swiss astronomer Paul Wild, who discovered it in 1978. (His name is pronounced "Vilt." Thus, comet Wild 2 is pronounced Vilt 2.)

Wild 2 is a relatively small comet with a nucleus measuring about three miles in diameter. A comet nucleus is a dense core of rock and frozen gas. The coma is the thick cloud of gases and sand that surrounds a comet nucleus. Comets follow heliocentric (sun-centered) orbits.

On February 7, 1999, Stardust was launched on its journey. The spacecraft carries a particle collector about the size of a tennis racket. (See Figure 6.2.) The collector is made of an ultra-lightweight material called aerogel that can capture and hold tiny comet dust particles. Following capture the collector folds down into the sample return capsule for its journey back to Earth. Stardust is also equipped with special detectors for analysis of comet dust and interstellar dust.

Stardust collected and analyzed interstellar dust in 2000 and 2002. On January 2, 2004, it successfully sampled particles from the coma of Wild 2. These particles are believed to be more than 4.5 billion years old.

As the spaceship approached Earth it released the sample return capsule. Shortly before 5:00 AM (Eastern Standard Time) on January 15, 2006, the capsule entered Earth's atmosphere. Parachutes were deployed, and the capsule landed safely in the Utah desert. The main spacecraft was put into orbit around the sun and will likely be used on a future mission.

A few days later NASA scientists confirmed that the mission had been a success. They reported finding "thousands of impacts" on the aerogel in the sample return capsule. Stardust was the first-ever comet sample return mission.

Genesis

In August 2001 Genesis was launched into outer space toward the L1 Lagrange point. It was a revolution-FIGURE 6.2 The Stardust spacecraft "Stardust Spacecraft," in Stardust Comet Flyby, Press Kit, National Aeronautics and Space Administration, Jet Propulsion Laboratory, January 2004, http://stardust.Jpl.nasa.gov/news/stardustfly.pdf (accessed January 31,2006)ary spacecraft designed to collect charged particles emitted from the sun and return them safely to Earth. Genesis successfully reached its destination and collected samples. It assumed a tight orbit around L1 for 2.5 years and then headed back to Earth. After reentering Earth's atmosphere Genesis was supposed to deploy its parachutes for a slow descent toward the surface. A specially equipped helicopter was to snag the spaceship and carry it to land.

On September 8, 2004, Genesis began its descent to a Utah landing site. However, its parachutes did not open, and the spacecraft plummeted at high speed into the ground. The capsule containing the samples split open during the crash, exposing the sample medium to the outside atmosphere. After six months of recovery and analysis NASA announced that some of the samples had survived intact and would be made available for scientific study.