NASA's Discovery Program Research Articles

Revealing the Mysteries of Venus: The DAVINCI Mission

The Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission described herein has been selected for flight to Venus as part of the NASA Discovery Program. DAVINCI will be the first mission to Venus to incorporate science-driven flybys and an instrumented descent sphere into a unified architecture. The anticipated scientific outcome will be a new understanding of the atmosphere, surface, and evolutionary path of Venus as a possibly once-habitable planet and analog to hot terrestrial exoplanets. The primary mission design for DAVINCI as selected features a preferred launch in summer/fall 2029, two flybys in 2030, and descent-sphere atmospheric entry by the end of 2031. The in situ atmospheric descent phase subsequently delivers definitive chemical and isotopic composition of the Venus atmosphere during an atmospheric transect above Alpha Regio. These in situ investigations of the atmosphere and near-infrared (NIR) descent imaging of the surface will complement remote flyby observations of the dynamic atmosphere, cloud deck, and surface NIR emissivity. The overall mission yield will be at least 60 Gbits (compressed) new data about the atmosphere and near surface, as well as the first unique characterization of the deep atmosphere environment and chemistry, including trace gases, key stable isotopes, oxygen fugacity, constraints on local rock compositions, and topography of a tessera.

Giant Success for NASA when the InSight Probe has Reached "Safety" on Mars

InSight-Studying the 'Inner Space' of Mars. InSight, short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport, is a Mars lander designed to give the Red Planet its first thorough checkup since it formed 4.5 billion years ago. It is the first outer space robotic explorer to study in-depth the "inner space" of Mars: Its crust, mantle and core. Studying Mars' interior structure answers key questions about the early formation of rocky planets in our inner solar system - Mercury, Venus, Earth and Mars - more than 4 billion years ago, as well as rocky exoplanets. InSight also measures tectonic activity and meteorite impacts on Mars today. The lander uses cutting edge instruments, to delve deep beneath the surface and seek the fingerprints of the processes that formed the terrestrial planets. It does so by measuring the planet's "vital signs": Its "pulse" (seismology), "temperature" (heat flow) and "reflexes" (precision tracking). This mission is part of NASA's Discovery Program for highly focused science missions that ask critical questions in solar system science.

MESSENGER at Mercury: Early orbital operations

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched in August 2004 under NASA's Discovery Program, was inserted into orbit about the planet Mercury in March 2011. MESSENGER's three flybys of Mercury in 2008–2009 marked the first spacecraft visits to the innermost planet since the Mariner 10 flybys in 1974–1975. The unprecedented orbital operations are yielding new insights into the nature and evolution of Mercury. The scientific questions that frame the MESSENGER mission led to the mission measurement objectives to be achieved by the seven payload instruments and the radio science experiment. Interweaving the full set of required orbital observations in a manner that maximizes the opportunity to satisfy all mission objectives and yet meet stringent spacecraft pointing and thermal constraints was a complex optimization problem that was solved with a software tool that simulates science observations and tracks progress toward meeting each objective. The final orbital observation plan, the outcome of that optimization process, meets all mission objectives. MESSENGER's Mercury Dual Imaging System is acquiring a global monochromatic image mosaic at better than 90% coverage and at least 250m average resolution, a global color image mosaic at better than 90% coverage and at least 1km average resolution, and global stereo imaging at better than 80% coverage and at least 250m average resolution. Higher-resolution images are also being acquired of targeted areas. The elemental remote sensing instruments, including the Gamma-Ray and Neutron Spectrometer and the X-Ray Spectrometer, are being operated nearly continuously and will establish the average surface abundances of most major elements. The Visible and Infrared Spectrograph channel of MESSENGER's Mercury Atmospheric and Surface Composition Spectrometer is acquiring a global map of spectral reflectance from 300 to 1450nm wavelength at a range of incidence and emission angles. Targeted areas have been selected for spectral coverage into the ultraviolet with the Ultraviolet and Visible Spectrometer (UVVS). MESSENGER's Mercury Laser Altimeter is acquiring topographic profiles when the slant range to Mercury's surface is less than 1800km, encompassing latitudes from 20°S to the north pole. Topography over the remainder of the southern hemisphere will be derived from stereo imaging, radio occultations, and limb profiles. MESSENGER's radio science experiment is determining Mercury's gravity field from Doppler signals acquired during frequent downlinks. MESSENGER's Magnetometer is measuring the vector magnetic field both within Mercury's magnetosphere and in Mercury's solar wind environment at an instrument sampling rate of up to 20 samples/s. The UVVS is determining the three-dimensional, time-dependent distribution of Mercury's exospheric neutral and ionic species via their emission lines. During each spacecraft orbit, the Energetic Particle Spectrometer measures energetic electrons and ions, and the Fast Imaging Plasma Spectrometer measures the energies and mass per charge of thermal plasma components, both within Mercury's magnetosphere and in Mercury's solar-wind environment. The primary mission observation sequence will continue for one Earth year, until March 2012. An extended mission, currently under discussion with NASA, would add a second year of orbital observations targeting a set of focused follow-on questions that build on observations to date and take advantage of the more active Sun expected during 2012–2013. MESSENGER's total primary mission cost, projected at $446M in real-year dollars, is comparable to that of Mariner 10 after adjustment for inflation.

Preliminary Results on HAT-P-4, TrES-3, XO-2, and GJ 436 from the NASA EPOXI Mission

AbstractEPOXI (EPOCh + DIXI) is a NASA Discovery Program Mission of Opportunity using the Deep Impact flyby spacecraft. The EPOCh (Extrasolar Planet Observation and Characterization) Science Investigation will gather photometric time series of known transiting exoplanet systems from January through August 2008. Here we describe the steps in the photometric extraction of the time series and present preliminary results of the first four EPOCh targets.

NASA mission to measure Moon's gravity

NASA has selected a new mission to measure the Moon's gravity field in unprecedented detail, according to the agency's associate administrator for science, Alan Stern. The Gravity Recovery and Interior Laboratory (GRAIL), which is part of NASA's Discovery Program series of scientist‐led, solar system exploration missions, is scheduled to launch in 2011 following the agency's 2008 launch of the Lunar Reconnaissance Orbiter. Scientists plan to use gravity field information from GRAIL's two spacecraft to X ray the Moon from crust to core to reveal subsurface structures and, indirectly, the Moon's thermal history. A camera aboard each spacecraft will allow the public to see observations from the satellites. GRAIL “offers to bring innovative Earth studies techniques to the Moon as a precursor to their possible later use at Mars and other planets,” Stern said. For more information, visit the Web site: http://discovery.nasa.gov/.

MESSENGER Mission Design and Navigation

Nearly three decades after the Mariner 10 spacecraft’s third and final targeted Mercury flyby, the 3 August 2004 launch of the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft began a new phase of exploration of the closest planet to our Sun. In order to ensure that the spacecraft had sufficient time for pre-launch testing, the NASA Discovery Program mission to orbit Mercury experienced launch delays that required utilization of the most complex of three possible mission profiles in 2004. During the 7.6-year mission, the spacecraft’s trajectory will include six planetary flybys (including three of Mercury between January 2008 and September 2009), dozens of trajectory-correction maneuvers (TCMs), and a year in orbit around Mercury. Members of the mission design and navigation teams optimize the spacecraft’s trajectory, specify TCM requirements, and predict and reconstruct the spacecraft’s orbit. These primary mission design and navigation responsibilities are closely coordinated with spacecraft design limitations, operational constraints, availability of ground-based tracking stations, and science objectives. A few days after the spacecraft enters Mercury orbit in mid-March 2011, the orbit will have an 80° inclination relative to Mercury’s equator, a 200-km minimum altitude over 60°N latitude, and a 12-hour period. In order to accommodate science goals that require long durations during Mercury orbit without trajectory adjustments, pairs of orbit-correction maneuvers are scheduled every 88 days (once per Mercury year).

The nucleus of Deep Impact target Comet 9P/Tempel 1

On UT 2000 August 21 we obtained simultaneous visible and mid-infrared observations of Comet 9P/Tempel 1, the target of the upcoming NASA Discovery Program mission Deep Impact. The comet was still quite active while 2.55 AU from the Sun (post-perihelion). Two independent analyses of our data, one parameterizing the coma morphology and the other modeling infrared spectrophotometry, show that the nucleus's cross section at the time the data were taken corresponds to an effective radius of 3.0 ± 0.2 km . Based on visible-wavelength photometry of the comet taken during this observing run and others in the summer of 2000, all of which show the rotational modulation of the nucleus's brightness, we find that the infrared data were obtained near the maximum of the light curve. If we assume that the nucleus's light curve had a peak-to-valley range of 0.6 ± 0.2 mag , then the mean effective radius is 2.6 ± 0.2 km . Visible-wavelength photometry of the nucleus, including data published by other groups, lets us constrain the nucleus's R-band geometric albedo: 0.072 ± 0.016 . The nucleus's flux contributed about 85% of the light in the mid-infrared images.

Deep Impact Mission Design

The Deep Impact mission is designed to provide the first opportunity to probe below the surface of a comet nucleus by a high-speed impact. This requires finding a suitable comet with launch and encounter conditions that allow a meaningful scientific experiment. The overall design requires the consideration of many factors ranging from environmental characteristics of the comet (nucleus size, dust levels, etc.), to launch dates fitting within the NASA Discovery program opportunities, to launch vehicle capability for a large impactor, to the observational conditions for the two approaching spacecraft and for telescopes on Earth.

An international program for Mercury exploration: synergy of MESSENGER and BepiColombo

Mariner 10 has been the only spacecraft to visit the innermost planet Mercury. Its three flybys, more than 25 years ago, yielded the first view of this little-understood world. With advances in spacecraft technology and a growing realization of how important Mercury is to our understanding of the solar system and its formation, two missions are now in development for more intensive Mercury exploration. The first is the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission, competitively selected under the NASA Discovery Program, that will send a spacecraft to fly by Mercury in 2007 and 2008 and to orbit Mercury for one Earth year beginning in April 2009. The second is the more comprehensive BepiColombo mission, consisting of three elements: the Mercury Planetary Orbiter (MPO), the Mercury Magnetospheric Orbiter (MMO), and the Mercury Surface Element (MSE). Still in final definition stage, BepiColombo is a partnership between the European Space Agency (ESA) and the Japanese Institute of Space and Astronautical Science (ISAS). With one or two launches (depending upon the final mission architecture) BepiColombo will use solar electric propulsion to send two orbiters (MPO from ESA and MMO from ISAS) and a lander (MSE) to Mercury as early as 2011. The BepiColombo orbiters, in orbits complementary to that of MESSENGER, will extend geochemical, spectral, and photometric mapping of the planet. With its factor-of-ten larger downlink, BepiColombo will complete the intensive study of Mercury begun with the exploration by MESSENGER. Synergistic strategies of exploration will enable efficient use of BepiColombo resources in a more detailed study of the planet than can be accomplished by MESSENGER alone. For example, the earlier MESSENGER mission can help identify appropriate landing sites for the MSE, while BepiColombo can provide complementary orbital measurements of surface features from different phase angles and exploit MESSENGER observations to target high-resolution measurements. Possible joint activities include cooperative use of ground stations and extension of the temporal baseline for geophysical measurements by combining data from all spacecraft. Were MESSENGER to be approved for an extended orbital phase, there is also the possibility of simultaneous dual-spacecraft measurements in the magnetosphere.

The nucleus of Deep Impact target Comet 9P/Tempel 1

On UT 2000 August 21 we obtained simultaneous visible and mid-infrared observations of Comet 9P/Tempel 1, the target of the upcoming NASA Discovery Program mission Deep Impact. The comet was still quite active while 2.55 AU from the Sun (post-perihelion). Two independent analyses of our data, one parameterizing the coma morphology and the other modeling infrared spectrophotometry, show that the nucleus's cross section at the time the data were taken corresponds to an effective radius of 3.0±0.2 km. Based on visible-wavelength photometry of the comet taken during this observing run and others in the summer of 2000, all of which show the rotational modulation of the nucleus's brightness, we find that the infrared data were obtained near the maximum of the light curve. If we assume that the nucleus's light curve had a peak-to-valley range of 0.6±0.2 mag, then the mean effective radius is 2.6±0.2 km. Visible-wavelength photometry of the nucleus, including data published by other groups, lets us constrain the nucleus's R-band geometric albedo: 0.072±0.016. The nucleus's flux contributed about 85% of the light in the mid-infrared images.

Overcoming Genesis mission design challenges

Genesis is the fifth mission selected as part of NASA's Discovery Program. The objective of Genesis is to collect solar wind samples for a period of approximately 2 years while in a halo orbit about the Sun–Earth colinear libration point, L1, located between the Sun and Earth. At the end of this period, the spacecraft follows a free-return trajectory with the samples delivered to a specific recovery point on the Earth for subsequent analysis. This type of sample return has never been attempted before and presents a formidable challenge, particularly with regard to planning and execution of propulsive maneuvers. Moreover, since the original inception, additional challenges have arisen as a result of emerging spacecraft design concerns and operational constraints. This paper will describe how these challenges have been met to date in the context of the better-faster-cheaper paradigm. [This paper addresses an earlier mission design, as of May 2000.]

The NEAR shoemaker mission to asteroid 433 eros

The Near Earth Asteroid Rendezvous (NEAR) mission inaugurated NASA's Discovery Program. It was the first mission to orbit an asteroid and made the first comprehensive scientific measurements of an asteroid's surface composition, geology, physical properties, and internal structure. NEAR was launched successfully on 17 February 1996 aboard a Delta II-7925. It made the first reconnaissance of a C-type asteroid during its flyby of the main-belt asteroid 253 Mathilde in June 1997. It became the first spacecraft to enter orbit around an asteroid, doing so at the large near-Earth asteroid 433 Eros in February 2000. The spacecraft, renamed NEAR Shoemaker, landed on Eros at 37.2 South by 278.4 West, ending its mission on February 12, 2001 with another spacecraft first. NEAR obtained new information on the nature and evolution of asteroids, improved our understanding of planetary formation processes in the early solar system, and clarified the relationships between asteroids and meteorites. The NEAR Mission Operations Center and Science Data Center were both located at APL. The latter maintained the entire NEAR data set on-line and made data from all instruments accessible over the Internet to every member of the NEAR science team.

LUNAR PROSPECTOR: FIRST RESULTS AND LESSONS LEARNED

Lunar Prospector, the first competitively selected mission in NASA's Discovery Program, is conducting a one-year orbital survey of the Moon's composition and structure. Launched on January 6 1998, the suite of five instruments is measuring water/ice to a sensitivity of 50 ppm (hydrogen), detecting key elemental constituents, gas release events and mapping the Moon's gravitational and magnetic fields. The mission is described with emphasis on the first scientific results and lessons learned from managing a very low cost project. A mission overview and systems description is given along with final mission trajectories. Lessons learned from government–industry teaming, new modes of project management, and novel contractual arrangements are discussed. The suite of five instruments (neutron spectrometer, alpha particle spectrometer, gamma-ray spectrometer, electron reflectometer and magnetometer) is outlined with attention to final technical performance as well as development on a constrained budget and schedule. A review of our novel approaches to education and public outreach is discussed and a summary with suggestions and implications for future missions is provided.

Lunar polar ice deposits: scientific and utilization objectives of the lunar ice discovery mission proposal

The Clementine mission has revived interest in the possibility that ice exists in shadowed craters near the lunar poles. Theoretically, the problem is complex, with several possible sources of water (meteoroid, asteroid, comet impact), several possible loss mechanisms (impact vaporization, sputtering, photoionization), and burial by meteorite impact. Opinions of modelers have ranged from no ice to several times 10 16 g of ice in the cold traps. Clementine bistatic radar data have been interpreted in favor of the presence of ice, while Arecibo radar data do not confirm its presence. The Lunar Prospector mission, planned to be flown in the fall of 1997, could gather new evidence for the existence of ice. If ice is present, both scientific and utilitarian objectives would be addressed by a lunar polar rover, such as that proposed to the NASA Discovery program, but not selected. The lunar polar rover remains the best way to understand the distribution and characteristics of lunar polar ice.

The Genesis mission: unifying science and engineering

Design of the Genesis spacecraft mission was derived from top-down flow of a basic and highly challenging science requirement: obtain samples of solar matter of such high quality and low background that they would sustain investigations of chemical and isotopic composition of the solar system for the coming decades, and well into the 21 st Century. Within the framework of several dozen competing mission concepts for planetary exploration under NASA's Discovery program, Genesis needed to perform extremely high quality science (solar collection and sample return) for an affordable yet realistic level of effort. Key issues included preservation of collector cleanliness, avoidance of spacecraft-generated con-tamination, control of collector temperatures, simplicity of long-term operation, ability to efficiently reach the L1 operations point, reliability of avionics and other support systems, return to a specific landing locale on Earth, and provision for soft capture of the descent capsule via mid-air parachute snatch. Genesis is now in the final stages of spacecraft testing and system validation, the culmination of a highly interwoven effort to meet science objectives with innovative solutions that also satisfy engineering challenges for reliability, affordability, rapid development and a comprehensive test program. Genesis is scheduled for launch in February 2001.

A comparison of NEAR actual spacecraft costs with three parametric cost models

Costs for modern (post-1990) U.S.-built small planetary spacecraft have been shown to exhibit significantly different trends from those of larger spacecraft. These differences cannot be accounted for simply by the change in size alone. Some have attributed this departure to NASA's “faster, better, cheaper” design approach embodied by the efficiency of smaller teams, reduced government oversight, increased focus on cost, and short development periods. With the Discovery, Mars Surveyor and New Millennium programs representing the new approach to planetary exploration, it is important to understand these current cost trends and to be able to estimate costs of future proposed missions. To address this issue, The Aerospace Corporation (hereafter referred to as Aerospace) performed a study to compare the actual costs of the Near Earth Asteroid Rendezvous (NEAR) spacecraft bus (instruments were not estimated) using three different cost models; the U.S. Air Force Unmanned Spacecraft Cost Model, Version 7 (USCM-7), the Science Applications International Corporation (SAIC) NASA/Air Force Cost Model 1996 (NAFCOM96) and The Aerospace Corporation's Small Satellite Cost Model 1998 (SSCM98). The NEAR spacecraft was chosen for comparison because it was the first Discovery mission launched, and recently recognized with a Laurel award by Aviation Week and Space Technology as a benchmark for NASA's Discovery program [North, 1997]. It was also selected because the cost data has been released into the public domain [Hemmings, 1996]which makes it easy to discuss in a public forum. This paper summarizes the NEAR program, provides a short synopsis of each of the three cost models, and demonstrates how they were applied for this study.

The Lunar Prospector Discovery Mission: mission and measurement description

Lunar Prospector, the first competitively selected planetary mission in NASA's Discovery Program, is described with emphasis on the radiation spectrometer instrumentation and anticipated scientific data return. Scheduled to be launched in January 1998, the mission will conduct a one year orbital survey of the Moon's composition and structure. The suite of five instruments are outlined: neutron spectrometer, alpha particle spectrometer, gamma-ray spectrometer, electron reflectometer and magnetometer. Scientific requirements and measurement approach to detect water/ice to a sensitivity of 50 ppm (hydrogen), measure key elemental constituents, detect radioactive gas release events and accurately map the Moon's gravitational and magnetic fields are given. A brief overview of the programmatic accomplishments in meeting a tightly constrained schedule and budget is also provided.

Lunar Prospector searches for polar ice, a metallic core, gas release events, and the Moon's origin

Lunar Prospector, the third mission in the “faster, better, cheaper” NASA Discovery Program, was successfully launched from Cape Canaveral on January 6, 1998 (see http://lunar.arc.nasa.gov). Lunar Prospector is now in lunar orbit and is the second Discovery spacecraft to visit a major planetary body in less than a year. Its scientific goals are to map the Moon's surface composition, with special emphasis on the search for polar ice deposits, and its magnetic and gravity fields and determination of the frequency and locations of gas release events. These data will provide a basis for better understanding the current state and resources of the Moon, as well as for further constraints on its origin and evolution.

Near‐Earth Asteroid Rendezvous: Mission overview

The Near‐Earth Asteroid Rendezvous (NEAR) mission, the first launch of NASA's Discovery Program, will be the first mission to orbit an asteroid. NEAR will make the first comprehensive scientific measurements of an asteroid's surface composition, geology, physical properties, and internal structure. NEAR launched successfully on February 17, 1996, aboard a Delta 11–7925. It will orbit the 20‐km‐diameter near‐Earth asteroid 433 Eros for about 1 year, at a minimum orbit radius of about 35 km from the center of the asteroid. The NEAR is a solar‐powered, three‐axis stabilized spacecraft with a launch mass including propellant of 805 kg. NEAR uses X band telemetry to the NASA Deep Space Network, with the data rates at Eros up to 8.8 kbits/s using a 34‐m High EFficiency (HEF) dish, and up to 26.5 kbits/s using a 70‐m dish. A solid‐state recorder is accommodated with a memory capacity of 1.8 Gbytes. Attitude control is to 1.7 mrad, line‐of‐sight pointing stability is within 50 μrad over 1 s, and post processing attitude knowledge is within 50 μrad. NEAR accommodates 56 kg of instruments and provides them with 84 W. The instruments are a multispectral imager (MSI), a near‐infrared spectrograph (NIS), an X ray/gamma ray spectrometer (XRS/GRS), a magnetometer (MAG), and a laser rangefinder (NLR), while a radio science (RS) investigation uses the coherent X band transponder. NEAR will make a flyby of the C‐type asteroid 253 Mathilde in June 1997 and will rendezvous with 433 Eros in February 1999. It will execute an initial slow flyby of Eros, with a flyby speed of 5 m/s and a closest approach distance of 500 km. Subsequently, its orbit will be lowered to 35 km. The NEAR Mission Operations Center and the Science Data Center are at the Johns Hopkins Applied Physics Laboratory. The Science Data Center will maintain the entire NEAR data set on‐line, and data from all instruments can be accessed by every member of the NEAR Science Team. Data, including images, are released over the Internet as soon as they are validated.

The lunar prospector discovery mission: A new approach to planetary science

Lunar Prospector, the first competitively selected mission in NASA's Discovery Program, will conduct a one year orbital survey of the Moon's composition and structure. To be launched in late 1997, the suite of five instruments will detect water ice to a sensitivity of 50 ppm (hydrogen), measure key elemental constituents, detect gas release events and accurately map the Moon's gravitational and magnetic fields. At a total real year cost of $63M, including launch vehicle and operations, and a development period of less than two years, the mission also demonstrates a new, rapid, cost-effective approach to planetary science investigations. As a joint effort of NASA's Ames Research Center and Lockheed Martin, Sunnyvale, Lunar Prospector is a model of government-industry cooperation.