Aug 9 2017

From The Space Library

RELEASE 17-070 Cassini to Begin Final Five Orbits Around Saturn

NASA's Cassini spacecraft will enter new territory in its final mission phase, the Grand Finale, as it prepares to embark on a set of ultra-close passes through Saturn’s upper atmosphere with its final five orbits around the planet.

Cassini will make the first of these five passes over Saturn at 12:22 a.m. EDT Monday, Aug. 14. The spacecraft's point of closest approach to Saturn during these passes will be between about 1,010 and 1,060 miles (1,630 and 1,710 kilometers) above Saturn's cloud tops.

The spacecraft is expected to encounter atmosphere dense enough to require the use of its small rocket thrusters to maintain stability – conditions similar to those encountered during many of Cassini's close flybys of Saturn's moon Titan, which has its own dense atmosphere.

"Cassini's Titan flybys prepared us for these rapid passes through Saturn's upper atmosphere," said Earl Maize, Cassini project manager at NASA's Jet Propulsion Laboratory (JPL) in California. "Thanks to our past experience, the team is confident that we understand how the spacecraft will behave at the atmospheric densities our models predict."

Maize said the team will consider the Aug. 14 pass nominal if the thrusters operate between 10 and 60 percent of their capability. If the thrusters are forced to work harder – meaning the atmosphere is denser than models predict – engineers will increase the altitude of subsequent orbits. Referred to as a "pop-up maneuver,” thrusters will be used to raise the altitude of closest approach on the next passes, likely by about 120 miles (200 kilometers).

If the pop-up maneuver is not needed, and the atmosphere is less dense than expected during the first three passes, engineers may alternately use the "pop-down" option to lower the closest approach altitude of the last two orbits, also likely by about 120 miles (200 kilometers). Doing so would enable Cassini's science instruments, especially the ion and neutral mass spectrometer (INMS), to obtain data on the atmosphere even closer to the planet's cloud tops.

"As it makes these five dips into Saturn, followed by its final plunge, Cassini will become the first Saturn atmospheric probe," said Linda Spilker, Cassini project scientist at JPL. "It's long been a goal in planetary exploration to send a dedicated probe into the atmosphere of Saturn, and we're laying the groundwork for future exploration with this first foray."

Other Cassini instruments will make detailed, high-resolution observations of Saturn's auroras, temperature, and the vortexes at the planet's poles. Its radar will peer deep into the atmosphere to reveal small-scale features as fine as 16 miles (25 kilometers) wide – nearly 100 times smaller than the spacecraft could observe prior to the Grand Finale.

On Sept. 11, a distant encounter with Titan will serve as a gravitational version of a large pop-down maneuver, slowing Cassini’s orbit around Saturn and bending its path slightly to send the spacecraft toward its Sept. 15 plunge into the planet.

During the half-orbit plunge, the plan is to have seven Cassini science instruments, including INMS, turned on and reporting measurements in near real time. The spacecraft is expected to reach an altitude where atmospheric density is about twice what it encountered during its final five passes. Once Cassini reaches that point, its thrusters will no longer be able to work against the push of Saturn’s atmosphere to keep the spacecraft's antenna pointed toward Earth, and contact will permanently be lost. The spacecraft will break up like a meteor moments later, ending its long and rewarding journey.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate in Washington. JPL designed, developed and assembled the Cassini spacecraft.

RELEASE 17-069 NASA Selects Proposals to Study Galaxies, Stars, Planets

NASA has selected six astrophysics Explorers Program proposals for concept studies. The proposed missions would study gamma-ray and X-ray emissions from clusters of galaxies and neutron star systems, as well as infrared emissions from galaxies in the early universe and atmospheres of exoplanets, which are planets outside of our solar system.

The selected proposals, three Medium-Class Explorers missions and three Explorers Missions of Opportunity, call for focused scientific investigations and developments of instruments that fill the scientific gaps between the agency’s larger missions.

“The Explorers Program brings out some of the most creative ideas for missions to help unravel the mysteries of the universe,” said Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate in Washington. “The program has resulted in great missions that have returned transformational science, and these selections promise to continue that tradition.”

The proposals were selected based on potential science value and feasibility of development plans. After concept studies and detailed evaluations, one of each mission type will be selected by 2019 to proceed with construction and launch. The earliest launch date would be in 2022. Medium-Class Explorer mission costs are capped at $250 million each, excluding the launch vehicle, and Mission of Opportunity costs are capped at $70 million each.

Each astrophysics Medium-Class Explorer mission will receive $2 million to conduct a nine-month mission concept study. The selected proposals are:

Arcus: Exploring the Formation and Evolution of Clusters, Galaxies and Stars

• Arcus would study stars, galaxies and clusters of galaxies using high-resolution X-ray spectroscopy to characterize the interactions between these objects and the diffuse million-degrees gas that surrounds and permeates them.
• Principal investigator: Randall Smith at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.

Fast INfrared Exoplanet Spectroscopy Survey Explorer (FINESSE)

• FINESSE would investigate the processes that govern planet formation and global climate, and probe the mechanisms that establish atmospheric chemical composition and shape atmospheric evolution. It would perform transit spectroscopy of at least 500 exoplanet atmospheres in the visible and near infrared range for planets ranging from super-Earths to sub-Neptunes to gas giants.
• Principal investigator: Mark Swain at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.

Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx): An All-Sky Spectral Survey

• SPHEREx would perform an all-sky near-infrared spectral survey to probe the origin of the universe, explore the origin and evolution of galaxies, and explore whether planets around other stars could harbor life.
• Principal investigator: James Bock at Caltech in Pasadena, California.

Missions of Opportunity will receive $500,000 to conduct a nine-month implementation concept study. The selected proposals are:

Compton Spectrometer and Imager Explorer (COSI-X), a Small Complete Superpressure Balloon Mission

• COSI-X is a balloon-borne, wide-field-of-view telescope designed to survey the gamma-ray sky at 0.2-5 MeV, performing high-resolution spectroscopy, wide-field imaging, and polarization measurements. COSI-X would map gamma-rays from antimatter around the Milky Way's center, as well as from newly-formed radioactive elements in the debris of stellar explosions.
• Principal investigator: Steven Boggs at the University of California, Berkeley.

Transient Astrophysics Observer on the International Space Station (ISS-TAO)

• ISS-TAO is a wide-field X-ray transient detector aboard the International Space Station that would observe numerous events per year of X-ray transients related to compact objects. The mission’s primary goal is the detection of X-ray counterparts to gravitational waves produced by neutron stars merging with black holes and other neutron stars. Other targets would be supernova shocks, neutron star bursts, and high redshift gamma-ray bursts.
• Principal investigator: Jordan Camp at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

A Partner Mission of Opportunity (PMO) has been conditionally selected to provide detectors for the Fine Guidance Sensor assembly of the Atmospheric Remote Sensing Infrared Exoplanet Large-Survey (ARIEL) mission -- one of three proposed missions currently under consideration by ESA (European Space Agency). The PMO would proceed with construction only if ARIEL is selected by ESA.

The conditionally-selected PMO is:

Contribution to ARIEL Spectroscopy of Exoplanets (CASE)

• CASE would provide packaged detectors to ARIEL’s Fine Guidance Sensor assembly. ARIEL would measure the spectra of hundreds of warm and hot transiting gas giants, Neptunes, and super-Earths around a range of host star types. Observations of these exoplanets will allow us to understand the early stages of planetary and atmospheric formation during the nebular phase and the following few millions of years.
• Principal investigator: Mark Swain at JPL

The Explorers Program is the oldest continuous NASA program designed to provide frequent, low-cost access to space using principal investigator-led space science investigations relevant to the Science Mission Directorate’s astrophysics and heliophysics programs. Since the Explorer 1 launch in 1958, which discovered Earth’s radiation belts, the Explorers Program has launched more than 90 missions, including the Uhuru and Cosmic Background Explorer (COBE) missions that led to Nobel Prizes for their investigators.

The program is managed by Goddard for NASA's Science Mission Directorate, which conducts a wide variety of research and scientific exploration programs for Earth studies, space weather, the solar system, and the universe.

MEDIA ADVISORY M17-090 NASA Television to Air Launch of Next Space Station Resupply Mission

NASA commercial cargo provider SpaceX is targeting its 12th commercial resupply services mission to the International Space Station for 12:31 p.m. EDT Monday, Aug. 14. Coverage will begin on NASA Television and the agency’s website Sunday, Aug. 13, with two briefings.

Loaded with more than 6,400 pounds of research, crew supplies and hardware, the SpaceX Dragon spacecraft will launch on a Falcon 9 rocket. The payloads include crucial materials to directly support several of the more than 250 science and research investigations to be conducted on the orbiting laboratory during Expeditions 52 and 53.

Complete coverage of CRS-12 activities is as follows:

Sunday, Aug. 13

• 2 p.m. – Prelaunch news conference

• 3:30 p.m. – “What’s on Board” science briefing

Monday, Aug. 14

• Noon – Launch coverage
• 2 p.m. – Post-launch news conference

Wednesday, Aug. 16

• 5:30 a.m. – Spacecraft rendezvous at the space station and capture
• 8:30 a.m. – Installation to the space station

About 10 minutes after launch, Dragon will reach its preliminary orbit and deploy its solar arrays. A carefully choreographed series of thruster firings are scheduled to bring the spacecraft to rendezvous with the space station. NASA astronaut Jack Fischer and ESA (European Space Agency) astronaut Paolo Nespoli will grapple Dragon using the space station’s robotic arm. It then will be installed on the station’s Harmony module.

The Dragon spacecraft will spend approximately one month attached to the space station, returning to Earth in mid-September with results of earlier experiments.

The deadline for media to apply for accreditation for this launch has passed, but more information about media accreditation is available by contacting Jennifer Horner at 321-867-6598 or jennifer.p.horner@nasa.gov.