JPL and NASA News

Bill Wheaton, IPAC

2000 July

Astronomy for the Next Decade:

The "Decadal Report" of the Astronomy and Astrophysics Survey Committee (AASC) of the US National Research Council has been released in draft form. It has become customary in the USA to prepare such reports every ten years, and they are extremely important in setting NASA's astronomical priorities for the coming ten years. Other, non-space agencies supporting astronomy are included as well, such as e.g., the National Science Foundation (NSF) for most ground-based programs. Planetary exploration and Earth observation missions, however, are not included in the committee's purview.

The AASC includes 13 astronomers and astrophysicists under co-chairs Chris McKee and Joe Taylor. It established nine sub-panels to report on wavelength subdisciplines and other major areas, including over 100 members in all. These panels then made a great effort to collect wide community inputs.

Although program details (and of course acronyms) may change, still, the list of top priorities is likely to organize NASA and US efforts in astronomy for years to come. Besides new initiatives, the committee particularly calls for completion of recommendations of the 1991 AASC (the Bahcall Committee):

SIRTF, the Space Infrared Telescope Facility (on schedule for launch in December 2001), at:

http://sirtf.caltech.edu/sirtf.html

ALMA, the Atacama Large Millimeter Array (previously known as the MilliMeter Array, MMA) is an international project to build a VLA-style array of at least 64 movable 12-m antennas at nearly 5000 m altitude in Chile; the URL is:

http://www.alma.nrao.edu/info .

SOFIA, the Stratospheric Observatory For Infrared Astronomy, is a 2.5-m airborne IR telescope expected to begin flying in 2002. The URL is:

http://sofia.arc.nasa.gov  

SIM, the Space Interferometry Mission, currently scheduled for launch in June, 2006, URL is:

http://sim.jpl.nasa.gov/index.html   and

MAP, the Microwave Anisotropy Probe, to continue the pioneering work of COBE, the Cosmic Background Explorer. Planned launch is April, 2001, and the URL is

http://map.gsfc.nasa.gov 

Evidently I cannot hope to recite more than a few superficial buzz phrases about each of the missions and plans mentioned in such a large-scale roadmap, laying out a decade of effort. Thus for now I will only be able to give minimal information and URLs so you can, I hope, take advantage of the huge resources of the World-Wide Web.

1. The committee confirmed the Next Generation Space Telescope (NGST), as its top recommendation. NGST is to be an 8-m space infrared telescope, working from the visible out to at least 10m , with 100 times the sensitivity and ten times the angular resolution of the HST in the infrared. It is intended to detect the light from the first stars and observe the formation of the first galaxies, as well as revolutionize our understanding of the current formation of stars and planets in our own galaxy, the Milky Way. The URL is   http://ngst.gsfc.nasa.gov  
   
2. The Giant Segmented Mirror Telescope (GSMT) is the committee's second priority, and top ground-based recommendation. It would have approximately 30 m aperture, and use adaptive optics to achieve diffraction-limited imaging in the atmospheric windows between 1 and 25m ,. The committee advised that the US seek approximately 50% cost sharing with private or international partners, and that construction begin within the decade. Being a ground-based project (like the EVLA and LSST, below) the US agency involved would presumably be the NSF. So far I have found no URL for this exciting project.

3. The Constellation-X Observatory is an array of large X-ray telescopes, designed to acquire high-quality spectra with grating spectrometers working in the 0.2-2 keV band, of sources as faint as the weakest sources observed in the ROSAT deep surveys. This will require a throughput 20 to 100 times higher than Chandra or XMM. In addition, it would include focusing hard X-ray telescopes operating to an energy of 40 keV, about three times higher than focusing optics in space astronomy so far. URL:   http://constellation.gsfc.nasa.gov
   
4. The Expanded Very Large Array (EVLA) is a major upgrade and improvement of the original Very Large Array radio telescope, now twenty years old; which revolutionized radio astronomy when it came into operation. The expansion will provide new receivers on all bands with wider bandwidth and lower system noise, continuous frequency coverage from 200 MHz to 50 GHz, fiber optic data transmission, many more spectral channels, and an increase in the number of antennas from 27 to 35, at baselines up to 300 km. The result will be an order-of-magnitude improvement in both sensitivity and angular resolution, and 1000 times better spectroscopic capability. The URL is:   http://www.aoc.nrao.edu/vla/html/Upgrade/Upgrade_home.shtml
   
5. The Large-aperture Synoptic Survey Telescope (LSST) is an approximately 6.5-m aperture ground-based telescope, designed to survey the visible sky every week, to a much fainter level than that reached by existing surveys. It would extend the ongoing 1-km survey, intended to catalog Near-Earth Asteroids, down a size of about 300 meters, which is still large enough to cause a huge disaster if a populated area were struck. Also, it will observe about 10,000 Kuiper-Belt objects, and thousands of supernovas. No URL is yet known to me, unfortunately.
   
6. The Terrestrial Planet Finder (TPF), described as NASA's most ambitious space science mission. TPF is a space-based IR interferometer array intended to detect and characterize Earth-like planets at distances out to about 50 light-years. It would have spectroscopic capabilities to detect water, carbon dioxide, ozone, and methane in the atmospheres of such potential abodes for life. The concept is still under development, but an array of four free-flying 3.5-m telescopes, operating from the near IR to perhaps 30m , with interferometric baselines of 75 to 1000 m, is under consideration. Launch could come in 2010. The URL is   http://tpf.jpl.nasa.gov
   
7. The Single-Aperture Far InfraRed (SAFIR) Observatory is an 8-m class telescope in space to work in the far IR, from 30 to 300m . It would follow-up and extend the work of NGST. The project could start near the end of the decade. As yet no WWW information seems to exist.

Moderate Initiatives:

The highest priority space missions in this category is GLAST, the Gamma-ray Large Area Space Telescope, which is an enlarged and improved follow-up to EGRET, the Energetic Gamma-Ray ExperimenT on the late, lamented, Compton Observatory. GLAST will have greatly improved angular resolution and sensitivity over its predecessor. The energy range would be from 10 MeV to 300 GeV. A URL for GLAST is   http://glast.gsfc.nasa.gov 

LISA, the Laser Interferometer Space Antenna, is a very ambitious gravity wave detector, a follow-on to LIGO, the Laser Interferometer Gravitational Wave Observatory now about to come into operation. The prospects for LIGO to detect gravity waves are somewhat controversial, at least in its initial configuration; some good luck may be needed. However, there seems little doubt that LISA should see cosmic signals, unless our understanding of either gravity waves or astronomy is somehow very mistaken. LISA would use phase-locked lasers on three widely separated spacecraft to achieve a large sensitivity gain over LIGO. The committee recommends a co-operative effort with the European Space Agency, to keep the cost reasonable. I understand from Prof. Tom Prince of Caltech, the Project Scientist, that LISA will measure the distance between its three spacecraft with a precision equivalent to measuring the distance to the nearest star to the thickness of a human hair. The URLs are  http://lisa.jpl.nasa.gov    for LISA, and   http://www.ligo.caltech.edu    for LIGO.

A number of other, smaller or lower-priority projects also received the committee's blessing, but those are some of the highlights. We may hope for an exciting decade, with such as these in store.

Other News

A problem has disabled NIS, the Near Infrared Spectrometer on NEAR, the Eros-orbiter mission I've written about here a number of times. NIS was an important instrument because its 64-channel, 0.8 - 2.6 m , spectra with about a 0.5° field-of-view gave the best means of mapping the surface composition of Eros in detail. NIS was turned off on May 13, after it began drawing abnormally heavy current from the spacecraft. The problem recurred during a brief turn-on attempt on June 5, and there are no plans for further attempts. However, about 58,000 spectra have already been obtained. Data from the X-Ray and Gamma-Ray Spectrometer (XGRS) show that asteroid 433 Eros is not of Class S, from a geologically differentiated parent body similar to the stony-iron meteorites, something of a surprise. Type S had been widely expected at the beginning of the mission. Instead, it appears similar to the chondritic asteroids -- which helps to resolve the mystery of the asteroidal sources of the most common class of meteorites, the ordinary chondrites. These consist of a primitive, unmelted mixture of small globules, or chondrules, in a background matrix. Winter on Eros began on June 25, when the Sun crossed its equator and the asteroidal south pole was illuminated for the first time. On July 7 the spacecraft will descend to 35 km from the 50-km polar orbit which it has been in since late April.

Major news from Mars is rumored to be in store as I write. By the time you read this, it will should be old hat. However, Mars Global Surveyor has indeed been doing an amazing job, working away quietly, despite all the disappointment here over the fate of its later kindred

Bill Wheaton
Waw@ipac.caltech.edu