Jonathan's Space Report No. 507 2003 Aug 25, Somerville, MA ------------------------------------------------------------------------------- Editorial - A New Home in Cyberspace for JSR -------------------------------------------- Although Jonathan's Space Report and its associated archives and data have always been primarily written and maintained on my personal computer at home, the Harvard-Smithsonian Center for Astrophysics (CfA) has kindly provided public distribution for it on the Internet (ftp, and later www) since 1988. For a number of reasons the time has now come to draw more clearly the somewhat fuzzy line between my official work in astrophysics and my off-duty work as a historian of space exploration, and to clarify that the JSR is my own personal analysis rather than the official position of the CfA. This will ensure that the JSR remains a fully independent source. I have therefore transferred the JSR to a new domain maintained at my own expense. This domain is: http://www.planet4589.org As before, the JSR will not accept any financial sponsorship and both the newsletter and the content on my site will remain freely available to all. Shuttle and Station -------------------- The Expedition 7 crew, Yuriy Malenchenko and Edward Lu, remain on board the Space Station. SIRTF ----- Congratulations to my friends and colleagues on the SIRTF team! The Space Infrared Telescope Facility (SIRTF), last of NASA's Great Observatories, was launched into solar orbit at 0535 UTC on Aug 25. SIRTF is built by Lockheed Martin/Sunnyvale with the Cryogenic Telescope Assembly (CTA) built by Ball; management is by JPL with science ops at the SIRTF Science Center across the street from the Caltech astronomy department in Pasadena. SIRTF follows on from the US/UK/Netherlands IRAS sky survey satellite (1983) and ESA's ISO observatory (1995-98); the US Defense Dept.'s MSX (1996-1997) was another notable IR mission which made a galactic plane survey. The other Great Observatories were the Hubble Space Telescope, the Compton Gamma Ray Observatory, and the Chandra X-ray Observatory. SIRTF has a 0.85-meter infrared telescope, with a liquid-helium cooled focal plane carrying the three main instruments, IRAC, IRS and MIPS. IRAC (built by Giovanni Fazio's team across the street from me here at the Harvard-Smithsonian) is a near infrared camera imaging in the 3 to 8 micron range. IRS is a spectrograph covering the mid infrared 5 to 40 micron range. The MIPS far infrared Multiband Imaging Photometer will cover the 12 to 160 micron range. The spacecraft is 4.45m high and 2.11m in diameter. It has solar arrays which are mounted along one side of the telescope and act as a sunshield; the telescope observes anywhere on a strip of sky roughly perpendicular to the line joining SIRTF to the Sun, with about 35 percent of the sky visible to SIRTF at any one time. The spacecraft has a dry mass of 851 kg; at launch it carries 50 kg of helium cryogen, 16 kg of nitrogen for attitude control, and a 6 kg telescope cover which will be ejected into solar orbit, for a total mass of 923 kg. SIRTF was launched by the second Delta II Heavy; the first, a model 7925H, put the MER-B Mars Exploration Rover into space in July. SIRTF's less powerful model 7920H doesn't have a third stage but is otherwise similar. The second stage entered a 166 x 167 km x 31.5 deg Earth parking orbit, and after about 33 minutes of coast, passing south of Madagascar, restarted at 0613 UTC to enter a hyperbolic orbit with a perigee of 170 km, an eccentricity of 1.0061, and a velocity of 11.05 km/s (about 40000 kph). If the Earth were the only source of gravity around, the spacecraft would eventually slow to a velocity of about 0.6 km/s relative to Earth. However, on Sep 1 SIRTF will reach the point at which its orbit is dominated by the Sun's gravity rather than that of Earth. Currently a rough approximation to the Earth's orbit is 0.983 x 1.017 AU x 0.00 deg in ecliptic coordinates (an AU is 149.6 million km, the mean distance of the Earth from the Sun, and the ecliptic plane is the mean plane of the Earth's orbit). The small extra speed of SIRTF compared to the Earth will change SIRTF's heliocentric orbit to about 0.996 x 1.019 AU x 1.14 deg with a year about 4 days longer than Earth's. Most of the energy goes into the small inclination change, but the higher average distance from Earth means that SIRTF moves more slowly around the Sun, until by a year after launch SIRTF trails Earth by 10 million km. By Kepler's second law, the slowest point in each orbit is the aphelion (farthest point from the Sun). The aphelic velocities of SIRTF and Earth are almost the same, but SIRTF will be at its aphelion - and thus slowest speed - at launch, while Earth is just past its aphelion and starting to speed up again. This means that SIRTF will start falling behind the Earth right away. To achieve this, the Delta must fire to give SIRTF speed backwards and outwards relative to the Earth's motion. [Note for those who, like me, know just enough orbital mechanics to be dangerous: decreasing the velocity around the Sun would normally reduce the orbital period. While SIRTF is still near the Earth, the fact that the Earth is just ahead of it and tugging on it helps to increase SIRTF's angular momentum relative to the Sun. By the time SIRTF leaves the Earth's gravitational sphere of influence, it is just enough further out from the Sun that the larger distance compensates for the smaller tangential velocity in producing larger total angular momentum and thus orbital period.] SIRTF's orbit is called an 'Earth-trailing orbit'; it has the advantage that the infrared-bright Earth is nice and small, so doesn't block out large interesting pieces of the sky SIRTF might want to look at. Also, the total velocity change needed from parking orbit to get to a distant circular orbit around the Earth by going to transfer orbit and then burning again to circularize is more than the velocity change needed for escape, letting you use a smaller rocket. On the other hand, after a number of years SIRTF will be so far from Earth it will drift out of communications range - but by then its helium will have run out anyway. I've put some diagrams of the SIRTF orbit on the web at http://www.planet4589.org/space/misc/sirtf/sirtf.html [Note: all of the numbers in this section are estimates I've made based on the prelaunch trajectory data available at JPL's Horizons web site.] SIRTF's Delta second stage was also in a hyperbolic Earth orbit at spacecraft separation. However, two further burns at 0642 UTC and 0647 UTC are reported to have reduced the velocity enough to make the orbit elliptical again, with a negative perigee. The stage will coast out to a high apogee and then fall back into the Pacific Ocean. If anyone can provide details of the stage's trajectory I'd appreciate it. Other Recent Launches --------------------- The Brazilian satellite launch vehicle, VLS-1 serial number V03, exploded on the launch pad during prelaunch tests on 2003 Aug 22 at around 1630 UTC. 21 rocket technicians were killed and a further 20 were injuered. It appears that one of the strapon boosters ignited by accident. The two satellite payloads, SATEC and UNOSAT, were also destroyed in the blast, as was the launch pad. VLS-1 flights V01 and V02 both ended in failure. Kosmos-2400 and Kosmos-2401 were launched on Aug 19 from the northern Russian launch site Plesetsk. A Kosmos-3M (11K65M) rocket placed the pair in 1467 x 1500 km x 82.5 deg orbits, similar to the profile of Kosmos-2390 and Kosmos-2391 in Jul 2002. The satellites are believed to be Strela-3 military communications satellites. As I predicted in JSR 506, Kosmos-2399 raised its perigee on Aug 14 to 205 km. In fact the apogee was also lowered to 330 km, which makes the orbit an even better fit for the standard operational orbit for Don (17F12) film-return capsule imaging satellites. A Russian newspaper report (Kommersant, 13 Aug) claims that Kosmos-2399 is a Neman (Yantar'-4KS1M) imaging satellite, which uses data relay satellites to return CCD imagery rather than physically recovering film. However, all previous Neman satellites have had higher perigees and lower apogees near 240 x 300 km, so I remain a little skeptical of this report. Table of Recent Launches ----------------------- Date UT Name Launch Vehicle Site Mission INTL. DES. Jul 8 0318 MER-B Opportunity Delta 7925H Canaveral SLC17B Mars probe 32A Jul 17 2345 Rainbow 1 Atlas V 521 Canaveral SLC41 Comms 33A Aug 8 0331 Echostar 9 Zenit-3SL Odyssey, POR Comms 34A Aug 12 1420 Kosmos-2399 Soyuz-U Baykonur LC31/6 Imaging 35A Aug 13 0209 Scisat-1 Pegasus XL Vandenberg RW30/12 Science 36A Aug 19 1050 Kosmos-2400 ) Kosmos-3M Plesetsk LC132/1 Comms 37A Kosmos-2401 ) 37B Aug 25 0535 SIRTF Delta 7920H Canaveral SLC17B Astronomy 38A .-------------------------------------------------------------------------. | Jonathan McDowell | phone : (617) 495-7176 | | c/o Harvard-Smithsonian Center for| | | Astrophysics | | | 60 Garden St, MS6 | | | Cambridge MA 02138 | inter : jcm@host.planet4589.org | | USA | jmcdowell@cfa.harvard.edu | | | | JSR: http://www.planet4589.org/jsr.html | | Back issues: http://www.planet4589.org/space/jsr/back | | Subscribe/unsub: mail majordomo@host.planet4589.org, (un)subscribe jsr | '-------------------------------------------------------------------------'