Jonathan's Space Report No. 528 2004 Jun 18, Somerville, MA ------------------------------------------------------------------------------- The Cassini space probe entered Saturn's gravitational sphere of influence on Mar 9. This is the Laplacian sphere at 54.8 million km; the Hill tidal sphere at 94.4 million km was crossed on Dec 16, while the equigravisphere (static gravitational force ratio) at 23 million km was not reached until May 18; the latter ignores the effects of Saturn's orbital acceleration, so the Laplacian sphere is the relevant one for deciding whether to approximate Cassini's orbit as being around Saturn rather than around the Sun. On 2004 Mar 8, Cassini was in a 1.40 x 9.28 AU x 0.7 deg heliocentric orbit approaching the Saturnian system (as usual, I give the orbital figures as periapsis - closest approach - x apoapsis - furthest distance - x inclination angle between orbit plane and reference plane, with the reference plane being the ecliptic in this case. The astronomical unit is 1 AU = 149.6 million km.) On Mar 10 the probe's osculating, hyperbolic Saturnian orbit was -24450 x infinity km, nominally an impact trajectory. The continuing effects of solar gravity raised the periapsis height (perichronon height, if you want to be preciously erudite) above zero on May 4, and by Jun 11 its orbit was +18093 x infinity km inclined 17.3 deg to Saturn's equator, with a mildly hyperbolic eccentricity of 1.06 and a Saturn distance of 11.7 million km. Cassini flew 2068 km from the moon Phoebe (Saturn IX) at 1933 UTC on Jun 11. The scheduled Saturn orbit insertion burn is from 0112 to 0248 UTC on Jul 1, putting Cassini in a 19980 x 10000000 km x 16.8 deg orbit and setting it up for a distant 339000 km flyby of Titan (Saturn VI) at 0930 UTC on Jul 1. Approximate heliocentric orbits, showing how Cassini's flybys set it up for the Saturn encounter: Earth 0.97 x 1.01 AU x 0.00 deg (Mar 2004) Saturn 9.03 x 10.09 AU x 2.49 deg (Mar 2004) Cassini 0.67 x 1.01 AU x 1.24 deg (Jan 1998) Post launch Cassini 0.73 x 1.58 AU x 3.51 deg (Aug 1998) Post Venus 1 Cassini 0.72 x 2.60 AU x 1.14 deg (Jul 1999) Post Venus 2 Cassini 0.86 x 7.16 AU x 0.71 deg (Oct 1999) Post Earth flyby Cassini 1.40 x 9.28 AU x 0.70 deg (Mar 2004) Post Jupiter flyby Transit of Venus: on Jun 8, we had the first transit of Venus across the face of the Sun that has been visible from Earth since 1882. Several hundred members of the public patiently queued up at 5 am here at Harvard to wait for the Sun to emerge from the horizon's murk; those who were far enough ahead in the queue to get a look before it clouded over at 6:30 am were rewarded with crisp telescopic views of the Venusian disk as a perfect black circle against the Sun. Not an intrinsically spectacular sight, but for those familiar with the travails of previous generations of astronomers who observed - or were clouded out at - the previous 1639, 1761, 1769, 1874, and 1882 transits, the emotional connection to the dawn of quantitative science was profound. The 1761/69 expeditions in particular seem to me to have been the 18th-century equivalent of Project Apollo, with the efforts of figures like Legentil, Captain Cook, and Mason and Dixon reminding us of a day when performing scientific observations from then-remote (to Europeans) parts of the planet was as difficult as landing rovers on Mars is now. Observations of the transit were used to determine the distance from the Earth to the Sun, setting the fundamental scale for the cosmos. If you missed this week's transit, mark your calendars for the next one in 2012 - the one after that is not until 2117. The Russian Space Forces have renamed Kosmos-2405 as Molniya-1T; Kosmos-2406 has been renamed Raduga-1. The US-PU satellite launched on May 28 was named Kosmos-2405, not Kosmos-2407 as I reported last issue. The new names are consistent with previous Russian practice, so it seems that the old Kosmos-2405/2406 names were just a bureaucratic error. The folks at Space Command are also competing in the 'confusing designation' game. There are now two debris objects called 1968-097CQ (SSN 05279 and SSN 05515) and two objects called 1968-097CY (SSN 05432 and SSN 05632). In each case one object previously had a designation in the 1970-089 series; both 1968-097 and 1970-089 launches have large numbers of debris objects in similar orbits resulting from antisatellite weapons tests. The logic of the new duplicate designations escapes me. A Tselina-2 electronic intelligence satellite for the Russian Defense Ministry was launched on Jun 10 and has been given the name Kosmos-2406. Launch vehicle was a Yuzhnoe Zenit-2, and the satellite entered an 846 x 865 km x 71.0 deg orbit characteristic of the series. The Intelsat 10-02 satellite, a 5575 kg Eurostar 3000 communications spacecraft built by EADS Astrium, was launched on a Proton-M with a Briz-M upper stage on Jun 16. This was the fourth orbital launch from Baykonur in less than a month. After a first Briz burn to a 173 x 173 km x 51.5 deg orbit, a second burn to a 258 x 5000 km x 50.3 deg orbit, and a third burn to 309 x 12967 km x 49.7 deg, the torus tank was jettisoned. At 0214 UTC on Jun 17 the fourth burn went to a 414 x 35849 km x 49.0 deg geostationary transfer orbit, and a final burn raised perigee and lowered inclination to deploy Intelsat 10-02 in a 4184 x 35804 km x 23.7 deg orbit. In contrast to other recent high altitude launches, Space Command quickly cataloged all three expected objects - Intelsat, Briz and the torus tank. Table of Recent Launches ----------------------- Date UT Name Launch Vehicle Site Mission INTL. DES. May 4 1242 DirecTV-7S Zenit-3SL Odyssey, Pacific Comms 16A May 19 2222 AMC-11 Atlas IIAS Canaveral SLC36B Comms 17A May 20 1747 ROCSAT-2 Taurus Vandenberg 576-E Imaging 18A May 25 1234 Progress M-49 Soyuz-U Baykonur LC1 Cargo 19A May 28 0600 Kosmos-2405 Tsiklon-2 Baykonur LC90/20 Sigint 20A Jun 10 0128 Kosmos-2406 Zenit-2 Baykonur LC45 Sigint 21A Jun 16 2227 Intelsat 10-02 Proton-M/Briz-M Baykonur LC200/39 Comms 22A .-------------------------------------------------------------------------. | Jonathan McDowell | phone : (617) 495-7176 | | Somerville MA 02143 | inter : jcm@host.planet4589.org | | USA | jcm@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 | '-------------------------------------------------------------------------'