domingo, 25 de maio de 2008
Aterragem da Phoenix em Marte dentro de poucas horas
A transmissão em directo pela NASA TV começa hoje pelas 11 horas da noite, hora de Lisboa. A aterragem deverá ser por volta da meia-noite e 53 minutos. As primeiras imagens poderão surgir por volta das 3 da madrugada. Vamos manter os dedos cruzados e esperar que tudo corra bem. Se tal acontecer, será a primeira vez em 32 anos que a NASA consegue aterrar uma sonda em Marte só com controlo por foguetes e sem o auxílio de airbags!
Nota - a todos os tempos abaixo deverá somar 8 horas, já que são a hora oficial da costa oeste.
NOTE: The times below for the Phoenix spacecraft events on May 25 are for a nominal scenario. Remaining navigational adjustments before May 25 could shift the times by up to about half a minute. In addition, the times for some events relative to others could vary by several seconds due to variations in the Martian atmosphere and other factors. For some events, a "give or take" range of times is given, covering 99 percent of possible scenarios from the atmospheric entry time. For events at Mars, times are listed in "Earth-receive time" (ERT) rather than "spacecraft event time" (SCET). This means the listed time incorporates the interval necessary for radio signals traveling at the speed of light to reach Earth from Mars. On landing day, May 25, the two planets are 275 million kilometers apart (171 million miles), which means it takes the signal 15 minutes and 20 seconds to reach Earth. For some spacecraft events, engineers will not receive immediate radio confirmation.
-- Trajectory correction maneuver opportunity (TCM6X), 8:46 a.m.
-- News briefing, noon
-- Begin non-commentary live television feed from JPL control room, 3 p.m.
-- Begin commentated live television feed from JPL control room, 3:30 p.m.
-- Propulsion system pressurization, 4:16 p.m.
-- Begin "bent-pipe" relay relay (continuous transmission of Phoenix data as it is received) through NASA's Mars Odyssey spacecraft to Goldstone, Calif., Deep Space Network station, 4:38 p.m.
-- Green Bank, W. Va., radio telescope listening for direct UHF from Phoenix, 4:38 p.m.
-- Cruise stage separates, 4:39 p.m.
-- Spacecraft turns to attitude for atmospheric entry, 4:40 p.m.
-- Spacecraft enters atmosphere, 4:46:33 p.m.
-- Likely blackout period as hot plasma surrounds spacecraft, 4:47 through 4:49 p.m.
-- Parachute deploys, 4:50:15 p.m., plus or minus about 13 seconds.
-- Heat shield jettisoned, 4:50:30 p.m., plus or minus about 13 seconds.
-- Legs deploy, 4:50:40 p.m., plus or minus about 13 seconds. -
- Radar activated, 4:51:30 p.m.
-- Lander separates from backshell, 4:53:09 p.m., plus or minus about 46 seconds.
-- Transmission gap during switch to helix antenna 4:53:08 to 4:53:14 p.m.
-- Descent thrusters throttle up, 4:53:12 p.m.
-- Constant-velocity phase starts, 4:53:34 p.m., plus or minus about 46 seconds.
-- Touchdown, 4:53:52 p.m., plus or minus about 46 seconds.
-- Lander radio off 4:54:52 p.m., plus or minus about 46 seconds.
-- Begin opening solar arrays (during radio silence) 5:13 p.m.
-- Begin NASA's Mars Reconnaissance Orbiter playback of Phoenix transmissions recorded during entry, descent and landing, 5:28 p.m. However, data for analysis will not be ready until several hours later.
-- Begin Europe's Mars Express spacecraft playback of Phoenix transmissions recorded during entry, descent and landing, 5:30 p.m. However, data for analysis will not be ready until several hours later.
-- Post-landing poll of subsystem teams about spacecraft status, 5:30 p.m.
-- Mars Odyssey "bent-pipe" relay of transmission from Phoenix, with engineering data and possibly including first images, 6:43 to 7:02 p.m. Data could take up to about 30 additional minutes in pipeline before being accessible. If all goes well, live television feed from control room may show first images as they are received. The first images to be taken after landing will be of solar arrays, to check deployment status.
-- News briefing, 9 p.m.
Fonte: New Scientist Space
Peanuts and Rolling Stones on hand for Mars landing
* 00:34 25 May 2008
* NewScientist.com news service
* Ivan Semeniuk, Pasadena
Bring on the peanuts; it's time to land on Mars.
One day before the Phoenix spacecraft arrives at the Red Planet, good luck charms and helpful aphorisms are on full display as engineers and scientists associated with the project deal with the stress of their mission's most critical hours.
Project manager Barry Goldstein has already ordered the peanuts that will be available tomorrow in the mission support area where his Entry, Descent and Landing team will track Phoenix's fiery plunge through the Martian atmosphere.
The peanuts are a Jet Propulsion Lab tradition, but unlike at the last Mars landing, these peanuts will still be in their shells. "I think we need to go through the process" of opening up the peanuts to calm edgy nerves, he told New Scientist.
In addition to the peanuts, lucky blueberries will also make an appearance - a nod to the Opportunity rover, which found iron-rich spherules, nicknamed blueberries, soon after it became the last spacecraft to successfully touch down on Mars.
If it lands successfully, Phoenix will dig into the soil near the northern polar cap to study ice thought to lie just below the surface. This should reveal whether Mars has maintained periodic habitability up to the present day, which would be possible if the planet periodically changes its tilt as a result of gravitational tugs by Jupiter. Such wobbles would cause the northern permafrost to melt and moisten the soil every so often.
At a press briefing today, principal investigator Peter Smith of the University of Arizona in Tucson, US, quoted poet Ralph Waldo Emerson while summing up the scientific rationale for the mission, which could be the first to touch water on Mars: "Go where there is no path; leave a trail for others to follow."
On a somewhat less poetic, but eminently more pragmatic note, Douglas McCuistion, NASA's Mars programme director, invoked a line famously sung by Mick Jagger: "You can't always get what you want, but if you try sometime you get what you need."
Certainly, regardless of the returns that scientists want to see coming back from Phoenix in the coming weeks, the spacecraft needs to land intact or the $420 million mission will effectively be a write-off. "We bet the whole farm on landing safely," says Smith.
Later today, Goldstein and his team will decide if a course correction is needed to nudge the lander's trajectory towards a destination that is roughly 10 kilometres or so eastward of its latest projected landing site. The correction would require the spacecraft to turn itself sideways and then fire its hydrazine propellant for six seconds before resuming to its Mars-facing orientation.
According to mission manager Joe Guinn, the manoeuvre would only be executed if Phoenix appears to be drifting away from a region of the Martian northern plains that has the most desirable landing profile.
The desirable region falls in a topographic "green zone" - so-called because of its colour code in Mars Reconnaissance Orbiter (MRO) images. The green zone is defined as having no more than three large boulders (1.5 metres across) per hectare.
In addition to the surface terrain, Phoenix's landing could also be affected by atmospheric conditions. MRO images reveal that a minor dust storm swept across the landing site earlier today, but the disturbance is expected to dissipate well before the probe's touchdown at 1653 PDT on Sunday (0053 GMT on Monday).
While Phoenix can accommodate a high-speed entry through a dusty atmosphere, a large amount of dust over the landing site would mean a reduction in the power available to spacecraft on the surface once its solar panels are deployed.
Goldstein said that a data set with updated information on atmospheric conditions can be sent to the spacecraft up to 3 hours before the landing. Such information will be crucial for determining when key events of the landing sequence take place, including deployment of the parachute that will slow the spacecraft to a point where its pulsing thrusters can take over for a soft landing.