Huygens ready for Titan

[Tormod]

LEFThttp://www.hypography.com/gallery/files/5/huygens_rentree_l_thumb.jpg[/img]Here is an updated timeline for the descent of the Huygens spacecraft through Titan's atmosphere on Friday, 15 january 2005. All times below are Earth received time, Central european Time (ie, GMT+1).

 

Actual spacecraft events occur 67 minutes earlier, as this is the time taken for signals to reach Earth from Cassini.

10.51 Huygens turns transmitters on

Although Huygens cannot contact Cassini during the first part of the descent, it turns on its transmitters in preparation.

 

11.13Huygens reaches 'interface altitude'

The 'interface altitude' is defined as 1270 kilometres above the surface of the moon where entry into Titan's atmosphere takes place.

 

11.16 Pilot parachute deploys

The parachute deploys when Huygens detects that it has slowed to 400 metres per second, at about 180 kilometres above Titan's surface. The pilot parachute is the probe's smallest, only 2.6 metres in diameter. Its sole purpose is to pull off the probe's rear cover, which protected Huygens from the frictional heat of entry.

 

2.5 seconds after the pilot parachute is deployed, the rear cover is released and the pilot parachute is pulled away. The main parachute, which is 8.3 metres in diameter, unfurls.

 

11.17 Huygens begins transmitting to Cassini and front shield released

At about 160 kilometres above the surface, the front shield is released.

 

42 seconds after the pilot parachute is deployed, inlet ports are opened up for the Gas Chromatograph Mass Spectrometer and Aerosol Collector Pyrolyser instruments, and booms are extended to expose the Huygens Atmospheric Structure Instruments.

 

The Descent Imager/Spectral Radiometer will capture its first panorama, and it will continue capturing images and spectral data throughout the descent. The Surface Science Package will also be switched on, measuring atmospheric properties.

 

11.32 Main parachute separates and drogue parachute deploys

The drogue parachute is 3 metres in diameter. At this level in the atmosphere, about 125 metres in altitude, the large main parachute would slow Huygens down so much that the batteries would not last for the entire descent to the surface. The drogue parachute will allow it to descend at the right pace to gather the maximum amount of data.

 

11.49 Surface proximity sensor activated

Until this point, all of Huygens's actions have been based on clock timers. At a height of 60 kilometres, it will be able to detect its own altitude using a pair of radar altimeters, which will be able to measure the exact distance to the surface. The probe will constantly monitor its spin rate and altitude and feed this information to the science instruments. All times after this are approximate.

 

11.56 Possible icing effects to probe

The probe has been designed to withstand possible icing as it descends to 50 kilometres above the surface, through the coldest part of the atmosphere.

 

12.57 Gas Chromatograph Mass Spectrometer begins sampling atmosphere

This is the last of Huygens's instruments to be activated fully. The descent is expected to take 137 minutes in total, plus or minus 15 minutes. Throughout its descent, the spacecraft will continue to spin at a rate of between 1 and 20 rotations per minute, allowing the camera and other instruments to see the entire panorama around the descending spacecraft.

 

13.30 Descent Imager/Spectral Radiometer lamp turned on

Close to the surface, Huygens's camera instrument will turn on a light. The light is particularly important for the 'Spectral Radiometer' part of the instrument to determine the composition of Titan's surface accurately.

 

13.34 Surface touchdown

This time may vary by plus or minus 15 minutes depending on how Titan's atmosphere and winds affect Huygens's parachuting descent. Huygens will hit the surface at a speed of 5-6 metres per second. Huygens could land on a hard surface of rock or ice or possibly land on an ethane sea. In either case, Huygens's Surface Science Package is designed to capture every piece of information about the surface that can be determined in the three remaining minutes that Huygens is designed to survive after landing.

 

15.44 Cassini stops collecting data

Huygens's landing site drops below Titan's horizon as seen by Cassini and the orbiter stops collecting data. Cassini will listen for Huygens's signal as long as there is the slightest possibility that it can be detected. Once Huygens's landing site disappears below the horizon, there's no more chance of signal, and Huygens's work is finished.

 

16.24 First data received on Earth

Getting data from Cassini to Earth is now routine, but for the Huygens mission, additional safeguards are put in place to make sure that none of Huygens's data are lost. Giant radio antennas around the world will listen for Cassini as the orbiter relays repeated copies of Huygens data.

 

Updated info can be found at:

http://www.esa.int/SPECIALS/Cassini-Huygens/SEMXYGQ3K3E_0.html

[Becca]

i was reading about that in new scientist mag and they dont really know that the surface is solid do they? it just looks solid from what we can see from other satalites etc. what do you think will happen if when they try to land they find out that entire place is made of some sort of acid?

[Tormod]

We have discussed that somewhere in the space forums and we couldn't quite agree. As far as I'm concerned the odds for finding liquid are vanishingly small, but if there are lakes or oceans they would consist of mostly hydrocarbons with ethane.

[Stargazer]

I suppose we will know plenty more when Huygens finally begins the descent, whether it will land on rocks, ice, or even a hydrocarbon lake (which would be cool, since there is a chance it could float and take measurements for a few more minutes). Also, imagine that in the future when we know more about Titan, we could design probes to land on Titan, when we know what to expect.

[Tormod]

First pictures have been posted!

 

http://www.esa.int/SPECIALS/Cassini-Huygens/index.html

[pgrmdave]

We have discussed that somewhere in the space forums and we couldn't quite agree. As far as I'm concerned the odds for finding liquid are vanishingly small, but if there are lakes or oceans they would consist of mostly hydrocarbons with ethane.

 

I suppose this has been answered by those incredible pictures!

[Tormod]

No, it's still too early to say whether there is liquid or not. Those images are extremely low resolution.