ESA Huygens Descent Sequence

click to a view of the anticipated panoramic mosaics during Huygens descent	Huygens landing spot

The probe landed at a speed of 10 mph (16 km/s), that is a decceleration of 15 Gs. The probe kept on sending data during 7 hours, instead of the 30 mn planned. During its descent to the surface, the probe was to collect various science and to image the moon with panoramic views at 20 different altitudes, down to 2 miles (3 km), and individual images down to 656 ft (200 m) from the surface. The landing point was to be at about 191°W / -8°S. As planned the probe took 2½ hours to descent to the Titan's surface, slowly spinning. One of both transmission channels did not work but the system was conceived as a backup hence most data could be received. It's Cassini which relayed the data, with a delay as it had to aquire the probe's data with its high-gain antenna and then only turn it back Earth. The Huygens probe is operated from the European ESA's Space Operations Center in Darmstadt, Germany, which serves as the operations center. In case the probe would have touched down at a lake or an ocean, it would have floated. Sunlight at Titan is 1,000 times brighter than full Moon, that is 1,000 times weaker than sunlight at Earth however and light is surely orange as filtered by the moon's atmosphere. The probe had successfully released from Cassini last Dec. 24 as it just kept coasting until Titan, rotating at a spin rate of about 7.5 revolutions per minute to ensure the path. Cassini successfully performed then a deflection maneuver on Dec. 27 to avoid crashing itself at Titan as it had been positioned on a colliding trajectory with Titan to put the probe onto the correct path.
Cassini could not image the Titan's entry as it had its high-gain antenna pointing there. Cassini has no scan platform but bolted sensing instruments instead, that is it has to perform a series of aerobatics to point such or such instrument to its target. A scan platform would allow the instruments to point by themselves only. Several optical telescopes on Earth as well as Hubble telescope were to be used to try to see the tiny speck that Huygens will represent as the atmosphere's friction will turn it into a fireball. The 10-meter Keck, Mauna Kea, was, by chance just be best placed for that. Radio-telescopes were also to participate. pictures NASA/JPL/University of Arizona/USGS improved by the site 'Amateur Astronomy' (left), ESA/NASA/JPL/University of Arizona (right)

Time Delays	Actions
entry -4:22	a timer triggers onboard electronics on as transmitter is set into low-power mode, awaiting the start of transmission. The probe is arriving at Mach 25, being heated, in the first moments, up to 21,600°F (12,000°C)
T0	interface (entry) altitude (790 mi (1,270 km) above Titan's surface); Huygens enters Titan's atmosphere at a speed of 11,200 mph (18,000 km/h). Temperature is reaching 3,200°F (1,800°C)
T+00:04	the probe tremendously deccelerates in a few minutes. When Huygens detects it has slowed down to a speed of 900 mph (1,440 km/h), the 8.5 ft-wide (2.6 m) pilot parachute deploys taking off the probe's rear cover
T+00:04:2.5	once the rear cover taken off, the main, 27 ft-wide (8.3 m) parachute deploys. Huygens is now at 110 mi (180 km) above Titan's surface
T+00:05	front shield released; Huygens begins transmission to Cassini. We are at 100 mi (160 km) above the surface
T+00:05:42	a pilot parachute opens, exposing the instruments. Instruments-bearing booms extend. First panoramic pictures are taken
T+00:19	main parachute separates (it would have slowed the probe too much as the batteries would not have stood the entire descent); it's replaced with the 10 ft-wide (3 m) drogue parachute. We are at 77 mi (125 km) of altitude
T+00:36	Surface proximity sensor begings to work. Huygens will now probe its altitude itself, beginning at 37 mi (60 km) of altitude, as until now actions were triggered by timers
T+1:44	the Gas Chromatograph Mass Spectrometer is the last instrument to be activated. The craft keeps spinning at a rate of 1 to 20 rotations per minute
T+2:17	Descent Imager/Spectral Radiometer headlight turned on. The lamp allows instruments to see the surface
T+2:21	touchdown (touchdown time may vary by plus/minus 15 minutes depending on how the descent was affected by the atmosphere and winds). Huygens has been designed to survive and gather data during the 3 minutes following touchdown whether the landing occurs on a solid, or a liquid, surface
touchdown+4:31	Cassini stops collecting data as its landing site has dropped below the view of the Cassini orbiter
touchdown+5:01	first data sent to Earth by Cassini

see an additional diagram of Huygens descent sequence