Destination Titan Page #5

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we switched the instruments on

and we ran through

what are called housekeeping tests.

How do you go into mode 4,

on time or on altitude?

This time we went in

using the 7 km as altitude.

We'd check out the instrument,

make sure the spacecraft was working

fine, that our instrument was working fine.

There were a few

minor things we monitored

and a few software bits we changed.

Nothing too major from our side.

What you have do understand

is that when Huygens

was planned to be descending

onto the surface of Titan,

it would be relaying its data

not directly back to Earth,

there just wasn't the power for that,

but sending the data up to Cassini,

which would be flying some

thousands of kilometres overhead.

Cassini would then relay it a

few hours later back to the Earth.

There was a major scare

on the spacecraft.

They tried a particular test of the

communication system and realised that there was a

problem and with the

mission as it was designed,

we weren't going to get

the science data back.

One thing that was tried was using

a radio telescope on the ground

to pretend to be Huygens and transmit

a signal as if it was Huygens,

to check that Cassini could

receive that signal correctly.

When the results of the test were

reported to us in a science meeting,

they said we did the test and we're

not sure quite what happened

because we didn't get

all of the data back.

To put it simply, it's as if

Huygens was transmitting on Radio 1

and Cassini was receiving on Radio 2.

In other words there was a

very slight mismatch

in the frequencies but it was enough

to potentially scupper

the whole of the Huygens project.

That was obviously a

huge, huge problem,

very frightening from the

scientists' point of view

but the system quickly got together and

came up with some options for solutions.

There were 11 possible

options that were found that might

be able to address this problem.

In the end we picked on one of them

as being the potential saviour.

This involved Cassini,

instead of releasing Huygens

on the first orbit around Saturn,

releasing it on the third orbit.

That would change the geometry between

Cassini and Huygens by just the right amount

to bring the two frequencies back

into synchronism, quite remarkable.

'Now how long does it take a

spacecraft to travel 2 billion miles

'between planet Earth and Saturn?

'Nearly seven years

is the answer and tonight,

'for the spacecraft Cassini,

the journey is nearly over.'

Well, today's the culmination

of our seven-year trip through

space and we are arriving at Saturn and we're going

to fire the engine to stop us into orbit around Saturn,

so it's the end of the trip but

really the start of the tour.

The excitement for me is in the

future when we get close to Titan

but this is a big moment so kind of a bit of a party

atmosphere here in Pasadena to celebrate the arrival.

There have been one or two occasions in planetary

exploration where spacecraft have blown up

on arrival when they've used

their engines for the first time.

Current Cassini altitude 20,700 km,

We are slowing down.

Cassini would have to use its main

engine for a very large burn

to break into orbit around

Saturn so it was a tense moment.

We'd be crossing the ring plain as well

which has some element of hazard to it.

Go ahead, Com.

The Doppler has blacked out.

OK, we have burn complete here

for the FY orbit insertion burn.

That was a big moment,

and then once it was in orbit then

everything was just quiet and

basically following the script

just the way it was supposed to.

It would actually be a little over six

months before Huygens was delivered to Titan.

# Oh, the weather outside

is frightful

# But the fire is so delightful

# And since we've no place to go

# Let it snow, let it snow

let it snow. #

Christmas Day 2004, it was the day

of the planned release of the

Huygens probe from Cassini.

Basically there were a set of

explosive bolts that released

Huygens, and a set of springs

pushed it off on spiral rails

that gave it a spin to stabilise it.

Everything was pre-programmed

on Cassini,

we were monitoring it

and it went fantastically.

From that point on, Huygens was on

its own, completely autonomous.

It didn't even

carry a radio receiver,

so from then on if we'd wanted

to change something we couldn't,

we were completely powerless.

The die was cast from that point.

When I got into the control centre,

basically everyone I met was as

excited also as nervous as I

was about the whole mission.

There was an enormous air

of expectation,

it had been building up

for the last few days.

We went into the science

room that morning knowing that

whatever was going to happen was

going to happen, this was the day.

Some people had said Oh,

nobody will be interested in this,

but by this time we had something

like 300 of the world's press there

waiting to see what would happen.

There was lots of

vans and TV cameras parked outside

and anyone who could be grabbed

by media guys were getting grabbed.

There was a little bit

of a siege mentality,

a scientist was kind of

walled away in our little room.

It was hard to concentrate on the

important work

and not get distracted by all the

calls for your time.

I couldn't stop thinking

that about 1.5 billion miles away

out there, there was something

that I had built about this size,

and it was hurtling through

space at 20,000 mph

and it was about to get

a rude awakening.

The plan was Huygens would hit

the top of Titan's atmosphere

at a speed of 7 km a second.

Over the next two minutes it would

slow down to about 400m a second.

At that point, Huygens would deploy

the first of three parachutes and that

would enable it to float down to the

surface at a relatively slow speed.

Then the six scientific

instruments would be switched on

to really perform their job

that they'd been waiting for

for about seven

and a half years.

Around 10:
30 in the morning,

a rumour comes through

that one of the largest radio

telescopes on the Earth

has picked up a signal

directly from Huygens.

It looks like we've

heard the baby crying.

We still can't understand

what it tells us,

but clearly it tells

us that the probe is alive,

the entry has been successful,

we are on the parachute,

and the probe is transmitting.

The project scientist Jean-Pierre

Lebreton announced that news and

there was a huge cheer, it

really meant a lot to all of us.

We knew that the most critical

part of the mission was successful.

It is absolutely fantastic news.

It's like hearing the

ringing tone on the phone,

it tells us the phone is working.

There's no information on it yet

but it's absolutely fantastic.

That was great news because it

means that it wasn't gone

without trace, that even if we

didn't get all the data back

or if the probe didn't make it down to

the surface, at least there was something.

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