Through The Rings
June 29th, 2004 - 12:15 pm
After a seven-year journey, Cassini arrives at Saturn tomorrow night, the voyage culminating with a 96-minute (!) orbital insertion burn that will carry the spacecraft through the planet’s outer rings. Here are a couple of sites for keeping up with history in the making:
That 96 minute burn time really isn’t so surprising. Back when I controlled DSCS-III comsats out at Falcatraz (now Schriever AFB), we performed inclination change maneuvers on each of the satellites several times a year. Those featured thruster burn time over 30 minutes.
Cassini is a large, massive vehicle with relatively small thrusters. It has to shed a lot of velocity to enter orbit. A long burn time actually allows for precise maneuvering. It’s kind of like trying to drive in a nail with one mighty hit verses several lighter whacks. You’re less likely to get good results when you hit with everything you have.
One cool feature of Cassini is the dual thruster arrangement. They’ll only burn one thruster for the insertion maneuver, but the other thruster is hot and ready to take over should the first thruster have problems. This should increase the probability of success for the insertion.
A 96 minute burn sounds like a long time, until you realize that the Cassini engine puts out only 445 Newtons of thrust (about 100 pounds) to move a spacecraft that weighs 5 tons…
I’m surprised TOE isn’t here crowing about how if only EUropeans had launched Cassini, they’d have had to fire a burn of half the time and duration.
Dean – and the damn thing would still smack into something with nary a bit of data sent back.
Anyway, clearly this is all being done with Hollywood special effects, or perhaps a camcorder, Michael Moore, and a Hula-hoop.
To: Dean
Just in case you didn’t notice:
It’s a joint US-European mission.
TOE:
How could it be a joint mission. YOU wrote here that EUrope has no space capabilities to speak of.
Who’s lying?
To Dean:
Still fond of taking sentences out of context?
Sounds like nearly a metric ton of propellant expended, depending on the Isp. I guessed something consistent with hydrazine/NTO biprop.