Orbital Mechanics

Using the Shuttle to get to Low Earth Orbit
 
There had been a management decision to only use the shuttle to launch payloads into low earth orbit. The idea was to put Galileo on top of a rocket stage booster, ride these up in the back of the shuttle, and shoot off toward Jupiter. This was supposed to have happened in 1982 but the design of the rocket stage kept getting re- designed. You also have to think in terms of launch windows, times when the relative positions of Earth and Jupiter add together to optimize travel time. Finally Galileo was scheduled to go up on the next flight after ... Challenger. After the Challenger disaster, safety considerations dictated yet another redesign of the rocket stage and the long story short is that this was not going to have enough fuel to launch Galileo directly to Jupiter.


From Earth to Jupiter via Gravity Assist
 
Because there wasn't enough fuel in the rocket stage to blast Galileo straight to Jupiter, they had to get pretty clever and use...that's right, Rocket Science! It couldn't have been easy but there was finally a schedule of events that had Galileo falling in toward Venus, picking up a gravity sling-shot boost there, flying back by Earth for a second gravity assist and then making a long loop out into space and back in a second time for Earth fly-by. With the second Earth fly-by, Galileo now had enough velocity to shoot for Jupiter. It made Jupiter orbit in ......, six years after it was launched!


More Rocket Science:
the Petal Plot Moon Flybys
 
At Jupiter, the next two years' worth of flight mechanics had been worked out in advance. There would be 22 moon flybys with Orbiter doing CCD imaging and collecting data through its other instruments, including infra-red detector, magnetometer and particle sensors.


Using the Lessons from Galileo
 
When the upper stage failed to boost it into geosynchronous orbit at 22,000 miles above the earth, the communications satellite known as HGS-1 was left in a useless trajectory around the earth. Now engineers are taking a page from the tried-and-true NASA script of using gravity assists to send spacecraft off on interplanetary missions.

During April and May, 1998, the satellite's on-board rocket motor was fired several times to nudge it out of its highly angled orbit of 217 miles by 22,300 miles (350 km by 36,000 km). The final firing on May 7 sent HGS-1 on a nine-day round trip to the moon where it followed a three-dimensional, figure-8 path and used lunar gravity to hurl it back toward Earth. Most of the 3,700 pounds (1,665 kg) of propellant aboard the satellite was used. But HGS-1 successfully assumed a circular orbit over Earth's equator.

This was the first time a commercial satellite traveled to the moon. It was also the first time commercial operators had tried anything this extreme to bring a satellite back into the proper orbit. The technique holds out the promise of reduced costs for future space missions or more payload into orbit for the same costs. Future satellite programs could benefit greatly.


JOI
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Basics of Space Flight
 
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The Trip
 
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The Trip
 
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