Mars Pathfinder will be launched atop a Delta II 7925 expendable launch vehicle from
launch complex 17B at Cape Canaveral, Florida, during the launch period of December 2-31,
1996. The launch window on December 2 opens at 2:09 a.m. EST and becomes progressively
earlier by several minutes each day thereafter.
The first-stage engine of the Delta II and six of its nine solid boosters will be ignited at liftoff. The remaining three boosters will be fired when the first six burn out approximately 67 seconds after launch. Those three boosters will be ejected when the spacecraft is about 54 kilometers (33 miles) above Earth’s surface. Main engine cutoff will occur next at an altitude of about 118 kilometers (73 miles).
Second-stage ignition will take place about 2.5 minutes later, with ejection of the fair-ing, or nosecone-like shell covering the payload, following eight seconds later. When the spacecraft reaches an altitude of about 189 kilometers (117 miles) above Earth, its second-stage engine will be turned off for the first time, approximately 9 minutes, 20 seconds after launch. Second-stage engine cutoff marks the end of the booster phase.
The craft will coast for nearly an hour to reach the proper orbital position from which to embark on its trajectory toward Mars. During this long coasting phase, two major spacecraft events will occur. Spinning at a rate of approximately 1 degree per second, the vehicle will first reposition itself so that its axis of rotation is perpendicular to the Sun. This attitude adjustment – called a “barbecue roll maneuver” -- will protect the spacecraft from uneven solar heating. A maneuver will be performed next to place the second stage into the correct orientation before it is fired a second time to provide enough energy for the injection burn. At the end of this burn, the spacecraft will be in a highly elliptical orbit of 173 by 2,974 kilometers (about 117 by 1,840 miles) around Earth. Then the PAM-D upper stage will be spun up to about 70 rpm using a set of spin rockets. The spacecraft and PAM-D will separate from the second stage shortly thereafter.
About 70 minutes after launch, the PAM-D will fire its engine again to prepare for third-stage separation. While Mars Pathfinder is still attached to the PAM-D, a yo-yo cable device will be deployed to slow down the spacecraft’s spin rate from 70 rpm to 12 rpm, plus or minus 2 rpm. Once the correct spin-down rate has been achieved, about two to five minutes later, the spacecraft will separate from the PAM-D booster. NASA’s Deep Space Network 34-meter (112- foot) antenna at Goldstone, CA, will acquire Pathfinder’s X-band signal.
