Location
Cocoa Beach, FL
Start Date
7-3-1966 8:00 AM
Description
Navigation for planetary missions is well understood as shown by the successful flights to Venus and Mars by the JPL Mariner spacecraft. However, when we consider the farther planets, such as Jupiter and ultimately Pluto, the trip time requirements are so .long (on the order of 2 years to Jupiter and 8 to 1 0 years to Pluto) that spacecraft reliability becomes the paramount consideration.
A basic approach to achieving reliability is to simplify the spacecraft system as much as possible within the limits of mission objectives, which usually arise from the scientific payload. System simplicity and reliability can be greatly enhanced if the spacecraft system is spin stabilized, since this reduces control system requirements substantially and in general minimizes onbeard navigation tasks.
However, spin stabilization itself imposes a number of problems which must be solved before such a simplifying technique can be adapted. As an illustration, the present Pioneer VI spacecraft is spin stabilized and has no onboard control requirements after the first few days of the mission; hence its lifetime appears to be limited only by the lifetime of the electronic components. Pioneer VI, shown in Figure 1, is injected in a heliocentric orbit while spinning and is then torqued by a nitrogen system to place its spin axis perpendicular to the plane of the ecliptic. A phased array antenna mounted along the spin axis then provides a fan beam pattern lying in the plane of the ecliptic, thus always illuminating the earth and assuring the constant communication with the DSIF for ranges up to 2 AU. All perturbing factors, such as solar pressure, have been accounted for and this spacecraft will apparently retain its attitude indefinitely. (There is a small change in body attitude during the course of 1/2 of the orbit around the sun but this change is cancelled out in the next 1/2 of the orbit).
Navigation for Spin Stabilized Deep Space Planetary Spacecraft
Cocoa Beach, FL
Navigation for planetary missions is well understood as shown by the successful flights to Venus and Mars by the JPL Mariner spacecraft. However, when we consider the farther planets, such as Jupiter and ultimately Pluto, the trip time requirements are so .long (on the order of 2 years to Jupiter and 8 to 1 0 years to Pluto) that spacecraft reliability becomes the paramount consideration.
A basic approach to achieving reliability is to simplify the spacecraft system as much as possible within the limits of mission objectives, which usually arise from the scientific payload. System simplicity and reliability can be greatly enhanced if the spacecraft system is spin stabilized, since this reduces control system requirements substantially and in general minimizes onbeard navigation tasks.
However, spin stabilization itself imposes a number of problems which must be solved before such a simplifying technique can be adapted. As an illustration, the present Pioneer VI spacecraft is spin stabilized and has no onboard control requirements after the first few days of the mission; hence its lifetime appears to be limited only by the lifetime of the electronic components. Pioneer VI, shown in Figure 1, is injected in a heliocentric orbit while spinning and is then torqued by a nitrogen system to place its spin axis perpendicular to the plane of the ecliptic. A phased array antenna mounted along the spin axis then provides a fan beam pattern lying in the plane of the ecliptic, thus always illuminating the earth and assuring the constant communication with the DSIF for ranges up to 2 AU. All perturbing factors, such as solar pressure, have been accounted for and this spacecraft will apparently retain its attitude indefinitely. (There is a small change in body attitude during the course of 1/2 of the orbit around the sun but this change is cancelled out in the next 1/2 of the orbit).
