The Orbit is the Key

An important aspect of the Phase-30 project is the choice of the orbit. Like the other satellite design considerations, it's been engineered to bring the most benefit to as many amateurs throughout the world as possible. Like OSCARs 10 and 13, Phase 3D will go into a highly elliptical orbit (see Fig 5). But unlike them, its apogee (high point) will be much higher, at 48,000 km instead of 36,000 km. The perigee (low point) will also be higher, about 4000 km.

OSCAR 13'S perigee is currently less than 600 km. It began at 2000 km, but has been dropping because of complex gravitational interactions. There are two principal reasons for choosing a higher perigee for Phase 3D. One is to improve coverage during that part of the orbit. The other is to help prevent a reoccurrence of the problem facing OSCAR 13.

The Phase-3D orbit has also been selected to exactly repeat passes on a two-day basis, rather than the 11-day sequence for OSCAR 13. This is intended to make it easier for us to remember when we'll be able to use the satellite. For amateurs in North America, western Europe and Japan, Phase 3D will rise rapidly to an almost overhead position and remain hanging there for many hours. In between those times, it will execute one low-elevation pass to the northeast and one to the northwest. These low-elevation passes will be especially good for DX and the high-elevation passed will be great for mobiles and small stations with fixed antennas.

Because the period of the orbit will be 16 hours, there will be an apogee every 16 hours. But because the Earth rotates once (360º) every 24 hours, in 16 hours it will rotate 240º. This will cause three apogee locations: One over Canada, one over northern Europe and one north of Japan---all occurring at about the same local time in each area, every two days.

If you have a personal computer and a satellite-tracking program, you can see what Phase 3D will do for you. Type these orbital elements into your program and imagine that it's 1996:

Epoch.91 80.00000000

Epoch Rev1

Mean Anomaly0.00000000 degrees

Mean Motion1.50000000

Inclination63.4343490 degrees

Eccentricity0.67743780

Argument of Perigee220.000000 degrees

Right Ascension of 225.0000000 degrees

Ascending Node

Some of these elements may vary slightly when the final orbit is achieved, but these are close enough to illustrate what tremendous coverage the satellite will provide (see Fig 6).

Fig 5--The orbital path of Phase 3D. Notice how the antennas are constantly pointing at the Earth

Fig 6--It's 1996 and this is the Instantrack view of Phase 3D at apogee over North America