A good page describing orbital mechanics can be found here.

GLOBAL POSITIONING SYSTEM

Click here for information related to the U.S. Department of Defense Navstar Global Positioning System, better known as GPS.

SATELLITE RADIO

Notes on the new satellite radio services: XM Radio XM Radio launched their service in November, 2001. By the end of December 2001 they had 30,000 subscribers. As of October 2002 they claim 200,000 subscribers. They offer 100 channels of music and talk with limited advertising for $10 a month. General Motors has invested $120 million in XM Radio. Sirius Satellite Radio The other player, Sirius Satellite Radio, as of October 2002 has "redefined" their end-of-year subscriber target to between 30,000 and 40,000. Sirius initially planmed to be commercial free and priced their service at $12.95 a month. They have partnered with Ford and DaimlerChrysler. WorldSpace WorldSpace operates a pair of satellites: AfriStar (launched October 28, 1998) and AsiaStar (launched March 21, 2000). Each satellite has three beams transmitting in L-band between 1467 to 1492 MHz. Each beam transmits two TDM signals, where each TDM signal contains 96 Prime Rate channels. One of these signals is from the on-board processor, the other is a "transparent" channel transponded from the ground. Prime Rate channels are 16 kbps. The satellite payload was designed by Alcatel in Toulouse, France. L-band transmit power is from a pair of 150 watt TWTs. Broadcasters access the satellite via FDMA uplink in X-band between 7025 and 7075 MHz. The uplink capacity is 288 Prime Rate channels. The satellite demodulates each uplink and combines them into a TDMA downlink at L-band.

DETERMINING SATELLITE ORBITS

Click here for an excerpt from the 1963 book Satellite Communications Physics that describes the method and mathematics for determining the orbit of a satellite.

LITTLE LEOs

Little LEOs are constellations of low-earth-orbit (LEO) satellites that provide data services in the VHF bands. The first in service and currently most active Little LEO is Orbcomm.

The Federal Communications Commission has granted licenses to five Little LEOs.

• E-SAT, Inc.
  
• Final Analysis Inc.
  
• Leo One
  
• Orbcomm Global LP (more detailed information is available here).
  
• Volunteers in Technical Assistance

BIG LEOs

Big LEOs are constellations of low-earth-orbit (LEO) satellites that provide voice (and now data) at frequencies above 1 GHz. Iridium and Globalstar are the two largest and most active systems.

• Iridium , the reconstituted global satellite phone system originated by Motorola. More information is available here.

• Globalstar , another struggling global satellite telephone system. More information is available here.

• Ellipso has issued a lot of press releases but hasn't gotten off the ground.

• Constellation is basically shutdown awaiting more money. Even their website appears to be defunct.

• TRW's planned system, Odyssey, was scrapped right out of the starting gate. A news report regarding this decision can be found here.

BROADBAND SYSTEMS

In October 2002 Teledesic suspended satellite construction and laid off a number of employees. Earlier in 2002 Teledesic had contracted with Alenia Spazio to build 2 of the 30 medium earth orbit (MEO) satellites.

[Prior to 2000]
A Saudi Arabian prince with an estimated net worth of more than $11 billion has investmented $200 million in the 288-satellite Teledesic system. Alwaleed bin Talal, who currently owns part of Netscape and Motorola, joins billionaire cellular pioneer and current CEO Craig McCaw and Microsoft Chairman Bill Gates in funding the planned "mega-LEO."

Major shareholders:

McCaw	30%
Gates	30%
Alwaleed	16%
AT&T Wireless Services	12%

Teledesic, which has received authorization from the FCC for it's planned high-bandwidth satellite network, has already launched a test satellite but remains tight-lipped about their technical progress.

Boeing is slated as the prime contractor, having won a contract worth an estimated $9 billion. Boeing will sink $100 million of its own into Teledesic, gaining a 10% share of the "Internet-in-the-sky" company. Boeing has been busy lately, merging with McDonnell-Douglas after completing the purchase of Rockwell's Defense Electronics group.

SkyBridge is another broadband hopeful.

LOW EARTH ORBIT SYSTEMS

Current and Proposed LEO/MEO Systems

IMAGING

Click here for an interesting composite of earth at night.

MILITARY SATELLITE SYSTEMS

Overview

Milstar Program Home Page

DSCS

Defense Meteorological Satellites Program