The following is taken from "An Overview Of The Petite Amateur Navy Satellite (PANSAT) Project", by Fred J. Severson, NPS Thesis, December 1995
After initialization, PANSAT will conduct normal operations by remaining in a receive-only mode at all times, waiting for a request-to-connect command from a ground station. After acknowledging the user, PANSAT will begin the information-relay phase, during which the user will be able to access a bulletin board service. The bulletin board offers services that allow the user to send and receive mail that is stored on-board PANSAT, upload and download files, and read spacecraft telemetry. The use of sophisticated protocols will allow users to interleave their activities with those of PANSAT, thereby enabling multiple users to communicate simultaneously with the satellite. When the infor mation-relay is complete, the user will log out and the station will send a request-to-disconnect command to end the session. [Ref. 1, pp. 1-5]
Information transfer is effected when the user interfaces with an application software which, in turn, communicates with the spacecraft via another software solution that manages and controls the communications link. Minimal interaction is required by the user because all protocol commands will be performed automatically by software. Packet transfer, or the relay of frames of information, will be transparent to the user, with the protocol closely resembling (in fact derived from) the computer networking protocol X.25. PANSAT will implement AX.25, which is a standard link-layer protocol used by amateur radio operators. Packet store-and- forward services will be provided by application software which will operate in a layer above the AX.25 link layer. [Ref. 2, pp. 1-2]
A point-to-point communications path for users over PANSAT's single physical communications channel is made possible by the use of AX.25, which embeds each message with a source and a destination address. In order to receive their messages, users will have to connect to the spacecraft. Users will have to accomplish message retrieval on a fairly routine basis, as PANSAT will only store messages until they are down-linked or until they are considered undeliverable and consequently purged from memory as a part of system administration. Thus, the PANSAT mode of message handling functions in much the same way as a terrestrial bulletin board system, with notable differences being that PANSAT will operate from orbit and no physical connection (i.e., medium) will be necessary. One foreseeable problem with this scenario is that PANSAT's mail storage is very limited in capacity, which will necessitate the removal of old, unread messages when lack of available storage dictates. The time frame for the removal of old messages will be dynamic and will be a function of the storage space available. Storage space will be provided by a redundant pair of four megabyte (MB) memory modules. After initialization and proof of successful operation, these two modules could be tasked to perform separately, thereby effectively doubling the storage space, with potentially only a very small reduction in reliability. [Ref. 2, p. 2]
The uploading and downloading of files, or file transfer, occurs in a manner similar to the orbiting mailbox concept. The difference, however, is that as a file transfer facility, PANSAT will allow the transfer of any format of file, including text and binary. Files may contain executable programs, graphics, images, encoded voice, and possibly even a word- processed file. Of course, due to storage limitations, there will still be limitations regarding file size, number of files, and length of time each file remains on PANSAT. [Ref. 1, p. 5]
A popular item that amateur users like to retrieve from orbiting satellites is spacecraft telemetry. PANSAT will allow users access to current spacecraft telemetry and will transmit the telemetry in an encoded form in order to minimize the number of bits of information exchanged with the ground station. Connection time will be further minimized by the fact that users will perform the necessary decoding after disconnecting from PANSAT. Decoding information and a program for personal computers to conduct this task will be made available by NPS. [Ref. 1, p. 5]
Assuming a minimum usable elevation of 10° and a 28.5° inclination, low earth orbit (LEO) insertion via the shuttle, NPS would have a maximum communications window of approximately 8 minutes with PANSAT during each of its approximately three passes per day. Using the STS-86 anticipated inclination of 51.6°, the communications window would remain at about 8 minutes but the number of passes would increase to roughly four per day. In addition to an increase in the number of passes per day, higher inclinations also equate to longer orbital lifetimes [Ref. 2, p. 1 and Ref. 3, pp. 93-98].
Potential users should be able to access PANSAT by using a personal computer, a Terminal Node Controller (TNC), radio transmission and receiving equipment, special spread spectrum hardware and PANSAT-specific user-interface software to match PANSAT's spread spectrum capability. The SSAG is developing a design for an inexpensive, generic Ham kit to provide an amateur radio operator with all of the necessary hardware and software required for the demodulation of the spread spectrum signal and communication with PANSAT. [Ref. 3, pp. 40-42 and Ref. 4, p. 4]
The use of digital technology in the form of the PARAMAX PA-100 chip in the Communications subsystem incurs numerous advantages. Digital technology uses less area on the satellite, reduces satellite power requirements, provides flexible data rates, and is programmable. Additionally, the increased flexibility inherent in digital design allows for the future addition of multiple spreading codes and ease of adaptation to other systems. The fact that the amateur radio kit was made more affordable by the application of digital technology is a key factor when considering the implications of monetary outlay on the part of the amateur radio operator. Another aspect of the proposed Ham kit is that to increase acceptance by the amateur radio community, the kit should be adaptable for possible use with other satellites and systems. This concern is satisfied by the employment of digital technology. To facilitate communications with PANSAT, an amateur radio operator must utilize a ground station that is nearly identical to the SSAG's command ground station. The software that amateur radio operators are provided via the Ham kit will differ from the command ground station software in areas such as command and control capability and security passwords, which, for obvi ous reasons, will only be available to the command station. [Ref. 3, pp. 42-43]
1. Horning, J. A., "Navy Education Through Amateur Satellite Development," AIAA 93-4211, Naval Postgraduate School, Monterey, CA.
2. Sakoda, Daniel, "Naval Postgraduate School Spread Spectrum Communication Satellite," AIAA 93-4229, Naval Postgraduate School, Monterey, CA
3. Rich, Markham K., A Systems Analysis and Project Management Plan for the Petite Ama teur Navy Satellite (PANSAT), Master's Thesis, Naval Postgraduate School, Monterey, CA, Sep. 1994.
4. Payne, Robert Andrew Jr., Applications of the Petite Amateur Navy Satellite (PANSAT) , Master's Thesis, Naval Postgraduate School, Monterey, CA, Sep. 1992.
Return to the SSAG page.
Last Updated: Wed., 30 Sept. 1998