PROPOSED MARScomm Operations Plan Draft 15 April 2004 ---------------------------------------------------------------------------- NNN0NNN BACKGROUND: MARScomm is a VHF uplink and HF downlink single channel repeater that will be launched in the Fall of 2005. Its mission is to experiment with SATCOM for the education and training of the MARS cadre. To simplify the international coordination of frequencies, both its uplink and downlink are on previously assigned MARS frequencies. This MARScomm operations plan provides procedures to minimize mutual interference and allow dual use of these frequencies. DOWNLINK: The downlink is on one of the underutilized HF frequencies in the 24-27 MHz band. Only one frequency is possible and it must be hardwired before launch. It should be hearable on a mobile HF whip antenna. UPLINK: The uplink shares the most common MARS VHF frequency that is in use in 70+ areas across CONUS. In most of these areas the frequency is the VHF repeater input frequency. In some areas, it may be the repeater output. To distinguish these two aplications in the following discussion, we will use the term VHFI and VHFO for repeaters using the MARScomm frequency as input and output respectively. This VHF frequency took years to get coordinated for this application and cannot be changed on orbit. The typical user uplink will be 50 Watts from a mobile whip antenna. CONSIDERATIONS: Since MARScomm will be in view of all existing CONUS VHF MARS repeaters about 6 times a day for 10 minutes per pass, there will be times when dual use of these frequencies must be managed by this operations plan. MARScomm is a short term experiment with a mission orbit lifetime of less than 2 years. THe following potential issues will be addressed: 1) Ground VHFI repeater user unknowingly getting into MARScomm 2) Ground VHFO repeater output unknowingly getting into MARScomm 3) MARScomm user bringing up ground VHFI repeaters 4) MARScomm user interferring direct with VHFO repeater local users 5) MARScomm HF downlink coming into view of ground HF use MITIGATION PLAN: DIRECTED NET: As a general rule, the MARScomm transponder will be operated as a directed net under the control of a volunteer Net Control Operator. For special events, drills, and other applications, an active and up-to-date schedule will be maintained on a MARS web-page and via normal MARS administrative nets. SCHEDULING: In general, MARScomm will be in view no longer than about 10 minutes at a time occuring about 6 times a day spread about every 90 minutes over about an 8 to 10 hour period of each day. For simulations, its orbit will be nearly the same as the International Space Station (ISS). Further, this pattern will move earlier every day by about 20 minutes. This causes the overall daily pattern to repeat about every 2 months. Thus, there will be weeks when the prime passes are during CONUS sleep hours and of no consequence. Similarly, however, there will be weeks when the passes are occuring during PRIME-TIME VHF ground Nets. MITIGATION: CASE1: Ground VHFI repeater user unknowingly getting into MARScomm. This case requires every potential user to have knowledge of the daily schedule of MARScomm and to know when the 10 minute MINIMIZE on the use of all local VHFI repeaters. There are easy techniques which will be discussed later, but one EASY mitigation which will allow concurrent dual use even during a pass is for the local VHFI repeater user to use only 1 Watt on his repeater input. This will be too low to interfere with MARScommm (but can unwittingly invite others who may not be running 1W or less). CASE2: Ground VHFO repeater output unknowingly getting into MARScomm. This is the toughest case, and requires knowledge of the daily schedule of MARScomm with which to declare the 10 minute MINIMIZE on the use of local VHFO repeaters. Automated techniques will be discussed later. CASE3: MARScomm user bringing up ground VHFI repeaters. In this case, everyone monitoring the local repeater will hear if someone in their area is using MARScomm, because his uplink will be heard on the local VHFI repeater. But it will be confusing to other local users, because it will appear to be a one-way transmission.. To mitigate this confusion, ALL UPLINKS in these areas SHOULD include the words "VIA MARSCOMM" to help signal other users that the channel is in use and MINIMIZE is in effect in the area of this VHFI repeater for the next 10 minutes. CASE4: MARScomm user interferring direct with VHFO repeater local users. This is similar to CASE3, except that only other local users within simplex range of a local MARScomm user will hear him. Thus, the chances are much smaller that other local VHFO repeater users will be alerted to MINIMIZE, thus leading to the worst case, CASE2. CASE5: MARScomm HF downlink coming into view of ground HF use. This case is mitigated by the fact that there are many HF frequencies assigned to MARS and so the one channel chosen for MARScomm should not be assigned to any other ground use for the duration of the MARScomm mission. Hopefully we will choose the best, clear channel availble prior to launch. The MARScomm mission will be occuring during a solar minimum and DX propogation is not expected. MINIMIZE TECHNINQUES: THe best way to alert local users of the 10 minute MINIMIZE windows for VHFI and VHFO repeater users is via automated techniques. A PC MARScomm tracking program has been written that can run on ANY PC (even old 286 DOS hardware)that can output a contact closure via a serial port I/O line whenever MARScomm will be in view. The program can also generate tones, CW announcemnts or even voice based on this period. It can also make pre-pass scheduling announcemnets when the repeater is not otherwise in use... There are several creative ways to use this contact closure: On either VHFI or VHFO repeaters, the PC can make occasional MINIMIZE scheduling annoucncements via the repeater alerting users to future passes when the repeater is otherwise not in use. For VHFI repeaters: The contacts can KEY the output of the repeater for the 10 minute pass and the audio can feed a tone, CW or voice announcement via the repeater output to ALL users that MARScomm is in use and can even count down the minutes. Secondly, if a spare HF receiver is available, the MARSCOM HF downlink can be fed into the repeater output so everyone can hear it in use. Note, this requires the PC to be at the repeater site, since the INPUT of the VHFI repeater must not be used during MINIMIZE. ***OR*** the PC may be remoted as long as it transmits at 100 mW or less on the input of the VHFI repeater. For VHFO Repeaters: The PC can be set to anticipate the pass by 10 minutes and to make pre-pass scheduling announcements as noted above. When MARScomm comes into view, the contacts DISABLE the repeater output. Local VHF operations can continue but only by simplex on the local VHFO input frequency between users. MAINTENANCE: The MARScomm satellite is in a low orbit with substantial drag that will limit its on-orbit life to under 2 years. The PC program will probably need to be updated with fresh tracking elements on the order of once every 3 months or so for the duration of the mission. OTHER OPERATIONS CONSIDERATIONS: TBD WEB REFERENCE: The latest version of this document is available on the web at http://www.ew.usna.edu/~bruninga/mars/marscommops.txt