Getting Data from Deep Space 2 and Mars Polar Lander:
Mars Relay Plans

Deep Space 2 Microprobe

Mars Global Surveyor in 1996--note Relay Antenna

Mars Polar Lander

To relay data from a lander on Mars, the Mars Relay (MR) radio system on Mars Global Surveyor (MGS) first transmits a beacon signal that the lander can "hear". This signal tells the lander that MGS is passing over the landing site. The lander then transmits its data to the MR. Subsequently, the MR hands the data off to the Mars Orbiter Camera, which stores the data until it can be sent back to Earth via Mars Global Surveyor's large, dish-shaped high gain antenna.

During December 1999, the MGS Mars Relay will be used to acquire all data from the Deep Space 2 Microprobes--Amundsen and Scott. Plans also call for relay of some of the Mars Polar Lander data through MGS, as well, but details will develop as the mission unfolds.

Below are technical descriptions of the plans for relaying the Deep Space 2 and Mars Polar Lander back to Earth via the MGS MR and MOC.

Deep Space 2 Operations Sequence

To support the Deep Space 2 probes, Amundsen and Scott, a complex sequence of primary and backup (contingency) attempts to contact the probes has been developed by the Jet Propulsion Laboratory. The DS-2 probes impact the surface very close in time and about 50 kilometers (31 miles) from Mars Polar Lander. The first attempt to hear them with the MGS Mars Relay occurs three MGS orbits (about 8 hours) after landing. The MR tries to communicate with both Deep Space 2 probes on five consecutive orbits, 2.4 minutes attempting to contact one probe, followed by 2.4 minutes attempting to contact the other, for 24 minutes per orbit.

If the probes have in fact been contacted and their data returned during these initial passes, the plan will be to contact them on two more consecutive orbits about 24 hours later (again alternating between the two probes for ten 2.4 minute periods), and then once every day thereafter in the same pattern. There are nine primary orbits to contact and retreive the probe data, and a total of 31 additional contingency contact orbits in case the first five do not succeed. For more information, visit the Deep Space 2 Microprobe Web Site. The figure shown below indicates the contact periods for Deep Space 2.

Mars Relay contact periods for Deep Space 2 and Mars Polar Lander. The light blue are primary contacts for Deep Space 2, pink and green are contingency contacts for Probe 1 or Probe 2, and dark blue is the MPL contingency contact. Thin dark lines are periods when MGS can see the landers: short lines means MGS is near the horizon while tall lines indicate when MGS flies nearly overhead. The times at the bottom are Earth Times; those at the top are Mars Time. [Click HERE for a larger version of this figure, or HERE for a much larger version.]

Mars Polar Lander Operations Sequence

Mars Global Surveyor (MGS) support of the Mars Polar Lander (MPL) mission will not be finalized until after landing on December 3, 1999. Two contingency sequences were prepared prior to landing: an on-board contingency test of the MR link and a MR-only plan in case MPL's direct-to-earth radio fails. The on-board contingency sequence will execute if the lander does not hear from Earth during the first day on Mars, or if the spacecraft is commanded to enter the contingency sequence. If either of these circumstances happens, the MPL will automatically switch its UHF radio on and listen for the MR tone around 2 AM local Mars time on the second martian day after landing. If the Lander is able to receive instructions from Earth but unable to communicate back to Earth directly, the MR-only sequence will be started, that will bring engineering and science data back via the MR starting about five or six martian days after landing (the time delay is used to make sure that all other avenues are examined before starting the MR-only sequence).

Image Credits: Artwork and Chart: NASA/JPL/Caltech; Photo: NASA/JPL/LMA annotated at MSSS

©1999 Malin Space Science Systems, Inc.