SPACE.com -- Radio Silence During MPL's Landing

MPL Aims for Keyhole in the Sky


	Radio Silence During MPL's Landing By Andrew Chaikin Executive Editor, Space and Science posted: 04:30 pm ET 02 December 1999

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On Friday afternoon, if you're hoping to hear word that Mars Polar Lander has arrived on Mars, be prepared to wait.

The spacecraft's radio transmitter will be turned off at 3:03 pm Eastern Time, approximately 10 minutes before the start of MPL's entry into the Martian atmosphere. There is no provision for transmitting data while the Polar Lander is making its descent from the surface. Touchdown, scheduled for 3:15 pm PST, will occur during this radio silence.

Because there will be no data from the spacecraft during its descent, no one will know whether the lander touched down safely until its first transmissions from the surface are received.

The opportunity to receive signals from the lander after it touches down will come at 3:39 pm EST. But engineers won't be too concerned if no signal comes at that time. It's possible, for example, that the lander's antenna might not be aimed exactly at Earth. The craft is pre-programmed to have its antenna scan the Martian sky to acuquire tracking stations on Earth, beginning at 10 pm EST Friday.

It's also possible that the lander will go into a "safe mode" after landing, in which case it will execute a different set of procedures to "phone home."

Trying all of these strategies could take several days.

Beginning Sunday, the lander will have a chance to send its signals via the orbiting Mars Global Surveyor spacecraft. There will be a new relay opportunity each day from that point on.

If no contact has been made with MPL by Sunday, engineers will explore other strategies for communications.

The twin Deep Space 2 microprobes will impact Mars at the same time as the Mars Polar Lander reaches the surface. The first data from the probes, sent to Earth via Mars Global Surveyor, will arrive no sooner than 10:50 pm EST on Friday. Signals from the probes could be delayed by such factors as the probes' orientations after landing, or the temperature at their impact sites. Engineers will be able to "listen" for its transmissions every two hours throughout the weekend, as MGS passes over the impact sites.