NASA's Mars Odyssey Enters Orbit

maddmike writes "Nasa's Mars explorer Odyssey is scheduled to brake and orbit about Mars today at 7:30PDT. Among the mission's objectives are to understand Mars' climate and geological history and to search for signs of life sustaining environments including water. Main web site is at the JPL website." Update: 10/24 13:12 GMT by T : The BrownFury writes cites a Space.com summary which says "The Mars Odyssey spacecraft appears to have succeeded Tuesday night in one of the most tricky and critical parts of its missions by slipping into orbit around the Red Planet."

Comments

Teflon was *not* a spinoff.

[kaszeta]

After all, space research has lots of practical spin-offs, like teflon for example.

Why does everyone feel the need to falsely attribute various inventions as space program spinoffs?

Teflon was invented in 1938, well before anything that could even remotely be considered modern space research.

Don't get me wrong, space research is good, and it produces a valuable product: knowledge.

False attributions to the space program don't help with their budget problems, though. I'm not blaming you, however, NASA themselves is quite guilty of exaggeration.

40 bits a second!

[netman133]

From Space.com

11:01 Odyssey turns on its telemetry and begins transmitting data at 40 bits per second. The Deep Space Network will take several minutes to synchronize their equipment with the pattern in the telemetry because of the slow rate at which the data is being received.

Re:40 bits a second!

[Longbow]

Actually the 40 bps is just the carrier signal that they use to keep a lock on the spacecraft.

The 40bps comes through the low gain omnidirectional antenna. Once they are back on the high gain antenna, the signal rate goes back
up. After the spacecraft is out of danger and back into normal operations the rate is switched back to something like 28,800 bps. Pretty good rate for communicating across 100 million miles.

turn off the fault protection software?

[guidobot]

here's a cool link about the steps they take to get into orbit. my favorite part is that the first step involves 'turning off the fault protection software'. its not as bad as you think, though my immediate reaction was to imagine mission control saying "Well, we're only 100 kilometers away, we should be safe so let's just turn that fault protection stuff off. Or was it 100 miles?"

Re:turn off the fault protection software?

[Buran]

This was done in order to prevent small errors that won't affect the spacecraft from shutting it down at a bad time. Fault control software on late-model NASA craft causes them to enter into a "safe mode" that shuts down nonessential functions and causes the craft to wait for instructions from Earth.

If this were to happen during the engine firing -- causing the probe to stop everything and just wait -- it'd sail right on past Mars, a fate which befell some of the earlier lunar probes.

If this were to happen, Mars Odyssey would be useless anyway... so better to risk the small problems rather than have them come back to bite you in a big way.

Distance, reliability

[s20451]

1. When the spacecraft first goes into orbit, you want a reliable, simple telemetry signal to indicate the basics of what is happening with the spacecraft. This means a low-gain, wide-beam transmitting antenna. The high-gain antenna will provide higher rates, but must be aimed much more carefully; such a system would not be robust if something went slightly wrong during orbit insertion.
2. From the Where is Mars Odyssey Right Now? page, the spacecraft is currently 1.53e+11 meters from Earth. Even with a directional antenna, signal power drops with distance squared, so the path loss is on the order of 200 dB. That is, if the transmitter power is (say) 50 watts/m^2 at 1 meter away from the spacecraft, as measured from Earth it would be something like 10^-20 watts/m^2, not counting antenna gains. At those powers you'd be lucky to get 40 bits/s, simply by running into Shannon's limit. (Somebody check my math, I haven't had coffee this morning.) Imagine the communications challenge for Voyager 2, which is now heading out of the solar system at a range of billions of kilometers; or Galileo, which lost its high-gain antenna at Jupiter ...

Re:40 bits a second

[Buran]

... except that that signal is only the carrier signal off the low-gain antenna. The high-gain antenna, which will be used for transmitting actual data, won't be activated until the probe finishes unfolding itself from cruise mode configuration. That antenna transmits data many times faster (I wasn't able to find the exact transmission speed when I looked for it last night.)

Re:Searching for water?

[Shadowlion]

NASA never found water. NASA has gobs of images of the Martian surface which /suggest/ water. Channels on the surface, etc., which look an awful lot like running water made them. There are even some features that hint at ancient oceans.

However, at the moment, these images are equivalent to ink blots. Yeah, maybe they look like something - but maybe you're just reading into them.

Odyessey seems like it's going to go a bit beyond that and actually do some surveying of the surface and subsurface for signs of actual water, as opposed to just saying, "Hey, that looks like it might've been made by water a million years ago!"