Marsian Artificial Satellites

Palomar · 2003-05-01 09:13:49

*Okay, this is a "spin-off" of the "Communications: Intra-Colony/Intra-Settlement" thread:

1. How will artificial satellites around Mars be repaired (for instance, if communications are linked through a satellite and it goes kaput or gets hit by a stray meteor)?

2. Given Mars' lower gravity and thin atmosphere, how much more quickly will the orbits of satellites decay as compared to Earth? Also, they will not burn up as well in the Marsian atmosphere as Earth's. What risk does this pose to the settlers/colonists? I suppose old satellites could be blasted into fragments and the fragments' orbits allowed to decay then burn up...but then you risk having multiple pieces of debris come crashing down versus just one (even if it is rather large).

Just wondering...like usual. If this has been discussed before, I super-apologize. I don't recall that it has, but if so would someone kindly refer me to the previous thread. I searched for any prior discussion, and Search didn't return any results.

--Cindy

MarsGuy2012 · 2003-05-02 08:38:12

I'm no expert on satellites, but satellites won't be absolutely necessary for planetwide communication. On Mars you can also use short wave radio (AM). From what I've read you can only use about 1/5 the power that you can on Earth. Mars will have less static though since it won't have thunderstorms or as many radio transmitters as Earth does. So, if all the satellites fail, short wave can be used while they're being replaced.
As for reparing the satellites it should be fairly straight forward. Most exploration/settlement plans call for SSTO vehicles. Martians will have relatively easy access to orbit.

RobertDyck · 2003-05-02 09:51:14

Satellites fall out of Low Earth Orbit because the atmosphere extends up there. You have to get into Medium Earth Orbit before there is no longer any atmosphere at all. Medium Earth Orbit is where the Van Allen radiation belts reside, so you have a problem with radiation. Actually, the Irridium satellites orbit in MEO at the special altitude that is between the radiation belts. Earth communication satellites are in Geosynchronous Earth Orbit, which is very high orbit. Any satellite in MEO or GEO will not fall down; satellites in LEO experience atmospheric drag, not a lot but just enough so they will eventually fall to Earth.

Mars has a much thinner atmosphere. Its lower gravity means the atmosphere extends higher than it would on Earth if it had that density, but still the upper extent of the Mars atmosphere is very low. Communication satellites can simply be placed above the Mars atmosphere so they will never fall out of orbit. The same for GPS satellites, survey satellites, weather satellites, etc.

To quote my favourite science fiction author "Any opinion, no matter how expert, is only opinion unless it can be expressed in numbers." Ok, what are the altitudes? The orbit of Mars Global Surveyor is 400km. Its first pass through Mars atmosphere during aerobraking was 262.897197 km, resulting a very little reduction of speed, but there was some. Later aerobraking passes dipped deaper: 149.288794 km on the 3rd, then between 110 and 178km for subsequent passes. This seems to indicate 400km is a stable orbit, and perhaps as low as 300km as well. On Earth an altitude of 100km is barely in orbit, expect the satellite to fall to Earth within a week. On Earth the thermosphere extends to between 800 and 1000km depending on weather. When there is strong solar wind the atmosphere heats and expands upward. An Earth satellite would have to orbit above 1000km to remain stable in all weather.

Palomar · 2003-05-02 14:40:46

Communication satellites can simply be placed above the Mars atmosphere so they will never fall out of orbit. The same for GPS satellites, survey satellites, weather satellites, etc.
To quote my favourite science fiction author "Any opinion, no matter how expert, is only opinion unless it can be expressed in numbers."

*Oh cool.

Actually I already knew all that, Robert; I was just checking to see if you did! <wink>

:laugh:

I guess I was under the impression from various news articles, etc., that -anything- which orbits a body was bound to come down sooner or later, due to inevitable orbit decay. I'm glad I've learned otherwise.

Thanks also for your input, MarsGuy.

As for your fav sci-fi author, Robert, I guess I could only have opinions to him. Expressing one's self in numbers is an absolutely foreign concept to me. Numbers drive me nuts, I hate them.

--Cindy

New Mars Forums

Announcement

#1 2003-05-01 09:13:49

Re: Marsian Artificial Satellites

#2 2003-05-02 08:38:12

Re: Marsian Artificial Satellites

#3 2003-05-02 09:51:14

Re: Marsian Artificial Satellites

#4 2003-05-02 14:40:46

Re: Marsian Artificial Satellites

Board footer