Radiation-safe orbits

I realize that all spacecraft require some degree of radiation hardening,
but within reasonable limits, what are the altitude ranges that might be
recommended for earth satellites for equatorial orbit? I understand that
there are two particularly intense belts of radiation; at what altitudes
might they best be avoided?

Jim McCauley

"Jim McCauley" wrote in message
...
I realize that all spacecraft require some degree of radiation hardening,
but within reasonable limits, what are the altitude ranges that might be
recommended for earth satellites for equatorial orbit? I understand that
there are two particularly intense belts of radiation; at what altitudes
might they best be avoided?

Jim McCauley


Equatorial orbit (geosynchronous orbit) is *only* at (approx) 35,000km.

Ken

In article ,
Jim McCauley wrote:
I realize that all spacecraft require some degree of radiation hardening...

LEO satellites don't really need anything beyond error-correcting memory...
and in an equatorial orbit, probably not even that. (Almost all of the
bit-flips in memory occur during passage through either the South Atlantic
Anomaly or one of the auroral ovals, and an equatorial orbit encounters
neither.)

...within reasonable limits, what are the altitude ranges that might be
recommended for earth satellites for equatorial orbit?

The fast answer is that anything between 1000km and geostationary altitude
(about 36000km) needs serious radiation hardening and is best avoided.
Those boundaries are fuzzy; sensitive applications (e.g. manned) would
want to give either a somewhat wider berth, while mildly hardened
satellites can intrude on either somewhat. And the outer region of the
belts is quite dynamic.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

On 2005-02-28, Ken Taylor wrote:
"Jim McCauley" wrote in message
...
I realize that all spacecraft require some degree of radiation hardening,
but within reasonable limits, what are the altitude ranges that might be
recommended for earth satellites for equatorial orbit? I understand that
there are two particularly intense belts of radiation; at what altitudes
might they best be avoided?

Equatorial orbit (geosynchronous orbit) is *only* at (approx) 35,000km.

Note that whilst geosynchronous orbits are equatorial, equatorial orbits
do not have to be geosynchronous; you can quite happily have a satellite
in LEO, just at an orbital inclination of zero degrees.

--
-Andrew Gray

Henry Spencer wrote:
In article ,
Jim McCauley wrote:

I realize that all spacecraft require some degree of radiation hardening...


LEO satellites don't really need anything beyond error-correcting memory...
and in an equatorial orbit, probably not even that. (Almost all of the
bit-flips in memory occur during passage through either the South Atlantic
Anomaly or one of the auroral ovals, and an equatorial orbit encounters
neither.)

This is a very optimistic statement! Bit flips may occur in memories
already when you are flying in a passenger aircraft across the poles.
IIRC the shuttle computers get a couple of hundred bit flips per mission
at 28 degrees inclination, even more at ISS orbit inclination.

--
th

In sci.space.science th wrote:
This is a very optimistic statement! Bit flips may occur in memories
already when you are flying in a passenger aircraft across the
poles. IIRC the shuttle computers get a couple of hundred bit flips
per mission at 28 degrees inclination, even more at ISS orbit
inclination.

Heck, terrestrial computers were/are getting bit flips and whatnot in
their caches and such even in places like Denver, necessitating ECC on
the caches and the like.

With enough bits sitting there waiting to be flipped...?

rick jones
--
a wide gulf separates "what if" from "if only"
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to raj in cup.hp.com but NOT BOTH...

"Andrew Gray" wrote in message
. ..
On 2005-02-28, Ken Taylor wrote:
"Jim McCauley" wrote in message
...
I realize that all spacecraft require some degree of radiation
hardening,
but within reasonable limits, what are the altitude ranges that might
be
recommended for earth satellites for equatorial orbit? I understand
that
there are two particularly intense belts of radiation; at what
altitudes
might they best be avoided?

Equatorial orbit (geosynchronous orbit) is *only* at (approx) 35,000km.

Note that whilst geosynchronous orbits are equatorial, equatorial orbits
do not have to be geosynchronous; you can quite happily have a satellite
in LEO, just at an orbital inclination of zero degrees.

--
-Andrew Gray


Touché. Mental note - keep fingers off keyboard before second cuppa.

Ken

JRS: In article , dated
Tue, 1 Mar 2005 18:05:56, seen in news:sci.space.science, Andrew Gray
posted :
On 2005-02-28, Ken Taylor wrote:
"Jim McCauley" wrote in message
...
I realize that all spacecraft require some degree of radiation hardening,
but within reasonable limits, what are the altitude ranges that might be
recommended for earth satellites for equatorial orbit? I understand that
there are two particularly intense belts of radiation; at what altitudes
might they best be avoided?

Equatorial orbit (geosynchronous orbit) is *only* at (approx) 35,000km.

But 35,000 km from where? Either "altitude" or "radius" is needed.

Note that whilst geosynchronous orbits are equatorial, equatorial orbits
do not have to be geosynchronous; you can quite happily have a satellite
in LEO, just at an orbital inclination of zero degrees.

Surely it is only geostationary orbits that have to be equatorial; and
they must also be circular.

Any orbit with a period of one day can reasonably be termed
geosynchronous.

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

In article ,
th wrote:
LEO satellites don't really need anything beyond error-correcting memory...
and in an equatorial orbit, probably not even that. (Almost all of the
bit-flips in memory occur during passage through either the South Atlantic
Anomaly or one of the auroral ovals, and an equatorial orbit encounters
neither.)

This is a very optimistic statement! Bit flips may occur in memories
already when you are flying in a passenger aircraft across the poles.
IIRC the shuttle computers get a couple of hundred bit flips per mission
at 28 degrees inclination, even more at ISS orbit inclination.

Please read what I wrote: the auroral ovals (around the magnetic poles)
and the South Atlantic Anomaly (which both a 28deg orbit and the ISS orbit
pass through) are the big hot spots for radiation effects. If you plot
memory errors vs. location on a map, they're very obvious. An equatorial
orbit *doesn't pass through those hot spots*.

Now, if I were building a satellite for an equatorial LEO, I probably
*would* put error-correcting memory in it, just on general principles.
But one might well be able to get away without it.

The severity of the radiation problem in space is much exaggerated. The
MOST astronomy satellite, in about the worst possible LEO -- relatively
high and polar -- has error-correcting memory, and some care was taken in
the design of its electronics, but it has no rad-hard parts. (The project
couldn't afford them.) It's coming up on two years in orbit, and the only
radiation effect yet visible is some drift in the calibration of some
sensors.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

th wrote:
Henry Spencer wrote:
LEO satellites don't really need anything beyond error-correcting
memory...
and in an equatorial orbit, probably not even that. (Almost all of the
bit-flips in memory occur during passage through either the South
Atlantic
Anomaly or one of the auroral ovals, and an equatorial orbit encounters
neither.)

This is a very optimistic statement! Bit flips may occur in memories
already when you are flying in a passenger aircraft across the poles.
IIRC the shuttle computers get a couple of hundred bit flips per mission
at 28 degrees inclination, even more at ISS orbit inclination.

And error correcting memories can correct for bit flips
as long as the rate is not too high. Specifically, given
a rate of buildup, a rate of cycling the memory and
correcting flips, and a degree of error correction you
arrive at a specific probability of memory corruption
over a specific time period given the known
characteristics of the radiation environment. You can
then adjust, if possible, the degree of error correction
used to give your mission a certain probability of
memory corruption during the mission (e.g. one in a
million). If you cannot adjust the amount of error
correction you use sufficiently to meet your reliability
goals, then you need to switch to different hardware or
accept different goals.

Of course, this is a simplified analysis, and there are
other important details, but that's the meat of the
problem, I think.