TO THE JAPANESE SPACE AGENCY

In message , Derek Lyons
writes
(Hallerb) wrote:
Furthermore, if there are no problems, the outcome is two operational
spacecraft, one of which can be assigned a different mission.

Sometimes. OK, rarely.


Or to looks at the same planet, like the old probes of mars. Invaluable if you
ask me.

Invaluable on the flyby missions where the 2nd probe will see a
different hemisphere. Not really useful on the long duration orbiter
missions. (Unless it's to Jupiter where you can visit different moons
with each orbiter.)

It also takes a lot of the limited DSN resources to communicate. And
how does each probe know when you are talking to it and not it's twin?
More complication, more ways for things to go wrong.

I don't know the specifics but surely the signals have some sort of tag
to tell the probe who the message is for (and who it's from, so I can't
send a message and destroy it :-)
Until the budget cuts of the 1970s it was routine to send two probes on
each mission, which saved Mariner 1/2, Mariner 3/4 and Mariner 8/9.
Mariner 11 was ready for launch but never used.
Of course sometimes the principle failed - the Russians lost both Phobos
craft for different reasons.
And in the case of HST they used the wrong mirror :-)
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Jonathan Silverlight
wrote:

Until the budget cuts of the 1970s it was routine to send two probes on
each mission, which saved Mariner 1/2, Mariner 3/4 and Mariner 8/9.
Mariner 11 was ready for launch but never used.

Given the total number of missions and the few that actually had
duplicates flown, I hesitate to term the practice 'routine'.

D.
--
The STS-107 Columbia Loss FAQ can be found
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(Derek Lyons) writes:

[...]

Or if the first probe arrives a month in advance and is lost their might be
time to find and fix the problem.

Maybe, maybe not.

Sure. That's better than "certainly not" if there's not a second probe.

I'm talking about planetary probes (i.e. beyond the moon) here.

(Derek Lyons) writes:

Jonathan Silverlight
wrote:

Until the budget cuts of the 1970s it was routine to send two probes on
each mission, which saved Mariner 1/2, Mariner 3/4 and Mariner 8/9.
Mariner 11 was ready for launch but never used.

Given the total number of missions and the few that actually had
duplicates flown, I hesitate to term the practice 'routine'.

He's saying of Mariners 1-11, only Mariner 5 was not part of a duplicate
set. That's 10 out of 11, or put another way, 5 out of 6 missions had
duplicate sets assigned, which resulted in 6 successful missions. The
one time we flew only one Mariner (#5) succeeded, 1 out of 1. Of the 5
remaining, 3 times (1/2, 3/4, 8/9) one out of two (coincidentally, the
higher numbered in each case) succeeded while one failed, 3 out of 5,
and once (6/7) both succeeded, and once the first succeeded and the
second wasn't flown. Now add the Pioneers and Vikings, and the numbers
increase, and all of those are part of duplicate sets too (I think all
the Pioneers until the post 11 Venus probes could be considered part of
duplicate sets, some sets maybe with more than two probes in them.
That's another 3 or 4 missions. So yes, you can say it's not routine,
it was the practice. What number do we have to hit before you wouldn't
hesitate to use the term routine?

In article ,
Derek Lyons wrote:
It also takes a lot of the limited DSN resources to communicate. And
how does each probe know when you are talking to it and not it's twin?

Either digitally-addressed messages or (preferably) slightly different
frequencies. (The latter has the advantage that you can talk to both at
once, equipment permitting.)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Chris Jones wrote:

He's saying of Mariners 1-11, only Mariner 5 was not part of a
duplicate set.

Mariner 10 (the Venus-Mercury one) was not part of a set. There was
no Mariner 11 although Voyagers 1 and 2 were called Mariners 11 and
12 during planning. You may be confusing Pioneers 10 and 11 with
Mariners.

Jim Davis

(Henry Spencer) wrote:

In article ,
Derek Lyons wrote:
It also takes a lot of the limited DSN resources to communicate. And
how does each probe know when you are talking to it and not it's twin?

Either digitally-addressed messages or (preferably) slightly different
frequencies. (The latter has the advantage that you can talk to both at
once, equipment permitting.)

Which however breaks, or at least bends, the rule of 'identical
twins'. Not a big deal, but worth noting.

D.
--
The STS-107 Columbia Loss FAQ can be found
at the following URLs:

Text-Only Version:
http://www.io.com/~o_m/columbia_loss_faq.html

Enhanced HTML Version:
http://www.io.com/~o_m/columbia_loss_faq_x.html

Corrections, comments, and additions should be
e-mailed to , as well as posted to
sci.space.history and sci.space.shuttle for
discussion.

In message , Jim Davis
writes
Chris Jones wrote:

He's saying of Mariners 1-11, only Mariner 5 was not part of a
duplicate set.

Mariner 10 (the Venus-Mercury one) was not part of a set. There was
no Mariner 11 although Voyagers 1 and 2 were called Mariners 11 and
12 during planning. You may be confusing Pioneers 10 and 11 with
Mariners.

No I'm not. That probe is what brought me to this newsgroup. An
article in the January 1974 "Sky and Telescope" said "An Atlas-Centaur
rocket carried Mariner 10 into a temporary orbit around the earth, while
a backup Mariner and launch vehicle stood on a nearby pad" and I asked
alt.astronomy what happened to it. (Ron Miller kindly reposted my
question here for me and I've been here ever since !)
If the backup had been launched it would presumably have been called
Mariner 11.
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In article ,
Derek Lyons wrote:
how does each probe know when you are talking to it and not it's twin?
Either digitally-addressed messages or (preferably) slightly different
frequencies. (The latter has the advantage that you can talk to both at
once, equipment permitting.)

Which however breaks, or at least bends, the rule of 'identical
twins'. Not a big deal, but worth noting.

Doesn't have to bend it very far. The different frequencies typically
will be in the same general band, so the same radio hardware works. The
difference can be as small as what values the on-board software programs
into the divider chains of the radio's frequency synthesizers, in which
case the *only* difference between the two spacecraft is different
constants in the software loads. It's more usual to have different
crystals or different jumper configurations in the radio hardware, but
even that means building the radios from the same drawings but with
different values for one or two components (to the point that care is
needed to make sure that the right radios get into each spacecraft!).
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Jonathan Silverlight wrote:

No I'm not. That probe is what brought me to this newsgroup. An
article in the January 1974 "Sky and Telescope" said "An
Atlas-Centaur rocket carried Mariner 10 into a temporary orbit
around the earth, while a backup Mariner and launch vehicle
stood on a nearby pad"...

This is interesting; I had not heard this before. Was this backup
Mariner only available in case of a launch failure or would it have
been launched at the next opportunity if Mariner 10 had failed en
route?

Jim Davis