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Cheap Realistic Space Flight



 
 
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  #52  
Old November 20th 03, 05:24 AM
Henry Spencer
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Posts: n/a
Default Cheap Realistic Space Flight

In article ,
ed kyle wrote:
And Saturn IB Centaur's payload to Mars was 2700 kg. An overrun of nearly
500 kg is not something that could have been overcome trivially.


According to "On Mars",
("http://history.nasa.gov/SP-4212/contents.html") NASA was
trying to meet a 3,000 kg spacecraft weight limit to fly on
Saturn IB/Centaur.


The 2700-kg number is also from "On Mars", interestingly enough.

Note that the 3000-kg mass estimate increased very substantially after the
true density of the Martian atmosphere became clear -- it was *not* a
realistic mass for the Voyager spacecraft, as it turned out.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |
  #53  
Old November 29th 03, 08:39 PM
ed kyle
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Posts: n/a
Default Cheap Realistic Space Flight

(Henry Spencer) wrote in message ...
In article ,
ed kyle wrote:
And Saturn IB Centaur's payload to Mars was 2700 kg. An overrun of nearly
500 kg is not something that could have been overcome trivially.


According to "On Mars",
("http://history.nasa.gov/SP-4212/contents.html") NASA was
trying to meet a 3,000 kg spacecraft weight limit to fly on
Saturn IB/Centaur.


The 2700-kg number is also from "On Mars", interestingly enough.

Note that the 3000-kg mass estimate increased very substantially after the
true density of the Martian atmosphere became clear -- it was *not* a
realistic mass for the Voyager spacecraft, as it turned out.


I've wondered about that reported 2.7-3 ton trans-Mars
limit for Saturn IB/Centaur. It sounded low to me.

According to "http://www.pma.caltech.edu/~chirata/deltav.html"
you need about 3800 m/s delta-v to go from low earth orbit
to a low-energy trans-mars trajectory.

Mark Wade has the only mass-budget source that I've found
for the never-built Saturn IB/Centaur. His numbers seemed
a bit optimistic, so I decided to use more conservative data
for the Saturn stages from NASA's Apollo 7 post-flight
report. I came up with the following, whe

Mi = Initial Mass, discounting S-IB thrust buildup
Mf = Final Mass, including residuals.

Saturn IB/Centaur

Stg Mi(kg) Mf(kg) ISP(effective)
---------------------------------------
1 444227 42574 279
2 116112 14067 421
3 16258 2700 444
Fairing 6000*
Payload 3000
---------------------------------------
Total 585597

*my estimate

Which gives the following delta-v results.

Saturn IB/Centaur
Stg Mint Mfinal DeltaV
kg kg m/s
-------------------------------------
1 585597 183944 3168
2 135370 33325 5786
3 19258 5700 5300
-------------------------------------
Total DeltaV 14254

During Apollo 7, SA-205 provided 9300 m/s ideal delta-v
to reach low earth orbit. If roughly the same were
required for a Voyager parking orbit, then the total
delta-v requirements should be 9300 + 3800 = 13100 m/s.
(That is about what Titan 3E provided.) If this is true,
Saturn IB/Centaur should have easily been able to boost
much more than 3 tons to escape velocity, perhaps as much
as 5 tons.

There must have been another limitation. One possibility
is that NASA was, at the time, planning to use a
single-burn Centaur profile. This would have required
the Saturn stages to provide all of the LEO delta V,
which would have limited the Voyager payload to something
around 3 tons or less. If true, the solution would have
been to modify the mission to a two-burn profile.

- Ed Kyle
  #54  
Old November 29th 03, 08:39 PM
ed kyle
external usenet poster
 
Posts: n/a
Default Cheap Realistic Space Flight

(Henry Spencer) wrote in message ...
In article ,
ed kyle wrote:
And Saturn IB Centaur's payload to Mars was 2700 kg. An overrun of nearly
500 kg is not something that could have been overcome trivially.


According to "On Mars",
("http://history.nasa.gov/SP-4212/contents.html") NASA was
trying to meet a 3,000 kg spacecraft weight limit to fly on
Saturn IB/Centaur.


The 2700-kg number is also from "On Mars", interestingly enough.

Note that the 3000-kg mass estimate increased very substantially after the
true density of the Martian atmosphere became clear -- it was *not* a
realistic mass for the Voyager spacecraft, as it turned out.


I've wondered about that reported 2.7-3 ton trans-Mars
limit for Saturn IB/Centaur. It sounded low to me.

According to "http://www.pma.caltech.edu/~chirata/deltav.html"
you need about 3800 m/s delta-v to go from low earth orbit
to a low-energy trans-mars trajectory.

Mark Wade has the only mass-budget source that I've found
for the never-built Saturn IB/Centaur. His numbers seemed
a bit optimistic, so I decided to use more conservative data
for the Saturn stages from NASA's Apollo 7 post-flight
report. I came up with the following, whe

Mi = Initial Mass, discounting S-IB thrust buildup
Mf = Final Mass, including residuals.

Saturn IB/Centaur

Stg Mi(kg) Mf(kg) ISP(effective)
---------------------------------------
1 444227 42574 279
2 116112 14067 421
3 16258 2700 444
Fairing 6000*
Payload 3000
---------------------------------------
Total 585597

*my estimate

Which gives the following delta-v results.

Saturn IB/Centaur
Stg Mint Mfinal DeltaV
kg kg m/s
-------------------------------------
1 585597 183944 3168
2 135370 33325 5786
3 19258 5700 5300
-------------------------------------
Total DeltaV 14254

During Apollo 7, SA-205 provided 9300 m/s ideal delta-v
to reach low earth orbit. If roughly the same were
required for a Voyager parking orbit, then the total
delta-v requirements should be 9300 + 3800 = 13100 m/s.
(That is about what Titan 3E provided.) If this is true,
Saturn IB/Centaur should have easily been able to boost
much more than 3 tons to escape velocity, perhaps as much
as 5 tons.

There must have been another limitation. One possibility
is that NASA was, at the time, planning to use a
single-burn Centaur profile. This would have required
the Saturn stages to provide all of the LEO delta V,
which would have limited the Voyager payload to something
around 3 tons or less. If true, the solution would have
been to modify the mission to a two-burn profile.

- Ed Kyle
 




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