Cheap Realistic Space Flight

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In article ,
ed kyle wrote:
Not correct. The reason Voyager was moved to the Saturn V was that it
simply *outgrew* Saturn IB/Centaur...

That was one of the stated reasons for stopping Saturn IB/Centaur, but
NASA's own history, SP-4212 "On Mars: Exploration of the Red Planet,
1958-1978", ("http://history.nasa.gov/SP-4212/contents.html") makes it
clear that money was the driving force behind the decision.
Begin Quote
(in mid 1965) NASA's "budget request for $5.26 billion yielded an
appropriation of $5.175 billion for fiscal year 1966. ... Voyager, as
a new start, was vulnerable, but other projects such as the adaptation
of the Centaur to the Saturn IB were also at risk, since such
development diverted money away from the completion of the Saturn V,
Apollo's powerful booster..."

And to continue that quote:

"The unfavorable budget was trouble enough without the additional bad news
brought by ... Mariner 4. The Martian atmosphere was much less dense than
previously estimated. All proposals for landing capsules had to be thrown
out... Given the 3000-kilogram launch weight for the spacecraft, much of
the scientific payload would have to be sacrificed... No matter which
approach to the problem was taken -- larger aeroshell, braking rockets,
larger parachutes -- it would mean too much weight for the Saturn IB."

While there was a lot of budget pressure weighing against continuation of
Saturn IB Centaur, it might have been resisted, had Voyager stayed within
that launcher's mass limits. The Mariner 4 atmosphere data was the fatal
blow: Voyager's case for keeping its own launcher was wrecked when it
outgrew that launcher. The advocates of Saturn IB Centaur previously had
successfully defended their choice against pressure from higher up, but
with Voyager unable to fly that way, they no longer had a leg to stand on,
and resistance to the outside pressures collapsed.

Whether a dense Martian atmosphere would have saved Saturn IB Centaur is
not clear. The pressures against it were strong. But the thin Martian
atmosphere was definitely what killed it.

The move to Saturn V doomed Mars Voyager by nearly doubling its costs.

"On Mars" again: "Considering the political climate, Voyager still might
have survived, but only if NASA were very careful about how it promoted
its planetary program. Unfortunately, the Manned Spacecraft Center in
Houston chose the first week of August 1967 to send 28 prospective
contractors a request for proposals to study a manned mission to Venus
and Mars... previous exercises of this kind ... had been billed as logical
extensions of the Voyager missions. This cast Voyager in the role of a
'foot in the door' for manned flights to the planets..."

Voyager was on thin ice already -- don't forget that summer 1967 was a
very bad time for the NASA budget in general, and that attempts to start
Voyager hardware development had already been postponed once by funding
shortages -- but it was political ineptitude by NASA that ultimately
killed it.

The greater costs of a Saturn V Voyager might someday have had an adverse
effect on the project, but in the end, Voyager never got far enough for
that to be a real issue.

In the end, the Titan IIIE Viking orbiter/lander combination massed
3330 kg versus the original 3175 kg for the Voyager orbiter/lander.

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.

And they were then the only definite customer for Saturn IB/Centaur,
so their departure (plus NASA's strong desire to reduce the number
of different launchers it was developing) doomed it.

Six Saturn IB/Centaur launches were planned (2 R&D and 4 Voyager).
Tentative plans called for future launches to Venus and the outer
planets...

All under the Voyager program. No Voyager, no customers. Yes, there were
other program concepts that *might* have used it, but that counted for
little in the final decision.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

(Henry Spencer) wrote in message ...

In the end, the Titan IIIE Viking orbiter/lander combination massed
3330 kg versus the original 3175 kg for the Voyager orbiter/lander.

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. Initial proposals were based on an
assumed 3,175 kg payload limit. Contemporary descriptions
of the launch vehicle (in AW&ST, for example) listed a
7,000 lb (3,175 kg) escape capability.

- Ed Kyle

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. |

(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