Jovian System has better colony sites than moon&mars

[marcus]

Here's what they say for moon mass and radius, so we can get the escape-from-surface velocities

Io 893.2 ****** 1821.6
Europa 480.0 ******** 1560.8
Ganymede 1481.9 ******* 2631.2
Callisto 1075.9 ******* 2410.3

units are E20 kilograms for the mass, and kilometers for the radius

Someone want to post the escape velocities? It gives a handle on how much use you can make of gravity assist from that moon.

 

[enigma]

Originally posted by marcus
Here's what they say for moon mass and radius, so we can get the escape-from-surface velocities

Io 893.2 ****** 1821.6
Europa 480.0 ******** 1560.8
Ganymede 1481.9 ******* 2631.2
Callisto 1075.9 ******* 2410.3

units are E20 kilograms for the mass, and kilometers for the radius

Someone want to post the escape velocities? It gives a handle on how much use you can make of gravity assist from that moon.

\mu's [km^3/sec^2]

Io: 5957
Europa: 3201
Ganymede: 9884
Callisto: 7176

Gives surface escape velocities of [km/sec]:

Io: 2.55
Europa: 2.02
Ganymede: 2.74
Callisto: 2.44

I still don't see how you're going to back out gravity assist potential without knowing the geometry of the trajectories...

 

[marcus]

Originally posted by enigma


...surface escape velocities of [km/sec]:

Io: 2.55
Europa: 2.02
Ganymede: 2.74
Callisto: 2.44

thanks! these agree except possibly in the second decimal place
with ones I was just now thinking of posting:

Io: 2.56
Europa: 2.02
Ganymede: 2.74
Callisto: 2.45

Glad for the agreement.

Your question about the possibilities for gravity asst. at the Jupiter end of the trip.
Obviously the full potential depends on the configuration of the system at the time of entry and the specifics involve geometric detail. I'm interested in quick rough guesstimates.

As Nereid already indicated in this thread, considerable use has already been made of gravity in the Jovian system and opportunties are good because there are a lot of massive objects (close together and going different speeds). The 1995 Galileo mission probably used gravity assist in the system a lot, not to mention 3 or 4 others that have been thru that neck of the woods.

From the rough guesstimates already done, I can see why the 5.5 km/s that you enter the system with might not be too hard to shed gravitationally. And for that matter, if your destination is Callisto, say, a good bit of the escape energy at Callisto's distance might also be shed.

(Once out of the Earth's well) I'm guessing that the delta V cost of getting into orbit around Jupiter is mainly the initial 8.5 km/s kickoff at our end. Too sleepy to think more about it tonight tho.

 

[meteor]

What about Titan, the satellite of Saturn, that will be reached in January 2005 by The Cassini-Huygens probe?
http://saturn.jpl.nasa.gov/index.cfm

Titan has plenty of methane lakes, and I personally think that they will find life there. Is Titan profitable like a base for a human colony?

 

[marcus]

Originally posted by meteor
... methane lakes, and I personally think that they will find life there...

Meteor, I can't respond to the issue of "profitable" (either scientifically or economically).

I tend to think of the colonization urge as a healthy species urge, like sex, building houses, art and music. Things that
healthy people naturally want to do.

I would find living on Mars or the Moon depressing. But then I don't appreciate the state of Texas either.
I wouldn't like Titan becasue of the permanent fog and extreme cold---a most dreary possible climate.

A liquid water phase (like Europa's) is intrinsically around zero Celsius, a temperature I can understand. I would not mind a zero
Celsius ice cave environment as long as there was plenty of electric lighting. the prospect is a bit like Antarctica or Greenland, under the ice. Reminds me of where they built that neutrino telescope AMANDA 2.

But a liquid methane phase (like Titan's) is pretty scary for me to contemplate. And the atmosphere is so opaque one would never see the stars.

The question you need to ask, I think, is not "Would you like to do Science there?"
but
"Would you like to raise children there?"

In space, Science is something done via robotic extensions, surrogates, probes.

Titan could be of considerable scientific interest, and need to be investigated on scientific grounds. But it does not strike me as attractive for colonization.

What other large moons does Saturn have and what are they like, do you know?

 

[marcus]

Originally posted by marcus
thanks! these agree except possibly in the second decimal place
with ones I was just now thinking of posting:

[EDIT: I've thrown in the corresponding maximal circular orbit velocities----escape divided by sqrt 2]

Io: 2.56********1.81 km/s
Europa: 2.02********1.43 km/s
Ganymede: 2.74********1.94 km/s
Callisto: 2.45************1.73 km/s

Glad for the agreement.

The surface escape velocity from a body gives a quick handle
on the greatest deflection angle you can get by flying by it.

Even more convenient is that esc. speed divided by sqrt 2, the
surface circular orbit speed, or the maximal circular orbit speed.

The conventional notation is that the deflection angle theta
is half the total deflection. So to speak you get theta on the
way in and another theta on the way out. Just trig convenience.

The quick and dirty says

tan \theta = \frac{circspeed^2}{incoming speed^2}

So the smallness of these escape velocities makes it look unpromising. If I approach Ganymede at 4 km/s and swing close by it, I don't get deflected very much. Too bad. But mission designers still do this kind of maneuver so it must be worth something.

"Low Ganymede Orbit" speed is around 2 so squaring that speed and the incoming 4 km/s gives

tan \theta = \frac{4}{16}

tan theta = 1/4
theta is 14 degrees
total deflection from the encounter is 28 degrees

Enigma will be chuckling---see I told you so.
But I know that mission designers use the Jovian moons' gravity to save fuel. So I have to think harder about how this is done.
Maybe someone who knows something about it can help.

If one knew the configuration of the moons very precisely one might be able to program TWO or maybe even three flybys. each one deflecting some. So that it added up, in effect, to the idealized oneshot "hairpin turn" thing imagined earlier.

some grav. assist links:
http://cdeagle00.tripod.com/omnum/flyby.pdf
http://www.go.ednet.ns.ca/~larry/orbits/gravasst/gravasst.html

A better formula for the maximum turn angle is

2arcsin \frac{1}{1+rv_{oo}^2/\mu}
2arcsin \frac{1}{1+rv_{\inf}^2/\mu}

where r is the planet radius and v-sub-infinity is
the speed at infinity, and mu is the usual GM thing
with the dimensions cubic length over square time

 

[Njorl]

So, if we're talking colonization, not a long-term research facility, how do we go about it? Do we remotely terraform first, then send people to fine tune the environment, or do we send people into try to do terraforming? How would you terraform one of these moons?

I suppose, if there are oceans, that's a good start. We'd need to create an atmosphere. We'd want it to be richer in CO2 and methane to enhance greenhouse warming. We could analyse the ambient chemistry of the oceans, and select organisms that might survive and reproduce. More likely, we'd need to geneticly engineer organisms that could consume what exists, and produce the necessary environment. This would have to be done in stages. When the environment changes significantly, the next engineered organism is introduced, and so on.

Njorl

 

[Nereid]

Not so romantic?

The temperature on the surface of Europa is -180^o C. It is much the same on the surface of all Galilean moons, except near the volcanos of Io, where the lava temperature has been measured at >1,000^o C.

The ice shell on Europa is ~20 km thick, though it may be as thin as 4km in places. In comparison, the lowest temperature recorded on Earth was at Vostok station (Antarctica), -100 ^oC. Lake Vostok (also in Antarctica) has a 4km thick layer of ice above it.
http://www.lpi.usra.edu/research/europa/thickice/

All the major moons of Jupiter and Saturn are fascinating targets for serious scientific studies.

Terraforming is contraindicated on almost all gas planet moons - they're mostly ices. Of course, if you like living in Antarctica or on the Greenland ice cap, terraforming without melting the ice is OK. The exception is Io. Millions of years of tidal heating have driven off the volatiles (just like for Mercury, Venus, Earth and Mars), leaving a rocky (silicate-based minerals) crust with an iron core.

I agree with marcus that there could be great satisfaction living on Europa or Callisto, but perhaps the primary group interested would be those who found living at Amundsen or Vostok in winter the pinnacle of their earthly existence.

Only Rhea and Iapetus may count as significant other sites for colonies in the Saturn system, and they both have a diameter less than half that of Europa's.

 

[marcus]

Originally posted by marcus
...some grav. assist links:
http://cdeagle00.tripod.com/omnum/flyby.pdf
http://www.go.ednet.ns.ca/~larry/orbits/gravasst/gravasst.html

A better formula for the maximum turn angle is

2arcsin \frac{1}{1+rv_{oo}^2/\mu}
2arcsin \frac{1}{1+rv_{\inf}^2/\mu}

where r is the planet radius and v-sub-infinity is
the speed at infinity, and mu is the usual GM thing
with the dimensions cubic length over square time

Enigma has thoughtfully tabulated some mu numbers for the Jove moons

mu's [km^3/sec^2]***********radius [km]

Io: 5957***********1823
Europa: 3201*********1561
Ganymede: 9884**********2631
Callisto: 7176*************2410

So I will recalculate the maximum turn at Ganymede, coming in at 4 km/s

2arcsin \frac{1}{1+2631*4^2/9884}

this time I get 22 degrees, not such a rough approximation, a bit more complicated but the right formula

 

[marcus]

Nereid I insist on being able to grow tomatos
so there has to be a lot of electric lighting down in the ice cave.

Be sure to put on warm clothing when you go sightseeing on the surface.

 

[marcus]

Using Enigma's mu numbers for the Jove moons again

mu's [km^3/sec^2]***********radius [km]

Io: 5957***********1823
Europa: 3201*********1561
Ganymede: 9884**********2631
Callisto: 7176*************2410

This time let's calculate the maximum turn possible at Callisto, coming in slower this time, at 2 km/s

2arcsin \frac{1}{1+2410*2^2/7176}

this time I get just over 50 degrees

I conclude that v-at-infinity has to be comparable to the escape velocity of
the orb if you want the turn to be a substantial angle.

 

[marcus]

This grav. assist link
http://cdeagle00.tripod.com/omnum/flyby.pdf

gives a formula for the maximum turn angle

2arcsin \frac{1}{1+rv_{oo}^2/\mu}

which is equivalent to

2arcsin \frac{1}{1+v_{inf}^2/v_{circ}^2}


where v-sub-infinity is the speed at infinity
where v-sub-circ is the circular orbit speed at surface

Again entering the Jovian system at 5.5 km/s this time let's go into Io distance (may be reserved for robot ships because of radiation)
at which point speed is 25 km/s

Io orbit speed is 17.3 km/s

So if our speed parallels Io (the configuration is right at time of entry) we are passing Io with a v-infinity of around 8 km/s.
But Io's v-circ is 1.81 km/s (from a table a few posts back)

comparing these looks uninteresting

 

[marcus]

It turns out we can streamline the whole proceedure. Here are circular orbit speeds around Jupiter for the four big moons

Io 17.3 km/s
Europa 13.7 km/s
Ganymede 10.9 km/s
Callisto 8.2 km/s

And here are the circular orbit speeds around each moon, at its surface.


Io 1.81 km/s
Europa 1.43 km/s
Ganymede 1.94 km/s
Callisto 1.73 km/s

The basic given is that a ship comes into the J system at 5.5 km/s relativie to Jupiter.

I think that should be enough to work with and get maximum turn angles. Will see.

 

[marcus]

Originally posted by Jimmy

What temperature differences did you have in mind?

And in the spirit of this thread:

http://members.aol.com/jrzycrim01/images/Europa.jpg
http://members.aol.com/jrzycrim01/images/Europa2.jpg

Images captured from Celestia

Here's a shot of Ganymede (doesnt have J in it, you may have something more out of the ordinary)

http://www.ifa.hawaii.edu/faculty/barnes/ast110/gwas/ganymede.jpg

I was thinking of the temperature difference between the say 275 degree Kelvin sub-ice ocean and the say 120 degree surface.
Nereid gave an estimate of 5 km or so ice thickness IIRC so those
two different temperatures are not so near each other!


Do you have a picture of Callisto?

My Galileo printouts from NASA say that Callisto is unusual in not having an iron core---not having undergone differentiation.
This means the ironcompounds and other rock is more mixed up with the ice. that could be good.

The NASA book on the system says Galileo found that Io, Europa and Ganymede all have iron cores (!) so underwent quite some differentiation. Makes Callisto very interesting (closer to primordial planetary material) I suspect. I will try to find a picture.

Here's what I found. It is big (filling more than two of my screens) while in the process of downloading. So I have to scroll around to see it all. But then my computer adjusts it down to half the screen size to make it all fit (something I don't know how to circumvent)

http://www.solarviews.com/raw/jup/callisto.gif

there is an interesting large impact bruise near what seems to be the south pole. a fracture system of concentric circles.
the small craters expose what looks like ice---spots of high albedo.

 

[Nereid]

horses and water?

Hey team! Didn't a post a really cool link a while back in this thread? All you ever wanted to know about the Galilean moons, but were afraid to ask, from the friendly folk at Galileo/JPL! More images than you can ever use too.

Callisto has two impact basins, Asgard and Valhalla - they're huge, have several concentric rings, etc. Similar structures can be found on Mercury (Caloris), the Moon (Orientale), Mars (Hellas), ...:
http://www.solarviews.com/cap/index/impactbasin1.html

 

[Vosh]

Originally posted by marcus
The Jovian system is a superior target for self-sustaining colonization.

[BUNCH SNIPPED]

I do not like the "moon-mars" initiative which seems to me a bad investment and destructive of human aspirations.

In Hell Nasa techs and engineers etc. will be homeless, afflicted with some kind of mental illness and/or unable to adapt to a society that does not allow any other way of living, they will be cold and hungry and have jobs that are dehumanizing and aren't worth doing and I, I will be living on an ivory tower of number crunching autistic geekazoids and managers sending gleaming ships packed with everyones money into space and when those in the pits reach up a hand asking for relief from their misery I will say, "nope, sorry, too busy with my work and prestigee which I need to keep that marvelous wife, in tow and anyway, some day, a hundred years from now, I'll be able to let YOU live on another planet where food, shelter and money appears like magic at your feet..." if I acknowledge your existence at all.

 

[marcus]

Originally posted by Nereid
...

The ice shell on Europa is ~20 km thick, though it may be as thin as 4km in places.
http://www.lpi.usra.edu/research/europa/thickice/
...
All the major moons of Jupiter and Saturn are fascinating targets for serious scientific studies.
...
...
I agree with marcus that there could be great satisfaction living on Europa or Callisto, but perhaps the primary group interested would be those who found living at Amundsen or Vostok in winter the pinnacle of their earthly existence.
...

Nereid, great link about the 19 km thick ice (floating on the saltwater ocean). Your article had something about a brave soul who was practicing ice-diving, to see how it might be on Europa (!)

Glad you mentioned Callisto in same breath as Europa. Callisto now seems even more interesting because supposed to be undifferentiated.

Your link mentions a proposed Europa orbiter mission. Have you more info on proposed missions to J moons.
The point is, even if the future may be being trashed, yet the past proposals contain interesting parameters and can be enlightening to read.

I would like to see a proposal for a Callisto mission, especially if it had some practical detail to learn from.

Today I learned that the Galileo JOI burn only gave them 643 km/s

They needed less than one km/s to snag Jupiter
because they briefly went in deep (even inside Io orbit).

the history of Galileo mission is incredible. it began as a Mars mission and was switched to venus. then they said try going to J.
but NASA had some bad trouble and the only booster available was only
big enough to go to Venus with. So they fired it and sent Galileo the long way round:
to flyby Venus (grav. assist)
back to flyby Earth (grav assist)
around again and flyby Earth (grav assist)
and finally it has enough go to get-up to Jupiter
(like driving the Freeway with a Lawn-mower engine)
Incredible epic story of doing more with less.
And then when they get there (approaching J with something like
5 km/s) they only need a delta-vee of 0.6 km/s to snag it.
and from then on all the maneuvers are gravity assist

never used the main engine again after the first loop.

I want to see how somebody proposes to put a machine down on Callisto

 

[marcus]

Oh, now I see the NASA link you mean, about getting the horses to drink.

Originally posted by Nereid
A few things about the Galilean moons ...

A nice site is JPL's Galileo one; it has all kinds of goodies about Jupiter, the inner moons, and the mission, including this, packed with facts about the moons:
http://galileo.jpl.nasa.gov/moons/moons.html

Snippets:
- all Galilean moons have synchronous rotation, so Jupiter will appear to stand still in the sky (or be below the horizon) on all moons.
- Io in particular is in a fierce radiation zone (like the van Allen Belts, as enigma said), and there's a flux tube connecting it with Jupiter, carries millions of amps?
- the tidal locking is what keeps each of the inner three in its orbit (look at the periods - 1.77, 3.55, 7.15 days)
- tidal heating gives Io its spectacular volcanos (surely one of the more awesome sights), and also Europa its ocean; jury's still out re relative importance of tidal heating for Ganymede to keep its ocean
- IMHO, Callisto may be a better place to start - not as deep in the well, undifferentiated (so likely to have more rocks and metals around)
- Galileo used gravity assist to a considerable extent to change orbits (still needed rockets, of course); with four moons there's a lot of choice

Ah HAH! You mentioned the bit about Callisto being undifferentiated!
I just realized that about her yesterday evening. Really makes that moon special!

Both for science and for possible eventual habitats.
Iron and aluminum ores near the surface, mixed with ice.
Forget terraforming. Takes centuries.
the moons are interesting, even if not terraformable.
but must have plenty of electric light down in the cave so that
plants can grow.


melting a pocket of liquid water far enough down under the ice to be safe (creating an accessible sub-ice lake) and giving that lake a big lightbulb to keep it warm and liquid, could make a place for sea-life (even if we couldn't live there)

so then you and I would go there and live like Eskimos (PC Inuit) on shrimp and walrus blubber. In effect we would fish thru the ice for whatever would grow in an illuminated underground lake

then we'd build an igloo of course. TS Eliot wrote a song about it with climate assumptions a bit different: (any old isle is just my style, under the bam under the boo under the bamboo tree) Igloos keep you nice and warm.

Who needs terraforming if you have lots of ice? (Old Inuit proverb)

 

[marcus]

Who needs terraforming if you got ice---Inuit proverb

I just read a 1995 account by Tod Barber of the Galileo team written 70 days before the craft entered the jovian system

http://www.planetary.org/html/news/Galileo/hot-top-galileo-jup02.html

it's exciting, a leaking oxidizer check valve was suspected
nitrogen tetroxide and the monomethyl hydrazine fuel are hypergolic

Tod says the first thing they planned on arrival was get a gravity assist from Io!
and only afterwards proceed to perijove and the JOI burn
that was what that first flyby of Io was about
passing forwards of a planet you give it some of your energy
passing astern of it you take energy from it
so they passed some 600 km in front of Io and it helped slow them.

the 49-minute JOI burn slowed them an additional 0.6 km/s (another document says 643 meter per second) these are tiny delta-vee amounts

then on the first loop they went out to apojove at 200 Radii and did another burn of I guess around 0.4 km/s to fatten the oval and raise the perijove up to 11 Radii. That was the socalled PJR (perijove raise)

They captured Jupiter with a total of only about one kilometer per second delta-vee. After the JOI and PJR burns the main engine was never used again. Everything after that was done with the gravity assists derived from flybys of the moons.

All that stuff is reversible. So you could get OUT of the jove system by gravity assist and be on your way to Earth with about one km/s of delta-vee.

at Earth you might use atmospheric braking for some of the 8 km/s
or might rendevous with some other craft in LEO, like a shuttle.

What this says to me is that the delta-vee for a round trip is not as great as one might suppose at first. Galileo got to Jupiter starting with only enough boost to slow it down enough so it would fall in towards the sun as far as Venus. That is about 3 km/s. It did not even need the boost of 8 km/s one would assume for a transfer ellipse.
When it got there is just needed one km/s to get into orbit around Jupiter and start doing flybys of the moons.
So I guess to get to Jupiter one can do it with 3 + 1
then since it is reversible the return trip is 1 + 3

so that is a round trip for under 10 km/s

Say that is a mothership that does not ever land. It carries a lander to land on and take off from a moon. The lander needs fuel but that is a separate question. I am talking about the mothership trucking out and back and cruising around in the jovian system

Btw. the Galileo craft massed 2 tons and had two sections----rotating and non-rotating. the main engine was in the rotating part and the gyros and cameras in the non-rotating. I am getting to appreciate the design.

It seems like a good idea for a long-distance craft to rotate, as Galileo did. At least one section of it.

The 400 Newton main engine was made by Messerschmidt (MBB).
Nitrogen tetroxide and Monomethylhydrazine. Sexy chemicals such as
hotrodders dream of. Kept aboard Galileo for 5 or 6 years stable in their separate tanks but ignite spontaneously whenever they come in contact.

Who can calculate the payload ratio if you want 10 km/s and are using Tet and Monomethyl. How much of the truck has to be fuel and how much can be payload. It would be nice to know that, I think.

 

[Cecil]

Originally posted by marcus

So I guess to get to Jupiter one can do it with 3 + 1
then since it is reversible the return trip is 1 + 3

so that is a round trip for under 10 km/s

Is the second 3km/s necessary? After applying the 1km/s to get out of Jovian orbit, you are on an ellipse that crosses Earth orbit (since that is where the last gravity assit was done on the way there). Some delta-v may be necessary to be captured by Earth but it might be possible to burn it off with a double lunar gravity assist.

 

[marcus]

Originally posted by Cecil
Is the second 3km/s necessary?...

I wonder about this too. The Apollo missions used atmospheric braking on the return and I don't know to what extent thrust played a role, if it did at all. I think they may have approached the Earth essentially at escape velocity and made a dive (at the right angle) thru the atmosphere. This seems pretty extreme, but I don't seem to recall that they went into LEO first or anything.

It seems conceivable to me that humans could do the Jove-Earth leg with the 1 km/s delta-vee to get out and onto an earth-crossing orbit, as you suggest. Just need the right kind of re-entry vehicle and the slowing down can happen in the atmosphere.

So maybe the minimum round trip delta-vee is 3+1+1
a lot less than what we thought when we began discussing it.


That said, suppose the bus that takes people on the J. tour is some big rotating hotel. If you don't spend the fuel to put that in LEO or some orbit when you get back, then that tour-bus is expended.
You can either let the bus go on by and have the people ride back in a little re-entry vehicle. Or you can slow the bus down and store it in LEO---hitch it to a space station or leave it for some future use. So the decisions make the problem more complicated.

I guess I am partial to the simplest form of the problem where you just say what is the minimum delta-vee for a round trip, not attempting to re-use anything.

If some people actually wanted to go live on Callisto, one would not be thinking so much of the problem of getting them home (although return could be provided for). Instead one would probably be thinking of a number of robot-ship one-way trips for machinery and supplies, setting down at some base on Callisto.

Only after a lot of unmanned tonnage had made the trip out there and was waiting on the ground, would you finally let the people travel.
And you might use more delta-vee for them to make the trip faster
(as well as sending them in a rotating cabin to keep them healthy).

But the unmanned supply trips out could be slow and use only the 3+1 km/s which we mentioned----or whatever it is Galileo used---plus whatever is needed to land on Callisto.

It does not seem a heck of a lot different from setting supplies and equipment down on the moon, delta-vee-wise, although the voyage takes a lot longer.

 

[enigma]

Originally posted by marcus
I wonder about this too. The Apollo missions used atmospheric braking on the return and I don't know to what extent thrust played a role, if it did at all. I think they may have approached the Earth essentially at escape velocity and made a dive (at the right angle) thru the atmosphere. This seems pretty extreme, but I don't seem to recall that they went into LEO first or anything.

Apollo didn't do a re-orbit maneuver once they got to Earth. They did a small maneuver to get themselves into the right path for the ballistic re-entry.

They screamed into the atmosphere at over Mach 25.

That's the reason why the half-angle of the Apollo re-entry module was around 45 degrees compared to Gemini's 20. It needed the flow from the front of the heat shield to separate almost immediately so it wouldn't heat up the nadir sides too much.

 

[Janus]

Originally posted by marcus


Who can calculate the payload ratio if you want 10 km/s and are using Tet and Monomethyl. How much of the truck has to be fuel and how much can be payload. It would be nice to know that, I think.

From a quick search on the performance of such engines I come up with a mass ratio of 25. (fully fueled ship vs fueled depleted ship)

I'll have to run some numbers to see if that can be theoretically brought down any by engine design parameters (combustion chamber pressure etc.

 

[enigma]

Originally posted by marcus
Who can calculate the payload ratio if you want 10 km/s and are using Tet and Monomethyl. How much of the truck has to be fuel and how much can be payload. It would be nice to know that, I think.

MMH/N204 has a vacuum Isp of ~333. N204/Hydrazine is slightly better at 340, but has tighter thermal restrictions.

Source:
http://www.astronautix.com

10,000 = - Isp * g_0 * ln \frac{M_0}{M_0 + M_P}

M_P = 19.1 * M_0

Not very good.

 

[marcus]

Originally posted by Janus
From a quick search on the performance of such engines I come up with a mass ratio of 25. (fully fueled ship vs fueled depleted ship)

Janus, this is very welcome input! Both you and Enigma have used the
rocket equation in this thread. Others of us might well be interested in a mini-tutorial showing how to do the payload fraction calculation.

Would you be willing to provide a basic explanation? As I recall one needs only to know the exhaust velocity (from Tet and Monomethyl in this case) and the desired delta-vee.

This set of problems is only gradually getting into focus for me, and perhaps others. I see now that
1.Callisto would be an interesting moon to explore and that
2.even if one imagines eventual manned missions the interesting case to look at, for propulsion requirements, is the one-way unmanned trip, and
3. the experience with Galileo suggests two parts: the initial boost out of low-earth-orbit into transjupiter orbit (or some indirect path involving gravity assists) which could use some less storable fuel, and then a second part for JOI, maneuvering and landing.
--------------
Nereid originally suggested Callisto might be interesting because undifferentiated. Richer chemistry maybe. risk of carbon monoxide?
well let's start by considering unmanned missions
Even if one imagines manned missions might eventually occur they would presumably be preceded by unmanned shipment of equipment and supplies. I am intrigued by the thought that a shipment might be done with something like 3+1+2 where the initial 3 is with non-storable fuel.

In any case, roughly what exhaust velocity should one assume for the fuel and oxidant used in Galileo

 

[marcus]

Well OK, Eric Weisstein's Mathworld
http://scienceworld.wolfram.com/physics/RocketEquation.html
gives it

\Delta v = u*ln(M_0/M)

where u is the exhaust velocity and M_0/M is the ratio
of the initial to the final mass

The exhaust velocity for MMH/N2O4 is about
3100 meters per second.

For JOI and maneuvering in the system suppose one allows
2000 m/s (twice what Galileo apparently got from its main engine)

2000 = 3100*ln(M_0/M)

I get a mass ratio of about 1.9, in that 2 km/s case,

that is, you boost the thing out of LEO and after it does its Jupiter-capture and all its maneuvering it weighs about half of what it did when it left low-earth-orbit.

 

[marcus]

some sources
http://dutlsisa.lr.tudelft.nl/Propulsion/Data/Rocket_motor_data.htm
http://fti.neep.wisc.edu/~jfs/neep533_lect41_chemRkt_99.html

for liquid hydrogen and oxygen the exhaust velocity seems to
be around 4400 meters per second

does anyone have different figures. If that is right for LH2/LOX
and if 3100 is right for MMH/N2O4, then I have to say I am
impressed with the latter pair of chemicals-----storable and still
quite a good exhaust velocity.

 

[enigma]

Originally posted by marcus

where u is the exhaust velocity and M_0/M is the ratio
of the initial to the final mass

Just FYI, you won't find terribly much information giving the exhaust velocities of engines. It is tied up into the specific impulse, Isp.

Isp * sea level acceleration = exhaust velocity.

You will also sometimes see it listed as a characteristic exhaust velocity, 'c'. 'c' is the velocity which the propellant would have if you expand it out the nozzle to an infinite area, which of course, you can't do. It's just the theoretical limit for a specific fuel. If that's all you find, it's usually a decent first cut unless the nozzle is really crappy.

Isp changes with ambient pressure because of the pressure difference between the front of the rocket and the engine outlet. That accounts for 'sea-level' and 'vacuum' Isp.

 

[enigma]

Originally posted by marcus
does anyone have different figures.

Check the astronautix website. They have statistics on practically every rocket, fuel combination, and mission ever built.

 

[marcus]

Originally posted by enigma
Check the astronautix website.

thanks for the link. I went to it earlier, when you gave the link, but was confused by the menu---couldnt see any menu item for propulsion data (may have been staring me in the face, it happens)

the Dutch page http://dutlsisa.lr.tudelft.nl/Propulsion/Data/Rocket_motor_data.htm
seems pretty good though
how does it compare with astronautix?

BTW I got curious about the TU-Delft site and looked further up
in the directory
http://dutlsisa.lr.tudelft.nl/Propulsion/Rocketpropulsion.htm

"In this lecture series the basics of space propulsion are delt with to a level sufficient for selecting the best propulsion system for a given space mission and to perform a preliminary dimensioning and sizing of the system. The lecture series consists of 8 lecture hours of 45 minutes each and forms part of a compulsory lecture series on the basics of space engineering given in the first three years (undergraduate program) of the study for aerospace engineer at TU-Delft, faculty of aerospace engineering."

I guess TU-Delft is the technical university at Delft in the Netherlands. The site has a lot of pages and so far I've only checked out a couple.