Jupiter/Saturn Mission Concepts

[kamaz]

Why did you choose just Iapetus... Assuming one could travel to the Saturn system, they would probably also have the ability to visit multiple moons in the system.

That's a lot of delta-v though... http://www.projectrho.com/public_html/rocket/appringraiders.php (the table is halfway through the page)

 

[TMac3000]

Is a optimization problem. But 6000 days are already a dwarf below 20 years - that's a lot of dedication for an astronaut, so a few years more will very likely be no problem for the already convinced.

Morale isn't necessarily the problem...although it is A problem...
The problem is, though you might save fuel with a series of slings, those slings would add some years to your travel time. More time means more food, more food needs more mass. So what efficiency you gain in fuel, you lose in consumables. Am I right?

---------- Post added at 10:34 AM ---------- Previous post was at 10:29 AM ----------

Either send an all-male crew, or have women undergo hysterectomy. You're not going to send anyone below 30 (training!), and with a 16-year trip it means they will be at least 46 at return -- that's generally past the child-bearing age, plus the radiation damage to ovaries is going to be considerable.

Good point. I just wanted to be inclusive--can't have anybody thinking I'm closed-minded:lol:

This is with breaking down CO2, or without?

Without, I think...

N2 is not consumed by humans You may however want to have enough of both O2 and N2 to repressurize the entire ship, possibly several times (in case of decompression).

Correct...N2 is rejected by the body, right? It's there in the ship's atmosphere so we don't have one spark that incinerates us. So you recommend maybe doubling the size of the O2 and N2 tanks?

---------- Post added at 10:38 AM ---------- Previous post was at 10:34 AM ----------

Why did you choose just Iapetus... Assuming one could travel to the Saturn system, they would probably also have the ability to visit multiple moons in the system.

Iapetus would be the primary target, but there is no reason we can't have Arroway do a Saturn sling and examine a few other moons before settling into a polar Saturn orbit.

 

[fsci123]

Im pretty sure sending a crew into the system just as a flyby will be far easier(but just as symbolic) than landing and colonizing a strange moon. You could carry along several thousand nano sats to observe the Saturn system and use robotics to remotely explore moons from orbit.

And the 16year trip...That sounds more like a prison than a mission. You should consider shortening it.

I developed a Saturn Tour mission. I could give you the details on my mission and you could base some things off that.

 

[kamaz]

So you recommend maybe doubling the size of the O2 and N2 tanks?

Take a look at this study of a Mars mission, page 207.

 

[TMac3000]

That is very interesting! I will give it a much closer look tonight.

---------- Post added at 01:28 PM ---------- Previous post was at 01:25 PM ----------

And the 16year trip...That sounds more like a prison than a mission. You should consider shortening it.

Sixteen years is for both ways, via Hohmann orbit, and assumes 4 years on site. It can be shortened to 13, depending on the date of the next Earth window after landing.

I don't know of any way to make it shorter than that without straining dv requirements

 

[Urwumpe]

I don't know of any way to make it shorter than that without straining dv requirements

You could for example look for a jupiter assist, which does only slightly strain the dv budget - or use Saturn or Titan aerobraking.

 

[TMac3000]

The Jupiter flyby sounds good--I think I'll avoid a Venus sling.

Next question: propellant tank size.

There is a Saturn launch window on Feb 21, 2017 with arrival March 10, 2023. This is when Arroway/Sharapova will launch.

If MINOTAUR launches at the next Hohmann window after that--March 6, 2018, with arrival March 23, 2024--we will need 15,732 m/s dv for the trip there. For the trip back, we can depart March 1, 2025 and return to Earth as triumphant heros on March 18, 2031. This would take another 15.7 km/s. Add a 20% fudge-factor, and we're going to need a dv budget of about 38 km/s.

I guess I need to know the ship's final mass before determining what sort of propellant is needed:hmm:

 

[kamaz]

Try that study:

https://info.aiaa.org/Regions/Weste...ip Discovery (SSD) Paper (AIAA-2009-5309).pdf

 

[TMac3000]

That's awesome! I have only one objection--maybe I just haven't read in enough detail yet, but LH2? I know that most NTRs call for this, but it's volatile stuff--that would need to be one heavily armored core tank, otherwise one pea-sized micrometeorite could blow you right to hell.

 

[Urwumpe]

That's awesome! I have only one objection--maybe I just haven't read in enough detail yet, but LH2? I know that most NTRs call for this, but it's volatile stuff--that would need to be one heavily armored core tank, otherwise one pea-sized micrometeorite could blow you right to hell.

Sorry - no. One pea-sized micrometeorite could punch a large hole into the tank and make it vent high-pressure H2.

But if you have no oxygen-hydrogen mixture you can also have no explosion. Pure hydrogen does not explode.

 

[TMac3000]

Ah...good point. I guess that's why we got by with using LH2 in the Shuttle

 

[Urwumpe]

Ah...good point. I guess that's why we got by with using LH2 in the Shuttle

At least the LH2 had always been a pretty simple risk. On the pad, you need some protection against H2 vapours, because excessive H2 is a sign for a leakage which could turn into a real danger.

But even if the completely filled LH2 tank in the ET would have ripped open and tons of LH2 evaporated and caught fire in the air.... the resulting deflagration would likely have been survived by the crew inside the Shuttle.

 

[kamaz]

That's awesome! I have only one objection--maybe I just haven't read in enough detail yet, but LH2? I know that most NTRs call for this, but it's volatile stuff--that would need to be one heavily armored core tank, otherwise one pea-sized micrometeorite could blow you right to hell.

In principle, an NTR will run on any fluid, including milk -- the problem is that Isp suffers greatly if you use anything but hydrogen (I think projectrho has Isp values for non-LH2 propellants somewhere).

However, since you are going to Saturn, and you want to stay for a couple of years, then you don't need to take return propellant -- because you will have a lot of ice available (all these moons are made of ice!).

You can also go jet-setting between the moons: after you land, load up some ice into the electrolysis module (bimodal NTRs double as power plant!) , and you are good to go for the next moon. You can also use produced oxygen for breathing. Or water for drinking / sanitation. So you need to take less water from Earth, which means less mass.

If I was designing the mission, I would never start with Iapetus, because it's out-of-plane. I would first go to a relatively small in-plane moon, refuel, and then go jumping around. Can also use Titan for gravity assists. Titan landing... um, it's a different pair of shoes. I think you need wings. On the other hand, you can land on the shore of Kraken Mare and just suck liquid CH4 into your tanks without electrolyzing stuff -- NTR performance on LCH4 is decent IIRC.

If you have water, then you are only limited by the fissile stock inside the reactors and the endurance of the engines -- these can be made arbitrarily large (within reason); the NERVA/ROVER program logged hours of combined burn time.

Better yet, switch your NTRs for LANTRs, at least in landers. Then you can trade thrust and Isp as needed. Sweet thing for landers/shuttles... Look for Stan Borowski's papers on NTRS.

One more thing... NTR stage disposal on returning home (you don't want a hot NTR core to enter Earth's atmosphere, because it's a Chernobyl-level contamination). The way it's normally addressed is that you do a hyperbolic Earth encounter, the crew transfers to an Orion or something like that, separates, and does a correction burn to aerobrake. The actual spacecraft zips past Earth on autopilot, then does a burn to raise periapsis to 1.1 AU. Another option is to crash it on the Moon, although that significantly complicates your encounter planning.

 

[fsci123]

NTR + H2O equals heaven. Everything beyond Ceres is covered in water ice which can be easily extracted for use in a rocket.

 

[dgatsoulis]

The Jupiter flyby sounds good--I think I'll avoid a Venus sling.

Next question: propellant tank size.

There is a Saturn launch window on Feb 21, 2017 with arrival March 10, 2023. This is when Arroway/Sharapova will launch.

If MINOTAUR launches at the next Hohmann window after that--March 6, 2018, with arrival March 23, 2024--we will need 15,732 m/s dv for the trip there. For the trip back, we can depart March 1, 2025 and return to Earth as triumphant heros on March 18, 2031. This would take another 15.7 km/s. Add a 20% fudge-factor, and we're going to need a dv budget of about 38 km/s.

I guess I need to know the ship's final mass before determining what sort of propellant is needed:hmm:

I definitely wouldn't choose a Hohmann trajectory to Saturn.
You need roughly 110.25 km²/sec² C3 → V∞ = 10.5 km/s → TSI burn from 200 km parking orbt ~7.43 km/s
semimajor axis ~5.5 AU, Flight time ~ 6 years

With slightly less C3 (~100 km²/sec² → about 7.1 km/s of dV for the TJI burn from the same parking orbit) you can get to Jupiter in less than 600 days and from there sling to Saturn in about another 700-800 days.
The downside is the high arrival velocity, (~16.5 km/s of hyperbolic excess velocity) which makes an aerocapture at Saturn impossible. But I think you can use Titan to slow you down enough, so that you stay in the system.

You get ~ 4 months stay in the Chronian system, so the manned ship will go straight for the target moon and the rest of the science will be done by robots.
For the way back you have ~1100 days to Jupiter and from there a sling to get to a hohmann transfer to Earth with a transfer time of ~850 days and an encounter velocity of ~18 km/s.

So for a preliminary study, we are looking at ~ 600+750+120+1100+850 = 3420 days for the round trip. (Slightly less than 9½ years).

So compared to the Hohmann-to-Saturn, you'll need ~0.6 times the consumables, and slightly less dV for the TJI burn, both of which mean less fuel to push all that mass around.
If you are interested, I can have a look during the weekend and post a more detailed trajectory plan.

 

[TMac3000]

If you are interested, I can have a look during the weekend and post a more detailed trajectory plan.

I am:yes: Thanks!

That flight plan sounds a bit tricky, especially the Saturn encounter--but the savings sound completely and utterly worth it

 

[TMac3000]

I can't believe I didn't think to ask this earlier--though I'm sure you guys would have said something if it mattered: How bad is the radiation at Saturn? Googleing the subject came up with nothing useful.

 

[ISProgram]

Saturn doesn't have radiation, at least nowhere near as the levels encountered at Jupiter. Cassini-Huygens is still standing strong after 10 years at Saturn, but Galileo was irreparably damaged by radiation after being in orbit for 8 years. Juno will only stay a Jupiter orbiter for only 1 year, the radiation is that bad...

No Saturn mission concept will mention requiring a radiation vault either.

 

[K_Jameson]

The Saturn environment is much more benign than at Jupiter. Saturnian radiation belts are comparable to the Uranian ones, and not much stronger than Earth's Van Allen belts.
At the Iapetus distance from Saturn, the belts are not a concern.

No Saturn mission concept will mention requiring a radiation vault either.

Exactly.

Shakespeare/Pope, that will encounter at Uranus an environment similar to Saturn, don't have a radiation vault. :thumbup:

 

[TMac3000]

Thanks guys!

Not to get too hypothetical here, but at Iapetus's distance from her primary (some 3.5 million km), the radiation would be too far away to be dangerous to humans even if it was as bad as Jupiter's, yes?