Author Topic: Missions To Titan  (Read 4920 times)

Offline Star One

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Missions To Titan
« Reply #20 on: 03/13/2017 06:34 PM »
Because the northern hemisphere of Titan will be entering its winter in the 2030s would it be worth launching a mission so that it did a tour of the Saturn system before being timed to reach Titan when it starts to exit this period. Or is that tempting fate asking a craft to last an additional period of time.
« Last Edit: 03/13/2017 06:40 PM by Star One »

Offline TakeOff

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Re: Missions To Titan
« Reply #21 on: 03/13/2017 11:01 PM »
One mission might collect samples of Titan's upper atmosphere and of Enceladus' geysers and of ring dust, and bring it home to Earth. The transfer vehicle could park in high (or highly eccentric) Saturn orbit, drop off a daughter vehicle that "clips" the moons and rings to collect flyby samples. When it returns to the mothership, all mass is discarded except for the samples and the return to Earth power.


Insanely expensive.

One problem with any sample return from that distance is that it takes at least as long to return as it does to get there. So you end up with a mission that might take 18 years to complete, and you only get your science payoff at the end. So if the spacecraft dies in year 17, the whole thing has been a waste. And designing and testing a spacecraft to last 18 years is expensive.
Cassini to Saturn cost about $3ŻB. A Falcon Heavy launch of about two-three times a Cassini mass sells today at $0.1B. So tenfolding the mass orbiting Saturn is a pretty trivial expenditure. Flying spacecrafts through comet tails to collect samples has already been demonstrated very successfully. A transfer spacecraft, maybe with fission electric propulsion with complementing chemical rockets taking advantage of "pericronus" for utmost eccentric orbital insertion, could enter an economic orbit of Saturn and release a small battery powered spacecraft to fly through the sample getting plumes, atmospheres and dust clouds. Then docking with the returning spacecraft with its microscopic payloads. Minimum mass sent into Saturn's gravity well.

Cassini was launched 20 years ago in October this year. It has made hundreds of orbits of Saturn, and it was built in the lousy early 1990s. Two decades is not in any way an upper limit for the duration of a space mission, as has been proven. But it would be more than plenty for a sample return from the Saturn system.
« Last Edit: 03/13/2017 11:06 PM by TakeOff »

Offline Dalhousie

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Re: Missions To Titan
« Reply #22 on: 03/13/2017 11:25 PM »
One mission might collect samples of Titan's upper atmosphere and of Enceladus' geysers and of ring dust, and bring it home to Earth. The transfer vehicle could park in high (or highly eccentric) Saturn orbit, drop off a daughter vehicle that "clips" the moons and rings to collect flyby samples. When it returns to the mothership, all mass is discarded except for the samples and the return to Earth power.


Insanely expensive.

One problem with any sample return from that distance is that it takes at least as long to return as it does to get there. So you end up with a mission that might take 18 years to complete, and you only get your science payoff at the end. So if the spacecraft dies in year 17, the whole thing has been a waste. And designing and testing a spacecraft to last 18 years is expensive.
Cassini to Saturn cost about $3ŻB. A Falcon Heavy launch of about two-three times a Cassini mass sells today at $0.1B. So tenfolding the mass orbiting Saturn is a pretty trivial expenditure. Flying spacecrafts through comet tails to collect samples has already been demonstrated very successfully. A transfer spacecraft, maybe with fission electric propulsion with complementing chemical rockets taking advantage of "pericronus" for utmost eccentric orbital insertion, could enter an economic orbit of Saturn and release a small battery powered spacecraft to fly through the sample getting plumes, atmospheres and dust clouds. Then docking with the returning spacecraft with its microscopic payloads. Minimum mass sent into Saturn's gravity well.


Most of the cost of a major science mission is the spacecraft, not the launch.  Regardless of what launches it.  Especially if you include nuclear electric propulsion.  However you look at it it's going to be a multi-billion dollar mission.
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Online Blackstar

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Re: Missions To Titan
« Reply #23 on: 03/14/2017 05:58 PM »

Cassini to Saturn cost about $3ŻB. A Falcon Heavy launch of about two-three times a Cassini mass sells today at $0.1B. So tenfolding the mass orbiting Saturn is a pretty trivial expenditure. Flying spacecrafts through comet tails to collect samples has already been demonstrated very successfully. A transfer spacecraft, maybe with fission electric propulsion with complementing chemical rockets taking advantage of "pericronus" for utmost eccentric orbital insertion, could enter an economic orbit of Saturn and release a small battery powered spacecraft to fly through the sample getting plumes, atmospheres and dust clouds. Then docking with the returning spacecraft with its microscopic payloads. Minimum mass sent into Saturn's gravity well.

Cassini was launched 20 years ago in October this year. It has made hundreds of orbits of Saturn, and it was built in the lousy early 1990s. Two decades is not in any way an upper limit for the duration of a space mission, as has been proven. But it would be more than plenty for a sample return from the Saturn system.

I have heard this before: Falcon Heavy is wonderful, it makes everything possible. I won't bother with that. I just say no to drugs.

"Two decades is not in any way an upper limit for the duration of a space mission, as has been proven."

So here's the thing: spacecraft are designed and tested to certain lifetimes. Generally the upper limit for designing and testing a spacecraft is about 10 years (I'm curious to know of any spacecraft that were designed and tested to a greater than 10-year lifetime). Most science spacecraft tend to be designed and tested to about five years. Designing and testing to longer lifetimes costs more money.

Now here's the other thing: a spacecraft designed and tested to a certain lifetime can last longer than that lifetime, sometimes much longer (see: Voyager, MER). In fact, because of conservative margins, many designers assume that they can probably double the lifetime of their spacecraft.

Now here's an even other thing: sometimes spacecraft die right at their lifetime limits. There was one a few years ago (I forget what--maybe an astrophysics spacecraft, but it died right around its predicted lifetime). So if you really want a spacecraft to last, say, 20 years, then you really have to design the spacecraft to last that long. And that costs a lot of money.

And then, well, here's the thing that I mentioned earlier: sample return usually means that the mission achieves its top science goals only when the sample is brought back. So for a sample return mission to Enceladus, that means that the science payoff only happens after 18+ years. And that's a heck of a long time to wait for the science return. And there are LOTS of other ways to spend that money that return science much much faster. So if somebody comes along and says "Give me that money and I will rewrite the science textbooks in 10 years" [like New Horizons] that's a much better return on investment.


Offline redliox

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Re: Missions To Titan
« Reply #24 on: 03/14/2017 11:30 PM »
And then, well, here's the thing that I mentioned earlier: sample return usually means that the mission achieves its top science goals only when the sample is brought back. So for a sample return mission to Enceladus, that means that the science payoff only happens after 18+ years. And that's a heck of a long time to wait for the science return. And there are LOTS of other ways to spend that money that return science much much faster. So if somebody comes along and says "Give me that money and I will rewrite the science textbooks in 10 years" [like New Horizons] that's a much better return on investment.

I agree about sample returns from the outer solar system.  The flight times are too long coupled with limited guarantees the probes will last forever.  For a better investment at Titan (or Enceladus) it's best to study on site.  At least, unlike Europa, there's nothing like radiation issues to further limit lifetime.
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Offline TakeOff

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Re: Missions To Titan
« Reply #25 on: 03/15/2017 01:12 AM »
Reaching Saturn is not unachievable, it has been done. Cassini entered orbit after 7 years.

After having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail. It could cruise for millennia, but it only takes a few years.

Private rocketry allows for multiplying the mass of space missions for only a fraction of the budget. Cassini spent $0.4B for its launch on Titan IV. Now you can buy ten times as much mass to orbit on 4 Falcon Heavies for that same amount of money (one eight of Cassini's total budget). Maybe missions can use cheaper heavier design and materials to achieve more science and have more redundancy and reach their targets faster? Isn't that pretty obvious?
« Last Edit: 03/15/2017 01:16 AM by TakeOff »

Offline hop

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Re: Missions To Titan
« Reply #26 on: 03/15/2017 04:42 AM »
After having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail.
This is incorrect. You can't lob a sample return capsule from Saturn and have it passively return to earth. For real world examples, see Genesis, Stardust and Hayabusa. All returned samples from targets much closer than Saturn, and two of them came very close to LOM failures in the return phase.

Offline TakeOff

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Re: Missions To Titan
« Reply #27 on: 03/15/2017 11:23 AM »
After having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail.
This is incorrect. You can't lob a sample return capsule from Saturn and have it passively return to earth.
What do you mean, of course one can? NASA missed the Moon when trying to hit it almost 60 years ago, but the precision of space navigation is fantastic today. The location of Saturn's center of mass is known to within one mile! A few grams of gas, ice and dust particles in a safe in a capsule with a heat shield and crash absorption zone, aimed at the middle of the Pacific, seems quite doable. If the return trip takes 7 years, nothing can go wrong with it since it doesn't need to do anything. It's a bullet on a trajectory.

Quote
For real world examples, see Genesis, Stardust and Hayabusa. All returned samples from targets much closer than Saturn, and two of them came very close to LOM failures in the return phase.
Those were the first attempts. A sample return from Venus would be a good quick rehearsal, and of course scientifically very interesting in itself since atmospheric isotope ratios have not been measured in Venus and because proof of active volcanism might be detected, giving data about Venus' inner. At least one of the sample return missions you mention failed because of an entangled parachute, that won't happen every time, and maybe even no proper parachute is needed to crash land a sample weighting less than a pound in the ocean.

A Venus atmospheric sample return mission is mentioned here, at the "Planetary Science Vision 2050 Workshop" very recently. I think it could be applied to all the 8 atmospheric bodies in the Solar system, even to sample Jupiter's Red Spot which might be a plume from deep below:
http://www.hou.usra.edu/meetings/V2050/pdf/8164.pdf
« Last Edit: 03/15/2017 11:29 AM by TakeOff »

Online JasonAW3

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Re: Missions To Titan
« Reply #28 on: 03/15/2017 12:52 PM »
After having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail.
This is incorrect. You can't lob a sample return capsule from Saturn and have it passively return to earth.
What do you mean, of course one can? NASA missed the Moon when trying to hit it almost 60 years ago, but the precision of space navigation is fantastic today. The location of Saturn's center of mass is known to within one mile! A few grams of gas, ice and dust particles in a safe in a capsule with a heat shield and crash absorption zone, aimed at the middle of the Pacific, seems quite doable. If the return trip takes 7 years, nothing can go wrong with it since it doesn't need to do anything. It's a bullet on a trajectory.


Well, in THEORY you could.

      However; there are numerous forces that can cause a deviation of course that would require both mid-course and terminal course corrections.  Some of these are unpredicted gravitational interactions, radiation pressures, micrometeoroid impacts, and solar magnetic variations, just to name a few.

      Yes, for the most part, these are very minor interactions, but the changes that they can inflict, over time, can cause huge course changes at the distances that such a return probe would be traveling.  This could cause a miss of anywhere from a few hundred to a few hundred thousand kilometers, absent at least one or two course corrections.
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Offline TakeOff

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Re: Missions To Titan
« Reply #29 on: 03/15/2017 01:40 PM »
After having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail.
This is incorrect. You can't lob a sample return capsule from Saturn and have it passively return to earth.
What do you mean, of course one can? NASA missed the Moon when trying to hit it almost 60 years ago, but the precision of space navigation is fantastic today. The location of Saturn's center of mass is known to within one mile! A few grams of gas, ice and dust particles in a safe in a capsule with a heat shield and crash absorption zone, aimed at the middle of the Pacific, seems quite doable. If the return trip takes 7 years, nothing can go wrong with it since it doesn't need to do anything. It's a bullet on a trajectory.


Well, in THEORY you could.

      However; there are numerous forces that can cause a deviation of course that would require both mid-course and terminal course corrections.  Some of these are unpredicted gravitational interactions, radiation pressures, micrometeoroid impacts, and solar magnetic variations, just to name a few.

      Yes, for the most part, these are very minor interactions, but the changes that they can inflict, over time, can cause huge course changes at the distances that such a return probe would be traveling.  This could cause a miss of anywhere from a few hundred to a few hundred thousand kilometers, absent at least one or two course corrections.
I think that NASA can recover a probe that lands in the Pacific Ocean, even if off by a thousand kilometers. It could transmit a radio signal once and again in order for its trajectory to be determined, and its atmospheric entry could be observed and it could have a radio or sonic beacon allowing it to be found after landing.

What evidence is there that micrometeorite impacts have put any space craft's landing site off course by any measurable degree? Solar pressure is well known and used in models that simulate tumbling asteroids for centuries. Solar magnetic variations is hardly a problem for space navigation. And how could "unpredicted gravitational interactions" be possible? Astronomers have ephemeris in their blood and have taken care of it extraordinarily well. It is absurdly well known where things are and where they will be. Especially Saturn and Earth. Are you making stuff up just in order to try to argue against me?

The challenge I can see is the propulsion stage that aims the sample return capsule towards Earth. Being active only a very short time in Saturn's neighborhood, taking advantage of a very eccentric orbit and the Oberth effect at perichronus, it could use its mothership Saturn orbiter as a communication relay and for precision localization since the orbiters position is known to within one mile and both the orbiter's and Earth's distance from the return vehicle can be measured down to centimeters by radio waves. More spectacular things have already been demonstrated. Don't need a Jupiter gravity assist or any other maneuver on the return voyage, the very low mass of the sample spacecraft could make the return quick anyway. A spacecraft can hit Earth from Saturn, I'm sure.
« Last Edit: 03/15/2017 01:59 PM by TakeOff »

Online Blackstar

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Re: Missions To Titan
« Reply #30 on: 03/15/2017 02:18 PM »
The next planetary science decadal survey is coming up in a little under four years. That's plenty of time to develop an engineering design and mission proposal to perform this mission. We look forward to seeing your proposal and independent cost estimate.

Offline eeergo

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Re: Missions To Titan
« Reply #31 on: 03/15/2017 02:37 PM »
I think that NASA can recover a probe that lands in the Pacific Ocean, even if off by a thousand kilometers. It could transmit a radio signal once and again in order for its trajectory to be determined, and its atmospheric entry could be observed and it could have a radio or sonic beacon allowing it to be found after landing.

You think ≠ it's reality.

A low-power beacon (and you're restricted to that if you're considering minimal-mass designs) certainly won't help in an off-course trajectory. Think full airplanes with working high-power beacons have been lost in oceans in this decade.

Furthermore, you're grossly underestimating what a small but constant dV can do to your trajectory. We're talking missing **the planet**, not the bullseye landing point.

Quote
Solar pressure is well known and used in models that simulate tumbling asteroids for centuries. Solar magnetic variations is hardly a problem for space navigation.

Really? Source please.

Summary: no, solar effects are not well-modeled over such long distances and timespans.

Quote
And how could "unpredicted gravitational interactions" be possible? Astronomers have ephemeris in their blood and have taken care of it extraordinarily well. It is absurdly well known where things are and where they will be. Especially Saturn and Earth. Are you making stuff up just in order to try to argue against me?

Adding "in their blood", "extraordinarily" and "absurdly" qualifiers to your claims make nothing to support them. In fact, it makes them sound pretentious.

Why do you think spacecraft ranging is performed, just to double-check? It's a critical operation. Bodies are not point-like and their gravitational field is not always well-modeled. Numerical integration errors of the (chaotic) deep space multi-body trajectory solutions are not negligible.

Quote
A spacecraft can hit Earth from Saturn, I'm sure.

So many wasteful TCMs being done...
-DaviD-

Offline denis

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Re: Missions To Titan
« Reply #32 on: 03/15/2017 08:49 PM »
Actually, the issue is not even the perturbations but simply the initial boost to leave Saturn and come back to Earth.
If you want to reach the Earth by a single boost, the applied velocity change should be very accurate in both amplitude and direction. There is absolutely no way you will achieve this accuracy and be on the correct trajectory leaving the Saturn system without additional corrections over time.

Super simplified order of magnitude reality check:
The minimum distance between Earth and Saturn is about 1.25 billion km.
Earth radius: 6370 km.
If you were to just aim at the centre of the Earth and going in straight line, you need to provide an initial velocity direction accurate to within 0.0003 degree, or 1 arcsecond, just to hit somewhere on the Earth (*)

The achievable accuracy on the direction is a function of attitude measurement accuracy (from star trackers) and of the accuracy of the force provided by the thruster's. This latter point is clearly the driver, with errors of the order of a fraction of a degree (0.1 to 0.5 deg would be typical)

So even with perfect knowledge of current position and all disturbances during the return journey, you won't be able to provide an initial delta-V with the correct direction and you won't reach the Earth.

(*) In reality it's a lot tighter as any initial error is likely going to be amplified over time due to orbital motion.

Offline Jim

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Re: Missions To Titan
« Reply #33 on: 06/12/2017 02:20 PM »

After having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail. It could cruise for millennia, but it only takes a few years.

That is completely undoable and nonsense. 

Offline JH

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Re: Missions To Titan
« Reply #34 on: 06/12/2017 03:39 PM »

Quote
Solar pressure is well known and used in models that simulate tumbling asteroids for centuries. Solar magnetic variations is hardly a problem for space navigation.

Really? Source please.

Summary: no, solar effects are not well-modeled over such long distances and timespans.

I'm pretty sure he's talking about YORP. See: https://en.wikipedia.org/wiki/Yarkovsky%E2%80%93O%27Keefe%E2%80%93Radzievskii%E2%80%93Paddack_effect.

It doesn't really have to do with incident solar pressure though. It is about the force on the asteroid by re-emitted energy in the thermal IR being unbalanced because of existing rotation as well as irregularities in the shape of the asteroid.

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