Author Topic: Battery Powered Titan Entry Probe  (Read 6243 times)

Offline Danderman

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Battery Powered Titan Entry Probe
« on: 05/01/2010 04:55 pm »
Assuming that there is a future Saturn orbiter SOMEDAY, what are the possibilities of building and launching a non-nuclear Titan entry probe independent of the orbiter? In particular, the probe would arrive at Titan when the orbiter was in proximity, to use the orbiter as a radio link.  I also assume that the probe would have some sort of service module for the cruise, and the service module could have solar panels useable during the early phases of the mission, but at some point, either batteries or an APU would have to be used for the later stages of the cruise and for the actual entry.

Another constraint is that the probe would have to be launched AFTER the orbiter, since the orbiter would be a mission requirement. Therefore, the probe trajectory would have to shorten the cruise, maybe by a year or so.

Another implied constraint is that radiation shielding would likely be required, due to a pretty sure requirement for a Jupiter swingby. The radiation shielding might be detached at the same time as the solar panels. Perhaps the solar panels would be designed so that they would not survive the Jupiter swingby (making them lighter), but the probe batteries would begin to operate at that point.

Given that Pioneer 10 had a mass of 258 kg, I am assuming that a 21st century interplanetary probe could have a similar mass. This is too big for a Falcon 1e to send to Titan, but maybe a Falcon 9 class LV with some upper solid stages could do the trick.

Offline ugordan

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Re: Battery Powered Titan Entry Probe
« Reply #1 on: 05/01/2010 05:29 pm »
What would be the added science value of yet another reentry probe which would provide just another surface data point, and an uncontrollable one at that and for only a very limited time? There is no way batteries could be made to support cruise and entry all the way after Jupiter flyby and be light enough at the same time. Although, a Jupiter flyby doesn't necessarily increase radiation dosage much if you compromise for a more distant flyby and corresponding longer total cruise time so solar arrays for cruise aren't completely out of the question.

Pioneer 10 is not a valid comparison as it was a probe with limited science payload and had no entry shielding which would rapidly increase mass. Even Huygens probe itself was heavier than that, and it piggybacked on Cassini so didn't have dedicated service/cruise modules.

Battery power on Titan's surface is also of limited use as the cryogenic temperatures there will freeze everything eventually, you'd get hours of science at the most. IMO, the next step in Titan exploration really mandates RTGs and a hot air balloon is one particularly intriguing concept.
« Last Edit: 05/01/2010 05:31 pm by ugordan »

Offline Danderman

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Re: Battery Powered Titan Entry Probe
« Reply #2 on: 05/01/2010 07:18 pm »
I guess I should have explained that I was looking at a short lived probe, similar to Huygens, not a rover or long term station. With the orbiter moving out of relay range within a few hours, there is not much point to a long term station on Titan, unless it contains its own long range communications system.

Offline ugordan

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Re: Battery Powered Titan Entry Probe
« Reply #3 on: 05/01/2010 07:26 pm »
Then my original question still stands - what would be the additional value of another Huygens probe and bear in mind we're talking about a mission that would cost at least several hundred million $. Sure, you could design your instruments and experiments on the basis of Huygens/Cassini findings, but we're talking about cca 20 years later for a repeat of Huygens.

If it were Mars instead where mission opportunities come up every 2 years, I'd agree with the incremental approach, but in the outer solar system I'd argue only more quantum-leap-ish missions can overcome the long design and transit times until actual science return. We're talking about timescales on the order of entire professional careers. If we could drastically cut down on transit times and launch cost to allow higher risk, higher payoff missions to be flown more often and in faster succession...

Also, why would the probe need to be launched after the orbiter and not together, again the same as Cassini-Huygens? Buying two boosters instead of one slightly larger doesn't sound like a cost reduction.
« Last Edit: 05/01/2010 07:36 pm by ugordan »

Offline hop

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Re: Battery Powered Titan Entry Probe
« Reply #4 on: 05/01/2010 11:01 pm »
Another constraint is that the probe would have to be launched AFTER the orbiter, since the orbiter would be a mission requirement. Therefore, the probe trajectory would have to shorten the cruise, maybe by a year or so.
Given the transit times, wouldn't it make more sense to send them together ? Even if you had to do two (or more) launches and assemble it in LEO, one interplanetary cruise vehicle vs. two should save you quite a bit.

As for non-nuclear surface power, it seems like a rough proposition on Titan. Yes, you could make a probe that lasted longer and did more than Huygens (especially if your orbiter is a Titan orbiter, not a Saturn orbiter), but given the overall cost of the mission, RTGs seem like a clear winner.

Offline Danderman

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Re: Battery Powered Titan Entry Probe
« Reply #5 on: 05/03/2010 02:03 am »
I guess if you are thinking of an entry probe that would cost hundreds of millions of dollar, the above opinion is probably accurate. On the other hand, I am considering a very cheap system, where is where the "battery powered" comes in.


Offline Patchouli

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Re: Battery Powered Titan Entry Probe
« Reply #6 on: 05/03/2010 02:18 am »
Why not use a beta battery as these are cheap to manufacture relatively speaking.
http://en.wikipedia.org/wiki/Betavoltaics

Then use a Sr-90 heat source to keep it all from freezing.

Another power source that may be present on Titian that could be used to argument the beta battery might be wind.
« Last Edit: 05/03/2010 02:19 am by Patchouli »

Offline hop

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Re: Battery Powered Titan Entry Probe
« Reply #7 on: 05/03/2010 04:11 am »
I guess if you are thinking of an entry probe that would cost hundreds of millions of dollar, the above opinion is probably accurate. On the other hand, I am considering a very cheap system, where is where the "battery powered" comes in.
What interplanetary (never mind outer solar system) mission has ever been done for less than hundreds of millions of dollars ? Given the transit time, operations alone will eat a pretty good chunk. Supporting a spacecraft team for 8-10 years for one day of data is really something to avoid unless you have no choice.

A minimal descent probe hitching a ride with something else might get close, but not if it also has to provide it's own launch and interplanetary cruise vehicle. Even the hitchhiker case is dubious: Huygens pretty much fits the bill and it cost well in the the hundreds of millions.

Offline Sparky

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Re: Battery Powered Titan Entry Probe
« Reply #8 on: 05/03/2010 05:34 am »
I was thinking that Titan would be a wonderful place to do ISRU. For starters, the atmosphere is partly Methane, and there are literally entire oceans of the the stuff just laying around. Also, there are ample amounts of water ice all over the place; a well protected astronaut could just pick it up in cobbles off the ground, and the atmosphere is nice and thick to allow for soft landings.

I've wondered if it's possible to run specially designed combustion engines on Titan. Only unlike engines on Earth, which get fuel from a tank and oxidizer from the atmosphere, a Titan engine would get it's fuel straight from the surroundings (like a hose stuck into a lake, or even the atmosphere, if you could remove the nitrogen quickly enough), and it's oxidizer from an on board reserve of Oxigen. An ISRU mission could replenish its supplies of Oxygen from electrolysis on the water it gathers. Great for fueling a sample-return rocket, or maybe a long duration rover.

Offline Robotbeat

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Re: Battery Powered Titan Entry Probe
« Reply #9 on: 05/03/2010 06:40 pm »
Why not use a beta battery as these are cheap to manufacture relatively speaking.
http://en.wikipedia.org/wiki/Betavoltaics

Then use a Sr-90 heat source to keep it all from freezing.

Another power source that may be present on Titian that could be used to argument the beta battery might be wind.
Agreed. There's been a lot of progress made in ultra-low-power (microwatt) electronics, and even getting regular basic readings like temperature, barometric pressure, conductivity, or even composition (and maybe an occasional low-res picture, using a capacitor to get enough energy for one picture a day). A few kilobytes a day (if that... there's a lot you can fit in 1000 bytes... the attached picture is only 949 bytes... imagine a tiny mirror could be rotated, allowing bigger images to be built up, while also detecting changes in weather) could be transmitted to the orbiter when it passes, enough for basic status reports on the weather, and a small, compressed picture. With a small receiver, it could also receive commands.

A small, long-lived probe like this could be quite useful, though it could be very, very small (less than 1 kilogram). There hasn't been a lot of luck with probes this small, but they could provide a very good "force multiplier" for any orbiter missions sent to the outer planets, if they can be made reliable.
See attached 949 byte image.

EDIT: Even powered by a small lithium-ion coin battery (much less than a kilogram) would provide years of microwatt power, though you may still want radioisotope heaters to keep the electronics alive... though, I think it's wise to figure out instead how to make the electronics survive the cold temperatures reliably.
« Last Edit: 05/03/2010 06:49 pm by Robotbeat »
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Offline hop

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Re: Battery Powered Titan Entry Probe
« Reply #10 on: 05/04/2010 05:19 am »
EDIT: Even powered by a small lithium-ion coin battery (much less than a kilogram) would provide years of microwatt power, though you may still want radioisotope heaters to keep the electronics alive...
Is there any battery chemistry that works at titan surface temps (-180c or so) ?

If you already have RHUs, getting a microwatts of electricity out of them shouldn't be a problem. The RHUs on Cassini are about 40 grams and 1 watt thermal.

Of course, you will need more than microwatts to transmit data to your orbiter.

Offline Sparky

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Re: Battery Powered Titan Entry Probe
« Reply #11 on: 05/04/2010 07:04 am »
So are the temperatures so low that internal combustion won't work, or is it simply so OT that it needs it's not relevant?

Offline Sparky

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Re: Battery Powered Titan Entry Probe
« Reply #12 on: 05/04/2010 07:59 pm »
Another thought:

Since the presence of Hydrocarbon lakes were anticipated, Huygens was designed to be buoyant in them. If a Huygens sized probe were to precision landed in such a body, and dropped an anchor to the sea-floor, it could use wave-power to gather and transmit data to an orbiter, assuming that there's enough wind to make any sort of waves. Something like this:


Offline ugordan

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Re: Battery Powered Titan Entry Probe
« Reply #13 on: 05/04/2010 08:07 pm »
If a Huygens sized probe were to precision landed in such a body, and dropped an anchor to the sea-floor, it could use wave-power to gather and transmit data to an orbiter, assuming that there's enough wind to make any sort of waves.

Current data suggests the lake surfaces are very smooth, i.e. calm. Also, drop a lander into a supercold liquid and you're going to be cooling off *very* rapidly. Huygens lived as long as it did because it landed on a solid surface, that was actually one of the early hints on landing day that it didn't land in liquid.

Offline Robotbeat

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Re: Battery Powered Titan Entry Probe
« Reply #14 on: 05/04/2010 08:12 pm »
EDIT: Even powered by a small lithium-ion coin battery (much less than a kilogram) would provide years of microwatt power, though you may still want radioisotope heaters to keep the electronics alive...
Is there any battery chemistry that works at titan surface temps (-180c or so) ?

If you already have RHUs, getting a microwatts of electricity out of them shouldn't be a problem. The RHUs on Cassini are about 40 grams and 1 watt thermal.
Very good point. Might as well stick a thermocouple on that sucker, since you've got a pretty darned good heat sink in the frigid and dense Titan atmosphere. A milliwatt of power could easily be generated.
Quote
Of course, you will need more than microwatts to transmit data to your orbiter.
50 microwatts, if charged up, could transmit more than 2 kilobytes of data a day to a satellite orbiting Titan, like one of the small Orbcomm satellites (42kg each, though will need an RTG, which would likely weigh 20kg). With the milliwatt-level mini-RTG proposed above, this should be cake. What's a good metric to use for transmitting data to a satellite orbiting Titan, assuming the ground transmitter emits in a 45 degree cone (one or two steradians), given an Orbcomm-sized satellite? 1 Joule per kilobyte?

You'd have to carefully time the satellite pass.
« Last Edit: 05/04/2010 11:54 pm by Robotbeat »
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Offline Robotbeat

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Re: Battery Powered Titan Entry Probe
« Reply #15 on: 05/04/2010 11:55 pm »
I wasn't TOO far off. Huygens transmitted at about 10 Watts, at about 2kB/s data rate, at a 120-degree cone (I take it that's about 3 steradians) and was about 60,000km from Huygens at the time. So, assuming that at 3000km, you're about 20 times closer and thus have 400 times the previous signal-to-noise ratio... boy, I'm running out of physics-fu... Let's just say that for Huygens, it was about 5 Joules per kB, or 200 bytes per Joule over 3 steradians, and you'd get much better if your relay satellite were closer, probably better than 1kB per Joule.

Also, if you increase the bandwidth of the transmitter, you'll get higher bitrates, even assuming the same power. So, 1 Joule per kB.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Danderman

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Re: Battery Powered Titan Entry Probe
« Reply #16 on: 05/08/2010 01:50 am »
All I am asking for here is a look at an entry probe that could be a companion to some future Saturn orbiter - what would be a minimum cost version? WHY such a probe should be flown is another story, why was the first one flown?

Offline hop

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Re: Battery Powered Titan Entry Probe
« Reply #17 on: 05/08/2010 09:58 pm »
All I am asking for here is a look at an entry probe that could be a companion to some future Saturn orbiter - what would be a minimum cost version?
Huygens was pretty minimal. That should provide you with a decent baseline for a hitchhiker probe. I wasn't able to find an authoritative cost number in a quick google, but $.5 billion should be a good ballpark. If you want the probe to fly alone, then add the cost of a minimum outer planets mission, say another $0.3 billion or so ?

A second probe could be a bit cheaper, since our knowledge of the planet is better and you can rely on analysis already done for Huygens.

If you are willing to accept more risk, you can probably knock a bit more off of the cost.
Quote
WHY such a probe should be flown is another story, why was the first one flown?
Science. However, re-flying a mission of similar (or less) capable mission would return a lot less science value that the first one.

Offline Danderman

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Re: Battery Powered Titan Entry Probe
« Reply #18 on: 10/25/2010 02:54 pm »
Since I sort of skated around this issue, what would be the marginal cost of adding an RTG to a Saturn probe?


Offline Jim

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Re: Battery Powered Titan Entry Probe
« Reply #19 on: 10/25/2010 04:25 pm »
100s of millions

Offline Danderman

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Re: Battery Powered Titan Entry Probe
« Reply #20 on: 10/25/2010 11:36 pm »
100s of millions

I don't doubt it, the paperwork alone would probably weigh more than the rocket.

Offline Danderman

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Re: Battery Powered Titan Entry Probe
« Reply #21 on: 10/25/2010 11:37 pm »
Here is another question for the experts: if a Titan lander carried LOX, is there a system that could generate power from burning methane?

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