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Blog: Science A Salute to the Voyagers
Christopher Jennings (Blog) - September 5, 2007 10:17 PM
Print E-mail del.icio.us 28 comment(s) - last by Eris23007.. on Sep 8 at 10:48 AM
September 5th marks the 30th anniversary of the Voyager duo

September 5th was a special date this year. It marks the 30th anniversary of the Voyager 1 spacecraft launch. Voyager 2 was launch shortly before it on August 20th both in 1977. Both spacecraft are still in operation and continue to send us data from space.

 

For those that remember, Voyager 1 and Voyager 2 were the first attempts to send probes to the edge of our solar system passing several planets along the way for analysis and imaging. Voyager 1 is further away from the sun than any other probe we have launched. No ordinary probe would be able to continue operating such a distance from the Sun as solar power from that distance is minimal. The solution was Nuclear Power.


Voyager 1 and 2 use a radioactive isotope (Pu-238) to provide 420W to power the spacecraft. As the isotope decays it generates heat to keep the craft from freezing and electricity to keep it functioning. It is estimated this power source will continue to provide enough power for scientific data transmission until 2020 at which time it is estimated the remaining power won’t be enough to continue operations.

 

Both Voyager spacecraft have a golden record inside that contains information that might enable another star faring race to find and contact or even visit the Earth. The golden disks themselves are copper plated in gold and is played like an old vinyl record. Not exactly high tech but it should get the job done if someone should ever find them.

 

Voyager 1 is estimated to have left our solar system completely and is now in the empty space between ours and the next. Voyager 2 should be crossing into this empty space soon if it hasn’t already.


Some Voyager Milestones:

  • Voyager 1 and 2 were the first to discover volcanic activity on Io.
  • Voyager 2 was the first to discover the dark spot storm on Neptune.
  • Voyager 1 was the first man-made object to exit the heliosheath.
  • Voyager 2 discovered three new moons of Jupiter and 10 new moons of Uranus.
  • Voyager 2 discovered the Great Dark Spot on Uranus, which has since dissapeared.
  • Voyager 1 discovered the first atmosphere on a moon, Titan.

To think that for 30 years probes based on 1960-70’s technology have operated in deep space snapping some of the best pictures of planets and moons of our solar system to date is impressive. Hopefully newer probes will pick up where these left off and breach the edge of the solar system much quicker than the Voyagers.

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deep space 2?
By kattanna on 9/6/2007 2:56:34 PM , Rating: 2
i'd really like to see a new probe using ion engines like on deep space 1, but that uses a RTG for power, maybe even 2 or 3.

our space craft move SOOOOOO slow still we really need to work on that, and solar power just isnt going to cut it.




RE: deep space 2?
By therealnickdanger on 9/6/07, Rating: -1
RE: deep space 2?
By masher2 (blog) on 9/6/2007 4:14:05 PM , Rating: 3
This isn't correct. An ion engine doesn't provide enough thrust to boost from a gravity well. But once in space, they're the most efficient engines we have, and are easily powerable by an RTG.

In fact, NASA has already launched an ion engine-driven spacecraft, powered by RTGs (Deep Space 1).


RE: deep space 2?
By therealnickdanger on 9/6/2007 4:28:25 PM , Rating: 2
You are correct that ion engines don't produce enough gravity to escape gravity, but I never said that they did. All discussion thus far has been assuming we're already in space. Second, DS1's engine was powered by solar arrays, not RTGs, because they lack the power output necessary.


RE: deep space 2?
By therealnickdanger on 9/6/2007 4:39:13 PM , Rating: 2
I should clarify: RTGs can power ion drives (technically nearly anything can), but it would be futile since their power output can't produce enough specific thrust. Even the horrible efficiency of solar arrays dwarfs the output of RTGs for use in space - specifically ion propulsion.

In the event that a probe reaches the limits of what solar energy can provide, RTGs offer a constant flow of power for low-power operations. They are great for many tasks, but not for the KW and MW reactions needed to power ion propulsion with decent thrust. Fission solves the dilema of lacking solar power in the far reaches and also achieves much higher specific thrust.

Once again, nuclear fission FTW.


RE: deep space 2?
By masher2 (blog) on 9/6/2007 5:13:17 PM , Rating: 2
> "All discussion thus far has been assuming we're already in space"

If we're assuming that, then an ion engine works fine. Better, in fact, than conventional propulsion.

> "DS1's engine was powered by solar arrays, not RTGs, because they lack the power output necessary. "

Oops, you're right about the solar array. But an RTG could have provided the power. DS1's engine required only 2.1 KW of power, which could be provided with an array of 5 Voyager-grade MHW-RTGs (or an upscaled version of same).

DS1 went with solar panels as the lifting cost is cheaper, for a probe that isn't going to stray far from the sun. (Despite the name, Deep Space 1 didn't go into "deep space"). But a long-range probe obviously can't use solar panels, so an RTG (or a full-fledged reactor) is really the only choice.

I did a little back-of-the-envelope calculation, and worked out when RTGs would become more efficient than a solar panel. DS1 achieved the best ever power/mass efficiency @ 0.05 kw/kg. The GPSH-RTG used on Galileo had a mass efficiency of 0.005 KW/kg -- 10 times worse. That means that the crossover point is SQRT(10) = 3.2 AU, or about halfway between the orbits of Mars and Jupiter. Outside that, and an RTG is going to be a better power source than a solar power array.

Of course, a true nuclear reactor is considerably more efficient than an RTG, and could well be a better choice than a solar panel even inside the Earth's orbit.


RE: deep space 2?
By kattanna on 9/6/2007 5:26:03 PM , Rating: 3
oh.. now i would LOVE to see a full fledged reactor pumping out power rated in the MW driving an ion engine cluster.

but with the damn near "end of the world" hysteria we see over RTG's, sending up a full scale reactor anytime soon just isnt going to happen. which is a shame.


RE: deep space 2?
By Master Kenobi (blog) on 9/7/2007 8:42:26 AM , Rating: 2
One we get a spacedock built or a moonbase, there is nothing preventing us from sending the pieces up and constructing it in space :)


RE: deep space 2?
By therealnickdanger on 9/7/2007 9:35:12 AM , Rating: 2
After posting, I thought you might break out the RTG-array and burst my bubble! A series of RTGs could certainly get you into the KW range, but at what cost to weight? Also, different probes/vehicles would obviously have different power/heat requirements.

To reach the 2.1KW needed by DS1's engine (2.5KW including other eqipment), you would need 8 RTGs, weighing in at just under 1,000lbs. That's damn heavy considering the probe as a whole weighed in at over 1,000lbs. Since the probe was staying "close to home" and testing out new PV technology as well, the use of RTGs was squashed.

I don't know how much the panels weighed on DS1, but IF they had used RTGs instead, then perhaps they could have programmed DS1 to actually spend the rest of its life testing out the ion propulsion rather than letting it drift near the sun. We'll never know, I guess.

I know that Cassini launched with 3 modern RTGs producing 850W just to power and heat the onboard equipment, so we can assume each RTG generates ~284W in application (the max output is supposedly 300W, but that assumes maximum efficiency). I haven't been able to find figures other than 124lbs for any given RTG design. PV would have been an unrealistic launch option given the weight of panels needed to collect light beyond Mars.

A PV array needed to power a probe like Ulysses (used only one RTG) out near Jupiter would have weighed in at roughly 1,200lbs. With a weight savings of over 1,000lbs, it's clear that RTG was the only answer in that case as well.

RTG is a sweet tech and certainly does a good job for trajectory-based missions, but I still don't think it can adequately serve the needs of an ion drive. One exception may be if we sent up an unpowered device with slots for 20 RTGs, then stockpiled RTGs that we brought up on other missions. Once we had them all "plugged in", then we could send the craft on a 25-year mission with over 5KW of power for the engine and other stuff.

Any idea how much the smallest fission reactor would weigh? Are there any plans to build reactors in space rather than launching them? I'm seriously nerding out over here.


RE: deep space 2?
By masher2 (blog) on 9/7/2007 12:35:23 PM , Rating: 1
> "Any idea how much the smallest fission reactor would weigh?"

NASA's SNAP program launched a reactor into space in the 1960s. I believe the total weight there was around half a ton.


RE: deep space 2?
By therealnickdanger on 9/7/2007 2:08:48 PM , Rating: 2
Those weren't exactly full-blown reactors though, were they?

Here's what I found:
http://nssdc.gsfc.nasa.gov/database/MasterCatalog?...

Snapshot was a military satellite launched from Vandenberg AFB aboard an Atlas Agena D rocket. It carried a SNAP-9A nuclear power source. The onboard reactor provided 500W of electrical power for a 2.2-lb ion engine. The entire weight of the craft was 968lbs. It lasted 43 days before the core was ejected due to failure.
------------

I know that some reactors provide different levels of reaction from material - resulting in different approaches and output, so I suppose it was a loaded question to begin with. I should clarify: how close are we (assuming no cockblocking by the Sierra Club) to getting/building MW reactors in space?


RE: deep space 2?
By masher2 (blog) on 9/7/2007 2:50:27 PM , Rating: 1
SNAP-9 wasn't, but SNAP-10A was a full-fledged reactor...albeit operating at very low power levels.

As for us launching a megawatt-level reactor, from a technological perspective, thanks to our military submarine reactor program (which emphasises high power densities) we've had that capacity to put such a reactor in orbit since the days of the Saturn V. Some submarines have reactors in the 100MW range.

The only barriers today are political, not technological.


RE: deep space 2?
By therealnickdanger on 9/7/2007 3:01:32 PM , Rating: 2
Well... DAMMIT!

Seriously, are there any campaigns, causes, or committees that I can join that would honestly make a difference in terms of advancing nuclear adoption? I'm so sick of this BS.


RE: deep space 2?
By unhingedmaster on 9/8/2007 4:33:30 AM , Rating: 2
Let's start one. I haven't heard of any. But that doesn't mean we couldn't start one.

As the sec. general of the un says on the voyager recordings: "[we]... are but a small part of this immense universe that surrounds us and it is with humility and hope that we take this step."


I could be wrong, but..
By masher2 (blog) on 9/6/2007 1:59:49 PM , Rating: 2
> "Voyager 1 is estimated to have left our solar system completely and is now in the empty space between ours and the next..."

I was rather sure Voyager I hadn't reached the Heliopause yet.




By therealnickdanger on 9/6/2007 2:10:08 PM , Rating: 2
Perhaps he was referring to the shock-layer? Besides, I thought we had a probe that had long since left our system?


RE: I could be wrong, but..
By KristopherKubicki (blog) on 9/6/2007 2:10:46 PM , Rating: 2
It has left the heliosheath though. I suppose it depends on where you claim our solar system ends. They're in coastal waters IMO!


RE: I could be wrong, but..