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NASA Europa Missions, projects and proposals for the 2020s
djellison
post Mar 17 2014, 09:31 PM
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QUOTE (algorimancer @ Mar 17 2014, 01:28 PM) *
All of this requires rather a lot of trust in autonomous navigation, but that's just a matter of software.


Navigation isn't a 'matter of software'. It's a matter of the huge, powerful and complex infrastructure of the DSN combined with comms onboard a spacecraft used as two way and indeed three-way links and regular Delta-DOR for accurate navigation. Your proposal would require quite extraordinarily accurate gravity assist for the return flight to Earth ( if the E-J-E free return trajectory is doable without significant propulsive maneuvers ) - that level of accuracy can't be coded away - it requires ground-in-the-loop hardware, comms etc.

Moreover - name a spacecraft - any spacecraft - that flew as far as Jupiter and Back - without requiring human intervention due to safe modes, TCM's, etc etc.

It's a non starter.
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ngunn
post Mar 17 2014, 10:04 PM
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First, a big round of applause for DSN Now. Everybody go look. I've just a small comment on getting low mass spacecraft back to Earth accurately from distant destinations. I think light sailing could play an important role here.
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djellison
post Mar 17 2014, 10:22 PM
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Doesn't matter if you get your delta-V from mono prop, bi prop, ion, solar sail...the navigation challenge still remains.
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Explorer1
post Mar 17 2014, 11:17 PM
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But saving all that mass by not carrying a gigantic HGA has to count for something, right? Galileo navigated just fine with low-gain only.
The main issues in that case would be limiting data corruption on the trip to Earth. And of course, waiting years instead of hours to find out if an experiment had a payoff will play havoc with blood pressure back home!
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mcaplinger
post Mar 18 2014, 02:22 AM
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QUOTE (Explorer1 @ Mar 17 2014, 04:17 PM) *
But saving all that mass by not carrying a gigantic HGA has to count for something, right?

A lot of the mass in a telecom system is in the modulation and RF circuits. The "Small Deep Space Transponder" http://en.wikipedia.org/wiki/Small_Deep_Space_Transponder weighs 3 kg and doesn't include the output power amplifier.

Define a detailed mass breakdown with components you can actually buy and I'll believe it. Until then you're just writing science fiction.


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Explorer1
post Mar 18 2014, 02:49 AM
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Oh, I know it's all SF (per Doug's reply to algorimancer). The accuracy needed for some sort of 'free return' from Jupiter/Europa is implausible.
And honestly the best way to show that it can't work is the fact that no one's tried it yet in 50+ years (even from as close as the Moon!)
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dvandorn
post Mar 18 2014, 03:18 AM
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Actually, the concept of a self-navigating Earth-return planetary probe goes back to the late 1950s, when Charles "Doc" Draper (of the MIT Instrumentation Lab) was approached to design an auto-navigation system for a Mars flyby-and-return probe. The concept was a probe that would autonomously navigate itself to a Mars flyby, expose several rolls of film using automated cameras, and come back for an Earth return.

The probe never made it out of an early study stage, but Draper's early work on it evolved into numerous applications of inertial guidance systems.

-the other Doug


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monitorlizard
post Mar 18 2014, 04:43 AM
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As far as maximizing science return for minimum cost, I've always liked the idea of a Europa flyby craft with high data rate sensors (e.g., high resolution) and a data recorder
of 10 terabytes or more. Do as many flybys as the recorder (and other mission constraints) allow, then boost the spacecraft to a high orbit, away from the intense
radiation. You could then take your time returning the data to Earth without the need for a return capsule or a large spacecraft antenna. Of course, laser communications
would make the whole idea moot.
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mcaplinger
post Mar 18 2014, 05:18 AM
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QUOTE (monitorlizard @ Mar 17 2014, 09:43 PM) *
a data recorder
of 10 terabytes or more...

Using what as a storage medium? Flash is quite radiation-soft and MRAM, while promising, is not dense enough yet.


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monitorlizard
post Mar 18 2014, 05:48 AM
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I am not an expert in such things, but I was thinking along the lines of the Honeywell Aerospace Satellite Data Server.

See http://www.honeywell.com/sites/aero/Data-P...A6EC2FAE1F6.htm

It's radiation-hardened, but of course that's for the Earth orbit environment. Perhaps a combination of this design and spot shielding would enable Jovian operations.
The Honeywell product is 16 Tbits. I believe there are larger recorders, but they may be classified.
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mcaplinger
post Mar 18 2014, 11:58 AM
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QUOTE (monitorlizard @ Mar 17 2014, 10:48 PM) *
I was thinking along the lines of the Honeywell Aerospace Satellite Data Server.

The lack of specs makes this hard to evaluate, but the box looks like it weighs multiple kilos and it doesn't say what memory technology it uses.

A typical box designed for the GEO environment will have a hard time at Jupiter without a lot of extra shielding. A lot.


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vjkane
post Mar 18 2014, 03:47 PM
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My understanding is that the core spacecraft electronics are less of a problem than the sensor electronics. The former can be put inside a radiation shielded vault (think aluminum plates and surrounding fuel tanks). The sensor heads, on the other hand, must be exposed to the environment (although they can be shielded on sides other than their viewing outlet).

NASA is using a lot of the preformulation money to fund radiation hardening of the instruments.


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mcaplinger
post Mar 18 2014, 04:48 PM
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QUOTE (vjkane @ Mar 18 2014, 08:47 AM) *
My understanding is that the core spacecraft electronics are less of a problem than the sensor electronics.

Less of a problem, though getting non-volatile memory to survive is still a significant issue.

At any rate, we were discussing this in the context of a very small spacecraft. IMHO, this is simply infeasible with current technology for a whole host of reasons.

As for sensors, there's nothing I can say without getting into competition-sensitive areas. From an engineering perspective, I don't see a lot of rational and realistic system trades having been made as far as Europa missions are concerned.


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Roly
post Mar 19 2014, 02:22 AM
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Many thanks Mcaplinger, this was very interesting to read. That issue of storage seems to always be "very soon now", I seem to remember chalcogenide / phase change and FRAM being promised in the JIMO-era studies. On the trades, does the option of spending much of the time "standing off" at Ganymede with a suitably massive and impressive mirror make any sense? I only ever saw it proposed in those MIDAS slides, and they were build around what seemed to be special optics.
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mcaplinger
post Mar 19 2014, 03:32 AM
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QUOTE (Roly @ Mar 18 2014, 07:22 PM) *
On the trades, does the option of spending much of the time "standing off" at Ganymede with a suitably massive and impressive mirror make any sense?

Not to me. Shielding is easier to make than big optics and may well weigh less.

If people want to get some insight into some of the engineering that goes into these sorts of missions, the JUICE proposal information is a good read http://sci.esa.int/juice/ JUICE is actually a fairly good start for a Europa mission, too bad they didn't pick our camera sad.gif


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