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Long life Venus rovers and probes

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Winston

Lorenzo von Matterhorn
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JPL's Design for a Clockwork Rover to Explore Venus

https://spectrum.ieee.org/automaton...design-for-a-clockwork-rover-to-explore-venus

Motor-free & wind turbine powered with all-mechanical linkages.

Phase II concept in image below - they're now looking into wheels instead of tracks for Phase III:





Excerpts:

The longest amount of time that a spacecraft has survived on the surface of Venus is 127 minutes. On March 1, 1982, the USSR’s Venera 13 probe parachuted to a gentle landing and managed to keep operating for just over two hours by hiding all of its computers inside of a hermetically sealed titanium pressure vessel that was pre-cooled in orbit. The surface temperature on Venus averages 464 °C (867 °F), which is hotter than the surface of Mercury (the closest planet to the sun), and hot enough that conventional electronics simply will not work.

It’s not just the temperature that makes Venus a particularly nasty place for computers—the pressure at the surface is around 90 atmospheres, equivalent to the pressure 3,000 feet down in Earth’s ocean. And while you can be relieved that the sulfuric acid rain that you’ll find in Venus’ upper atmosphere doesn’t reach the surface, it’s also so dark down there (equivalent to a heavily overcast day here on Earth) that solar power is horrendously inefficient.

The stifling atmosphere that makes the surface of Venus so inhospitable also does a frustratingly good job of minimizing the amount that we can learn about the surface of the planet from orbit, which is why it would be really, really great to have a robot down there poking around for us. The majority of ideas for Venus surface exploration have essentially been the same sort of thing that the Soviets did with the Venera probes: Stuffing all the electronics inside of an insulated container hooked up to a stupendously powerful air conditioning system, probably driven by some alarmingly radioactive plutonium-powered Stirling engines. Developing such a system would likely cost billions in research and development alone.

A conventional approach to a Venus rover like this is difficult, expensive, and potentially dangerous, but a team of engineers at NASA’s Jet Propulsion Laboratory (JPL), in Pasadena, Calif., have come up with an innovative new idea for exploring the surface of Venus. If the problem is the electronics, why not just get rid of them, and build a mechanical rover instead?
(No, obviously NOT ALL of them - otherwise how are measurements and comm relay of those measurements accomplished - just to the greatest extent possible where possible, such as in the mobility technique used for the rover - W)

NASA Glenn Demonstrates Electronics for Longer Venus Surface Missions

https://www.nasa.gov/press-release/...electronics-for-longer-venus-surface-missions

https://www.ozarkic.com/2016/05/17/conference-2016-high-temperature-electronics-conference/

Venus Long Life Surface Package - ESA - Sep 2016

https://arxiv.org/ftp/arxiv/papers/1611/1611.03365.pdf

Just the concept of a probe or rover able to operate long-term at 900°F with computer and comm electronics on-board is just too cool... or hot. From that ESA PDF:

Computing and memory

A general purpose programmable microcontroller is fairly straight forward to design, and is completely digital. Digital electronics has been demonstrated up to 600°C by several groups [Patil et al., 2009, Lanni et al., 2015]. Designs for a 4 bit demonstrator with around 5000 transistors is ongoing at KTH. With a microcontroller unit (MCU) and memory data can be collected from the sensors, and filtered for events to be transmitted. Basic error correcting codes can be added (parity). Some programmability could be added in terms of changing sampling rates or sampling at specific times, with commands received on the radio. The integration level is high enough for a Venus lander microcontroller, the bottle neck is the high temperature memory. Static random access memory (SRAM) is straightforward to design, but requires 6 transistors per bit. At data rates of 1000 bits/second several kilobytes are needed, and this will have to be split on several chips. Non-volatile memory is another alternative, some initial results on ferroelectric materials that maintain their ferroelectricity at 460°C have been achieved, and the density is higher for these (1 transistor per bit). However, total memory sizes is expected to be less than 1 MB.

Radio transmission and reception

The amplifier for the radio transmitter needs to have high enough operating frequency for the 400 MHz band. This requires transistors with high enough gain at these frequencies, and the temperature of 460 °C. The cut-off frequency is also dependent on parasitic capacitances and inductances resulting from the layout of the transistor and its parallel connection. Fortunately the parasitic properties are not temperature dependant. SiC MESFETs and SiC SIT (static induction transistors) have been operated in L and S bands (1 – 4 GHz) but their temperature performance is not well known [Kimoto et al., 2014]. Bipolar transistors have not yet been operated at these frequencies, but their temperature dependence is known, the gain drops about 50 % from room temperature at 300°C and then levels off or even improves. The simultaneous measurement of high frequency and high temperature performance is challenging, since most high frequency probes can only handle 250 °C. Work is being pursued at KTH in the Working on Venus project to demonstrate basic radio circuits at high temperature. A backup solution is to use GaN MMICs for the radio transceiver.

Power supply

The power supply regulates the voltage from the radioisotope thermoelectric generator (RTG). This is typically built from discrete SiC transistors. Several SiC transistor types are commercially available, although their commercial packaging is not operative at 460 °C. Discrete transistors have been tested by KTH and typically the bipolar transistor does not degrade above 300°C. A larger challenge is high temperature decoupling capacitors with enough capacity, but if the RTG delivers a stable output voltage this could be handled. Linear voltage regulators have been demonstrated in SiC operating at 500°C [ValleMayorga et al., 2014, Kargarrazi et al., 2015].

Packaging and module assembly

Commercially used plastic packaging and circuit boards can’t be used at 460 °C. Some ceramic packages for integrated circuits might be usable at these temperatures since the ceramic firing and metal lead assembly is performed at 700°C or higher. However, since normal circuit boards can’t be used, hybrid module technology is a better bet. This uses alumina (Al2O3) substrates with Ag/Pd screenprinted for connections, and wire bonding of chips directly on the substrate without packaging. This type of thick film technology is established in power electronic modules, but has not been tested yet at elevated temperatures. Preliminary work is being pursued at KTH in the Working on Venus project.

 

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