"Dragonfly" Titan explorer drone, NASA funds Johns Hopkins University Applied Physics Laboratory (APL) Options

[rlorenz]

A new post on the Dragonfly website about sampling system testing in APL's new Titan simulation chamber

https://dragonfly.jhuapl.edu/News-and-Resou...he-Flight-Line/

[vjkane]

The latest annual GAO (Government Accounting Office) report on NASA missions provides an update on Dragonfly (there's some more detail on potential technical issues (the focus of the report is on risks to missions; these seem normal for a mission so early in its development).

GAO report


PROJECT SUMMARY

NASA has not yet approved a preliminary cost and schedule estimate for Dragonfly. In September 2020, NASA directed Dragonfly to start planning for a launch readiness date in 2027 because NASA said it was not possible to fund the project's plan for an earlier launch date due to competing budget priorities. This will require replanning development efforts. Dragonfly is continuing to finalize the designs of its science payload and develop its critical technologies before its preliminary design review. The project is tracking a risk that it may experience delays acquiring Domestic Phenolic-Impregnated Carbon Ablator (PICA-D) material used for its spacecraft thermal protection system. Further, the delayed launch readiness date now means the project may benefit from a heavy-lift class launch vehicle that would allow it to arrive at Titan sooner than the medium-class launch vehicle included in the original design proposal. Such a change would affect the design, and the project is currently evaluating its launch vehicle options.
Launch

Uncertainty surrounding the project's launch vehicle could affect the project's design. According to NASA officials, the project could benefit from using a heavy-lift class launch vehicle as it would allow Dragonfly to arrive at Titan almost 3 years earlier, even with a delayed launch. However, in accordance with its original proposal, the project is baselining its design to a medium-lift vehicle, which would allow Dragonfly to arrive at Titan in 2036. In addition, the launch vehicle will need to be nuclear-certified because Dragonfly will use a Multi-Mission Radioisotope Thermoelectric Generator for power. However, of the five candidate launch vehicles, only one is nuclear certified as of August 2020. The project would prefer to have the vehicle selected early in case changes are needed to the design based on the selection. Currently, the project is evaluating its launch vehicle options, which will inform NASA's selection.

[charborob]

According to this article, as of August 2020, the Atlas 5 was the only nuclear-certified launch vehicle.

[Hungry4info]

Apparently Dragonfly might get to Titan three years early thanks to an approved decision to place it on a different, more capable launch vehicle. This is more important than getting the science earlier, it extends the amount of the lifetime of the RTG that's spent on Titan, and reduces how much of the RTG decays meaninglessly en route to the destination.
https://twitter.com/ThePlanetaryGuy/status/...547710372311042

This is information from Lori Glaze, during today's NASA PAC meeting.

[dtolman]

For context, assuming the 2027 launch date is the same, then the arrival date will now be 2033! That slashes the cruise phase from 9 years to 6 years.

I can't find anything on the expected useful lifespan of the RTG for powering flight - but the baseline was 32 months. Does that imply with the reduced cruise phase that we should expect the RTG to be able to power flight for almost 6 years now?

[mcaplinger]

I can't find anything on the expected useful lifespan of the RTG for powering flight...

The RTG charges batteries, which then power flight. Reduced electrical output from the RTG means it will take longer for the batteries to charge, which only affects flight cadence, not the ability to fly, up to the point that the batteries simply can't be charged up enough to keep the vehicle alive at all.

Minor nit: RTG useful lifetime for electrical generation is set by thermocouple degradation, not by Pu decay.

[vjkane]

The RTG charges batteries, which then power flight. Reduced electrical output from the RTG means it will take longer for the batteries to charge, which only affects flight cadence, not the ability to fly, up to the point that the batteries simply can't be charged up enough to keep the vehicle alive at all.

Minor nit: RTG useful lifetime for electrical generation is set by thermocouple degradation, not by Pu decay.

RTG lifetimes are usually quoted, if I remember correctly, as ~14 years. With the original flight time to Saturn of ~7 years and a nominal ~3 year prime mission, this would have left ~4 years for an extended mission.

However, as mcaplinger notes, the power drop off from the RTG is gradual. As long as the battery can still recharge, then the mission could go on for many years, but perhaps with a reduced flight frequency and/or time per flight. Other parts of Dragonfly such as the rotors may go first.

Curiosity works much the same way - the RTG powers a battery that powers travel and high-powered instrument use. There has been talk about the need for reduced levels of activity for Curiosity starting in a couple of so years. One goal has been to get well in into the sulfate-bearing layers before this becomes a hindrance.

[mcaplinger]

Curiosity works much the same way - the RTG powers a battery that powers travel and high-powered instrument use.

It should also be observed that while waste heat from the RTG -- which doesn't tail off very quickly -- is used to keep the internals of MSL warm, the actuators and external instruments use electrical heaters, and that can be a substantial use of energy, especially in the winter.

How Dragonfly compares as far as thermal design I don't know. But at -180C typical temperatures, Titan makes Mars look downright balmy.

[vjkane]

It should also be observed that while waste heat from the RTG -- which doesn't tail off very quickly -- is used to keep the internals of MSL warm, the actuators and external instruments use electrical heaters, and that can be a substantial use of energy, especially in the winter.

I once read a paper or conference abstract on what it would take to enable a rover on Mars to travel hundreds of kilometers during its mission. The key was low temperature lubricants for the wheels. Apparently, a substantial amount of the battery's output goes to warming the lubricant in the wheels.

[Brian Swift]

I once read a paper or conference abstract on what it would take to enable a rover on Mars to travel hundreds of kilometers during its mission. The key was low temperature lubricants for the wheels. Apparently, a substantial amount of the battery's output goes to warming the lubricant in the wheels.

In this podcast interview with JPL material scientist Dr. Douglas Hofmann, I believe he mentioned a goal of developing materials that would allow creation of gears and bearings that could operate without lubricant in off-earth environments. http://omegataupodcast.net/247-bulk-metallic-glass/

[mcaplinger]

Some may recall that a substantial part of the reason for the launch slip of MSL was the failure to get dry lubricants to work. https://www.thespacereview.com/article/1319/1 And as far as I know, they aren't used on M2020 either.

[vjkane]

The Dragonfly science team has just published a paper on the science goals for the Dragonfly mission n The Planetary Science Journal:

https://iopscience.iop.org/article/10.3847/PSJ/abfdcf/pdf

It is an open access paper. I learned quite a bit from it.

[vjkane]

At today's meeting of the Decadal Survey, the chief of the Planetary Science Division, Lori Glaze, provided an overview of the budget and several missions. I captured this screenshot of the Dragonfly slide, which confirms the switch to a heavy lift launcher and the earlier arrival date.

In the QA, she was asked if this switch meant the Falcon Heavy. She said that the actual vehicle would be selected through NASA's launch procurement process which has not started, but that the procurement would be for this class of launcher.

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[JRehling]

As a topic that's more general than any one mission: It seems like there could be a lot of missions returning data during the same timeframe in the early 2030s. If most of Dragonfly, Veritas, EnVision, JUICE, Europa Clipper, and Lucy are all in their prime missions at the same time, that would be a busy time for the data downlink assets.

[Fox]

Many missions like these receive extensions and the spacecraft last far longer than their original timelines. In light of that, I wonder if there is any chance that Dragonfly could eventually reach the Huygens probe landing site, and photograph Huygens?