Uranus Orbiter and Probe (UOP)

[redliox]

Ariel seems like the potential Europa of Uranus; granted, with the limited data, that might be a stretch.

[vjkane]

There's an abstract on Uranus orbiter design challenges for the March LPSC conference

https://www.hou.usra.edu/meetings/lpsc2024/pdf/1285.pdf

This paragraph is interesting:

Power vs Data Return: The Decadal assumption of
three NextGen Mod 1 RTGs provided more than 490 W
of power through end of mission, enabling Ka-Band
communications for science data return. A notional
schedule of daily 8-hr passes was sufficient to return all
data with margin for additional operations. Ka-band at
Uranus (19.5 kbps) is comparable to the lowest data
rates returned by Cassini, which operated at 10 AU
using X-band (14 to 166 kbps [2]).

Recent summaries of RPS availability [3], indicate
that only a single NextGen Mod 1 unit may be available
by 2030; at that reduced power level it is likely that only
X-band communication would be possible, further
reducing UOP data return capability by a factor of ~4.

[Don2]

NASA has to do some sensible priority setting. What do they really need plutonium for? Jupiter missions and mars rovers all work just fine with solar. Solar has even been proposed for Saturn. However Ice giants and the Dragonfly mission can't be done without it. Dragonfly is next in line so that gets its 5 kg. UOP should get most of what is left. That won't leave enough for NF5, but  they will have some good solar powered missions to choose from. The RTG option should be removed from New Frontiers 5 unless DOE finds some more plutonium they forgot to tell NASA about.

I can't find a reference but my recollection is that there is 30kg available. Give Dragonfly 5kg for their MMRTG. Then Uranus gets at least 20kg for two NGRTGs. The 2010 study used three MMRTGs which had equivalent power to 1.5 MMRTGs. Two NGRTGs will be enough for a Uranus flagship, although it will limit what they can do.

What happens to the last 5kg? Maybe put it in an MMRTG, and give it to UOP. Or maybe hold it back for some other use.

With two NGRTGs UOP would start the mission with 490W. That is about the same as Voyager which had 480W. That is enough to work with

One problem that NASA is likely to have with UOP is stopping it from blowing up into an unaffordable mega-project. There are a lot of good instrument ideas. A lot of science will have to be left behind in order to keep it affordable. Limiting the power supply will help with that.

RTG data from Wikipedia and NASA OIG report
https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator
https://oig.nasa.gov/docs/IG-23-010.pdf

[redliox]

NASA has to do some sensible priority setting. What do they really need plutonium for? Jupiter missions and mars rovers all work just fine with solar. Solar has even been proposed for Saturn. However Ice giants and the Dragonfly mission can't be done without it.

Agreed there.  I was surprised when Curiosity got an RTG, so I can only presume they wanted to ensure it'd be long-lived.  I wish they had done the same with InSight so we'd still be receiving seismic data.  I guess the bigger the Mars project the more weight it carries, although if anyone knows the specifics on why RTGs were given to the big rovers do mention.

With two NGRTGs UOP would start the mission with 490W. That is about the same as Voyager which had 480W. That is enough to work with

New Horizons managed with 245W, so anything better than that should be ample with modern technology.  UOP, especially as a flagship, probably would carry more than NH did so it makes a lil sense it'd need 2 or more RTGs of one form or another.  Because of the production limits I wager plans will have to work around 2.

[Blackstar]

New Horizons managed with 245W, so anything better than that should be ample with modern technology. 

NH was a flyby mission that only used its instruments for a short period of time and then took months to transmit the data. That drove the power consumption.

[skizzo]

I'm assuming nothing will be left for Enceladus then?

[vjkane]

I'm assuming nothing will be left for Enceladus then?

Hard to tell. In part, the production of the radioisotopes is scaled to the expected demand, which is driven by overall budgets.

In at least a couple of meetings in the past year, NASA has emphasized that budgets for new missions is a bigger limiting factor than production.

An Enceladus multiple flyby probably can be solar powered. At least a few such missions have been proposed.

[skizzo]

I'm assuming nothing will be left for Enceladus then?

Hard to tell. In part, the production of the radioisotopes is scaled to the expected demand, which is driven by overall budgets.

In at least a couple of meetings in the past year, NASA has emphasized that budgets for new missions is a bigger limiting factor than production.

An Enceladus multiple flyby probably can be solar powered. At least a few such missions have been proposed.

Sure they could go with that one, but definitely not the orbilander they've been talking about

[Blackstar]

In part, the production of the radioisotopes is scaled to the expected demand, which is driven by overall budgets.

I'd emphasize the "in part" part of that sentence. It's been awhile since I heard a briefing on this, but I think that they may have ramped up to a certain production rate by now, but to ramp up to the next level will require an increase in funding. And there's also the aspect of making the Pu-238 into the pellets ("clads") that go into the RTGs. There is a limit to how many of those they can make per year, so increasing the Pu-238 production rate might still run into a processing limitation.

I think the biggest problem facing the planetary program right now is that they don't have a champion in Congress who is willing to fight for big programs and the budgets to achieve them. In the past, the astrophysics program had Senator Barbara Mikulski, and the planetary program had Congressman John Culberson. They are both gone. So who is going to carry the torch for their respective programs? I don't know of anybody. And the traditional ways that Congress worked in the past have really broken down, as one can see with the House of Representatives' record last year (and even tonight). There is much less interest in actually doing things.

[Don2]

I'm assuming nothing will be left for Enceladus then?

Very long term, I think there is a problem. DOE has never come close to meeting their promise of 1.5kg per year of plutonium. The most recent thing I read was that they are claiming to be more than halfway to meeting the 1.5kg per year target. I suppose that means that they produced at least 0.75kg of plutonium in 2023. At that rate it will take 27 years to produce another two NGRTGs for a mission to Neptune. I think they are spending $100 million per year on plutonium production, so that works out to $1.35 billion per NGRTG.  That works out to about 2000x more expensive per kilogram than gold.

I'm sure DOE will be happy to take more of NASA's money in return for promises of more plutonium, but we have seen in the past just what DOE promises are worth. It just doesn't seem like a good investment.

[vjkane]

This slide is from Lori Glaze's presentation at OPAG last November. Note the tag line at the bottom. Presentation available at https://www.hou.usra.edu/meetings/opagnov2023/presentations/Tuesday/0915_Glaze.pdf

[Comga]

New Horizons managed with 245W, so anything better than that should be ample with modern technology. 

NH was a flyby mission that only used its instruments for a short period of time and then took months to transmit the data. That drove the power consumption.

A few issues:
If memory serves, NH launched with 209 Watts of power due to a last minute issue with Plutonium allocation. 
(I had a nice conversation with the guy Alan Stern berated for that, although it really wasn’t under his control.)
It took years, not months, for NH to send back its data using both polarizations, which had power implications.  One can imagine the data bottlenecking for an orbiter with ongoing observations, even if it mandated the use of data compression, which NH chose not to use.
The real limit on operating the instruments on NH was the capacity of the solid state data recorders (2x8 GB) which were filled during the fly-by.  However, those instruments were designed with tight constraints on power usage, which had its costs and limitations.
None of which really changes the arguments about the UOP.

[Zed_Noir]

<snip>
It took years, not months, for NH to send back its data using both polarizations, which had power implications.  One can imagine the data bottlenecking for an orbiter with ongoing observations, even if it mandated the use of data compression, which NH chose not to use.
The real limit on operating the instruments on NH was the capacity of the solid state data recorders (2x8 GB) which were filled during the fly-by.  However, those instruments were designed with tight constraints on power usage, which had its costs and limitations.
None of which really changes the arguments about the UOP.

Don't think they make SSD drives with only 8GB of storage anymore. Or operated a modern chromeBook with 8GB of storage. However they still make 8GB SD memory cards for legacy devices.

From Google lookup, the highest capacity consumer SSD now have 100TB of storage. But even a run of the mill 8TB SSD can hold more data than the current and near future DSN can download for several centuries at the highest current data transmission rate available.

So what is the estimated full storage capacity of the SSD units in the Uranus Orbiter and what is the estimated time to download the contents of those SSDs back to Earth?

[Blackstar]

This slide is from Lori Glaze's presentation at OPAG last November. Note the tag line at the bottom. Presentation available at https://www.hou.usra.edu/meetings/opagnov2023/presentations/Tuesday/0915_Glaze.pdf

Although that's true, it's not the entire story. For instance, how much Pu-238 will be available for a mission if it is approved? The extreme example is the Pluto orbiter. If that was approved, there would not be enough Pu-238 to power it.

The amount of Pu-238 has long been a chicken/egg situation. In some cases, NASA has ruled out missions that required Pu-238 because there was not enough of it. I think in general we'd all like more--more Pu-238 and more missions. I'd also like a supercar and a yacht.

[LouScheffer]

New Horizons managed with 245W, so anything better than that should be ample with modern technology. 

NH was a flyby mission that only used its instruments for a short period of time and then took months to transmit the data. That drove the power consumption.

If the need for more RTGs is driven by the downlink data rate (as opposed to instruments) then it would seem that NASA should put more emphasis on perfecting optical downlink, which can offer roughly 10x the data for the same power (during nighttime at the receiver, so maybe 5-7X over the course of a year).   This would need optical terminals suitable for outer planets, and likely a number of ground terminals more widely dispersed than the current DSN stations, to both allow nighttime access over a wider span of Earth positions, and to allow for weather diversity.   These are engineering and cost challenges for sure, but maybe easier than increasing plutonium production, and entirely under NASA's control.

[Don2]

This slide is from Lori Glaze's presentation at OPAG last November. Note the tag line at the bottom. Presentation available at

I've looked through some of those slides, and they are disappointingly short on hard numbers. It is hard to disagree with Lori Glaze's statement that NASA selections and budgets are the most important factor in how many RTG powered missions get flown. That has been true over the past twenty years. However, if you start asking for 30-40 kg for a Uranus orbiter with 3-4 NGRTGs then you are probably going to find that there isn't enough plutonium.

In principle, with enough lead time and money, it should be possible to produce whatever amount of plutonium is needed. However, I am very worried by how far short of their promised deliveries DOE has fallen. Organizational competence tends to decline over time. As we see with Boeing, that is often irreversible. DOE lost a lot of their mission when the Cold War ended.

Also, changes in health, safety and environmental laws may have made some of their old processes illegal.

[DanClemmensen]

New Horizons managed with 245W, so anything better than that should be ample with modern technology. 

NH was a flyby mission that only used its instruments for a short period of time and then took months to transmit the data. That drove the power consumption.

If the need for more RTGs is driven by the downlink data rate (as opposed to instruments) then it would seem that NASA should put more emphasis on perfecting optical downlink, which can offer roughly 10x the data for the same power (during nighttime at the receiver, so maybe 5-7X over the course of a year).   This would need optical terminals suitable for outer planets, and likely a number of ground terminals more widely dispersed than the current DSN stations, to both allow nighttime access over a wider span of Earth positions, and to allow for weather diversity.   These are engineering and cost challenges for sure, but maybe easier than increasing plutonium production, and entirely under NASA's control.

Better, put the Earthside optical receivers in orbit (maybe 3, in GEO), and connect them via ISL to Starlink. The very expensive link (deep space to GEO) is then not subject to atmospheric conditions. You stay at 10x all the time and no new groundside equipment is needed. As a separate issue, put optical relays at Sun-Venus L4 and L5 to handle conjunctions.

[jimvela]

Don't think they make SSD drives with only 8GB of storage anymore. Or operated a modern chromeBook with 8GB of storage. However they still make 8GB SD memory cards for legacy devices.

From Google lookup, the highest capacity consumer SSD now have 100TB of storage. But even a run of the mill 8TB SSD can hold more data than the current and near future DSN can download for several centuries at the highest current data transmission rate available.

So what is the estimated full storage capacity of the SSD units in the Uranus Orbiter and what is the estimated time to download the contents of those SSDs back to Earth?

I don't believe there are any deep space spacecraft now flying or planned that use consumer SSDs for storage. 

A deep space flight SSR uses heavily EDAC protected storage and has little resemblance to a consumer SSD other than the words "Solid State".

As an example, the next mission I'm working on will have something on the order of 32Gb to 64Gb of storage available, and data from one encounter will take until the next encounter to get downlinked.  Multiple encounters with multiple inner solar system bodies over not quite a decade.

As you point out, generally today the limitation on science collection is the downlink of data from deep space. 

[LouScheffer]

If the need for more RTGs is driven by the downlink data rate (as opposed to instruments) then it would seem that NASA should put more emphasis on perfecting optical downlink, which can offer roughly 10x the data for the same power (during nighttime at the receiver, so maybe 5-7X over the course of a year).   This would need optical terminals suitable for outer planets, and likely a number of ground terminals more widely dispersed than the current DSN stations, to both allow nighttime access over a wider span of Earth positions, and to allow for weather diversity.   These are engineering and cost challenges for sure, but maybe easier than increasing plutonium production, and entirely under NASA's control.

Better, put the Earthside optical receivers in orbit (maybe 3, in GEO), and connect them via ISL to Starlink. The very expensive link (deep space to GEO) is then not subject to atmospheric conditions. You stay at 10x all the time and no new groundside equipment is needed. As a separate issue, put optical relays at Sun-Venus L4 and L5 to handle conjunctions.

Agree that satellites and Earth L4/L5 would be technically better, but they will likely cost a lot more, and would need development.  On the other hand, projects like Cherenkov Telescope Array Observatory are already building lots of large light buckets fairly cheaply (by satellite standards).  Cost of the initial project is 331 million Euros, which includes 4 big telescopes, and many smaller ones, at two sites.   Since the data rate should be roughly proportional to receiver area, and area in space is much more expensive, almost surely the most cost-effective approach would be big mirrors on Earth (even if you need to suspend operations during solar conjunctions).

[Don2]

I don't think that limited power necessarily means limited data return. There are a lot of things that could be tried.

PROBE SIDE:
1/ A large SSD would help some. The ability to store several months worth of data would allow data to be downlinked when antennas were available. Ka band transmission is very vulnerable to weather. Artemis missions will sometimes use a lot of antennas for a few weeks. With a very large data store, it would be possible to work around those interruptions.

2/New space computer technology enabling better compression. This might be particularly useful for videos of the Uranus atmosphere.

3/ New space computer technology enabling on probe processing. Modern cellphones have impressive photo processing capabilities. A processor on the probe could access a much larger volume of data than could ever be downloaded. That could be useful for searches for moons, plumes, lightning and aurora.

4/Large deployable antennas. Data rate is proportional to the square of the antenna diameter. Here is a link to the specs for a 5m Ka band antenna from L3Harris. I think bigger ones are also available.
https://www.l3harris.com/sites/default/files/2021-04/l3harris-5m-unfurlable-ka-band-reflectors-spec-sheet-sas.pdf

GROUND SIDE:
5/ Add antennas at current DSN sites. New 34m antennas are about $60million each . Multiple antennas can be linked together to synthesize a larger dish.

6/ Ka-band performance is very much reduced by atmospheric moisture. There are much higher and dryer sites available than the current DSN stations. There is a lot of land available in the western US at over 7000 feet elevation. In the European time zone, the Canary Islands already host astronomical facilities at over 7000 feet. They have a much dryer climate than Madrid. New antennae could be built in these locations.

7/ For example, the VLA in New Mexico is at over 7000 ft. The ng-VLA will mass produce 18m antennas for about $10 million each. NASA could buy some of those, locate them at a high altitude location, and then rent them to the radio-astronomers when Uranus is below the horizon or when they are no longer needed.

I wrote about the cost of DSN expansion on this thread here: https://forum.nasaspaceflight.com/index.php?topic=55869.0

8/ W-band (about 90 Ghz) could potentially move more data, and it might be worth trying this if you had a high and dry receiving site.

OPTICAL:
9/ I've seen estimates of 250kbits/s for optical from Neptune. However, there are problems with pointing the unit from beyond the orbit of Saturn, and some new technology would be needed. This technology could probably be integrated with laser distance measurement, which could offer millimeter level precision. That would open up some very interesting capabilities for dark matter detection, gravity measurement and radio interferometry, among others.
References in this thread: https://forum.nasaspaceflight.com/index.php?topic=56579.0