New Frontiers 4: Argo? Options

[Mongo]

There does not appear to be a thread about this proposed New Frontiers mission, so I am starting this one. If there is an existing thread that I am unaware of, then by all means merge them.

Argo is a proposed outer solar system multiple flyby mission, rather like an updated Voyager mission, but based on the New Horizons bus, and using a similar instrument suite. It would launch between 2017 and 2019, with either a Jupiter / Neptune / KBO or a Trojan / Saturn / Neptune / KBO trajectory. Even a combined Jupiter / Saturn / Neptune / KBO trajectory is possible.

Neptune would present a much different system than in 1989, as telescopic observations show a more dynamic Neptune atmosphere, due to the change in season, and much more of Triton and the other Neptune satellites would be visible (most of Triton's northern hemisphere was in darkness in 1989, but will be well lit in 2030).

The second big payoff would be the vastly greater access to KBOs (~4000 times the accessable volume of New Horizons), with several already-known large KBOs (400km diameter or larger) within reach. The objects reachable with Argo are expected to include:

18 cold classical KBOs (interesting because they apparently formed in situ beyond Neptune's orbit, rather than further inward)
40 KBOs with diameters between 200km and 400km
9 KBOs with diameters greater than 400km
several binary KBOs

plus the possible Jupiter Trojan early in the mission. The wide expected range of choices allows for the selected KBO to be of very high scientific interest (and naturally, follow-on KBO targets could be selected after the primary KBO target has been selected).

Typical flight times from launch to the Neptune flyby are about 10 years (Jupiter gravity assist) or 13 years (Jupiter Trojan flyby), with the large KBO flyby 2 or 3 years later.

Expected cost including launch vehicle (according to the linked pdf): under $800M with the following strawman instrument package:

High resolution visible camera: New Horizons (NH) or reduced Cassini heritage
Near-IR spectrometer: NH heritage
UV solar & stellar occ. spectrometer: reduced Cassini heritage
Far-IR linear radiometer: Diviner heritage
Magnetometer: replaces NH dust instrument
Charged particle spectrometer: NH heritage
Gimballed high-gain antenna: heritage radio science instrument

The big uncertainty at this point seems to be the availability of plutonium-powered RTGs by the time of launch.

[elakdawalla]

What makes me think that is that clearly Hansen and Hammel believe that the plutonium will be available. I assume it will be purchased from the Russians. Looking back at my notes from an OPAG meeting more than two years ago it seems that there was 15 kilos over and above what MSL will be using available for purchase (maybe more), and that the Russians could start production more easily than the US could, and that they're raising their prices because they realize how much NASA needs it. But it also seems that at least some of those 15 kilos has to be earmarked for the next flagship mission, I don't know how much. The same notes state that each MMRTG uses 2.9 kilos.

Actually, if I understand the situation correctly, as of the time I wrote those notes, MSL was being powered with two MMRTGs, but now they only have one, which is one of the main reasons they'll be limited to MER-like traverse rates -- can anyone confirm this?

One other thing to throw into the mix: NASA appears to be encouraging Discovery proposals employing the new Stirling RTG. I don't think though that a Discovery mission could be selected and flown in time to demonstrate the Stirling technology to make it available for NF4. Hmm. In that link, I quote Alan Stern as saying an MMRTG needs 18 kilos of plutonium, which is rather different from what I wrote above. Anybody who knows anything about this topic, please step in to clear up the numbers!

--Emily

[vjkane]

Both outer planet flagship proposals include the option for Stirling RTG's as an option to the more traditional MMRTG. There was no information in the presentations about which is preferred or how/when the decision would be made. If the Stirling RTGs are used, they would require only about 1/2 the plutonium, as I recall.

From the accountings I have seen, NASA seems to be confident of having enough plutonium for MSL, an outer planet flagship mission powered with MMRTG, and a Discovery mission using Stirling RTGs. Assuming no new supplies of plutonium, Argo could either use the plutonium currently reserved for a Discovery mission or any plutonium not used by the flagship mission if it uses Stirling RTGs. Actually, if the flagship mission uses the Stirling RTGs, there should be enough plutonium left over for a couple of smaller Stirling RTG-based missions.

[Mark6]

From the accountings I have seen, NASA seems to be confident of having enough plutonium for MSL, an outer planet flagship mission powered with MMRTG, and a Discovery mission using Stirling RTGs. Assuming no new supplies of plutonium, Argo could either use the plutonium currently reserved for a Discovery mission or any plutonium not used by the flagship mission if it uses Stirling RTGs. Actually, if the flagship mission uses the Stirling RTGs, there should be enough plutonium left over for a couple of smaller Stirling RTG-based missions.

I hope you are right, but my understanding has been that the total amount of Pu-238 in US and Russia together is just sufficient for MSL, next Flagship, and one Stirling RTG presumably for a Discovery mission. That's how I interpreted the line in Emily's blog: "[Argo] can't happen in the next New Frontiers opportunity because the U.S. doesn't have enough plutonium available for the next New Frontiers to be nuclear-powered." -- as in, the world's current supply is already allocated but more would be produced in time for a 2019 launch. Which presumes that SOMEBODY will restart production of Pu-238.

[vjkane]

I hope you are right, but my understanding has been that the total amount of Pu-238 in US and Russia together is just sufficient for MSL, next Flagship, and one Stirling RTG presumably for a Discovery mission.

It has not been decided whether or not to allow the plutonium to be used for a Discovery mission. I hope not. The New Frontiers class missions which could be done with the Stirling RTG (including several that are being scoped as part of the Discovery program, but which seem to me from very brief descriptions to be too ambitious for the Discovery program -- remember that Grail, which is a very simple (but scientifically very valuable) mission is $375M (although with two spacecraft)). Also, if the outer planets flagship mission can be done with Stirling RTGs, they will use only about half the plutonium currently budgeted (for MMRTGs). That would free up enough plutonium for 1 or 2 New Frontiers class missions. The tradeoff, of course, is the risk of using a new technology on a $3B mission.

I'm hoping for a very frugal and careful use of the remaining plutonium to allow MSL, an outer planets flagship, and 2 New Frontiers class missions.