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.

[vjkane]

This is my favorite mission option for the 2nd New Frontiers selection from now. In addition to all the reasons stated above for flying this mission, it would also carry modern instruments that would be much more capable than the mid-1970s technology carried by Voyager.

I wonder if there would be the mass margin to carry an atmospheric probe if it were supplied by another nation.

[tedstryk]

This is my favorite mission option for the 2nd New Frontiers selection from now. In addition to all the reasons stated above for flying this mission, it would also carry modern instruments that would be much more capable than the mid-1970s technology carried by Voyager.

I wonder if there would be the mass margin to carry an atmospheric probe if it were supplied by another nation.

Not only that, but It would catch different seasons on Triton and Neptune. I spoke with those involved with the project at the LPSC in March, and the mass margins would be pretty tight - a probe is unlikely. Still the science and the long range imaging capability is incredible.

[Greg Hullender]

In one of the backup slides, they noted that they would save money by using an Atlas 541 instead of a 551. Using Wikipedia's numbers, that suggests they could increase payload 8.6% if someone (e.g. ESA) wanted to pick up the tab. Unfortunately, I can't find anything in the Argo slides that says what the payload to Neptune would be.

--Greg

[Mongo]

New Horizons masses 478 kg. I assume that Argo would have a similar mass, since it appears to be based on the same bus, with many of the same instruments. 8.6% of 478 kg is 41 kg extra. Is this sufficient for an atmospheric probe plus its carrier, or would the extra mass be better used for more and/or better long-range instruments?

[ugordan]

Is this sufficient for an atmospheric probe plus

I think probe batteries alone would eat up a significant fraction of that margin so I'm not inclined to think you can cram an atmospheric probe into that much mass. Another instrument seems like a much better bet.

[Greg Hullender]

The Galileo atmospheric probe weighed 339 kg, of which 152 was for the heat shield. The Huygens probe weighed 319 kg. Pioneer Venus had four atmospheric probes: a big one, weighing 315 kg, and three small ones weighing 90 kg each.

That last stat sounds promising.

A better question, though, would be whether this would interfere too much with the other work Argos is supposed to do. All these other probes were monitored by orbiters, so it didn't matter if they blew one orbit's observations tracking probes. But every minute of a flyby mission is precious -- or so it seems to me, anyway. Even if it could carry a probe, could it afford to collect the data from it?

--Greg

[Ken90000]

Actually, the Pioneer Venus sent their data directly to Earth. The orbiter had not yet arrived. Of course, I am not advocating the same is possible from Neptune.

[vjkane]

The Galileo atmospheric probe weighed 339 kg, of which 152 was for the heat shield. The Huygens probe weighed 319 kg. Pioneer Venus had four atmospheric probes: a big one, weighing 315 kg, and three small ones weighing 90 kg each.

A better question, though, would be whether this would interfere too much with the other work Argos is supposed to do. All these other probes were monitored by orbiters, so it didn't matter if they blew one orbit's observations tracking probes. But every minute of a flyby mission is precious -- or so it seems to me, anyway. Even if it could carry a probe, could it afford to collect the data from it?

I remember reading that with modern instruments and materials that atmospheric probes can be much lighter today. The probes listed above were all mid-70s technology.

It sounds like Argo would have steerable antenna, so it could in theory handle the relay while still gathering data. Actually, I wonder why it has the steerable antenna since that adds mass and risk. New Horizons has a fixed antenna.

Some alternatives to a traditional atmospheric probe would be (1) a small carrier that takes a Juno-like microwave radiometer to Neptune (such an instrument has been proposed to be carried by possible Saturn entry probes (and discarded prior to entry)) although I have a vague memory that the depth of the water vapor level on Neptune would be so deep that the instrument couldn't measure that far; (2) a carrier that traverse the upper Triton atmosphere for composition measurements; (3) a really good remote sensing radiometer to study the Neptune atmosphere

[mchan]

A steerable antenna would add complexity and cost.

I also find this the most exciting of all the next NF mission proposals. From a self-centered view, it will be the only chance in my lifetime for a revisit to Triton / Neptune.

The key appears to be getting the budget and the RTGs. The Outer Planets Flagship will be underway, and possibly MSR. Constellation will be at high sustained activity on the manned side. All will demand money and Pu-238 (though I am not aware the Constellation will require Pu-238).

[Greg Hullender]

Actually, the Pioneer Venus sent their data directly to Earth. The orbiter had not yet arrived. Of course, I am not advocating the same is possible from Neptune.

Wow! Forgive me, but I found that so hard to believe, I looked it up, and you are correct:

http://www.honeysucklecreek.net/dss44/pioneer_venus.html

Even though Venus was just past inferior conjunction, it was still at least 41 million km away, so that's pretty impressive.

The Small Probes fell through the atmosphere in times varying from 53 to 55 minutes, transmitting telemetry data with only 10 watt transmitters. Though weak, the signals were capable of being received by the 64 metre antennas of the DSN at a rate of 64 bits per second. Once they reached a height of 30 kilometres the data rate dropped to 16 bits per second.

If Argos' antenna were 6.4m, then, one might expect it to be able to collect data from the probe from 4.1 million km away, which ought to be enough in advance of the flyby to present no problems.

All four probes were designed for a descent time of approximately 55 minutes before impacting the surface. None were designed to withstand the impact. However the Small Day Probe did survive and sent data from the surface for an extra 67 minutes. Engineering data radioed back from the Day Probe showed that its internal temperature climbed steadily to a high of 126°C. Then the batteries went flat and its signal disappeared.

One then wonders just how long such a probe might survive on Neptune. Could it even float above its crush depth and still be able to transmit anything?

--Greg

[vjkane]

One then wonders just how long such a probe might survive on Neptune. Could it even float above its crush depth and still be able to transmit anything?

A balloon, if I remember correctly, would work in the atmosphere, and a parachute could allow the probe to transmit for a considerable time, especially since (from memory) the water vapor level is down around 400 bars. In fact, one of the problems with a Neptune probe is that it takes so long to reach the warmer atmosphere that there are (1) severe pressure issues (2) transmission issues (lots of methane to absorb radio waves and (3) relay problems because the relay craft has to stay in line of sight for hours.

One person once told me that a Juno-like microwave radiometer would not work at Uranus and Neptune because of the depth of the atmosphere before you sample all the regions (e.g., water vapor) desired. However, it was an off the cuff remark and I don't know the source. It seems credible.

[Mongo]

It is interesting that from what I read here at Unmanned Spaceflight, NASA is leaning toward a Jupiter orbiter for the third New Frontiers mission, with the candidates from the existing list being Io Observer and Ganymede Observer (I would prefer Io, myself). That would (if Argo is also chosen) result in the first four New Frontiers starts being 'outer solar system' missions (where the outer solar system begins at Jupiter's orbit) and the 11 Discovery starts being 'inner solar system' missions.

New Frontiers 1 : New Horizons --> Jupiter flyby / dwarf planet (Pluto) flyby / small KBO flyby -- launched 2006
New Frontiers 2 : Juno --> Jupiter polar orbiter (focus on Jovian gravity & magnetic fields) -- launch 2011
New Frontiers 3 : Io Observer --> Jupiter orbiter (focus on Io) -- launch 2013
New Frontiers 4 : Argo --> Jupiter Trojan flyby / Saturn flyby / Neptune flyby / dwarf planet flyby -- launch 2017-19

To fly all of these NASA would have to use the Advanced Stirling Radioisotope Generator (ASRG), which it seems they would like to do (at least for Discovery-class missions).

It makes sense that the slightly larger budget per mission New Frontiers program be focused on the more expensive to explore outer solar system, although I would not be upset if New Frontiers 3 ends up being the Venus In Situ Explorer, which is another favourite of mine.

[vjkane]

That would (if Argo is also chosen) result in the first four New Frontiers starts being 'outer solar system' missions (where the outer solar system begins at Jupiter's orbit) and the 11 Discovery starts being 'inner solar system' missions.

The next New Frontiers (#3) will be solar powered because the the tight plutonium supply. I think that makes a Jovian system mission unlikely, although it is probably technically feasible for the Ganymede observer and possibly an Io observer, although the interaction of radiation and solar cells is a big risk.

My guess is that the next New Frontiers (3) will be a comet or a Venus mission and New Frontiers 4 will be an outer planet mission with Argo in competition with a mission to whichever system (Jovian or Saturnian) does get the choice for the Flagship mission.

It's possible that Stirling plutonium Discovery mission could go to the Jovian system, but Juno barely fits in the New Frontiers cost cap. I have doubts that any Discovery mission could, even with a free power source.

[Mongo]

According to this report entitled Radioisotope Power for NASA's Space Science Missions, New Frontiers 3 would be non-nuclear-powered; however Io Volcanic Observer would be a nuclear-powered Discovery-class mission. From Jason's site:

"NASA has commissioned several concept studies for Discovery-class mission that make use of the new Advanced Stirling Radioisotope Generator (ASRG) power source, a more efficient RTG that makes use of plutonium for power. One of these concepts is the Io Volcanic Observer (IVO), a mission to study Io's volcanic activity."

And this entry:

"NASA has decided to make two ASRGs available for the next Discovery-class mission, to be launched in 2013-2014. All previous Discovery-class missions have used solar panels for power. The cost of the RTGs will not be counted against the Discovery mission cost cap. [...] I had thought this was a study for a New Frontier-class mission. I didn't even think of this being a Discovery-class mission."