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.

[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.

[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.