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Phil Stooke
Interesting news item from The Asian Age:

Quick summary - looks like it's only a feasibility study, so I don't know how far it has gone along the planning and proposal process. But the veteran French planetary balloon proponent Jacques Blamont has been working with Indians on the plans, and one or more balloons in the atmosphere are part of the mission plan.


This is very nice to read about. Although the word "orbiter" does not appear, it seems that an orbiter with no probe/lander is the intention.

There is a lot of potential for Venus exploration, and I'm delighted that India is joining the effort. I was just reading about ESA's Envision mission proposal, and it seems like any Indian orbiter and Envision could accomplish complementary science. For example, SAR at different wavelengths could offer contrasting measurements of surface roughness, more valuable than either alone. But without knowing if Envision will be selected or the instruments of the Indian Venus orbiter, it's too early to say.

I would love to see these orbiters carry out major portions of what can be accomplished from a low orbit, and then perhaps the next U.S. competitive mission selection could focus on goals that can be accomplished with an entry probe/lander.
The AO lists the total scientific payload as ~100 kg, presumably to be divided between the Indian instruments listed as selected in the AO (see below) and any foreign contributions. By comparison, the 2016 EnVision proposed mission's radar unit would have been 176 kg, it's Venus Emissivity Mapper at 14 kg.

Listed instruments to be provided by India:

1. S-Band Synthetic Aperture Radar (SAR)
2. Advanced Radar for Topside Ionosphere and subsurface sounding
3. Ultra Violet (UV) Imaging Spectroscopy Telescope
4. Thermal Camera
5. Cloud Monitoring Camera
6. Venus Atmospheric SpectroPolarimeter
7. Airglow photometer
8. Radio Occultation Experiment
9. Ionospheric Electron Temperature Analyser
10. Retarding Potential Analyser
11. Mass Spectrometer
12. Plasma Wave Detector (Langmuir Probe, Electric Field Sensor and Magnetometer)

The elliptical orbit, initially 500 x 60,000 km, likely will limit the highest resolution imaging by the SAR to the latitude of periapsis.
Bit of buzz about this in Indian press sites recently (via aggregator). E.g.,
a date with Venus in 2023

"We have received great response from across the world, and more than 20 payloads planned," said Isro chairman K Sivan
20 instruments would be quite a packed mission – none of Mars Observer, Voyager, and Cassini had more than 12! I'm hopeful that the Venus Emissivity Mapper is part of the set. This mission would have a highly elliptical orbit, so coverage at high resolution would be limited, but even getting this data for a stripe around Venus could be a nice addition to our understanding.
It appears two Russian payloads by Russian Space Research Institute and Moscow Institute of Physics and Technology have been shortlisted.

From Venus Exploration Analysis Group (VEXAG) 2019

Science objectives:
* Mapping the Venusian surface at high spatial resolution of 30 to 40 meters
* Determining the structure and stratigraphy of surface/subsurface features -- volcanic hotspots
* Determining the structure and composition of the atmosphere
* Understanding Cloud Dynamics
* Investigating Venusian Ionosphere

Indian Proposals: 54
Recommended: 16

International Proposals: 21
Recommended: 7 (USA-3, Russia-1, Russia/France-1)

Collaborative payloads:
* India/Germany: 1
* India/Sweden: 1

This is cheery news. Four (not necessarily fresh) reactions:

1) There is a surface emissivity instrument! Getting this dataset for Venus' surface will be a breakthrough.
2) That's some very high resolution radar, the long-awaited upgrade to Magellan.
3) The sheer number of instruments is unprecedented. That's exciting; maybe creates some risk or complications, at least? How do 23 instruments (actually, the fraction of 23 that needs a line-of-sight) even get a view of Venus at the same time?
4) This mission will be in a highly elliptical orbit, so I'm not sure how the planet will get a comprehensive mapping with [take your surface instrument of choice]. If the latitude of periapsis is equatorial, the high latitudes will get worse coverage unless that latitude migrates throughout the mission.
QUOTE (JRehling @ Nov 6 2019, 06:10 PM) *
This is cheery news. Four (not necessarily fresh) reactions:

I agree that this is a wonderful instrument list, but it would be considered ambitious for a NASA or ESA mission. More means more risk and more tradeoffs between instrument observations.

I'd like to know what the expected volume of returned data is. I also have a memory that the orbiter will be in an elliptical orbit. If so, I'd like to know the latitude of the periapsis and whether that will change over the course of the mission.

My guess is that some instruments will take global measurements while the more data hungry instruments (radar especially but also the thermal emissivity instrument) will take localized measurements, especially if the spacecraft is in an elliptical orbit.

Even if I'm correct in my conservatism, this could be a very nice mission. I don't think it will be a replacement for more focused orbiters designed for large data volume global measurements.
Just came across this tidbit from a presentation to the Planetary Science Advisory Committee summarizing the status of the proposed ESA/NASA EnVision mission (NASA would provide some or all of the SAR instrument). The spacecraft would carry three instruments plus radio science. Here's it's coverage of Venus after it's prime mission:

78 Tbit data return in 4-cycle, with >60% IR and sounder coverage, >15% InSAR and polarimetry coverage (30 m resolution), and 2% high resolution (~2 m resolution)

VEXAG updata
John Moore
Slightly off topic, but appropriate, possible locations for future missions, the IAU yesterday (6 Oct, 2019) approved two new tesserae on Venus -- Jyestha and Istustaya (below).

Note, the singular is 'Tessera', plural 'Tesserae' (Tesserae are the most tectonically, deformed regions on Venus, therefore, representing the oldest materials, according to geological experts).

John Moore

Lest there be any doubt, the planned orbit is highly elliptical: peri=500km, apo=60,000km. That is very similar to Venus Express' orbit, has about the same apoapsis as Venera 15/16 and Pioneer Venus and similar to the planned orbit for Akatskui (the actual apoapsis ended up much more remote). For what it's worth, Mariner 9's apoaspsis at Mars was 16,860 km while Mars Express' is 10,107 km.

Circularizing the orbit on a mission like this is costly and that ends up being paid somehow in mass and complexity. This high instrument count is part of a tradeoff for the elliptical orbit. It means that coverage will not be so complete in time (atmosphere) or space (surface), but given the novelty and diversity of the instruments, it's a pretty good tradeoff. Magellan is the only Venus orbiter that's had a circular orbit, which is ideal for surface instruments, but Shukrayaan-1 is poised to give us great new surface science that will cover a lot of the surface (probably the low latitudes) at high resolution and leave us hungry for a future mission to cover the rest. If it succeeds, it may shift the balance of Venus science goals to surface missions rather than incremental gains from orbit.
ISRO's full presentation on 'Venus Orbiter Mission' at VEXAG 2019 is now available among others.

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