VERITAS and EnVision

[Orionwillstay]

My first post at NASASpaceflight.com - greetings to all! 

I'm very excited about the recent selection of 3 missions to Venus, and yet puzzled by the similarities (or differences) between VERITAS and EnVision. I realize that EnVision features atmospheric studies of Venus and has a ground-penetrating radar - both will be absent on VERITAS, while VERITAS will have better ground-mapping coverage of Venus, as well as better altimetry and gravity measurement accuracy. But may I know what makes the differences? Is that because of the presence or absence of an equipment, or other factors like using a different orbit or different operational approaches?

Also, apart from the ppt slides from VEXAG, may I know if there's a detailed proposal/report for VERITAS out there, similar to EnVision's Yellow Book please?

Many thanks,
William 

[dsmillman]

The best write-up:

https://trs.jpl.nasa.gov/bitstream/handle/2014/45906/15-4648_A1b.pdf?sequence=1

[Orionwillstay]

The best write-up:

https://trs.jpl.nasa.gov/bitstream/handle/2014/45906/15-4648_A1b.pdf?sequence=1

Thank you!!

[vjkane]

After their selections, I put together a table comparing the VERITAS and EnVision missions. A big caveat - I don't understand SAR systems and variations, so I may well have captured information incorrectly.

Key difference is in the types of radar systems including their frequencies, but the nuances of these are beyond my knowledge.  What I did get out:

VERITAS - strengths
- Global mapping at 30 m resolution
- Targeted mapping of ~27% of the surface at 15 m
- High quality global altimetry maps
- <0.2% of the surface studied for deformation changes

EnVision - strengths
- More intense studies over the 30% of surface judged to be most interesting based on previous maps
- 30 m resolution over the entirety of the focal areas, 2-3% of the planet (within focal areas) mapped at 10 m
- ~7% of the surface studied for deformational changes
- Stereo coverage over the focal areas that will also produce a lower quality altimetry map than VERITAS
- Radiometric studies over 93% of the planet
- I believe that the subsurface sounding radar will map almost the entire planet

Both missions will carry what appears to be an identical/very similar Venus Emmisity Mapper that will map surface composition in a few bands plus some studies of clouds and water vapor.  EnVision will also carry two addition spectrometers for atmospheric studies.

Net: Both missions will overlap goals for mapping the surface at 30 m and in using the VEMS instrument. Otherwise, their goals appear to be complementary.

[Orionwillstay]

After their selections, I put together a table comparing the VERITAS and EnVision missions. A big caveat - I don't understand SAR systems and variations, so I may well have captured information incorrectly.

Key difference is in the types of radar systems including their frequencies, but the nuances of these are beyond my knowledge.  What I did get out:

VERITAS - strengths
- Global mapping at 30 m resolution
- Targeted mapping of ~27% of the surface at 15 m
- High quality global altimetry maps
- <0.2% of the surface studied for deformation changes

EnVision - strengths
- More intense studies over the 30% of surface judged to be most interesting based on previous maps
- 30 m resolution over the entirety of the focal areas, 2-3% of the planet (within focal areas) mapped at 10 m
- ~7% of the surface studied for deformational changes
- Stereo coverage over the focal areas that will also produce a lower quality altimetry map than VERITAS
- Radiometric studies over 93% of the planet
- I believe that the subsurface sounding radar will map almost the entire planet

Both missions will carry what appears to be an identical/very similar Venus Emmisity Mapper that will map surface composition in a few bands plus some studies of clouds and water vapor.  EnVision will also carry two addition spectrometers for atmospheric studies.

Net: Both missions will overlap goals for mapping the surface at 30 m and in using the VEMS instrument. Otherwise, their goals appear to be complementary.

Thank you very much vjkane!

In addition to the features you've pointed out for each of the mission, I read that VERITAS will conduct gravity measurement  better than what EnVision will do. Wonder if that's something to do with the orbit of each? Seems VERITAS will have an orbit more circular than EnVision's, if I'm not mistake. 

[vjkane]

VERITAS orbit: 180 x 255 km, 88.5°

EnVision orbit: 220 x 520 km, 88.5

It would make sense that VERITAS would make better gravity measurements than EnVision given its tighter orbit.

At a briefing just after the VERITAS selection, the PI stated that the mission has considerable mass margin and hinted (strongly I think) that additional instruments of opportunity might be considered*.  If launch is now ~2028, they may have time to consider such an option.  Another possibility might be to add a communications relay to the orbiter to support possbile future landed or balloon missions.

*The idea of prime missions carrying CubeSats to deploy has been suggested several times and is the plan for the Hera mission. I have wondered about a spacecraft hosting attached CubeSat units that contain the instrument and supporting electronics but that have simple (a power cable and a USB cable?) interfaces to the main spacecraft. Might simplify the design of the "CubeSats" (don't need to be independent spacecraft) but also minimizes the complexity of the interface and hosting of additional instruments. But I'm not a spacecraft engineer, so this may just be a wild speculation.

[Orionwillstay]

VERITAS orbit: 180 x 255 km, 88.5°

EnVision orbit: 220 x 520 km, 88.5

It would make sense that VERITAS would make better gravity measurements than EnVision given its tighter orbit.

At a briefing just after the VERITAS selection, the PI stated that the mission has considerable mass margin and hinted (strongly I think) that additional instruments of opportunity might be considered*.  If launch is now ~2028, they may have time to consider such an option.  Another possibility might be to add a communications relay to the orbiter to support possbile future landed or balloon missions.

*The idea of prime missions carrying CubeSats to deploy has been suggested several times and is the plan for the Hera mission. I have wondered about a spacecraft hosting attached CubeSat units that contain the instrument and supporting electronics but that have simple (a power cable and a USB cable?) interfaces to the main spacecraft. Might simplify the design of the "CubeSats" (don't need to be independent spacecraft) but also minimizes the complexity of the interface and hosting of additional instruments. But I'm not a spacecraft engineer, so this may just be a wild speculation.

Maybe adding Cupid's Arrow to VERITAS  ~ that will be even more scientifically appealing and similar to the VOX concept you had wrote about in your blog.

I fully agree that CubeSats add value to the prime missions and am very exciting to see more and more proposals of such lately! Not a spacecraft engineer here as well, but I also think that CubeSats having simple interfaces with the main spacecraft do deserve R&D - they'll be like extra pair of "hands" to the main, and can be immensely useful especially for a lander mission.

[vjkane]

At a briefing just after the VERITAS selection, the PI stated that the mission has considerable mass margin and hinted (strongly I think) that additional instruments of opportunity might be considered*.  If launch is now ~2028, they may have time to consider such an option.  Another possibility might be to add a communications relay to the orbiter to support possbile future landed or balloon missions.

*The idea of prime missions carrying CubeSats to deploy has been suggested several times and is the plan for the Hera mission. I have wondered about a spacecraft hosting attached CubeSat units that contain the instrument and supporting electronics but that have simple (a power cable and a USB cable?) interfaces to the main spacecraft. Might simplify the design of the "CubeSats" (don't need to be independent spacecraft) but also minimizes the complexity of the interface and hosting of additional instruments. But I'm not a spacecraft engineer, so this may just be a wild speculation.

Maybe adding Cupid's Arrow to VERITAS  ~ that will be even more scientifically appealing and similar to the VOX concept you had wrote about in your blog.

I fully agree that CubeSats add value to the prime missions and am very exciting to see more and more proposals of such lately! Not a spacecraft engineer here as well, but I also think that CubeSats having simple interfaces with the main spacecraft do deserve R&D - they'll be like extra pair of "hands" to the main, and can be immensely useful especially for a lander mission.

With the DAVINCI+ atmospheric probe, there's no need for Cupid's Arrow.

[Orionwillstay]

At a briefing just after the VERITAS selection, the PI stated that the mission has considerable mass margin and hinted (strongly I think) that additional instruments of opportunity might be considered*.  If launch is now ~2028, they may have time to consider such an option.  Another possibility might be to add a communications relay to the orbiter to support possbile future landed or balloon missions.

*The idea of prime missions carrying CubeSats to deploy has been suggested several times and is the plan for the Hera mission. I have wondered about a spacecraft hosting attached CubeSat units that contain the instrument and supporting electronics but that have simple (a power cable and a USB cable?) interfaces to the main spacecraft. Might simplify the design of the "CubeSats" (don't need to be independent spacecraft) but also minimizes the complexity of the interface and hosting of additional instruments. But I'm not a spacecraft engineer, so this may just be a wild speculation.

Maybe adding Cupid's Arrow to VERITAS  ~ that will be even more scientifically appealing and similar to the VOX concept you had wrote about in your blog.

I fully agree that CubeSats add value to the prime missions and am very exciting to see more and more proposals of such lately! Not a spacecraft engineer here as well, but I also think that CubeSats having simple interfaces with the main spacecraft do deserve R&D - they'll be like extra pair of "hands" to the main, and can be immensely useful especially for a lander mission.

With the DAVINCI+ atmospheric probe, there's no need for Cupid's Arrow.

I see there might be much less merit for Cupid's Arrow now that we have DAVINCI+, but would that mean the data for the upper-most part of the Venusian atmosphere being left out, assuming DAVINCI+ will not start collecting atmospheric data until the heat shield and backshell drop?

[vjkane]

I see there might be much less merit for Cupid's Arrow now that we have DAVINCI+, but would that mean the data for the upper-most part of the Venusian atmosphere being left out, assuming DAVINCI+ will not start collecting atmospheric data until the heat shield and backshell drop?

Cupid's Arrow was going to get as deep as it could to get well-mixed atmosphere (although there apparently was controversy whether or not it would get deep enough to do that).  It wasn't going to sample a profile of the atmosphere - dive, collect sample, ascend, process sample. At best it would add just one point to the sampling column.

[Orionwillstay]

I see there might be much less merit for Cupid's Arrow now that we have DAVINCI+, but would that mean the data for the upper-most part of the Venusian atmosphere being left out, assuming DAVINCI+ will not start collecting atmospheric data until the heat shield and backshell drop?

Cupid's Arrow was going to get as deep as it could to get well-mixed atmosphere (although there apparently was controversy whether or not it would get deep enough to do that).  It wasn't going to sample a profile of the atmosphere - dive, collect sample, ascend, process sample. At best it would add just one point to the sampling column.

Understood  Thanks vjkane!

[Don2]

The radars for both missions appear to be developed by the same JPL team, lead by Scott Hensley. Presumably they will try to build radars with complementary capabilities.

VERITAS uses an interferometric design at 8GHz. The strength of the mission is global topography, with a 250m post spacing and 5m height accuracy. It can measure surface deformation with 2mm precision. The radar is called VISAR. They mention a 300W TWTA, which is a lot less powerful than the EnVision radar.

EnVision is more imagery focused. It operates at 3 GHz. It is sensitive to polarization which can measure surface roughness. At one time they were talking about 1m resolution over small areas, but at present the highest resolution they are promising is 10m. The instrument is called VenSAR. Transmit power is 2kw and it has a 5.8 by 0.7 m antenna.This radar appears to be a lot more powerful than VISAR. It can also function as a radiometer, and measure temperature with 1.7K accuracy.

Link to ESA yellow book. https://www.cosmos.esa.int/documents/5763359/5763378/EnVision_YB_final.pdf/e9612355-67de-42a3-c25a-af1683f6fda3?t=1616679461807

[vjkane]

EnVision is more imagery focused... At one time they were talking about 1m resolution over small areas, but at present the highest resolution they are promising is 10m.

The 1 m resolution was based on a prior plan to use a European-supplied SAR instrument instead of the JPL-supplied instrument.

[Don2]

EnVision is more imagery focused... At one time they were talking about 1m resolution over small areas, but at present the highest resolution they are promising is 10m.

The 1 m resolution was based on a prior plan to use a European-supplied SAR instrument instead of the JPL-supplied instrument.

Yes, I know, but the specs for power, antenna size and frequency don't seem to have changed much from the earlier European radar. I wonder why they backed off on their performance promises? 1m resolution would be real nice, even if it only covered a small area.

There is a December 2020 paper that compares the two radars. I don't have access, but maybe somebody here does.

S. Hensley, B. Campbell, D. Perkovic-Martin, K. Wheeler, W. Kiefer and R. Ghail, "VISAR and VenSAR: Two Proposed Radar Investigations of Venus," 2020 IEEE Radar Conference (RadarConf20), 2020, pp. 1-6, doi: 10.1109/RadarConf2043947.2020.9266323.

[Orionwillstay]

EnVision is more imagery focused... At one time they were talking about 1m resolution over small areas, but at present the highest resolution they are promising is 10m.

The 1 m resolution was based on a prior plan to use a European-supplied SAR instrument instead of the JPL-supplied instrument.

Yes, I know, but the specs for power, antenna size and frequency don't seem to have changed much from the earlier European radar. I wonder why they backed off on their performance promises? 1m resolution would be real nice, even if it only covered a small area.

There is a December 2020 paper that compares the two radars. I don't have access, but maybe somebody here does.

S. Hensley, B. Campbell, D. Perkovic-Martin, K. Wheeler, W. Kiefer and R. Ghail, "VISAR and VenSAR: Two Proposed Radar Investigations of Venus," 2020 IEEE Radar Conference (RadarConf20), 2020, pp. 1-6, doi: 10.1109/RadarConf2043947.2020.9266323.

Thanks for the specs of the two radars Don2. Wow 1m resolution would be like revealing the Venus surface in photo quality, the "MRS" for Venus!

[vjkane]

Thanks for the specs of the two radars Don2. Wow 1m resolution would be like revealing the Venus surface in photo quality, the "MRS" for Venus!

EnVision will no longer have the 1 m spot resolution.  That potential capability was dropped long ago when the mission switched from a potential European-based SAR derived from an Earth observation mission to one from JPL.

[Orionwillstay]

Thanks for the specs of the two radars Don2. Wow 1m resolution would be like revealing the Venus surface in photo quality, the "MRS" for Venus!

EnVision will no longer have the 1 m spot resolution.  That potential capability was dropped long ago when the mission switched from a potential European-based SAR derived from an Earth observation mission to one from JPL.

Such a lost opportunity! Perhaps they've encountered technical / budgetary difficulties?

[vjkane]

Thanks for the specs of the two radars Don2. Wow 1m resolution would be like revealing the Venus surface in photo quality, the "MRS" for Venus!

EnVision will no longer have the 1 m spot resolution.  That potential capability was dropped long ago when the mission switched from a potential European-based SAR derived from an Earth observation mission to one from JPL.

Such a lost opportunity! Perhaps they've encountered technical / budgetary difficulties?

The mission could not meet the budget limitations of ESA's medium class missions without NASA contributing the SAR instrument. I haven't read the dollar (or Euro) value of that contribution, but I suspect that it is substantial.

The EnVision plan to study only a portion of Venus also is another cost saving feature, although I don't know whether that is in reducing the power requirements on the spacecraft to transmit the additional data, the limitations of existing Earth tracking stations (I don't know if EnVision will use just European deep space stations or NASA's also), operations costs, or all the above.

I did look through the published mission plans and pulled out the following information about the data volumes for EnVision and VERITAS:

VERITAS: >40Tbits, >14.8Tbits/year
EnVision: 210 Tbits, 35/Tbits/year

Don2 in a previous post has mentioned that the EnVision SAR instrument is more focused on imagery, and this may explain the difference.  Note that the higher EnVision data rates given the much smaller area of Venus that it will study compared to VERITAS.

However, I did once read that the key factor in SAR data rates is how much compression is done on the spacecraft. Some of the difference may be because EnVision has less compression, either for greater scientific fidelity or because of limitations on the spacecraft. Does anyone here know?

[Orionwillstay]

Thanks for the specs of the two radars Don2. Wow 1m resolution would be like revealing the Venus surface in photo quality, the "MRS" for Venus!

EnVision will no longer have the 1 m spot resolution.  That potential capability was dropped long ago when the mission switched from a potential European-based SAR derived from an Earth observation mission to one from JPL.

Such a lost opportunity! Perhaps they've encountered technical / budgetary difficulties?

The mission could not meet the budget limitations of ESA's medium class missions without NASA contributing the SAR instrument. I haven't read the dollar (or Euro) value of that contribution, but I suspect that it is substantial.

The EnVision plan to study only a portion of Venus also is another cost saving feature, although I don't know whether that is in reducing the power requirements on the spacecraft to transmit the additional data, the limitations of existing Earth tracking stations (I don't know if EnVision will use just European deep space stations or NASA's also), operations costs, or all the above.

I did look through the published mission plans and pulled out the following information about the data volumes for EnVision and VERITAS:

VERITAS: >40Tbits, >14.8Tbits/year
EnVision: 210 Tbits, 35/Tbits/year

Don2 in a previous post has mentioned that the EnVision SAR instrument is more focused on imagery, and this may explain the difference.  Note that the higher EnVision data rates given the much smaller area of Venus that it will study compared to VERITAS.

However, I did once read that the key factor in SAR data rates is how much compression is done on the spacecraft. Some of the difference may be because EnVision has less compression, either for greater scientific fidelity or because of limitations on the spacecraft. Does anyone here know?

Thanks for your insight re the budgetary issue vjkane!

The data rate of EnVision is much higher than that of VERITAS while it will study a smaller area of Venus - may I know the reason behind please? Thank you!

[vjkane]

The data rate of EnVision is much higher than that of VERITAS while it will study a smaller area of Venus - may I know the reason behind please? Thank you!

As suggested in the previous post, two possibilities:

The greater focus on imagery and repeat coverage for change detection may cause data rates to be higher for EnVision all other things being equal

SAR instruments, as I understand them, inherently produce very large amounts of data off the instrument that must be processed and reduced to provide information, and the secondary products are smaller. We don't know if EnVision and VERITAS will perform equal levels of onboard processing and data compression or not.