# Could Tianwen-1, Hope, or Mars 2020 image one another en route to Mars?

Which of the optical sensors in operation on the three spacecraft currently en route to Mars (China's Tianwen-1, UAE's Emirates Mars Mission (Hope), USA's Mars 2020 (Perseverance)) could image one of the other spacecraft, with resolution more than one pixel, assuming a correctly aimed sensor or spacecraft?

I couldn't find technical details of Tianwen-1's (orbiter's?) optical navigation sensor.

The Hope orbiter's EXI imager has an angular resolution of 22 arc seconds, but it might be turned off during cruise.

The Perseverance rover is inside an aeroshell. Photos from Lockheed Martin show that it has at least one small circular window. I couldn't find details of optical instruments outside Perseverance, nor whether an interior instrument is aimed at such a window.

So it might come down to Tianwen-1's sensor's angular resolution and how densely packed this convoy ever becomes.

• It seems unlikely that you'll be able to get resolution of more than one pixel. Just for a comparison, the aeroshell of Perseverance is 4.5 m in diameter. For such an object to subtend more than 22 arcsec in Hope's field of view, it would have to be less than 42 km away. I don't know for certain whether they'll get that close, but I strongly suspect that they won't. Aug 6 '20 at 20:19
• What's more, if you take into account the diffraction limit, a mirror of diameter $d_a$ can only see an object of size $d_b$ using light of wavelength $\lambda$ if it is closer than (approximately) $d_a d_b/\lambda$. For objects with $d \approx 5$ m and visible light, this works out to be something like 50,000 km, or about 8 Earth radii. If they never get any closer than that, there's no real hope. Aug 6 '20 at 20:26
• Mars2020 is en route with about 39,600 kph, that is 11 km/s. In 24 hours that is 950,400 km. The spacecrafts launched some days sooner or later are millions of km apart.
– Uwe
Aug 6 '20 at 20:43
• It may be necessary to first have an answer to Will the Emirate Mars Mission, Tianwen-1 and Mars 2020 Mission get closer to each other or spread out on their way to Mars? before this can be answered. However, you might consider also asking in a new question if they can see each other as star-like objects without necessarily resolving each other. I think there is certainly a chance, but that calculation would not answer this. See also Have spacecraft photographed each other beyond Earth orbit?
– uhoh
Aug 6 '20 at 22:56
• The small circular window on Perseverance was used to install the MMRTG and is now closed. Aug 20 '20 at 10:14