# Does Tianwen-1 have a near-repeat ground track orbit in order to scan the same general area on each of its low altitude passes?

Though it's not as easy1 to get details on Chinese missions in English, it seems that Tianwen-1 is in a 12,000 x 256 km highly eccentric orbit around Mars, with its hi res cameras able to resolve 0.5 meters during "periMars"2. If so that makes the semimajor axis $$(256 + 3396 + 12,000 + 3396)/2 = 9524$$ km and with $$GM=4.283 \times 10^{4} \ km^3/s^2$$ that makes the period 7.8 hours, or not quite Mars' sidereal day of 24.62 hours divided by three.

Question: Does it turn out that the period is a little longer than the number above and the orbit is much closer to repeat ground track3 over the proposed landing site than this envelope-back estimate suggests?

Or are the weeks or months of orbit before landing enough to scan the area over time by "filling in the blanks" over successive passes?

• I presume this higher period, will make ground track regress east to west. So one will have 1 more try over some 20 days I guess over the landing zone Feb 28, 2021 at 7:01
• @Prakhar I see what you mean, good point! it's an unofficial estimate only, an answer will need to find the actual orbit before it can speculate on the exact strategy strategy. The problem is very sensitive to the period; If it's 7.5 or 8 hours instead of 7.8 that "20 days" changes by lot!
– uhoh
Feb 28, 2021 at 7:18