How stable is an orbit of 335.9 km?

Question

Spacex has recently begun deployment of its satellite constellation that will provide internet services. In their initial filings with the FCC they propose that they may have over 7,000 VLEO (very low Earth orbit) satellites in addition to the 4,425 satellites in "83 orbital planes (at altitudes ranging from 1,110 km to 1,325 km)". Some of these may have an altitude of just 335.9 km (see top of page 8 for the table).

From page 2:

Second, SpaceX would add a very-low-Earth orbit NGSO constellation, consisting of 7,518 satellites operating at altitudes from 335 km to 346 km, using V-band spectrum for all links to and from associated earth stations. These assets, referred to herein as the “VLEO Constellation,” would enhance capacity where it may be needed most, enabling the provision of high speed, high bandwidth, low latency broadband services that are truly competitive with terrestrial alternatives.

How stable would the satellites be in this VLEO orbit? It is almost 20% lower than the ISS orbit, and the ISS requires constant resupplies to keep it in orbit. With 7000 satellites that are not being resupplied wouldn't there be constant issues with satellites falling out of orbit and burning up in the atmosphere?

Answer 1

Stability of low Earth orbits is highly dependent on the mass and cross-section of the satellite, and the effect of solar weather on the upper atmosphere. According to the calculator at lizard-tail.com, depending on the assumptions made, the lifetime of a satellite at 335km altitude could be anywhere from 6 months to 4 years.

If the satellites have propulsive capability, they could reboost for a while without resupply.

Another possibility is that SpaceX expects the VLEO group to be essentially disposable, and plans to launch upgraded replacements when and as the satellites re-enter.