I thought it’s worth mentioning that the asteroid 2012 TC4 is estimated to be at it’s closest to us on October 12th 2017 and the JPL orbit diagram is giving a minimum altitude of 3.0E-4.
In case you are unable to view the orbit diagram due to java problems, there are images below.
The JPL link for this asteroid is https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2012%20TC4;orb=1;old=0;cov=0;log=0;cad=0#phys_par
I am no mathematician but I did manage to work out the distances.
On 12th October 2017 this asteroid 2012 TC4 will be a distance of 3.0e-4 AU.
3.0e-4 AU equals 0.00030 AU.
This equals 27886.7 miles.
That’s 44879 km and the distance is given from earth’s centre so minus the earth radius of 6371km, it gives an altitude from average earth surface of 38508 km – same altitude as Molniya-3 communications satellite.
Other similar satellites are in the same altitude range, for example, Bulgaria launched their first communications satellite in June this year according to this article, http://uk.reuters.com/article/us-space-launch-bulgaria/bulgarias-first-communications-satellite-launched-into-orbit-idUKKBN19F05U
“The satellite will be positioned into orbit at 36,000 km (22,000 miles) above the Earth and be operational up to 20 years.”
This is pretty close to 38508 km.
On the JPL website there is an error margin for the fly by distance of 2012 TC4:
Orbital margins for 2017-Oct-12 05:42 distances from Earth calculated on 2017-Sep-05
Time uncertainty 00:01
Nominal distance 0.000335370338966099 AU
Maximum distance 0.000333848671968589 AU
Minimal distance 0.000336892964761902 AU
As shown in the images below, the orbit diagram is currently giving 3.0e-4 for closest to earth and this equals 0.00030 AU