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Note: 75950 km radius is the apogee of a "24 hour" geosynchronous (but NOT geostationary) orbit with a 8378 km radius (2000 km equatorial altitude) perigee. The same 42164 km semimajor axis as a circular geostationary orbit. This is a High Eccentricity Earth Orbit (HEEO), suggested by space scientist John Lewis at the University of Arizona. Given the high perigee velocity of a launch loop, this orbit is easier to achieve with much less apogee insertion ΔV than a GEO orbit. The perigee velocity of this HEEO orbit is high, and that is an excellent place for a high ΔV thrust into an interplanetary orbit. Subnote: due to the J₂ nonlinearity of the Earth's gravity field, this orbit will precess, so an exact synchronous orbit will have a slightly smaller semimajor axis.  '''Note:''' 75950 km radius is the apogee of a "24 hour" geosynchronous (but NOT geostationary) orbit with a 8378 km radius (2000 km equatorial altitude) perigee. The same 42164 km semimajor axis as a circular geostationary orbit. This is a High Eccentricity Earth Orbit (HEEO), suggested by space scientist John Lewis at the University of Arizona. Given the high perigee velocity of a launch loop, this orbit is easier to achieve with much less apogee insertion ΔV than a GEO orbit. The perigee velocity of this HEEO orbit is high, and that is an excellent place for a high ΔV thrust into an interplanetary orbit. '''Subnote:''' due to the J₂ nonlinearity of the Earth's gravity field, this orbit will precess, so an exact synchronous orbit will have a slightly smaller semimajor axis. 
Propellant Plume Gas Scattering
H density versus altitude

alt km 
radius km 
#/m3 
1000 
7378 
21000e6 

2000 
8378 
12000e6 
Constr. perigee 
5000 
11378 
3100e6 

10000 
16378 
820e6 

20000 
26378 
180e6 

30000 
36378 
67e6 

35786 
42164 
45e6 
GEO circular 
40000 
46378 
35e6 

50000 
56378 
22e6 

60000 
66378 
14e6 

69572 
75950 
11e6 
Constr. apogee 
70000 
76378 
10e6 

. https://www.sciencedirect.com/science/article/pii/0022407372900052
Estimated hydrogen mass per 1000 km height, 1.67e27kg/H 

Altitude km 
1000 
2000 
10000 
20000 
30000 
35786* 
40000 
50000 
60000 
69572* 
70000 
Radius km 
7378 
11378 
16378 
26378 
36378 
42164* 
46378 
56378 
66378 
75950* 
76378 
Volume km³ 
6.8e11 
1.6e12 
3.4e12 
8.7e12 
1.7e13 
2.2e13 
2.7e13 
4.0e13 
5.5e13 
7.2e13 
7.3e13 
#H / m³ 
2.1e10 
1.2e10 
8.2e8 
1.8e8 
6.7e7 
4.5e7 
3.5e7 
2.2e7 
1.4e7 
1.1e7 
1.0e7 
H kg 
240000 
32000 
4700 
2600 
1900 
1700* 
1000 
1500 
1300 
1300* 
1200 
Less than 20 tonnes of hydrogen (and almost nothing else) above GEO, out to the bow shock.
Note: 75950 km radius is the apogee of a "24 hour" geosynchronous (but NOT geostationary) orbit with a 8378 km radius (2000 km equatorial altitude) perigee. The same 42164 km semimajor axis as a circular geostationary orbit. This is a High Eccentricity Earth Orbit (HEEO), suggested by space scientist John Lewis at the University of Arizona. Given the high perigee velocity of a launch loop, this orbit is easier to achieve with much less apogee insertion ΔV than a GEO orbit. The perigee velocity of this HEEO orbit is high, and that is an excellent place for a high ΔV thrust into an interplanetary orbit. Subnote: due to the J₂ nonlinearity of the Earth's gravity field, this orbit will precess, so an exact synchronous orbit will have a slightly smaller semimajor axis.
Collision cross section table
Gas 
(nm)² 
(nm)² with H₂ 
H₂ 
0.27 
1.02 
He 
0.21 
0.99 
Ar 
0.36 
1.06 
O₂ 
0.40 
1.07 
N₂ 
0.43 
1.08 
CH₄ 
0.46 
1.09 
CO₂ 
0.52 
1.11 
Cl₂ 
0.93 
1.22 
The second column is the combined collision cross section with an H₂ molecule ... the square of the sum of the square roots.
from libretexts
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