Differences between revisions 46 and 47
 ⇤ ← Revision 46 as of 2020-08-27 07:42:29 → Size: 3339 Editor: KeithLofstrom Comment: ← Revision 47 as of 2020-08-28 05:20:39 → ⇥ Size: 4132 Editor: KeithLofstrom Comment: Deletions are marked like this. Additions are marked like this. Line 34: Line 34: '''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 trajectory.  '''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. === 24 hour "Construction" Orbit ==='''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 trajectory. '''Subnote 1:''' 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.'''Subnote 2:''' launchloop launches slows portions of the rotor; restoring rotor position and velocity requires enormous power. Larger vehicles would slow the rotor more, requiring more peak electrical power generation capacity. It is cheaper to assemble large interplanetary vehicles at a permanent orbiting construction station from dozens, perhaps hundreds of daily launches, then launch the propellant to fuel them after they are assembled. Since a launch to an interplanetary Hohmann must occur at a specific time of day for a particular mission, the perigee of the construction orbit must occur at that specific time. This is an annoying constraint for infrequent Mars missions, but less so for missions to many different asteroids.

# 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
 Estimated hydrogen mass per 1000 km height, 1.67e-27kg/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.

### 24 hour "Construction" Orbit

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 trajectory.

Subnote 1: 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.

Subnote 2: launchloop launches slows portions of the rotor; restoring rotor position and velocity requires enormous power. Larger vehicles would slow the rotor more, requiring more peak electrical power generation capacity. It is cheaper to assemble large interplanetary vehicles at a permanent orbiting construction station from dozens, perhaps hundreds of daily launches, then launch the propellant to fuel them after they are assembled. Since a launch to an interplanetary Hohmann must occur at a specific time of day for a particular mission, the perigee of the construction orbit must occur at that specific time. This is an annoying constraint for infrequent Mars missions, but less so for missions to many different asteroids.

### 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

GasScatter (last edited 2020-08-28 17:21:33 by KeithLofstrom)