K
keermalec
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This topic came about while trying to understand gravity losses on the Missions & Launches Forum but to me the subject seemed important enough for it to merit its own thread.<br /><br />I believe this is an important discovery, as it demonstrates the fact that certain specific orbits around a planet offer minimum delta-v gates for interplanetary travel.<br /><br />.............................<br /><br />There is an "optimal altitude" at which the delta-v needed to send a ship to Mars (with 2.94 km/s at SOI) on a Hohmann transfer is minimal. IE: the delta-v is more important at lower or higher orbits than this one. The "optimal altitude" is: <br /><br />85'800 km above the surface of the Earth, or about 92'300 km from its center. <br /><br />At this altitude the necessary delta-v required to get to Mars is 2.08 km/s. Above, or below, this orbit the necessary delta-v's are higher...<br /><br />On Mars the optimal altitude is at 8'900 km above the surface, or 12'300 km from the center. Here the required delta-v to attain 2.64 km/s at MSOI for Hohmann transfer to Earth is only 1.87 km/s. <br /><br />It seems strange but the math checks out right.<br /><br />At the moment it seems the best location to launch a Mars expedition from is at the 92'300 km orbit. Getting there requires 5.63 km/s delta-v for orbital transfer, but getting from there to Mars requires only 3.95 km/s!!! and this does not include any speed saving by aerobreaking or otherwise at Mars.<br /><br />This gives us a 31% payload capacity if using a 372s ISP CH4/O2 drive... (assuming the ship is tugged to the IGO and refuelled there by another ship). This capacity can certainly be augmented if we optimise the arrival burn at Mars by aerobreaking.<br /><br />Just imagine what we could do with the extra delta-v or capacity: <br /><br />1. make the Mars mission cheaper by making the ship smaller <br />2. make the mission safer by launching 2 ships <br />3. get there faster by choosing faster-than-Hohmann transfers, thereby also <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>