A
arobie
Guest
I would greatly appreciate any help I get. I'm trying to learn this stuff, and the best way for me to learn is to actually try, so I did.<br /><br />Earlier today, I started to figure numbers for a suborbital hop of an apogee of about 316 km. I started with the gravity losses. I figured it would loose 1.98 km/s in grav loss using this formula: (Don't worry about all these numbers. They are mainly for my benefit...to review my work as I post it...and to have a place to see it all organized. Although if anyone wants to look it over, you're welcome too. <img src="/images/icons/smile.gif" />)<br /><br />dVgrav = g,eff * t,b * sin(phi)<br />g,eff = local gravity on way up<br />g,eff = (g + g,end of flight) / 2<br />g = 9.807<br />g,end of flight = Earth's GM/ Rb<br />Earth's GM = 398600.44 km^3 / s^2 <br />Rb = Re + altitude<br />Earth's Re = 6371 km <br />Altitude = 316 km<br />Rb = 6687 km<br />g, end of flight = 398600.44 / 6687 = 0.008914051<br />--g, eff = (9.807 + 8.914051) / 2 = 9.3605255<br /><br />t,b = engine burn time<br />t,b = sqrt ( ( 2 * y ) / a)<br />y = 316000 m<br />a = 14.11 m / s^2<br />t,b = sqrt ( (2 * 316000) / 14.11)<br />--t,b = 211.6 seconds<br /><br />Sin(phi)<br />phi = flight angle<br />Phi = 90 degrees<br />--Sin(90) = 1<br /><br />dV = 9.3605255 * 211.6 = 1980.68 m/s = 1.98 km/s<br /><br />I have two questions. First, what is and how do I find 'a'? I already feel foolish for that question. I'm just learning this, and looking over my work on paper, I have no idea how I got 'a'. All that I started out knowing for that portion of the equation was y (altitude m).<br /><br />Second, what is the next step to figuring out how much total dV I need to get to 316 km altitude? <br /><br />Total dV = dV + gravity losses + drag losses<br />I quess I have one more question, is the above correct?