Okay, I'll keep this one short, but I really had to address this problem.
So, a short calculation revealed that the RS-68, that produces about 3,370,000 Newtons of thrust, gives me about 350,000 kgf of thrust.
That's way too much, considering that I have 2 of these engines on the Arrowhead and it weighs about 42,500 at gross takeoff weight (by gross takeoff weight I mean fully loaded, no fuel.).
Now I saw that the J-2X gives me about 1,310,000 Newtons, about 131,000 kilograms force of thrust. 2 of these engines means that I have about 262,000 kgf total, which is enough for my purpose I suppose.
Now here's the logic behind the transfer to the J-2X:
1. It has a higher Isp.
2. A single RS-68 at its lowest thrust setting can shoot an empty Arrowhead straight up at an acceleration of 5 g. That's a lot, and I plan on using two: for redundancy's sake. 2 J-2Xs have about 3/4 of the RS-68's full thrust, and so at full power can only take the Arrowhead at an acceleration of about 7.4 g straight up, and anyway it's going to be full of fuel for most of the flight, making it about 3-5 g and they are also throttleable, making it possible to accelerate slower.
That's about it, I just thought I'd give you this heads-up so you'll see that I'm serious about it, and I work about it, and I want it to be totally realistic.
~Take care, Oz. :tiphat:
So, a short calculation revealed that the RS-68, that produces about 3,370,000 Newtons of thrust, gives me about 350,000 kgf of thrust.
That's way too much, considering that I have 2 of these engines on the Arrowhead and it weighs about 42,500 at gross takeoff weight (by gross takeoff weight I mean fully loaded, no fuel.).
Now I saw that the J-2X gives me about 1,310,000 Newtons, about 131,000 kilograms force of thrust. 2 of these engines means that I have about 262,000 kgf total, which is enough for my purpose I suppose.
Now here's the logic behind the transfer to the J-2X:
1. It has a higher Isp.
2. A single RS-68 at its lowest thrust setting can shoot an empty Arrowhead straight up at an acceleration of 5 g. That's a lot, and I plan on using two: for redundancy's sake. 2 J-2Xs have about 3/4 of the RS-68's full thrust, and so at full power can only take the Arrowhead at an acceleration of about 7.4 g straight up, and anyway it's going to be full of fuel for most of the flight, making it about 3-5 g and they are also throttleable, making it possible to accelerate slower.
That's about it, I just thought I'd give you this heads-up so you'll see that I'm serious about it, and I work about it, and I want it to be totally realistic.
~Take care, Oz. :tiphat:
