Unfortunately OpenRocket and RasAero do not have the capability for doing orbital trajectory sims. The best you can do with these programs is see if you can get a rocket that can achieve both the tangential, i.e., horizontal velocity for orbit and the needed altitude above 100 km. This though will be a rocket traveling straight-up so isn't really showing an actual trajectory to orbit. Attached is an attempt at such a rocket.
It is derived from the Cesaroni rocket that powers Up Aerospace's Spaceloft XL suborbital rocket. It consists of 4 stages with the first stage being the Cesaroni rocket. For the subsequent stages we will use a smaller motor by a factor of 1/4th at each stage. So the 2nd stage will be 1/4th that of the Cesaroni, the 3rd will be smaller by an additional factor of 1/4th, and the fourth stage smaller again by an additional factor of 1/4th.
Here's the specifications on the Cesaroni motor:
View attachment 549717
Here's the thrust data for the Cesaroni motor in RASP format from its .Eng file:
;
; Cesaroni Booster motor for UP Aerospace.
; @File: CTI_UPA-264-C.eng, @Pts-I: 42, @Pts-O: 31, @Sm: 0, @CO: 5%
; @TI: 438207.0, @TIa: 437890.0, @TIe: -0.05%, @ThMax: 52454.9, @ThAvg: 37051.4, @Tb: 11.827
; Exported using ThrustCurveTool, www.ThrustGear.com
S37029 265 3018 P 186.8801 242.672 NEW
0.037 540.773
0.061 1406.008
0.073 13086.69
0.086 48561.4
0.147 52454.9
0.257 50616.3
0.355 49859.2
0.698 48453.2
0.918 46073.8
1.175 44667.8
1.591 43586.3
2.338 42829.2
4.199 42288.4
4.701 41855.8
8.006 35907.3
9.658 32230.0
10.234 26606.0
10.368 23577.7
10.637 21414.6
11.176 21414.6
11.262 21847.2
11.335 21090.1
11.445 19575.96
11.543 17737.33
11.629 14600.85
11.69 11464.37
11.764 6813.73
11.825 4001.72
11.911 2163.09
12.021 648.927
12.376 0.0
;
The format of .ENG files is described here:
==============================================================
- The common name of the motor; just the impulse class and average thrust.
- The casing diameter in millimeters (mm).
- The casing length, also in millimeters.
- The list of available delays, separated by dashes. If the motor has an ejection charge but no delay use "0" and if it has no ejection charge at all use "P" (plugged).
- The weight of all consumables in the motor. For solid motors this is simply the propellant itself, but for hybrids it is the fuel grain(s) plus the oxidizer (such as N2O). This weight is expressed in kilograms (Kg).
- The weight of the motor loaded and ready for flight, also in kilograms.
- The motor manufacturer abbreviated to a few letters. NAR maintains a list of manufacturer abbreviations on page 2 of the combined master list.
==============================================================
The lines preceded by a ; symbol are regarded as comments and are not interpreted by the sim programs.
For the smaller upper stages, I successively made the dry mass, propellant mass, length, and thrust smaller by a factor of 1/4th. I kept the same diameter for each stage. I didn't change the comment lines, other than saying it's one-quarter size, since I didn't know what they meant anyway. Here's the thrust data for my created 2nd stage in RASP format:
;
; Cesaroni Booster motor for UP Aerospace - quarter size.
; @File: derived from CTI_UPA-264-C.eng, @Pts-I: 42, @Pts-O: 31, @Sm: 0, @CO: 5%
; @TI: 438207.0, @TIa: 437890.0, @TIe: -0.05%, @ThMax: 52454.9, @ThAvg: 37051.4, @Tb: 11.827
; Exported using ThrustCurveTool, www.ThrustGear.com
Q9000X 265 755 P 46 61 NEW
0.037 135
0.061 350
0.073 3270
0.086 15411
0.147 13110
0.257 12654
0.355 12465
0.698 12110
0.918 11518
1.175 11166
1.591 10900
2.338 10707
4.199 10572
4.701 10463
8.006 8976
9.658 8057
10.234 6651
10.368 5894
10.637 5353
11.176 5353
11.262 5461
11.335 5272
11.445 4894
11.543 4434
11.629 3650
11.69 2866
11.764 1703
11.825 1000
11.911 540
12.021 162
12.376 0.0
;
Note the thrust values are 1/4th those of the full-size Cesaroni motor. For center burning solid motors, the thrust is made proportionally larger or smaller according to the length of the motor since that determines the burning surface area.
The 3rd and 4th stages are made successively, proportionally smaller as described.
For the orbital velocity for low Earth Orbit, that is ~7,800 m/s. But for low latitude launch sites such as Cape Canaveral you get ~400 m/s for free from the Earth's rotation. So I took the required velocity needed to be attained as 7,400 m/s. I simulated no airframes by given the body tubes in the OpenRocket sim a mass of 0 kg.
The payload mass is taken as 500 grams. For this ~330 kg gross mass rocket, this is a payload to gross mass fraction of 1 to ~660.
Issues and Problems.
1.)Notable I used a rounded ogive nose cone rather than conical or von Karman shape. The reason is a quirk in OpenRocket is that it sometimes for hypersonic flights will give a higher altitude for a short, squat nozzle than a long, pointed one. Aside from that, I also didn't assign a mass for the nose cone since I really didn't know what the size and shape it would wind up being. And anyway based on orbital rockets it should be only a fraction of the payload mass anyway. For example for the Falcon 9, it's payload fairing is at about 2 tons for an expendable payload of ~23 tons. So based on that, a 500 gm payload might need only a 50 gm nose cone.
2.)Not really an issue or problem but OpenRocket counts stages downwards from top to bottom, in contrast to the usual practice in the industry. Also, it starts up always with a single stage present as default which it calls the "Sustainer", even if you don't give that "stage" a motor. So in this case OpenRocket calls this rocket a 5 stager with the top stage, which it calls the 1st stage, only consisting of the nose cone and payload. I could probably change that by editing the names but didn't bother to.
3.)I am worried about the stability of the upper, powered stages. The rocket overall has the center of gravity CG ahead of the center of pressure CP, but for each stage above the booster, the CG is behind the CP. I'm thinking for the top most stages that won't matter since they fire at near vacuum. But it should matter for the stage above the booster stage.
4.)I'm interested in find out what the vacuum Isp is for the upper stages. We might be able to get improved performance using longer nozzles.
Attached is the .ORK file using OpenRocket version 15.03.
Robert Clark
View attachment 549721